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(1853, 1, '2023-02-27 13:43:00', '2023-02-27 08:13:00', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly, dragging up a cylindrical ribbon of glass 13 m high, the diameter of the cylinder being maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:43:00', '2023-02-27 08:13:00', '', 1809, 'https://civilengineeringlectures.com/?p=1853', 0, 'revision', '', 0);
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(1852, 1, '2023-02-27 13:42:05', '2023-02-27 08:12:05', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process and recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly, dragging up a cylindrical ribbon of glass 13 m high, the diameter of the cylinder being maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:42:05', '2023-02-27 08:12:05', '', 1809, 'https://civilengineeringlectures.com/?p=1852', 0, 'revision', '', 0);
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(1854, 1, '2023-02-27 13:43:52', '2023-02-27 08:13:52', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly, dragging up a cylindrical ribbon of glass 13 m high, the diameter of the cylinder being maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:43:52', '2023-02-27 08:13:52', '', 1809, 'https://civilengineeringlectures.com/?p=1854', 0, 'revision', '', 0);
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(1857, 1, '2023-02-27 13:47:38', '2023-02-27 08:17:38', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly. It drags up a cylindrical ribbon of glass 13 m high. The diameter of the cylinder is maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:47:38', '2023-02-27 08:17:38', '', 1809, 'https://civilengineeringlectures.com/?p=1857', 0, 'revision', '', 0);
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(1856, 1, '2023-02-27 13:46:33', '2023-02-27 08:16:33', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly. It drags up a cylindrical ribbon of glass 13 m high. The diameter of the cylinder is maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:46:33', '2023-02-27 08:16:33', '', 1809, 'https://civilengineeringlectures.com/?p=1856', 0, 'revision', '', 0);
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(1858, 1, '2023-02-27 13:48:08', '2023-02-27 08:18:08', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly. It drags up a cylindrical ribbon of glass 13 m high. The diameter of the cylinder is maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:48:08', '2023-02-27 08:18:08', '', 1809, 'https://civilengineeringlectures.com/?p=1858', 0, 'revision', '', 0);
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(1861, 1, '2023-02-27 13:50:51', '2023-02-27 08:20:51', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly. It drags up a cylindrical ribbon of glass 13 m high. The diameter of the cylinder is maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass and also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:50:51', '2023-02-27 08:20:51', '', 1809, 'https://civilengineeringlectures.com/?p=1861', 0, 'revision', '', 0);
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(1860, 1, '2023-02-27 13:49:50', '2023-02-27 08:19:50', '<!-- wp:heading -->\n<h2><strong>GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The term <em>glass </em>refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1810,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Glass.png\" alt=\"Glass\" class=\"wp-image-1810\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Glass made from sand, lime, and soda ash has been known in Egypt for 5000 years. For many centuries glass was worked by drawing the molten material from a furnace. The glass was then rolled out or pressed into appropriate moulds and finally shaped by cutting and grinding.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Adding different metallic compounds to the melt, various coloured glasses can be manufactured. The blue colour was obtained by the addition of cobalt. Copper gives blue or red and iron or chromium produced green. In the fifteenth century, white opaque glass was produced by the addition of tin or arsenic. In the seventeenth century, ruby-red glass was made with the addition of gold chloride. Clear glass could be obtained by using antimony or manganese as a de-colourizer. These remove the green colouration caused by iron impurities within the sand.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the late twentieth century, with the advent of fully glazed facades, the construction industry has become a major consumer of new glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>MANUFACTURE</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Soda lime silicate glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Modern glass is manufactured from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate). Small additions of salt cake (calcium sulfate) and dolomite (magnesium limestone) are also used. This gives a final composition of typically 70–74% silica, 12–16% sodium oxide, 5–12% calcium oxide, and 2–5% magnesium oxide with small quantities of aluminium, iron, and potassium oxides. The addition of 25% broken glass or <em>cullet </em>to the furnace mix accelerates the melting process. It also recycles the production waste. The production process is relatively energy intensive at 15,000 kWh/m<sup>3</sup>.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alkaline earth silicate, borosilicate, and ceramic glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Alkaline earth silicate and borosilicate glasses are also used in the construction field. These have considerably different chemical compositions, and, give their particular physical properties. The composition of alkaline earth silicate glass is typically 55–70% silica, 5–14% potassium oxide, 3–12% calcium oxide, and 0–15% aluminium oxide, with small quantities of zirconium, strontium, and barium oxides.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Borosilicate glass is typically 70–87% silica, 0–8% sodium oxide, 0–8% potassium oxide, 7–15% boron oxide, and 0–8% aluminium oxide, with small quantities of other oxides. A particular characteristic of borosilicate glass is that it has a coefficient of expansion of one-third that of standard soda lime silicate glass. This property makes it considerably more resistant to thermal shock in case of fire.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass-ceramics have a zero coefficient of expansion. It makes them highly resistant to thermal shock. The composition of glass ceramics is complex comprising typically 50–80% silica, and 15–27% alumina, with small quantities of sodium oxide, potassium oxide, barium oxide, calcium oxide, magnesium oxide, titanium oxide, zirconium oxide, zinc oxide, lithium oxide, and other minor constituents.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The glass is initially produced by a standard float or rolling technique, but subsequent heat treatment converts part of the normal glassy phase into a fine-grained crystalline form, giving rise to particular physical properties.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FORMING PROCESSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Early methods</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Initially, crown glass was formed by spinning a 4 kg cylindrical gob of molten glass on the end of a blowpipe. The solid glass was blown, flattened out, and then transferred to a solid iron rod<em>. </em>After reheating it was spun until it opened out into a 1.5 m diameter disc. The process involved considerable wastage including the bullion in the center.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An alternative process involved the blowing of a glass cylinder which was then split open and flattened out in a kiln. Subsequently, in a major development, circular metal bait was lowered into a pot of molten glass and withdrawn slowly. It drags up a cylindrical ribbon of glass 13 m high. The diameter of the cylinder is maintained with compressed air. The completed cylinder was then detached, opened up, and flattened out to produce flat window glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the development of the Fourcault process in Belgium and the Colburn process in America that it became possible to produce flat glass directly. A straight bait was drawn vertically out of the molten glass to produce a ribbon of glass, which was then drawn directly up a tower, or in the Colburn process turned horizontally, through a series of rollers; finally, appropriate lengths were cut off. However, such drawn sheet glass suffered from manufacturing distortions. This problem was overcome by the production of plate glass, which involved horizontal casting and rolling, followed by grinding to remove distortions and polishing to give a clear, transparent but expensive product. The plate glass manufacturing process is now practically obsolete. It has been replaced by the <em>float process.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>FLOAT GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1811,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/FLOAT-GLASS-1024x339.jpg\" alt=\"\" class=\"wp-image-1811\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A furnace produces a continuous supply of molten glass at approximately 1100°C, which flows across the surface of a large shallow bath of molten tin contained within an atmosphere of hydrogen and nitrogen (this prevents oxidation of the surface of the molten metal). The glass ribbon moves across the molten metal, initially at a sufficiently high temperature for the irregularities on both surfaces to become evened out leaving a flat and parallel ribbon of glass. The temperature of the glass is gradually reduced as it moves forward until, at the end of the molten tin, it is sufficiently solid at 600°C not to be distorted when supported on rollers. Thickness is controlled by the speed at which the glass is drawn from the bath. Any residual stresses are removed as the glass passes through the 200 m annealing lehr or furnace, leaving a fire-polished material. Then, the glass is washed, and substandard material is discarded for recycling. The computer-controlled cutting, firstly across the ribbon, then the removal of the edges, is followed by stacking, warehousing, and dispatch.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Float glass for the construction industry is made within the thickness range of 2–25 mm, although 0.5 mm is available for the electronics industry. Many surface-modified glasses are produced by incorporating metal ions into the glass within the float process. Body-tinted glass, which is of uniform colour, is manufactured by blending additional metal oxides into the standard melt.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>NON-SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass fibres</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Continuous filament</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Continuous glass fibres are manufactured by constantly feeding molten glass from a furnace into a forehearth fitted with 1600 accurately manufactured holes. Molten glass is drawn through these holes, at a rate of several thousand metres per second. The fibres are as small as 9 microns in diameter. They pass over a size applicator and are gathered together as a bundle before to being wound up on a collet. The material may then be used as rovings, chopped strand, or woven strand mats for the production of glass-fibre reinforced materials such as GRP (glass-fibre reinforced polyester), GRC (glass-fibre reinforced cement), or GRG (glass-fibre reinforced gypsum).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass wool</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass wool is used as an insulation material.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Cast glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass may be cast and pressed into shape for glass blocks and extruded sections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Profiled sections</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Profile trough sections in clear or colored 6 or 7 mm cast glass are manufactured in sizes ranging from 232 to 498 mm wide, 41 and 60 mm deep, and up to 7 m long, with or without stainless steel longitudinal wires. The system can be used horizontally or vertically, as single or double glazing, and as a roofing system spanning up to 3 m.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1812,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Profiled-sections.jpg\" alt=\"\" class=\"wp-image-1812\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A large radius curve is possible as well as the normal straight butt jointed system. The joints are sealed with a one-part translucent silicone.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Amber or blue-tinted versions are available for solar control or aesthetic reasons. The double-glazed system produces a sound reduction within the 100–3200 Hz range of typically 40 dB.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The incorporation of 16-mm-thick translucent aerogel-insulated polycarbonate panels into profiled trough sections significantly increases the thermal insulating properties of the units. Airborne sound insulation is enhanced. Light transmission through the translucent aerogel panels is approximately 50%.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Glass blocks</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks for non-load-bearing walls and partitions are manufactured by casting two half blocks at 1050°C, joining them together at 800°C. The process is then followed by annealing at 560°C. The void space is partially evacuated. The standard blocks are 115, 190, 240, and 300 mm square with thicknesses of 80 and 100 mm, although rectangular and circular blocks are also available. The variety of patterns offering differing degrees of privacy includes clear, frosted, and crystal designs with colours from blue, green, and grey to pink and gold. For exterior and fire-retarding applications natural or coloured mortar (2 parts Portland cement, 1 part lime, 8 parts sand) is used for the jointing. Walls may be straight or curved. Bullet-proof blocks are available for higher security situations. For interior use, blocks can be laid with sealant rather than mortar.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Glass blocks jointed with mortar give a fire resistance of 30 or 60 minutes of stability and integrity. But, it will not give insulation. Fire stop blocks (F-30) are manufactured from 26 mm rather than 8 mm glass. It offers increased fire protection of two hours’ integrity and 30 minutes’ thermal insulation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>SHEET PRODUCTS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Standard float glass sizes</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The standard thicknesses for float glass are 3, 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm to maximum sheet sizes of 3 to 12 m. Thicker grades are available in smaller sheet sizes.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Traditional blown and drawn glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Traditional blown and drawn glasses are available commercially both clear and in a wide range of colours. Drawn glass up to 1600 - 1200 mm is optically clear but varies in thickness from 3 to 5 mm. It is normally used for conservation work where old glass requires replacement. The blown glass contains variable quantities of air bubbles. Also, it has significant variations in thickness giving an antique appearance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Curved sheet glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Curved glass can be manufactured by heating annealed glass to approximately 600°C when it softens and sag-bends to the shape of the supporting mould. Sheets up to 3 m - 4 m can be bent with curvature in either one or two directions. Bent glass can subsequently be sandblasted, toughened, or laminated, even incorporating coloured interlayers if required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Self-cleaning glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has an invisible hard coating of 15 microns thick. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These coatings include two special features. The surface incorporating titanium dioxide is photocatalytic. It absorbs ultraviolet light, which with oxygen from the air breaks down or loosens any organic dirt on the surface. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Furthermore, the surface is hydrophilic. It causes rainwater to spread evenly over the surface, rather than running down in droplets. Therefore, the surface is uniformly washed and prevents any unsightly streaks or spots from appearing when the surface dries. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Self-cleaning glass has a somewhat greater mirror effect than ordinary float glass, with a faint blue tint. It is available as normal annealed glass and also in toughened or laminated form. The surface coating, which reduces the transmittance of the glass by about 5%, is tough but as with any glass can be damaged by scratching. A blue solar control version reduces the solar heat gain by approximately 60% depending upon the thickness of the glass used and its combination in a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Clear white glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard float glass is somewhat greener due to the effect of iron oxide impurities in the key raw material sand. However, clear white glass can be produced, at a greater cost, by using purified ingredients. The light transmittance of clear white glass is approximately 2% greater than standard glass for 4 and 6 mm glazing.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Embossed pattern glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>A wide range of 3, 4, 6, 8, and 10 mm patterned glass is commercially available. The degree of privacy afforded by the various glasses is not only dependent upon the pattern. It also depend upon the relative lighting levels on either side and the proximity of any object to the glass. Patterned glasses may be toughened, laminated, or incorporated into double-glazing units for thermal, acoustic, or safety considerations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Screen printed glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>White or coloured ceramic frit is screen printed onto clear or tinted float glass. It is then toughened and heat soaked, causing the ceramic enamel to fuse permanently into the glass surface. Standard patterns or individual designs may be created, giving the required level of solar transmission and privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Decorative etched and sandblasted glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Acid etched glass, 4 mm and 6 mm in thickness, is available to a maximum sheet size of 2140 – 1320 mm with a small range of patterns. Etched glasses need to be handled carefully on-site, as oil, grease, and finger marks are difficult to remove completely. Similar visual effects can be achieved by sandblasting techniques, but it gives the surface finish less smooth. Patterns may be clear on a frosted background or the reverse, depending upon the aesthetic effect and level of privacy required.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Georgian wired glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Georgian wired glass is produced by rolling a sandwich of a 13 mm electrically welded steel wire mesh between two ribbons of molten glass. This produces the standard cast 7 mm sheet, suitable when obscuration is required. Wired glass is not stronger than the equivalent thickness of annealed glass. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1821,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Georgian-wired-glass.jpg\" alt=\"\" class=\"wp-image-1821\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>However, when cracked, the pieces remain held together. On exposure to fire, the wire mesh dissipates some heat. But, ultimately Georgian glass will crack, particularly if sprayed with water when hot. Accidental damage may cause the breakage of the glass. But again it is retained in position by the mesh, at least until the wires are affected by corrosion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Toughened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass is up to four or five times stronger than standard annealed glass of the same thickness. It is produced by subjecting preheated annealed glass at 650°C to rapid surface cooling by the application of jets of air. This causes the outer faces to be set in compression with balancing tension forces within the centre of the glass. As cracking within glass commences with tensile failure at the surface, much greater force can be withstood before this critical point is reached. Toughened glass cannot be cut or worked. Therefore all necessary cutting, drilling of holes, and grinding or polishing of edges must be completed in advance of the toughening process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1819,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Toughned-glass.jpg\" alt=\"\" class=\"wp-image-1819\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Toughened glass will withstand considerable extremes of temperature and sudden shock temperatures. When broken, it shatters into small granules. This is not likely to cause serious injuries related to the accidental breakage of annealed glass. Any standard float, coated, roughcast, and patterned glasses can be toughened.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Heat-strengthened glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Heat-strengthened glass is manufactured by a similar process to toughening. But, it is done at a slower rate of cooling which produces only half the strength of toughened glass. On severe impact, heat-strengthened glass breaks into large pieces like annealed glass. Therefore it cannot be considered a safety glass. Heat-strengthened glass is frequently used in laminated glass where the residual strength after fracture gives some integrity to the laminate. Typical applications include locations where resistance to wind pressure is necessary, such as the upper storeys and corners of high buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Laminated glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Laminated glass is produced by bonding two or more layers of glass together with a plastic interlayer of polyvinyl butyral (PVB) sheet or a polymethyl methacrylate low-viscosity resin. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1817,\"sizeSlug\":\"large\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-large\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass-2-585x1024.png\" alt=\"Anti bandit glass\" class=\"wp-image-1817\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>The lamination process increases the impact resistance compared to annealed glass of the same thickness. Furthermore on impact, whilst the glass laminations crack, they do so without splintering or disintegration, being held together by the interlayer. Therefore, laminated glass can be defined as <em>safety glass</em>. The impact resistance of laminated glass may be increased using thicker interlayers or increasing the number of laminates or the inclusion of polycarbonate sheets. Typically, anti-bandit glass has two or three glass laminates while, depending on the anticipated caliber and muzzle velocity,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>bullet-resistant glass has four or more glass laminates. To prevent spalling, the rear face of bullet-resistant glass may be sealed with a scratch-resistant polyester film.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Insulating glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Insulating glasses are manufactured from float glass laminated with either intumescent or gel materials. Intumescent laminated glass has clear interlayers. When exposed to fire, intumescent or gel materials expand to a white opaque material. It prevents the passage of conductive and radiant heat. The glass layers adjacent to the fire crack but retain integrity owing to their adhesion with the interlayers. The fire resistance, ranging between 30 and 120 minutes for insulation and integrity, depends on the number of laminations, usually between 3 and 5.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1816,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Laminated-glass.png\" alt=\"Laminated glass\" class=\"wp-image-1816\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Fire-resistant glass with intumescent material laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:heading -->\n<h2><strong>SPECIAL GLASSES</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>One-way observation glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Where unobserved surveillance is required, one-way observation mirror glass can be installed. To maintain privacy, the observer must be at an illumination level no greater than one-seventh that of the observed area. Also, he should wear dark clothing. From the observed area, the one-way observation glass has the appearance of a normal mirror. One-way observation glass is available in annealed, toughened, or laminated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Mirror glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Standard mirror glass is manufactured by the chemical deposition onto float glass of a thin film of silver, from aqueous silver and copper salt solutions. The film is then protected with two coats of paint or a plastic layer. Mirror glass is produced by the online application of a three-layer coating of silicon-silica-silicon, which acts by optical interference to give the mirror effect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Alarm glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><strong> </strong>Glass containing either a ceramic loop or a series of straight wires can be incorporated into an intruder alarm system. It is set to activate when the glass is broken. Usually, straight-wired alarm glass is incorporated into a laminated system, while a ceramic loop circuit would be fixed to the inner face of the toughened outer pane within a double-glazing system.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electrically-heatable laminated safety glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It incorporates fine electrically conducting wires which may be switched on when there is a risk of condensation. Typical applications are in areas of high humidity, such as swimming pools, kitchens, and glass roofs, particularly when there are significant differences between the internal and external temperatures.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electromagnetic radiation-shielding glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Itcan be used to protect building zones containing magnetically stored data from accidental or deliberate corruption by external electric fields. For maximum security, the conducting laminates within the composite glass should be in full peripheral electrical contact with the metal window frames and the surrounding wall surface screening.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>X-ray protection glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>It contains 70% lead oxide, which produces significant shielding against ionizing radiation. The glass is amber in colour due to the high lead content. A 6 mm sheet of this lead glass has the equivalent shielding effect of a 2 mm lead sheet against radiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Variable transmission (smart) glasses</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Variable transmission or <em>smart </em>glasses change their optical and thermal characteristics under the influence of light (photochromic), heat (thermochromic), or electric potential (electrochromic). These glasses offer the potential of highly responsive dynamic climate control to building facades. These smart materials including thermotropic products are also available as plastic laminates for incorporation into laminated glass systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Electro-optic laminates</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Electrically operated vision-control glass consists of a laminated system of glass and polyvinyl butyral layers containing a polymer-dispersed liquid crystal layer, which can be electrically switched from transparent to white/translucent for privacy.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Conventional glass coatings reduce both light and heat transmission. However, a coating based on tungsten-modified vanadium dioxide allows visible light through at all times but reflects infrared radiation at temperatures above 29°C. Thus, at this temperature, further heat penetration through the glass is blocked. Therefore the intelligent glass, which has a slight yellow/green colour, admits useful solar gain in cooler conditions but cuts out excessive infrared solar gain under hot conditions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>Intelligent glass facades</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>An intelligent glass building facade changes its physical properties, in response to sensors detecting the external light and weather conditions. It results in reducing the energy consumption necessary to maintain the appropriate internal environment. Therefore intelligent facades have ecological significance in reducing global greenhouse emissions. It also reduces the operational building costs to clients and users.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>STRUCTURAL GLASS</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Glass columns are frequently used as fins to restrain excessive deflection caused by wind and other lateral loads to glass facades. The fixings between the façade glazing and fin units are usually stainless steel clamps bolted through preformed holes in the toughened or laminated glass, although silicone adhesives can also be used. A soft interlayer between the metal fixing and the glass is incorporated to prevent stress concentrations on the glass surface and to allow for differential thermal movement between the glass and metal. Glass is strong in compression and therefore an appropriate material for load-bearing columns and walls, providing that the design ensures sufficient strength, stiffness, and stability. <strong></strong></p>\n<!-- /wp:paragraph -->', 'Glass - as construction material', 'The term glass refers to materials, usually blends of metallic oxides, mainly silica, which do not crystallize when cooled from the liquid to the solid state. It is the non-crystalline or amorphous structure of glass that gives rise to its transparency', 'inherit', 'closed', 'closed', '', '1809-revision-v1', '', '', '2023-02-27 13:49:50', '2023-02-27 08:19:50', '', 1809, 'https://civilengineeringlectures.com/?p=1860', 0, 'revision', '', 0),
(1862, 1, '2023-02-27 23:01:28', '2023-02-27 17:31:28', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement. They used it for constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime putty may be blended with Portland cement in mortars where its water-retention properties are greater than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air. Then, it gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', 'Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans', 'publish', 'open', 'open', '', 'lime-as-a-construction-material', '', '', '2023-02-28 19:22:46', '2023-02-28 13:52:46', '', 0, 'https://civilengineeringlectures.com/?p=1862', 0, 'post', '', 2),
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(1867, 1, '2023-02-27 22:56:39', '2023-02-27 17:26:39', '', 'Carbonation', '', 'inherit', 'open', 'closed', '', 'carbonation', '', '', '2023-02-27 22:56:39', '2023-02-27 17:26:39', '', 1862, 'https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg', 0, 'attachment', 'image/jpeg', 0);
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(1868, 1, '2023-02-27 22:56:52', '2023-02-27 17:26:52', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement suitable for use in constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. Lime putty may be blended with Portland cement in mortars where its water-retention properties are greater than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air, which gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', '', 'inherit', 'closed', 'closed', '', '1862-revision-v1', '', '', '2023-02-27 22:56:52', '2023-02-27 17:26:52', '', 1862, 'https://civilengineeringlectures.com/?p=1868', 0, 'revision', '', 0),
(1869, 1, '2023-02-27 23:00:53', '2023-02-27 17:30:53', '', 'window-wall-stone-wall-484596', '', 'inherit', 'open', 'closed', '', 'window-wall-stone-wall-484596', '', '', '2023-02-27 23:00:53', '2023-02-27 17:30:53', '', 0, 'https://civilengineeringlectures.com/wp-content/uploads/2023/02/window-wall-stone-wall-484596.jpg', 0, 'attachment', 'image/jpeg', 0),
(1870, 1, '2023-02-27 23:01:28', '2023-02-27 17:31:28', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement suitable for use in constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. Lime putty may be blended with Portland cement in mortars where its water-retention properties are greater than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air, which gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', 'Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans', 'inherit', 'closed', 'closed', '', '1862-revision-v1', '', '', '2023-02-27 23:01:28', '2023-02-27 17:31:28', '', 1862, 'https://civilengineeringlectures.com/?p=1870', 0, 'revision', '', 0),
(1905, 1, '2023-05-09 00:02:38', '2023-05-08 18:32:38', '<!-- wp:paragraph -->\n<p>Contract administration is a term used to describe the functions that are performed after the contracting parties have signed the contract.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>As a precise term, contract administration refers to those activities that take place after contract award and can include a plethora of activities ranging from routine to unusual.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It requires the contract manager to remain focused on the program goals and objectives. Good contract administration fails when program goals and objectives are not met.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Contract administration includes the development of a contract administration plan, performance monitoring, contract closeout, and analysis.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Contract administration activities include payment, monitoring of progress, inspection and acceptance, quality assurance, monitoring and surveillance, modification, negotiation, contract closeout, and many others.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Purpose of contract administration</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Contract administration focus on the achievement of stated goals and objectives that fall within the framework of the negotiated contract.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Contract administration protects the rights of the parties and ensures that the obligations of the parties are met.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>From the public sector perspective, contract administration is concerned with the wise expenditure of public funds and the design and application of a decision-making process, which results in outcomes that are in the best interests of the citizens it serves.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Strategic Contribution</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Contract administration requires the effective and efficient management of executed contract agreements.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Contracts are created to meet the validated requirements of public organizations. So each contract makes some contribution to the operational effectiveness of any organization. Contractual arrangements are mission-oriented so contribute to the success of the mission of the organization</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Typical Contract Administration Problems</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>1. Wrong or unsatisfactory product is delivered.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>2. Delay in delivery or completion.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>3. Dispute over the definition of acceptance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>4. Change orders.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>5. Personality conflicts between the contractor and the agency representatives.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>6. Limited or no replacement sources of supply.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>7. Poor performance.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>8. High risk of failure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>9. Use of subcontracts.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>10. High costs.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>To effectively manage a contract, the procurement department should anticipate which of these contract administration problems will most likely be encountered and then develop specifications, contract clauses, and a contract-monitoring plan to avoid or manage the problems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Benefits of Good Contract Administration</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>1. <strong>Effective Control</strong> - ensuring that both parties know their obligations and implementing a contract control system that reflects the performance requirements of the contract and provides mechanisms for the coordination and dissemination of information.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>2. <strong>Performance to the required standard</strong> - Full use should be made of a contractor’s own management information and performance measurement system, with the contractor reporting progress through the agreed procedure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>3. <strong>Compliance with contract conditions</strong> - Managing the contract conditions will help to ensure that they are met; if they are not met, they provide remedies to be applied properly and promptly.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>4. <strong>Clear and documented records</strong> – These are essential in the event of invoking default procedures or seeking correction of failures to perform.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>5. <strong>Management of change</strong> - It is the contract administrator’s responsibility to define appropriate change control procedures which enable him/her to anticipate, manage and control changes to requirements and/or costs.</p>\n<!-- /wp:paragraph -->', 'Contract Administration', '', 'inherit', 'closed', 'closed', '', '1904-revision-v1', '', '', '2023-05-09 00:02:38', '2023-05-08 18:32:38', '', 1904, 'https://civilengineeringlectures.com/?p=1905', 0, 'revision', '', 0),
(1872, 1, '2024-06-26 19:37:34', '2023-02-27 17:33:20', ' ', '', '', 'publish', 'closed', 'closed', '', '1872', '', '', '2024-06-26 19:37:34', '2024-06-26 14:07:34', '', 0, 'https://civilengineeringlectures.com/1872/', 77, 'nav_menu_item', '', 0),
(1875, 1, '2023-02-28 19:22:45', '2023-02-28 13:52:45', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement. They used it for constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime putty may be blended with Portland cement in mortars where its water-retention properties are greater than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air. Then, it gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', 'Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans', 'inherit', 'closed', 'closed', '', '1862-revision-v1', '', '', '2023-02-28 19:22:45', '2023-02-28 13:52:45', '', 1862, 'https://civilengineeringlectures.com/?p=1875', 0, 'revision', '', 0);
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(1874, 1, '2023-02-28 19:21:40', '2023-02-28 13:51:40', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement. They used it for constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime putty may be blended with Portland cement in mortars where its water-retention properties are greater than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air, which gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', 'Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans', 'inherit', 'closed', 'closed', '', '1862-revision-v1', '', '', '2023-02-28 19:21:40', '2023-02-28 13:51:40', '', 1862, 'https://civilengineeringlectures.com/?p=1874', 0, 'revision', '', 0),
(1876, 1, '2023-02-28 19:27:10', '2023-02-28 13:57:10', '<!-- wp:paragraph -->\n<p>The term <strong><em>cement</em></strong><em> </em>refers to materials that act as adhesives. However, in this context, its use is restricted to that of a binding agent for sand, stone, and other aggregates within the manufacture of mortar and concrete.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Hydraulic cement sets and hardens by internal chemical reactions when mixed with water.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Non-hydraulic materials such as lime will only harden slowly by absorption of carbon dioxide from the air.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans, who used the material to produce lime mortar. Romans frequently mixed lime with volcanic ashes, such as pozzolana, to convert a non-hydraulic lime into hydraulic cement. They used it for constructing aqueducts and other buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>LIME – as a construction material in Sri Lanka</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>There is a long history of production and use of lime in Sri Lanka. It was mainly used as a cementing agent and also as a decorative whitewash in the building industry. The use of lime as a building material dates back to the Anuradhapura and Polonnaruwa periods. The famous gallery of Sigiriya known as “Kadapath paura” had been coated with lime plaster. It was polished so well that even today, it shines like glass.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In recent years, the demand for lime has increased in other areas. It is now used for water treatment works, in the sugar industry, and also for agricultural purposes. There are other miscellaneous applications such as earth stabilization works in road construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Traditional methods of lime production are still used in Sri Lanka. However, few efforts have been made to improve upon these methods, mainly by improving the kiln design.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell deposits, the raw materials traditionally used for lime production, are mainly confined to the southwestern and southern coastal belts of Sri Lanka.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the central hill country, lime is produced by making use of dolomite deposits. Dolomite is a type of limestone containing a proportion of magnesium carbonate (MgCO<sub>3</sub>) as well as calcium carbonate (CaCO<sub>3</sub>).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Manufacture of Lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1863,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaCO3.jpg\" alt=\"\" class=\"wp-image-1863\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:image {\"id\":1864,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Reaction.jpg\" alt=\"\" class=\"wp-image-1864\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime is manufactured by calcining natural calcium carbonate, typically hard-rock carboniferous limestone. The mineral is quarried, crushed, ground, washed, and screened to the required size range. The limestone is burnt at approximately 950°C in either horizontal rotary kilns or vertical shaft kilns which drive off the carbon dioxide to produce quicklime or lump lime (calcium oxide).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In Sri Lanka limestone occurs in various forms, which include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>Miocene limestone (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Coral (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Shell (over 95% CaCO<sub>3</sub>)</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Dolomite (MgO (variable 8% -21%))</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Calcite (CaCO<sub>3</sub> (100% pure))</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>Miocene limestone is mostly used for the manufacturing of hydraulic cement. Calcite is limited in its occurrence. It is used in the ceramic industry. Shell, coral, and dolomite are used for lime production. However, coral and shell deposits will likely be exhausted within the next 8 to 10 year time. Therefore, Dolomite deposits and the Miocene limestone would finally have to be the raw materials for lime manufacture.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Coral and shell occur in the size range which can be directly used in kilns. Dolomite, which is used in the hill country, is readily accessible. But it needs to be quarried and broken down into lumps of the required size. It is extracted manually using crowbars, picks, and hammers. Large boulders are blasted by using dynamite. The dolomite is then broken down by hammer to a kiln feed size of 50-80 mm diameter.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The kiln and firing methods</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The main type of firewood used is the trunk of the coconut palm cut into lengths of about 75 cm. Coconut palm leaves, husks, and coconut shells are normally used to start the fire in the kiln.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:image {\"id\":1865,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/klin.png\" alt=\"\" class=\"wp-image-1865\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>A typical kiln in a coastal area has a cylindrical inner wall that ranges in diameter from about 1 to 1.5 meters. The height ranges from 2.5 to 3.0 meters. The kiln is constructed with normal cottage-type clay engineering bricks set in a lime clay mortar. The firing openings are at the bottom of the kiln. The kiln is charged with alternate layers of fuelwood and limestone (coral). At the base are placed fuelwood and other materials to rapidly initiate a fire. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For each batch, about 1.5 to 3 tons of coral are used together with around 0.75 to 1.5 tons of fuelwood. The kiln is ignited and allowed to burn for approximately 48 hours and then cooled to recover about 0.75 to 1.5 tons of quicklime (CaO). Discharging is carried out from the bottom. Batch-type kilns are normally used to burn coral and shell. Depending on capacity, the output of the kilns varies considerably.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the hill country, with dolomite as the raw material, kilns are of the continuous type and are taller than the kilns in the coastal area. They are 3.0 to 3.5 meters high with an inner diameter of 1 to 1.5 meters. About 2 tons of dolomite is loaded into these kilns alternating with fuelwood (coconut palm trunks), and daily a ton of quicklime is recovered from the bottom with stone and fuelwood continuously being replenished at the top.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking of lime</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:heading {\"level\":3} -->\n<h3><strong>(</strong><strong>Hydration of quicklime)</strong></h3>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Most of the quicklime taken from the kiln is of reasonable particle size for hydration. In any case, there is a fair amount of air slaking before the actual slaking operation is carried out, which is done by pouring water over a fairly large pile of quicklime which is then mixed manually with a shovel. The hydrated lime is then sieved to remove the larger lumps of lime which have not hydrated properly before the product is bagged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>No milling is undertaken because the building industry and other users of lime are satisfied with the product in this state, and to keep the processing costs low. The average calcium oxide content by mass in lime samples from the coastal area is 58 percent and in dolomitic lime samples 43 percent. The magnesium oxide content by mass in the hill country dolomitic samples of lime is around 26 percent.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Mode of operation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Production in the coastal area is on a batch basis with the recovery of about a ton of lime each day. Kilns are fired depending on the availability of coral, which is getting scarcer each day. Lime is normally sold by ton, although units of 50 kg and 25 kg are also available.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>With the production of dolomitic lime, it should be noted that in dolomite the magnesium carbonate (MgCO<sub>3</sub>) components dissociates to magnesium oxide (MgO) at around 775°C. The dolomite when heated to 900°C, the lowest temperature normally used to break down the calcium carbonate (CaCO<sup>3</sup>) component to calcium oxide (CaO), will produce MgO which is over-burnt and not readily converted to the hydroxide, Mg(OH)<sub>2</sub>. If this material is used without allowing the hydration to be completed, blistering of plasters can occur if used for plastering walls. If the dolomite lime is to be used for mortar it need only be kept for about three days after slaking. Masons and plasterers claim that dolomitic lime should be added to water and not water to dolomitic lime for satisfactory results and kept for as long a period as possible.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Slaking</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1866,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/CaO.jpg\" alt=\"\" class=\"wp-image-1866\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Slaking is the addition of water to quicklime which is a highly exothermic reaction. The controlled addition of water to quicklime produces hydrated lime (mainly calcium hydroxide) as a dry powder. It is suitable for use within mortars or in the manufacture of certain aerated concrete blocks. Generally, the addition of lime to cement mortar, render or plaster increases its water-retention properties, thus retaining workability, particularly when the material is applied to absorbent substrates such as porous brick. Lime also increases the cohesion of mortar mixes allowing them to spread more easily. Lime-based mortars remain sufficiently flexible to allow movement but additionally, due to the presence of uncarbonated lime, any minor cracks are subsequently healed by the action of rainwater. Hydrated lime absorbs moisture and carbon dioxide from the air, and should therefore be stored in a cool, draught-free building and used whilst still fresh.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Lime putty</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Lime putty is produced by slaking quicklime with an excess of water for several weeks until a creamy texture is produced. Alternatively, it can be made by stirring hydrated lime into the water, followed by conditioning for at least 24 hours. However, the traditional direct slaking of quicklime produces finer particle sizes in the slurry; the best lime putty is produced by maturing it for at least six months. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Lime putty may be blended with Portland cement in mortars. It gives greater water-retention properties than that afforded by hydrated lime. Additionally, lime putty, often mixed with sand to form <em>coarse stuff</em>, is used directly as a pure lime mortar, particularly in restoration and conservation work. It sets, not by reaction with sand and water, but only by carbonation, and is therefore described as <em>non-hydraulic</em>. Limewash, as a traditional surface coating, is made by the addition of sufficient water to lime putty to produce a thin creamy consistency.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Carbonation</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:image {\"id\":1867,\"sizeSlug\":\"full\",\"linkDestination\":\"none\"} -->\n<figure class=\"wp-block-image size-full\"><img src=\"https://civilengineeringlectures.com/wp-content/uploads/2023/02/Carbonation.jpg\" alt=\"\" class=\"wp-image-1867\"/></figure>\n<!-- /wp:image -->\n\n<!-- wp:paragraph -->\n<p>Lime hardens by the absorption of carbon dioxide from the air. Then, it gradually reconverts the calcium oxide back to calcium carbonate. The carbonation process is slow, being controlled by the diffusion of carbon dioxide into the bulk of the material. When sand or stone dust aggregate is added to the lime putty to form a mortar or render, the increased porosity allows greater access to carbon dioxide and a speedier carbonation process. The maximum size of aggregate mixed into lime mortars should not exceed half the mortar-joint width. Typical lime mortar mixes are within the range of 1:2½ and 1:3, lime putty: aggregate ratio. Because of the slow carbonation process, masonry lifts are limited, and the mortar must be allowed some setting time to prevent its expulsion from the joints.</p>\n<!-- /wp:paragraph -->', '<strong>LIME – as a construction material</strong>', 'Lime was used throughout the world by ancient civilizations as a binding agent for brick and stone. The concept was brought to Britain in the first century AD by the Romans', 'inherit', 'closed', 'closed', '', '1862-autosave-v1', '', '', '2023-02-28 19:27:10', '2023-02-28 13:57:10', '', 1862, 'https://civilengineeringlectures.com/?p=1876', 0, 'revision', '', 0);
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(1878, 1, '2023-03-07 00:55:02', '2023-03-06 19:25:02', '<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Employer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The employer is also called the client or building owner. He is the organization or person who commissions the construction project. The important thing is that employer is the person who pays the cost of the work.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Much of the success of a building contract will depend on the employer and the motivation given by him.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer’s prime role is to establish a structure for the management of the project and to make sure that it works.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer has a substantial influence on the design of the project with respect both to functional efficiency and overall appearance. Therefore, he has to take particular care to:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>understand fully the purpose of the building;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>guarantee that the necessities of the end user are accommodated;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>communicate those necessities to the architect/designer;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>appoint an architect/designer with proven ability in designing buildings that satisfy users’ requirements.</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>To ensure a satisfactory outcome, the employer should collaborate well with the architect/designer and his team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>However, these conditions do not often operate in practice. For example, the employer impatiently demands drawings, and cost estimates. &nbsp;Then, he requires bids and ultimately a completed building in a short space of time. This will result inadequate drawings and other contract documents, prepared in hurry. Final, this may be a reason for many problems and disputes when the work is underway on the site. Therefore, sufficient time must be allowed for the proper planning of the project and for contractors to price and return the bills of quantities and form of bid. Otherwise, contractors have to price high to cover themselves against unidentified risks.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>As far as possible, the employer should refrain from requesting changes to the original design as the work proceeds. Such variations often result in delays and disorganization of the work. It also gives rise to increased costs and claims from the contractor.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is very important that the employer shall honour the payment certificates issued by the architect within the period indicated in the appendix to the form of the contract. Contractors should be promptly paid to prevent cash flow problems. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>However, it should be borne in mind that most employers want what they need when they want it, and at a price, they can afford.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer’s purpose in starting a building project is usually driven by the need for the project as a functional unit or as an investment.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The possible objectives of the employer are as follows:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(a) Cost-related</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize capital cost</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>maximize capital cost/value ratio</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reach necessary income cash flow profile</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize management costs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize maintenance and insurance costs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize tax liability</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>be energy efficient.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(b) Marketability - maximize present value or at future disposal (freehold or otherwise).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(c) Use-related</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>optimize operational requirements of the intended occupier(s)</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reflect the intended occupier’s requirements/ability to afford</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>meet social / occupier’s special needs (e.g. disabled).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(d) Environmental</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize health and safety risks</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>choose materials that reflect sustainability</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>Aesthetically please (e.g. impression on occupier’s customers)</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize any alterations to specific features</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reflect planning authority’s policies</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize possible opposition</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>maximize the comfort of occupants</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize inconvenience to others during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(e) Timing</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>construct within a defined period</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize risks of delay during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer also has a dual management function:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>to manage the client input;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To co-ordinate functional and administrative needs;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To resolve conflicts;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To act as the formal point of contact for the project;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>to supply the technical expertise, to assess, procure, monitor, and control the external resources needed to implement the project.</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>The employer should also coordinate and resolve conflicts between all interested sections of the employer’s organization. He is responsible for ensuring that all necessary decisions are made on time. Timely decisions will avoid unnecessary delays and reduce increased costs. &nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Architect</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><em>The term ‘design professional’ is often used to refer to the architect, and engineer as they perform their planning, design, and construction liaison tasks on a construction project. </em><strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>It is common to use the words architect-engineer, and architectural-engineering firm, for the party engaged in carrying out these tasks.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>The role played by each of these two professionals varies considerably depending on the type of project.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>If it is a building or other facility project, such as a new residence, school, hotel, or apartment building, the architect is likely to lead the planning and design team.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>If the project involves constructing a highway, bridge, dam, pipeline, or industrial plant, the architect role will be very small role. Depending on the project, the engineer (actually many specialties) may be involved with utility studies, structural design, heating, ventilating, and air conditioning (HVAC) systems, data communications systems, roadway layout, pavement design, and earthwork and foundation systems.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is often regarded as the leader of the building team in a building project. He normally receives a commission to design and supervise the construction of the building.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect will most likely need assistance from other specialists. For example, structural engineers may be required to design the structural frame, mechanical and electrical engineers to design the M &amp; E services, and quantity surveyors to advice on contractual and cost aspects and prepare bills of quantities and contract documentation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is usually responsible for the preparation of the contract, including the formulation of designs for the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is practically in sole control of the project until the contract is signed. But, he should make it clear to all bidders that he is acting on behalf of the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Once work has started on the site, he is responsible for ensuring that the contractor carries out the whole of the work under the contract to the architect’s reasonable satisfaction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is normally the only member of the building team with an overall view of the project. His functions usually include liaison with the employer, representatives of local authorities, consultants, and specialists. Liaison with the contractor may start at an earlier or later stage, depending on the type of the contract.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect’s first task, after the appointment, is to discuss with the employer his building requirements. This usually emerges as a list of needs, commonly referred to as “the brief”.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong><em>The brief</em></strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><em>The brief is a statement that specifies the scope of the project. It defines the objectives to be achieved and lays out in a general way what the final product will accomplish. The brief can be prepared by the owner as a means of clarifying the need for the project, even before the project manager or design professionals are engaged; if used in this way, it will be the basis upon which those prospective consultants prepare their proposals. On the other hand, it can also be prepared with the help of the project manager or design professional after they are engaged. These consultants, with experience on similar projects, can assist the owner in identifying and clarifying needs and setting forth the project’s scope. A well-prepared brief, consisting of only a few pages, is essential in forming the basis for all that follows throughout the project life cycle. The development of the </em><em>programme</em><em> will logically follow from this initial defining statement.<strong></strong></em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>When both site details and the major building requirements are known, preliminary designs can be prepared. At this stage, the architect will begin to select his team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>When preparing preliminary schemes, it is necessary to consider the comparative costs of alternative proposals, and for that purpose, a quantity surveyor should be appointed.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect’s process then follows often on the following lines:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list {\"ordered\":true,\"type\":\"a\"} -->\n<ol type=\"a\"><!-- wp:list-item -->\n<li>Preparation of preliminary schemes, including estimates, as part of a feasibility study.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>After approval by the employer, preparation of sketch plans and approximate estimates.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of structural and services schemes either by consultants / specialist sub-contractors.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of cost plans in consultation with the quantity surveyor.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of working drawings, invitations for bids from specialist suppliers and sub-contractors, if these items are to be dealt with as prime cost sums.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of bills of quantities with the quantity surveyor.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Invite suitable contractors to bid. To enable them to reach a firm decision, they will be informed of the general nature of the work, the date when bills will be available, and the dates for submission of bids and completion of works.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Formal invitation to bid with full documentation.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Receipt of bids, advice to employer on the selection of contractor, and preparation of contract document.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Supervision of construction work.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Certifying payments to the contractor during the contract.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Issuing variation orders and other architect’s instructions as necessary.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Directing how provisional sums are to be spent.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Securing and remedying defects at the end of the defects liability period.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Certifying the final account.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Closing–out the contract.</li>\n<!-- /wp:list-item --></ol>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>The architect acts as an expert adviser / agent for the employer. Where the architect is named in the articles of agreement, the contractor is justified in treating every order received from the architect as a direct order from the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is, however, unwise for the architect to issue a variation orders covering a significant variation to the contract, without receiving the employer’s prior approval.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Some architects’ main faults are issuing inadequate details, working to unrealistic programs, and mainly excessive changes to designs during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>For non-facility projects, the overall role of the engineer is much the same as that provided by the architect on facilities projects.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The engineer takes charge of the planning and design phase, coordinating the various parties and their activities, often including the contractor selection and project inspection tasks.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Depending on the project, the engineer (really many specialties) may be involved with utility studies, structural design, heating, ventilating, and air conditioning (HVAC) systems, data communications systems, roadway layout, pavement design, and earthwork and foundation systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For a facilities project, the engineer typically fills a supporting role, providing planning and design services in the geotechnical, structural, mechanical, and electrical aspects of the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Quantity Surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The quantity surveyor prepares schedules of quantities of the various project elements. Sometimes, this work is performed in conjunction with that of the cost estimator.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In many construction works, a schedule of quantities is prepared for most types of contracts, including lump sum and unit price. In other works, the quantity surveyor prepares schedules of quantities for unit-price contracts, while the quantity take-off work for lump-sum contracts is left to individual bidders.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Quantity surveys are conducted at various points during the planning and design phase, not only during construction document development.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Depending on the stage at which a quantity survey is performed, the quantities might include such detailed information as the number of cubic meters of a certain type of concrete and the number of linear meters of a certain size of communication cable. With less detail available, they might indicate the areas of different types of interior walls or even simply the volume or area of a facility devoted to certain types of use.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Construction cost, construction management, and construction communications are key problem areas for an employer who has commissioned an important building or engineering project. A quantity surveyor is professionally trained, qualified, and experienced in dealing with these problems on behalf of the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is essentially a cost expert whose main task is to ensure that the project is kept within the agreed budget and that the employer obtains value for money.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Some of the services he offers are preliminary cost advice and cost planning, preparation of bid documents, advice on the type of contract and method of obtaining bids, negotiation with contractors, valuation of work in progress, and settlement of the final account. He will at all times need to cooperate very closely with the architect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Range of services that Quantity Surveyors can offer:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>a) Feasibility studies.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>b) Procurement procedure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>c) Budget Estimating.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>d) Cost / Design comparison.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>e) Contractual procedure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>f) Value advice.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>g) Preparation of Bill of Quantities.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>h) Bid evaluation and reporting.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>i) Site re-measurements.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>j) Rate negotiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>k) Checking of monthly payments and final accounts.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>l) Financial reporting and cash flow projections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>m) Claims assessment and negotiations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>n) Advice on and participation in arbitration.&nbsp; <strong>&nbsp;</strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Role of the Quantity Surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As building work increased in volume and complexity, employers became dissatisfied with the method used for settling the cost of the work and recognized the advantage of employing an independent quantity surveyor. His job was to prepare an accurate bill of quantities to be priced by bidding contractors and measure and value any variations that might occur during the progress of the works.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An authoritative RICS report (1970) stated “the quantity surveyor’s role is to ensure that resources of the construction industry are utilized to the best advantage of society by providing, financial management for projects and a cost consultancy service to client and designer during the whole construction process”.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list {\"ordered\":true,\"type\":\"1\"} -->\n<ol type=\"1\"><!-- wp:list-item -->\n<li>Preliminary Cost Advice</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>From the inception of a new building project, the quantity surveyor can give practical advice on the likely cost of the scheme.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He can advise on the comparative costs of alternative layouts, materials, components, and methods of construction.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He can also assess how long it will take to build and can produce estimates of future maintenance and operating costs.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Once the employer’s brief is finished, the quantity surveyor can prepare a realistic budget and a cost plan showing the distribution of costs over the various elements.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cost Planning</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cost planning aims to help all members of the design team to arrive jointly at practical and efficient designs for the project and to keep within the budget.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Effective cost planning will help to ensure that everything follows in accordance with the estimate, from the successful contractor’s bid to the final project cost.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>If the employer decides to change his plans and introduce variations, the quantity surveyor will assess the cost implication.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Constant monitoring means that the risk of overspending can be identified at an early stage and early corrective action can be taken.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cooperation between Architect and Quantity Surveyor – for cost planning</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The Quantity Surveyor acts as a specialist adviser to the architect on all matters concerned with building and engineering costs.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He offers considerable assistance to the architect in advising on the financial effect of the design proposal. It helps in ensuring the money available is put to the best possible use and that final costs are kept within the agreed budget.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Where the estimated cost of an element exceeds the cost target, then either the element must be re-designed or other cost targets reduced.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Where several design elements would have to be adjusted to keep costs within the total cost limit, and if this would result in a building of undesirably low quality, the design team should request additional funds from the employer.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The quantity surveyor’s cost information will vary from major design alternatives, such as the size and height of residential blocks, to cost studies into alternative forms of construction, cladding, and finishes.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The fundamental question must often be asked such as “is this expenditure really necessary?” or “is there a better way of meeting the particular need?”&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li>\n<!-- /wp:list-item --></ol>\n<!-- /wp:list -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\">I<strong>n the public and private Sectors</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>In both the public and private sectors, the quantity surveyor as a member of the design team and advises the employer and architects on the likely costs of alternative designs.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>His advice enables design and construction at all stages to be controlled within predetermined limits of expenditure. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He prepares bills of quantities, negotiates with contractors, and prepares forecasts of final costs and valuation for payments to the contractor as work proceeds. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is responsible for the measurement and valuation of variations in the work during the contract and for the preparation and agreeing of the contractor’s final account.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Appointment of an independent quantity surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As long ago as 1983 the RICS (Quantity Surveying Division) encouraged the appointment of independent quantity surveyors to provide clients with truly independent and authoritative advice.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The client guide issued by the RICS on the above matter illustrates the advantages of appointing the quantity surveyor at the inception stage of a scheme so that he can give advice on costs and contractor procurement.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\">I<strong>n the Contracting Organization</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>In contracting organizations, the duties of the quantity surveyor will vary according to the size of the firm employing him.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The quantity surveyor employed by the contractor will aim to secure maximum payments for the work done at the earliest possible time to avoid any possible cash flow problems. However, this has to be undertaken within the provisions of the contract. The contractor cannot receive more than his contractual entitlements.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The contractor’s quantity surveyor’s activities can include;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing bills of quantities for small projects,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Collecting information about the cost of various operations from which the contractor can prepare future estimates,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing precise details of the materials required for the contracts in hand,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Compiling target figures so that operatives can be paid production bonuses,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing interim costing so that the financial position of the contract can be ascertained as the work proceeds and appropriate action is taken when necessary,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Planning contracts and preparing progress charts in conjunction with site management,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Making application to the architect for variation orders if drawings or site instructions vary the work,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Agreeing on the value of variations and subcontractors’ accounts, and</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Comparing the costs of alternative methods of carrying out various operations such as temporary works so that the most economical can be adopted.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Project Manager</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The project manager and their staff become important members of the building team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is likely that the project manager will be engaged early in the planning process and will serve throughout the project life cycle.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>Also, the project manager might be engaged somewhat later in the process, after some of the preliminary planning and feasibility analysis is completed, especially if those early efforts were conducted within the owner’s organization.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The project manager will act on the owner’s behalf for the <em>entire </em>project and may serve in this role on multiple simultaneous projects.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Land surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As various sites are being investigated and especially after one has been selected, land surveyors may be engaged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For building projects, this work includes investigation of property records, easements and rights of way, establishment or re-establishment of property corners and boundaries, determination of land contours and slopes, and location of existing improvements, natural features, and obstructions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>A pipeline or highway project can involve much preliminary route layout as various alternative routes are investigated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>This effort includes on-the-ground, aerial/photogrammetric, and satellite-based global positioning system methods that lead to route layouts, various kinds of maps, and geographic information system databases for use in project planning.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Surveyors may also be involved in the construction phase, but they are equally important as part of the planning and design team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Cost estimator</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>If funding is limited, the owner will desire an estimate of the final cost beginning early in the project’s life.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Obviously, until final construction contracts are arranged, this estimate can only be an approximation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The cost estimator is responsible for compiling this information.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Cost estimates can be prepared at various levels of detail.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the planning stage, little information is available about the physical properties of the project elements. Therefore, the estimate of cost has little detail. As more design is developed, the cost estimator provides more detailed cost numbers. The degree of accuracy improves as more detail is developed.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For example, early in the planning process, when little more than the total project area is known (and that perhaps only preliminarily), the cost estimate is probably accurate to within ±30%. Part-way through the design process, cost estimates has to be accurate to within ±20%. When final construction documents are ready for the tender process, an estimate of the accuracy of ±10% can be expected.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Although we imply that the cost estimator is a separate member of the team, often the architectural or engineering designer performs this task in association with the various design activities.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The term <em>engineer’s estimate </em>is often used for that estimate prepared after design development.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Structural Engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>He is commonly a consultant to the architect. The structural engineer would look at the proposed design from a ‘practicability of construction’ point of view. The architect will provide an artistic approach to the clients’ idea but the structural engineer will look at the design of the structure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Structural Engineer provides specialized design advice which is coordinated by the architect. In civil engineering projects, the lead design engineer will generally be a civil engineer and will coordinate the design advice from other specialist engineers.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These specialist designers will often take on supervisory duties as well as design. The purpose would be to visit the site and inspect the work to ensure that the work is produced in accordance with the design. &nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Civil engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Civil engineers are involved with the design, development, and construction of a huge range of projects in the built and natural environment.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Their role is central to ensuring the safe, timely, and well-resourced completion of infrastructure projects in many areas, including highway construction, waste management, coastal development, and geotechnical engineering.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Consulting civil engineers liaise with clients to plan, manage, design, and supervise the construction of projects. They work in several different settings and, with experience, can run projects as project managers. Within civil engineering, consulting engineers are the designers; contracting engineers turn their plans into reality.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Typical work activities include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Undertaking technical and feasibility studies and site investigations</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Developing detailed designs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Assessing the potential risks of specific projects, as well as undertaking risk management in specialist roles</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Supervising bidding procedures and putting together proposals</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing, supervising, and visiting contractors on site and advising on civil engineering issues</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing budgets and other project resources</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing change (as the client may change their mind about the design) and identifying, formalizing, and notifying relevant parties of changes in the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Scheduling material and equipment purchases and delivery</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Attending public meetings and displays to discuss projects, especially in a senior role</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Adopting all relevant requirements around issues such as building permits, environmental regulations, sanitary design, good manufacturing practices, and safety on all work assignments • Ensuring that a project runs smoothly and that the structure is completed on time and within budget</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Correct any project deficiencies that affect production, quality, and safety requirements before final evaluation and project reviews.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The Contractor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The contractor is the person or the firm who undertakes to complete a building project in accordance with the contract documents on behalf of the employer. He should have full control of all operations on site. It includes the works carried out by nominated subcontractors, with whom he has a direct contractual relationship through subcontracts.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Under the conditions of contract (JCT80), the contractor is to proceed regularly and diligently with the works and complete them by a specified date. Failure to comply with this requirement may render the contractor liable for the payment of liquidated damages.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He must insure the building operations against fire and possible injury to persons or property during the construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He receives all his instructions through the architect. But he has dealings with other parties to the contract, such as the quantity surveyor, when he measures and values completed work. </p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The contractor employs personnel to take charge of work on the site. For large projects, there can be a site agent, while on small schemes, a foreman will probably be sufficient. The contractor often employs a quantity surveyor to safeguard his financial interests. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>Building services engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Building services engineers are responsible for ensuring the cost-effective and environmentally sound and sustainable design and maintenance of energy-using elements in buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>They have an important role in developing and maintaining buildings and their components, to make the most effective use of natural resources and protect public safety.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>This includes all equipment and materials involved with heating, lighting, ventilation, air conditioning, electrical distribution, water supply, sanitation, public health, fire protection, safety systems, lifts, escalators, façade engineering, and even acoustics.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>While the role increasingly demands a multidisciplinary approach, building services engineers tend to specialize in one of the following areas:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Electrical engineering</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Mechanical engineering, and</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Public health.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Activities will vary according to the specialist area of work and whether the building services engineer is employed by a single organization or a consultancy, but tasks typically involve:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Advising clients and architects on energy use and conservation in a range of buildings and sites, aiming to minimize the environmental impact</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Managing and forecasting spending, using whole life cycle costing techniques, ensuring that work is kept to budget</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Developing and negotiating project contracts and agreeing on these with clients, if working in consultancy, and putting out tenders</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Attending a range of project groups and technical meetings</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Working with detailed diagrams, plans, and drawings</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Using specialist computer-aided design (CAD) software and other resources to design all the systems required for the project</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Designing site-specific equipment as required</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Commissioning, organizing, and assessing the work of contractors</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Overseeing and supervising the installation of building systems and specifying maintenance and operating procedures</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Monitoring building systems and processes</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Facilities management</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Ensuring that the design and maintenance of building systems meet legislative and health and safety requirements.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2 class=\"wp-block-heading\"><strong>The clerk of works</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The clerk of works is the architect’s representative on site. He is usually a tradesman with many years of practical experience.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>The job title ‘clerk of works’ is believed to derive from the thirteenth century when ‘clerics’ in holy orders were accepted as being more literate than their fellows and were left to plan and supervise the ‘works’ associated with the erection of churches and other religious property.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>By the nineteenth century, the role had expanded to cover the majority of building works. Therefore, clerk of works was drawn from experienced tradesmen who had wide knowledge and understanding of the construction process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The clerk of works is the person who must ensure the quality of both materials and workmanship. To this end, he must be impartial and independent in any decisions and judgments. They cannot normally, under the quality role, be employed by the contractor – only the client, and normally by the architect on behalf of the client.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Their role is not to judge, but simply to report (through exhaustive and detailed diary notes) all occurrences that are relevant to the role.</p>\n<!-- /wp:paragraph -->', '<strong>The Building Team</strong>', '', 'publish', 'open', 'open', '', 'the-building-team', '', '', '2023-05-12 18:21:31', '2023-05-12 12:51:31', '', 0, 'https://civilengineeringlectures.com/?p=1878', 0, 'post', '', 0);
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(1884, 1, '2023-03-07 08:58:09', '2023-03-07 03:28:09', '<!-- wp:heading -->\n<h2><strong>The Employer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The employer is also called the client or building owner. He is the organization or person who commissions the construction project. The important thing is that employer is the person who pays the cost of the work.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Much of the success of a building contract will depend on the employer and the motivation given by him.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer’s prime role is to establish a structure for the management of the project and to make sure that it works.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer has a substantial influence on the design of the project with respect both to functional efficiency and overall appearance. Therefore, he has to take particular care to:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>understand fully the purpose of the building;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>guarantee that the necessities of the end user are accommodated;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>communicate those necessities to the architect/designer;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>appoint an architect/designer with proven ability in designing buildings that satisfy users’ requirements.</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>To ensure a satisfactory outcome, the employer should collaborate well with the architect/designer and his team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>However, these conditions do not often operate in practice. For example, the employer impatiently demands drawings, and cost estimates. &nbsp;Then, he requires bids and ultimately a completed building in a short space of time. This will result inadequate drawings and other contract documents, prepared in hurry. Final, this may be a reason for many problems and disputes when the work is underway on the site. Therefore, sufficient time must be allowed for the proper planning of the project and for contractors to price and return the bills of quantities and form of bid. Otherwise, contractors have to price high to cover themselves against unidentified risks.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>As far as possible, the employer should refrain from requesting changes to the original design as the work proceeds. Such variations often result in delays and disorganization of the work. It also gives rise to increased costs and claims from the contractor.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is very important that the employer shall honour the payment certificates issued by the architect within the period indicated in the appendix to the form of the contract. Contractors should be promptly paid to prevent cash flow problems. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>However, it should be borne in mind that most employers want what they need when they want it, and at a price, they can afford.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer’s purpose in starting a building project is usually driven by the need for the project as a functional unit or as an investment.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The possible objectives of the employer are as follows:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(a) Cost-related</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize capital cost</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>maximize capital cost/value ratio</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reach necessary income cash flow profile</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize management costs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize maintenance and insurance costs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize tax liability</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>be energy efficient.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(b) Marketability - maximize present value or at future disposal (freehold or otherwise).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(c) Use-related</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>optimize operational requirements of the intended occupier(s)</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reflect the intended occupier’s requirements/ability to afford</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>meet social / occupier’s special needs (e.g. disabled).</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(d) Environmental</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize health and safety risks</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>choose materials that reflect sustainability</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>Aesthetically please (e.g. impression on occupier’s customers)</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize any alterations to specific features</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>reflect planning authority’s policies</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize possible opposition</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>maximize the comfort of occupants</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize inconvenience to others during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>(e) Timing</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>construct within a defined period</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><strong>• </strong>minimize risks of delay during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer also has a dual management function:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>to manage the client input;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To co-ordinate functional and administrative needs;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To resolve conflicts;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>To act as the formal point of contact for the project;</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>to supply the technical expertise, to assess, procure, monitor, and control the external resources needed to implement the project.</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>The employer should also coordinate and resolve conflicts between all interested sections of the employer’s organization.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The employer is responsible for ensuring that all necessary decisions are made on time. Timely decisions will avoid unnecessary delays and reduce increased costs. &nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Architect</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><em>The term ‘design professional’ is often used to refer to the architect, and engineer as they perform their planning, design, and construction liaison tasks on a construction project. </em><strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>It is common to use the words architect-engineer, and architectural-engineering firm, for the party engaged in carrying out these tasks.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>The role played by each of these two professionals varies considerably depending on the type of project.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>If it is a building or other facility project, such as a new residence, school, hotel, or apartment building, the architect is likely to lead the planning and design team.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>If the project involves constructing a highway, bridge, dam, pipeline, or industrial plant, the architect role will be very small role. Depending on the project, the engineer (actually many specialties) may be involved with utility studies, structural design, heating, ventilating, and air conditioning (HVAC) systems, data communications systems, roadway layout, pavement design, and earthwork and foundation systems.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is often regarded as the leader of the building team in a building project. The architect normally receives a commission to design and supervise the construction of the building.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect will most likely need assistance from other specialists. For example, structural engineers may be required to design the structural frame, mechanical and electrical engineers to design the M &amp; E services, and quantity surveyors to advice on contractual and cost aspects and prepare bills of quantities and contract documentation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is usually responsible for the preparation of the contract, including the formulation of designs for the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is practically in sole control of the project until the contract is signed. But, he should make it clear to all bidders that he is acting on behalf of the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Once work has started on the site, he is responsible for ensuring that the contractor carries out the whole of the work under the contract to the architect’s reasonable satisfaction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect is normally the only member of the building team with an overall view of the project. His functions usually include liaison with the employer, representatives of local authorities, consultants, and specialists. Liaison with the contractor may start at an earlier or later stage, depending on the type of the contract.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect’s first task, after the appointment, is to discuss with the employer his building requirements. This usually emerges as a list of needs, commonly referred to as “the brief”.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong><em>The brief</em></strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p><em>The brief is a statement that specifies the scope of the project. It defines the objectives to be achieved and lays out in a general way what the final product will accomplish. The brief can be prepared by the owner as a means of clarifying the need for the project, even before the project manager or design professionals are engaged; if used in this way, it will be the basis upon which those prospective consultants prepare their proposals. On the other hand, it can also be prepared with the help of the project manager or design professional after they are engaged. These consultants, with experience on similar projects, can assist the owner in identifying and clarifying needs and setting forth the project’s scope. A well-prepared brief, consisting of only a few pages, is essential in forming the basis for all that follows throughout the project life cycle. The development of the </em><em>programme</em><em> will logically follow from this initial defining statement.<strong></strong></em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>When both site details and the major building requirements are known, preliminary designs can be prepared. At this stage, the architect will begin to select his team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>When preparing preliminary schemes, it is necessary to consider the comparative costs of alternative proposals, and for that purpose, a quantity surveyor should be appointed.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The architect’s process then follows often on the following lines:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list {\"ordered\":true,\"type\":\"a\"} -->\n<ol type=\"a\"><!-- wp:list-item -->\n<li>Preparation of preliminary schemes, including estimates, as part of a feasibility study.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>After approval by the employer, preparation of sketch plans and approximate estimates.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of structural and services schemes either by consultants / specialist sub-contractors.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of cost plans in consultation with the quantity surveyor.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of working drawings, invitations for bids from specialist suppliers and sub-contractors, if these items are to be dealt with as prime cost sums.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Preparation of bills of quantities with the quantity surveyor.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Invite suitable contractors to bid. To enable them to reach a firm decision, they will be informed of the general nature of the work, the date when bills will be available, and the dates for submission of bids and completion of works.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Formal invitation to bid with full documentation.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Receipt of bids, advice to employer on the selection of contractor, and preparation of contract document.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Supervision of construction work.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Certifying payments to the contractor during the contract.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Issuing variation orders and other architect’s instructions as necessary.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Directing how provisional sums are to be spent.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Securing and remedying defects at the end of the defects liability period.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Certifying the final account.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Closing–out the contract.</li>\n<!-- /wp:list-item --></ol>\n<!-- /wp:list -->\n\n<!-- wp:paragraph -->\n<p>The architect acts as an expert adviser / agent for the employer. Where the architect is named in the articles of agreement, the contractor is justified in treating every order received from the architect as a direct order from the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is, however, unwise for the architect to issue a variation orders covering a significant variation to the contract, without receiving the employer’s prior approval.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Some architects’ main faults are issuing inadequate details, working to unrealistic programs, and mainly excessive changes to designs during construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>For non-facility projects, the overall role of the engineer is much the same as that provided by the architect on facilities projects.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The engineer takes charge of the planning and design phase, coordinating the various parties and their activities, often including the contractor selection and project inspection tasks.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Depending on the project, the engineer (really many specialties) may be involved with utility studies, structural design, heating, ventilating, and air conditioning (HVAC) systems, data communications systems, roadway layout, pavement design, and earthwork and foundation systems.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For a facilities project, the engineer typically fills a supporting role, providing planning and design services in the geotechnical, structural, mechanical, and electrical aspects of the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Quantity Surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The quantity surveyor prepares schedules of quantities of the various project elements. In some cases, this work is performed in conjunction with that of the cost estimator.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In many construction works, a schedule of quantities is prepared for most types of contracts, including lump sum and unit price. In other works, the quantity surveyor prepares schedules of quantities for unit-price contracts, while the quantity take-off work for lump-sum contracts is left to individual bidders.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Quantity surveys are conducted at various points during the planning and design phase, not only during construction document development.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Depending on the stage at which a quantity survey is performed, the quantities might include such detailed information as the number of cubic meters of a certain type of concrete and the number of linear meters of a certain size of communication cable. With less detail available, they might indicate the areas of different types of interior walls or even simply the volume or area of a facility devoted to certain types of use.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Construction cost, construction management, and construction communications are key problem areas for an employer who has commissioned an important building or engineering project. A quantity surveyor is professionally trained, qualified, and experienced in dealing with these problems on behalf of the employer.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is essentially a cost expert whose main task is to ensure that the project is kept within the agreed budget and that the employer obtains value for money.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Some of the services he offers are preliminary cost advice and cost planning, preparation of bid documents, advice on the type of contract and method of obtaining bids, negotiation with contractors, valuation of work in progress, and settlement of the final account. He will at all times need to cooperate very closely with the architect.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Range of services that Quantity Surveyors can offer:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>a) Feasibility studies.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>b) Procurement procedure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>c) Budget Estimating.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>d) Cost / Design comparison.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>e) Contractual procedure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>f) Value advice.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>g) Preparation of Bill of Quantities.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>h) Bid evaluation and reporting.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>i) Site re-measurements.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>j) Rate negotiation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>k) Checking of monthly payments and final accounts.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>l) Financial reporting and cash flow projections.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>m) Claims assessment and negotiations.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>n) Advice on and participation in arbitration.&nbsp; <strong>&nbsp;</strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Role of the Quantity Surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As building work increased in volume and complexity, employers became dissatisfied with the method used for settling the cost of the work and recognized the advantage of employing an independent quantity surveyor. His job was to prepare an accurate bill of quantities to be priced by bidding contractors and measure and value any variations that might occur during the progress of the works.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>An authoritative RICS report (1970) stated “the quantity surveyor’s role is to ensure that resources of the construction industry are utilized to the best advantage of society by providing, financial management for projects and a cost consultancy service to client and designer during the whole construction process”.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:list {\"ordered\":true,\"type\":\"1\"} -->\n<ol type=\"1\"><!-- wp:list-item -->\n<li>Preliminary Cost Advice</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>From the inception of a new building project, the quantity surveyor can give practical advice on the likely cost of the scheme.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He can advise on the comparative costs of alternative layouts, materials, components, and methods of construction.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He can also assess how long it will take to build and can produce estimates of future maintenance and operating costs.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Once the employer’s brief is finished, the quantity surveyor can prepare a realistic budget and a cost plan showing the distribution of costs over the various elements.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cost Planning</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cost planning aims to help all members of the design team to arrive jointly at practical and efficient designs for the project and to keep within the budget.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Effective cost planning will help to ensure that everything follows in accordance with the estimate, from the successful contractor’s bid to the final project cost.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>If the employer decides to change his plans and introduce variations, the quantity surveyor will assess the cost implication.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Constant monitoring means that the risk of overspending can be identified at an early stage and early corrective action can be taken.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Cooperation between Architect and Quantity Surveyor – for cost planning</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The Quantity Surveyor acts as a specialist adviser to the architect on all matters concerned with building and engineering costs.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>He offers considerable assistance to the architect in advising on the financial effect of the design proposal. It helps in ensuring the money available is put to the best possible use and that final costs are kept within the agreed budget.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Where the estimated cost of an element exceeds the cost target, then either the element must be re-designed or other cost targets reduced.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Where several design elements would have to be adjusted to keep costs within the total cost limit, and if this would result in a building of undesirably low quality, the design team should request additional funds from the employer.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The quantity surveyor’s cost information will vary from major design alternatives, such as the size and height of residential blocks, to cost studies into alternative forms of construction, cladding, and finishes.</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>The fundamental question must often be asked such as “is this expenditure really necessary?” or “is there a better way of meeting the particular need?”&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</li>\n<!-- /wp:list-item --></ol>\n<!-- /wp:list -->\n\n<!-- wp:heading -->\n<h2><strong>The Role of the Quantity Surveyor in the public and private Sectors</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>In both the public and private sectors, the quantity surveyor as a member of the design team and advises the employer and architects on the likely costs of alternative designs.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>His advice enables design and construction at all stages to be controlled within predetermined limits of expenditure. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He prepares bills of quantities, negotiates with contractors, and prepares forecasts of final costs and valuation for payments to the contractor as work proceeds. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He is responsible for the measurement and valuation of variations in the work during the contract and for the preparation and agreeing of the contractor’s final account.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Appointment of an independent quantity surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As long ago as 1983 the RICS (Quantity Surveying Division) encouraged the appointment of independent quantity surveyors to provide clients with truly independent and authoritative advice.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The client guide issued by the RICS on the above matter illustrates the advantages of appointing the quantity surveyor at the inception stage of a scheme so that he can give advice on costs and contractor procurement.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Role of the Quantity Surveyor in the Contracting Organization</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>In contracting organizations, the duties of the quantity surveyor will vary according to the size of the firm employing him.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The quantity surveyor employed by the contractor will aim to secure maximum payments for the work done at the earliest possible time to avoid any possible cash flow problems. However, this has to be undertaken within the provisions of the contract. The contractor cannot receive more than his contractual entitlements.&nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The contractor’s quantity surveyor’s activities can include;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing bills of quantities for small projects,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Collecting information about the cost of various operations from which the contractor can prepare future estimates,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing precise details of the materials required for the contracts in hand,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Compiling target figures so that operatives can be paid production bonuses,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Preparing interim costing so that the financial position of the contract can be ascertained as the work proceeds and appropriate action is taken when necessary,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Planning contracts and preparing progress charts in conjunction with site management,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Making application to the architect for variation orders if drawings or site instructions vary the work,</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Agreeing on the value of variations and subcontractors’ accounts, and</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Comparing the costs of alternative methods of carrying out various operations such as temporary works so that the most economical can be adopted.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Project Manager</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The project manager and their staff become important members of the building team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>It is likely that the project manager will be engaged early in the planning process and will serve throughout the project life cycle.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>Also, the project manager might be engaged somewhat later in the process, after some of the preliminary planning and feasibility analysis is completed, especially if those early efforts were conducted within the owner’s organization.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The project manager will act on the owner’s behalf for the <em>entire </em>project and may serve in this role on multiple simultaneous projects.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Land surveyor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>As various sites are being investigated and especially after one has been selected, land surveyors may be engaged.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For building projects, this work includes investigation of property records, easements and rights of way, establishment or re-establishment of property corners and boundaries, determination of land contours and slopes, and location of existing improvements, natural features, and obstructions.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>A pipeline or highway project can involve much preliminary route layout as various alternative routes are investigated.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>This effort includes on-the-ground, aerial/photogrammetric, and satellite-based global positioning system methods that lead to route layouts, various kinds of maps, and geographic information system databases for use in project planning.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Surveyors may also be involved in the construction phase, but they are equally important as part of the planning and design team.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Cost estimator</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>If funding is limited, the owner will desire an estimate of the final cost beginning early in the project’s life.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Obviously, until final construction contracts are arranged, this estimate can only be an approximation.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The cost estimator is responsible for compiling this information.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Cost estimates can be prepared at various levels of detail.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>In the planning stage, little information is available about the physical properties of the project elements. Therefore, the estimate of cost has little detail. As more design is developed, the cost estimator provides more detailed cost numbers. The degree of accuracy improves as more detail is developed.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>For example, early in the planning process, when little more than the total project area is known (and that perhaps only preliminarily), the cost estimate is probably accurate to within ±30%. Part-way through the design process, cost estimates has to be accurate to within ±20%. When final construction documents are ready for the tender process, an estimate of the accuracy of ±10% can be expected.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Although we imply that the cost estimator is a separate member of the team, often the architectural or engineering designer performs this task in association with the various design activities.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The term <em>engineer’s estimate </em>is often used for that estimate prepared after design development.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Structural Engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>He is commonly a consultant to the architect. The structural engineer would look at the proposed design from a ‘practicability of construction’ point of view. The architect will provide an artistic approach to the clients’ idea but the structural engineer will look at the design of the structure.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Structural Engineer provides specialized design advice which is coordinated by the architect. In civil engineering projects, the lead design engineer will generally be a civil engineer and will coordinate the design advice from other specialist engineers.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>These specialist designers will often take on supervisory duties as well as design. The purpose would be to visit the site and inspect the work to ensure that the work is produced in accordance with the design. &nbsp;</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Civil engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Civil engineers are involved with the design, development, and construction of a huge range of projects in the built and natural environment.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Their role is central to ensuring the safe, timely, and well-resourced completion of infrastructure projects in many areas, including highway construction, waste management, coastal development, and geotechnical engineering.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Consulting civil engineers liaise with clients to plan, manage, design, and supervise the construction of projects. They work in several different settings and, with experience, can run projects as project managers. Within civil engineering, consulting engineers are the designers; contracting engineers turn their plans into reality.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Typical work activities include:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Undertaking technical and feasibility studies and site investigations</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Developing detailed designs</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Assessing the potential risks of specific projects, as well as undertaking risk management in specialist roles</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Supervising bidding procedures and putting together proposals</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing, supervising, and visiting contractors on site and advising on civil engineering issues</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing budgets and other project resources</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Managing change (as the client may change their mind about the design) and identifying, formalizing, and notifying relevant parties of changes in the project.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Scheduling material and equipment purchases and delivery</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Attending public meetings and displays to discuss projects, especially in a senior role</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Adopting all relevant requirements around issues such as building permits, environmental regulations, sanitary design, good manufacturing practices, and safety on all work assignments • Ensuring that a project runs smoothly and that the structure is completed on time and within budget</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Correct any project deficiencies that affect production, quality, and safety requirements before final evaluation and project reviews.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The Contractor</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The contractor is the person or the firm who undertakes to complete a building project in accordance with the contract documents on behalf of the employer. He should have full control of all operations on site. It includes the works carried out by nominated subcontractors, with whom he has a direct contractual relationship through subcontracts.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Under the conditions of contract (JCT80), the contractor is to proceed regularly and diligently with the works and complete them by a specified date. Failure to comply with this requirement may render the contractor liable for the payment of liquidated damages.<strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He must insure the building operations against fire and possible injury to persons or property during the construction.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>He receives all his instructions through the architect but has dealings with other parties to the contract, such as the quantity surveyor, when he measures and values completed work. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The contractor employs personnel to take charge of work on the site. For large projects, there can be a site agent, while on small schemes, a foreman will probably be sufficient. The contractor often employs a quantity surveyor to safeguard his financial interests. <strong></strong></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>Building services engineer</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>Building services engineers are responsible for ensuring the cost-effective and environmentally sound and sustainable design and maintenance of energy-using elements in buildings.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>They have an important role in developing and maintaining buildings and their components, to make the most effective use of natural resources and protect public safety.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>This includes all equipment and materials involved with heating, lighting, ventilation, air conditioning, electrical distribution, water supply, sanitation, public health, fire protection, safety systems, lifts, escalators, façade engineering, and even acoustics.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>While the role increasingly demands a multidisciplinary approach, building services engineers tend to specialize in one of the following areas:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Electrical engineering</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Mechanical engineering, and</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>• Public health.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Activities will vary according to the specialist area of work and whether the building services engineer is employed by a single organization or a consultancy, but tasks typically involve:</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Advising clients and architects on energy use and conservation in a range of buildings and sites, aiming to minimize the environmental impact</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Managing and forecasting spending, using whole life cycle costing techniques, ensuring that work is kept to budget</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Developing and negotiating project contracts and agreeing on these with clients, if working in consultancy, and putting out tenders</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Attending a range of project groups and technical meetings</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Working with detailed diagrams, plans, and drawings</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Using specialist computer-aided design (CAD) software and other resources to design all the systems required for the project</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Designing site-specific equipment as required</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Commissioning, organizing, and assessing the work of contractors</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Overseeing and supervising the installation of building systems and specifying maintenance and operating procedures</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Monitoring building systems and processes</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Facilities management</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Ensuring that the design and maintenance of building systems meet legislative and health and safety requirements.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:heading -->\n<h2><strong>The clerk of works</strong></h2>\n<!-- /wp:heading -->\n\n<!-- wp:paragraph -->\n<p>The clerk of works is the architect’s representative on site and is usually a tradesman with many years of practical experience.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><em>The job title ‘clerk of works’ is believed to derive from the thirteenth century when ‘clerics’ in holy orders were accepted as being more literate than their fellows and were left to plan and supervise the ‘works’ associated with the erection of churches and other religious property.</em></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>By the nineteenth century, the role had expanded to cover the majority of building works, and the clerk of works was drawn from experienced tradesmen who had wide knowledge and understanding of the construction process.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>The clerk of works is the person who must ensure the quality of both materials and workmanship. To this end, he must be impartial and independent in any decisions and judgments. They cannot normally, under the quality role, be employed by the contractor – only the client, and normally by the architect on behalf of the client.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Their role is not to judge, but simply to report (through exhaustive and detailed diary notes) all occurrences that are relevant to the role.</p>\n<!-- /wp:paragraph -->', '<strong>The Building Team</strong>', '', 'inherit', 'closed', 'closed', '', '1878-revision-v1', '', '', '2023-03-07 08:58:09', '2023-03-07 03:28:09', '', 1878, 'https://civilengineeringlectures.com/?p=1884', 0, 'revision', '', 0);
