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<p>Cement and aggregates are the main ingredients in making concrete. Water is the third.</p>
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<p>The quantity of water in the concrete mix strongly influences the strength of the resulting concrete. Undoubtedly, water is necessary to make the concrete mix adequately workable. There is another important thing. Water is necessary to hydrate the cement in the concrete.</p>
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<p>But, in this document, we discuss the quality of water necessary for making concrete.</p>
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<p>Water is not just a liquid used to make concrete. It is involved in the whole life of the concrete. Several actions on concrete in service, other than loading, involve water. The important influences of water, in addition to those on workability and strength, are as follows:</p>
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<p>setting, hydration, bleeding, drying shrinkage, creep, ingress of salts, explosive failure of concrete with a very low water-cement ratio, staining of the surface, chemical attack of concrete, corrosion of reinforcement, freezing and thawing, carbonation, alkali-silica reaction, thermal properties, electrical resistivity, cavitation and erosion, and quality of drinking water passed through concrete pipes or mortar-lined pipes.</p>
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<p>For these reasons, the suitability of water for mixing and curing purposes should be considered.</p>
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<p>A clear distinction must be made between the quality of mixing water and the attack on hardened concrete by aggressive waters. Some water that badly affects hardened concrete may be harmless or even beneficial when used in mixing.</p>
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<p>Mixing water should not contain undesirable organic substances or inorganic constituents in excessive proportions.</p>
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<p>In many textbooks, the quality of water for mixing concrete is simply mentioned as it should be fit for drinking. Such water not often contains dissolved inorganic solids above 2000 parts per million (ppm). Most probably, it is less than 1000 ppm. For a water/cement ratio of 0.5, the latter content tallies to a quantity of solids representing 0.05 percent of the mass of cement. Therefore, any effect due to these solids would be small.</p>
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<p>However, there are a few exceptions when using potable water as mixing water. For instance, in some dry areas, local drinking water is saline. It may contain an excessive amount of chlorides. Also, some natural mineral waters contain undesirable amounts of alkali carbonates and bicarbonates which could contribute to the alkali-silica reaction.</p>
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<p>On the other hand, some water not fit for drinking may be used in making concrete. As a rule, water with pH of 6.0 to 8.0, which does not taste brackish, is suitable for use. Similarly, dark colour or bad smell does not necessarily mean that deleterious substances are present.</p>
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<p>A simple way of determining the suitability of such water is to compare the setting time of cement and the strength of mortar cubes using the water in question with the results obtained using known good water.</p>
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<p>It is harmful to introduce large quantities of clay and silt into the concrete. Therefore, mixing water with a high content of suspended solids should be allowed to stand in a settling basin before use.</p>
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<p>Natural waters that are slightly acidic are harmless. However, water containing humic – <em>resulting from the decomposition of plant and other animal residues</em> - or other organic acids may adversely affect the hardening of concrete. Such water, as well as highly alkaline water, should be tested before use.</p>
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<p>The presence of algae in mixing water results in air entrainment with a resulting loss of strength. Brackish water contains chlorides and sulfates. When chloride does not exceed 500 ppm, or SO<sub>3</sub> does not exceed 1000 ppm, the water is harmless.</p>
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<p>Sea water has a total salinity of about 3.5 percent. 78 percent of the dissolved solids are NaCl and 15 percent are MgCl<sub>2</sub> and MgSO<sub>4.</sub> It produces a marginally higher early strength but a lower long-term strength. The loss of strength is usually no more than 15 percent which can often be tolerated. Some tests suggest that seawater slightly accelerates the setting time of cement. Others show a substantial reduction in the initial setting time but not necessarily in the final set. Generally, the effects on setting time are unimportant if water is acceptable from strength considerations. According to BS EN 1008-2002, the tolerances may be 25 minutes in the initial setting time and a maximum final setting time of 12 hours.</p>
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<p>Water containing large quantities of chlorides (e.g. seawater) may cause dampness and surface efflorescence. Such water should, therefore, not be used where the appearance of unreinforced concrete is of importance, or where a plaster finish is to be applied. Also, the presence of chlorides in concrete containing embedded steel can lead to its corrosion.</p>
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<p>It is important to remember that water discharged into the mixer is not the only source of mix water. Aggregates also contain surface moisture. This water may represent a considerable proportion of the total mixing water. Therefore, it is, important that the water brought in by the aggregate is also free from harmful material.</p>
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<p>There is a possible effect of cement on the interior surface of a pipe on water intended for human consumption. As long as water moves through a concrete pipe (or a mortar-lined conduit) at speed, no significant chemical reaction with cement occurs. However, when water is near-stagnant, for example during the night in domestic water conduits, leaching of cement may occur. This may raise the pH of the water and increase the content of CaCO<sub>3. </sub>It is referred to as carbonate alkalinity or water hardness. The increase in CaCO<sub>3</sub> is induced by carbon dioxide dissolved in the water.</p>
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<p>Curing water should generally satisfy the requirements for mixing water. However, it should be free from substances that attack hardened concrete.</p>
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<p>Also, flowing pure water dissolves Ca(OH)<sub>2</sub> and causes surface erosion of concrete. Curing very young concrete with seawater may lead to an attack on reinforcement.</p>
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