5.7
Quality of Water
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Q1: Why is water quality important for concrete mixing?
Water quality directly affects concrete strength and durability because it aids in cement hydration. Potable water is preferred, but it must be free of excessive sodium or potassium ions, which compromise concrete integrity. Water with a pH between 6 and 8, impurity-free, and slightly acidic natural water ensures optimal concrete performance and long-term durability.
Q2: What impurities should be avoided when selecting water for concrete?
Water for concrete should avoid high levels of dissolved solids, chlorides, sulfates, and organic matter. Seawater poses risks of reinforcement corrosion and efflorescence. Additionally, water containing free carbon dioxide can cause surface erosion in hardened concrete, while iron or organic matter may result in visible stains on the concrete surface.
Q3: Can silt-laden water be used for concrete mixing?
Water with excess silt can be treated before use by allowing it to stand in a settling basin, which removes suspended particles. Once settled, the clarified water becomes suitable for concrete mixing. Additionally, impurity-free concrete mixer wash water can be reused if properly settled, reducing waste while maintaining concrete quality standards.
Q4: What are the ideal pH and chemical characteristics for concrete mixing water?
Concrete mixing water should have a pH between 6 and 8 and must not be saline or brackish. Water should be free of harmful organic matter and algae. These chemical characteristics ensure proper cement hydration and prevent degradation of concrete strength and durability over time.
Q5: How does curing water quality differ from mixing water requirements?
Curing water must maintain essential moisture for ongoing cement hydration post-setting. However, curing water containing free carbon dioxide causes surface erosion in hardened concrete. Iron or organic matter in curing water may cause staining, making it critical to use clean water free of these contaminants during the curing phase.
Q6: Why is seawater generally not recommended for concrete?
Seawater poses significant risks to concrete durability and reinforcement integrity. Using seawater for mixing or curing may lead to corrosion of steel reinforcements and result in persistent dampness and efflorescence on the concrete surface. These effects compromise structural performance, making seawater inadvisable except in extreme freshwater scarcity situations.
Q7: What standards govern acceptable water quality for concrete?
Water quality for concrete is evaluated based on impurities such as dissolved solids, chlorides, and sulfates according to standards like BS 3148:1980, BS EN 1008:2002, and ASTM C 1602–06. These standards establish permissible limits for various contaminants and pH ranges, ensuring consistency and reliability in concrete quality across different applications and regions.