![]() Hardening occurs because of the chemical reaction, called hydration, between the cementitious materials and water. Upon hardening, the paste or glue consisting of the cementitious materials and water binds the aggregates together. The w/cm ratio equation is: w/cm ratio = (weight of water – weight of water absorbed in the aggregates) divided by the weight of cementitious materials. To avoid confusion between the w/cm and w/c ratios, use the w/cm ratio for concretes with and without supplementary cementitious materials. Because most concretes today contain supplementary cementitious materials such as fly ash, slag cement, silica fume, or natural pozzolans, the w/cm ratio is more appropriate. The w/cm ratio is a modification of the historical water-cement ratio (w/c ratio) that was used to describe the amount of water, excluding what was absorbed by the aggregates, to the amount of the portland cement by weight in concrete. ![]() The ratio of the amount of water, minus the amount of water absorbed by the aggregates, to the amount of cementitious materials by weight in concrete is called the water-cementitious ratio and commonly referred to as the w/cm ratio. For these reasons, limiting and controlling the amount of water in concrete is important for both constructability and service life. ![]() ![]() The amount of water in concrete controls many fresh and hardened properties in concrete including workability, compressive strengths, permeability and watertightness, durability and weathering, drying shrinkage and potential for cracking. ![]()
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