What Is Curing
Curing is much more than retaining moisture for a pro
longed period on the concrete surface. Curing is the process that ensures that the concrete attains its desired strength. The strength of concrete is dependent on crystal growth within the concrete matrix. These crystals grow due to the hydration that is the reaction between the water and Portland cement. If water is not adequate, the crystals cannot grow, due to which the concrete is unable to attain the desired strength. The presence of water facilitates the crystal growth that encloses the gravel and sand mix, causing interweaving with each other.
Controls During Curing
It is important to maintain the proper curing temperatures otherwise the hydration reaction will be affected. If the concrete is too hot, the hydration reaction will be too rapid for a proper crystal
growth. Thus, concrete will not attain proper strength. The reaction being exothermic, temperature differentials will be created within the concrete that may cause cracks. Unsuitable hydration on the concrete surface may produce rough surface and a porous concrete structure. Such permeable concrete structures will permit calcium hydroxide to contact the concrete surface causing efflorescence. The concrete structure is also weakened. Other important aspects that need care during the curing are proper humidity, circulation, insulation, and time control.
Autogenous shrinkage occurs when the cement paste has lost shape due to inadequate water for hydration. Autogenous shrinkage happens when the volume of the hydrated cement products is less than the volume of the cement and water mix before hydration. It is not caused by external factors, such as loss of moisture or temperature changes. Autogenous shrinkage is usually not significant in concrete with a water-cement ratio of greater than about 0.4. However, as this ratio is decreased below that limit, autogenous shrinkage is likely to be increased. Mixes with a water-cement ratio less than 0.40 do not have adequate water in the concrete for curing. In the early stages, when the tensile strength is low, and concrete is under the effects of high temperature disparity, concrete may crack if autogenous shrinkage occurs.
The specific controls of temperature, humidity, and time required during the process of curing are difficult to attain accurately, due to which proper concrete strength and other characteristics may be affected. Self-curing technologies have been developed that use substances for internal curing. Appropriate materials are applied to the wet concrete surface to decrease the loss of water from the concrete. The materials developed are emulsions of paraffins that are scattered on to the surface. An improved concrete is produced that has lesser permeability, and therefore improved durability and strength.
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