Question

What type of cracking is primarily caused by rapid evaporation of surface moisture in freshly placed concrete?

Accepted Answer

The type of cracking primarily caused by rapid evaporation of surface moisture in freshly placed concrete is plastic shrinkage cracking. Plastic shrinkage cracking occurs when the rate of evaporation from the concrete surface exceeds the rate at which bleed water (water migrating to the surface) can replace it. This rapid evaporation causes the surface concrete to shrink. Because the concrete is still in its plastic state (before it has gained significant strength), it cannot resist the tensile stresses induced by this shrinkage. As a result, cracks form on the surface. These cracks are typically shallow, random in orientation, and can be quite wide. Factors that contribute to rapid evaporation include high air temperature, low humidity, and high wind speed. For example, placing concrete on a hot, windy day without taking precautions to reduce evaporation will likely result in plastic shrinkage cracking. Proper curing practices, such as using windbreaks, shading the concrete, applying fog sprays, or using evaporative retardants, are essential to minimize plastic shrinkage cracking.

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What type of cracking is primarily caused by rapid evaporation of surface moisture in freshly placed concrete?