True or False: Before a concrete slab on ground is placed under severe drying conditions that threaten plastic shrinkage cracking, water should be sprayed on the subgrade until puddles are formed and the surface is soft.

True or False: Before a concrete slab on ground is placed under severe drying conditions that threaten plastic shrinkage cracking, water should be sprayed on the subgrade until puddles are formed and the surface is soft.

• A. True
• B. False
• C. Not sure
• D. Cannot determine

Answer: (B)

Controlling evaporation and providing a stable, well-prepared base are essential when placing a slab on grade to minimize plastic shrinkage cracking. Spraying water on the subgrade until puddles form would saturate and soften the base, creating an unstable footing that can lead to differential settlement and weak support for the concrete. The subgrade should be damp enough to reduce moisture loss from the concrete but free of standing water, providing a uniform, firm surface. If drying is severe, the focus should be on curing the concrete surface and moderating evaporation, not on flooding the subgrade. So this practice is not recommended.

Controlling evaporation and providing a stable, well-prepared base are essential when placing a slab on grade to minimize plastic shrinkage cracking. Spraying water on the subgrade until puddles form would saturate and soften the base, creating an unstable footing that can lead to differential settlement and weak support for the concrete. The subgrade should be damp enough to reduce moisture loss from the concrete but free of standing water, providing a uniform, firm surface. If drying is severe, the focus should be on curing the concrete surface and moderating evaporation, not on flooding the subgrade. So this practice is not recommended.