Dampening the subgrade before concrete placement primarily helps to prevent which issue?

• A. Cracking
• B. Rapid extraction of mixing water
• C. Delayed strength gain
• D. Adhesion problems

Answer: (B)

Dampening the subgrade before concrete placement primarily helps to prevent the rapid extraction of mixing water. When concrete is poured onto a dry subgrade, the ground can absorb water from the concrete mix, leading to problems such as insufficient moisture in the mix. This dehydration can result in an overly dry concrete that may not achieve its intended strength or proper curing.

By dampening the subgrade, you maintain a more stable moisture level, allowing the concrete to cure properly without losing vital water content too quickly. This practice is crucial for ensuring the hydration process occurs effectively, which in turn supports the ultimate strength and durability of the concrete.

The prevention of cracking, delayed strength gain, and adhesion problems are also important considerations in concrete placement, but they are more directly influenced by factors such as mix design, curing methods, and temperature. Dampening is specifically focused on managing the water relationship between the subgrade and the concrete.