The elapsed time after placement before curing operations must not exceed how many hours?

• A. 2 hours
• B. 4 hours
• C. 6 hours
• D. 8 hours

Answer: (B)

The timing of curing after placement is crucial because the concrete is still undergoing hydration and is highly susceptible to moisture loss while it’s still plastic. If curing doesn’t start promptly, within about four hours, the surface can dry out and form a crust, making moisture-retaining methods (water, damp curing, burlap, or curing compounds) far less effective. That early moisture loss can lead to plastic shrinkage cracks, reduced hydration, lower early strength, and durability issues. Requiring curing to begin within four hours ensures you can apply curing methods while the concrete is still receptive to moisture and actively setting, helping to develop proper strength and a durable surface. After curing starts, you continue the curing process for the recommended duration to maintain moisture and temperature during the critical early hydration period.