The curing of concrete continues as long as its relative humidity remains above __________.

• A. 90%
• B. 70%
• C. 80%
• D. 60%

Answer: (C)

Moisture is essential for concrete to keep hydrating. Curing continues as long as there is enough moisture present, and the surrounding environment’s humidity helps supply that moisture. When relative humidity stays above about 80%, moisture loss is slowed and the hydration reactions can proceed, even at the surface, allowing strength to develop properly. If humidity drops below that level, water can evaporate faster than it can be replenished, especially at the surface, which slows or stops curing and can lead to weaker concrete. That’s why 80% relative humidity is the practical threshold used.