CSLB General Building (B)Site Work, Foundations and ConcreteEasy
A contractor finishes a residential concrete slab and immediately covers it with plastic sheeting for seven days. What is the primary purpose of this practice?
- ATo prevent rebar corrosion before the concrete sets
- BTo retain moisture in the concrete so it can properly hydrate and gain strength
- CTo keep the slab warm enough to prevent early-age cracking in hot weather
- DTo protect the finished surface from staining by construction debris
Show answer & explanationAnswer & explanation
Correct answer: B. To retain moisture in the concrete so it can properly hydrate and gain strength
Curing keeps the concrete moist so the cement can continue to hydrate, which is essential for developing design strength. Plastic sheeting is a common moisture-retention curing method used for at least 7 days for normal concrete.
Why the other options are wrong
- A. Rebar corrosion protection comes from adequate cover, not curing.
- C. Temperature control is a secondary concern; moisture retention is the main goal.
- D. Debris protection is incidental, not the reason for curing.
Concrete Curing
The process of maintaining adequate moisture and temperature in concrete after placement so cement hydration continues and design strength develops.
- Minimum 7 days moist curing is standard for normal concrete
- Methods include plastic sheeting, wet burlap, curing compounds, and ponding
- Inadequate curing reduces strength and increases shrinkage cracking
Memory trick: Keep it wet, keep it strong — cure for a week or more.