NASCLA Accredited Commercial General ContractorConcreteMedium
A general contractor is pouring a concrete foundation in hot weather conditions, with ambient temperatures consistently above 90°F (32°C). To prevent plastic shrinkage cracking, which of the following measures should be implemented immediately after concrete placement and finishing?
- AApply a liquid membrane-forming curing compound or wet burlap.
- BDelay all finishing operations until the concrete has fully hardened.
- CIncrease the concrete slump to a very high level before placement.
- DAdd additional water to the concrete surface to increase workability.
Show answer & explanationAnswer & explanation
Correct answer: A. Apply a liquid membrane-forming curing compound or wet burlap.
In hot weather, rapid evaporation of surface moisture leads to plastic shrinkage cracking. Applying a curing compound or wet burlap immediately after finishing prevents this water loss, thus mitigating cracking.
Why the other options are wrong
- B. Delaying finishing operations would allow the surface to dry out even more, worsening plastic shrinkage cracking.
- C. Increasing slump without proper mix design adjustments can lead to segregation, reduced strength, and increased shrinkage potential.
- D. Adding water to the surface weakens the concrete and increases the water-cement ratio, exacerbating cracking.
Plastic Shrinkage Cracking Prevention
Plastic shrinkage cracks occur when the rate of evaporation of surface moisture exceeds the rate at which bleed water rises to the surface, causing the concrete surface to shrink.
- Common in hot, windy, or low-humidity conditions.
- Occurs before concrete sets.
- Prevented by reducing surface evaporation.
Memory trick: Don't let the sun bake your slab; cover it fast, or cracks you'll grab!