NASCLA Accredited Commercial General ContractorConcreteMedium
A concrete crew is preparing to place concrete for a foundation wall in an area where the ambient temperature is expected to drop below freezing overnight. To mitigate the risk of damage to the fresh concrete, which of the following practices is MOST effective in preventing freezing of the concrete before it gains sufficient strength?
- APlacing the concrete at a lower slump for increased density.
- BUsing Type III (High Early Strength) cement.
- CRemoving the formwork as soon as possible after placement.
- DAdding extra water to the mix to lower its freezing point.
Show answer & explanationAnswer & explanation
Correct answer: B. Using Type III (High Early Strength) cement.
Type III cement, also known as High Early Strength cement, develops strength more rapidly than ordinary portland cement. This accelerated strength gain allows the concrete to achieve sufficient resistance to freezing much faster, significantly reducing the risk of freeze-thaw damage in cold weather.
Why the other options are wrong
- A. Lower slump indicates a stiffer mix, which is generally better, but doesn't directly prevent freezing as effectively as accelerated strength gain.
- C. Removing formwork too early exposes the concrete to colder temperatures and hinders proper curing.
- D. Adding extra water weakens the concrete and increases its susceptibility to freezing.
Cold Weather Concreting
Practices and procedures used when placing, finishing, and curing concrete at ambient temperatures below 40°F (4°C) to prevent damage from freezing.
- Prevent freezing before strength gain.
- Use accelerators or Type III cement.
- Protect and insulate concrete after placement.
Memory trick: Winter concrete needs heat and speed.