Cold weather protection prevents early freezing of the concrete and ensures the concrete strength necessary to continue construction practices. Once concrete reaches 500-psi compressive strength it won't be damaged by a single freeze-thaw cycle. Getting 500 psi in 1 day can save an extra day's expense in heater fuel and labor to maintain the heaters. The American Concrete Institute's report on "Cold Weather Concreting" (ACI 306) recommends three ways to accelerate strength gain:
- Use Type III cement: Concrete made with Type III cement is almost 50 percent stronger at 1 day than concrete made with Type I cement.
- Use an extra 100 pounds of cement: Increasing the cement content by 100 pounds provides about the same early strength as using a Type III cement.
- Add accelerators: Instead of using a straight accelerator, many concrete suppliers are using a Type E water reducing and accelerating admixture. This accelerator also increases the 3-day strength by at least 125 percent and allows a decrease in the water content by at least 5 percent.