Many concrete contractors dread late fall because temperatures drop and the risk of placing concrete rises. Generally, you should take cold-weather precautions when the temperature is expected to fall below 40° F. But frost damage to concrete isn't the only concern during cold weather. Delays in finishing also can be a problem because the time required for concrete to reach initial set increases dramatically. A drop in concrete temperature from 70° to 40° F more than doubles the time from concrete placement to the end of finishing.
Contractors have many options for avoiding finishing delays and protecting concrete from frost damage. These include changing the mix, preparing the jobsite, using calcium-chloride admixtures or nonchloride accelerators, and installing cold-weather protection such as curing blankets and other insulating materials.