Date: December 4, 2013
News - Pouring Concrete in Cold Weather
Special precautions should be taken when pouring concrete in cold weather, because it can slow, or stop, what is known as hydration, a term used to describe the chemical process of concrete hardening.
Concrete hydrates more slowly as temperatures decrease and slows even more when temperatures are below 32°F, but concrete can still gain strength when temperatures are in the teens.
Due to the fact that concrete gains strength slowly in cold weather, expanding ice within the curing concrete may cause small fractures that prevent the concrete from reaching its full strength, and reduce its durability. While concrete placed in cold temperatures may need longer time to cure, the final strength may be higher than concrete cured at warmer temperatures.
The contractor has several options to maintain quality during cold weather placement:
- Concrete paving should never be placed on frozen subgrade. The temperature difference between concrete and subgrade should be no more than 30°F.
- The most important precaution for concreting in cold weather is to prevent concrete from freezing until it achieves the strength of 500 psi, which usually occurs within the first 24 hours.
- Insulate the concrete with polystyrene foam sheets, foamed vinyl blankets, or straw while taking advantage of concrete’s natural heat of hydration for warmth.
- Edges and corners should receive extra protection because they are exposed to heat loss in multiple directions.
Mixes can also be optimized for cold weather concreting:
- The use of accelerating admixtures will help the concrete gain strength faster.
- Using higher strength concrete will help it gain strength more quickly, and allow for faster formwork removal.
- In cold weather, concrete slump should be lower than normal to avoid retarding setting; because the hydration process is slowed, the setting process is also slowed.
- Using heated aggregates and/or mixing water helps raise the temperature of the concrete.
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