Cold Weather presents many problems for the concrete industry. The most common problem is with having the concrete freeze and/or go through freeze thaw cycles before acquiring adequate strength. This and other problems can be avoided with precautionary steps. Protecting exposed concrete in these conditions can prevent costly issues down the road.
What is cold weather?
ACI 306 defines cold weather when the following conditions exist for three consecutive days:
- The average daily temperature is below 40°F
- Air temperature does not rise above 50° for more than half a day in any 24-hour period.
What’s The Problem?
- Water begins to freeze in voids of concrete at 28°F
- Water expands when it freezes causing cracks in the concrete.
- Up to 50% strength reduction can occur if concrete freezes before reaching 500-PSI, which typically takes about two days after concrete placement.
- What’s The Solution?
The following facts and guidelines should be followed to assure quality of the concrete in cold weather:
1. Use air-entrained concrete when exposure to moisture and freezing and thawing conditions are expected.
2. Keep surfaces in contact with concrete free of ice and snow and at a temperature above freezing prior to placement.
3. Place and maintain concrete at the recommended temperature.
4. Place concrete at the lowest practical slump.
5. Protect plastic concrete from freezing or drying.
6. Protect concrete from early-age freezing and thawing cycles until it has attained adequate strength.
7. Limit rapid temperature changes when protective measures are removed.