American Concrete Institute (ACI) Committee 306 defines Cold Weather as any period when the average daily air temperature is less than 40° F for three consecutive days and the air temperature is not greater than 50° F for more than one-half of any 24 hour period.
Cold weather is not just winter. Cool autumn nights can necessitate the use of cold weather concrete practices.
Placed concrete will freeze when the mix temperature falls below 29° F. Once frozen, hydration will not occur and concrete will not set.
Cold weather can have the following negative effects on concrete.
- Slower set time
- Low strength
- Poor durability
- Freezing of plastic concrete
Good Cold Weather Concrete Practices should include the following.
- Plan ahead for cold weather concrete placements
- Prevent sub grade from freezing
- Protect fresh concrete from freezing until it has maintained a compressive strength of at least 500 psi.
- Maintain curing conditions that foster normal strength development
- Use warm concrete ingredients
- Use set controlling admixtures (accelerators)
- Use minimum amount of water in concrete mix
- Limit rapid concrete temperature changes
Average Set Time of Concrete at Various Temperatures
| Temperature |
Approximate Setting Time |
| 70°F (21°C) |
6 hours |
| 60° F (16° C) |
8 hours |
| 50° F (10° C) |
10 hours 40 minutes |
| 40° F (4° C) |
14 hours 40 minutes |
| 30° F (-1° C) |
19 hours |
| Below 30° F |
Concrete freezes and set will not occur |
