Cold Weather Concreting
Cold weather is defined as a period when the average daily temperature falls below 40⁰F for more than three successive days. Special considerations are required when batching, placing, finishing, curing, and protecting concrete against the effects of cold weather.
- Care should be taken to prevent concrete from freezing.
- Plastic concrete below 25⁰F freezes and potential strength may be reduced by more than 50% and durability will be affected.
- Protect Concrete for the first 2 to 3 days following placement.
- Protect concrete from deicing salts, including fertilizers, for the first year after placement to avoid discoloration and scaling issues.
Chemical admixture accelerators
Chemical admixture accelerators, increased cement contents, and straight cement mixes can be used to accelerate the set time of concrete.
Calcium chloride can be used in placements without structural steel at dosages up to 2% by weight of cement.
Non-chloride accelerators can be used in all applications.
Please note that accelerators will not prevent freezing. Increase the cement content of the mix design will accelerate concrete.
Follow ACI Recommendations for minimum concrete temperature during cold weather placements
Low concrete temperature has a significant effect on set time. Once concrete temperature drops below 40⁰FLow concrete temperature has a significant effect on set time. Once concrete temperature drops below 40⁰Fhydration and setting essentially stop.
TO THINK ABOUT:
- Concrete should be placed at the lowest practical slump as this reduces bleeding and setting time.
- Adding 1 to 2 gallons of water per cubic yard will delay set time by ½ to 2 hours. Retarded set times will prolong the duration of bleeding and delay finishing operations.
- Take care to prevent the surface of the concrete drying out as this causes plastic shrinkage cracking.
- Placing on plastic will affect the bleed rate of the concrete and prolong finishing operations.
- Forms should not be stripped for 1 to 7 days depending on the setting characteristics, ambient conditions, and anticipated loading on the structure.
- Special care should be taken with the concrete test specimens used for acceptance of concrete.
- Cylinders should be stored in insulated boxes which may need temperature controls to ensure that they are cured at 60⁰F to 80⁰F for the first 24 to 48 hours.
- Snow, ice, and frost should be removed and the temperature of surfaces and metallic embedments should be above freezing if they will come in contact with concrete.
- Never place on frozen ground, ice, or snow. Thaw the ground and keep it insulated prior to placement.
Contact us if you have questions about how to handle concrete after it has been poured. We are the Concrete Specialists>