Cold weather curing is defined as a period where average daily temperatures fall below 4º C for more than three consecutive days. Concrete can be placed safely throughout the colder months if precautions are taken. During colder weather, the mix should be adapted to the ambient temperature by heating the concrete, adding accelerators, and providing protection. On Vancouver Island, because of historical temperatures from November 1 through March 15, Hyland Ready Mix heats all concrete to meet the requirements of CSA and to maintain reasonable setting times and strength gain.
The temperature of concrete during and after placement is critical since concrete sets more slowly as the temperature drops. Hydration is affected by initial concrete temperature, ambient air temperature, the dimensions of the concrete and mix design. Concrete generates heat during hydration, the chemical process by which cement reacts with water to form a hard stable paste. Finishing and form removal should be delayed in cool weather and strength development can be impaired if appropriate precautions are not taken.
Do not place on frozen ground, on snow, or in freezing weather. If concrete freezes while in a saturated condition, surface problems like scaling, spalling or cracking can arise due to the expansion and contraction of frozen water inside the concrete. During freezing weather, water curing of concrete should be terminated 12 hours before the end of the protection period. Do not use a curing agent if there is any chance that the concrete will freeze during the curing period.
- Protect from freezing temperatures for 3 to 7 days after placing.
- Leave forms in place as long as possible. Corners and edges are most vulnerable (cover and heat if necessary).
- Protect flatwork by covering and heating, or using insulated blankets, or covering with plastic and straw.
This information has been provided to assist you with your cold weather construction. The complete standards guideline for concrete constructions is CSA A23.1-09 Section 21.