Like the warm weather that has come and gone, cold weather brings a set of challenges to the concrete industry that must be accounted for to ensure a strong, durable structure. The speed at which concrete sets and hardens is greatly affected by the temperature of the concrete. Concrete at low temperatures delays the setting of the concrete, which means the strength is also delayed.
As defined by the National Ready Mixed Concrete Association (NRMCA) cold weather concreting occurs when the average daily temperature falls below 40 F (4C) for more than three consecutive days. If proper precautions and planning are not executed during this time, problems will arise, such as slowing the rate of cement hydration. Delayed cement hydration results in slower setting and rate of strength gain for concrete. Also, when plastic concrete freezes, potential strength is decreased by more than 50%, which then adversely affects its durability.
Thankfully, proper precautions and planning can avoid these issues. Here are a few simple guidelines for concreting in cold weather:
- Heat the substrate or forms (never pour over a frozen substrate or into a frozen form);
- Place concrete at the lowest practical slump and protect from freezing or drying;
- Place and maintain concrete at the recommended temperature;
- Reduce the amount of water and consider a non-chloride accelerator;
- Capture hydration heat with insulating blankets, batt insulation, canvas or polyethylene tarapaulins; and
- Limit rapid temperature changes where removing protective barriers.
Freeze-thaw cycles are of a particular concern for concreting in cold weather as the final compressive strength of the product can be considerably weakened. Tweaking your concrete mix to compensate for these measures, like using air-entrained concrete or considering a non-chloride, and taking the proper precautions for the harshness of the environment could save the viability your concrete project.
It comes down to simply being aware of cold conditions and planning adequately in order to deal with them. For a more detailed depiction of concreting in cold weather, consult the American Concrete Institute’s ACI 306R-10for complete recommendations, or the NRMCA’s CIP 27– Cold Weather Concreting for an overview.