Placing concrete in cold weather (commonly defined as below 40 degrees fahrenheit) can be a risk but if placed correctly and within proper cold weather placement parameters, successful results can be achieved. Like any construction activity, working in cold weather can employ more resources, reduce productivity, and in turn require additional costs.
When it comes to concrete, the first item of importance is maintaining the critical mix temperatures needed for proper curing while getting the concrete delivered to the project, during placement, and well into the hydration process. This will require that warm or hot water be added to the mix to resist dropping below accepted temperatures from the batch plant to the placement location. Also, the aggregate, cement, and sand piles at the ready mix plant must be kept from freezing before being batched.
The next item of concern will be protecting the concrete by accelerating the cure immediately after the concrete is placed and finished. If ambient temperatures are low enough that they may drop the temperature of the concrete mix, often calcium chloride (non-reinforced concrete) or non-chloride accelerators (reinforced concrete) will be added to speed up the curing process.
The next item of concern will be the subgrade or materials that the concrete will come in contact with when it is placed. If this material is cold or frozen, it can be very damaging to the concrete curing process. In such instances the subgrade or forms will be covered with insulated blankets or tarped and heated prior to concrete placement.
The last item of importance is assuring the curing environment is suitable long term. If exposed to cold weather, this often involves tarping off or installing insulated blankets on the surface of the concrete to keep the warm temperatures in and cold temperatures out during the hydration phase. When concrete is curing within a cold environment, it must be maintained a minimum of 7 days if not the entire 28 days to resist complications resulting from cold weather exposure.