Concrete can prove challenging to work with during the winter season unless you know the right way of curing, placing, and preparing it by understanding how low temperatures affect the mixture. The concrete sets in several complicated chemical reactions, which are sensitive to the temperature.
These reactions produce a high amount of heat in normal conditions. However, during the cold, these reactions slow down, and there is a delay in the process. The result? The strength of the concrete reduces drastically. Fortunately, there are ways to combat using concrete in low temperatures.
Temperature Limits for Pouring Concrete
Concrete prefers to set in a mild temperature between 50°F and 60°F. if the temperature is below this threshold, then the exothermic reactions causing the transformation of wet cement to concrete significantly slows. As a result, you experience long delays as you have to wait for the concrete to set before moving on with your project.
This is the reason why it gets difficult to work with concrete during the cold weather. If you use the concrete in freezing temperatures, the water in the mix will freeze and expand during the setting process. As a result, concrete becomes brittle, weak, and flaky.
Fortunately, there are various tips and tricks to work with concrete efficiently during the cold season without losing its quality.
You can enhance the curing of concrete during winters through the following preparation practices:
- Preheat at least one of the constituent materials, aggregate or water, to ensure that the concrete reaches the right temperature during the pouring process. Instead of heating the Portland cement, you can heat the water or the gravel and sand before mixing them. Generally, when the concreate leaves in trucks from the plant, the temperature is about 65°F. You can mix a small amount of concrete by using hot water or simply storing the aggregate in a warm location before it is mixed.
- You may have to adjust the mixture components by increasing the cement ratio. You can also add Sodium Naphthalene Sulfonate (SNS), which is highly suitable for concrete construction during the winters.
- Utilize Portland cement, and add in SNS as it helps the concrete is setting with lowering its quality. Don’t use slag cement or fly ash cement during the winters as these set slowly and produce lower internal heat.
Placement and Pouring Tips During Winters
Aside from preparing the concrete mixture, placement, and pouring practices also assist in the proper setting and curing of the concrete in the winters. Here are some useful tips:
- Ensure that the crew is on the construction site for a longer duration. When the concrete is exposed to low temperatures, it takes longer to set initially, which might mean that the finishing crew must be present when the concrete sets.
- Add in windbreakers to protect both workers and concrete from cold winds that would drop the temperate quickly. Six feet high windbreaks would be sufficient.
- You might need heated enclosures, which can be made from polyethylene sheets, canvas tarps, or wood. Electric heaters are the best way to heat the enclosure. If using fuel-burning heaters, use indirect-fire heaters that funnels the warm air inside the enclosure from a burner unit that is located outside. You can even use a hydronic system that uses a warm mixture of water and glycol, which circulates through the enclosure through hoses or pipes.
The aim is to pour and place the concrete at a minimum temperature of 40°F and keep it there till the concrete is set. In the case of high-early strength concrete that isn’t exposed to freeze and thaw cycle, a day at 40°F and above is sufficient.
Keep in mind that the concrete foundation built to endure high loads needs about 20 days at a minimum of 50°F. Whichever concrete you are using, the exothermic reaction during cement curing produces heat of its own. Generally, it is enough to cover the concrete with insulating blankets or polyethylene sheets to trap that heat. Therefore, make the adjustments and preparations according to the type of concrete you use.
Never allow concrete to freeze within the first 24 hours after you pour and place it.
Considerations for Curing Concrete
Following are some of the tips for curing concrete during winters:
- If you expect frosty or icy conditions immediately after the concrete has been poured, avoid using water to cure the surface. Doing this would disrupt and freeze the top surface before the concrete develops the strength.
- Cover the concrete with plastic and straw to make sure it stays above the freezing temperature. However, keep in mind that straw may discolor the concrete if it gets wet. You can instead use an insulation mat, like polystyrene.
- Remove the mat once the concrete has survived the first night, and spray a curing compound. If the temperature is harsh, replace the insulation mat for a few more days for good measure.
- Avoid sealing freshly placed concrete unless you use a special sealer designed for new concrete at low temperatures.
- In case the concrete is still warm after the insulation, remove the mat carefully to make sure the concrete’s temperature doesn’t drop suddenly for more than 20 degrees in the next 24 hours to prevent thermal shock cracks.
Winter season creates challenges when working with concrete. Preparing the material, using Sodium Naphthalene Sulfonate in the mixture, and following the right tips help minimize the risk of the concrete losing its strength, cracking, or other issues. Make sure to follow these tips whenever you work on a project using concrete to ensure you get the best possible results.