How to Maintain the Strength of Fresh Ready Mix Concrete in the Colder Months
Pouring concrete in cold weather is inevitable for contractors who work in colder climates such as ours. The colder seasons take up a good portion of our year, leaving less warm and hospitable weather to pour concrete successfully. Since concrete loses its compressive strength, durability, and weather resistance if it freezes during the pouring and setting process, it is imperative for concrete contractors and suppliers to protect concrete from the damage of cold weather. So, if your project requires you to have to pour concrete in the colder fall and winter months, consider these steps that you and your ready mix concrete supplier can take to maintain the concrete’s strength and durability even when it’s cold out.
Change the Mix
When ordering your concrete mix, let your ready mix concrete supplier know that you intend to pour it in colder temperatures. They will take the necessary measures to mix the concrete appropriately for cold weather. These changes in mixing could include:
- Using hot water in the mix to maintain a warm temperature throughout transportation;
- Adding more cement to heat up the concrete and speed up the hydration (drying) reaction;
- Using high-early strength cement that will set and cure quickly;
- Using air-entrained concrete to decrease bleeding;
- Determine (test) the slump of the concrete at less than four inches;
- Adding accelerators to the concrete mix to speed up the setting time that is usually longer in cold weather. Accelerators increase the hydration reaction so the concrete will cure faster;
- Not using fly ash and slag cement in cold weather because they generate less heat and set slowly; and,
- Not using admixtures on site if they have frozen.
Protecting Concrete from Cold Temperatures
When the air temperature drops below 4 degrees Celsius, you must take precautions to keep the concrete warm and avoid losing compressive strength during the setting process. Here are some ways to ensure that the concrete stays warm, sets and dries well, and maintains strength even when the outside temperature is cold:
- Set up insulation and vented heaters prior to pouring the ready mix concrete;
- Avoid placing concrete on frozen subgrades—either thaw the subgrades with steam, or place insulation between subgrades and concrete;
- Apply triple-insulation thickness at the corners of walls and edges of slabs;
- Protect the concrete from freezing until it reaches the compressive strength of 500 psi;
- Avoid exposing concrete to rapid drops in temperature —reduce the temperature gradually over a 24-hour period when removing insulation and enclosures;
- Don’t leave heaters unattended since they are a fire hazard and may stop working throughout the setting process; and,
- Keep forms in place for as long as possible to ensure even distribution of heat and to avoid overheating and drying.
Although working in cold weather is inevitable for Canadian concrete contractors, the quality of concrete doesn’t have to be compromised once the temperature drops. By keeping these tips in mind, you and your ready mix concrete provider can make sure your concrete project is successful, even if the weather may be too cold for comfort and concrete.