According to the American Concrete Institute, “cold-weather concreting” refers to any period in which the average air temperature dips below 40 degrees Fahrenheit over three successive days, or remains below 50 degrees Fahrenheit for more than half of any 24-hour period. If this sounds familiar, then make sure you follow the special tips below for laying concrete in cold weather.
What Happens to Concrete in Cold Weather?
Without the proper precautions, concrete laid in cold weather can create a major safety hazard, and will ultimately need to be torn up, poured, and cured again. When laying concrete in cold conditions, it must be protected from freezing for at least a 24 hour minimum, or until it reaches a strength of 500 pounds/sq. inch. If the concrete freezes too early, it may lose up to 50% of its final strength. Below freezing temperatures also pose the risk of water freezing inside the concrete, which will eventually expand and cause cracks. If you’re laying concrete in cold weather conditions, using heated enclosures and insulated blankets during the curing process are two ways to prevent premature and unwanted freezing.
Pouring and Curing Concrete in Cold Weather
In an ideal world, it’s best to pour concrete when the temperature will remain between 40 and 60 degrees Fahrenheit. If you find yourself having to work a concrete job when the temperature is 40 degrees or below, follow these steps to ensure that the concrete is poured and cured successfully.
Have you ever had a cold gust of wind knock the air out of you? Cold bursts of air can cause the temperature to drop (too) quickly, which isn’t good for the concrete, or the crew. Using windbreaks measuring 6 feet high will prevent drops in temperature as well as evaporation that can negatively affect the concrete’s curing process. Windbreaks as well as other heating tools discussed below will prevent freezing, as freshly laid concrete must be protected from freezing for at least the first 24 hours.
Turn Up the Heat
Using heated enclosures is an excellent way to protect concrete against cold temperatures as it sets. Canvas, wood, or polyethylene sheets are excellent options to set up the enclosures, while inside you’ll want to use electric heaters to keep the work site and concrete at an optimal temperature for curing. The use of insulated blankets or burlap paving covers over the fresh concrete will help maintain proper hydration and temperature throughout the curing process. Keep an eye on the concrete’s temperature by using an infrared temperature gun, and make sure that the concrete maintains its temperature of at least 40 degrees Fahrenheit while curing. If the ground is frozen or covered in snow or ice, do not begin pouring concrete. Heaters should be used to thaw the ground before starting any part of the concrete process.
You might find that using a heated mix of cement is best for your cold weather concrete operation, or mixing the cement with hot water before pouring. If you don’t choose to use a heated mix, you can instead use 100 extra lbs. of cement per each cubic yard of concrete to ensure the concrete’s final strength.
Account for Time for Curing and Your Crew
When exposed to cold weather, concrete will take a longer time to properly set, and crews will need to stay on site for a longer period of time to finish the job. As the concrete takes longer to cure, it will also require more time before the bleed water has evaporated. While accounting for a longer set and cure time, you’ll also want to be prepared for more bleed water than you’d expect with concrete that’s being cured in warmer temperature. Using a vacuum or squeegee will assist with removing the excess bleed water.
Don’t Forget to Seal
After the concrete has finished curing, using a sealant is a necessary step in order to prevent excess water seeping into the concrete. Leave frames in place as well as any insulating blankets or paving covers until you are ready to begin the sealing process, which will extend the life of the concrete while reducing the chance of faulty curing.
While cold-weather concreting requires a few extra precautions, a cold day won’t prevent you from getting the job done. From keeping an eye on the temperature to turning up the heat, following these steps for pouring and curing during cold winter days will help ensure the quality, durability, and longevity of your concrete.