Tips for Pouring Concrete in Winter

When it comes to pouring concrete in winter, weather can pose significant challenges. Concrete sets best at 50-60°F; pouring concrete in winter means the ambient temperature will likely fall well below this range. Fortunately, there are steps you can take to effectively tackle cold weather concrete curing.

Concrete Pouring Temperature Limits

As mentioned above, concrete prefers a mild temperature between around 50 and 60°F to set. Below this, the exothermic reactions that cause wet cement to transform into strong concrete will slow significantly. This could mean long delays in work while you wait for concrete to set and strengthen before continuing with a project. Additionally, If concrete reaches freezing temperatures during the setting process, the water in the cement mix will freeze and expand. This will cause concrete to become weak, brittle and even flaky when it sets.

 

Successfully Pouring Concrete in Winter

Fortunately, strategies can be implemented to increase the temperature of cement mixtures. Here are some tricks you can use to keep the cement flowing all winter long:

  • Use heaters or heated blankets to thaw surfaces where concrete will be poured. Pouring concrete on frozen ground will quickly cool concrete well below ideal temperatures. Using a heater to prep surfaces will prevent too-quick cooling or freezing and help keep the necessary reactions going.
  • Mix cement using hot water to help increase the temperature of the concrete.
  • Store materials in a warm location.
  • Use quick-set cement; during cold weather. It may set more slowly than the instructions indicate, but will still harden more quickly than traditional cement mix.
  • Mix in additives that accelerate set time.
  • Use extra cement (typically 100 lb/ cubic yard) to make the reaction hotter and cause concrete to hydrate more rapidly.
  • Utilize squeegees or a vacuum to remove bleed water that has a difficult time evaporating during colder weather.

Cold Weather Concrete Curing

After the concrete has been poured, it needs to be kept at the correct temperature to cure. Most importantly, it needs to be kept from freezing. Ideal temperatures (50-60°F) should be maintained for about 48 hours for the concrete to reach optimal strength as it sets. This can be tricky during the winter; even if temperatures are optimal during the day, they can plummet at nighttime. Maintaining warmer temperature will require some sort of external heat source. One option is a heated enclosure. These are effective but can be time-consuming to install. If you choose to use an enclosure, be aware that excess carbon dioxide from the heater can cause bubbling in the surface of concrete. This can typically be avoided with proper ventilation.

Concrete Blankets

Another option for temperature maintenance during cold weather concrete setting is concrete blankets. Concrete blankets can be used to thaw ground before pouring concrete and again after finishing to keep concrete from freezing. They are easy to install and transport and require only an outlet to use. This means no time wasted setting up complex heating mechanisms. If you’re interested in minimizing downtime involved pouring concrete in winter, these blankets are an excellent heating option to look into.

Concrete Curing Time

pouring concrete

Waiting for the curing of concrete can easily test patience, especially when you’re ready to move on to the next step of a project. However, it’s important to remember that quality is the end goal, not quickness. Rushing ahead and not allowing enough time for concrete to properly cure before allowing foot traffic or heavy machinery to travel across your newly placed cement can seriously compromise the integrity of a concrete slab.

 

Cement Curing Factors

Several factors influence concrete slab cure time, including:

 

Typical Concrete Setting Time

Typically, concrete is recognized to have reached full strength 28 days after placement; however, this does not mean you need to wait 28 days to walk, or even continue construction on newly placed concrete. After placement, concrete increases in strength very quickly for 3-7 days, then gradually for the next 3 weeks. This means that concrete hardening time is typically 24-48 hours, at which point it’s safe for normal foot traffic. After one week, concrete is typically cured enough to handle continued construction including heavy machinery.

concrete curing time

The “70 in 7” Rule

When in doubt, remember the “70 in 7” rule: Most concrete mixes will have reached 70% of specified compressive strength after 7 days. At this point, it’s ready for exposure to normal traffic.

concrete curing blanket

Concrete Curing Blankets

Unfortunately, cold weather during winter months can seriously slow down concrete cure time and significantly hold up construction projects. The best temperature to cure concrete is above 5o°F, which can be difficult to replicate if the air is below freezing.

Luckily, solutions, such as concrete curing blankets that maintain optimum temperatures during cure time, are available. Concrete Blankets are an effective option that cure concrete 2.8 times faster than a typical insulated blanket and properly maintain moisture throughout the hydrating process. Concrete Blankets are easily transported and installed and maintain ACI compliance for cold-weather concreting. If you’re looking for a solution to maintaining optimum concrete cure time during cold winter, using a Concrete Blanket is the best method for drying and curing concrete.