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Curing Concrete in Cold Weather Part II

Concrete in Cold Weather

In our last post, we started talking about curing concrete in cold weather. Sometimes covering your work area in blankets simply won’t cut it when you’re pouring concrete in cold weather. If your job requires more insulation in order for the cold weather concrete to set, there are more options.

If regular blankets alone aren’t enough to insulate your concrete, you can use hydronic heating pipes. You can lay the pipes over the concrete that you’re curing, and the heat will help add to the warmth within the covered work area. Additionally, you can use electric heating blankets instead of normal blankets, which will increase the temperatures surrounding the setting concrete.

Sometimes you may be involved in a job that requires placing concrete where it’s too cold to even pour it outside. In circumstances such as these, you need to enclose your workspace and heat the air within the space. Setting up a temporary enclosure is an expensive operation, but sometimes it’s the only option if a job must be completed at such a time.

Carbonation

Carbonation becomes a problem when you’re working with concrete in an enclosure, or even in a building that’s using a temporary heat source. Unvented heaters and gas-powered equipment can increase the levels of carbon dioxide in the workspace, which can create a chalky, carbonated layer on the surface of concrete. The layer created by this reaction is soft and an unacceptable result for the job. For this reason, it’s important to use heathers that can exhaust to the outside of your enclosed workspace. Always be sure to have someone monitoring the heater overnight, so that it remains fueled and functioning.

Another problem that occurs when curing concrete within an enclosure is that dry, hot air may sometimes cause the concrete to cure too quickly, which dries the concrete out and crusting may occur. If you’re using propane-powered heaters, you also run the risk of fire, which is something to be aware of at all times.

If the concrete stays at about 50°F, you can remove the protection you’ve put in place after two days. It’s best to wait about 4 weeks before using the area where the new concrete has been placed.




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Curing Concrete in Cold Weather

Method for Curing Concrete

After following our tips for pouring concrete in cold weather, your concrete has been placed and you’re ready to protect and cure it. What’s the next step? The traditional, tried-and-true method for curing concrete in cold weather is to cover it with blankets. This method is successful even if the air temperature falls below 20°F. Between the ground temperature, the heat generated by the concrete, and the insulation of the blankets, it’s enough to protect the concrete as it cures. Cold weather techniques are necessary whenever you’re working in a climate where the air temperature is below 40°F.

The Process

Regardless of the weather, part of the process when curing concrete is waiting for the bleed water to evaporate. As the concrete particles begin to settle, they push out any water that wasn’t absorbed during the hydration process. The bleed water is that excess that collects on the surface of the concrete. It’s important to let the bleed water evaporate, because the surface of your concrete will be weakened if any bleed water is finished into it. When it’s cold out, the concrete will set more slowly, which means the bleeding will start later and last longer. An alternative to waiting is trying to squeegee or vacuum some of the bleed water off, but more often than not you just have to wait.

If the concrete is kept at 50°F or warmer, you’ll only need to keep it covered with blankets for a couple of days. You can measure the temperature of your concrete by using an infrared temperature gun. The insulation that you’ll require to keep your concrete at 50°F will depend on how thick the concrete is, what the mix is made from, and the lowest you expect the air temperature to drop during the curing process.

You should wrap any rebars that are sticking out from the covered area, and secure the blankets so they won’t blow off overnight. Also, triple the layers of insulation at the corners or edges where freezing may occur.

Check back with us for more cold weather concrete curing tips.




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