How to Pour Concrete in Cold Weather

Many people do not realize that concrete can be poured during the winter. Of course, there are some added challenges in casting concrete in colder temperatures, but by taking some extra precautions, the concrete installed in the winter also works as well as the one installed at any other time of the year. Therefore, keep calm as it’s not too late to correct that trip hazard after all. Follow this tips learned from a concrete contractor in St. Louis.

How does it work?

For concrete to harden properly, a chemical reaction called hydration (also known as curing) must occur. To put it simply, the process of hydration is when the chemicals in the concrete react with water to bind the mixture. Hardening is one of the most important steps in concrete construction. The appropriate hardening considerably increases the strength and durability of the concrete.

Concrete sets much slower in cold weather. For hydration to occur, the temperature of the concrete must be ≥ 40 ° F. Anything below that will slow down the hydration process, and may even stop it completely. It is essential that the concrete sets before it is exposed to freezing temperatures. The problem is that when all the water gets frozen; it expands, causing cracks on the concrete. The key is to do what you can to ensure that the concrete sets fast enough to avoid this freeze/unfreezing disaster.

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Credit: Pouring Concrete how-to

Precautions that must be taken when casting concrete in cold weather

In the case of concrete laying, when we say “cold weather”, we refer to a period when the average daily temperature drops below 40 ° F for more than three consecutive days. These conditions require special arrangements to be made in placing, protecting and curing the concrete against the effects of cold. In its plastic state (like a malleable liquid) concrete will freeze if its temperature drops below 25 ° F. If the plastic concrete freezes, its strength can be reduced by more than 50% and its durability will suffer. The concrete must be protected from freezing until it reaches a minimum compressive strength of 500 psi, which is equivalent to about two days after placement for most concrete maintained at 50 ° F.

To get your site ready to pour concrete, make sure you have all the proper insulation and heating equipment at hand. The floor must be thawed before placing any concrete. The concrete must not be poured onto the frozen ground. It simply will not work. If the concrete is placed on frozen subgrade, irregular settling will occur when the subgrade unthaws, resulting in cracking. Subgrade temperature should be as close to the temperature of the concrete that is being poured. If the depth of the frozen subgrade is only a few inches, there are a number of de-icing options, such as spreading hot sand or gravel, steam, or covering it with insulation for a few days.

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