Pouring concrete below 40 degrees Fahrenheit?

Old 02-26-06, 11:37 PM
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Question Pouring concrete below 40 degrees Fahrenheit?

What's the name of the chemical that's added to concrete so it'll harden when it's less than 40 degrees Fahrenheit outside?

Around what temperature is the chemical used? Is 40 F right?

Old 02-27-06, 02:49 AM
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There are many chemicals that will accellerate the set. The most common and cheapest is calcium chloride. However, chloride accellerators have their limitations. For one, they attack and corrode any reinforcing steel that may be in the slab. For another, they discolor the slab by darkening it significantly.
Type 3 cement instead of regular portland cement sets up quickly in cold weather too. It does not darken the slab.
There are products like pozzitech, freeze guard, polar set, etc that guarantee that concrete will not freeze unless the concrete reaches 20 degrees farenheit within 3 hours of initial set.
Concrete can technically be poured at any temperature, but the freezing mark is usually the determining factor. At cold temps the concrete cures extremely slowly. A slab that may reach its designed strength in 1 week in the summer, may take a month or more in the winter.
For more complete info, call your local ready mix concrete provider or association and talk to a knowledgeable person as to what is used in your area.

Old 02-27-06, 01:45 PM
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Pouring concrete below 40 degrees Fahrenheit?

The important thing is how the concrete is protected after it is poured. As Pecos mentioned, the temperature has a bearing on the rate of curing.

If you are not going to put design or heavy loads on the concrete immediately, the curing is not as important.

The temperatures referred to are CONCRETE temperatures and not AIR temperatures. Type III (high early strength cement) cures faster and generates more heat that normal Type I cement. In the winter, it is well worth the minor extra cost. An insulation or protection gives you more latitude on when you pour.


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