I've been watching a street widening in my neighborhood where the pavement is concrete (used to be asphalt, but they tore it up, leveled the "prairie pimples" and are repaving with concrete). I got to wondering how warm does it have to be to pour concrete or how cold does it have to be before they can't?
I don't know the exact temperature required for concrete curing... it can't freeze that's for sure, and probably any temperature below 4 degrees Celsius when water starts to expand in density probably isn't that desirable either.
As concrete cures, however, it does produce heat, it's called the heat of hydration, and it's from the chemical reaction of the water bonding to the other ingredients. So, with that in mind, concrete can usually be poured in cold conditions, so long as it is sufficiently insulated so that the outer level does not freeze. This can be done using simple plastic sheets, or through more elaborate measures using propane salamanders to supply an artificial heat source to an insulated cure.
Quote from: AsphaltPlanet on December 25, 2017, 10:45:33 AM
I don't know the exact temperature required for concrete curing... it can't freeze that's for sure, and probably any temperature below 4 degrees Celsius when water starts to expand in density probably isn't that desirable either.
As concrete cures, however, it does produce heat, it's called the heat of hydration, and it's from the chemical reaction of the water bonding to the other ingredients. So, with that in mind, concrete can usually be poured in cold conditions, so long as it is sufficiently insulated so that the outer level does not freeze. This can be done using simple plastic sheets, or through more elaborate measures using propane salamanders to supply an artificial heat source to an insulated cure.
I've seen tarps over concrete before which I figured was for insulation. I've never heard of using salamanders before ;)
The AHTD Blue Spec Book states (section 501.05 (e)) a minimum air temperature of 40 degrees for pouring concrete. Under no circumstances shall concrete be poured onto a frozen subgrade. If the air temperature is to go below 35 before the concrete sets up, it is supposed to be covered & remain that way until it is set.