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It is recommended to keep concrete above 40 degrees. With the proper insulation covering all areas exposed to the cold it will maintain this temperature in most cases. Keep in mind that this insulation must extend below the frost line as well. Rigid polystyrene foam insulation board can be used below the grade and left in place. The warmer the weather the less insulation required.
It is also important to keep the moisture in the concrete as it cures. To do this you can cover it with polyethylene and seal or tape all joints, or spray it with a heavy coat of concrete sealing compound such as "Cure and Seal". Freezing and rapid drying are the 2 main problems you need to be concerned about.
You may also want to try to keep track of is the amount of water in the concrete and the time it is poured. Concrete should be placed within 1 hour after it leaves the plant. The "slump" test is used to determine the amount of liquid in the concrete. Concrete should not be poured over a 4" slump. The lower the slump the less water in the mix and the stronger the concrete will be. Excess amounts of water cause the concrete to shrink more as it cures and as a result stress cracks will begin to form and weaken it.
Another item I should mention is the addition of calcium to the mix. This is often used in cold weather pours to accelerate the curing time and prevent freezing. The one major draw back with using calcium (and many other accelerators) is they have a tendency to deteriorate or oxidize (rust) the reinforcing steel that is used in the concrete. Chances are you will have steel rebar in your foundation and I would advise you do not permit the use of accelerators in the concrete mix. This will mean they will HAVE to use insulation to protect the concrete from freezing but you will get a stronger product that will last longer.
I hope this helps,
Glenn Good www.consultationdirect.com