Depending on how cold. If the reinforcing is cold enough to form ice, there can be a concern for bond development. Ice formation on formwork can cause durability and finish quality issues. As for the concrete itself, the mechanism by which wet concrete turns to hard concrete doesn't happen properly at very low temps.
Do not get confused with the air temperature. The temperature of the concrete and rate of curing are the driving forces behind the amount protection for the poured concrete.
The important things are:
1.The temperature and condition of the base.
2. The mix design and whether a Type III cement is required.
3. The temperature of the concrete mix when placed.
This will be a guide to what kind of protection is required and for how long.
The concrete temperature is critical, since the warmer concrete will kick off the exothermal reaction between the water and the Portland Cement and result in a faster strength gain and less protection required. Cold concrete mixes end up giving everyone a double "whammy" because the aggregate will absorb heat from the reaction, slowing the curing, and the reaction will be much slower.
I don't know where you are located, but in the cold climates, heated concrete (water heated, cement probably heated and protected and the aggregate hopefully acclimated in heated bins) is always a good investment in terms of labor cost and continuity of construction.
Even on a lowly basement at 0F to -15F, the footings are protected and the mortar is always made with heated sand and warm water.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
Different jurisdictions have different temperature thresholds to start considering the concreting as cold weather concreting. You should check on your area's applicable standard.
In one of the areas I have worked, cold weather concreting kicks in if air temperature is predicted by nearest metereological office is predicted to drop below 5 degrees centigrades over the curing period.
You might want to visit the National Ready Mix Concrete Assoiciation website. They have a brief but very informative tech-note on cold weather concreting, complete with solid references for further information. I know because I read it on Tuesday.
