::Point Lakeview Redi-Mix::  A "Footing" In The Right Direction!
  • Concrete sets more slowly when it's cold - extremely slow below 50 degree F, below 40 degree F the hydration reaction
    basically stops and the concrete won't gain strength.        
But these are concrete temperatures not air temperatures. So when it's cold, we need to protect the concrete until it
can handle the cold on its own. The general rule is that once the concrete has gained strength to about 500 psi then
it's OK.  The magical thing that happens is that at almost the same time that the concrete achieves 500 PSI
compressive strength, hydration of the cement has consumed enough of the water in the original mix so that even if
it does freeze, there's not enough water left int he pores to damage to concrete.  With most concrete, even at 50
degrees, this happens during the second day.
To help it reach that 500 PSI strength, then, there are two things we can do in cold weather; change the mix to get it
to set more quickly or protect the concrete from the cold - or more likely, both.
Cover concrete after finishing with straw or insulating blankets to help maintain temperature.
What to remember when placing concrete in cold weather:
  • NEVER place concrete on frozen ground
There are a couple of reasons for this. First, frozen ground settles when it thaws, cracking the concrete. Second, the
concrete will set more slowly if you place directly on cold or frozen ground. You can even get "crusting," with the top
part of the concrete set and the bottom still soft.
If the ground is frozen, you can thaw it using heat pipes and blankets.
Remove all snow and ice in placement areas. Also, remove any standing water that could be mixed into the
concrete.
Warm up everything that will come in contact with the concrete, including forms and embedment. If it's not too cold
and you cover everything the day before the pour, it should stay dry and warm enough.

There will be some heat loss from the ready mix plant to the job site. For a one-hour delivery time, the concrete temperature will
drop about one-forth the difference between the air temperature and the concrete temperature.