What happens to freshly laid concrete if it freezes?

Answer 1

The first thing that happens is the Hydration process is interrupted by the water in the mix no longer being able to properly mix with and have time to react [Hydrate] the Portland Cement. Since the cement is the ingredient that "glues" the fines and aggregate together to form this artificial rock, there is a loss of the compressive strentgh intended for that particular mix.

A concrete floor meant to develop 3500 psi may only test out at 2500. With a bad cure you will see dusting, scaling and flaking of a finished surface almost immediately. Very Important to observe ambient temperatures hot and cold when placing concrete. If you live in a cold area, Freeze Thaw Damage is a condition where excess moisture that is allowed to accumulate IN a Cured concrete will expand on freezing [10-15%] and cause surface delaminations, pop outs and scaling of a surface long after it has set or cured. That's why it is so important to waterproof even an aged concrete with a penetrating sealer to decrease the moisture content and avoid this also.