How soon after concrete has been poured can it be frozen without sustaining damage?
In "Recommended Practice for Winter Concreting Methods" ACI Committee 604 noted that the principal factor is the rate at which the concrete gains strength. Experience indicates that concrete may not be seriously damaged by one or two cycles of freezing if it has attained a strength of more than 500 psi. Limited tests indicate that concrete placed at a temperature of 75 degrees must be subjected to severe freezing within about 6 hours for any serious damage to be sustained. If it is placed at 40 degrees F. even a mild freezing at 25 degrees may result in a 50 per cent strength loss.