Concrete and freezing temperatures

[eatapeach]

For three nights the temperatures under the contractors curing blankets fell below 32 degrees on several tilt wall panels. The total width of the tiltwall panel is 11" however this occurred on the exterior side which is 3" in thickness. A 3"insulation board was placed over the concrete placement except for 6" around the perimeter. The temperature monitoring device was placed within this 6"space to get the reading at the edge. The device was suspended 1 1/2" off the concrete placement to get a reading of the surrounding area. It was recorded at 29 degrees for about two hours each night and below 50 for about 12 hours each day. Does anyone know what is the likelihood of having a problem or what would be an early indication that something is likely to happen later?

 

[Ron]

Most likely problem is significantly delayed strength gain. Don't tilt the panels yet!

If the concrete had frozen in a low strength state, you would already see evidence.

 

[dik]

It depends on when and if the concrete froze... 32F is pretty close and it is unlikely that it did freeze if that's as cold as it got. If it did freeze, then it may be several weeks before there was any effect... if the concrete/cement gel froze during hydration, the panels are likely toast. Any frost patterns at the edge of the formwork? Sometimes a 'jackfrost' pattern is visible on the edge of the formwork. With low temperatures and little/no heat, it could take months to develop strength to lift the panels.

Dik

 

[cvg]

since you measured air temperature only, you have no way of knowing what the internal temp of the concrete was. at this point, about your only option to determine the quality of the concrete would be to take cored samples to a lab for examination.

 

[CELinOttawa]

I'd do three 2" cores (plenty large enough to be of good indication in your situation, and easily patched), one at each location of concern and ideally anywhere with differing appearance. After this I'd supplement with a thorough passing over of rebound hammer non-destructive testing.

Like others have said, DO NOT LIFT these panels until you know you're good to go.

I'm guessing your Contractor is not going to be pleased about the delay. Don't let their problem become your problem.