Testing residential foundation poured in cold

[fredhead]

We're having a house built. The foundations for the main house and for the attached garage were poured separately. The main house foundation was exposed to cold, but not freezing, temps (40s F day/30s F night) for the first few days, but then freezing temperatures since. The garage foundation was poured in freezing weather and then exposed to freezing temperatures (mid-20s F night) for the first few days as well as having 8" of snow fall on it the day it was poured. No heating or insulation was used in either case.

Now I am concerned about the effect of this weather on the strength of the concrete. I am primarily concerned about the garage foundation since the top surface of the concrete is easily flaked off. The main foundation at least has a much better appearance. A structural engineer I've spoken to said that he would be reluctant to take core samples now while the concrete is frozen for fear that it would yield inaccurate data.

Are there any suggestions as to how to check the quality of the foundations without having to wait for months?

I'm actually a mechanical engineer, so I've had to do a lot of research on this topic to figure out how to proceed. The more I learn, the more I wish I had just told them to wait until spring!

Thanks!

 

[conceng]

Fredhead,

Being from the northern plains, we see this quite often. The flaking away of your garage footings may be an indication that it is experiencing freeze/thaw deterioration. It would take closer examination of the concrete and aggregate sockets to determine if it has experienced freezing damage. Look at the surface and aggregate sockets to see if you can find any sign of frost patterns (aka chicken tracks). If you're not sure what to look for, I have at least one digital photo of an aggregate socket from frozen concrete I could send you. If it has frozen, the damage may be irreversible and the strength of the foundation may be severly compromised.

Concrete must attain 500 psi compressive strength prior to be exposed to freezing in order to withstand the forces of one freeze thaw cycle. The other concern with the cold temperatures is the rate of strength development. Concrete gains strength very very slowly in temperatures below 50'F. As a minimum, before continueing with the structure, I would recommend enclosure and heating of the concrete to assure adequate strength development for the proposed construction. How long? I'd go seven days just to be sure unless you do cut cores, then that may give you a better idea as to where you're at.

Another concern would be the potential for frost penetration into the soils below the footings. This may lead to excessive structural movement once the area is enclosed and heated.

I hope this helps and best of luck to you.