field test of concrete for potential freezing

[structSU10]

I have a situation where the measured concrete temperature at time of placement was 45 degrees - colder than defined by ACI 306. The concrete has no air, and a 4500 psi mix, and the cylinder break (cured on site in insulated box, then lab cured) came back at 7 days as 6300. This was marked as a non-conformance item by the special inspector that needs direction to clear.

Is an insitu compressive strength test to confirm strength a reasonable approach to something like this? They say they had blankets down - pour was a topping element for a slab on deck (overpour to create steps , some placed on XPS blocks to shape steps, other directly on other slab on deck), and air temp at placement was 21 degrees. Not sure if I feel great that freezing was precluded, don't know if other testing is prudent.

 

[dik]

What did the temperature drop down to? below freezing? It's when you can see frost patterns on the concrete surface that it gets a little more interesting. If it stayed at 45F, then I wouldn't be too concerned... it it dipped to 30F, I'd be looking for more. The problem occurs when the concrete starts to hydrate and then freezes... it breaks up the gel.

Dik

 

[Ron]

Agree with dik. A petrographic examination will show microcracking that develops as concrete freezes during the initial hydration process. Compressive strength testing might not show the issue, since there can be enough autogenous healing of microcracking to mask the long term durability issue this can create. Since you had no air entrainment, I would expect some initial scaling and pop-outs from freezing. These would be readily apparent at the surface.

 

[dik]

How cold did it get?

Dik