A question about Concrete and freezing temps

[Ryan]

So, concrete for my new shop was poured on December 4th. It was a nice day with a high in the low 70's. They started at 3:00 pm because the concrete truck was late and worked until 3:00 am the next morning. During that time, it never got colder than 60-degrees.

On December 5th, a cold front started moving in. At 6am it was around 60-degrees outside, however by 9am the temps were in the 40's. By 11pm the temps were in the upper 30's.

Today, it's even colder. Right now, it's 32-degrees.

How screwed am I? It's 5000 PSI concrete with really deep footers. Nothing has really been done to protect it since the cold weather moved in.

Do I need to have my contractor start over? Is it that bad?

I've got zero experience with this kind of thing.

 

[dcs Inc]

You should be fine. Concrete creates its own heat and it was warm enough at the time of pour for this to happen. The ground is still pretty warm so that will help also.

 

[Ryan]

Hearing you say that makes me feel ALOT better as I know how seriously you take this concrete stuff. Thanks man.

 

[Strouty]

If it had frozen the night of the pour you may have been in trouble. How does the surface look? As always pictures help.

 

[NUTTSGT]

I don't think you'll have much of an issue. Since you have really deep footers, it'll help keep the concrete warm. An over night drop in temp isn't going to get too far into the ground.

 

[soapii]

No issues at all to worry about.

--Joe

 

[rlitman]

You should be fine. Concrete creates its own heat and it was warm enough at the time of pour for this to happen. The ground is still pretty warm so that will help also.

All quite true. I agree that there would be no worries.

First off, it was pretty warm when poured. Then it stayed warm for a day, and then it only cooled to approach freezing. It isn't like it got down into the teens overnight.

It takes a long time at well below freezing temperatures to cool a heavy mass down to below freezing. From what it sounds like, it was neither cold for sufficiently long, nor even cold enough in any case. The ground below still holds warmth, and being solid, and in direct contact with the concrete, it is almost certainly pouring heat into the concrete faster than the air is removing it.

Poke your finger into the ground near the concrete. If the surface is frozen (and from your reported temperatures, I can pretty safely assume it is not), then you MIGHT have something to worry about, except for the fact that as stated above, curing concrete does indeed produce its own heat.
If the surface dirt around the concrete is not frozen, then there is no chance the concrete was frozen.
If you only just saw a frost on the tips of grass, don't sweat it at all.

BTW, do you own an infrared thermometer. That would tell you the surface temperature for sure.

 

[ConCretin]

I concur with the previous posters - you are fine.

ACI says that concrete that reaches 500 psi has gained sufficient strength to weather freeze/thaw conditions without damage. A 5000 psi concrete will easily acheive 500 psi in 24 hours as long the concrete temp remains above 50 degrees. Given the ambient temps you mention, your concrete probably never dropped below 70 degrees

Curing isn't quite as important in cold weather but I'd still suggest you cure the slab for seven days.

 

[Sureshot]

That sounds like an ideal way for the slab to cure.

 

[duckkilla]

So what are the coldest temps that you would be able to pour at? I've got a building "in the works" and the forecast highs for the next week are all in the low 30's. What temperature do I need to wait for, and for how long of a sustained period of time? I'm in the midwest, and the building is going to have a 40 x 50 4" thick slab.

I want to make sure if contractor pours, that I'm not going to suffer any quality losses due to pouring in temps that are too cold for it.

Thanks.

 

[ConCretin]

We'll place slabs on grade in the open with day time temps in the high 30's as long as night time lows don't get too far into the 20's. It can be touch and go to get a finish on the slab and get it covered before the surface freezes.

To pull it off you need an early start, a sub grade that isn't frozen, a serious dose of accelerator and preferably some sunshine. A overcast windy day can be the kiss of death.

Keep in mind that once the concrete temp drops below 50, it will basically go to sleep. If you haven't got a finish on it by then, you probably won't. Be prepared to cover the slab immediately with insulated blankets and live with what you've got. The worst thing you can do is let it freeze while you wait for it to set up.

If it sounds like risky business, it's because it is.

 

[ddawg16]

The 1st 7 days or so, your slab is giving off a lot of heat as it cures.

Add to that the temp of the soil....yea....your fine.

If anything....toss some plastic over it.....but I don't think you really need to worry.

It's Texas....don't like the weather? Wait 5 min.

I was just there...S of Dallas....we have a crew there now....freezing their buns off.....poor guys....

I'll be back in a week or so....