Cold weather concrete

[JohnCR]

Footings for a foundation were poured today for a house near me. The kind that sit on top of the grade in forms, not excavated below grade. The grade was excavated below the frost line to be clear.

I'm a bit new to cold weather foundations, but I thought they needed to be covered with blankets for three days. It is getting below zero here at night. These guys didn't. Am I missing something? Is there an additive which would eliminate the blanket requirement? I'd ask them but they are jerks.

Thanks, John

[Ohiobuilder]

Just as important as covering the concrete is covering the ground that is to be poured on and making sure it does not freeze. As soon as excavated it should be covered with blankets or straw to protect from freezing.

Hate winter pours - I will do it if we have to.

[Ted S.]

There are additives to help set the concrete, Polarset is one. Grace makes it.

But the prudent thing to do is cover the footings with blankets, there are 3' x 25' or 40' insulated blankets for this purpose. If it is the first night then it probably will be ok because of the heat of hydration, but I would cover it asap.

It sounds like an true concrete sub because:

1) they never covered the concrete
2) they are jerks

[JohnCR]

I thought your father in law was a concrete sub?

[parkwest]

Curious; John, you employ people you can't talk with???

[Ted S.]

I thought your father in law was a concrete sub?

That's pretty humorous.

Yes, he is, but they are not jerks' -at least to me anyway.

But if I asked them to cover footings, if it wasn't brutally cold, they would just laugh and call me a book smart architect. Even through they have flatbeds full of those blankets.

[JohnCR]

PW: Not employed by me, just a job in the neighborhood.

[dave_k]

Cold weather can have a detrimental effect on concrete. If the concrete freezes or gets close to freezing it before initial set it's garbage. Concrete generates heat so if the air is freezing it won't be cole enough to affect more than the surface, which isn't a big deal in footings.

If it doesn't freeze during the first 24 hours but then gets cold the concrete will be fine however frost getting into the soil beneath the footing can be very bad depending on the soil. The real problem is with the free water in concrete freezing. The concrete that's left in cold conditions won't gain strength as fast as concrete that remains protected though. That's not usually a problem in footings but can be a problem with beams and suspended slabs

[jimAKAblue]

The new pour, and the ground supporting them, must be kept from freezing. If the ground freezes, it will heave, rise and break apart the footings. When the ground thaws, the ground will sink and leave some voids under the footings, unless the footing somehow manage to all settle into the exact pocket of soil. That is unlikely, because during the thaw cycle, water moves some soil around, and under, the raised footings.

If the poured walls are placed on heaved footings, it can lead to voids between the poured wall and footings when everything thaws and shakes out.

In MI, we always layed a thick blanket of straw. That will keep jack frost from messing with the crete and soil. Of course, the straw must be removed when prepping the soil for foundation drains and the concrete slab.

8" thick straw will keep it all warm till spring.