some concerns about a concrete footer poured in cold weather

[LMHmedchem]

Hello,

I am in the process of trying to finish some repairs of termite damage on my porch. I am now starting to replace the temporary supports with proper posts. On Tuesday I poured the footer for a 6"x6" post using a 12" tube form. I used high strength Sakrete (4000). I didn't measure the water as I never have done that before. I added water and mixed with a hoe until the dry mix was moistened a little and then I added small amounts of water until the concrete was a good consistency to work with. I guess I just made it up like I always have.

The post and post base were cast in place and are supported with temporary supports. Everything went well but the temperature has been lower than I would like and lower than it has ever been when I poured concrete before. 24 hours after pouring, the surface of the concrete in the tube was still damp, which I have never seen before. The temperature was in the mid 60s on the day I poured the footer but it went down into the 40s over night and has only got to into the 50s for the 2 days following the pour. I would want it to be 55 degrees for 48 hours before removing the form. It is supposed to go up to the mid 60s tomorrow and the highs will be in the 60s for the next 2 weeks. It will likely get down into the mid to high 40s overnight on several of those nights.

My current plan is to wait a full week before removing the form and then wait 28 days before replacing the soil and removing the temporary supports. I will also cover the area with plastic when it is supposed to rain. Does this make sense or am I being too conservative? I have never done anything before other than pour the form, wait 2 days, and remove the form. I have never had any issues when doing that.

Advice would be appreciated.

LMHmedchem

 

[tomtheelder2020]

What does the bag say about temperature limits? Waiting the full 28 day cure is always a good idea even if frequently unnecessary. Here in CA central valley freezing has always been uncommon, and ever rarer now, but I suspect freezing is the only real concern.

 

[bud16415]

I think you will be fine.



My only worry is with the ready mix products I have seen them sometimes light on Portland. Mostly with off brands. The type you listed is probably the name brand and type I would have wanted to use.



Giving it a few more days won’t hurt anything but IMO it should be cured good enough to strip the form now. If you used a tube form IMO you could just leave it on.

 

[Steve123]

No problem.
Concrete will simply cure slower in cold temperatures.

Only problem can be if the concrete freezes within the first 24 hours or so. So pouring concrete on frozen ground is a no-no. The curing process generates a bit a heat, so temperatures have to be a few degrees below freezing to cause issues. The issues would normally be seen on the surface --- the core would likely be warm enough to be fine.

After 24 or so hours of curing, the concrete would have sufficient strength to resist effects of freezing.

 

[LMHmedchem]

Thanks for all of the replies. I removed the tube form yesterday and everything looked fine.

I added a box of about 6" deep additional concrete to stabilize the base of the concrete column. I haven't done footers like this very many times but I had always added a box of extra concrete at the bottom when I have. My understanding is that this helps to keep the footer from moving with the soil when it freezes.

Since the column and box are not poured at the same time I insert 2 sections of 1/2" rebar into the bottom of the tube form in a cross. This is done by drilling 1/2" holes in the side of the tube about 3" up from the bottom and sliding in the rebar. One set of holes has to be 1/2" further up the tube than the other. I cut the tubing from the holes down to the bottom of the tube to make it easier to remove and then reinforce the bottom of the tube with duct tape. When I remove the form, I have the 4 ends of the rebar sticking out of the sides of the tube down at the bottom. I pour additional concrete to cover the rebar ends by 3 inches.

This may be completely unnecessary/unhelpful but I really don't want to do this again any time soon so I tend to go overboard a bit.

I will be doing another footer today while it is a very nice 70 degrees out. It is supposed to rain tomorrow afternoon or evening and then again some on Monday. My plan is to wrap the post and newly poured footer with a plastic tarp sealed with tape against the post to make a tent over the footer. I will leave that on until the weather clears.

Does that make sense?

I assume I can just backfill the first footer now and that it won't be bothered by the rain. I could wrap that one as well if it is necessary.

Thanks again for the advice,

LMHmedchem

 

[Stimpy]

FDOT spec for concrete working range is 40-80. There's special considerations for 80-100, but no placement is allowed below 40. The temps you ran into should be of no concern. There's also very tight tolerances on materials, ratios, mixing times, etc. so you're probably just seeing a mix that had too much water for the temp drop. Shouldn't be a problem it hardened up like it was supposed to.