Concrete curing question

[captmello]

Any concrete guys out there?

I recently poured a large concrete slab. About a week ago to be more accurate.
The next day we got a big snow/slush storm which slowed the dry time on the slab. I also have foam insulation beneath the slab which slows the dry time as well.

I've been covering the slab with a tarp at night to try to keep it warmer as temp drop to the 20s overnight. The slab is now fairly dry but still very green and clearly not dry. Temps are supposed to drop into the single digits next week and I'm trying to decide if I need to go further to insulate the slab while it continues to dry slowly, or if I'm being paranoid.

Any advice is appreciated.

 

[DianneB]

Re: Concrete curing question

From an engineering standpoint in construction if concrete is to be poured in cold weather we advise the concrete company and they modify the formula for cold weather use.

Once poured it is desirable to keep the concrete above 5C (41F) for at least 48 hours so it cures properly - 4 days is better. This is normally done with tarps and heaters. If the heaters suck the humidity out of the hording, you also need to introduce water to keep the surface of the concrete moist. After the 4 days temperature doesn't effect the curing very much.

Considering you are 7 days from pouring, there isn't much you can do at this point. It will not reach its full cure for almost a year anyway, regardless of weather.

 

[Guest]

Re: Concrete curing question

You should have gotten the cement with a chemical heating agent added to it to help keep it warm during the curing procces.
Now maybe get some straw bails and put them over the tarp to insulate it. But only after you get some warmish weather to warm the concrete up and then do it to hold what ever heat there is in. It is very hard to get it to set up in cold weather. But eventually it will. Just don't do any work on it untill you are sure it is cured.

 

[captmello]

Re: Concrete curing question

From an engineering standpoint in construction if concrete is to be poured in cold weather we advise the concrete company and they modify the formula for cold weather use.

Once poured it is desirable to keep the concrete above 5C (41F) for at least 48 hours so it cures properly - 4 days is better. This is normally done with tarps and heaters. If the heaters suck the humidity out of the hording, you also need to introduce water to keep the surface of the concrete moist. After the 4 days temperature doesn't effect the curing very much.

Considering you are 7 days from pouring, there isn't much you can do at this point. It will not reach its full cure for almost a year anyway, regardless of weather.

Thanks for the reply. That is good info. I guess what I'm really trying to find out is if I need to be concerned about the freezing temps and if they could damage the slab since it is still relatively soft. I've heard about the surface "popping" from freezing but I'm not sure if this is still an issue or not now that I'm a week into it.

 

[captmello]

Re: Concrete curing question

You should have gotten the cement with a chemical heating agent added to it to help keep it warm during the curing procces.
Now maybe get some straw bails and put them over the tarp to insulate it. But only after you get some warmish weather to warm the concrete up and then do it to hold what ever heat there is in. It is very hard to get it to set up in cold weather. But eventually it will. Just don't do any work on it untill you are sure it is cured.

we added Calcium chloride to the mix and used hot water. It was hard by the end of the day and had it power toweled nicely.

I don't expect to get any warmer temps in the near future.

I could get some hay if I really thought it was necessary to protect the slab from the single digit temps coming next week. I'm not trying to speed up the cure, just want to protect it from damage.

 

[Tim Frank]

Re: Concrete curing question

http://www.concretenetwork.com/cold-weather-concrete/curing.html

 

[captmello]

Re: Concrete curing question

http://www.concretenetwork.com/cold-weather-concrete/curing.html

Thanks for the link.

Unfortunately, I haven't been monitoring the temp of the concrete itself, just the air temp. It sounds like most of the initial reaction/curing takes place during the first 48 hours, more in the cold weather. by the time it gets to the single digits next week, It will have been 10-12 days. I'm trying to figure out if it will be cured enough to whether the cold, so to speak.

Can anyone answer how long the concrete will continue to produce its own heat? If it's not heating anymore, I don't think covering it makes much difference. Especially since I've got it insulated from the bottom as well so heat from the ground doesn't help much. If it's still putting off heat, I may consider covering with hay before the temps really get cold, middle of next week.

thanks again for the responses.

 

[huntndakota]

Re: Concrete curing question

It shouldn't peel/pop on you if you poured it a week and a half ago. Whatever you do do not put salt on it for at least 2 yrs. Rock salt will suck out the moisture and crater the surface.

 

[BlkY2k]

Re: Concrete curing question

We poured a 30x40 garage floor 2 years ago on nov. 14th. We used hot water and chloride to set it up and buy the end of the day it still hadn`t set enuff to get on it so we covered it with tarps and hay to keep it warm and crossed our fingers that we would be able to finish in the morning. Well we came back the next morning and pulled the tarps and what did we find? It looked like every deer in the county found that hay that night hoof prints everywhere and it was setup as hard as... well concrete. We had to triple up the bottom plates on the walls and come back in the spring and pour a cap over the floor. So far its holding up fine.

 

[DianneB]

Re: Concrete curing question

Sorry BlkY2k, I shouldn't laugh but that was funny as he11 !

 

[dockwrecker]

Re: Concrete curing question

I really hope you guys aren't using chloride with any metal reinforcing in your slabs...that's a NO NO!

 

[j_martin]

Re: Concrete curing question

We poured a 30x40 garage floor 2 years ago on nov. 14th. We used hot water and chloride to set it up and buy the end of the day it still hadn`t set enuff to get on it so we covered it with tarps and hay to keep it warm and crossed our fingers that we would be able to finish in the morning. Well we came back the next morning and pulled the tarps and what did we find? It looked like every deer in the county found that hay that night hoof prints everywhere and it was setup as hard as... well concrete. We had to triple up the bottom plates on the walls and come back in the spring and pour a cap over the floor. So far its holding up fine.

Should have been defending your work. Yum.

 

[MTboatguy]

Re: Concrete curing question

I am sorry, I know its not funny, but I am still clearing the tears from my eyes!

I know living here in Montana, we deal with the cold as well as the wildlife all the time, I have a friend that really nice garage floor with a lift in it and it has the nicest set of Grizzly bear tracks going right across the middle of it!

 

[BlkY2k]

Re: Concrete curing question

Thats ok guys, at the time we were not amused but looking back now I can laugh with ya. Shoulda seen the look on the homeowners face when we peeled back that tarp .... WT*

 

[BlkY2k]

Re: Concrete curing question

I am sorry, I know its not funny, but I am still clearing the tears from my eyes!

I know living here in Montana, we deal with the cold as well as the wildlife all the time, I have a friend that really nice garage floor with a lift in it and it has the nicest set of Grizzly bear tracks going right across the middle of it!

I would leave those there and tell everybody, thats my gaurd dog.