Cold Concrete cure option help.

   / Cold Concrete cure option help. #1  

jdmar

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Yes, I took the risk...I poured concrete last thursday in northeast ohio...brrr. It got cold that night (17 degrees to be exact).

The concrete was poured in a semi sealed building. It was poured on R-10 reflective foil/foam on gravel with poly underneath. It has wire mesh/WWR and radiant tubing (not yet with heat in them too bad huh!?). It was 6 1/2 sack made with heated water. It was SUPPOSED to have accelerators in it (the guy who ran the pump said no but the mix delivery guy said yes)...I think it did have the accelerator. It also has fiber in it. As soon as I could safely do (the next am...about 8-10 hours after final finish) I covered with R-10 foam on top. Therefore it was then in a full R-10 "package/envelope." About 12-24 hours after it was poured the temp on the top was 37-41 degrees F. Some spots near the garage door and wind side were 35 degrees. So it got cold enough to stop hydrating (below 40)but not so cold it frooze. No surface measures were freezing. After covering and attempting to heat the building the temp did climb...in fact it hit 56 degrees F on the slab surface in spots. 8 days later I still got surface temps of 41 to 48 degrees in various spots. The slab is 4-5 inches thick.

Now, for my question. When I lift the foam insulation board it is mildly damp on the surface...not standing water. Think condensation/dew amount of water. Should I now remove the foam and let the concrete dry more or should I leave the foam on as long as possible. My thoughts are as follows but I need smarter advice than my guesses.

1. Leaving the foam would keep it warmer longer and therefore help it hydrate and harden as much as possible. But if/when it does start to freeze...will the higher moisture put the slab or surface at higher risk of cracks or surface popping? But since there is good insulation it may stay warm (i.e above 40 degreesF) for a looong time since it is getting ground warmth. Not sure what wins out here. I think my heat generated but the hydration process is probabble minimal now (10 days after pour).

2. Removing the foam now would likely slow the final cure (but it is likely hard enough to survive the winter now). But it would also allow evaporation of moisture and in theory decrease the risk of cracks/surface pops/chips if/when it does freeze. I know concreete likes moisture to cure...but I doubt that is such a big deal now 10 days later.

I need some opinions advice from those with experience and a lot more knowledge than me. ANd sadly yes...there are spots at the edge of the exposed slab at the garage door that I could chip a couple days ago by pushing a screwdriver into the edge...so you think this part will "heal" or will I just have to repour that edge (not a big deal really). Thanks for your help/advice.

Peter
 
   / Cold Concrete cure option help. #2  
I'm not in the concrete business. But, I am Italian.

I have been involved in some below freezing pours, one of them being the approach to my business years ago. It was a County supervised road widening, and the concrete was poured in conditions just like you had. The inspector insisted that the concrete will generate enough heat to keep its self from freezing, at least initially, (several days), if it was covered properly. They used tarps with insulation under them. These were left in place for 10 days. I never had any trouble with the concrete.

I say leave it covered, and keep the heat in it as long as possible.

My barn was poured in cold weather and it did take about 4x longer to reach full cure, than in summer conditions. It is fine now. That is probably what you have encountered.
 
   / Cold Concrete cure option help. #3  
I would tent and heat the edge by the door until it turns "white". The worst that could happen is if it frose it could have weaken the material. The rest I would not worry about unless the ground under the slab was damp or wet. I've seen slabs that heaved form frost and caused it to crack. Even with the insulation if not closed in the cold could work it's way under the slab if it gets cold enough. You should to close the building up.
 
   / Cold Concrete cure option help. #4  
I'm not in the concrete business. But, I am Italian.

I have been involved in some below freezing pours, one of them being the approach to my business years ago. It was a County supervised road widening, and the concrete was poured in conditions just like you had. The inspector insisted that the concrete will generate enough heat to keep its self from freezing, at least initially, (several days), if it was covered properly. They used tarps with insulation under them. These were left in place for 10 days. I never had any trouble with the concrete.

I say leave it covered, and keep the heat in it as long as possible.

My barn was poured in cold weather and it did take about 4x longer to reach full cure, than in summer conditions. It is fine now. That is probably what you have encountered.



Well keep that concrete covered!. The concrete naturally produces heat as it hydrates and it also realeases water vapor. It is suppose to do that. Actually the best curing conditions for concrete is 100% humidity or under water. We have a materials testing lab in our engineering firm and that is actually what you do with the cyninders to get them at the highest strength possible.

The insulation will serve to preserve the natuaral heat of hydration for the initial 14 day period or so. I would leave the foam on that long and make sre it does blow off. that R-10 should keep your concrete good down to close to zero through the curing period. Hopefullly they gave you conbncrete with entrained air (another additive that most plants will put in in winter weather. The entrained air actually gives the water in the concrete a location to expand into, if it does freeze (water expands 11% when it freezes) later before the water is all hydrated out. Try to not remove the styrofoam until the end of at least 14 days to preserve that heat. You should be good to go!

Jack Mentink, P E
Principal Engineer
Integrity Engineering, Inc.
1714 East Tenth Street
Rolla, MO 65401
 
   / Cold Concrete cure option help. #5  
agree 100% with jack. keep it covered at least two weeks. moisture is the best thing for it as is retaining the heat from curing.

you did the right thing - just keep it up and resist the urge to pull it all off and check it. there is nothing you can do to it now that will help it more than leaving it covered....

amp
 
   / Cold Concrete cure option help. #6  
I was working way north in Siberia several years ago. When they build on permafrost they have to do it in the winter when it is frozen otherwise the machinery would sink in about three feet of mud. I saw a machine (kind of oversized heavy duty wichditch on steroids) to dig the trench several feet wide. Then they filled it with dry concrete mix, compacted it and built a building on top of it. Apparently the concrete would hydrate when it gets wet during early summer thaw.
 
   / Cold Concrete cure option help.
  • Thread Starter
#7  
Well, looks like I have my answer. I will leave it covered as long as I can...likely 2-3 weeks at least. I am doing some wiring now, so I just walk on the foam board...doesn't even dent it...but then again I am a little guy! Thanks for all the answers. And the concrete was air entrained...sorry I forgot to add that originally. Once again, thanks for all the answers...its nice when smart people all come back in agreement (you guys...I am not counting me in the "smart" group here!) I feel much more comfortable that it will work out well.

Merry Christmas
Peter
 
   / Cold Concrete cure option help.
  • Thread Starter
#8  
It still seems to be getting tougher. The most exposed portion is at 45 degrees and not so brittle (happily it has been 41-48 degree weather the last 36 hours!). The rest of the slab is moist, hard and at 46 degrees...so far so good. Thanks again for the advice.
Peter
 

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   / Cold Concrete cure option help.
  • Thread Starter
#9  
Another update. Today most slab surface temps were about 41 degrees...I am happy with that! I also got a call at 7:30 and my garage door was ready. They wanted to come out and put it up on Christmas eve! I said they are welcome too but don't feel obligated. But they said they wanted to work...go for it. The good news is that I had to chissel (?sp) some area at the wind/water stop where the door sits down 1" below the slab. That area is 8" from the most exposed/windy area. It was hard as a rock...not at all easy to chip away the concrete. So It looks like it has set up well. So this may help those pouring in the cold. Using a good mix (higher cement, air entrained, fiber, warmed water, accelerators) and covering with foam/insulation/ etc will let you pour in the cold. I will update later with any good or bad news. Thanks to all for your help and advice! And Merry Christmas.
Peter
 

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