Fun Days, Cold Concrete

[Diggin It]

3'x5'x4" pad needed. Temps forecast to be 40s today and tomorrow with low 30s overnight. No major differences for the next two weeks, but rain possibly after tomorrow. Ground is wet from past rains, was partially frozen down an inch or so yesterday morning.

Plan is to mix and pour either today or early tomorrow morning. Let it set as much as possible during the daytime, then cover with a tarp before night to help hold ground heat as much as possible. There will be a small amount of wire grid, no rebar. A bit of gravel underneath.

I know it will take longer than normal to cure, so I won't be able to do much beyond that for at least a week.


Just rambling ....

 

[s219]

Slow cure is actually better and I think you will be fine. Last winter I poured some footings when we had overnight temps in the low-mid 20s. I threw a heavy stack of folded tarps over the top at night, was probably 4" thick of folded tarps. I doubt it had great insulation value, but I just wanted to provide a thick buffer from the cold air temperature. I have seen folks use horse blankets, scrap insulation, foam sheets, etc... to do the same thing.

 

[MossRoad]

A tarp has about zero insulation value. Especially if it's plastic-type fabric. I'd throw a cheap harbor freight moving blanket over the tarp, then another tarp on top of that to keep it dry. $7.99.

72" x 80" Mover's Blanket

 

[not2old]

A few years back I found myself with a similar situation when I had to unexpectedly build a dry well. I built a tent over the cement with a tarp and put a kerosene heater inside, with a full tank of fuel set on low. The next morning it was out of fuel but the cement wasn't cold to the touch. Didn't worry about it after 24 hours.

 

[Diggin It]

Well, it's down. All 8 bags. Not a great finish since I don't have a float. Did the board sawing motion thing, so it's what I can do. I'll let it air cure until just before sundown, then cover. Yeah, I've got one of those pad/blankets and some 1" styrofoam I can lay over the tarp.

 

[caver]

Andrew Camarata's buddy Jesse Muller just poured a foundation in freezing temps. It's interesting to see the temps on a thermal imager. Installing a foundation under an existing building part 1: demo, excavation, footings - YouTube FF to maybe 50 minute mark for the meat and taters part of it.

 

[dodge man]

Slow cure is good but you don’t want it freezing. I know some redi mix places a setup to heat the water, for extra of course.

 

[Smokeydog]

Been repairing spring house foundation and valve box. Mixed the last of about twenty 80# bags of 5000psi concrete yesterday. Covering with even plastic helps keep the windchill off and drying the concrete. Higher strength concrete better for cold weather. Spring flow 500gallons per minute at a constant 58 year round. Feels warm in cold weather. No joy being wet this time of year. Glad that part of the job is done.

 

[Hay Dude]

Well, it's down. All 8 bags. Not a great finish since I don't have a float. Did the board sawing motion thing, so it's what I can do. I'll let it air cure until just before sundown, then cover. Yeah, I've got one of those pad/blankets and some 1" styrofoam I can lay over the tarp.

The board sawing thing is called screeding. It will be fine if you covered it. Might want to build a small airspace into the blanket or rigid foam so it doesnt stick in the concrete or make marks in it. :laughing:

We heat the water and the sand to help in freezing temps

 

[Diggin It]

Might want to build a small airspace into the blanket or rigid foam so it doesnt stick in the concrete or make marks in it.

Did that. Laid a few scrap boards across it on top of the forms, then a couple of scraps of OSB, then the plastic tarp and blanket. Most of the undersides were wet this morning from condensation or evaporation. Surface looks OK and was starting to turn color by this afternoon.

 

[Hay Dude]

One way to tell concrete froze is it will turn a tan-ish color. My uncle tried to squeeze in a block basement and it dropped into the low 20s. All the mortar joints were tan. I was very young and working for my dad on a weekend when we went to visit and my dad, a mason by trade, had to inform him it all had to be knocked down. Luckily it was only partially completed

 

[Diggin It]

Nawh, this is the usual dark grey to light grey. Temp only hit 30, maybe 29 and only for a few hours just before sunrise. It had several hours to cure before it got that low and we've been warmer than normal for a week or more so the ground was warm.

 

[Streetcar]

You should never pour concrete on frozen subgrade
Also cover the concrete as soon as it firm enough to not leave marks.
If you can leave tarp on for a week.

 

[s219]

I wanted to post a couple pics of what I did yesterday to protect some concrete pole barn footings from an overnight temperature of 20F. This was based on how we used to layer hay over the top of winter concrete pours back when I grew up in New England.

First off, these were 28-32" below grade, which helps a lot (our frostline here is 12"). Due to a rainy year, these holes begin to fill with water as soon as they are drilled, and that eventually covers the concrete -- which is OK for the concrete, but drastically slows the cure time. Because of that, the concrete needs extended protection.

After I poured the concrete, I placed a plastic grocery bag full of leaves on top of the footing. Then I dumped another handful of leaves on top of that to fill the hole about halfway.





On top of the leaves I placed scrap radiant barrier bubble wrap (comes in frozen food shipments my wife gets periodically).



Then on top of the hole is another layer of radiant barrier, a thick layer of scrap carpet or folded up tarp, a piece of cardboard, and a piece of wood to weigh it down.



I've use this method down to 20F temps and it has worked fine. I think having the concrete so far down in the ground makes this a lot easier than if it was a slab or shallow footing. Really, all this method does is provide a couple buffers between the ground temperature and the outside air temperature.