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concrete slab curing near freezing
2

concrete slab curing near freezing

concrete slab curing near freezing

(OP)
Hello all,

I am in the middle of a very important project - pouring my garage pad.  It is an 18' x 24' 4" thick slab, with 8" thickened edges (for one foot in).  Since I am installing hydronic heating, the under side of the slab is insulated with 2" rigid foam (R10).  I am using 10m rebar for reinforcement as per the Concrete Design Manual.

My problem is this: I  want to pour next week.  The problem is that at night, it is dropping below freezing a bit (25*F), and warms back up to 50 to 60*F during the day.  The ground is not frozen yet.  My plan is to lay down plastic sheeting once the concrete has been finished, cover with 12" of straw and cover with a tarp.

My problem is that being in my backyard, I have no way of really hoarding and heating.  Given that I am going to use 27.5 MPa concrete with calcium for cold weather curing, can I continue as I plan, or should I pull the plug and wait until spring??

Can anyone think of a good way of taking advantage of using my hydronic heating in some temporary fashion to keep the temperature of the slab up for the first 3 days?

Thanks!
K.A.
Calgary, AB, CA

RE: concrete slab curing near freezing

Mr. Wolf,
Here in Anchorage a lot of curb and sidewalk is placed in similar conditions to yours.  Insulating blankets are used; your 12" straw would be comparable.  I'd say go ahead and pour.  You can lay a thermometer on slab to make occasioanal checks, I'll bet you'll find concrete stays above 40 degrees, what with the heat of hydration and ground heat.  Type III cement (high-early) would allow you to remove cover sooner than if Type I is used.

Use of hydronic heat may cause more problems than help, and is not necessary.

Carl

RE: concrete slab curing near freezing

(OP)
Thank you Carl.  I thought the in slab heating was more headache than it was worth, but I threw it out as a brainstorm idea.

I have had difficulty finding good easy to access info on "cold weather" curing, that is relative to North of the 49th!  I have seminar notes coming tomorrow from our corporate library from an ACI Seminar put on here in Alberta.

RE: concrete slab curing near freezing

(OP)
Yoinks!  Well, I won;t be able to schedule a pour before I leave for holidays, so it looks like I'll have a big hole in my backyard for the winter and it has to wait for spring.  At least I learned something about cold weather curing for future reference!

RE: concrete slab curing near freezing

I don't see why you shouldn't go ahead since you have insulation under the slab and you can insulate the top as you suggested. The heat generated during setting will keep the unreacted water from freezing. The construction industry does not grind to a halt every time there is a frost.

Carl Bauer
www.bauerconsultbotswana.com

RE: concrete slab curing near freezing

I agree with Carl.  In our area (northern Minnesota) the standing joke is that we wait until January to pour concrete (-20F for the high).  With blankets or straw as insulation, you should have no problems.  I would suggest to seal it with a curing and sealing compound so that if/when chlorides from the car drip on the slab from winter roads, they don't end up spalling the surface.

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