When to pour concrete

[sawtooth]

Im going to tell him to put off the job. Im pissed that i gave him a deposit in early october and now have to wait but I want it done right. This will be done out in the country so theres no hot water and no heaters. Slab has to be done first so no building over it or insulation. Not a happy camper right now but very much appreciate the info from everyone.

 

[Fossil Farm]

Good idea to wait. Suppose to be in the teens for a few nights. Should have air temps above 35 degrees and if you are on site, be sure the slump is around 4 inches. Too many are poured with slumps of 5 or 6 or more and then the owner wonders why the slab cracks or flakes. Too much water and you lose the strength of the concrete. They just poured a basement wall down the road a few days ago and the forms are already off. I would not want that house. Forms should be on for at least 7 days and weather in the teens and 20's without being enclosed and heated is not good for concrete strength.

 

[BuilderML]

Good idea to wait. Suppose to be in the teens for a few nights. Should have air temps above 35 degrees and if you are on site, be sure the slump is around 4 inches. Too many are poured with slumps of 5 or 6 or more and then the owner wonders why the slab cracks or flakes. Too much water and you lose the strength of the concrete. They just poured a basement wall down the road a few days ago and the forms are already off. I would not want that house. Forms should be on for at least 7 days and weather in the teens and 20's without being enclosed and heated is not good for concrete strength.

I have been doing this for a while now. I can say when walls are poured today the forms are removed tomorrow. As for leaving them on due to the cold that is what heat blankets are for not what the forms are for.

 

[JeffinIA]

If You Have frost in the ground , You Must get it out first. If not cover the area with concrete blankets (You Paid a deposit ? see if he will supply his), Or a heavy layer of straw and wait for a decent stretch of weather.In Cooler weather if the slab you are pouring ,you want 4000 psi , get 4500 psi . Get a NO flyash mix . Use an exterior mix (with air ) Unless you are covered and can pour and have heat inside. don't use turbo heaters or something like those as they will cause the surface to dust. The ready mix can provide you with Heated ag and water and will bring the concrete temp up to at least 75 Degrees. You can ad calcium chloride up to 2% , Yes over time it can eat your Rod/wire. You can get a noncorrosive accelerator which is about double the cost of Calc.Chloride. Wait for a day and nite combo of temps above freezing and pour your Concrete! Finish and cover with Concrete blankets. Leave them on a few days but make sure they come back the next day to saw the joints and recover. They should not uncover the slab all at once and send it into shock. A good rule of thumb to remember is , once the concrete reaches 500psi (about the time you can walk on it to finish) it can go thru a freeze thaw cycle and continue to gain strength. Or just wait for spring . But I would not be afraid to pour in cold weather. I Batch Concrete to Contractors and on state jobs every day.

 

[newbury]

Im going to tell him to put off the job. Im pissed that i gave him a deposit in early october and now have to wait but I want it done right. This will be done out in the country so theres no hot water and no heaters. Slab has to be done first so no building over it or insulation. Not a happy camper right now but very much appreciate the info from everyone.

GOOD MOVE!
Better to wait till spring than have major problems for life. If he couldn't GUARANTEE in writing it would be problem free it probably wouldn't be problem free.

Concrete is not very forgiving.

 

[jmc]

I was in the same spot 10 years ago. Here's the thread:

http://www.tractorbynet.com/forums/projects/31278-pouring-cement-winter.html

Poured it in December and no random cracks so far, even with a 14000 lb backhoe in there. (5 inch floor) Forget if the thread mentioned it but I covered the slab with straw while curing.

 

[JimRB]

I wanted my driveway done around Christmas. They did not get around to doing it until January 2. The temp dropped from cool to windy and bone cold. Lower 20's or so with the ground starting to freeze. In Georgia 20's is cold, or maybe I should say in Atlanta. The base was gravel I had been driving on the past 15 years. They added a bag of calcium to each truck. They tooled in the control joints when the concrete was wet. No protection from wind or cold. 2 years later and I see hairline cracks where they did the joints. Control joints did what they were supposed to do. No visible change in grade or plane. I really did not believe it was good time to do concrete but so far so good. Maybe when I am 75 in 20 years I will be annoyed. On the other hand the other driveway slab poured in the summer/early fall 18 years ago is cracked where cut control joint are not. That slab was on fill that was probably not properly compacted.

I do need to caulk those hairline cracks in the new driveway and the bigger cracks in the older driveway.

My car weighs 3,500 pounds. The truck 6,000 pounds. The truck and trailer hauling hay only weighs 12-13,000 pounds over 4 axles so my driveway never gets any real weight on it.

 

[Tractor Seabee]

Here is the specification for cold weather concrete placement used on military construction:
"3.8.6 Cold Weather
ACI/MCP-2. Do not allow concrete temperature to decrease below 10 degrees C
50 degrees F. Obtain approval prior to placing concrete when the ambient
temperature is below 4 degrees C 40 degrees F or when concrete is likely to
be subjected to freezing temperatures within 24 hours. Cover concrete and
provide sufficient heat to maintain 10 degrees C 50 degrees F minimum
adjacent to both the formwork and the structure while curing. Limit the
rate of cooling to 3 degrees C 37 degrees F in any 1 hour and 10 degrees C
50 degrees F per 24 hours after heat application.

On military projects anti-freeze products such as calcium are not allowed. Exterior concrete is always minimum 4-6% air entrainment. It costs more but specifying "high nearly cement" and water reducing additives and 2" slump will reduce the curing time greatly and shorten the heating time. The sub-grade cannot be frozen and should be at the same 40-50 degree temp. The average finisher will hate you for following this spec, but ACI certified finishers knows this stuff and is used to following it. Well specified commercial work follows the same spec as it is proven success formula tested and approved by the American Concrete Institute.

If you cannot or do not want to pay for this procedure wait till spring. An ACI supporting contractor will guarantee his work butg there is a cost associated with proper workmanship.

Ron

 

[sawtooth]

Thanks Ron. I contacted the builder this am and said to hold the project till spring. Not happy with this but too much money to jeopardize project so will just have to wait. Thanks for the info though.

 

[Qapla]

I have been doing this for a while now. I can say when walls are poured today the forms are removed tomorrow.

During the summer we were working at a house in new construction. They were pouring the house on the lot next to us. They started the pour around 7 AM and had it done by around 10 - poured that is ... still needed some secrete work. The forms were off before they went to lunch.