Best temperature to pour cement

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Old 05-23-09, 07:56 AM
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Best temperature to pour cement

I plan to have my driveway repaved with cement and was wondering if it would be a bad idea to have it done this summer. I heard cement shrinks as it dries and the heat makes it dry faster making it more prone to cracking. Is this true? Should I wait until cooler weather in the fall? thanks for the help.
 
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Old 05-23-09, 08:19 AM
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Well, if that was true, there wouldn't be much work getting done in the summer months. If you are having this done by a Pro..there shouldn't be any problems. IF they know what they are doing of course.

Concrete gets placed in the winter spring summer and fall, under water and when it's snowing. As long as its done CORRECTLY...it shouldn't be prone to anything except lasting a long time.

One of the experts will be able to give specifics...give them time.
 
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Old 05-23-09, 11:29 AM
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Concrete can be poured about anytime except when freezing, and with some additives even that can be done. However, in very hot weather (90 degrees plus) you are much more likely to get a bad job. This is because A) the concrete can flash set, which can mean the finishers won't get it properly finished before it's too far gone. B) When that happens, finishers typically add a lot of water to the truck to make it more pourable/workable. This leads to a high water:cement ratio which weakens the concrete. C) They may throw water on the surface and work it in to get a better finish. This creates a high water:cement ratio just on the surface, which causes delamination and flaking later on. D) Concrete dries a lot faster in hot weather, which is bad for curing and ultimate strength. The optimum curing temp for concrete is around 50-60 degrees Fahrenheit. This leads to a slow, thorough cure and stronger concrete.
If you pour in summer, schedule the pour for early morning. Thoroughly wet down the base prior to pouring, but do not leave puddles of standing water. Make sure they pour at no more than a 6 inch slump, and do not let them put water on it and work it in. Finally, make sure they apply a liquid cure-n-seal compound after final finish to retain moisture in the slab. Good luck.
 
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Old 05-23-09, 11:38 AM
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There ya go..I knew an expert would pop in eventually.

Hey Pecos....if you look at this again.....why do some people "place" concrete...and others "pour" it? Just a regional thing?
 
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Old 05-23-09, 03:01 PM
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Thanks Pecos. I didn't want to ask a contractor because I was sure he would say anytime is fine. What you said validates what I thought and since I am able to, I will wait on this.
 
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Old 05-23-09, 07:36 PM
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Gunguy,
it's said both ways here. I just say pour because it's easier somehow. Really, concrete that can be "poured" is too wet, so "placed" is more correct.
Sharc, I don't mean to dissuade you from doing it in the summer. It's just that there are things to watch out for. I pour/place concrete from March to December with no problems, and I'm in the same type of climate as you are.
 
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Old 05-24-09, 08:35 PM
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Originally Posted by Pecos View Post
Gunguy,
it's said both ways here. I just say pour because it's easier somehow. Really, concrete that can be "poured" is too wet, so "placed" is more correct.
Sharc, I don't mean to dissuade you from doing it in the summer. It's just that there are things to watch out for. I pour/place concrete from March to December with no problems, and I'm in the same type of climate as you are.
When I pour Crete in Puerto Rico with my crew down there they use the phrase "Throw" some cemento. Part of that is because its just about all pumped..

Good Job Pecos on the advice.

I would like to add its not always about the temp you pour the Crete. The humidity in the air and or breeze plays a big factor. Also it not what the temp reaches at mid day all the time either. Its also how hot the night before was on the truck being chiller or hot starting out on the load. Another big factor is the wetter you pour the Crete the more it shrinks...
 
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Old 05-25-09, 05:25 AM
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Yeah, the shrinkage thing is a biggie. Most people think that concrete cracks are caused by some outside force such as a heavy load, frost heave, poor workmanship, or lack of reinforcement. These can all be causes, but the majority of cracks are caused by shrinkage. Most occur within a couple of days of the pour, but are hairline cracks and so are not seen. They open up over time to become noticeable. Shrinkage is why joints are needed in concrete. When the concrete shrinks, the joints make the concrete crack there instead of randomly. That's why they're properly called contraction joints or crack control joints, instead of expansion joints like most people call them.
Very wet concrete shrinks a lot when drying and/or curing. However, it is a LOT easier to pour so contractors do it. Even properly placed concrete shrinks and cracks though, so just because you have cracks doesn't mean your contractor messed up. If the cracks (especially interior ones) open up wider than 1/8 to 1/4 inch, the concrete was probably poured too wet.
 
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