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Post The Details Of Your Best Slabs

 
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Old 10-14-2019, 08:45 PM   #1
edward trowelhands
 
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Post The Details Of Your Best Slabs


So many posts here about concrete cracking, and I hear the standard, "Concrete cracks, period." too often on the job. I've had a great number of slab pours that essentially didn't crack, at least for a couple years of follow up visits. In my limited experience, the most important details for this success are, in order:

Sub base prep

Mix design (especially W/C ratio)

Control joints. I put this last because I've had no cracking on 16x24' without joints, and 55x55 cut into almost 14' squares. Both were Low water, 5-6" 3500 PSI. On the other hand this could be number one, because 4x4 sidewalk sections pretty much won't ever crack as long as the cuts are deep enough, no matter what soup you pour.
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Old 10-14-2019, 09:49 PM   #2
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Re: Post The Details Of Your Best Slabs


There are two kinds of concrete. Concrete that's cracked and concrete that's gonna crack!


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Old 10-14-2019, 11:32 PM   #3
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Re: Post The Details Of Your Best Slabs


It's all about the sump and low water and a very good cure. Keeping it wet as long as possible will keep the crack down the most.
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Old 10-15-2019, 08:31 AM   #4
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Re: Post The Details Of Your Best Slabs


Most import are:
* A good, well compacted, level base to pour atop.
* Correct mix poured at the correct slump and thoroughly consolidated.
* Applying the finish when time is right and not over working it.
* Saw cut control joints immediately after finishing.
* Follow proper curing procedures and protection from the elements.
* Properly constructed cold joints between pours.

We've poured acres of 10" & 12" industrial roadway, building and storage yard slabs with zero wire mesh, rebar or other reinforcement and they hold up well.

You see a lot of random cracking on residential and light commercial jobs. I think most of it is the result of:
a. Not spending enough time leveling and compacting the base.
b. Pouring too wet to make things easier.
c. Reliance on fibermesh (which is a pretty worthless).
d. Not cutting enough control joints, and not cutting them quickly enough after finishing.
e. No protection from extreme heat or cold temps.

Most residential and light commercial slabs I see are 4" thickness. They should have control joints on 8' to 12' spacing max both directions, yet you rarely see this. 6" Slab 12' to 18' spacing.
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Old 10-15-2019, 07:54 PM   #5
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Re: Post The Details Of Your Best Slabs


Quote:
Originally Posted by Calidecks View Post
There are two kinds of concrete. Concrete that's cracked and concrete that's gonna crack!


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Old 10-16-2019, 06:17 AM   #6
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Re: Post The Details Of Your Best Slabs


Quote:
Originally Posted by Fishindude View Post
.........
d. Not cutting enough control joints, and not cutting them quickly enough after finishing.
e. No protection from extreme heat or cold temps.

...........
Those 2. Once you eliminate all the reasons for the bad and the ugly, the good comes comes down to those 2 things.

And it is still gonna crack. Just how it is.

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