Concrete Strength?

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Old 12-02-06, 07:09 PM
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Concrete Strength?

Was going to do several monolith slabs at 3000psi fibercrete. A carpenter (yup! willing to listen to anyone) told me it would be better to go with 2500psi fibercrete since the less heat generated during cooling would make it less suseptable to crack.

Any opinions?

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Old 12-02-06, 07:24 PM
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Yes, but the moderators would just delete them.
 
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Old 12-02-06, 07:28 PM
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Concrete Strength?

Where are you located?? What kind of concrete pour?

Generation of heat has nothing to do with cracking if you have reasonable curing. It is hard to get anything as weak as 2500 psi.

A minimum strength should be 3000 psi. Where I am, most concrete companies will refuse to sell anything less than 4000 psi for durability purposes on driveways.

Adding strength to concrete is cheap and gives you a lot of insurance.

All concrete will crack and that is the reason you cut or create control joints for. Proper curing will reduce shrickage and increase the ultimate strength.

Fibermesh is concrete will reduce the tendancy to crack, but it has disadvantages. For the same slump (required for placement and finishing), it will have slightly lower compressive strengths.

My last driveway was 5000 psi, air entrained (for durability) and 6x6 wire mesh with fibermesh. I would never substitute fibermesh for wire mesh (6x6), but I will use it in addition since the cost is low.

Dick
 
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Old 12-02-06, 07:39 PM
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I agree. 2500 psi concrete would be crap, and hard to finish as well. There would not be sufficient cement paste to get a good top on it. The heat of hydration in a slab is minimal. If you were pouring bridge piers requiring hundreds of cubic yards, the heat in the middle of them would be pretty high, but in something as thin as a slab the difference between 2500 and 4000 psi concrete would be about the same. Certainly not enough to induce or prevent cracking.
What makes slabs more prone to cracking is too much water in the mix, poor subgrade preparation, and lack of crack control joints.

Pecos
 
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Old 12-03-06, 09:06 AM
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Originally Posted by Concretemasonry View Post

My last driveway was 5000 psi, air entrained (for durability) and 6x6 wire mesh with fibermesh. I would never substitute fibermesh for wire mesh (6x6), but I will use it in addition since the cost is low.

Dick
I like using both wiremesh and fibermesh in slabs. Plus where else can you get hairy concrete....
 
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Old 12-03-06, 05:20 PM
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Thanks for the replys.

Pouring in Central Florida (Deland, 30 mins NE of Orlando)
 
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