Concrete Patio Slab W/out Rebar


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Old 07-14-06, 08:19 AM
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Concrete Patio Slab W/out Rebar

I'm wanting to have an 11' x 22' rectangular concrete patio floor to be poured in my back yard (4" thick). A contractor recommended to use "6 bag" strength concrete mix with fiberglass instead of a rebar mesh. Have you heard about this technique? Is it as effective as rebar in avoiding cracks and keeping the patio together in one piece?

Thanks for your comments/suggestions

BTW, this is a very flat surface and he did suggest to dig at least 6" so that there is at least 2" of gravel below the slab
 
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Old 07-14-06, 09:08 AM
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Concrete Patio Slab W/out Rebar

Three methods will reduce cracks.

1. For strength, rebar is the best. It is structural reinforcement that also reduces cracks.

2. Wire mesh (6x6) is the most effective for eliminating shrinkage cracks in properly sized slabs. People with poor concrete placing skills do not have an interest in using mesh correctly and blame it for their poor efforts and laziness.

3. Fiber mesh mixed in the concrete helps to eliminate shrinkage cracks. Both the ready-mix supplier and the contractor must be familiar with using it. Some contractors like a combination of both wire mesh and fiber mesh.

For a patio of your size, all are adequate. Make sure you break the patio into 2 - 11 x 11 sections with a control joint. The joint can be tooled while finishing or sawed late the same day or the next day, depending on curing. A sawed joint should be filled with a quality elastic caulk several weeks after sawing for the best appearance. Both types of control joints should be a minimum of 1" deep to be effective in a 3" or 4" slab.

If you are in a cold climate it would be wise to use air entrained concrete for maximum freeze/thaw durability.

Good luck!

Dick
 
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Old 07-15-06, 03:28 AM
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I disagree with some of what Dick said. Specifically, that wire mesh is best for reducing shrinkage cracks. I think fiber is just as good for reducing the cracks, but neither wire or fiber will eliminate them. The fiber is a better product in my opinion because it is mixed throughout the entire matrix of the slab, instead of lying there in only one plane. This is true whether you get a good finishing crew or a "lazy" one as Dick referred to. Neither wire mesh or fiber are primary reinforcement. They add no real strength to a slab, but can hold the pieces together somewhat when the slab cracks. Rebar IS structural reinforcement and should be used. I use a combination of fiber and rebar in my slabs.

Pecos
 
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Old 07-19-06, 03:07 AM
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There's one more thing to focus on. A common tendancy might be to pour the concrete wetter because is it easier to handle and finish. But........as the hydration process continues and the concrete ages the water is eliminated from the concrete and what do you think is left in it's place? Nothing but empty space is the correct answer. So, if you can reach a happy medium and pour the concrete no wetter than absolutely necessary to finish the final surface than your slab will be a bit more resistant to cracks. less water in the initial concrete mix means less shrinkage and fewer cracks.

There are some other obvious considerations favorable to quality concrete construction such as slowing the hydration (curing) and using well drained and well compacted bearing surfaces.

bs5
 
 

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