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I don't have a lot of concrete experience, just a few foundation and slab pours. I have been told rebar isn't needed anymore because of the fiber added in the mix. Is this true for normal slabs and foundations, generally when is it needed or not needed?
 

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Pro
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Yes it is a must . When it first came pushing from supplier I tried it . The fibers are junk in my mind . Did couple of slabs without and looks like a city street .
 

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Project Superintendent
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Fiber mesh is kind of a poor substitute for wire mesh in a slab on grade. But it will never replace rebar for applications that require rebar, such as footings, walls, and elevated slabs.
 

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Project Superintendent
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Hoover dam has neither
It actually has quite a bit, but the dam structure itself did not require much because it doesn't have any tensile forces going on, since it is a horizontal arch.

What you gotta remember is that concrete is strong in compression(which is the type of load Hoover Dam puts on it) but weak in tension. In other words, if you have a long piece of concrete supported on each end, it is real easy to break by applying a load to the center. Put a rebar in the bottom of it: much stronger.
 

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I like using this example.

Take a mini-ex and do a tear out on a 20 year old walkway with mesh and a similar one with fiber and see which is a bigger pain in the ass to bust up.

That said, I do like micro fibers, I think they help prevent surface spalling and cracking during curing, the full sized fibers look like hell though.
 

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Even the fiber mesh manufacturer's have stopped trying to sell the stuff as a replacement to steel, which it never was. That should tell you something.........
 

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Rebar is necessary when it is necessary, and not when it isn't. Concrete is an engineered material, which means that the requirements need to be factored into design of the mix and the reinforcing of the structure.

Rebar is not required for a sidewalk, but may be for a cantilevered counter top of the same size and shape. When in doubt, do not throw more steel into the design, throw in more knowledge.
 
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