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Re: Wire reinforcement in salbs on ground

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Kevin,

Providing reinforcement in SOG will keep the cracks under control.  Unless the slab is in someone's backyard, it is better to construct a reinforced SOG.

If the construction is done correctly, there is no reason why the reinforceent should end up at the bottom of the slab. It is a bad, bad practice to pull the reinforcement grid after the concrete is placed. Some stupid contractor started that practice and other cheap contractors have followed suit. Whenever I was called upon to supervise slab construction, I have disallowed that practice of lifting the rebar grid. I insist on properly spaced chairs to support reinforcement.

Rajendran



Kevin Below <kevinbelow(--nospam--at)videotron.ca> wrote:
I was having a discussion with a client about using wire fabric reinforcement in a slab on grade.  His "other" engineers are becoming very gung-ho about using steel fibres.
But the present project is an office building, with mostly light loads on the ground floor (except for the library), not a highly loaded distribution or warehouse building with racking and fork lifts.
I recommended a 100 mm slab with wire fabric and control joints at 4 metres.
It's about the same price as 125 mm without wire fabric and control joints at 4 metres.  The "other" engineers prefer the latter.
I prefer the former, since it's a system that has been used in this area for at least 28 years, no, that's a joke.
Conventional wisdom here is that wire mesh is no good since it's always at the bottom, never in the slab.  But I remember reading an article once in Concrete Construction arguing that the bottom is the best place for the reinforcement, since that is where the sub-grade friction is, and this is what causes the cracking.
 
We all know that the mesh ends up on the bottom, since we have seen it there when we demolish old slabs.  But if the mesh is pulled up into the slab occasionally, like say 1 metre c/c, I would say that there will be some sort of composite action between the slab and the mesh, and that the mesh will be at least partially effective in resisting cracking.
 
I have used a 100 mm slab without mesh, for a lightly-loaded slab with no floor covering, where the occasional crack is not a huge problem.  Using a Soff-cut saw for the joints worked wonderfully to control cracking, at least to date - 1 year old.
But I am reluctant to forego the mesh on the present job, because the floor covering is linoleum, which will reflect cracks.
 
Any thoughts on this - what do you prefer - a 4" slab with mesh, or a 5" without ?
 
Kevin

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