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RE: Wire reinforcement in slabs on ground

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The only thing that you should rely on with any type of slab on grade reinforcement is for crack control due to shrinkage. If crack control is critical, I would be inclined to use rebar.

Regards,
Harold Sprague





From: Kevin Below <kevinbelow(--nospam--at)videotron.ca>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Wire reinforcement in salbs on ground
Date: Wed, 22 Feb 2006 23:00:43 -0500

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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