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Re: Wire reinforcement in salbs on ground

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I have gone through a few jobs with floor problems,
caused (thankfully) by others.  As Bill P said steel
fibres are expensive.  The wire mesh is next to useless
unless you stand over the workers.  It is impossible to
lift the mesh when the workers are standing on it and
then you don't know where it is in the slab.  One of
those afore-mentioned jobs had to be ripped out in part
--guess where the mesh was--right, still lying on the
sub-base.  Now I only specify heavy guage welded wire
fabric in mats or rebar and that the reinforcing has to
be blocked up and I send someone to watch them.  I also
prefer rebar at 14 to 16" o.c. so the workers can step
between the bars.  The w.w.fabric has to have planks put
down for access to the work. I also specify saw-cuts at
30 x the slab thickness in inches (from some conc
publication) with saw-cutting to 1/4 depth in approx 10-
12 hours after placing.  My 2 cents worth :-).

On 22 Feb 2006 at 23:00, Kevin Below 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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> 2006-02-21

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