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RE: Wire reinforcement in salbs on ground

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On 23 Feb 2006 at 8:51, Bruce Holcomb wrote:

> For a typical office SOG, I've specified fibers quite a bit.  I don't
> use steel fibers in this situation... I use fibrillated polypropylene
> fibers at 1.5 pounds / cubic yard.  I specify steel fibers for heavy
> floors... warehouse, etc.  We always give an alternate for WWF for
> lightly loaded floors (offices) and rebar (typically #4's @ 18" oc)  for
> heavily loaded floors (warehouses).  We typical space control joints at
> 3 - 4 times the slab thickness.
> 
> From the test results and the few floors I've seen with fibers, they are
> great at crack control.  They can't be used for strength... you must
> have WWF or rebar for a structural slab.  But for an office SOG, fibers
> are a good option.
> 
> But, I'll admit that I don't have a lot of data on my own projects with
> fibers.  Most contractors around here use our WWF or rebar alternate
> simply due to lack of experience with fibers.  This is the case even
> though the final installed cost is less with fibers than with rebar.  We
> also work with national corporations which require stained slabs and
> embeds stamped in slabs.  We don't use fibers in these cases because
> they can affect the finished appearance.
> 
> One thing I like about fibers is that it is more difficult to use them
> incorrectly than rebar or WWF.  It is rare to find the reinforcing mat
> in the correct location.  Of course, fibers can be used incorrectly...
> for one thing, they can "ball up" in the concrete mix.
> 
> Just one opinion.
> 
>  
> BDH
>  
> -----Original Message-----
> From: Gary Hodgson & Associates [mailto:ghodgson(--nospam--at)bellnet.ca] 
> Sent: Thursday, February 23, 2006 7:01 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Wire reinforcement in salbs on ground
> 
> Kevin,
> 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 :-).
> Gary
> 
> 
> 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
> > 
> > 
> > -- 
> > No virus found in this outgoing message.
> > Checked by AVG Free Edition.
> > Version: 7.1.375 / Virus Database: 268.0.0/266 - Release Date:
> > 2006-02-21
> >  
> > 
> 
> 
> 
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