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Re: Fiber Reinforced slab

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If you anticipate a fair amount of bending stress due to heave, settlement, heavy load etc, fibers won't do it alone.  You'll need steel reinf, and you can use fibers for crack control.  That's where you use the 3/4 #/ cu.yd.
I've used them quite a lot on decent soils (in-situ and engr fill).  I would use ~1.7 #/yd of polypropylene, fibrillated fibers. 1" to 1.5".  Longer fibers and too many fibers may cause them to "ball up" in the mixer.  On that note get a mf'r w/ an ICC code report documenting good distribution.  Don't use this as a recommendation, just a go-by.  Ask the mf'r for a recommendation.
A few notes.
I never spaced the saw joints more than 10 ft.  These things forget to micro-crack, and just do the big cracks.  And they'll be bigger than you want.
Also, use a SOF-CUT saw for control joints.  waiting 6-8 hours is too late.
This is a must-do for suing a laser screed, for obvious reasons.
Steel fibers carry their own set of different problems.

>>> On 11/8/2007 at 11:45 AM, "Jason Christensen" <jason(--nospam--at)> wrote:
I have a client wishing to put a fiber reinforced slab in a small office
building.  The slab on grade is 4" thick.  Reinforcing will be for
temperature/crack control only.  I have never called this out, we
typicall call out #4 at 24"oc each way w/ f'c=3000psi.  I am not sure
how to spec this on my drawings.  Is there a typical poundage per mix?
I guess the question is which is the best way to spec it on the my


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