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Re: SLAB - Control Joints in Concrete Slab on Grade

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I have used Fibermesh in slabs-on-grade in lieu of wwf for two or
three projects for the same owner.  I think it works quite well 
but great care must be taken in the early stages of the slab to 
ensure excess shrinkage does not occur.  If Fibermesh (or an approved 
equal) is to be used in lieu of steel reinforcing, ALL parties 
involved (owner, architect, SE, contractor, testing agency, etc.) 
need to be keenly aware of the unique advantages and shortcomings of 
fiberous reinforcing.

The deletion of the wwf in these projects was a result of a value
engineer process for the first project and became the "standard" for
the subsequent projects.  The slabs under the office buildings
turned out very well but very large random cracks appeared in slabs
under the fre standing parking garages.  The cause of this cracking 
was due to the fact that the slabs in the garage were exposed to the 
elements (direct sunlight, warm temperatures and breeze) while the 
slabs under the buildings were protected (formwork and basement 
walls) as soon after being finished.  Once the cracks in the garage 
slabs had reached a certain width the Fibermesh was of no use and no
backup method remained to distribute the shrinkage throughout the 
slab.  We ended up epoxy injecting some of the smaller cracks and 
replacing a few other sections (20'x20').

Michael Bramhall, PE