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Re: Separating slab on grade

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Your fibers are probably either polypropylene or nylon (not fiberglass).  At the typical dosage of 1 to 1-1/2 lbs/cy, they have no effect on the properties of hardened concrete,  all they do is reduce plastic shrinkage cracking.  If polymeric fibers are very highly dosed, they can theorectically replace temperature and shrinkage reinforcement, but the concrete is awful hard to place.  Steel fibers can serve as temperature and shrinkage reinforcement but don't do much to stop the curling at joints.

If your panels are 17 ft by 17 ft, and the slab is only 4 in. thick,  you are going to get alot of cracking.  About the furthest you should go with a 4 in. slab is 12 ft (36t), and even then you are likely to get cracking.  The vapor barrier directly under the slab is probably exacerbating the cracking.  I am not sure there is anything you can do as a "repair".

If you do not have ACI 302 "Concrete Slab and Floor Construction" you should probably get it.  It is not exactly well written but it is about the best there is.

Gail Kelley

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