Polypropylene fibers have been suggested as an alternative to using welded fabric wire for crack control purposes in concrete slabs. Because wire mesh won't function properly if it's lying on the subgrade or has bowed up near the surface, advocates of fiber reinforcement argue that uniformly distributed fibers will more reliably control cracking.

JOINT SPACING, REINFORCEMENT AND CRACK CONTROL

Polypropylene fiber manufacturers recommend their product as an alternative to welded wire fabric for crack control purposes. No recommended increase in joint spacing for concrete slabs containing polypropylene has yet been proposed.

RESULTS OF A FIELD PERFORMANCE SURVEY

Three of the slabs on ground that were inspected had maximum joint spacings in feet that were less than 2 to 3 times the slab thickness in inches. In these slabs there was very little cracking and cracks that did form weren't wider than about 0.04 inch. Two other slabs on ground had joint spacings greater than those recommended for plain concrete. One of these was nearly crack free and the other had about 80 lineal feet of cracking in a 625-square-foot area. One of the cracks had faulted with a vertical displacement of about 0.125 inch. Two slabs on ground that were built using polypropylene-fiber concrete and welded wire fabric had joint spacings up to 30 feet. Cracks had occurred between joints, some of them up to 0.05 inch wide, but there was no faulting.