To control cracking best, reinforcement should be placed as close as possible to the concrete surface. Steel typically can't be placed less than 1 or 2 inches from the surface, however, because it might corrode and spall the surface concrete. Polymer grids are an alternative to steel mesh used for crack control. Because they don't corrode, the grids can be placed closer to the surface where they'll do the most good.
POLYMER GRID PROPERTIES
Polymer grids are made from sheets of heavy-gauge polymer. Before the grids were put on the market, a university research team studied the behavior of concrete reinforced with polymer grids. In flexure tests, concrete slabs reinforced with the grid had significantly better post-crack ductility than either plain or steel-reinforced concrete. Polymer grids are an alternative to steel reinforcement except where sustained loads are imposed over a period of time.