THE USE OF POLYPROPYLENE FIBERS AGAINST PLASTIC SHRINKAGE CRACKING

Abstract

Plastic shrinkage cracking (PShC) occurs within a few hours after fresh concrete formed into the molds and it takes part on the surface of the concrete. When concrete formed into the molds, the aggregates settle because of the gravity and in contrast, water bleeds. If the rate of evaporation is higher than the rate of bleeding, surface of concrete starts to shrink. However, under the surface, the fresh concrete cannot shrink as much as the surface. Because of this condition, cracking occurs on the surface of concrete. In this respect, the quantity of PShC majorly depends on the temperature of concrete, temperature of air, rate of relative humidity and the wind velocity. Use of short fibers in concrete is one of the most effective ways to prevent concrete from PShC. The aim of this research was to evaluate the effect of polypropylene fibers having different geometries and content on PShC. For this purpose, the principles of ASTM C 1579 standard was considered. Results have shown that the use of polypropylene fibers in limiting PShC is obvious. Moreover, fibrillated fibers has shown better performance than monofilament fibers.