COMPARISON OF THE PERFORMANCE OF MACRO-POLYMERIC FIBERS AND STEEL FIBERS IN CONTROLLING DRYING SHRINKAGE CRACKS OF CONCRETE

This study investigates the effect of polymeric and steel fibers in controlling drying shrinkage cracking of concreteby the restrained ring test according to ASTM C1581 and determines the cracking potential of various mixes. In addition the effect of various fibers on physical and mechanical properties of concrete such as a compressive and tensile strength and free shrinkage was investigated. Fibers used include macro polymeric fiber of single-strand type, spun multi-strand type and a hooked end steel fiber, which were used at dosages of 0.25, 0.5 and 1 %. Furthermore a micro polymeric fiber at dosage of 0.25% was investigated. The results showed that the use of steel fibers up to 1% and macro polymeric fibers up to 0.5% have no appreciable effect on compressive strength. With regards to tensile strength, the effect of fibers up to 0.5% was similar to that described for compressive strength. However, at the dosage of 1%, the use of steel fibers increased the tensile strength while macro polymeric fiber slightly decreased this parameter. Free shrinkage test results indicate that the effect of fibers on free shrinkage was negligible. The effect of micro and macro polymeric fibers at the dosage of 0.25% in decreasing the cracking potential of concrete is low, and cracking potentials are classified as ``High''. At this dosage, steel fiber showed a slightly better performance and the cracking potential was ``Moderate to High''. By increasing the dosage of fibers to 1%, the cracking potential for macro polymeric fibers and steel fibers were determined as ``Moderate to Low'' and ``Low'' respectively. Crack width measurements showed that macro polymeric fiber and steel fiber at a dosage of 0.25% decreased crack widths by about 35% relative to the control mix. At fiber contents of 1%, the maximum crack opening for the macro polymeric fibers showed a decrease of about 60% compared to the control mix. The steel fiber showed the best performance at this dosage and was able to completely prevent shrinkage cracking.