Flexural Characteristic of Rubberized Hybrid Concrete Reinforced With Steel and Synthetic Fibers

To enhance the low strain capacity and brittleness of concrete, several researchers have already reported on the mechanical properties of rubberized concrete, which lead to reduced environmental concerns, direct cost reduction, low unit weight, high toughness, and improved absorption of impact. However, to overcome the drawbacks of low flexural strength and the low stiffness of rubberized concrete and to improve the crack resistance, steel, or synthetic (polypropylene) fibers, or both, were added into the rubberized concrete in this study. Based on the flexural performance test according to ASTM C1018 and ASTM C1609, this study investigates the combination of crumb rubber, steel or synthetic fibers, or both, in zero-slump concrete mixtures used in the dry-cast production method for concrete pipes. A series of concrete mixes were examined with the variation of the fiber volume fraction (Vf) (steel: 0.17 % and 0.33 %/synthetic-polypropylene: 0.17 %, 0.33 %, and 0.52 %), and crumb rubber with different replacement ratios of 3 % to 20 % (by volume) for sand (fine aggregate) in the concrete mixture. Seventeen rubberized mixtures were developed by incorporating different dosages of steel and polypropylene fibers and their combinations. The influence of fiber type, dosages of fibers, and rubber are analyzed on the basis of experimental results. Results indicate that the effect of hybrid reinforcement using both steel and polypropylene fiber in rubberized concrete is considerable in terms of increase in both peak load and toughness. The specimen of hybrid fiber-reinforced rubberized concrete (HYFRC) with 44 lb/yd3 (0.33 %: Vf) of steel fiber, 8 lb/yd3 (0.33 %: Vf) of polypropylene fiber and 3 % of crumb rubber (replacement with fine aggregates) showed higher peak load, modulus of rupture, and toughness than other mixtures. However, excessive replacement of rubber into the specimens had a negative effect on the flexural properties (strength and toughness).