Influence of a hybrid combination of steel and polypropylene fibers on concrete toughness

The toughening effect of a hybrid combination of steel and polypropylene fibers on high-strength concrete (HSC) is investigated using bending, quasi-static, and dynamic splitting tensile tests. The bending strength and quasi-static splitting tensile strength of polypropylene-fiber-reinforced HSC improves only when the volume fraction of polypropylene fiber reaches 0.22%. The bending strength of steel-fiber-reinforced HSC is higher still, while its quasi-static splitting tensile strength is slightly lower when the steel fiber volume is higher than 2.0%. When an appropriate amount of steel and polypropylene fibers are employed together in HSC, the bending strength and quasi-static splitting tensile strength increases further. By analyzing the toughness ratio, toughness index, and energy dissipation, it is found that the toughness of HSC can be greatly increased by the introduction of steel fiber, but it is only slightly affected by polypropylene fiber. The toughness of HSC can be further improved by introducing an optimal hybrid combination of steel and polypropylene fibers. Hybrid-fiber- reinforced HSC with 0.12% polypropylene fiber has better bending toughness when the volume fraction of steel fiber reaches 2.0%similar to 3.0%. When 2.5% steel fiber and 0.12% polypropylene fiber are mixed in HSC, the dynamic and quasi-static splitting tensile toughness of hybrid-fiber-reinforced HSC reaches the best. (C) 2020 Elsevier Ltd. All rights reserved.