Impact resistance of plain and rubberized concrete containing steel and polypropylene hybrid fiber

Hybridization of polypropylene-steel fiber leads to improvements of both the mechanical properties and impact resistance of concrete. This paper provides the results of an experimental impact test, which has been conducted using a low-velocity drop hammer (with an impact velocity of 2.8 m/s) on fiber-reinforced concrete (FRC) and fiber-reinforced rubberized concrete (FRRuC) prisms. Prism specimens, measuring 100 x 100 x 500 mm (depth x width x length), were prepared. The variables were different ratios of micro steel (MS) fiber (0%, 0.75, 0.825, 0.9 %, 1.0 %) and polypropylene (PP) fiber (0%, 0.1 %, 0.175, 0.25 %, 1%) with/without crumb rubber (CR) with a partial replacement of fine aggregate at a ratio of 20 % by volume. FRC with CR produced higher first and final impact energy compared with prisms without CR. By contrast, the density, as well as the compressive and tensile strengths decreased, whereas the voids and water absorption of concrete increased due to the CR replacement. The specimen, which was reinforced with 0.9 % MS + 0.1 % PP hybrid FRRuC, produced high final impact energy of approximately 887.2 J, which was 10 times higher than that of plain concrete ; the impact ductility index was 4.15, which was twice the value of plain concrete. Furthermore, the most significant improvement in mechanical properties was found for specimens with 0.9 % MS + 0.1 % PP hybrid fiber.