High energy absorbent ultra-high-performance concrete with hybrid steel and polyethylene fibers

To improve the tensile performance of ordinary ultra-high-performance fiber-reinforced concrete (UHP-FRC) with single steel fibers, a portion of the steel fibers was replaced with polyethylene (PE) fibers, showing a slip hardening response. For this study, three different types of steel fibers, i.e., short straight, long straight, and twisted steel fibers, and four different replacement ratios of steel fibers to PE fibers, i.e., 0, 0.5, 1.0, and 1.5%, were considered. In addition, fiber pullout patterns at localized cracks were examined under tensile loading using a camera installed with a magnifier. Test results indicate that twisted steel fibers were the most effective in improving the tensile strength and cracking performance of ultra-high-performance concrete, but led to reduced post-peak ductility due to matrix fragmentation during the pullout process. The compressive and tensile strengths and crack performance of UHP-FRCs were deteriorated when the PE fibers were added and when their replacement ratio increased. However, the strain capacity and energy absorption capacity of UHP-FRCs significantly improved when the PE fibers were incorporated and the replacement ratio was increased. The effectiveness of PE fibers on the strain and energy absorption capacities was higher for the short straight steel fibers than for the long straight and twisted steel fibers. Finally, a high energy absorbent ultra-high-performance hybrid steel and PE fiber-reinforced concrete was successfully developed at a 2% fiber volume fraction. It exhibited an energy absorption capacity of 251 kJ/m ³ at peak strength, which is about 2.2–4.1 times higher than that of the ordinary UHP-FRCs with only steel fibers at the identical 2% volume fraction.