Enhancing the tensile performance of ultra-high-performance concrete through strategic use of novel half-hooked steel fibers

This study improved the tensile performance of ultra-high-performance concrete (UHPC)through hybrid reinforcing system. Four types of steel fibers, i.e., smooth-straight (SS),hooked-end (HE), half-hooked (HH), and straightened half-hooked (SH), were consideredat replacing ratios of 0.5% and 1.0%. To precisely evaluate the tensile performance, theirpullout behaviors from UHPC were simultaneously analyzed. Test results indicated that theHE fiber provided the best pullout performance for the bond strength and pullout work, 4.7and 3.7 times higher than those of the SS fiber, respectively. The order of pullout resistancewas as follows: HE fiber > SH fiber > HH fiber > SS fiber. The UHPC matrix with hybrid 0.5% SHfibers and 1.5% SS fibers showed the best tensile performance regarding the deformabilityand energy absorption capacity, about 45% and 47% higher than those of the control speci-men with 2% SS fibers, whereas the ultimate tensile strength was not affected by the hybridreinforcing system. The hybrid 0.5% HE (or SH) fiber and 1.5% SS fiber, and 1.0% HH fiberand 1.0% SS fiber were effective in improving the tensile performance of UHPC available onthe market. The hybrid fiber specimens also exhibited better cracking behaviors than thecontrol specimen.