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

Abstract

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 considered at replacing ratios of 0.5% and 1.0%. To precisely evaluate the tensile performance, their pullout behaviors from UHPC were simultaneously analyzed. Test results indicated that the HE fiber provided the best pullout performance for the bond strength and pullout work, 4.7 and 3.7 times higher than those of the SS fiber, respectively. The order of pullout resistance was as follows: HE fiber˃ SH fiber˃ HH fiber˃ SS fiber. The UHPC matrix with hybrid 0.5% SH fibers and 1.5% SS fibers showed the best tensile performance regarding the deformability and energy absorption capacity, about 45% and 47% higher than those of the control specimen with 2% SS fibers, whereas the ultimate tensile strength was not affected by the hybrid reinforcing system. The hybrid 0.5% HE (or SH) fiber and 1.5% SS fiber, and 1.0% HH fiber and 1.0% SS fiber were effective in improving the tensile performance of UHPC available on the market. The hybrid fiber specimens also exhibited better cracking behaviors than the control specimen.