Mechanical properties of a novel UHPC reinforced with macro basalt fibers

Adding fibers in ultra-high performance concrete (UHPC) significantly enhances its mechanical properties. This study investigated the effects of the novel macro basalt fibers (MBF) content and geometric characteristics on flowability and mechanical properties of UHPC, the MBF which was a kind of minibar composited of basalt fiber reinforced polymers (BFRP). Two fiber shapes, including straight and twisted shape, and two aspect ratios with the volume fractions ranging from 0% to 3% were employed. The fiber distribution, interfacial bonding behavior between MBF and UHPC were tested and evaluated. The effects of MBF on the flowability, compressive strength, flexural strength and toughness of UHPC were revealed. The toughness, compressive strength, and flexural strength of UHPC increased with the increase of MBF content, but the flowability decreased. The relatively uniform fiber distribution was observed when the MBF content was lower than 3%. Compared with the straight MBF, the twisted MBF showed higher bonding behavior between fiber and UHPC. It resulted in that the twisted MBF performed more efficient in enhancing mechanical properties of UHPC than the straight MBF. The flexural post-cracking strength of UHPC with various MBF contents and geometric characteristics could be accurately predicted using the quadratic model and the modified model based on the Composited Theory because the values of R2 were more than 0.95.