Bond performance of abraded arch-type steel fibers in ultra-high-performance concrete

The feasibility of newly developed abraded arch-type steel fibers as reinforcement in ultra-high-performance concrete (UHPC) is investigated in this study. To this end, twelve abraded arch-type steel fibers with two different curvatures of 0.04/mm and 0.10/mm, three different sandpaper grits of 120, 400, and 800, and two different sanding directions, i.e., longitudinal and transverse, were adopted along with the commercial smooth, straight (plain) steel fiber. To evaluate the effect of surface roughness on the interfacial bond behavior, the surface roughness parameters of plain and abraded steel fibers were quantitatively analyzed with atomic force microscopy. Test results indicate that the surface roughness of plain fiber increased substantially by the sanding process, while smaller grit with coarse particles produced higher roughness on the surface. The abraded arch-type fibers provided better pullout performance than the plain fiber in the same UHPC matrix: the highest bond strengths and energy absorption capacity were approximately two times greater than those of the plain fiber. The higher fiber curvature, smaller sandpaper grit, and longitudinal sanding process were more effective in enhancing the pullout performance of the steel fiber from the UHPC matrix than the counterparts. The abraded arch-type steel fibers generated relatively minor matrix damages during the pulling out process in comparison with conventional deformed steel fibers from the UHPC matrix, thus they can be considered as effective alternatives to the deformed fibers for enhancing the tensile performance of UHPC.