Achieving slip-hardening behavior of sanded straight steel fibers in ultra-high-performance concrete

This study develops a slip-hardening straight steel fiber in ultra-high-performance concrete (UHPC). For this, a surface treatment using sandpaper with various grits was adopted in both parallel and perpendicular directions to the fiber axis. Surface roughness was assessed by atomic force microscopy (AFM), and its correlation with the pullout resistance was evaluated. Test results indicate that although the surface treatment using sandpapers in both parallel and perpendicular directions is effective for enhancing the pullout resistance of straight fiber in UHPC, the latter is recommended since it exhibits better slip-hardening characteristics. The benefits resulting from inclination were more significant in the sanded fiber case and increased with increasing the grit. The higher surface roughness resulted in better pullout resistance, and the effectiveness was higher when the fibers were aligned. The sanded fiber achieved superior resistance and excellent slip-hardening response but exhibited smaller magnitude of frictional shear stress than the twisted fiber.