Enhancing the rate dependent fiber/matrix interfacial resistance of ultra-high-performance cement composites through surface abrasion

Surface-treated steel fibers were developed for enhancing the dynamic pullout performance from ultra-high-performance cement composites (UHPCC). To this end, three types of straight steel fibers with a smooth surface (plain) and longitudinal and transverse abrasions were prepared and tested in impact loading conditions. Sandpapers with various grits were used to abrade the fiber surface; hence, various surface roughness parameters could be achieved. Test results indicated that the surface of smooth steel fiber became much rougher upon abrading it using the sandpapers. The pullout resistance of the abraded steel fibers from UHPCC was better than that of the smooth fiber from the same matrix under the static and impact loads. Some of the transversely abraded steel fibers demonstrated a slip-hardening response, which has been rarely observed in commercial smooth, straight steel fiber products. Considering the pullout resistance and rate sensitivity, the transversely abraded steel fiber was the most effective reinforcement for UHPCC subjected to high loading rates, and these fibers could achieve approximately three times greater equivalent bond strength than the plain fiber. The static and dynamic bond strengths increased almost linearly with the surface roughness of the fiber, whereas the pullout energy had no apparent relation with the roughness.