Improvement of UHPFRC matrix-fiber interfacial properties through a highly efficient and applicable fiber surface modification

The incorporation of steel fibers is responsible for the excellent tensile performance and toughness of UHPFRC, the prominent superiority of UHPFRC distinguish from conventional concrete. However, the insufficient interfacial bonding properties between steel fibers and the UHPFRC matrix restrict the full utilization of steel fibers. This study explores a feasible method for improving the UHPFRC matrix-fiber interfacial bonding performance through surface modifications of steel fibers. The steel fibers were roughened by exclusive stirring with steel fibers, mixing with manufactured sand, or utilizing a combined processing method (stirring with steel fibers + mixing with manufactured sand). Subsequently, the interfacial bonding properties were assessed using single fiber pullout tests, along with evaluations of flowability, mechanical properties, and microstructural analyses. The results indicate that steel fibers roughened by fiber stirring and the combined processing method are effective in improving both the bonding performance and mechanical properties of UHPFRC. Specifically, the average bond strength and pullout energy of steel fibers modified by exclusive stirring with steel fibers increased to 13.79 MPa and 234.22 N·mm (increments of 29.8% and 72.7% compared with non-refined fibers), respectively. In contrast, for steel fibers modified by the combined processing method, the average bond strength and pullout energy increased to 14.15 MPa and 225.56 N·mm (increments of 33.1% and 66.4% compared with non-refined fibers), respectively. The findings demonstrate that surface modification of steel fibers via dry friction stirring can significantly improve interfacial bonding performance, characterized by high efficiency, environmental friendliness, and construction convenience. • This study proposes the surface modifications on steel fiber for improving the UHPFRC matrix-fiber interfacial bonding performance, which simultaneously explores a feasibility approach for addressing cost-effective and eco-friendly demands. • The surface modifications of the steel fibers in this study have a substantial improvement in both the tensile strengths and toughness of the UHPFRC, but exert a negligible influence on its flowability and compressive strength. • The drying friction stirring modifications of steel fibers significantly improve the interfacial bonding performance of UHPFRC.