Geometry-driven optimization of profiled GFRP macro fibers for enhanced bond behavior in concrete

The development of corrosion-resistant and high-performance fibers is crucial for advancing ultra-high-performance concrete (UHPC) applications in aggressive environments. This study proposes and evaluates profiled glass fiber-reinforced polymer (GFRP) macro fibers as a geometry-driven solution to enhance fiber-matrix bond behavior. Fourteen GFRP designs with systematically varied rib shape, height, width, and spacing were fabricated using precision abrasive waterjet cutting and tested in single-fiber pullout, alongside hooked-end and crimped steel fibers and polypropylene fibers. Microstructural observations were conducted to characterize the interfacial transition zone (ITZ) and clarify its relationship with bond performance. Within the tested design space, the favorable profiled GFRP macro fiber configuration enhanced pullout strength and bond stiffness compared to conventional fibers. Specifically, the best-performing profiled-end configuration achieved bond strengths up to 1.8 times, 2.8 times and 3.3 times those of hooked-end steel, crimped steel fibers and polypropylene fibers, respectively. The findings highlight the crucial role of rib geometry in determining bond behavior, emphasizing the balance between anchorage efficiency and post-peak ductility. The study provides a basis for optimizing GFRP macro fibers for UHPC reinforcement and indicates that a balanced rib geometry with moderate height and width can enhance both bond strength and energy dissipation.