Effects of steel and polypropylene fibers on mechanical and durability properties of high-performance concrete

This study investigates the individual and synergistic effects of fiber morphology (hooked-end vs. straight micro steel) and material type (steel vs. polypropylene) on the workability, and selected mechanical and durability properties of high-performance concrete (HPC). Five mix designs comprising mono- and hybrid-fiber blends were analyzed. Experimental results revealed a distinct trade-off between workability and reinforcement efficiency; notably, polypropylene (PP) fibers resulted in the largest reduction in slump flow (18%). In contrast, the inclusion of 2% hooked-end steel fibers (HF) maintained flowability comparable to that of the control mix without fibers. Mechanically, the 2% HF mixture exhibited superior performance, achieving a 28-day compressive strength of 101.65 MPa and enhancing flexural strength to 13.22 MPa, attributed to the enhanced mechanical anchorage of the HF. Conversely, the hybrid matrix including PP and straight micro steel fibers (SF) (0.1% PP+1% SF) exhibited a multiscale crack-control mechanism and a favorable flexural response despite the reduced steel-fiber content. Furthermore, water absorption and abrasion tests indicated that PP incorporation was most effective in minimizing wear loss, thereby improving selected durability-related indicators. These findings provide useful guidance for optimizing fiber dosage to balance fresh-state workability, mechanical performance, and selected durability-related indicators in HPC applications.