Structural Performance of UHPC Reinforced with Bioinspired Silica-Coated Steel Fibres

Ultra-high-performance concrete (UHPC) has been widely investigated for its superior strength and durability; however, despite extensive research on fibre reinforcement, limited attention has been given to validating fibre surface modification strategies at the structural scale. Improvements in fibre–matrix bonding are commonly demonstrated through single-fibre tests, with limited evidence of their translation into the mechanical performance of UHPC elements. This study investigates the influence of bioinspired surface-modified steel fibres on the mechanical behaviour of UHPC, focusing on whether interfacial enhancements lead to measurable structural-scale performance gains. Steel fibres were coated under mild aqueous conditions and incorporated into UHPC at a volume fraction of 1%. Compressive strength was evaluated at 7, 14, 28, 56, and 90 days, while flexural behaviour was assessed at 7 and 28 days using three-point bending tests on notched beams and four-point bending tests on prisms. The incorporation of surface-modified fibres resulted in consistent strength enhancement at all curing ages. Compared with mixes containing uncoated fibres, compressive strength increased by approximately 15% at 7 days and remained 5–7% higher at later ages up to 90 days. More pronounced improvements were observed in flexural performance, with coated specimens exhibiting up to 51% higher peak load at 7 days and 29–32% higher peak load at 28 days in both bending configurations. These results demonstrate that fibre surface modification effectively enhances both early-age and long-term mechanical performance of UHPC, confirming that interfacial bond improvements are directly translated into structural-scale response. The findings highlight fibre surface engineering as a practical approach for improving the mechanical efficiency of UHPC without altering mix composition or fibre dosage.