New insights into the interfacial bonding performance of nano-TiO₂ modified steel fiber-reinforced paste composites：experimental，numerical and theoretical studies

This study establishes a three-level coupled system- “pure paste-single fiber-multiple fibers”-to investigate the mechanism of nano-TiO₂ (NT) on interfacial bonding in steel fiber-reinforced paste composites (SFPC). Through the systematic investigation of 1,848 pull-out specimens, the effects of fiber geometry, spacing, embedment length, NT dosage, and curing age were examined. Analysis of variance (ANOVA) quantified the main effects and interaction effects of each factor. ANSYS finite element (FE) simulations verified the influence of fiber spacing and embedment length on interfacial damage evolution, ultimately establishing a semi-empirical model for interfacial bond strength. Results indicate that NT content is the critical factor: at 2%-3%, bond stress increases by 30%-40% while delaying performance degradation. End-hooked fibers exhibit higher peak load capacity and ductility due to mechanical anchoring. The bonding performance shows a "first increase, then decrease" trend with the increase of fiber spacing, and 8 mm is the optimal value. The embedment length of 15.25-17.25 mm can enhance the interfacial load-bearing capacity and alter the failure mode. Multifactor coupling analysis revealed significant interactions between NT content and fiber spacing, as well as between embedment length and curing age ( p < 0.001, η 2 =0.276). A semi-empirical model ( R 2 =0.93) quantifies the coupled effects of chemical adhesion, frictional resistance, and mechanical anchoring, with FE simulations showing <10% deviation from experimental results. This study reveals the synergistic enhancement mechanism between NT modification and fiber parameters, providing theoretical support for designing high-performance SFPC. • The optimal parameter combination was identified as an NT content of 2% to 3%, a fiber spacing of 8 mm, and a fiber embedment length of 15.25 to 17.25 mm. • Its dual mechanism of “pore filling + heterogeneous nucleation” improves the density and uniformity of the ITZ. • Developing a semi-empirical model for predicting the interfacial bond strength of SFPC. • Providing a quantifiable and generalizable theoretical foundation for designing high-performance SFPC interfaces.