Enhancing fiber–matrix interfacial bond in ultra-high-performance concrete containing titanium dioxide

This study investigated the interfacial bond behavior of straight steel fiber in ultra-high-performance concrete (UHPC) containing titanium dioxide (TiO₂) as an alternative to silica flour. Experiments were conducted for five replacement ratios (i.e., 0%, 25%, 50%, 75%, and 100%) of TiO₂. The results indicated a significant improvement in the bond performance of the steel fiber of UHPC containing TiO₂. The best performance was exhibited by the 50% replacement ratio specimen, which showed the highest average bond strength and pullout energy of 7.22 MPa and 447.9 mJ, respectively. Although the benefits of adding TiO₂ decreased beyond the replacement ratio of 50%, the 100% replacement ratio specimen demonstrated higher bond strengths and pullout energy than those without TiO₂. Thus, TiO₂ helps suppress the pullout of steel fiber from UHPC more effectively, which was verified by the presence of severe surface scratches on the steel fiber.