Sharpey's fiber-inspired gradient anchoring and multiscale synergistic modification of the new–old concrete interface for bridge widening applications

Inspired by the reinforcement mechanism of Sharpey's fibers at the bone–soft tissue interface, this study proposes a cement-based composite modified with polypropylene fiber (PPF) and silica fume (SF) for the interface between cast-in-place and existing concrete in bridge widening structures. Experimental investigations quantified the enhancement effects of PPF and SF, both individually and in combination, on interfacial bond splitting strength and diagonal shear strength. Nanoindentation techniques were used to characterize the gradient distribution and thickness evolution of the elastic modulus within the interfacial transition zone (ITZ). In conjunction with deconvolution algorithms, these techniques also enabled quantitative analysis of the compositional evolution of hydration products. The results demonstrate that PPF and SF, through a multiscale synergistic effect of bridging, toughening, and crack resistance, significantly enhance the mechanical performance of the interface. This study provides a new theoretical foundation and technical approach for developing high-strength, tough, and sustainable widening structures.