Titanate Coupling Agent Dual-Modified Carbon Fiber/Nanosilica Cement Composites for Improved Interfacial Performance and Mechanical Properties

Cement composites are essential building materials, but their inherent brittleness and high cracking risk compromise structural safety and raise maintenance costs. The combined use of carbon fiber (CF) and nanosilica (NS) causes interfacial debonding and particle agglomeration due to poor compatibility, limiting the reliability of building materials. A research gap lies in the insufficient understanding of how multiscale interfacial chemistry regulates pore evolution, stress transfer and macroscopic mechanical performance. In this study, both CF and NS were pretreated with a titanate coupling agent (TCA), namely dual modification, for the cross-scale synergistic reinforcement of cement composites. Mechanical tests, CT pore analysis, SEM, XRD/FTIR and molecular dynamic simulations were used to reveal reinforcement mechanisms. The TCA strengthened CF/C–S–H interfacial bonding via CF–O–Ti and Ti–O–Ca interactions and restrained NS agglomeration through Si–O–Ti bonds and alkyl chain steric hindrance. It promoted Ca(OH)2 consumption and C–S–H formation, lowering total porosity from 12.38% to 8.11% and harmful pores (>0.1 mm3) to 4.1%. The modified composite reached 8.9 MPa flexural and 39.6 MPa compressive strengths. This study clarifies cross-scale links among interfacial bonding, pore structure and mechanical properties, advancing reinforcement theory and offering technical support for high-performance building cement composites.