Effect of nano-SiO₂ coating modification and process on bond behavior of CFRCM bundles

To address the insufficient fiber-matrix interfacial bond behavior of carbon fabric-reinforced cementitious matrix (CFRCM) in structural strengthening, this study investigated the effect of nano-SiO₂ pre-impregnation modification on carbon fiber bundles. Tensile tests on modified fiber bundles and pull-out tests on CFRCM bundles were conducted. The influences of SiO₂ particle size, formulation, and coating process on the fiber properties and fiber-matrix interfacial behavior were examined. The results indicated significant differences among coatings: VKS01B, VKS01W, and NS300 showed the best performance, increasing the peak load by 23.78 %, 7.64 % and 21.94 %, respectively, and raising fiber utilization to 72.45 %, 65.63 % and 74.35 %. Some coatings did not improve the bond behavior, and wet-process treatment even reduced certain performance indicators. The bond behavior of CFRCM bundles is jointly determined by the fiber properties and the fiber-matrix interfacial performance. Nano-SiO₂ enhances interfacial bonding through filling and bridging effects; however, differences in particle size, formulation, and process lead to varied or even opposite pull-out behaviors. This study provides a quantitative basis and design insights for selecting and optimizing interfacial modification coatings for CFRCM.