Influence of In-situ-grown nano-SiO ₂ /silane coupling agent on the flexural performance of basalt fiber-reinforced cementitious composites

Basalt fiber (BF) has low surface energy and relatively poor bonding with the cement matrix. This can weaken the BF-cement matrix interface, hindering the toughening effect of BF. To improve the bonding at the basalt fiber (BF)-cement matrix interface, three modification measures were implemented to investigate the effect of modified BF on the flexural performance of basalt fiber-reinforced cementitious composites (BFRCCs). The BF was modified with silane coupling agents γ-aminopropyl triethoxysilane (AP), γ-glycidoxypropyl trimethoxysilane (GP), and γ-methacryloxypropyl trimethoxysilane (MA) to introduce additional reactive functional groups, resulting in AP/GP/MA-BF. A thin layer of in-situ-grown nano-SiO2 coating was deposited on the surface of the original BF to provide high surface energy, forming NS-BF. On this basis, a secondary modification combining both methods was conducted to achieve synergistic enhancement of BF, yielding NS/AP/GP/MA-BF. The test results show that when nano-SiO2 and GP co-enhance BFRCC, the NS/GP-BF group has the greatest increase in flexural strength and peak deflection deformation compared to the unmodified BFRCC (Raw-BF group), with increases of 14.06% and 11.54% respectively. The bending toughness coefficient σb¯ is used to quantify the toughening effect of the modified and enhanced BF on BFRCC, and the NS/GP-BF group achieves the maximum value, which is 26.47% higher than that of the Raw-BF group. Compared to the single-modified fiber BFRCC group, it is further increased by 16.22%. The microstructure and functional groups of the modified and enhanced BF and BFRCC are characterized by infrared spectroscopy (FTIR), energy dispersive spectrometer (EDS), and scanning electron microscopy (SEM), indicating that nano-SiO2 and GP have been successfully grafted onto the surface of BF and have formed some cement hydration products with the matrix, increasing the overall density of BFRCC.