Effects of brass coating and nano-SiO₂ coating on steel fiber–matrix interfacial properties of cement-based composite

This study focused on the effects of steel fiber coatings on the interfacial properties of a fiber-reinforced cement-based composite. The impact of a brass coating on the interface between the steel fibers and cement matrix was examined, and the improvement effects of a nano-SiO₂ coating and nano-SiO₂ powder on both the microstructure and interfacial bond properties were compared. A chemical simulation experiment was designed to analyze the brass coating state in a cement hydration environment. The backscattered electron image analysis (BSE-IA) method was used to conduct quantitative analyses of the calcium hydroxide (CH), porosity, and unhydrated cement (UHC) to investigate the microstructure of the fiber–matrix interfacial transition zone (ITZ). Pull-out tests were conducted to determine the interfacial bond performance, and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for micro-observation and element analyses. The results indicated that because of the destruction of the coating structure and the aggregation of CH caused by the dezincification of the brass in a cement hydration environment, the brass coating did not improve (but weakened) the interfacial microstructure and bond performance. Adding the nano-SiO₂ powder directly was a useful method for achieving microstructure densification and defect reduction in both the ITZ and bulk paste, while the nano-SiO₂ coating provided a more targeted improvement in the fiber–matrix ITZ, particularly near the fibers, leading to a more effective enhancement of the bond performance.