Effects of nano-SiO₂ coating and induced corrosion of steel fiber on the interfacial bond and tensile properties of ultra-high-performance concrete (UHPC)

In this study, the effects of nano-silica (SiO₂) coating and induced corrosion of steel fibers on the interfacial bond and tensile properties of ultra-high-performance concrete (UHPC) were investigated. Two different types of steel fibers were prepared: plain and nano-SiO₂-coated. Corrosion was induced in each of these to two different degrees (2% and 5% by weight) using a 3.5% standard sodium chloride (NaCl) solution. The test results indicate that nano-SiO₂ coating increases the bond strengths of steel fibers embedded in UHPC by approximately 50%. Furthermore, more scratches and higher hydrate contents were detected on the surface of nano-SiO₂ coated steel fibers after pulling out from UHPC. Under tension, the UHPC containing nano-SiO2-coated steel fibers exhibited double the strain energy density, compared to that containing plain steel fibers. Moderately corroded steel fibers resulted in higher interfacial bond strength and energy absorption capacity owing to the increased surface roughness. In addition, the nano-SiO₂ coating enhanced the tensile performance of UHPC even under corrosive environments. This enhancement was however diminished by steel fiber corrosion, so that fiber corrosion needs to be carefully controlled when nano-SiO₂-coated steel fibers are used for UHPC.