Improvement of fiber corrosion resistance of ultra-high-performance concrete by means of crack width control and repair

This study aims to investigate the influences of the pullout state and pre-crack width on steel fiber corrosion in ultra-high-performance concrete (UHPC) and its implication on the interfacial bond and tensile performances. For this, two pullout states, such as partial and full debonding, and five pre-crack widths, ranging from 0.02 to 0.5 mm, were considered. An epoxy-based crack repair process was also proposed, and its benefits on limiting steel fiber corrosion were evaluated. The average bond strength of steel fiber from UHPC could be improved by 54%–59% after exposure to a corrosive environment for 4 weeks, mainly due to partial surface corrosion. The debonding region was the main passage of the NaCl solution and led to the growth of ferric oxide. The crack width of ultra-high-performance fiber-reinforced concrete (UHPFRC) clearly affected the degree of steel fiber corrosion and the tensile performance. The tensile behavior of the micro-cracked UHPFRC with a small crack width below 0.15 mm was insignificantly influenced by the 4 week corrosion; whereas, the 0.3-mm cracked UHPFRC provided 10%–14% higher tensile strength and maintained higher stress levels in the softening region because of the moderately corroded fiber surface. Given the wider pre-crack condition (0.5 mm), no increase in the tensile strength was detected by partial ruptures of steel fibers. The steel fiber corrosion in cracked UHPFRC could be effectively prevented by the crack repair process, and no change in tensile behavior was thus obtained after exposure to a corrosive environment for 4 weeks.