Combined chelating and corrosion effects of steel fiber on the interfacial bond and tensile behaviors of ultra-high-performance concrete

This study evaluates the effect of corrosion on the pullout and tensile properties of ultra-high-performance concrete (UHPC) including steel fibers treated with ethylenediaminetetraacetic acid (EDTA) containing electrolyte solution for 3–9 h. For this, the steel fibers were intentionally corroded through a 3.5% sodium chloride (NaCl) solution to obtain two different corrosion degrees of 2% and 5% by weight. The roughness of the smooth steel fiber surface increases, owing to the chelating effect of the EDTA electrolyte solution, which is positive in enhancing the pullout and tensile performances of UHPC. The pullout resistance of steel fiber from UHPC increased after the treatment for up to 9 h, while the best tensile performance was obtained after 6-h treatment under non corrosive environments. The steel fibers were more severely oxidized when treated with the EDTA electrolyte solution. The pullout performance of the plain and 3-h treated steel fibers from UHPC improved for up to 2% degree of corrosion. Beyond this value, the pullout energy was deteriorated by premature ruptures. The pullout energy of steel fibers treated for 6 h or more decreased by corrosion. Under corrosive conditions, the best tensile performance was found for the steel fibers treated with the EDTA electrolyte solution for 3 h. Therefore, by considering inevitable corrosive environmental conditions, the steel fiber treated for 3 h is recommended as a suitable reinforcement for UHPC.