Corrosion effect on tensile behavior of ultra-high-performance concrete reinforced with straight steel fibers

In this study, the effect of steel fiber corrosion on the tensile behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) was examined. Macro straight steel fibers with five different corrosion degrees ranging from 0 to 8% were used, and unwashed and washed corrosion fibers were simultaneously used to evaluate the effect of the rust layer formed at the fiber surface on the tensile performance. The post-cracking tensile response of the strain-hardening UHPFRC is strongly affected by the fiber bridging capacity, which is related to the interfacial bond resistance. Thus, the surface roughness of plain and corroded steel fibers was also quantitatively evaluated based on scanning electron microscope (SEM) images. The test results indicated that the surface roughness of steel fiber increases with an increase in the corrosion degree, and a severe and irregular roughened surface is found at a high-corrosion degree of greater than 8% by weight. The tensile behavior of UHPFRC was generally improved by the steel fiber corrosion up to a certain value of 4 or 6%, leading to the complete pullout failure mode without any breakage, whereas beyond the threshold value, it was rather deteriorated due to the fiber ruptures. Even though there was deterioration in the tensile performance, UHPFRC with the maximum corrosion degree of 8% even satisfied the international recommendations on the strength and energy absorption capacity limits. Lastly, the unwashed, corroded fibers exhibited a better tensile performance than the washed ones because of the appropriately moderated bond resistance.