Development of cost effective ultra-high-performance fiber-reinforced concrete using single and hybrid steel fibers

This study investigates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with single and hybrid steel fibers. To do this, three different types of steel fibers, i.e., hooked, twisted, and straight fibers, were considered, and a UHPFRC commercially available in North America was used as a comparison. To suggest a low-cost UHPFRC exhibiting the best flexural performance, test data and cost of fibers were analyzed based on a literature review. Test results indicate that straight steel fibers provide the best flexural performance, including strength, deflection capacity, energy absorption capacity, and cracking behavior, compared with hooked and twisted fibers, especially when many fibers (2% by volume) were incorporated. Hybrid reinforcement (hooked + straight fibers) efficiently improved the flexural performance of the UHPFRC with single hooked fibers, but the twisted + straight fibers were less effective than the UHPFRC with single twisted fibers. The optimum UHPFRCs contained 2 vol% single straight steel fibers (lf/df of 19.5/0.2) or hybrid 0.5 vol% long (lf/df of 30/0.3) and 1.5 vol% medium-length (lf/df of 19.5/0.2) straight steel fibers; they showed better flexural strength and cost effectiveness than other types of UHPFRCs.