Properties of Ultra-High Performance Fiber Reinforced Concrete with different types of steel fibers under axial tension

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) exhibits exceptional axial tensile strength and a plastic fracture behavior distinct from conventional fiber-reinforced concrete. This distinction arises from a strain-hardening phase, characterized by the formation of multiple, uniformly distributed microcracks and an increase in tensile stress beyond the cracking threshold. This study investigates the axial tensile performance of UHPFRC specimens reinforced with varying types and volumetric contents of fibers. Brass-coated corrugated steel fiber with length-to-diameter ratios of 15/0.3 mm and 22/0.3 mm, along with straight fiber with a ratio of 13/0.2 mm, were employed as dispersed reinforcements, with fiber content ranging from 1% to 3% by volume. The findings reveal that neither fiber type nor content significantly influences the cracking stress. However, the maximum tensile stress and fracture energy demonstrate a linear increase with the fiber factor, which integrates fiber volume fraction and geometric characteristics. For equivalent fiber factor values, both corrugated and straight fibers exhibit similar tensile stress, but corrugated fibers contribute to higher fracture energy. Based on the experimental results, an equation was derived to determine the minimum required fiber volume, given specific geometric properties, to achieve strain-hardening behavior under axial tension.