Tensile properties of ultra-high-performance concrete improved by novel curvilinear steel fibers

Abstract This study developed a novel curvilinear steel fiber to improve the tensile behavior of ultra-high-performance concrete (UHPC) and to mitigate the stress concentration observed in conventional deformed steel fibers. To achieve this, four curvilinear steel fibers of different curvatures (0.02–0.10 mm range−1) and a commercial smooth, straight steel fiber were employed. The average and equivalent bond strengths could be improved using the curvilinear steel fibers than the straight fiber from the UHPC matrix. The tensile performance of UHPC was improved by using the curvilinear fibers of curvature (κ) up to 0.04 mm−1. The tensile strength and energy absorption capacity were significantly increased up to 52% and 174%, respectively, by replacing the straight steel fiber to the moderately curved steel fibers with κ = 0.04 mm−1, which is the optimum fiber type. The highly curved steel fibers, i.e., with curvatures beyond 0.04 mm−1, slightly deteriorated the tensile performance because of the poorer fiber dispersibility and excessive matrix damage. A comparison of the pullout and tensile parameters showed that the equivalent bond strength of inclined steel fibers in UHPC is the most appropriate indicator for predicting the tensile performance.