Impact of Steel Fiber Size and Shape on the Mechanical Properties of Ultra-High Performance Concrete

This investigation focused on identifying the impact of various steel fiber types, including size and shape, on the mechanical responses of an ultra-high performance concrete (UHPC) known as Cor-Tuf Baseline (CTB). CTB specimens were fabricated with four fiber types. The experimental program included testing for quasi-static and dynamic properties, focusing on penetration resistance. Fiber shape and size had a limited impact on quasi-static properties in compression but had a significant impact on quasi-static tensile properties and dynamic penetration resistance. The smaller fibers exhibited up to a 100 percent increase in tensile strength compared with their larger counterparts. However, the benefits offered by the smaller fibers primarily occurred prior to reaching the ultimate load carrying capacity. Once the ultimate strength was reached, larger fibers were more effective at bridging larger cracks. The smaller fibers also provided improved penetration resistance, with reduced residual projectile velocities and loss of material from cratering and/or spallation. Fiber shape and size did not have an impact on the transition between projectile perforation and nonperforation. The results provide insights into optimal fiber reinforcement and potential strategies to further improve the properties of UHPCs, make fiber-reinforced UHPCs more cost competitive by altering fiber dosage rates, and developing hybrid reinforcement schemes.