This investigation focused on identifying the impact of various steel fiber types on the mechanical response of an ultra-high performance concrete (UHPC) known as Cor-Tuf (CT). CT specimens were fabricated with four steel fiber types: hooked-end 3D 55/30 BG fibers, undulated NYCON type V fibers, straight brass coated OL 10mm fibers, and straight brass coated OL 6mm fibers. 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 use of smaller fibers resulted in up to a 100 percent increase in component/test article tensile strength compared with their larger fiber size 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. Smaller fibers provided improved penetration resistance, with reduced residual projectile velocities and loss of material from cratering and/or spallation. The overall goal of the study was to identify the relationships between fiber characteristics and the multi-strain rate response of UHPCs in order to better optimize fiber reinforcement for various loading conditions.

The U.S. Army Engineer Research and Development Center (ERDC) has conducted research on ultra-high performance concretes (UHPCs) since the late 1980 s. The primary focus has been on military and civil works infrastructure applications. The research included the development of a UHPC material called Cor-Tuf Baseline, which includes several derivatives including a patented material. This paper presents the ERDC's historical experience with UHPCs, including constituent materials, laboratory-scale production, and heat treatment, typical microstructure, and pathways for scaling up production. Case studies are also presented on ongoing research focused on the use of fiber-reinforced UHPCs for repair and retrofit of armor plate systems in U.S. Army Corps of Engineers (USACE) inland navigation civil works infrastructure and ongoing long-term field durability testing at the Treat Island Natural Weathering Station near Eastport, ME.