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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.

One of the benefits of calcium sulfoaluminate (CSA) cements is that these materials gain strength rapidly, and strength development is often measured in hours instead of days. This property makes these materials desirable for use in temporary, nonreinforced repairs of roadways, airfields, and navigable locks. The rapid repair of these infrastructure elements is critical to transporting supplies into regions devastated by disaster. In these austere environments, potable water may not be available in sufficient quantities to make vital repairs, and the use of impure water in the production of CSA cement–based concrete would be advantageous. However, the hydration products formed by CSA cement are significantly different from those formed by portland cement and may react differently to alkalis, chlorides, sulfates, and other contaminates that these impure water sources may contain. This article investigates the impact of calcium, sodium, potassium, and magnesium chloride and calcium, sodium, and magnesium sulfate on the early-age unconfined compressive strength development of commercially available CSA cement–based concrete. Of these salts, calcium chloride had the greatest effect on early-age concrete properties, retarding unconfined compressive strength development. The strength results obtained from CSA cement–based concrete mixed with these saline solutions are compared with those obtained from potential real-world sources of mixing water, including seawater and greywater.

By adding annealed plain carbon steel fibers and stainless steel fibers into Ultra-High Performance Concrete (UHPC), researchers have increased UHPC's toughness through optimized thermal processing and alloy selection of steel fiber reinforcements. Currently, steel fiber reinforcements used in UHPCs are extremely brittle and have limited energy dissipation mainly through debonding due to matrix crumbling with some pullout. Implementing optimized heat treatments and selecting proper alternative alloys can drastically improve the post-yield carrying capacity of UHPCs for static and dynamic applications through plastic deformations, phase transformations, and fiber pullout. By using a phase transformable stainless steel, the ultimate flexural strength increased from 32.0 MPa to 42.5 MPa (33 percent) and decreased the post-impact or residual projectile velocity measurements an average of 31.5 m/s for 2.54-cm-and 5.08-cm-thick dynamic impact panels.

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The U.S. Army Engineer Research and Development Center (ERDC) solves the nation's toughest engineering and environmental challenges. ERDC develops innovative solutions in civil and military engineering, geospatial sciences, water resources, and environmental sciences for the Army, the Department of Defense, civilian agencies, and our nation's public good. Find out more at www.erdc.usace.army.mil. To search for other technical reports published by ERDC, visit the ERDC online library at http://acwc.sdp.sirsi.net/client/default.

The Engineer Research and Development Center, Geotechnical and Structures Lab (ERDC-GSL) has used Fort Polk as a large-scale testing site for many years. Many cementitious materials have been developed for design validation testing. These cementitious materials, their constituents, and their mechanical properties often went undocumented, making it difficult for researchers to replicate or draw comparison from previous testing. This report aims to begin a process of detailed cementitious material reports for all research efforts in the region.