Investigation of Ultra-High Performance Concrete for Longitudinal Joints in Deck Bulb Tee Bridge Girders

Abstract

In recent decades, many state DOTs have implemented ultra-high performance concrete (UHPC) in bridge construction because of its advanced mechanical properties beyond those of conventional concrete. The Federal Highway Administration (FHWA) has extensively tested a proprietary class of UHPC, but WSDOT has been hesitant to adopt this mix because of its high cost and associated high risk. In this study, a mix design developed by Washington State University was tested for its structural performance when used in a reinforced spliced connection between adjacent concrete deck-bulb tee (DBT) bridge decks. The important parameter for this application is the bond strength of epoxy-coated reinforcing bars to the UHPC as well as the tension strength of the UHPC when the rebar in the connection is stressed axially in tension. ASTM-standard test procedures in this study showed that compressive strengths up to 16 ksi, tension strengths above 2 ksi, and bond strengths up to 7 ksi can be achieved with this particular UHPC, all with improved ductility beyond that of conventional concrete due largely to the steel fiber reinforcement. Structural experiments were performed on idealized “bond curbs” as well as a section of deck representing actual DBT girders to determine the available bond strength and the corresponding required joint width. These experiments and the subsequent analysis showed that a UHPC joint width of 7.11 inches, corresponding to a splice length of 5.11 inches, is satisfactory to fracture the reinforcement within the connection. To account for construction tolerances, this joint width should, in practice, be increased to 10 inches.