The use of UHPC in accelerated bridge construction

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Ultra-high performance concrete (UHPC) is a new construction material exhibiting rapid strength gains, strengths four times higher than concrete, and excellent durability. Over the last decade, the use of UHPC in bridge construction has increased. Between 2006 and 2019, over 300 bridges with UHPC components were built in the United States and Canada. Most frequent use of UHPC is in field-cast construction joints, or as bridge overlays. Rapid bridge deck construction minimizes the time that critical transportation infrastructure is out of service, and UHPC is capable of enabling this. High quality deck panels can be prefabricated, but field-casting high quality joints remains a challenge. Poor quality joints are detrimental to overall bridge deck durability. Bond strength plays a significant role in the shear transfer between precast bridge girders and field-cast connections. The proposed research focuses on determining the bond strength of UHPC with precast concrete, and cast-in-place UHPC. The goal of this research program is to quantify important bond parameters and to modify existing design equations governing shear transfer in bridge deck UHPC joints. Several studies on bond performance between UHPC and precast concrete under static load, including two completed by the applicant's research group, found increase in interface bond strength with the degree of substrate roughness. The results however are qualitative rather than quantitative at this time. This research program will use several methods to assess surface roughness in order to establish quality control and construction protocols for measurement of roughness when UHPC is used in field-cast joints. Coefficient of friction and cohesion/adhesion will be determined, as function of surface roughness and UHPC age. This will lead to optimization of the design of UHPC connections. This research program will investigate the shear friction mechanism for both UHPC-concrete, and UHPC- cast in place UHPC interface. Design equations will be developed for shear friction mechanism as function of reinforcement ratio, roughness and UHPC age under static and cyclic loads. This research program will investigate fatigue behavior of UHPC interface bond, a topic that has yet to be effectively studied. The results of this research program will provide engineers with design values of critical bond parameters, such as cohesion and friction, and guidelines for optimization of joint reinforcement. It will also develop methods for evaluating critical parameters on the construction site leading to more controlled outcomes and better long-term joint performance. This research program will train seven HQP in understanding this leading edge construction material behaviour, application, and design. Because design standards for use of UHPC are currently under development, I will bring my HQP as observers to the discussions that are held in the ACI and CSA committees.