The use of UHPC as an overlay and repair material in the bridge industry has been increasing recently. Ensuring sufficient interface shear strength between the substrate and UHPC is necessary for adequate performance and the structural integrity of the composite section. Due to the lack of structural design code for UHPC members, designers often rely on experimental data developed by researchers or on existing conventional concrete design code to predict the interface shear capacity of sections containing UHPC. The various test methods currently used to quantify the interface shear strength oftentimes produce different results. The objectives of this paper are to create a database of the studies on the interface shear strength of UHPC members available in the literature and carry out a statistical assessment. Moreover, a reliability analysis is conducted on the collected experimental database, and the probability of failure is determined for UHPC–concrete, UHPC–UHPC, and monolithic UHPC interfaces. The paper also investigates the dependence of the reliability index on two different test methods used for interface shear capacity prediction. Additionally, a simpler interface shear capacity model with readily determined parameters is proposed for the monolithic UHPC interface, with a better reliability index compared to current design specification.

Post-tensioned Box Girder (PTBG) bridges are frequently used when spans range from 100 to 250 ft, especially in the western US. Due to aging, environmental factors, and increasing traffic load demands, the decks of these bridges are the first elements to show signs of deterioration. Replacing the deck of a PTBG bridge is difficult and costly. This paper summarizes the progress made in a research project using the UHPC deck overlay concept to rehabilitate PTBG bridge decks in California cost-effectively. To confirm the beneficial outcomes of the proposed solution, a large-scale test unit is under construction and will be tested under different loading conditions. In addition to demonstrating the benefits of using UHPC to rehabilitate PTBG bridge decks, the large-scale tests will examine the ultimate-limit state behavior of the decks rehabilitated with thin UHPC layers under positive and negative moments and their punching shear capacity.