Comparative studies on interfacial bond performance of ultrahigh performance concrete (UHPC) for sustainable repair of bridges and pavements

• This study examined the bond performance at substrate-UHPC interfaces using smooth, exposed aggregate/fiber, and groove surface preparations. • The presence of steel fibers at the interface plays an important role in bond capacity. • The pressure washed and exposed aggregate surface preparations exhibited superior bond performance. Ultra high performance concrete (UHPC) is emerging as an innovative sustainable solution to rehabilitate deteriorated concrete pavements and bridges. In such usage, UHPC may be cast against different substrate materials such as normal strength concrete (NSC) for bridge strengthening and rehabilitation or against high strength concrete (HSC) for shear key connections. UHPC may also be cast against precast UHPC due to the rapid increase in using precast UHPC components. Although the UHPC usage in above applications has recently increased, an investigation of bond performance between UHPC and three different substrate materials have not yet been investigated. The study examined the bond performance between cast-in-place UHPC and three different substrate materials. Three different surface preparations were considered in the current study: smooth, exposed aggregate/fibers and grooved. To generalize the outcomes from the present study, three different test methods including, splitting, bi-shear and slant shear with three different slants were selected. The experimental results demonstrated that the UHPC adhered better with NSC and HSC substrates when the pressure washing was used to expose the aggregate. Meanwhile, the UHPC had better bond with grooved surface preparation of UHPC substrate. The smooth surface should be avoided when UHPC cast against all substrates. Furthermore, the friction coefficients from the codes were overestimated for smooth surface regardless the substrate strengths. However, the design codes provided a conservative estimate for both cohesion and friction coefficients for exposed aggregate/fibers and grooved interface surface preparations.