Interface strength of High-Strength concrete to Ultra-High-Performance concrete

High-Strength Concrete (HSC) has been used in the production of precast concrete structures while Ultra-High Performance Concrete (UHPC) has been considered an option for filling the connection between HSC elements due to outstanding mechanical properties and durability. However, it is necessary to investigate how these connections would benefit from using UHPC. This study explores the influence of HSC surface preparation on the strength developed at the interface with UHPC. Surfaces with Exposed coarse aggregates, Shear keys, Exposed fine aggregate, Expanded mesh, Exposed fiber and without any special surface treatment (Smooth) were considered. Both contact measurement and sand patch test were used for quantification of surface roughness. The strength at the interface was evaluated by third-point flexural loading, push-off, slant shear and splitting tension. The flexural test was considered more representative of the adhesion than the splitting test because the failure mode of the first occurred totally at the interface. Depending on the surface preparation, HSC/UHPC interface showed a bond strength comparable or superior to that of the monolithic HSC specimen. Among the surfaces evaluated, the one with Exposed coarse aggregate achieved the best results.