Influence of Wetting Conditions and Concrete Strength of Both Substrate and Repair Material on the Bond Capacity of Repaired Joints

Ultra-high performance concrete (UHPC) is an appropriate material to repair and rehabilitateaged structures due to its excellent properties, such as high compressive strength and durability.Several studies have demonstrated the effectiveness of applying UHPC in old buildings as a rehabilitationor repair material, but the bond between concretes needs more investigation. In this sense,the bond between normal-strength concrete (NSC) and UHPC is currently being studied. Threemain parameters are responsible for ensuring a good bond: the surface treatment of the substrate(roughness), the wetting conditions, and the mechanical strength of the substrate. Thus, the presentstudy investigated the bond between concretes experimentally. The concrete of the substrate wascarried out in three grades: C25, C45, and C60. The repair concretes were C25, C45, C60, and UHPC.The following parameters were evaluated: wetting conditions, air surface dry (ASD), saturatedsurface dry (SSD), substrate strength, and repair concrete strength. All models received surfacetreatment by wire brushing. Slant shear and splitting tensile tests were performed to evaluate themechanical behavior and the failure modes of the bond between concretes. The bond strength wasclassified and compared to existing predicting models. The results showed that most expressivestrength gains occurred in SSD models with lower strength substrates and UHPC. Furthermore, theinfluence of surface wetting conditions becomes smaller as the strength of the substrate is reduced.