Bonding strength between ultra high-performance concrete (UHPC) and the surface of normal and high-strength concrete

Concrete is a construction material that is widely used in structural engineering due to its reasonable cost and strong compressive strength, making it a traditional material of choice. Aging, steel corrosion, and unexpected heavy loads can cause damage to concrete structures. Repairing concrete involves removing the damaged layer and replacing it with new material. In this study, ultra-high-performance steel fiber concrete UHPSFC is employed as the repair material. Investigating different concrete grades, including high-strength concrete substrate, still represents a gap in the literature. This study applied three different grades of concrete: normal, medium, and high-strength concrete. The aim is to investigate the interfacial bonding between the concrete substrate and the new UHPSFC under pure shear loads. Bi-shear tests were conducted on nine specimens in their original cast state and thirty-six composite specimens with various surface treatments. The results indicate that substrate’s compressive strength and roughness method significantly affect the bond strength. In high-strength substrate, shear strength increases by at least 56% compared to normal concrete substrate. In addition, it was observed that among the different surface treatments, chiseling surface specimens produced the highest interfacial shear strength. For high-strength concrete substrate, although the chiseling method reached 88.8% of the shear strength of the corresponding control specimens, the straight groove surface specimens achieved the highest strength (93.8%). Eventually, different failure modes were observed, including adhesive, cohesive, and mixed failure modes.