Characterization of cementitious substrate-to-overlay interface bonds using strength and fracture tests

Adequate development of the substrate-to-overlay bond is crucial in repaired concrete structures. Poorly developed bonds may facilitate crack propagation, a concern evaluated through fracture tests. However, the scarcity of fracture tests, especially for in-plane shear-type cracks (Mode II), coupled with the reliance on strength-based bond characterizations in field tests, emphasizes the need to understand the relationship between fracture and strength behavior. Therefore, this study compares tensile, shear, and Mode I and Mode II fracture tests in characterizing shotcrete-to-concrete interface bonds with different substrate surface preparation techniques (chipped (C), sandblasted (SB), pressure-washed (PW), and as-cast (AC)). Results indicate that all three test methods are sensitive to the substrate surface preparation technique. The shear bond strengths in C, SB, and AC specimens are over two times the corresponding tensile bond strengths. In contrast, the shear bond strength of PW specimens is about 73% of the corresponding tensile strength. It is also evident that the Mode II fracture and shear behavior closely resemble each other and are more sensitive to surface roughness than the tensile bond strength. The comparative tests conducted in this study can assist in screening surface preparation techniques for cementitious overlays.