Investigation on shear behavior of the interface between engineered cementitious composites and normal-strength concrete

Engineering cementitious composites (ECC), possessing excellent mechanical properties for good durability, can be applied to repair and strengthen reinforced concrete structures. In the present study, the interface shear behavior between ECC and normal-strength concrete was studied. Thirty bonded joint specimens were fabricated and subjected to push-out direct-shear tests. The construction methods of ECC mixture (precast and cast-inplace), ECC strength, and interface bonding methods (i.e., Epoxy resin, UHPC, cast-in-place ECC, cast-in-place ECC with chiseling, and bolts) were investigated. The results indicated that interface bonding methods have a significant influence on the failure modes and interface shear strength between ECC and existing concrete. There were three failure modes: interface debonding, interface debonding converted to concrete fracture, and concrete matrix destruction failure. Epoxy resin bonded specimens exhibited the highest shear strength, and cast-in-place ECC bonded specimens showed the lowest shear strength. Moreover, the shear performance of the ECC and the normal-strength concrete interface was analyzed in terms of interfacial shear strength and shear stiffness, bondslip curve, and shear transfer mechanism. Finally, an analytical model for estimating the interfacial shear strength considering the interfacial bonding methods was established, with its predictions having high accuracy.