Experimental Investigations on Tensile and Shear Behavior of the Interface Between UHP-ECC and Concrete

Ultra-high performance engineered cementitious composite (UHP-ECC), which is known for its exceptional compressive strength, tensile strength, and ductility, has been emerged as a promising option for repairing and strengthening reinforced concrete (RC) structures. The bond between UHP-ECC and normal concrete is the key issue for the material to be successfully implemented. This paper presents an experimental investigation focused on understanding the tensile and shear behavior of the bonding interface between UHP-ECC and concrete. A total of 78 specimens were prepared and tensile splitting tests and push-out tests were carried out. The study examined key parameters including the strength of the concrete substrate, the roughness of the interface, and the moisture condition at the interface. Various failure modes are observed in the specimens under tensile splitting force and direct shear force, and it is found that the influence of the key parameters varied depending on the type of failure mode. In specimens experiencing full interface debonding or interface failure combined with substrate cracks, the roughness of the interface and the moisture degree have a significant impact on the tensile and shear strength. Conversely, in specimens with full substrate disruption, the strength of the substrates plays a more significant role. Additionally, the study reveals that the grooving treatment is highly effective in improving the shear strength of the interface, but its impact on enhancing the tensile strength is comparatively less pronounced. Prediction models for the tensile and shear strength of the interface are established and verified against the test results. The proposed models provide valuable insights into the behavior of the UHP-ECC to concrete interface and can aid in predicting its performance in practical applications.