Experimental study on the shear performance of the CFRP plate-ECC-concrete composite interface

To solve the problems of early debonding (insufficient use of CFRP) from the reinforced concrete of concrete structures strengthened with CFRP plates, and a limited increase in the load-carrying capacity of reinforced concrete structures strengthened with ECCs, a novel strengthening method containing these two materials was developed in this paper. A CFRP plate-ECC-concrete composite interface was proposed to take full advantages of both the high tensile strength of CFRP plates and the good durability of ECCs with multiple cracks. Single-shear specimens of the CFRP plate-ECC-concrete composite interface were designed for 9 groups and 27 specimens (include a reference group without ECC layer), and the interface treatment method, concrete/ECC strength, and CFRP plate thickness were set as research variables. The test results showed that the specimen with the ECC layer could effectively delay the debonding of the CFRP plate and transfer the interfacial shear stress effectively. The high-pressure water jet method was demonstrated to be a good method for ensuring the effective bonding of concrete and ECC. For single-shear specimens with an ECC layer, the average bearing capacity, ultimate slip, and ultimate strain were 49%, 23%, 42%, respectively, higher than the reference specimen without an ECC layer. With the increase in the thickness of the CFRP plate and concrete/ECC strength, the average ultimate bearing capacity increased by 23%–27% and 37%–39%, respectively. The model of Ferracuti et al. considered more comprehensive factors and fit better with the test results than other models.