Experimental and Analytical Study of Bond Stress–Slip Behavior at the CFRP-to-Concrete Interface

The application of externally bonded (EB) carbon fiber reinforced polymer (CFRP) systems for strengthening existing structures, such as RC beams, has been widely approved in the construction industry worldwide for its numerous benefits. The CFRP-to-concrete bond has a governing role in the reliability and effectiveness of EB-CFRP systems. Indeed, failure of the CFRP-to-concrete bond can lead to rupture of CFRP-strengthened structures. Hence, ongoing research into assessment of bond behavior at the CFRP-to-concrete interface helps to bring more insightful clarity to the use of EB-CFRP strengthening techniques. The aim of this study is to evaluate the bond behavior between CFRP and concrete by conducting a series of pullout tests. The parameters considered include CFRP type (sheet versus laminate), bonded length, and bonded CFRP width. The results show that using CFRP fabric sheets can contribute to higher bond load-carrying capacity and ductility than CFRP laminates. Furthermore, through the analyses of databases in the literature, a bilinear bond–slip model is proposed that takes into account the CFRP width factor. Through a comparison, it is shown that the proposed model performs well in terms of predicting the maximum local bond stress and CFRP slippage.