Effect of concrete heterogeneity on interfacial bond behavior of externally bonded FRP-to-concrete joints

This study presents an experimental investigation of the effect of concrete heterogeneity on the bonding behavior between carbon fiber reinforced polymer (CFRP) and concrete. The variations in concrete heterogeneity are achieved using different aggregate sizes and varying aggregate content while mixing concrete. The effects of interfacial characteristics of the inhomogeneous concrete on the bond strength, ultimate slip, peak shear stress, effective bond length, and bond-slip behavior are comprehensively evaluated and discussed. The results indicate that the aggregate sizes and content significantly affect the FRP to concrete bond properties for the concrete with similar strength. To unify the effects of interfacial characteristics with different aggregate sizes and contents, the study proposed a coarse aggregate area ratio to reflect the interface characteristic (i.e., an exposed coarse aggregate area on the bond surface to the total bond surface area). Based on understanding how the coarse aggregate area relates to the CFRP-concrete interface area, a fracture energy-based bond strength model is proposed, incorporating the aggregate area ratio parameter to reflect the aggregate size and content effects. A comparison of the proposed model with the test results from this study and open literature verified the accuracy and applicability of the proposed model.