New mesoscale phase field model for analysis of FRP-to-concrete bonded joints

Abstract

Externally bonded fiber-reinforced polymer (EB-FRP) laminates have become popular for strengthening existing reinforced concrete (RC) structures. However, the high tensile strength of the FRP laminate is often not fully utilized due to premature debonding failure of the FRP-to-concrete interface, typically occurring in a thin layer beneath the bond interface. Numerical simulations have gained significant attention as a supplement to experimental tests, as they have the ability to provide valuable insights into the debonding process. However, most existing numerical models for EB-FRP joint debonding are unable to explicitly consider cracks within different concrete phases [i.e., mortar and interfacial transition (ITZ)], or precisely capture the corresponding failure mechanisms involving mortar cracking, ITZ debonding, and kinking. This study proposes a novel mesoscale phase field model for concrete, which is capable of accurately modeling complex failure behaviors, including mixed-mode fracture in both the mortar and ITZ, as well as friction on cracked surfaces. The ITZ is regularized using an auxiliary interface phase field and then the overall mixed-mode failure behaviors in both the mortar and ITZ are modeled using a unified damage phase field. To validate the proposed mesoscale model, three pull-off tests of FRP-to-concrete bonded joints, which have been well reported in the existing literature, are simulated. Moreover, the model is used to investigate the effects of adhesion and the FRP laminate on the debonding behavior of the FRP-to-concrete joints.