Temperature and Water-Immersion Effect on Mode II Fracture Behavior of CFRP-Concrete Interface

Rehabilitation and retrofit of concrete structural members using externally bonded Fiber Reinforced Polymer (FRP) strips has been gaining steadily use in recent years because of its many advantages, such as ease and speed of construction, low cost, low maintenance, and high strength to weight ratio. An important design issue with significant performance and safety implications is the debonding of externally bonded FRP strips in flexural members, where the delamination is primarily due to Mode II facture. A lot of research has been done in this area, but there are concerns about interface durability. This study is based on a fracture mechanics approach using Mode II single shear test to evaluate the durability of Carbon FRP (CFRP)-concrete interface subject to two combined environmental conditioning variables: (1) immersion in deionized water varying from 0 to 15 weeks; and simultaneously (2) controlled temperatures varying from 25 degrees C to 60 degrees C of the same samples immersed in water. A new method to obtain the fracture energy release rate and the cohesive law is proposed based on J-integral, by measuring load and slip at the debonding end only, which was verified by the traditional strain-based method. The durability of the interface is characterized by the fracture energy release rate. By comparing the results with those from unconditioned companion specimens, it is found that considerable degradation of the interface integrity resulted with increased moisture duration and temperature. The test results will be further used to develop a model to predict the long-term behaviour of the interface based on Arrhenius or other relations.