Investigation on interfacial defect criticality of FRP-bonded concrete beams

Bonding fiber reinforced polymer (FRP) has been proven to be an effective and efficient method to strengthen and/or retrofit deficient concrete components and structures. Interfacial defects may easily arise due to improper construction or environmental deterioration during the designed service life and they may cause an unfavorable effect on the local bond behavior and global performance of FRP-bonded concrete systems. However, the information on the interfacial defect effect and the guideline for distinguishing the criticality of interfacial defect is limited, making it difficult to assess the long term integrity. In this study, FRP-bonded concrete beams containing various interfacial defects are under four-point bending test to evaluate the defect effect and determine the interfacial defect criticality from location and size aspects. Meanwhile, finite element models representing different sizes of FRP-bonded concrete beams are built and simulated to study the size effect of beam. Both the experimental observation and numerical results indicate that the deep beam is more sensitive to interfacial defect than normal beam. The threshold for critical interfacial defect varies significantly depending on the beam type and defect location. The small, medium and large categories of interfacial defect can be classified according to the beam type, defect location and defect size sequentially. Different maintenance strategies should be adopted corresponding to small, medium and large interfacial defects. The interfacial defect criticality unveiled from this study can provide guidelines for maintenance when defect is detected during inspection and it can be beneficial to a more precise performance evaluation and service life prediction of FRP-bonded concrete structures.