Numerical Study on the Influence of Bubble Defection on the Bond Strength of Externally Bonded Fiber-Reinforced Polymer-to-Concrete Joints

The influences of bubble defects on the bond strengths of externally bonded fiber-reinforced polymer (EB-FRP) concrete joints were investigated using numerical method in this research. Studies of the influences of increasing bubble defect areas on interfacial bonding performance were first conducted. It was observed that the influence of a bubble deficiency located in the middle of the bond region is not significant when the size of the bubble area is less than 2.5% of the effective bond area. Then, further investigation was conducted on the influences of the distances between the bubble and the loaded end, as well as the distance between the bubble and the side of the FRP, the ratio of the bubble's width to the width of the FRP, the number of bubbles with a fixed total area and the distribution of multiple bubbles. It was found that the distances of the bubble to the loaded end and different numbers of bubbles distributed within a fixed area do not significantly affect the bond strength. When the bubble is positioned closer to the side of the FRP, a decrease in load capacity tends to occur earlier, and the amount of decrease also slightly increases. The bond capacity can be influenced by the shapes of the bubbles, and as the bubble width in the lateral direction increases while keeping the bubble areas constant, the load capacity decreases.