How do brick microstructural and mechanical properties affect GFRP bond strength?

To enhance structural safety of existing masonries, FRP application is an effective strategy. Alongside the nature and characteristics of fibers and matrix, mechanical properties of bricks are generally recognized as the most important parameters affecting the FRP/masonry strength of adhesion. However, additional parameters may play an important role, such as brick surface roughness and microstructure, which are expected to influence the resin penetration ability. Therefore, in the present study, four brick types were selected and strengthened with the same fiber/matrix system and subjected to bond tests to evaluate the debonding force. The influence of several brick mechanical, physical and microstructural parameters on the debonding force was then investigated. The results of the study pointed out that mechanical parameters alone are insufficient to accurately predict the debonding force, but a more precise prediction can be obtained by taking into account also the brick surface roughness and the resin penetration depth.