Open issues on the investigation of PBO FRCM-Concrete debonding

This paper addresses some open issues of the bond behavior of fiber-reinforced cementitious matrix (FRCM) composites applied to a concrete substrate. The study is focused on the effect of the number of fiber layers on the peak load, the effect of the loading rate on the load response, the relationship between peak load and bonded length (considering also bonded lengths substantially longer than the effective bond length), and the information that can be gained by measuring the slip at the free end of the bonded composite. The FRCM composite investigated is comprised of polyparaphenylene benzobisoxazole (PBO) fibers and a polymer-modified cementitious mortar. The experimental results are compared with results from the literature. The results indicate that the peak load must be carefully interpreted considering the effect of friction (interlocking), which is observed to occur between fibers and matrix and the fibers themselves. In addition, the effect of the loading rate requires additional investigation. Finally, the peak load of specimens with two layers of PBO fiber mesh is approximately double the peak load of tests with one layer of fiber mesh if the bonded length is longer than the effective bond length determined from tests with one layer of fiber mesh.