Investigation of the Interface Fracture during Debonding between FRP and Masonry

The masonry-FRP interface fracture is a topic of considerable research interest due to the heterogeneity of the masonry subgrade. The size of the material inhomgeneity associated with the presence of mortar joints is significant compared with the length scale of fracture process. In this paper, the results of an experimental investigation into the shear debonding of FRP sheets from brick, mortar and masonry blocks are reported. The test procedures (Ali-Ahmad et al. 2006,2007) developed previously for obtaining the FRP-concrete cohesive fracture response are applied to study interface debonding from the three substrates. During each test, spatially continuous measurements of the surface strains on the FRP and masonry are obtained using an optical technique known as digital image correlation. The interface cohesive fracture response of FRP-brick and the FRP-mortar interfaces are obtained from the results of the strain analysis. The interface fracture energy associated with the FRP-mortar interface is shown to be significantly smaller in magnitude than that of the FRP-brick interface. The contributions of the mortar and the brick to the overall load response of the masonry are analyzed using the cohesive material response of the FRP-brick and the FRP-mortar interfaces. It is shown that complete debonding is achieved at the FRP-mortar joint while the FRP is still attached to the bricks on either side of the joint. The cohesive crack front stretches across the fully debonded mortar joint before the cohesive crack completely crosses the joint. The local debonding at the mortar joint produces stresses higher than those associated with the main cohesive crack front in the brick-FRP interface close to the joint, thereby accelerating the crack advance.