Fracture behavior of masonry bond

In this study, three different mechanical tests and video microscopy experiments were preformed to characterize the fracture behavior of masonry bond.; Mortars were fabricated under two different conditions: Mortars cast in plexiglass molds and; Mortars exposed to the interactions with dry masonry units. The mechanical properties of the mortar were significantly modified when the mortars experienced mortar/unit interactions. Also, different surface textures for the masonry units altered the strength of embedded mortar when identical mortars were used. It is strongly recommended that the in-situ mortar strength should be used rather than the cast mortar strength because dependence upon laboratory test results for determination of structural performance invites significant error.; For masonry bond fracture, a test method was developed and used successfully to measure load-CMOD behavior until complete failure maintaining stable crack growth. It was found that the strength of in-situ mortar was an important indication of bond strength. Admixtures that had similar purposes for the bulk materials were dramatically different in bond strength. The bond strength was also significantly altered with different surface textures for the masonry.; A new technique was performed to investigate the details of the fracture surface using video microscopy. Degree of bond was defined as an area fraction of the net bonded area. The bond strength was a strictly linear function of the degree of bond and when the bond strength was normalized with degree of bond.; The applied fracture mechanics model, when both elastic and inelastic deformations were considered, always over-estimated the post-peak behavior. However, the post-peak behavior was successfully predicted when the model was modified to consider only elastic deformation. The analysis indicated that little toughening action took place during the fracture process and the fracture process zone at the crack tip was small relative to plain concrete and mortar. This was due to the highly brittle fracture nature associated with pre-determined weak crack path and relatively smooth crack surfaces. Using the relationship between degree of bond and bond strength, and the established fracture model, it was possible to describe the fracture behavior for an ideal perfect bond. As the degree of bond approaches 100%, bond strength increases but the work of fracture does not improve as a simple function of increase in the degree of bond.