Bond slip behaviour of deep mounted carbon fibre reinforced polymer strops confined with a ductile adhesive in clay brick masonry

Retrofitting clay brick masonry using Deep Mounted (DM) Carbon Fibre Reinforced Polymer (CFRP) strips embedded in grooves filled with a ductile adhesive considerably increases the out-of-plane flexural capacity of slender unreinforced masonry walls. In order to investigate the bond-slip behaviour of CFRP-strips in a viscous-elastic adhesive, an extensive experimental program was initiated. Direct pull-out tests were conducted with clay brick masonry. Two parameters were investigated, namely, the type of adhesive (2 types) and the groove widths (10 and 15 mm). The second part of the experimental program focused on the pull-out capacity when surface treatment (primering or sandblasting) was applied to the CFRP-strips. In literature dealing with bond behaviour the critical bond length was found using masonry prisms of approximately 350 mm in height. In the current study with CFRP strip application in conjunction with ductile epoxy, the critical bond length was not reached for specimens of nearly 1000 mm in length. This finding was an indication of a significantly improved stress distribution over the length of the embedded CFRP-strip as the appearance of peak stresses was prevented. No premature brick splitting was initiated despite the depth of the groove being 65% of the specimen thickness, whereas in literature this phenomenon was reported for groove depths of only 30%