Comparative study of field durability of externally bonded CFRP based on direct tension pull-off test

A comparative study between the field durability test and the direct tension pull-off (DTP) test in the outdoor exposure test of externally bonded carbon fibre reinforced polymer (CFRP) composites is implemented. A comprehensive review of the characteristics of the DTP test was conducted by comparing them with those of other bond tests. The results of field tests of bonded CFRP from two to 27 years old and a long-term outdoor exposure test of CFRP bonded specimens for 30 years were then analysed and compared. The failure modes observed in the field showed adhesive failure or cohesive failure in the CFRP, while the results of the outdoor exposure test showed cohesive failure in the substrate. The comparison showed that the DTP bond strength for adhesive failure at the CFRP/epoxy interface can decrease by up to 8% after 7.7 years of outdoor exposure. Similarly, the DTP bond strength in adhesive failure at the CFRP/substrate interface can decrease by up to 35% after 6.6 years of outdoor exposure. The thermal effect on specimens exposed for 30 years may be limited because the estimated surface temperature was lower than the recommended minimum in fewer than 1% of cases. The results of the comparative field study will help to inform the planning of future durability investigations. • The results of direct tension pull-off tests on bonded CFRP from two to 30 years old were compared. • A conservative assessment was made of the durability of bonded CFRP compared with other bond tests. • Bond strength can be less than the minimum substrate strength after eight years of exposure. • Results of the comparative field study will help to inform the planning of future durability investigations.