Bond performance of deteriorated CFRP-concrete interface under different shear lap configurations: A Champlain Bridge case study

Carbon fiber-reinforced polymer (CFRP) has been adopted as an alternative to externally bonded steel for structural retrofitting; however, the long-term performance of CFRP composites in actual in-service applications remains under-explored. Laboratory experiments on pristine CFRP samples indicate improved structural capacity and highlight the adverse impact of premature debonding. This study aims to gather essential field data regarding the performance of CFRP composites on deteriorated 57-year-old concrete through 27 concrete samples subjected to three distinct mode II (in-plane shear) loading conditions. The samples were extracted from the diaphragms of the recently deconstructed Champlain Bridge in Canada. To test the field samples, modified single and double lap shear configurations were developed that eliminated the need for directly gripping the CFRP sheets, and the results were subsequently compared to a more conventional single lap shear test. The influence of existing defects on bond behaviour and the effect of test configuration on interface performance under single-mode loading were evaluated. Three-dimensional digital image correlation (DIC) was employed to capture full-field in-plane and out-of-plane displacement data, thereby addressing the strain measurement challenges in bonded interfaces and confirming the occurrence of mode I deformations (out-of-plane peeling) during debonding. Experimental strain measurements at failure predominately ranged from 2500 to 3400 microstrain, with a maximum of 4739 microstrain, which is approximately 56 % of the debonding strain predicted by ACI PRC-440.2.23. The strain limit set by the Canadian Highway Bridge Design Code (CAN/CSA S6:19) exceeded the maximum experimental strain by 27 %. Results indicated that the double lap shear test provided more consistent peak loads, while the single lap shear configuration exhibited greater variability. The bond stress-slip behaviour along the length of the CFRP sheet was found to vary significantly; an analytical comparison of experimental data with existing cohesive zone models demonstrated a strong correlation with local bond stress-slip results in certain regions that reached high levels of bond stress. In contrast, other regions showed both lower peak stresses and lower stiffness than predicted by most models, which may be attributed to local deterioration or defects at the CFRP-concrete interface. • Lab specimens with lower concrete strength and CFRP stiffness, attained higher strain than the deteriorated field specimens. • The new shear-lap setup effectively characterizes the bond behaviour, with 0.6 mm out-of-plane displacement and 11.2 % load variation. • Chen and Teng's model closely predict stress transfer length, while Ko et al. [60] overestimated bond stress by 58 %.