Evaluating the Effect of Defects on CFRP-Concrete Bond Performance: Experimental and Analytical Insights

Abstract

The use of Carbon Fibre Reinforced Polymer (CFRP) as a strengthening material for concrete structures has gained popularity in recent decades due to its lightweight, high stiffness, high strength, and corrosion resistance, making it a viable alternative to conventional materials like steel plates. However, the effectiveness of this repair technique depends largely on its bond performance and interfacial quality, which ensure the structural integrity and reliability of the strengthening solution. A gap currently exists in efficiently investigating bond integrity in the presence of interfacial deteriorations and defects.

This study investigates the bond behaviour of ten high-strength concrete prisms externally strengthened with CFRP laminates under various ply and defect conditions. Single-Lap Shear Tests (SLST) and 3D Digital Image Correlation (DIC) analysis were employed to examine strain distribution, shear and slip behaviour, and load-slip characteristics in the presence of interfacial imperfections.

The results revealed that specimens primarily failed due to adhesive cohesive failure in a mixed-mode rupture, with stress concentrations near defects leading to localized peeling and bond deterioration. Reduced axial stiffness decreased load capacity, caused less uniform stress distribution, and promoted localized peeling, ultimately reducing system efficiency. Experimental bond-slip curves were derived for control specimens, and a unified model based on the bilinear model by Lu et al. (2005) showed strong agreement with experimental results, offering a balance of practicality and accuracy. Future work should focus on refining the calibration with specimen-specific coefficients and incorporating environmental factors to improve predictive accuracy.

Defects near the loaded end weakened stiffness locally, increasing slip around the defect region. Full-width defects showed limited capacity for stress redistribution, while middle-positioned defects caused load drops proportional to their size, potentially triggering localized debonding. Edge-aligned defects reduced load capacity by 33% compared to the control specimen and created stress concentrations on the opposite side of the bond area. Dual defects exhibited reduced initial stiffness, intermediate load drops, and potential recovery toward ultimate capacity, though not always resulting in significant strength reduction. Calibration of Li et al.'s (2023) load drop model reduced mean absolute percent error (MAPE) from 45.1% to 13.5%.

Overall, this study provides valuable insights into CFRP-concrete bond behaviour in the presence of defects and offers a solid foundation for future research and practical applications.