Effects of interfacial defects on plate-end shear stress in bonded joints of CFRP-corroded steel

Over the past decade, CFRP strips have been increasingly used worldwide to repair or strengthen steel bridges. However, a large number of researchers use uncorroded steel as the target object before attaching CFRP. This approach is somewhat unreasonable as most steel members that require repair have suffered corrosion damage to different degrees. Additionally, before CFRP retrofitting, the corroded steel should be cleaned first, and the level of steel surface cleanliness is dependent upon the rust-removal method used. Even so, it is difficult to entirely remove all corrosion rust from the steel surface in practical applications. This means that in some cases, interfacial defects are almost inevitably going to occur. Therefore, in this study, the effects of interfacial defects on the corroded steel surface, following three kinds of rust-removal methods (acid solvent, disk sander, and abrasive blast), were primarily evaluated by means of the debonding shear stress at the plate end. In addition, several interfacial defects such as air bubbles, kissing bonds, and secondary rust, were observed based on surface and cross-section analyses using SEM-EDX, respectively. Varying amounts of rust residues tend to induce rust-back, and over time, cause visible under-film corrosion based on the observation of fracture interface. These observations can also provide strong evidence to explain why there is a certain reduction in strengthening effectiveness when using CFRP strips to repair corroded steel, compared to uncorroded steel. Finally, the authors argued that the disk sander in a single way for rust removal was insufficient in the case of repairing corroded steel members with a lot of relatively deep corrosion pits. Because severe rust residues and under-film corrosion observed was likely the primary reason for the adhesive's separation from the steel surface, thereby causing very premature failure of CFRP retrofitting.