Bond Behavior of CFRP Sheets Attached to Concrete through EBR and EBROG Joints Subject to Mixed-Mode I/II Loading

The bond behavior of carbon fiber–reinforced polymer (CFRP) sheets attached to concrete surface subject to mixed-mode I/II loading through single lap-shear tests is assessed. A 63 concrete prism specimens of 150 × 150 × 330 mm were prepared through externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) techniques, using CFRP sheets of constant width and 100 /150-mm bond lengths. To instigate mode I loading, 31 of the specimens were tested in a manner that the loaded end of FRP sheets were angled inward −6.0 to −2.3 degrees; while in 24 of the specimens, the FRP strips were angled outward 2.4–4.7 degrees. By applying a noncontact digital image correlation (DIC) technique, load-slip responses of both EBR and EBROG joints were obtained and are discussed in detail. The failure criteria for CFRP sheets attached to a concrete substrate applying different bonding techniques subject to mixed-mode I/II loading are developed based on the experimental results. In general, it was observed that the EBROG technique in mixed-mode I/II loading improves the FRP-concrete bond strength by delaying or fully eliminating the inappropriate debonding failure mode.