Bond behavior of CFRP-to-pre-heated concrete joints: Comparative study of EBROG and EBR techniques

Premature debonding of fiber-reinforced polymer (FRP) composites remains one of the most critical limitations in the strengthening of reinforced concrete (RC) structures. The externally bonded reinforcement on grooves (EBROG) technique has introduced as a promising alternative to the conventional externally bonded reinforcement (EBR), as it enables deeper stress transfer within the concrete substrate. Groove classification, defined as the systematic optimization of groove dimensions, spacing, and orientation to enhance mechanical interlock and bond performance, represents the latest advancement in this strengthening technique. However, despite the increasing application of FRP systems in structures exposed to elevated temperatures, the bond behavior of FRP–concrete joints under this conditions is still not fully understood. A review of the existing literature reveals two major research gaps: (1) no experimental study has evaluated the performance of the EBROG technique under elevated temperatures. (2) The influence of groove classification, despite its direct role in stress redistribution, has not been previously investigated. Therefore, the combined effect of the grooving method and pre‑heating of the concrete substrate on the bond behavior of FRP-concrete joints remains entirely unexplored. To address these gaps, a total of 24 single-lap shear tests were performed on prismatic specimens. The specimens were first exposed to temperatures of 25, 200, 400, and 600 °C, and after cooling to ambient temperature, they were strengthened using both EBR and EBROG techniques. All tests were then conducted under ambient laboratory conditions. The findings demonstrate that the EBROG technique substantially enhances bond strength on concrete pre‑exposed to elevated temperatures. The proposed groove classes with dimensions of 5 × 5 mm at 15 mm spacing and 10 × 10 mm at 20 mm spacing resulted in bond strength increases of 42 % and 51 %, respectively. Nevertheless, the compressive strength of concrete progressively decreased with pre‑heating temperature, retaining only 34 % of its original capacity at 600 °C. These outcomes provide new experimental evidence on the bond behavior of EBROG FRP-concrete joints with pre‑heated concrete substrates and demonstrate the practical potential of groove classes for post-heated strengthening, that is, the repair of RC structures after thermal exposure, to enhance the performance of FRP-strengthened members.