Advance repairing technique for enhancement of stiffness of post-heated concrete cylinders

The present study investigates the effectiveness of epoxy injection on the performance of post-heated concrete cylinders confined with carbon fiber-reinforced polymer composites (CFRP). A total of 42 standard dimensions (diameter of 150 mm × 300 mm) were tested under uniaxial compression. These cylinders were divided into two groups regarding the heating, i.e., un-heated and post-heated. Furthermore, the post-heated concrete specimens were further divided into four specimen groups with respect to various temperatures, i.e., 400 °C, 600 °C, 700 °C, and 800 °C, and then cooled to room temperature. The axial compressive behavior of un-heated unconfined (UHUC), un-heated CFRP confined (UHC), post-heated unconfined (PHUC), post-heated CFRP confined (PHC), and epoxy-injected post-heated CFRP confined concrete cylinders (PHEC) were investigated in terms of axial compressive strength (fc′), stiffness (k), energy dissipation capacity (EDC), and restorability. The test results showed that CFRP confinement significantly enhances the fc′ and EDC of the PHC subjected to the mentioned temperatures. Furthermore, the CFRP confinement effectiveness was increased with increasing the level of fire damage (i.e., at a higher temperature). It was found that the fc′ of PHEC at 400 °C was restored up to the design value of UHUC. However, the PHEC was unsuccessful in restoring the design value for temperatures higher than 400 °C.