Effectiveness of FRP wrapping of heat-damaged concrete in compression for different cooling procedures

This study explores the application of FRP strengthening for enhancing the performance and resilience of fire-damaged concrete elements subject to different cooling regimes, with a focus on their effectiveness in restoring structural capacity and durability following fire exposure. To achieve this aim, 90 concrete cylinder specimens were produced and exposed to high temperatures of 200, 400, and 600 °C to induce fire damage. They were then subjected to different cooling methods, including natural cooling in the furnace, natural cooling in air, and fast cooling by water. In the last technique, the specimens were first immersed in water to shock them, and then water spraying was applied for ten minutes. Subsequently, strengthening was applied using two layers of FRP sheets, and compression tests were performed. The investigation is aimed at assessing to what extent the different cooling procedures may impair the effectiveness of FRP wrapping, with specific reference to FRP contribution to the improvement of concrete residual compressive strength. Based on the test results, and as expected, FRP strengthening was found to mitigate the adverse effects of different temperature levels and cooling regimes on the compressive strengths of specimens. Furthermore, the findings indicate that the cooling rate or process does not significantly affect residual strength and that the effectiveness of FRP wrapping should be assessed with reference not only to strength, but also to structural behavior. It is, therefore, necessary to extend the analysis to the structural context.