Investigation of flexural repairing techniques for heat-damaged reinforced concrete T-beams using BFRP and CFRP composites: Experimental and numerical approach

This research explores the performance of Carbon Fiber Reinforced Polymer (CFRP) and Basalt Fiber Reinforced Polymer (BFRP) systems in enhancing the structural integrity of reinforced concrete (RC) T-beams exposed to elevated temperatures. A total of eight T-beams were assessed, including both unstrengthened specimens and those retrofitted using Near-Surface Mounted (NSM) and Externally Bonded (EB) strengthening approaches, employing various arrangements of CFRP and BFRP ropes and sheets. The specimens were subjected to heating at 650°C for three hours to replicate severe thermal effects. Test results showed a 20.49% average decline in flexural strength for the heat-damaged beams. Nonetheless, all strengthened specimens regained and surpassed their pre-heating load-bearing capacity, with recovery values ranging from 127.03% to 237.92%. Among the tested BFRP systems, the double-layer, low-dense sheet configuration achieved the highest strength increase (160.44%), closely aligning with the gains observed in CFRP-strengthened beams (up to 199%). Using two layers of BFRP sheets notably enhanced flexural performance compared to single-layer applications. The BFRP rope also delivered strong results, showing a 180.95% strength recovery along with improved ductility and toughness, rivaling CFRP in some cases. Analytical outcomes based on ACI 440.2R-08 corresponded well with the experimental data, though they tended to slightly underestimate ultimate strength, with deviations ranging between 1.71% and 10.54%. Overall, the results support the effective use of both CFRP and BFRP systems for restoring the strength of heat-damaged RC beams. BFRP, in particular, presents a cost-efficient solution for moderate-strengthening applications, making it suitable for projects with budgetary limitations.