Experimental Investigation on the Ultimate Strength of Corroded Composite Concrete Beams Strengthened with NSM GFRP Bars

This study examined the impact of corrosion on the ultimate strength of composite concrete beams and assessed the effectiveness of Glass Fiber Reinforced Polymer (GFRP) bars applied using the Near-Surface Mounted (NSM) technique. Five composite beams were cast and tested, each comprising a self-compacting concrete (SCC) web and a normal-strength concrete (NC) slab connected by vertical steel links. The primary variables were corrosion level and the location of GFRP strengthening. One specimen was used as a control, while the remaining four were exposed to either partial corrosion (50 mm into the slab) or full-depth corrosion across the entire cross-section. GFRP bars were applied through the NSM technique at two positions: within the slab region and in the tensile zone of the beam. Experimental results showed that corrosion significantly reduced load-carrying capacity, especially in fully corroded specimens, which failed earlier. However, NSM-GFRP bars enhanced the structural execution of corroded beams. Strengthening applied in the tensile zone yielded greater recovery in strength compared to slab-region application. The findings highlighted the importance of both corrosion severity and reinforcement placement in determining structural behavior. The study offered practical guidance for strengthening deteriorated composite beams using NSM GFRP systems.