Flexural Performance of NSM-CFRP Strengthened Corroded RC Prisms under Freeze-Thaw and Wet-Dry Cycles

This study investigates the combined effects of corrosion level and environmental exposure on flexural behaviour of corroded reinforced concrete (RC) prisms repaired with self-compacted concrete (SCC) and strengthened with a near-surface-mounted (NSM) carbon fibre-reinforced polymer (CFRP) system. Two accelerated corrosion levels (10% and 30%) were introduced before repair. The damaged concrete cover was removed and recast using self-compacting concrete (SCC), followed by NSM-CFRP strengthening. The repaired prisms were then exposed to standard laboratory conditions (ST), 300 freeze-thaw (FT) cycles, or 50 wet-dry (DW) cycles before flexural testing. Corrosion reduced the stiffness and load-carrying capacity of the RC prisms. The NSM-CFRP system significantly improved the structural response, increasing the maximum load by up to 29.5%, although the strengthening efficiency was lower at the higher corrosion level. Environmental exposure further influenced the repaired specimens. Compared with the corresponding strengthened prisms under standard conditions, wet-dry cycles reduced the maximum load by up to 10.5%, whereas the reduction after freeze-thaw exposure remained below 4%, indicating a less pronounced effect. Strengthening also shifted the governing failure mode from flexural failure to shear-compression failure, with rupture of the CFRP sheet under standard conditions and debonding of the CFRP sheet after environmental exposure. Overall, the results show that the structural performance of NSM-CFRP repaired corroded RC prisms is governed by the combined influence of corrosion level and environmental exposure, with wet-dry cycles producing the most pronounced deterioration.