Experimental investigation on reinforced concrete with corroded stirrups strengthened by CFRP grid and GFRP jacket

Abstract Steel corrosion is a critical form of degradation in reinforced concrete (RC), triggered by moisture, chlorides, and other environmental factors, which compromises the mechanical strength of RC and leads to cracking, spalling, and potential failure. Carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) have emerged as popular retrofitting materials for strength improvement after corrosion due to their light weight, corrosion resistance and high tensile strength. Recent studies have extensively investigated the application of CFRP or GFRP reinforcement in different forms to corroded RC, while overlooking the potential of combining both treatments. Herein, the current study experimentally investigated a novel combination of CFRP grid and GFRP jacket to strengthen RC columns with corroded stirrups. With a focus to compression behavior, axial compression tests were conducted on four unstrengthened and thirteen strengthened short-column specimens. The failure modes and load-strain curves were assessed, showing the influence of CFRP grid layers and stirrup corrosion levels on ultimate load-carrying capacity, ductility, and overall failure patterns. A corresponding axial compression strength formula was then developed for corroded RC columns strengthened by CFRP grid and GFRP jacket. The results showed a significant increase in ultimate bearing capacity and enhanced plastic deformation in strengthened specimens. When GFRP jackets alone were used, ductility improved by up to 45.77%, while adding CFRP grid raised this improvement to as high as 74.84%. Moreover, both ultimate axial compressive strength and ductility coefficients increased with more CFRP grid layers, albeit with diminishing marginal gains, aligning with trends noted in earlier FRP confinement studies.