Chloride environments effects on the axial compressive behaviour of high ductile FRP confined rectangular concrete columns

To investigate the effect of a salt fog corrosion environment on the mechanical properties of rectangular concrete columns confined with high-ductile FRP (HDFRP, PP/glass-fiber interlayer hybrid), axial compression tests were conducted on HDFRP-confined rectangular concrete columns (HDFRP-CRCC) under room temperature conditions and after exposure to salt fog corrosion. The salt fog environment was simulated using a 5% NaCl solution at a constant temperature of 40 °C. The experiment focused on examining the effects of corrosion duration, cross-sectional aspect ratio, and corner radius on the mechanical properties of the specimens. The results indicate that salt fog corrosion leads to a reduction in both the load-carrying capacity and the deformability of HDFRP-CRCC. After 90 days of corrosion exposure, the average peak strength of the specimens decreased by approximately 10.8%, while the ultimate strain exhibited a reduction of 25.7%. Nevertheless, compared with the unconfined rectangular concrete column, the specimen with an aspect ratio of 2.0 still exhibited a 45.0% increase in peak strength, while the enhancement in strain reached as high as 4499.1%. This observation indicates that the HDFRP material possesses favorable corrosion resistance. Based on the experimental results, a unified design‑oriented stress–strain model was developed for HDFRP‑CRCC. The proposed model can accurately describe the axial compressive response of the specimens in both the uncorroded state and after salt fog corrosion, thereby providing a theoretical basis for the engineering application of HDFRP strengthening systems for rectangular columns in marine environments.