Axial compressive behavior of BFRP-steel-concrete composite columns subjected to seawater corrosion

Seawater chlorides accelerate concrete and steel corrosion, whereas basalt fiber-reinforced polymer (BFRP) offers excellent mechanical properties and corrosion resistance, making BFRP-steel-concrete composite columns (BFRP-SCCC) promising for marine structures. This study investigates axial compressive behavior of BFRP-SCCC under four exposure conditions (natural curing, low- and high-concentration seawater immersion, and wet-dry cycling) for 30, 60, and 90 days. Stress-strain responses exhibit four stages: linear elastic, elastoplastic, descending, and stable. Wet-dry cycling causes greater reductions in initial stiffness, peak load, and residual capacity than continuous immersion, and high-concentration seawater imposes more degradation than low concentration. After 90 days, residual load-bearing capacities were 98.9% (low-concentration), 97.5% (high-concentration), and 96.0% (wet-dry cycling), corresponding to peak-load reductions of 1.1%, 2.5%, and 4.0%; the minimum initial stiffness (89.4 kN/mm) occurred under 90-day wet-dry cycling. By combining theoretical models, BFRP corrosion data, and experimental results, a predictive approach is proposed to estimate capacity degradation with corrosion time under various exposures. These findings support durability-oriented design, environmental assessment, and maintenance of BFRP-SCCC in marine environments.