Effects of Accelerated Seawater Corrosion on Hollow-Core FRP-Concrete-Steel Columns under Sustained Axial Load

The hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) column is a relatively new structural system consisting of an outer fiber-reinforced polymer (FRP) tube, an inner steel tube, and a concrete shell encased between the two tubes. HC-FCS columns have displayed superior structural performance compared to conventional reinforced concrete columns. However, there is a lack of experimental data on the durability of HC-FCS columns subjected to long-term saltwater exposure and elevated temperatures. This study experimentally investigates the performance of HC-FCS stubs immersed in simulated seawater solution with different elevated temperatures for up to 450 days. Sustained axial loads were also applied to the stubs during the immersion period to simulate the service load for a bridge column. After the conditioning regime, compression tests were conducted on the HC-FCS stubs. Split-disk tensile tests, scanning electron microscopy, energy-dispersive X-ray, Fourier transform infrared spectroscopy, and differential-scanning calorimetry tests were performed on the associated FRP rings for both the control and conditioned samples. The seawater immersion of the HC-FCS stubs caused resin cracks and fiber/resin interface debonding on the glass fiber-reinforced polymer (GFRP) tubes due to the swelling stresses generated by the absorbed moisture. No chemical reaction took place on the GFRP tube with seawater immersion. The normalized strengths, axial strain, hoop strain, and strength enhancement ratios of the conditioned HC-FCS cylinders continuously degraded as the immersion time and ambient temperature were increased, with the degradation of approximately 41% for 450 days of conditioning at 60°C. Using these results and the Arrhenius model, it is estimated that HC-FCS columns will display degradation up to 52% in their axial capacity during a 100-year service life if subjected to seawater at 27°C.