Durability of discrete BFRP needle-reinforced seawater sea-sand concrete-filled GFRP tubular columns in the ocean environment

Abstract

In this paper, a long-term durability test on a new type of seawater sea-sand concrete (SWSSC)-filled glass fiber-reinforced polymer (GFRP) tubular column, which was previously proposed by the authors, was conducted. The adopted inner-filled concrete included seawater sea-sand gravel aggregate concrete (SSGC), discrete basalt fiber reinforced polymer (BFRP) needle-reinforced SSGC (BNSSGC), seawater sea-sand coral aggregate concrete (SSCC), and discrete BFRP needle-reinforced SSCC (BNSSCC). The naked concrete columns and GFRP tube-confined columns were immersed in artificial seawater under ambient temperature for up to 22 months. The variation laws of the axial compressive properties of the short columns were tested and compared, and the performance degradation mechanisms were microscopically analyzed by scanning electron microscopy (SEM). In addition, a long-term prediction model was adopted to predict the degradation of the load-bearing capacity of the environmentally conditioned concrete-filled GFRP tubular columns. The test results showed that for the SWSSC-filled GFRP tubular columns, the strength degradation of the specimens with gravel aggregates was not obvious, while the strength of the columns with coral aggregates all showed a stable degradation trend. Pits and resin shedding were observed on the surfaces of the BFRP needles and GFRP tubes, and fiber/resin debonding was the internal mechanism of the degradation of mechanical properties. The predicted stable axial compression strength retention of the FRP-SSGC columns, FRP-SSCC columns, and FRP-BNSSCC columns was 0.944, 0.917, and 0.823, respectively.