Abstract To investigate the durability of structures containing basalt fibre-reinforced polymer (BFRP) bars wrapped in seawater sea sand concrete (SWSSC) in marine environments, three sizes (including bare BFRP bars) of SWSSC-wrapped BFRP bars were subjected to laboratory accelerated corrosion tests in simulated seawater environments. The SWSSC thicknesses were set at 10 mm and 20 mm; the immersion temperatures were room temperature (~28 °C), 40 °C, and 60 °C; and the immersion media included a seawater, tap-water, and alkaline solution. The tensile properties of the SWSSC-wrapped BFRP bars after immersion were determined, and the degradation mechanism of the BFRP bars was investigated. Based on the results, the alkaline solution is more damaging to the BFRP bars than tap-water or seawater. Alkalinity is a key factor causing the degradation of the BFRP bars. Thus, the tensile strength retention of BFRP bars wrapped with thicker SWSSC, which has a higher alkalinity environment, could be lower than that of bare BFRP bars. In addition, prediction of the tensile strength retention of the SWSSC-wrapped BFRP bars based on Arrhenius relationship was conducted, and the prediction resutls agree well with the experimental results.