Mechanical properties of seawater and sea sand concrete-filled FRP tubes in artificial seawater

Application of the hybrid structure system utilizing seawater and sea sand concrete (SWSSC) and fiber reinforced polymer (FRP) is promising as it is resource beneficial as well as FRPs are corrosion resistant. This paper presents an experimental study on the durability of SWSSC-filled glass/carbon/basalt-FRP tubes exposed to artificial seawater (3.5% salt solution) at 40 degrees C for up to 6 months. The mechanical properties of conditioned and unconditioned plain concrete, FRPs, and concrete-filled FRP tubes (fully filled and double-skin tubes) were measured by means of compressive test and split-disk test. Compressive strength of SWSSC did not degrade after exposure, but an obvious degradation in hoop strength was observed for GFRP and BFRP. Mechanical properties, such as strength and ultimate axial strain of SWSSC-filled FRP tubes were reduced by environmental aging and the major mechanism is the hoop strength deterioration of FRP. Load-axial strain curves and ultimate capacity of SWSSC-filled FRP tubes were predicted by using an existing method with proper modification to account for the environmental effects. The predictions were in good agreement with experimental results. Finally, the environmental factor specified in current guidelines for FRP degradation was assessed using the data obtained in this study. (C) 2018 Elsevier Ltd. All rights reserved.