Effects of combined environmental exposures and axial load on CFFT

Concrete-filled fiber-reinforced polymer tube (CFFT) columns have demonstrated superior advantages on mechanical behavior and ease of construction during the past few decades. The fiber-reinforced polymer (FRP) tube not only improves the mechanical properties of the concrete core by confinement, but also provides a protection layer for the concrete against the outer corrosive environment. However, one obstacle hindering the greater acceptance of the FRP composite as a conventional construction material in civil engineering applications is the susceptibility of FRP to complex, severe environmental exposure. The purpose of this study is to investigate the durability of CFFT cylinders with glass fiber reinforced polymer (GFRP) tubes under exposure to combined freeze/thaw, heating/cooling, and wet/dry cycles. The effects of combined sustained load and environmental conditions were also investigated during this study. Compression and hoop tensile tests were carried out on both conditioned and controlled specimens. In addition, scanning electron microscopy (SEM) and differential-scanning calorimetry (DSC) tests were used to characterize the aging effect on physical and thermal properties of FRP material. Test results showed that more pronounced degradation occurred on the ultimate strain than on the ultimate strength. The sustained load had a negative effect on CFFT cylinders by creating more microcracks in the GFRP tube.