Performances of Concrete-filled Gfrp Or Gfrp-steel Circular Tubes Subjected To Freeze-thaw Cycles

This paper presents an experimental investigation of the performances of concrete-filled glass fiber-reinforced polymer (GFRP) and GFRP externally wound steel circular tubes, subjected to freeze-thaw cycles ranging from -18°C to 18°C. The variation in hoop strains of the tubes during the freeze-thaw cycles was monitored by embedded fiber Bragg Grating (FBG) strain sensors in GFRP layers or between GFRP and steel tube. The residual hoop strain after each freeze-thaw cycle indicates the possible degradation of GFRP materials, such as cracks, debonding of GFRP-concrete or GFRP-steel due to mismatch of the coefficient of thermal expansion, as well as water immersion. A synergistic effect of FRP and steel tubes on the confinement of inside concrete was revealed, resulting in well-improved ductility. After 56 freeze-thaw cycles, remarkable degradation were found in the axial strength, modulus, and strain for concrete-filled GFRP tubes. However, the GFRP-steel tube system showed a negligible reduction in the ultimate axial strain by the freeze-thaw cycles with less degradation in the axial strength and modulus.