The mechanical properties of GFRP bars embedded in geopolymer concrete after high temperature exposure

Geopolymer concrete prepared with fly ash and slag has exhibited excellent thermostability and thermal insulation performance. Through combining geopolymer concrete with glass fiber reinforced polymer (GFRP) bars, the existing problems like high energy consumption, massive CO2 emission and steel bars corrosion in traditional reinforced concrete structures can be solved. To investigate the mechanical properties of GFRP bars embedded in geopolymer concrete after high temperature exposure, a test was conducted on 419 specimens in this study. Factors that influence the performance include exposure temperature, exposure time and type of concrete cover. The results demonstrated that the tensile properties of bare GFRP bars decreased significantly in the temperature range from 400 °C to 600 °C, and the ratio of tensile strength loss was as high as 50%–90%. The geopolymer concrete cover can effectively slow down and mitigate the degradation in tensile strength and elastic modulus of GFRP bars after high temperature exposure (400–600 °C), but this effect weakens following the rise in exposure temperature and time. In addition, the degradation mechanism of GFRP bars within geopolymer concrete was further analyzed by scanning electron microscopy (SEM) in the microscopic level. Finally, the contribution ratio of each influence factor to the residual tensile strength of GFRP bars after high temperature exposure was numerically illustrated using the statistical method of analysis of variance (ANOVA).