Steel fiber-reinforced recycled aggregate concrete-filled GFRP tube columns: Axial compression performance

The enhancement of the mechanical properties of recycled aggregate concrete (RAC) has long piqued the interest of researchers. Based on a brief review of the existing methods for improving the mechanical properties of RAC, this paper proposed a new composite column-steel fiber-reinforced recycled concrete-filled GFRP tube (SFRACFFT) column. To investigate the axial compressive performance of concrete-filled GFRP tube (CFFT) columns, 36 specimens were designed and fabricated. The variables considered included the mass replacement rate of recycled coarse aggregate (MRCA: 0, 50%, and 100%), steel fiber volume content (VSF: 0, 0.6%, 1.2%, and 1.8%), and GFRP tube thickness (T: 4 mm, 6 mm, and 8 mm). The failure patterns of these CFFT columns were compared, the contribution of the GFRP tube to the axial bearing capacity was quantified, and the axial stress-strain responses were analyzed. Results showed that as the GFRP tube thickness increased, the peak axial stress of the CFFT columns increased by 20.8%-54.2%. Replacing natural coarse aggregate (NCA) with 100% recycled coarse aggregate (RCA) resulted in a reduction of 8.6%-12.4% in peak stress; while adding an appropriate amount of steel fibers could improve the peak stress. Finally, based on the evaluation of existing models, a strength enhancement model and a strain enhancement model for SF-RACFFT columns were proposed.