Structural behaviour of geopolymeric recycled concrete filled steel tubular columns under axial loading

Geopolymeric recycled concrete (GRC) is a new construction material which takes environmental sustainability into account. In this paper, an experimental study was carried on 12 concrete filled steel tubular columns under axial loading, in order to fill a knowledge gap on the engineering and structural properties of GRC filled steel tube (GRCFST). Two section sizes of square hollow sections filled with GRC and recycled aggregate concrete (RAC) respectively, with different recycled aggregate (RA) replacement ratios of 0%, 50% and 100%, were used in the experiments. The test results indicated that the ultimate strength was reduced when adding more RAs in the columns, while the peak strain increased. The ductility of the columns was improved by increasing the RA replacement ratio. Overall, the influence of RA on the strength and ductility of GRCFST columns is greater than that of RAC filled steel tubular (RACFST) columns. The assumed theoretical model for predicting load versus deformation relation of GRCFST columns under axial loading was examined, and a revised theoretical model proposed. The results of the new model show good correlation with the experimental results.