Eccentric loading of circular double skin self-compacting concrete columns incorporating recycled aggregate.

The use of recycled concrete aggregate has positive environmental and economic contributions to the sustainability of the materials. However, when recycled aggregate (RA) is used instead of natural aggregate, the mechanical and structural performance of concrete are negatively influenced. Therefore, the development of practical techniques that reduce these negative influences are very important. Due to the confinement effect, the mechanical behaviors of the RA can be improved by encasing it in a circular steel tube. This paper describes a series of comparison tests on steel tubular columns of circular sections filled with normal self-compacting concrete and recycled aggregate self-compacting concrete. Ten specimens consist of 5 recycled aggregate concrete filled double skin steel tubular (RACFDST) columns and 5 normal concrete filled double skin steel tubular (CFDST) columns divided into three groups according to the type of load were tested under (axial, uniaxial, and biaxial) compression loads. Loading eccentricity and full replacement of natural coarse aggregate with recycled coarse aggregate were the main parameters in this study. Overall, the failure mode, ultimate capacities, and general deformational behavior have been presented in this paper. The results clearly showed that the failure mode of the RACFDST columns is generally similar to their normal CFDST counterparts with a slight reduction in ultimate bearing capacity. Specimens under axial compression were subjected to local buckling failure, while the global buckling failure was the mode of all eccentrically loaded columns. As expected, due to the confinement effect of the steel tubes, the strength of the sandwich concrete was enhanced, and all tested columns exhibited ductile failure. [ABSTRACT FROM AUTHOR]