Abstract
This study investigates the axial compressive behaviour of concrete filled steel tubes with rubberised alkali-activated concrete as infill. A high-strength slag-based alkali-activated concrete mix is chosen as a reference and rubber contents of 0, 30 and 60% replacements by volume of natural aggregates are considered. Steel tubes with circular and square cross-sections having length-to-diameter/width ratios of 2 and 4 are investigated. The maximum axial capacity and the axial load-shortening response are observed. The results show a reduction in the axial capacity and elastic stiffness of the confined specimens with higher rubber content. The circular tube sections provide greater confinement to the concrete core, evidenced from the higher ultimate stress, in comparison with the square tube sections. Circular confined specimens also exhibit a softer post-peak axial load-shortening response when compared to the square confined specimens. The axial capacity and overall behaviour of the confined specimens with the same cross-section is generally similar for specimens with length-to-diameter/width ratios of 2 and 4, with a slight reduction in the axial stiffness for the taller specimens. Eurocode 4 axial strength design expressions for concrete filled steel tubes are shown to be applicable for the specimens tested in this study.