<p>Concrete-filled circular steel tube columns have become popular for their ductility, high strength, and excellent hybrid action. This study investigates the axial behavior of concrete-filled circular steel tube columns with recycled coarse aggregate and nano-silica that encourage sustainable construction. The study was conducted on short circular steel tube columns filled with concrete mixes comprising varying percentages of recycled coarse aggregate and nano-silica. The axial load–deformation behavior, ultimate load capacity, stiffness, ductility, and different failure mechanisms were studied. The results reveal that nano-silica greatly improves the compressive strength of concrete-filled circular steel tube experiments, with an optimal nano-silica level of 2% for both 50% and 100% recycled coarse aggregate mixtures. In addition to this point, the addition of greater nano-silica causes a steady decrease in strength due to particle agglomeration and decreasing matrix efficiency. SEM and XRD were used to analyze microstructural features. The findings indicate that nano-silica greatly enhances matrix integration and the interfacial transition zone. Improved confining and composite interaction resulted in better axial behavior for recycled coarse aggregate-based concrete-filled circular steel tube columns. Furthermore, the experimental findings were compared to the ACI and Eurocode 4 projections. The study indicates that recycled coarse aggregate and nano-silica may be employed efficiently in concrete-filled circular steel tube columns while maintaining structural integrity.</p>