Study on axial compressive bearing capacity of coal gangue coarse aggregate concrete-filled steel tube columns

Coal gangue, as a major solid waste from coal mining, poses serious challenges in terms of land occupation, environmental pollution, and resource utilization. Its effective recycling in structural engineering not only helps reduce environmental burdens but also promotes sustainable development in the construction industry. Concrete-filled steel tube (CFST) structures, due to the confinement provided by the steel tube, subject the core concrete to triaxial compression, which significantly enhances its load-bearing capacity while simultaneously improving the steel tube’s resistance to local buckling. Against this background, this study investigates the effects of varying amounts of expansive agent (EA) and coal gangue coarse aggregate replacement rates on the axial compressive behavior of CFST columns incorporating coal gangue coarse aggregate concrete. Using the EA content and coal gangue coarse aggregate replacement rate as variables, axial compression tests were conducted on eight CFST columns. The failure modes, load-displacement curves, load-strain curves, and lateral deformation coefficients of the specimens were analyzed to evaluate their mechanical performance. The test results indicate that an appropriate amount of EA positively influences the compressive strength of coal gangue concrete. However, as the EA content increases, its effectiveness in improving strength diminishes. When the EA content reaches 12%, the inclination angle of the shear failure surface is minimized, and the failure mode tends to shift towards mid-section bulging failure. Nevertheless, excessive EA may impair the performance of coal gangue CFST columns, reducing their structural capacity.