Compressive testing of circular concrete-filled steel tubes containing demolished concrete lumps

Compound concrete (CC) can be cast by mixing fresh concrete with coarsely crushed demolished concrete lumps that have been obtained from a demolished structure. A significant challenge for the broader application of CC is the lower compressive strength and ductility stemming from the weak interface between the demolished concrete lumps and the fresh concrete. However, the use of CC in Concrete-Filled Steel Tubes (CFSTs) has the potential to mitigate this issue due to the lateral confinement provided by the steel tube. Therefore, an innovative composite cross-section, i.e., compound concrete-filled steel tubular section, is proposed and investigated in this study. The research project involved the compression testing of 22 circular CFST stub columns, employing two cross-section dimensions (244.5 × 6.3 mm and 244.5 × 5.0 mm) in combination with a range of CC mixes. The CFST experimental failure loads were shown to be strongly correlated with the values of the CC compressive strengths. Furthermore, the applicability of the design rules for conventional CFST members in the European Code (EC4), the American Specification (AISC360) and Han's method are evaluated by comparing the experimental failure loads to the axial compressive capacity predictions.