Axial compressive behavior and seismic performance of recycled-component concrete columns

Waste concrete members can be converted into recycled components through minimal processing, thereby avoiding the generation of large quantities of fine powder. Moreover, the recycled components can directly replace up to over 50% of the freshly mixed concrete, substantially reducing the consumption of both natural aggregate and cement. This study focuses on recycled-component concrete (RCC) columns and investigates their axial compressive and seismic performance through axial compressive tests and low-cycle reversed loading tests, respectively. The effects of a recycled component, the total longitudinal reinforcement ratio, the configuration and amount of new stirrups, the strength of the new concrete, the surface treatment of the recycled component, and the connection between the new and old stirrups were examined. A prediction formula for the axial load-bearing capacity of RCC columns was also developed by accounting for the dual-layer confinement effect provided by the new and old stirrups. The main findings are as follows: (i) installing post-installed rebars on the surfaces of the recycled components or connecting the new and old stirrups has minor effects on the axial load-bearing capacity and seismic performance of the columns; (ii) when the strength of the old concrete is relatively low, the axial load-bearing capacity of the RCC column can be made comparable to that of the reference column without recycled component by appropriately increasing the strength of the new concrete; (iii) when the total longitudinal reinforcement ratio and the volumetric ratio of the new stirrups are kept constant, incorporating a recycled component and correspondingly reducing the diameter of the new longitudinal reinforcements does not noticeably impair the seismic performance of the column; (iv) new inclined-crossed stirrups are recommended for RCC columns in practical applications because they maintain satisfactory axial and seismic performance while greatly facilitating the placement and construction of recycled components; (v) the proposed method, which accounts for the confinement effects of both the new and old stirrups, provides reasonably accurate predictions of the axial load-bearing capacity of RCC columns.