Axial load-displacement response and ductility of sustainable steel-reinforced compression-cast recycled aggregate concrete columns

The newly developed compression casting technology effectively addresses the inherent deficiencies of recycled aggregate concrete (RAC), such as low strength and poor durability, by removing excess water and air through compression. This innovative approach contributes to eco-friendly, low-carbon, and sustainable construction practices. However, existing studies have primarily focused on the material properties and stress-strain models of compression-cast RAC, with no research reported at the structural level, which significantly restricts its engineering applications. To bridge this gap, this study experimentally investigated the axial compression behavior of steel-reinforced compression-cast RAC columns. The design combined normal-strength steel longitudinal reinforcement with high-strength steel spiral transverse reinforcement to mitigate the brittleness induced by compression casting. Experimental variables included the RAC water-cement ratio, casting method, and spiral reinforcement strength. A novel compression casting device was developed specifically for the steel-reinforced columns to overcome the critical challenge of steel bar deformation during the high-pressure process, thereby enabling, for the first time, the fabrication and structural-level investigation of reinforced compression-cast members. The test results demonstrated that compression casting significantly enhanced the load-carrying capacity of steel-reinforced RAC columns, though accompanied by steeper post-peak load reduction. The descending slope became more pronounced with higher RAC strength. High-strength spiral stirrups were capable of effectively improving the ductility of compression-cast RAC columns, restoring it to a level even higher than that of normal-cast RAC columns reinforced with normal-strength spiral stirrups. Through component-based decomposition of the load-displacement curves, it is found that the mechanical behavior of the columns can be accurately predicted using a superposition method combining the stress-strain relationships of the compression-cast RAC, longitudinal reinforcement, and stirrups, demonstrating the good synergistic performance among three load-carrying components.