Strength development mechanism of compacted recycled concrete powder material

Building demolition and recycled aggregate production generate substantial amounts of recycled concrete powder (RCP) that remains largely underutilised. Previous studies have suggested that RCP can be converted into low-carbon construction materials through compaction and carbonation; however, the underlying hardening mechanism remains unclear. To address this, a multiscale investigation involving several characterisation techniques was conducted in the current study. The results indicated that owing to weak interparticle bonding, non-carbonated samples predominantly failed by shear, whereas carbonation tended to shift the failure mode towards splitting tension. In sample H-70-50%, the interparticle cohesion was increased by 446% after carbonation, confirming the mesoscale strengthening effect of calcium carbonate (CaCO 3 ) at particle interfaces. CaCO 3 crystals exhibited three-dimensional stacking growth, leading to three types of crystal bridges between particles. Mechanical interlocking and friction accounted for 79% of the overall strength in non-carbonated samples, whereas polar interactions and crystal bridging became dominant after carbonation. This study offers valuable insights for understanding the solidification mechanism of compacted construction materials.