Recyclable calcium carbonate-based concrete: Utilizing calcium carbonate to bond recycled concrete fines through an in-situ heterogeneous dual-precipitation approach

This study introduces a novel approach for in-situ CO₂ sequestration using recycled concrete fines (RCFs). The method employs heterogeneous dual‑calcium carbonate (Cc) precipitation from wet carbonation and calcium bicarbonate (Ca(HCO₃)₂) solution to form a Cc binder between RCFs. The results demonstrate that metastable aragonite is significantly promoted and stabilized in wet carbonation by leveraging the seeding effects from semi-dry carbonated RCFs. A carbonated cement paste layer attached to the surface of RCFs facilitates the combination of precipitated aragonite crystals, while K (Na)-feldspar and quartz-based aggregates exhibit a relatively lower affinity for combining with Cc. The entanglement of aragonite crystals provides most of the strength in the carbonated RCF system. In the non‑carbonated recycled cement paste powders system, wet carbonation primarily produces calcite, while precipitation from Ca(HCO₃)₂ yields aragonite, forming a Cc solid skeleton that contributes to the strength.