Enhancement of Mechanical Properties and Strengthening Mechanism of Fully Recycled Aggregate Concrete via Calcium-Based Composite Mineralization

To achieve the dual goals of construction waste reutilization and carbon dioxide emission reduction, this study proposes a reinforced treatment method for recycled aggregates based on composite mineralization and further improves the secondary mineralization technique for fully recycled aggregate concrete (FRAC) to enhance its mechanical and durability properties. A chemical modification process using Ca(OH)₂ combined with composite mineralization was introduced to analyze its effects on both the macroscopic performance and microstructure of recycled aggregates. The optimized mineralized aggregates were then used to prepare FRAC, and the compressive strength after secondary mineralization was tested. In addition, a carbonation depth prediction model was established based on Fick’s first law to assess the carbonation behavior of FRAC. The results indicate that: (1) the optimal modification scheme for recycled concrete aggregates is 12 h composite mineralization using 0.3% Ca(OH)₂ solution, which reduces water absorption and crushing index by 15.68% and 19.15%, respectively. (2) A significant positive correlation exists between aggregate apparent density and CO₂ uptake (R2 = 0.965). (3) When recycled and mineralized aggregates are mixed in a 1:1 ratio in composite mineralized FRAC, the compressive strength after 7 day curing with secondary mineralization is comparable to that of natural concrete after 28 day standard curing. (4) The carbonation depth prediction model demonstrates a good fit (R2 > 0.85 in all cases), with prediction errors below 5%.These findings demonstrate that the synergistic effect of Ca(OH)₂-based composite mineralization and secondary mineralization can significantly improve the quality of recycled aggregates and their performance in concrete, offering strong potential for practical engineering applications.