Abstract: Utilizing recycled concrete aggregate in cementitious composite shows great potential for sustainable composite materials. However, broader application is hindered by poor mechanical properties resulting from numerous microdefects and residual old mortar. This study proposes a superior calcium-supplemented carbonation strategy to repair microdefects in recycled concrete fine aggregate, aiming to realize high-efficiency enhancement for utilization in cementitious composite. The relationship between calcium phase evolution, microstructural development, and physical properties of recycled aggregate and their impact on the microstructure and mechanical properties of cementitious composite was explored. By integrating deep cleaning, functional penetration, and reaction enhancement, the proposed carbonation strategy enables superior calcium supplementation of recycled aggregate, allowing in-depth repair of microdefects by carbonation products. The indentation modulus of carbonated recycled aggregate increases by 32.5 %, and crushing resistance improves by 20.2 % compared with direct carbonation. Moreover, the unique calcite-rich coating with well-crystallised hexahedral calcite provides additional nucleation sites for calcium silicate hydrate growth, resulting in a compact and homogeneous interfacial transition zone for adequate stress-transfer capability. The novel carbonation strategy facilitates significant enhancement in the physical properties of recycled aggregate and promotes its utilization in cementitious composite, offering a sustainable approach for low-carbon composite materials and natural resource conservation in construction.

Key words: High-performance cementitious composite, Recycled concrete fine aggregate, Superior calcium supplementation, Carbonation enhancement mechanism