Effect of carbonated recycled concrete fines on the performance of limestone–calcined clay cement

The viability of converting recycled concrete fines (RCF) into low-grade artificial limestone, through carbonation in aqueous systems, for use as a sustainable replacement for high-grade limestone in limestone–calcined clay cement (LC3) was explored. The experimental results suggest that the carbonated RCF (CRCF) exhibited high pozzolanic activity, generating additional calcium (aluminium) silicate hydrate (C-(A)-S-H) to serve as nucleation sites for LC3 hydration. The refined particle size of the CRCF and the presence of fine-sized calcium carbonate further facilitated initial ions dissolution, accelerating early-age hydration and improving the pore structure of the LC3. Moreover, the incorporation of CRCF significantly enhanced the compressive strength of the LC3. Specially, when CRCF were used as a complete replacement of limestone, the compressive strength improved by 19.82% at 3 days and 2.50% at 28 days, respectively, relative to the control. These findings demonstrate the potential of CRCF as a sustainable alternative to limestone, contributing to both efficient concrete waste utilisation and environmentally friendly LC3 production.