From demolition to decarbonization: Synergistic hydration and sustainability of thermally activated recycled concrete...

This study investigates the synergistic hydration and sustainability of thermally activated waste concrete powder (WCP) combined with recycled cement (RC) for developing fully recycled, low-carbon binders. At replacement levels above 50%, WCP regulates hydration through coupled dilution, nucleation, and filling effects, while the rehydration of β-C₂S in RC governs long-term strength. Quantitative XRD, TG, and SEM analyses revealed that the RC-based system forms predominantly amorphous C-S-H with strong interfacial bonding, whereas the CEM-based system yields more crystalline but less integrated hydrates. The R30 mixture, containing 70% WCP and 30% RC, achieved the best synergy, with 28-day strength exceeding that of the corresponding CEM system. The inert phase content of R30 is approximately 15%. The WCP-RC paste combination exhibits superior synergistic effects compared to the WCP-CEM paste combination, and the WCP-CEM system demonstrates that thermally activated WCP possesses cementitious activity. From a sustainability perspective, substituting clinker with thermally activated WCP is estimated to reduce 2.47-4.94 × 10⁸ t CO₂ annually, providing a practical pathway for high-value recycling of construction waste into sustainable cementitious materials.