Synergistic effect of waste concrete powder and traditional SCMs in preparing clinker-free cement: Hydration and microstructure evolution

This study systematically examines the hydration behavior, microstructure, and mechanical performance of waste concrete powder (WCP) paste modified with ground granulated blast-furnace slag (GGBS) and fly ash (FA). Isothermal calorimetry, mercury intrusion porosimetry (MIP), quantitative X-ray diffraction (QXRD), thermogravimetry analysis (TG), 1H nuclear magnetic resonance spectroscopy (1H NMR), scanning electron microscopy (SEM), and mechanical strength tests were employed. Results indicate that incorporating GGBS significantly enhances the hydration performance, refines the pore structure, and improves the mechanical properties of WCP-based materials. Compared to pure WCP paste, the content of small capillary and gel pores in GGBS-blended specimens increases by 51.2 %–115.2 %, while the content of large capillary pores decreases by 83.1 %–86.7 %. The compressive and flexural strengths improve by 22.3 %–61.4 % and 4.7 %–25.1 %, respectively. In contrast, FA incorporation shows minimal or even detrimental effects on the properties of WCP-based materials. The refined pore structure in GGBS-blended specimens may enhance chloride penetration resistance, while the inherent low alkalinity of WCP-based systems raises concerns regarding carbonation susceptibility.