Hydration mechanism of alkali-activated cementitious materials entirely prepared by solid wastes

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This study explores the hydration mechanisms and mechanical performance of alkali-activated cementitious materials made entirely from industrial solid waste, specifically fly ash and blast furnace slag. With increasing demand for sustainable construction solutions, these materials are alternatives to traditional cement. However, despite recent advancements, challenges remain in optimizing their hydration processes and enhancing material performance. Using 6.45 %NaOH as the base activator, the Si−O and Al−O bond vibrations were significantly stronger at 28 and 90 days of hydration compared to 5.13 %Na2CO3 and 20 % CCS, with the Si−O vibration peaks shifting from 459 cm−1 to 451 cm−1, suggesting that the solvation and aggregation of silicates and aluminates were enhanced, producing more C−S−H and N(C)−S−H gels. The compressive strength of NaOH reached 29.76 MPa at 28 days and 52.30 MPa at 90 days as compared to the compressive strengths of 29.12 MPa and 11.6two MPa for Na2CO3 and CCS, respectively. Scanning electron microscope scans showed that the microstructure of NaOH was denser, which allowed for a rapid stimulation of the raw material activity. After 25 freeze-thaw cycles, the loss of strength was less than 1.46 %, and the mass loss was less than 0.41 %, showing excellent durability. Corrosion resistance is also high, with coefficients of 143.54 % and 119.96 % in NaOH and Na2SO4 environments, respectively. This study optimized the alkali activator ratio in alkali-activated cementitious materials made from solid waste, enhancing freeze-thaw stability, corrosion resistance, and mechanical properties by promoting the formation of C−S−H and N(C)−S−H gels. Using sodium carbonate, sodium hydroxide, and calcium carbide slag as activators accelerated hydration and reduced hardening time, offering a theoretical and technological foundation for green, sustainable construction materials.