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Phase Analysis of Alkali-Activated Slag Hybridized with Low-Calcium and High-Calcium Fly Ash

Author

Listed:
  • Tao Jiang

    (Test Station for Mechanics and Structural Engineering, National Center for Materials Service Safety, University of Science and Technology Beijing, Kunlun Road 12, Beijing 102206, China)

  • Ying Jin

    (Test Station for Atmospheric Environment Corrosion, National Center for Materials Service Safety, University of Science and Technology Beijing, Kunlun Road 12, Beijing 102206, China)

Abstract

This paper investigates the hydrated phase assemblage, microstructure, and gel composition of sodium hydroxide (NaOH)-activated fly ash–slag blends with either low-calcium or high-calcium fly ash. The results show that the nature of precipitated calcium–aluminosilicate–hydrate (C-A-S-H) and alkali aluminosilicate-hydrate (N-A-S-H) depends on the fly ash composition and slag-to-fly ash ratio. However, regardless of fly ash composition and slag-to-fly ash ratio, a universal linear compositional relationship exists between Al/Ca ratio and Si/Ca ratio in precipitated gels. This indicates that there exists a structural limitation on the incorporation of Al 3+ for Si 4+ in the tetrahedral silicate of C-A-S-H, N-A-S-H, or metastable N-C-A-S-H gels. In a hybrid slag–fly ash system, the framework structure of precipitated gels is an assemblage of aluminosilicate units with heterogeneous Ca 2+ and Na + distribution. The amount and reactivity of calcium and alkalis seem to play a critical role in determining the structure and properties of precipitated gels in hybrid systems. The low cementitious capability in alkali-activated high-calcium fly ash may be attributed to the unstable N-C-A-S-H gel structure with concurrent high Na and Ca contents.

Suggested Citation

  • Tao Jiang & Ying Jin, 2022. "Phase Analysis of Alkali-Activated Slag Hybridized with Low-Calcium and High-Calcium Fly Ash," Sustainability, MDPI, vol. 14(7), pages 1-13, March.
    • Handle: RePEc:gam:jsusta:v:14:y:2022:i:7:p:3767-:d:777337
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