Alkali-activated cements (AACs) are promising alternatives to Portland cement, but they currently require costly alkali activators that affect their durability. Na2O(K2O)–CaO–Al2O3–SiO2 (R–C–A–S) precursors were synthesised by calcination. AAC pastes were produced from the resulting precursor powders activated with a small amount of sodium silicate solution and the mechanisms were explored through comprehensive characterisation methods. The research revealed that precursors calcined at 1300°C were self-cementing, which resulted in high strength of the resulting AAC when activated with an alkali (sodium oxide (Na2O)) content of 2.7%. Under the same activator, the precursors exhibited more intense hydration than ground granulated blast-furnace slag (GGBFS), and the resulting hydrates were likely to have been calcium (alkali) aluminosilicate hydrate (C–(N)–A–S–H) gels. The vitreous precursors with a small amount of crystalline phases resulted in higher compressive strength than the completely vitreous ones. R–C–A–S vitreous precursors could be synthesised without using industrial alkalis. This suggests that alkali oxides contained in the precursors can obviously reduce the calcination temperature and alkali activator consumption, potentially enhancing performance across various applications.
Peng et al. (Fri,) studied this question.