A WEAK ALKALI BOND IN (N, K)–A–S–H GELS: EVIDENCE FROM LEACHING AND MODELING

Abstract

The alkali bond in (N, K)–A–S–H gels presents an up-to-date insufficiently resolved issue with significant consequences for efflorescence in alkali-activated materials. A series of experiments shows nearly all alkalis are leachable from alkaliactivated fly-ash and metakaolin in excessive amounts of deionized water. A diffusion-based model describes well the alkali leaching process. Negligible changes of the (N, K)–A–S–H gel nanostructure indicate that Na,K do not form the gel backbone and H3O+ is probably the easiest substitution for the leached alkalies. Small changes in the long-term compressive strength of leached specimens support this hypothesis.

Keywords

• Aluminosilicate gel
• N–A–S–H gel
• Geopolymer
• Leaching
• Efflorescence