Ceramics-Silikáty 56, (4) 374 - 382 (2012) |
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A WEAK ALKALI BOND IN (N, K)–A–S–H GELS: EVIDENCE FROM LEACHING AND MODELING
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Škvára František 1, Šmilauer Vít 2, Hlaváček Petr 2,
Kopecký Lubomír 2,
Cílová Zuzana 1
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1 ICT Prague, Faculty of Chemical Engineering, Department of Glass and Ceramics,
Technická 5, 16628 Prague 6, Czech Republic
2 Czech Technical University in Prague, Faculty of Civil Engineering, Department of Mechanics,
Thákurova 7, 16629 Prague 6, Czech Republic
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Keywords: Aluminosilicate gel, N–A–S–H gel, Geopolymer, Leaching, Efflorescence
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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. |
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