Weakening of alkali-activated metakaolin during aging investigated by the molybdate method and infrared absorption spectroscopy

Claus H. Rüscher, Elzbieta Mielcarek, Wolfgang Lutz, Attila Ritzmann, Waltraud M. Kriven

Research output: Contribution to journalArticle

Abstract

Aluminosilicate gels were synthesized by mixing metakaolin with potassium water glass solution. Mechanical strength values showed a strong increase between 25 and 100 h but decreased again above 200 h for aging at 25°C. A similar curve was observed during aging at 50°C but the maximum strength shifted to shorter time. Aging at 90°and 130°C revealed only the decreasing wing in mechanical strength. The strengthening and weakening during aging at 25°C were further investigated by the molybdate method and infrared absorption spectroscopy. The results indicate basically that different time-dependent formations of two structural units dominate the mechanical properties: (i) A fast formation of longer (polymeric) silicate chains is enforced by the consumption of hydroxide in the solution of metakaolin up to about 25 h of aging. (ii) An aluminosilicate network grows slowly and encloses the chain-like units giving rise to an initial increase in strength within 100 h. During further aging the destruction of the polysilicate chains weakens the geopolymer. The destruction of the chain-like units is explained by the increasing amount of hydroxide produced during network condensation. The results imply that the same reactions occur for aging at a higher temperature but on faster time scales.

Original languageEnglish (US)
Pages (from-to)2585-2590
Number of pages6
JournalJournal of the American Ceramic Society
Volume93
Issue number9
DOIs
StatePublished - Sep 1 2010

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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