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

authored by: Claus H. Rüscher, Elzbieta Mielcarek, Wolfgang Lutz, Attila Ritzmann, Waltraud M. Kriven
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.
Organisation(s): Institute of Mineralogy
External Organisation(s): University of Illinois at Urbana-Champaign
Type: Article
Journal: Journal of the American Ceramic Society
Volume: 93
Pages: 2585-2590
No. of pages: 6
ISSN: 0002-7820
Publication date: 09.2010
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Ceramics and Composites, Materials Chemistry
Electronic version(s): https://doi.org/10.1111/j.1551-2916.2010.03773.x (Access: Closed)

BibTeX

@article{60820f8ae381406eaa5fb993122dc735,
title = "Weakening of alkali-activated metakaolin during aging investigated by the molybdate method and infrared absorption spectroscopy",
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.",
author = "R{\"u}scher, {Claus H.} and Elzbieta Mielcarek and Wolfgang Lutz and Attila Ritzmann and Kriven, {Waltraud M.}",
year = "2010",
month = sep,
doi = "10.1111/j.1551-2916.2010.03773.x",
language = "English",
volume = "93",
pages = "2585--2590",
journal = "Journal of the American Ceramic Society",
issn = "0002-7820",
publisher = "Wiley-Blackwell",
number = "9",
}