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Weakening of Alkali‐Activated Metakaolin During Aging Investigated by the Molybdate Method and Infrared Absorption Spectroscopy
Author(s) -
Rüscher Claus H.,
Mielcarek Elzbieta,
Lutz Wolfgang,
Ritzmann Attila,
Kriven Waltraud M.
Publication year - 2010
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.03773.x
Subject(s) - metakaolin , aluminosilicate , geopolymer , infrared spectroscopy , materials science , chemical engineering , absorption (acoustics) , inorganic chemistry , chemistry , composite material , compressive strength , organic chemistry , catalysis , engineering
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.