Materiales de Construcción, Vol 66, No 322 (2016)

K-Based Geopolymer from metakaolin: roles of K/Al ratio and water or steam Curing at different temperatures

A. Tawfik
Department of Refractories, Ceramics and Building materials, National Research Center, Egypt

F. Abd El-Raoof
Department of Refractories, Ceramics and Building materials, National Research Center, Egypt

H. Katsuki
Saga Ceramics Research Laboratory, Japan

K. J.D. MacKenzie
MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, New Zealand

S. Komarneni
Materials Research Institute and Department of Ecosystem Science and Management, The Pennsylvania State University, United States


K-based geopolymer binder was prepared by reacting metakaolin with alkaline solutions having different potassium contents and by water curing at room temperature and 80 °C as well as steam curing at 150 and 180 °C. The phase formation, microstructure and Al and Si nearest neighbor environments were studied using XRD, TEM and 27Al and 29Si MAS NMR spectroscopy, respectively. The results revealed that amorphous alumino-silicates were predominant in geopolymer prepared by curing up to 28 days at room temperature or at 80 °C. The amorphous alumino-silicates persisted after hydrothermal treatment at 150 °C/48 hrs and even at 180 °C/30 hrs. However, the samples cured hydrothermally at 180 °C/48 hrs revealed formation of crystalline potassium aluminum silicate and chabazite phases. The Al nearest neighbor environments was not significantly affected by increasing the K/Al ratio up to 1.55 or by the curing temperatures. On the other hand, the geopolymer reaction appears to have increased when cured at 80 °C or steam cured at 150° and 180 °C and crystalline aluminosilicates resulted when the geopolymer sample was hydrothermally treated at 180 °C/48 hrs.


K-based geopolymer; Steam curing; Microstructure; NMR

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