The suitability of thermally activated illite/smectite clay as raw material for geopolymer binders A. Buchwald a, ⁎, M. Hohmann a , K. Posern a , E. Brendler b a Bauhaus-University Weimar, Building Chemistry, Coudraystr. 13C, D-99421 Weimar, Germany b TU Bergakademie Freiberg, Institute of Analytical Chemistry, Faculty of Chemistry and Physics, Leipziger Str. 29, D-09599 Freiberg, Germany abstract article info Article history: Received 25 November 2008 Received in revised form 20 August 2009 Accepted 26 August 2009 Available online 4 September 2009 Keywords: Thermally activated clays Geopolymers Alkali-activated material Illite So called geopolymers or geopolymeric binders and cements are made by means of an alkaline activation of materials reactive in this respect. Such material has to consist of a certain amount of silicate and aluminate phases which can be dissolved by the alkaline medium. In the consequence stable polymeric networks of alumosilicates will be formed. Metakaolins and alumosiliceous fly ashes, in particular, have by now achieved noteworthy significance. The search for alternative low cost or high available materials may lead among other things to “normal clays”. This material is widely available all over the world and may show certain reactivity after a thermal activation process. This investigation focuses on the suitability of illite/smectite clay to form a geopolymer after thermal and alkaline activation. Therefore clay containing mainly illite was thermally activated between 550 and 950 °C. The degree of dehydroxylation and the reached reactivity were followed by X-ray diffraction, NMR spectroscopy and dissolution techniques. The performance of the geopolymer binder in terms of strength as well as the phase composition was studied. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Geopolymers are inorganic binders. The term “geopolymer” was coined by Davidovits in the 1970s, originally referring to the inves- tigations on the reaction of metakaolin in alkaline media forming aluminosilicate polymers (Davidovits, 1976, 1999). The prefix “geo” was selected to symbolize the constitutive relationship of the binders to geological materials, i.e. natural stone and/or minerals. Previously, similar materials have already been investigated by Glukhovsky (1965), and have been made known by the term “soil cements” in the late 1950s. Nowadays, the utilisation of natural raw materials (beside meta- kaolin) is out of focus. The use of secondary resources such as fly ash and slags to form geopolymers has been widely proven (Buchwald, 2006; Duxson et al., 2007; Palomo et al., 1999). The use of fly ash promises high ecological benefit and lower cost, but secondary raw materials may enclose difficulties in availability, handling or product quality. The search for alternative low cost or easily available materials may lead among others to “normal clays”. This material is widely available all over the world and may show certain reactivity after a thermal activation process as well (He et al., 1995a). The thermal activation of clay minerals in the temperature range between 500 and 800 °C results generally in the dehydroxylation of the clay mineral (Heller-Kallai, 2006). The octahedral sheet looses water and decomposes into a disordered meta state in case of collapsing clay minerals (Evans and White, 1959; Mendelovici, 1997). This metastable state is widely addressed as being reactive as pozzolana (Baronio and Binda, 1997; He et al., 1995a,b, 2000; Kakali et al., 2001; Liebig and Althaus, 1997; Sabir et al., 2001). Firing to higher temperatures results in the formation of new phases such as spinel and mullite (Mendelovici, 1997). The dehydroxylation of kaolinite clay to metakaolinite is widely investigated in terms of structural changes (Anthony and Garn, 1974; Bergaya et al., 1996; Freund, 1967; Massiot, 1995; Meinhold et al., 1985; Pampuch, 1966; Rocha and Klinowski, 1990a,b). The octahedral layer undergoes massive structural changes; aluminium changes its coordi- nation from six into four and five as indicated by 27 Al MAS NMR. Two dimensional MQ 27 Al MAS NMR measurements on metakaolin showed the existence of strongly disordered fourfold coordinated Al nuclei rather than a five coordinated signal as deduced from the one dimensional measurement (MacKenzie, 2000; McManus et al., 2001). Clay generally consists of a mixture of different clay minerals and associated minerals. The quantification of the clay mineral mixtures is difficult and needs experience and a combination of methods (Brigatti et al., 2006; Moore and Reynolds, 1997; Srodon, 2006). The variability of clay composition and parameters of the thermal activation process complicate a general statement about the suitability of clay resources for the production of geopolymers as shown in different papers with partly controversial position (Buchwald et al., 2007; Kaps and Buchwald, 2002; Mackenzie et al., 2005). This investigation focuses on an illite–smectite dominated clay and the possible reactivity as a raw material for geopolymeric binders. The clay was thermally activated at 550, 650, 750, 850 and 950 °C and Applied Clay Science 46 (2009) 300–304 ⁎ Corresponding author. Present address: ASCEM B.V., Holleweg 19, 6191 RA Beek, The Netherlands. Tel.: +31 464374192; fax: +31 464377620. E-mail address: a.buchwald@ascem.nl (A. Buchwald). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.08.026 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay