. The final product consists of an amorphous three dimensional network of tetravalent silica and alumina species with the charge compensating single valent cations, e.g. Na þ . The water used in synthesis is expelled during reaction to form the pores after drying [7,8]. Geopolymers with different microstructure may be formed by varying the alumino- silicate precursor type [7], the stoichiometric ratio of silica [9], the alkali hydroxide and water contents [10] as well as the reaction temperature and pressure [7].