Preparation and characterization of foamed geopolymers from waste glass and red mud

New foamed geopolymer materials were successfully synthesized from two waste i.e. red mud and cullet soda-glass, by thermal treatment at 600-800 degrees C for 1 h. The geopolymers were obtained by the alkali activation with sodium hydroxide solution or the liquid part of red mud slurry (filtrate) of waste glass (cullet) with/without red mud admixture. Thermal treatment of these geopolymers, at temperatures between 600 and 800 degrees C determined an important volume increase, due to a foaming process specific for sodium silicate (aluminate) hydrates, the main components of these materials. When red mud substitutes 25% of brown glass, softening and partial melting of material occurs at higher temperatures (due to the presence of complex refractory crystalline phases with Al content); for these compositions the increase of volume due to foaming process is noticed at higher temperatures. Open pores with a wide range of sizes (1-100 mu m) were assessed by scanning electron microscopy; this highly porous microstructure, formed by the bubbling and coalescence of bubbles, is specific for foam materials. The compressive strength values of foamed geopolymers are in the range 2.1-8.6 MPa, and as expected, decrease with the increase of open porosity. (C) 2015 Elsevier Ltd. All rights reserved.