Thermal behavior and characteristics of fired geopolymers produced from local Cameroonian metakaolin

The thermal behavior along with certain characteristics of geopolymers produced from local Cameroonian metakaolin and heated up to 1000 °C were examined. Geopolymers fired up to 900 °C had the same physical aspect as initial ones and those fired at 1000 °C warped, were glazed and blistered. The TG showed elimination of water according to two stages. The dilatometric curves of preheated samples showed shrinkage between 90 and 250 °C followed by expansion and sintering. The samples heated up to 700 °C were amorphous and new crystalline phases appeared around 900 °C. The microstructure of geopolymers heated between 300 and 900 °C showed progressive disruption and the linear shrinkage increased. The water absorption of the samples fired up to 700 °C increased slightly and tremendously around 900 °C. A drastic decrease of compressive strength was observed with the samples fired between 300 and 900 °C. Hence, the characteristics of geopolymers lessened with elimination of the water which forms hydration spheres around the compensating cations (Na+) opposed to tetrahedral groups AlO4− along with transformation of amorphous phase.