MICROSTRUCTURE, MINERALOGY AND PHYSICAL PROPERTIES OF GROUND FLY ASH BASED GEOPOLYMERS

Fly ash was characterised and used as the main component of geopolymers. The particle size distribution, moisture content, real and bulk density and specific surface area of the raw fly ash were investigated and mechanical activation was used to improve the reactivity of the raw material. Test specimens were produced by geopolymerisation using a caustic spent liquor (NaOH) and the compressive strength was determined on cylindrical specimens. Finally, samples of the ground fly ash-based geopolymer specimens were analysed using XRD, optical microscopy and SEM. Results showed that geopolymer production using F-type deposited fly ash was possible and the uniaxial compressive strength depended on the fineness of the ground fly ash. XRD showed that zeolite-A appeared in different geopolymer samples and its amount increased gradually from 0T sample to 30T and then decreased for the 60T sample. The same trend held for sodalite type phases, however its amount was lower than for zeolite-A. SEM/EDS revealed that the Na-content was increased in the interstitial fine-grained matrix, especially for the 30T sample when the highest strength was observed. Si and Al were abundant mainly in anhedral and spherical grains and in crystalline grains.