Enhancing the thermal performance of Class F fly ash-based geopolymer by sodalite

Class F Fly ash-based geopolymers are prone to various high-temperature phenomena, such as cracking, spalling, and thermal shrinkage. Here we study the effect of enriching the Class F fly ash with synthetic sodalite phase in order to enhance the thermal properties of the formed geopolymer. The morphological changes, compositional changes, alterations in porosity, high-temperature gel behaviour, and the effect of sodalite on the deformation of the material after thermal exposure up to 1000 °C are investigated by a multiple-analytical approach. Results indicate that adding 5 wt% of the sodalite phase enhances considerably high-temperature performance by inducing phase formation, including anorthoclase, wollastonite, and leucite. Besides, the sodium-bearing sodalite phases lowered the glass transition temperature, thanks to the formation of a mixed K-Na glass phase. Moreover, thermal shrinkage at high temperature is substantially reduced by the addition of sodalite, suggesting its function as a skeletal reinforcement.