Abstract
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.
Highlights
Increased awareness and demand for fire safety of buildings are promoting research on fire-resistant materials, especially inorganicbased materials
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 research conducted by Ozawa and Shaikh [7] showed that pure fly ashbased geopolymer did not exhibit the abrupt decrease in vapour pressure reported in cement-based and fly ash/slag-based materials, resulting in spalling and cracks, which may demonstrate the advantageous utilization of fly ash in synthesis of geopolymer
Summary
Increased awareness and demand for fire safety of buildings are promoting research on fire-resistant materials, especially inorganicbased materials. Geopolymers are formed by alkaline activation of aluminosilicate sources such as fly ash [4,5]. The lower water demand of fly ash-based geopolymers ben efits in minimizing the damage caused by water evaporation during high-temperature exposure. Compared to metakaolinbased geopolymers continuous sintering of fly ash particles triggered particle binding and strength increase with temperature increase. Geopolymers release the physically and chemically bound water at elevated temperatures, which can destabilize the material structure and cause the thermal shrinkage and crack for mation [6]. The vapor pressure produced by both the physically and chemically absorbed water within the matrix will attempt to escape at elevated temperature. Taking into account the enormous influence of the microstructure on geopolymer thermal degradation, the research focusing on the improvement of the matrix in order to address these issues is of great significance
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