Thermal and fire resistance of Class F fly ash based geopolymers – a review

In recent years, the construction industry has striven to promote environmentally friendly materials. A growing body of literature has recognised fly ash-based geopolymers as a promising alternative to Portland Cement. However, a detailed and in-depth review specifically concerning high-temperature exposure and fire resistance of fly ash-based geopolymers is still missing. This review provides a comprehensive summary on the recent research progress concerning mix design, curing and their effects on thermal and fire resistance of Class F fly ash geopolymers. Due to the wide variety of characteristics, the performance of class F fly ash is recommended to be assessed in terms of its reactive phases. The influence of different alkali sources and their effects on thermal resistance are discussed, showing that potassium-based activators contribute to better performances. By applying Factsage calculations, the role of minor elements in controlling melting temperature and phase formation as well as the mechanisms behind the initial strength increase of fly ash-based geopolymers during heating are discussed. Moreover, the evolution of material properties during high-temperature exposure and the key parameter pore interconnectivity to avoid damage such as spalling is reviewed. Finally, recommendations for further investigations are provided.