Thermal and compressive behaviors of fly ash and metakaolin-based geopolymer

This paper studies the heat evolution and compressive behavior of KOH activated geopolymer materials based on low-calcium fly ash, metakaolin, and fly ash with slag. An isothermal calorimeter was adopted to study the heat evolution. Study variables include alkali activator concentration, curing temperature, and slag replacement ratio. It was found that the cumulative released heat for both fly ash and metakaolin-based geopolymer increased with the increase in alkali concentration and slag replacement ratio. The increase in curing temperature significantly increased both the heat flow and the cumulative heat of the heat evolution during geopolymerization, especially the fly ash-based geopolymers. The compressive behavior of geopolymers with different initial curing temperatures was also investigated experimentally. Results showed that the 28-day compressive strength for all geopolymers increased with the increase of alkali concentration and slag replacement ratio cured under ambient temperature. The initial curing temperature has a significant influence on the compressive strength of the fly ashbased geopolymer, but a negligible influence on the compressive strength of the metakaolin-based geopolymer.