Mechanistic insights into lattice activation in improving high-temperature performance of alkali-activated fly ash geopolymers

To promote the high-temperature application of Alkali Activated Fly Ash Geopolymer (AAFA), a "lattice activation" method was employed to prepare AAFA. The microstructure and morphology of the supernatant and precipitation during the lattice activation process were systematically analyzed. In addition, the nanostructure, chemical composition and pore structure evolution of AAFA slurry exposure to different temperatures were characterized. The results revealed that the crystal structure of mullite and quartz in FA is changed by lattice activation, and 83 % mullite is activated and transformed into amorphous phase. After exposure to 1000 °C, the residual compressive strength of the lattice activation method increased by 73.4 %, reaching 43.7 MPa, compared to the conventional paste. Furthermore, the activation mechanism of mullite during lattice activation and the roles of the supernatant and precipitation in the polymerization process were deeply investigated. These findings demonstrate that the lattice activation method effectively enhances the utilization of crystalline and amorphous phases in fly ash, improves the thermal stability of the gel structure, and significantly optimizes the high-temperature performance of AAFA. This study provides new insights into the development of thermally durable, low-carbon cementitious materials and highlights the potential of lattice activation as an innovative strategy in the field of alkali-activated materials.