Thermal and microwave synthesis of silica fume-based solid activator for the one-part geopolymerization of fly ash

This paper tests the development of a silica fume-based material, capable to be used as a solid activator for the one-part geopolymerization of fly ash. Through a simple procedure, a mixture of silica fume, an amorphous and silicon-rich by-product, sodium hydroxide and water, is converted, after a low-temperature treatment, to a new powder product mainly containing sodium silicate (Na₂SiO₃). Two different treatment methods are tested for the synthesis of the solid activator: heat and microwave treatment. Microwave processing is more sustainable and more efficient than thermal treatment, since purer products are produced with less energy consumption. The use of these low embodied energy products, as the only solid activator of fly ash, leads to geopolymers with comparable mechanical performance to those prepared with commercial products revealing their potential successful addition in the geopolymer market.