Fly Ash High-strength Geopolymers: Effect of Grinding and Extra Water Content

Fluidized bed boiler fly ash, previously calcined at 650 °C (FAT), was used to obtain geopolymers, after treatment with 8 M, and 10 M NaOH, as well with sodium silicate (silicate modulus MS = 2.5). The volume ratio of alkaline activating solution/FAT = 0.38 L/kg was kept constant; whereas that the molar ratios SiO2/Na2O = 1.18–1.50, and H2O/Na2O = 14.7–20.4, was used. The addition of extra water to the geopolymeric paste was done in two ways, in order to determine the effect on the dissolution rate of aluminosilicates and the strength development of the geopolymers obtained. By pre-grinding the FAT, controlling the mixing time, the H22O/Na22O ratio = 14.7 and thermal activation at 80 °C for 24 h, it was possible to obtain geopolymers with high strengths