Comparison of Two Alkali-activated Systems: Mechanically Activated Fly Ash and fly Ash-blast Furnace Slag Blends

Poor reactivity of fly ash (FA) in alkali activation process can be improved either by mechanical activation of fly ash or by blending fly ash with more reactive material, such as blast furnace slag (BFS). Both options were explored in this paper and comparison was performed. Mechanical activation of fly ash was conducted in a planetary ball mill, while blends of fly ash and blast furnace slag were prepared with different ratios (FA/(FA+BFS) = 1; 0.75; 0.50; 0.25; 0). Alkali activation was carried out at 95 °C by use of sodium silicate solution as an activator. In both cases significant increase of geopolymer strength was observed in respect to the geopolymer based on the initial fly ash. Optimal geopolymer strength was correlated with the chemical composition of the binding gel. Empirical values of optimal gel composition could serve as a basis for tailoring properties of alkali-activated binders based on different precursors. Both alkali-activated systems represent promissing routes for geopolymer technology development.