Pore solution composition of alkali-activated slag/fly ash pastes

The pore solutions of a series of hardened alkali-activated slag/fly ash pastes were extracted by the steel-die method, and analyzed using ICP-OES analysis technique. According to the saturation index from thermodynamic calculations, the pore solutions of alkali-activated slag pastes kept oversaturated with respect to solid reaction products with time. In the pore solutions of alkali-activated fly ash pastes, an increase of temperature (from 40 degrees C to 60 degrees C) led to decreases of the concentrations of Si, Al, Ca, Na, OH-, K, Fe and Mg, while the soluble silicate in the alkaline-activator resulted in increases of the concentrations of these elements. Compared to the alkali activated slag paste with the same alkaline activator, 50% replacement of slag by fly ash did not result in a substantial change of the pore solution composition. Based on the experimental results, conceptual models were proposed to describe the elemental concentrations in the pore solutions.