Importance of cation species during sulfate resistance tests for alkali-activated FA/GGBFS blended mortars

Abstract

In this study, the changes in mass, compressive strength, and length of blended mortars were analyzed to investigate their sulfate resistance according to the ground granulated blast furnace slag (GGBFS) blending ratio and type of sulfate solution applied. All alkali-activated mortars showed an excellent sulfate resistance when immersed in a sodium sulfate (Na2SO4) solution. However, when immersed in a magnesium sulfate (MgSO4) solution, different sulfate resistance results were obtained depending on the presence of GGBFS. The alkali-activated GGBFS blended mortars showed a tendency to increase in mass and length and decrease in compressive strength when immersed in a magnesium sulfate solution, whereas the alkali-activated FA mortars did not show any significant difference depending on the types of sulfate solution applied. The deterioration of alkali-activated GGBFS blended mortars in the immersion of a magnesium sulfate solution was confirmed through the decomposition of C-S-H, which is the reaction product from magnesium ions, and the formation of gypsum (CaSO4·2H2O) and brucite (Mg(OH)2).