Effect of Dolomite Filler on the Sulfuric Acid Resistance of Alkali-Activated Slag Binders

Abstract

In this work, the influence of a dolomite filler, in combination with pulverized fly ash, on the sulfuric acid (H2SO4) resistance of alkali-activated slag (AAS) is studied. The evolution of compressive strength and mass loss, as well as mineralogical, compositional, and molecular structural alteration of hardened AAS binders containing 0%, 20%, and 40% dolomite filler, or a combination of 20% dolomite and 20% fly ash, exposed to 0% (deionized water), 1%, 2.5%, and 5% H2SO4 solutions, are investigated. The results show that the dolomite and fly ash incorporation in AAS pastes exacerbates the alkalis leaching and alkalinity loss and tends to enhance the strength loss in the H2SO4 solutions, likely due to a coarsened pore structure and, thus, enlarged permeability. Under the H2SO4 attack, AAS is decomposed into gypsum, glauberite, and amorphous calcium-magnesium aluminosilicate hydrates, with little thaumasite, ettringite, or magnesium-bearing mineral formations. While decalcification and the silica polymerization of gel products take place in AAS upon an acid attack, it has strong dealumination resistance. In low and intermediate acid concentrations, the dolomite incorporation reduces the amount of gypsum and glauberite formed in AAS due to the dilution effect, while in strong acid media, dolomite dissolution occurs and contributes to the deleterious sulfate minerals formation.