Sulfate Durability of Type IL-Slag Blended Cement under Different Curing Exposures

To improve concrete sulfate durability, supplementary cementitious materials (SCMs) like slag, fly ash, and silica fume have been widely used as partial replacements for ordinary portland cement. This study examines how different conditions used to accelerate sulfate attack mortar bar tests affect the cement reaction products and deterioration measured. Type IL-slag cement combinations with different slag alumina contents were used to determine how these materials perform when used in combination and to see how the test conditions impact the results. The sulfate resistance of Type IL-slag cement blended with slags with Al2O3 contents of 8.8%, 13.4%, and 17.6% at cement replacement levels of 0%, 30%, 40%, and 50% were tested. A 20% fly ash mixture was tested for comparison. Sulfate expansion rate was also measured in ternary blended mortar bars consisting of Type IL-slag (30% and 50%) containing 13.4% alumina and silica fume (4% and 6%). Based on the results of this study, all binary and ternary cementitious mixtures tested for sulfate attack resistance qualified as highly sulfate resistant. The low alumina slag cements demonstrated higher sulfate resistance under standard ASTM C1012 exposure, whereas the high alumina slag cements proved to be of higher sulfate resistance under accelerated exposure at 15 months. The findings indicate for the high alumina slag- IL cementitious blends, an additional drying period under accelerated exposure, resulted in the chemical binding of most of Al2O3 in hemicarboaluminates and monocarboaluminates, and other aluminate hydrates (hydrotalcite, stratlingite). This effectively reduced the amount of monosulfate present. The sulfate attack test results of this study revealed that high alumina slag blended IL cements can possess significant long-term sulfate resistance even at low replacement level with sufficient cement hydration along with suitable calcite content.