Improvement on sulfate resistance of blended cement with high alumina slag

This paper is focused on the effect of limestone and calcium sulfate content on sulfate resistance of ground granulated blast furnace slag (GGBS) blended cement. Sulfate resistance was evaluated using ASTM C 1012, and a variety of mechanisms of the sulfate resistance of GGBS blended cement were revealed by the analyses of hydration products and sulfate ion ingress. Although GGBS suppresses sulfate ion ingress, it is probable that alumina in GGBS tends to form ettringite with externally supplied sulfate ions. Addition of limestone and increase in calcium sulfate content allow both monocarboaluminate and ettringite to form prior to immersion in sulfate solution. These hydration products remain in the hardened cement matrix and act to suppress further formation of ettringite with external sulfate ions during immersion in sulfate solution. GGBS blended cement with a suitable amount of limestone powder and a controlled content of calcium sulfate exhibits markedly long term sulfate resistance.