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Description: This report briefly discusses the mechanism of sulfate attack and the role of selected supplementary cementitious materials (SCMs) in reducing this attack in concrete. The relationship between sulfate resistance and the chemical, physical, and mineralogical composition of SCMs has been elucidated. Based on a number of bench-scale studies, several of models predicting sulfate resistance in fly ash-containing concretes have been cited and discussed. The report has also discussed sulfate resistance of concrete that contained SCMs interground and optimized at the cement plant as compared to that mixed at the concrete batch plant. From the very limited data available on the subject, use of interground SCMs with clinker have shown improved sulfate resistance for concrete, primarily attributed to finer and better particle size distribution that enhance the reactivity and reduce the permeability in concrete. The report also recommends that the optimization of sulfate should be based on 3-day strength instead of 1-day strength as in ASTM C 563. This may require a higher sulfate addition that can potentially improve sulfate resistance as the porosity of the system would be markedly reduced.
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