Effects of Cement Type and Water to Cement Ratio on Concrete Expansion Caused by Sulfate Attack

Abstract

When groundwater or soils containing concentrations of sulfates come in contact with concrete, a reaction takes place that may be harmful to the concrete. Sulfate reacts with the hydrated tricalcium aluminate in the cement to form crystals of ettringite that occupy a larger volume than the reactants. The forming of these crystals can cause expansion and distress in the concrete. Data collected by the Bureau of Reclamation, United States Department of the Interior, over 18 years of accelerated testing, designed to model a period of time exceeding 100 years, are analyzed as part of this investigation. The analysis of this data demonstrates that the water to cement ratio of the concrete has only a limited impact of the sulfate attack expansion of the concrete for each type of cement tested. The service life of concrete in sulfate environments made with sulfate resistant cements does not necessarily benefit from the use of low water to cement ratios. The analysis of the data demonstrates that the relationship between the sulfate attack expansion and time is not linear. This relationship varies from an exponential curve for non-sulfate resistant cements with low water to cement ratios, to an S-curve for sulfate resistant cements with high water to cement ratios.