Low Temperature Sulfate Resistance of Concrete Produced with Portland-limestone Cements and Supplementary Cementitious Materials

Portland-limestone cement with up to 15% interground limestone was included in the Canadian Standard A3000 for Hydraulic Cements in 2008. However, due to the lack of data on sulfate resistance of concrete especially the potential for thaumasite sulfate attack at low temperatures, the use of portland-limestone cement in concretes subjected to moderate or severe sulfate exposures, even when blended with supplementary cementitious materials (SCMs) was not allowed. In this experimental research, the sulfate resistance of fifty three concrete mixtures produced with several combinations of portland and/or portland-limestone cements and SCMs at three different water-to-cementitious materials ratios of 0.40, 0.50, and 0.70 exposed to both sodium and magnesium sulfate solutions was evaluated in both laboratory and field exposures at low temperatures by measuring changes in length, mass, and resonant frequency of concrete prisms as well as making visual inspections. Also, the causes, mechanisms, and depth of deterioration in damaged concrete mixtures having insufficient levels of SCMs was investigated by mineralogical analysis using X-ray diffraction and microstructural analyses using micro X-ray fluorescence spectrometry and scanning electron microscopy. It was found that SCMs at sufficient replacement levels significantly improve the resistance of concrete to sulfate attack and in such mixtures there was no impact of limestone additions. The sulfate resistance of PC+SCMs and PLC+SCMs concrete mixtures is equal to or better than that of currently allowed highly and moderately sulfate-resistant portland and blended cements. Exposure to magnesium sulfate solution is more aggressive than sodium sulfate solution. The sulfate resistance of concrete prisms in the selected field exposures is better than that of prisms in the selected laboratory exposures due to more reasonable concentrations of sulfate solutions, larger prism size, and possibly including the variable temperature used in the field exposure. Since there is no standard test method for evaluating the sulfate resistance of concrete due to the potential threat from thaumasite sulfate attack at low temperature and previous research focused on mortar tests, the results of this research can be used to develop a standard test method for evaluating the sulfate resistance of concrete.Ph.D