Sulfate resistance of Portland dolomite cement: performance and mechanisms

This study investigated the sulfate resistance of Portland-dolomite cement (PDC) cured at different temperatures. Mortars of Portland cement (PC) and PDC with different dosages of dolomite, 10, 20, 30% by weight, were cured in water at 20 °C and 60 °C for 28 days before immersed in 50 g/L Na₂SO₄ solution at 20 °C. In addition to monitoring the length changes of mortars, MIP and XRD were performed to investigate microstructure and evolution of phase assemblages. Results show that PDC mortars cured at 20 °C give a poorer sulfate resistance than PC, and the higher the dosage of dolomite, the worse the sulfate resistance. On the contrary, when cured at 60 °C, PDC gives a much better sulfate resistance than PC, and the higher the dosage of dolomite, the better the sulfate resistance. The increases of critical pore size and porosity with the incorporation of dolomite lead to a poor sulfate resistance of PDC cured at 20 °C. However, for PDC cured at 60 °C, it is not the pore structure but the lack of available aluminate caused by the formation of hydrotalcite contributes to its sound sulfate resistance. The higher the dosage of dolomite from 10 to 30%, the larger amounts of hydrotalcite formation and the better the sulfate resistance. Hydrotalcite is stable in the presence of sulfate.