Effect of sulfate concentration and associated cation type on concrete deterioration and morphological changes in cement hydrates

This paper reports results of a study conducted to evaluate the effect of sulfate concentration and the associated cation type on concrete deterioration and morphological changes in cement hydrates. The concrete specimens were exposed to 5% NaCl solution admixed with varying concentrations of sodium sulfate or magnesium sulfate (to yield 1%, 2.5%, and 4% SO₄^{2 -}) for a period of 4 years. The concrete specimens were visually examined to determine the extent of concrete deterioration due to the sulfate attack. Some selected specimens were examined under scanning electron microscope to evaluate the morphological changes occurring in the cement hydrates due to sulfate exposure. Concrete specimens exposed to sodium chloride or sodium chloride plus sodium sulfate for 4 years did not show any deterioration. However, deterioration was noted in the plain and fly ash cement concrete specimens exposed to sodium chloride admixed with magnesium sulfate in which the SO₄^{2 -} concentration was 2.5% or more. Deterioration was also noted on the silica fume and blast furnace slag cement concrete specimens exposed to magnesium sulfate solution with a SO₄^{2 -} concentration of 1% and more.