Effect of protogenetic alkali sulfates on the hydration and hardening of cement with different tricalcium aluminate content

The reaction of protogenetic alkali sulfates including arcanite (K₂SO₄), thenardite (Na₂SO₄) and aphthitalite (K₃NS₄) with calcium aluminate have a great influence on cement hydration and hardening. Considering the increased protogenetic alkali sulfates with the widespread use of rotary kilns and low-quality fuels during cement production, the effect of alkali sulfates under different dosages of C₃A on hydration heat evolution, initial setting time, compressive strength, volume stability and hydration product were studied. The results show that protogenetic alkali sulfates combined with C₃A have unfavorable effects on setting time, compressive strength, and linear expansion ratios by dry and water curing. The effect is negatively correlated with [Na₂O_eq]·[C₃A]/[SO₃]² molar ratio of cement. The [Na₂O_eq]·[C₃A]/[SO₃]² molar ratio <0.5 contributes to a lower reduction of strength and volume stability. Through the evaluation of 28-day compressive strength by forty types of cements, it is proposed the [Na₂O_eq][C₃A]/[SO₃]² molar ratio can evaluate the function of protogenetic alkali sulfates combined with C₃A in cement and provide guidance of the improvement on cement properties.