Ying Ma;Jueshi Qian;Yan Shen;
<正>Sulfate of Portland cement paste dissolves into aqueous phase to participate in cement hydration and a small part would be adsorbed on C-S-H gel usually for high curing temperatures at early hydration ages.The effect of gypsum content,temperature and alkalinity on dissolution and adsorption behaviors of sulfate in cement paste are focused in this study.Dissolution behaviors were studied with a large water-cement ratio at early 10 hours.Aqueous sulfate solution from cement paste was extracted and mixed with prepared C-S-H samples at different conditions to investigate adsorption behaviors of sulfate.Sulfate content was measured using gravimetric determination. The results show that sulfate ions concentration of aqueous solution in cement paste increases with the gypsum content so that more sulfate ions are adsorbed on C-S-H samples.An increase of temperature would accelerate the rate of dissolution, precipitation and hydration reaction of cement paste.As the temperature increasing, fewer sulfate ions enter into the aqueous solution of cement paste and the equilibrium of sulfate ions comes forth after 4 hours hydrating.Sulfate adsorption on C-S-H samples would increase with temperature elevation.Higher alkalinity is unfavorable for sulfate dissolving into aqueous solution of cement paste and also for sulfate ions adsorption on C-S-H samples. Originality In this research,aqueous solution of cement paste containing sulfate ions but not pure sulfate solution is employed,which takes account of the adsorption behavior of other ions,such as sodium ions and the variation of ions concentration with hydration process and reflects the adsorption behavior of sulfate factually.The experimental system of the aqueous sulfate solution from cement paste with prepared C-S-H samples is one originality of this work. Combing dissolution process with the adsorption process of sulfate is in favor of giving better understanding and explanation about the adsorption behavior of sulfate.
sulfate ions;;C-S-H samples;;dissolution;;adsorption
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