Abstract
The initial setting time of Portland cement containing sodium gluconate is quickly than that of cement without sodium gluconate. Such a behavior of early hydration is due to an action of the formation of ettringite. The formation process of ettringite from hydration of synthesized C3A and CaSO4⋅2H2O with the addition of sodium gluconate was investigated from the changes in composition of liquid phase within several minutes with standing time. The results are summarized as follows. Calcium and sulfate contents in liquid phase increase by the addition of sodium gluconate, and the solubility of CaSO4⋅2H2O is also enlarged. The time shown high concentration of calcium and sulfate contents is longer than that without additives. It is resulted to form Ca complex with gluconic acid and Ca2+ in liquid phase. Ettringite was produced in this period and unreacted CaSO4⋅2H2O was disappered. The concentration of calcium content in liquid phase immediately increased after contact with water, and decreased after their, That is, the phenomenon of deposition happens rapidly after the dissolution. After the formation of Ca complex, gluconic acid was adsorbed on the surface of unhydrated particles. CaSO4⋅2H2O depressed the adsorption of gluconic acid on C3A.
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