| 摘要 |
PROBLEM TO BE SOLVED: To prepare a cement admixture which can impart a sufficient curing time and an excellent strength property to a cement composition, by formulating an inorganic sulfate, a retarder and specific calcium aluminate having specific Li2O and SiO2 contents and a specified CaO/Al2O3 molar ratio. SOLUTION: This cement admixture comprises an inorganic sulfate, a retarder and specific calcium aluminate having a Li2O content of from 0.1 to <7 wt.%, a SiO2 content of 0.5 to 7 wt.% and a CaO/Al2O3 molar ratio of 1.5 to 2.0. The calcium aluminate is obtained by thermally treating a mixture of a CaO raw material, an Al2O3 raw material, a Li2O raw mate, a SiO2 raw material, and the like, has a Blaine specific surface area of preferably about 1,500 to 8,000 cm2/g and is contained in an amount of 25 to 85 pts.wt. per 100 pts.wt. of the cement admixture. The inorganic sulfate salt includes anhydrous gypsum, and is contained in an amount of 10 to 70 pts.wt. per 100 pts.wt. of the cement admixture. The retarder includes citric acid, and is contained in an amount of 0.5 to 10 pts.wt. per 100 pts.wt. of the cement admixture.
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