Denki Kagaku Kogyo Kabushiki Kaisha

Ryoetsu Yoshino

Takayuki Higuchi

Minoru Morioka

Taiichiro Mori

Hideaki Ishida

Tsutomu Kida

The invention provides a cement admixture that improves the ability of concrete to bring about high initial strength, works in favor of enhancing the effect on hexavalent chromium reductions, and is less likely to decrease in the effect on hexavalent chromium reductions even upon storage as well as a method for reducing hexavalent chromium. The invention is embodied as (1) A cement admixture, characterized by comprising an expanding material containing free lime, a hydraulic compound and calcium sulfate anhydrite, and a tin sulfate-containing substance; (2) The cement admixture according to (1), characterized in that the tin sulfate-containing substance is contained in an amount of 0.2 to 8 parts by mass&#x2014;as calculated on a tin sulfate basis&#x2014;in a total of 100 parts by mass of the expanding material and the tin sulfate-containing substance; (3) The cement admixture according to (1) or (2), characterized in that the expanding material has been treated with carbon dioxide gas to form calcium carbonate therein; (4) The cement admixture according to any one of (1) to (3), characterized in that the expanding material has been surface treated with a shrinkage reducer; (5) A cement composition, characterized by containing cement, and the cement admixture according to any one of (1) to (4); and (6) A method for reducing hexavalent chromium, characterized by use of the cement composition according to (5).

Cement admixture and cement composition

The invention provides an expansive material that allows for large expansion of concrete at a material age of 2 to 7 days after pouring and permits concrete to have higher initial compressive strength and makes sure good storage stability, and a process for preparing that expansive material. The invention provides an expansive material and a process for preparing that expansive material, characterized in that clinker or pulverized clinker containing free lime, a hydraulic compound and calcium sulfate anhydrite is heat treated in a carbon dioxide gas atmosphere to form calcium carbonate in it. Preferably, the expansive material contains a particle in which the free lime, hydraulic compound, calcium sulfate anhydrite and calcium carbonate are all present; the content of calcium carbonate is 0.5 to 10% by mass; and the expansive material has a Blaine's specific surface area of 1,500 to 90,000 cm/g. The expansive material is blended with cement into a cement composition. The preparation conditions are preferably a carbon dioxide gas flow rate of 0.01 to 0.1 L/min. and a temperature of 200 to 800&#xb0; C., under which conditions there is calcium carbonate formed.

Growing community of inventors

Itoigawa, Japan

Ryoetsu Yoshino