Mitsubishi Corporation

Mizusawa Kagaku Kogyo Kabushiki Kaisha

Nobuo Omori

Hiroyuki Naito

Yujiro Sugahara

Tokio Okubo

A water-resistant shaped structure of gypsum comprising (A) calcium sulfate dihydrate formed by hardening of calcium sulfate capable of hydration reaction, (B) a calcium type filler for filling up spaces among crystalline particles of said calcium sulfate dihydrate and (C) a water-insoluble or hardly water-soluble salt of a polybasic acid having a second stage dissociation constant of 10.sup.-3 to 10.sup.-10, especially 10.sup.-4 to 10.sup.-9, as measured at 25.degree. C., said calcium type filler (B) being at least one calcium compound selected from the group consisting of calcium hydroxide, calcium carbonate, calcium silicate, calcium aluminosilicate, and non-water-hardenable anhydrous gypsum and partially hydrated products thereof, wherein the amount of the calcium type filler (B) and the water-insoluble or hardly water-soluble calcium salt (C) is 15 to 75% based on the total amount of the components (A), (B) and (C) as calculated as calcium, the amount of the water-insoluble or hardly water-soluble calcium salt (C) is 0.1 to 30% based on the total amount of the components (A), (B) and (C) as calculated as calcium, the water-insoluble or hardly water-soluble calcium salt (C) is distributed predominantly in the surface portion of the shaped structure, and said surface portion has a pore volume smaller than 0.50 ml/g in pores having a radius in the range of 75 to 75000 A and a pore volume smaller than 0.20 ml/g in pores having a radius in the range of 4000 to 10000 A.

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Tsuruoka, Japan

Nobuo Omori