Casting of articles from compositions containing calcined gypsum and Portland cement

• US 4,202,857 A
• Filed: 07/18/1978
• Issued: 05/13/1980
• Est. Priority Date: 07/19/1977
• Status: Expired due to Term

• Current Assignee: Pitun-Unicrete Limited
• Original Assignee: Pitun-Unicrete Limited
• Inventors: Lowe, James N.
• Primary Examiner(s): Arnold, Donald J.
• Application Number:
  US05/925,670
• Time in Patent Office: 665 Days
• Field of Search: 106/89, 106/90, 106/111, 264/333, 264/86, 264/DIG. 43
• US Class Current: 264/333
• CPC Class Codes: C04B 22/06 Oxides, Hydroxides C04B22/0013 takes precedence
• CPC Class Codes: C04B 22/10 containing carbon in the anion
• CPC Class Codes: C04B 24/26 obtained by reactions only involving carbon-to-carbon unsaturated bonds C04B24/243 takes precedence
• CPC Class Codes: C04B 28/14 containing calcium sulfate cements gypsum-paper plates E04C
• CPC Class Codes: C04B 40/00 Processes, in general, for influencing or modifying the properties of mortars, concrete or artificial stone compositions, e.g. their setting or hardening ability active ingredients C04B22/00 - C04B24/00; hardening of a well-defined composition C04B26/00 - C04B28/00; making porous, cellular or lightening C04B38/00; mechanical aspects B28, e.g. conditioning the materials prior to shaping B28B17/02
• CPC Class Codes: C04B 40/02 Selection of the hardening environment
• CPC Class Codes: C04B 40/0263 Hardening promoted by a rise in temperature C04B40/024 takes precedence
• CPC Class Codes: C04B 7/02 Portland cement
• CPC Class Codes: Y10S 264/43 Processes of curing clay and concrete materials

Abstract

An article is cast from a composition comprising a binding agent containing, by weight, from 90% to 10% calcined gypsum and from 10% to 90% Portland cement mixed with water to produce a fluid mixture which is caused to flow into a mould or other supporting device and is there allowed to set. To increase the durability of the cast article in the presence of moisture, sodium carbonate in an amount up to 5% by weight of the dry weight of the cement is added to the composition. The sodium carbonate is preferably present in an amount between 0.1% and 0.5% of the dry weight of the cement and the composition preferably also contains an acrylic resin emulsion in an amount from 0.25% to 4% of the dry weight of the gypsum and cement in the composition and a pigment such as iron oxide, titanium oxide or cobalt oxide in an amount from 0.25% to 4% by weight of the dry weight of the gypsum and cement in the composition.

Claims

1. In a method of casting an article comprising the steps of mixing a composition comprising an hydraulic binding agent consisting essentially of, by weight, from 90% to 10% calcined gypsum, from 10% to 90% Portland cement and from 0% to 15% Pozzalana cement with water to produce a fluid mixture, causing said fluid mixture to flow into a supporting device, and allowing said mixture to set in said supporting device, the improvement wherein said composition further contains sodium carbonate in an amount of from about 0.1% to about 5% by weight of the dry weight of said cement in said composition, said sodium carbonate reducing local expansion or general expansion of said mixture with a consequent loss in compressive strength upon setting said mixture.

4. A method as claimed in claim 1, wherein said cement is sulphate-resisting Portland cement.

5. A method as claimed in claim 1, wherein said sodium carbonate content of said composition is between about 0.1% and 1.0% of the dry weight of said cement.

6. A method as claimed in claim 1, in which said sodium carbonate content of said composition is between about 0.1% and about 0.5% of the dry weight of said cement.

7. A method as claimed in claim 1, in which said mixture also contains an acrylic resin emulsion.

8. A method as claimed in claim 7, wherein said acrylic resin emulsion is present in an amount from about 0.25% to about 4% by weight of the dry weight of said gypsum and said cement in said composition.

9. A method as claimed in claim 7, wherein said acrylic resin emulsion is present in an amount of from about 0.5% to about 1.5% by weight of the dry weight of said gypsum and said cement in said composition.

10. A method as claimed in claim 1, in which said composition further contains a pigment selected from the group consisting of iron oxide, titanium oxide and cobalt oxide in an amount of from about 0.25% to about 4% by weight of the dry weight of said gypsum and said cement in said composition.

11. A method as claimed in claim 10, wherein said pigment is present in an amount of from about 0.5% to about 1.5% by weight of the dry weight of said gypsum and said cement in said composition.

12. A method as claimed in claim 1, wherein said binding agent contains, by weight, from about 50% to about 40% calcined gypsum and from about 50% to about 60% Portland cement.

2. In a method of casting an article comprising the steps of:

a. mixing water with a composition comprising a binding agent consisting essentially of, by weight, from 90% to 10% calcined gypsum and from 10 to 90% Portland cement, to produce a fluid mixture, at least one of said composition and said water being heated whereby said mixture has a temperature of from 70°

to 130°

F.;

b. pouring said fluid mixture into a supporting device;

c. allowing a reaction between said calcined gypsum and said water in said mixture to cause said mixture to set in said supporting device, said reaction producing heat which causes the temperature of said mixture to begin to rise;

d. removing said mixture from said supporting device after said mixture has set sufficiently to be self supporting and thus form said cast article;

e. controlling the dissipation of both heat and moisture from said set mixture forming said cast article whereby the temperature of said set mixture rises to from 90°

to 180°

F.;

f. maintaining the temperature and moisture content of said set mixture for a period of at least two hours to cure said cement, the improvement comprising the additional step of;

g. including sodium carbonate in an amount of from about 0.1% up to 5% by weight of the dry weight of said Portland cement in said composition, said sodium carbonate reducing local expansion or general expansion of said mixture with the consequent loss of compressive strength upon setting said mixture.

3. In a method of casting an article comprising the steps of mixing a composition comprising a binding agent consisting essentially of, by weight, from 90% to 10% calcined gypsum, from 10% to 90% Portland cement with water to produce a fluid mixture, causing said fluid mixture to flow into a supporting device, and allowing said mixture to set in said supporting device, wherein during the set of the mixture the mixture is contacted with water which causes a reaction between the calcined gypsum and the Portland cement to result in expansion of the mixture and a local or general expansion of the mixture with a loss in compressive strength thereof upon setting, the setting involving a period of time, wherein said expansion would occur without sodium carbonate, the improvement wherein said composition further contains sodium carbonate in an amount of about 0.1% up to about 5% by weight of the dry weight of said cement in said composition, said sodium carbonate reducing the local expansion or general expansion of said mixture whereby the consequent loss in compressive strength upon setting said mixture is reduced.