Method for In-Situ Manufacture of a Lightweight Fly Ash Based Aggregate

• US 20120167804A1
• Filed: 09/14/2011
• Published: 07/05/2012
• Est. Priority Date: 12/30/2010
• Status: Active Grant

• Current Assignee: United States Gypsum Company (GEBR Knauf Verwaltungsgesellschaft KG)
• Original Assignee: United States Gypsum Company (GEBR Knauf Verwaltungsgesellschaft KG)
• Inventors: PEREZ-PENA, Marianela
• Granted Patent: US 8,795,429 B2
• Time in Patent Office: Days
• US Class Current: 106/677
• CPC Class Codes: C04B 18/021 agglomerated by a mineral binder, e.g. cement
• CPC Class Codes: C04B 18/027 Lightweight materials
• CPC Class Codes: C04B 18/08 Flue dust , i.e. fly ash
• CPC Class Codes: C04B 18/146 Silica fume
• CPC Class Codes: C04B 22/143 Calcium-sulfate
• CPC Class Codes: C04B 24/06 containing hydroxy groups
• CPC Class Codes: C04B 38/10 by using foaming agents C04B38/02 takes precedenceor by using mechanical means, e.g. adding preformed foam
• CPC Class Codes: C04B 7/02 Portland cement
• CPC Class Codes: Y02W 30/91 Use of waste materials as fillers for mortars or concrete

Abstract

A method of making a rapid setting lightweight homogeneous foamed fly ash based cementitious aggregate composition with improved compressive strength for products such as panels is disclosed. The method mixes fly ash, alkali metal salt of citric acid, foaming agent for entraining air, optional foam stabilizing agent, a calcium sulfate such as stucco or gypsum, and water. Compositions are also disclosed which include mixtures of fly ash, particularly Class C fly ash alone or in mixtures with Class F fly ash, alkali metal salts of citric acid, foaming agents, a calcium sulfate such as calcium sulfate dihydrate or hemihydrate and an optional portland cement.

Claims

1. A method of providing a lightweight cementitious mixture for making aggregate particles comprising:

form a mixture by mixing

water,

cementitious reactive powder comprising fly ash and a calcium sulfate selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof,

an alkali metal salt of citric acid selected from the group consisting of sodium citrate, potassium citrate and mixtures thereof,

a foaming agent, and

in situ forming aggregate particles comprising the fly ash and calcium sulfate in the mixture and a crystalline form of hydration products of fly ash and calcium sulfate which are also formed in situ and are interspersed within and between the aggregate particle to bind the aggregate particles.

2. The method of claim 1, wherein the wet density of the resulting mixture is about 40 to 65 pounds per cubic foot.

3. The method of claim 1, wherein the fly ash in the reactive powder comprises 88.5 to 100% class C fly ash, and wherein the mixture has a set time of about 4 to 6 minutes.

4. The method of claim 1, wherein the calcium sulfate is calcium sulfate dihydrate.

5. The method of claim 1, wherein the cementitious reactive powder is selected from the group consisting of class C fly ash and calcium sulfate hemihydrate or stucco, mixtures of class C and class F fly ash, calcium sulfate hemihydrate or stucco and/or Portland cement and mixtures of class F fly ash with class C fly ash and/or Portland cement and calcium sulfate hemihydrate or stucco.

6. The method of claim 1, wherein the wet density of the resulting mixture is about 46 to 51 pounds per cubic foot.

7. The method of claim 1, wherein the alkali metal salt of citric acid is in an amount of about 1.5 to 6 wt. % based on the weight of the cementitious reactive powder.

8. The method of claim 1, wherein the cementitious reactive powder comprises 60 to 95 wt. % fly ash and 5 to 40 wt. % calcium sulfate selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof.

9. The method of claim 1, further including setting the cementitious mixture comprising the aggregate particles in situ and recovering the aggregate particles from the set cementitious mixture by a suitable recovery process to separate the aggregate particles from the set mixture.

10. The method of claim 1, wherein the reactive powder further comprises silica fume and no Portland cement.

11. The method of claim 1, wherein the cementitious reactive powder and water are present in a weight ratio of about 0.200 to 0.287:

1 part by weight water to reactive powder.

12. The method of claim 1, wherein the cementitious reactive powder and water are present in a weight ratio of about 0.22-0.287:

1 part by weight water to reactive powder.

13. A composition of a lightweight cementitious mixture for forming an aggregate comprising a mixture of:

a cementitious reactive powder comprising 60 to 95 wt. % fly ash. and a calcium sulfate selected from the group consisting of calcium sulfate dihydrate, calcium sulfate hemihydrate, and mixtures thereof;

an alkali metal salt of citric acid, as an accelerator for the reactive powder;

a foaming agent; and

water,

wherein aggregate particles comprising the fly ash and calcium sulfate are formed in situ in the mixture with a crystalline form of hydration products, of fly ash and calcium sulfate which are also formed in situ and interspersed within and between the aggregate particle to bind the aggregate particles, and

wherein the ratio of water to cementitious reactive powder solids in the mixture is about 0.17 to 0.35;

1.

14. The composition of claim 13, wherein the reactive powder comprises fly ash comprising 88.5 to 100 wt. % Class C fly ash, calcium sulfate, optional silica fume and no Portland cement.

15. The composition of claim 13, wherein the mixture comprises about 1.5 to 6.0 wt. %, based upon the weight of cementitious powder, of at least one alkali metal salt of citric acid selected from the group consisting of sodium citrates, potassium citrates and mixtures thereof.

16. The composition of claim 13, wherein the cementitious reactive powder is selected from the group consisting of class C fly ash and calcium sulfate hemihydrate or stucco, mixtures of class C and class F fly ash and calcium sulfate hemihydrate or stucco;

and mixtures of class F fly ash with class C fly ash and/or Portland cement and calcium sulfate hemihydrate stucco.

17. The composition of claim 13, wherein the cementitious reactive powder mixture comprises 30-46 wt % class F fly ash and 54-70 wt % class C fly ash and no portland cement.

18. The composition of claim 13, wherein the cementitious reactive powder comprises 46 to 60 wt. % Class F fly ash, 10 to 32 wt. % Class C fly ash, and 10-29 wt % calcium sulfate hemihydrate or stucco and wherein the weight ratio of water to the total weight of fly ash and calcium sulphate is less than about 0.33 to 0.37.

19. A composition comprising a lightweight cementitious aggregate, said composition comprising an essentially homogeneous mixture of spherical shaped particles of fly ash based cementitious material and a calcium sulfate having a diameter of less than about 1 mm and a crystalline form of hydration products, of said fly ash and calcium sulfate which are also formed and interspersed in and between the particles and binding said particles together in the aggregate.

20. The composition of claim 19 further comprising a binder of cementitious material, said aggregate distributed within the cementitious material.