WO2007083120A2

WO2007083120A2 - Building products

Info

Publication number: WO2007083120A2
Application number: PCT/GB2007/000147
Authority: WO
Inventors: Andrew John Briggs
Original assignee: Akristos Limited
Priority date: 2006-01-18
Filing date: 2007-01-18
Publication date: 2007-07-26
Also published as: WO2007083120A9; GB0600941D0; GB2434365A; WO2007083120A3

Abstract

A building product comprising clay mixed with a processed gypsum source product (PGSP) to provide a formed composite component, the product including up to 95% of PGSP crushed to provide a desired particle size and/or limit for fibre length when mixed with the clay.

Description

Building Products

The present invention relates to building products and more particularly to building products based upon clay with a significant recycled material content.

It will be understood that clays are used in a wide range of products and components including those in relation to building construction. It will be appreciated with regard to building products that cost it is important. Furthermore, it is known that raw material industries and allied trades consume significant amounts of primary energy in order to create such building products. In such circumstances, there is a desire as well as an objective to recycle core wastes from gypsum product manufacture, construction and demolition. It will be appreciated that an air dried or unfired or fired clay based product which includes re-cycled material which could be used instead of conventional building products would achieve a number of advantages including energy savings as well as the re-use of some wastes from other products.

One source of potentially troublesome waste products is calcium sulphate found within plasterboard and other gypsum based products. It will be understood that wastes from these products enter landfill sites, but the relatively high sulphate level within gypsum waste products can necessitate special treatment or confinement with regard to disposal and containment of these wastes.

Although utilisation of waste products is desirable, it should be appreciated that the eventual building product should have sufficient strength and inertness for acceptability. In such circumstances unfired clay masonry products, although having clear advantages with regard to lower energy consumption, have in the past been considered to have poor product performance characteristics. Furthermore with fired clay bricks containing calcium compounds there is always some concern that they may convert to calcium oxide during the firing process. This may hydrate to produce Calcium Hydroxide (Ca(OH)₂), which may cause lime blowing within the finished bricks whilst on stock or in service. With calcium sulphate (gypsum) there is decomposition during elevated firing temperatures to form sulphur dioxide as a gas leaving calcium oxide in a clay body at temperatures between 1000- 1200⁰C. If these calcium oxide particles are greater than one millimetre in size then, as indicated, there is potential for detrimental lime blows once the bricks have cooled and re-absorbed moisture from the environment. This can also be a problem when bonding blocks or bricks within conventional mortars.

In view of the above plasterboard and gypsum waste products have generally not been considered suitable for use with clay in order to form either a fired or unfired clay building product. The building products could comprise bricks, blocks, tiles or boards.

Fig. 1 illustrates graphically the different phases of gypsum dependent upon temperature and environmental conditions. Thus, in the Alpha and Beta phase respectively under steam and atmospheric pressure conditions the gypsum moves through a hemi hydrate to an anhydrite phase but under steam pressure at a temperature of 25O⁰C the Alpha phase becomes an anhydrite Il whilst the temperature must be elevated to 400⁰C in order for the Beta phase under atmospheric conditions to similarly became an anhydrite II.

The anhydrite Il must reach a temperature in excess of 250⁰C in a steam environment for the gypsum to become an anhydrite I.

Water will combine with Hemi-hydrate (CaSO₄-V₂H₂O) or anhydrite (CaSO₄) to form gypsum (CaSO₄.2H₂O). The different transition states of gypsum combined with clay within the building unit dictate the performance characteristics of the resulting building unit.

In accordance with the present invention there is provided a building product comprising clay mixed with a processed gypsum source product

(PGSP) to provide a formed composite component, the product including up to 95% of PGSP crushed to provide a desired particle size and/or limit for fibre length when mixed with the clay.

The PGSP used as the raw material feedstock for the manufacture of a building unit can be introduced in a number of forms (figure 2):

(i) the raw state,

(ii) dried up to 100⁰C,

(iii) dried between 100-150⁰C,

(iii) dried at or above150°C (to form the hemi-hydrate form of gypsum),

(iv) dried at 200⁰C (to form the anhydrite form of gypsum).

The most probable feedstock will be a raw or partially dried (sub 100⁰C) recovered gypsum or plasterboard product.

The plasterboard backing paper, used to contain the gypsum within the board structure, can either be removed or included within the PGSP prior to being utilised as a feedstock for the production of a building unit. Including the paper will result in fibres within a dried building unit that can enhance strength and fixing characteristics.

Typically, the limit to particle size of PGSP is less than 5mm.

Additionally, the limit to fibre length is less than 25mm when used in a dried clay block. Normally, up to 20% of the product weight is PGSP for the fired product, but between 50-80% PSGP to be used in the dried block/brick product.

Generally, the product also includes other additives such as glass, sawdust, straw, sugar solution, lignosulphonat.es, cellulose, frits and other wastes such as ceramic glazes.

The use of clay with the PGSP facilitates the forming of a composite product. Generally, the building product is formed in a mould, by stiff extrusion or plastic pressed.

Also in accordance with the present invention there is provided a method of forming a building product comprising:

a) Taking waste or recovered gypsum product and processing that waste or recovered gypsum product to provide a processed gypsum product having a desired particle and/or resultant fibre length. The PGSP can be in the form of raw, dried (~100°C),

100-150⁰C, 150⁰C or +200⁰C to produce gypsum in a number of states (Figure 2);

b) Normally, contaminants are removed from the waste or recovered gypsum product when processed to provide the processed gypsum product. Typically contaminants include metal fixtures and/or paper normally as presented in the waste or recovered gypsum product. Alternatively, certain contaminants or a proportion of contaminants are retained within the processed gypsum source product. c) Blending the processed gypsum product with clay or marl up to 20% by weight of the PGSP in the fired product or 50-80% in the dried block/brick product. This can be achieved by bucket blending with the raw clay feedstock using a front-end loading machine or by using controlled box-feeders or silo facilities and introduced to the un-ground or ground clay feedstock. Grinding of the clay and/or PGSP is then carried out using a dry-pan, wet- pan or hammer mills. Mixing is then carried out using single shafted or double shafted mixers at which point water is added to the process to form the building unit;

d) Adding water to form a composite of a desired consistency and plasticity for product formation;

e) Forming of the product either via extrusion, dry-dust pressing, soft-mud pressing, etc. Typically, the mould / die is sized to accommodate for shrinkage to a desired final product size.

f) Drying of the product (Figure 2) for a predetermined period will produce a building unit containing gypsum in a number of different states depending upon the drying temperature used, either:

(i) No drying - i.e. the product can be used in the un-dried ("green") state,

(ii) Nascent/ambient air drying,

(iii) Forced drying at or below 100⁰C,

(iv) Forced drying between 100⁰C - 15O⁰C,

(v) Forced drying at 15O⁰C (to produce the hemi-hydrate form of gypsum within the building unit),

(vi) Forced drying at or above 200⁰C (to produce the anhydrite form of gypsum within the building unit). Possibly, the method includes specifying the PGSP content to produce a colour change in the building product. Possibly, with a red clay, marl or shale adding 25-50% by weight of PGSP at a firing temperature of 1000-1200⁰C in oxidising conditions produces a buff or yellow building product.

Further in accordance with aspects of the present invention there is provided a mortar for unfired building products, the mortar including sodium silicate to inhibit delamination of the building product in use through rehydration and drying cycling.

Generally, the building product includes PGSP.

Typically, the mortar includes ball clay, china clay and silica flour.

A dried building unit will then be produced which can be packaged ready for despatch. The drying temperature of the product and the nature of the PGSP will influence the performance characteristics of the building unit (e.g. compressive strength). For, example a building unit containing hemi-hydrate (CaSO₄.¹/₂H2O) will revert to gypsum (CaSO₄) by the addition of water (either by natural absorption from the atmosphere or forced steam/moisture addition as part of the manufacturing process (see below). The crystal growth associated with the formation of gypsum (CaSO₄) forms a strong bond with the clay matrix improving the building unit physical properties (e.g. compressive strength).

Introduction of moisture / steam to the building units will enable hemi-hydrate to gypsum conversion. A dried and "cured" building unit will then be produced which can be packaged ready for despatch.

h) If a fired product is to be produced, firing of the product in a kiln to an appropriate temperature is required in order to develop the required ceramic properties. This would typically be between 1000-1200⁰C. The PGSP feedstock may require fine-grinding (<1 mm) to reduce the potential of "lime-blowing" within the final fired product, should the gypsum (CaSO₄) decompose during firing to produce calcium oxide (CaO) which subsequently re- hydrates (with an associated expansion) to form Ca(OH)₂.

A fired building unit is then produced which can be packaged ready for despatch.

As indicated above, the gypsum source material in accordance with aspects of the present invention will typically be taken from recovered plasterboard but it will also be understood that gypsum source material can be achieved by utilising recycled gypsum from other industrial processes such as casting moulds used in slip cast ceramic product production. It will also be understood that virgin gypsum can also be used as a source product.

By the present method and products plasterboard and other waste gypsum based products, which may be difficult to conveniently place in landfill sites, can be advantageously recycled.

There are a number of potential, advantages in the use of gypsum/plasterboard in the manufacture of a construction blocks:-

• Improved compressive strength

• Improved flexural strength • Improved fixing strength - for wall plugs

• Improved fire resistance

• Improved thermal properties

• Improved "chasing" properties to allow recessed cabling/pipework • Resistance to water deterioration

• Moisture and odour absorption

Enhanced strength characteristics have been shown by the use of plasterboard when added to clay - this is due to a number of factors:

• Lignosulphonate within the plasterboard - enhances the strength of a clay.

• Calcium cations (from the gypsum) will substitute sodium cations within the clay (through a process known as cation exchange capacity - CEC) to flocculate the clay particles to produce a group of small grains - thereby improving the strength development.

• High temperature drying (at 140 - 160⁰C) using waste heat form the brick making process, may also enhance dried strength. At these temperatures (which are slightly higher than used to dry clay bricks prior to firing) the gypsum will decompose to form the hemi-hydrate

(CaSO₄ V₂ H₂O), which will subsequently re-hydrate - either naturally or through an accelerated process. CaSO₄ V₂ H₂O crystal growth then occurs which will enhance bonding and strength development.

It will be understood that the particular proportion of processed gypsum based recycled products used in the clay building product will be dependent upon particular performance criteria. Furthermore the particle size, addition rates and synergistic effects of adding the processed gypsum product to the cocktail of other additives which may include glass cullet and glass fibres can be varied as required by desired properties. In addition to processed gypsum taken from recovered plasterboard or other sources, it will be appreciated that present building products whether they be dry or fired, can contain other additives including glass, sawdust, straw, glucose by-products, lignosulphonates, cellulose, etc.

A further advantage with regard to addition of PGSP to a base clay, marl or shale body is that when the product produced is fired there is an alteration in clay colour. For example, with regard to a red firing clay, marl or shale by addition of 25-50% by weight PGSP when fired that clay, marl or shale turns to a buff or yellow colour at firing temperatures between 1000 and 1200⁰C in oxidising conditions within the kiln, that is to say in relatively normal atmospheres. Although it is known to produce yellow fired colour by addition of calcium carbonate in the form of powdered chalk or limestone in order to render red firing clay to buff or yellow colours it is necessary to use reducing conditions, that is to say low oxygen in the kiln in order to achieve the colour change. This may be inconvenient. In such circumstances aspects of the present invention allow adjustment of the building product colour by appropriate choice of firing temperatures and PGSP content.

With regard to unfired clay blocks, and in particular those incorporating PGSP, bonding in order to form structures can be achieved using natural clay mortars which may have a high moisture content. A high moisture content within the mortar will tend to rehydrate unfired clay blocks such that there can be delamination of the block during subsequent in use or storage drying or frost cycling leading to degradation of the block. By use of a sodium silicon based mortar such problems can be avoided. These sodium silicon based mortars generally incorporate a ball clay, a china clay and a silica flour. These mortars by their nature include a reduced moisture content and therefore tend to lead to the lower delamination problems with unfired clay blocks. Typical sodium silica based mortars are used for high temperature refractory usages in view of their low moisture content. The particular grade of sodium silica based mortar used will depend upon the type of the unfired clay blocks and whether those blocks incorporate PGSP. Generally any reduction in moisture content will be beneficial with respect to unfired clay blocks bonded together using mortar.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims:-

1. A building product comprising clay mixed with a processed gypsum source product (PGSP) to provide a formed composite component, the

5 product including up to 95% of PGSP crushed to provide a desired particle size and/or limit for fibre length when mixed with the clay.

2. A product as claimed in claim 1 wherein the limit to particle size of PGSP is less than 5mm.

I O

3. A product as claimed in claim 1 or claim 2 wherein the limit to fibre length is less than 25mm when used in a dried clay block.

4. A product as claimed in any of claims 1 , 2 or 3 wherein up to 20% of 15 the product weight is PGSP for the fired product, but between 50-80% PSGP to be used in the dried block/brick product.

5. A product as claimed in any preceding claim wherein the product includes glass and/or sawdust and/or straw and/or sugar solution and/or

20 lignosulphonates and/or cellulose and/or frits and/or other wastes such as ceramic glazes.

6. A product as claimed in any preceding claim wherein the PGSP is obtained from recovered plasterboard and/or cast mouldings used in slip cast

25 ceramic product production.

7. A product as claimed in any preceding claim wherein the product incorporates virgin gypsum.

30 8. A building product substantially as hereinbefore described with reference to the accompanying drawings.

9. A method of forming a building product comprising: (a) Taking waste or recovered gypsum product and processing that waste or recovered gypsum product to provide a processed gypsum product having a desired particle and/or resultant fibre length.

(b) Contaminants are removed from the waste or recovered gypsum product when processed to provide the processed gypsum product.

(c) Blending the processed gypsum product with clay or marl up to

20% by weight of the PGSP in the fired product or 50-80% in the dried block/brick product.

(d) Adding water to form a composite of a desired consistency and plasticity for product formation.

(e) Forming of the product either via extrusion, dry-dust pressing, soft-mud pressing, etc.

(f) Drying of the product for a predetermined period to produce a building product containing gypsum in a number of different states depending upon the drying temperature used, either:

(i) No drying - i.e. the product can be used in the un-dried ("green") state,

(ii) Nascent/ambient air drying,

(iii) Forced drying at or below 100⁰C,

(iv) Forced drying between 100⁰C - 15O⁰C,

(vi) Forced drying at or above 200⁰C (to produce the anhydrite form of gypsum within the building unit).

10. A method as claimed in claim 9 wherein the PGSP used as the raw material feedstock for the manufacture of a building unit can be introduced in a number of forms including:

(i) the raw state,

(ii) dried up to 100⁰C, (iii) dried between 100-150⁰C,

(iii) dried at or above150°C (to form the hemi-hydrate form of gypsum), (iv) dried at 200⁰C (to form the anhydrite form of gypsum).

11. A method as claimed in claim 10 wherein the feedstock is principally provided by a raw or partially dried (sub 100⁰C) recovered gypsum or plasterboard product.

12. A method as claimed in claim 11 wherein the plasterboard backing paper, used to contain the gypsum within the board structure, can either be removed or included within the PGSP prior to being utilised as a feedstock for the production of a building unit.

13. A method as claimed in any of claims 9 to 12 wherein the limit to particle size of PGSP is less than 5mm.

14. A method as claimed in any of claims 9 to 13 wherein the limit to fibre length is less than 25mm when used in a dried clay block.

15. A method as claimed in any of claims 9 to 14 wherein in order to form the fired product up to 20% of the product is PGSP.

16. A method as claimed in any of claims 9 to 14 wherein order to produce a dried block/brick product 50-80% is PGSP.

17. A method as claimed in any of claims 9 to 16 wherein the product includes glass and/or sawdust and/or straw and/or sugar solution and/or lignosulphonates and/or cellulose and/or frits and/or other wastes such as ceramic glazes.

18. A method as claimed in any of claims 9 to 17 wherein the building product is formed in a mould, by stiff extrusion or plastic pressing.

19. A method as claimed in any of claims 9 to 18 wherein the contaminates include metal fixtures and/or paper normally as presented in the waste or recovered gypsum product.

20. A method as claimed in any of claims 9 to 19 wherein certain contaminates or a proportion of contaminates are retained within the process gypsum source product.

21. A method as claimed in any of claims 9 to 20 wherein blending of the process gypsum product is provided by bucket blending using a front end loading machine or by using controlled box fillers or silo facilities.

22. A method as claimed in any of claims 9 to 21 wherein grinding of the clay is carried out using a dry pan, wet pan or hammer mills.

23. A method as claimed in any of claims 9 to 22 wherein mixing is carried out using single shafted or double shafted mixers at which point water is added to the process to form the building unit.

24. A method as claimed in claim 18 and any claims dependent thereon wherein the mould or die is sized to accommodate for shrinkage to a desired final product size.

26. A method as in any of claims 9 to 25 wherein the method includes specifying the PGSP content to produce a colour change in the building product.

27. A method as in claim 26 wherein a red clay, marl or shale by adding 25-50% by weight of PGSP at a firing temperature of 1000-1200⁰C in oxidising conditions produces a buff or yellow building product.

28. A method of forming a building product substantially as hereinbefore described with reference to the accompanying drawings.

29. A mortar for unfired building products, the mortar including sodium silicate to inhibit delamination of the building product in use through rehydration and drying cycling.

30. A mortar as claimed in claim 29, wherein the building product includes PGSP.

31. A mortar as claimed in claim 29 or claim 30 wherein the mortar includes ball clay, china clay and silica flour.

32. A mortar substantially as hereinbefore described.

33. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.