WO2004050578A2

WO2004050578A2 - Building product material

Info

Publication number: WO2004050578A2
Application number: PCT/GB2003/005155
Authority: WO
Inventors: David Joseph Read; Michael Anderson; David Dowler
Original assignee: Staffordshire University
Current assignee: Staffordshire University
Priority date: 2002-11-29
Filing date: 2003-11-26
Publication date: 2004-06-17
Anticipated expiration: 2005-05-29
Also published as: AU2003286269A8; GB0227823D0; EP1565412A2; AU2003286269A1; WO2004050578A3

Abstract

A method of making a building product material. The method comprising mixing particulate recycled glass with a sodium silicate binder, pressing the mixture to form a compact, introducing carbon dioxide gas to cure the binder immediately following pressing, and subsequently firing the compact.

Description

Building Product Material

This invention concerns a method of making a building product material, such a material, a method of making an article from such a building product material, and such an article.

A significant amount of waste glass is now available for recycling. However, difficulties are often encountered in attempting to use this material. For example, contaminants are often present in such a material. These contaminants can include labels caps etc mixed with the waste bottles and jars. With automobile glass products, problems can be encountered with contaminants such as laminating layers. A significant amount of glass from discarded cathode ray tubes is also available but appropriate uses for this are not readily identifiable, particularly due to the high lead barium and strontium content of such glass. Furthermore when such recycled glass has been used in the past to produce products such as tiles, organic binders have invariably been incorporated which in themselves can produce difficulties in terms of toxic emissions during firing, and hence produce increased cost implications.

All percentages given in this specification are by weight.

According to the present invention there is provided a method of making a building product material, the method including forming a compact of a product material, the product material including particulate recycled glass and an inorganic binder, and firing the compact.

The product material preferably includes greater than 95% recycled glass.

The recycled glass may be colour sorted.

The recycled glass may be obtained from one or more of: container glass such as bottles or jars; glass used in cathode ray tubes; vehicle windscreen or window glass; flat plate glass.

The product material may comprise a mixture of one or more different types of recycled glass .

The recycled glass in the product material may have a particle size of less than 4mm.

The recycled glass may be crushed prior to formation of the compact. The recycled glass may be primary milled following crushing. The recycled glass may be secondary milled following primary milling.

Contaminants are preferably removed during and/or after crushing and/or milling.

The recycled glass may be coloured, and may be coloured by the addition of a colouring material which may be in the form of metallic oxides, pigments, or stains.

The recycled glass is preferably mixed with the colouring material prior to mixing with the binder.

The inorganic binder may be cured during or following formation of the compact but prior to firing.

The inorganic binder may comprise sodium silicate, desirably in liquid form. Preferably less than 3.5% inorganic binder is included, and desirably less than 2%. The sodium silicate may be cured by carbon dioxide gas. The carbon dioxide gas is desirably introduced at a pressure of between 1 and 4 Bar, and for a time period of between one and twenty seconds. The pressing pressure is preferably in the range 15.4 to 61.8 MPa.

The compact may be formed by pressing the product material in a mould space. The inorganic binder is preferably cured following pressing or ramming of the compact, but whilst the compact is still in the mould space. A perforated punch, other permeable item, or inlet into the mould space, may be provided through which carbon dioxide is passed to enter the compact.

One or more surfaces of the compact may be profiled. This may be achieved by using any of a profiled punch, a profiled mould, or a profiled former provided in the mould space. Alternatively or in addition, a surface of the compact can be treated prior to firing, and desirably by any of brushing, compressed air or glass blasting.

A different product material may be provided just near a surface of the compact, and this can be achieved by initially filling the mould space with the different material, or finally filling the mould space with the different material.

A surface of the compact may be decorated and this can be achieved by spraying, atomisation, brushing, and/or printing and in particular screen printing.

The compact can be finished following firing, and by any of edge grinding, surface grinding, surface polishing and/or cutting.

Material rejected during formation is preferably recycled in the method.

Firing preferably takes place at a peak temperature of between 600 and 725°c, with a peak temperature dwell of between five and sixty minutes.

The invention also provides a building product material made by a method according to any of the preceding nineteen paragraphs.

The invention further provides a method of making an article, the method comprising using a method according to any of said nineteen paragraphs, with a mould space of a required shape to form the article. The invention further provides an article made by such a method.

The article may comprise a building product, including any of interior/exterior bricks, pavers, blocks, cladding or garden ware.

Embodiments of the present invention will now be described by way of example only, and with reference to the single figure of the accompanying drawing which is a diagrammatic cross sectional view of apparatus usable in a method according to the present invention.

A general example will now be briefly described followed by specific examples.

A compact is formed by pressing a product material formed largely of particulate recycled glass. The compact is formed in the apparatus 10 shown in the accompanying drawing. The apparatus 10 includes a press table 12 which mounts a mould box 14 which defines a pressing space 16. A lower punch 18 is provided in the bottom of the space 16.

In use, product material 20 to be pressed is located in the space 16 above the lower punch 18. An upper punch 22 is located in the spacer 26 on the top of the material 20, and pressing takes place.

Following pressing, the upper punch 22 is raised to the position shown in the drawing and an inflating seal 24 which extends around the perimeter of the upper punch 22 and in this position remains in the space ι6, is inflated. An accelerant which in this instance is carbon dioxide to cure the inorganic binder in the product material 20, is introduced from a supply 26 through a channel 28 into the mould space 16. A sealing valve 30 is provided over the opening of the channel 18 leading into the space 16, to prevent product material entering the channel 28. After a required exposure time to the accelerant gas, injection of the gas is stopped and the seal 24 is deflated. The upper punch 22 is then fully withdrawn from the mould box and the hardened product is ejected from the mould box by the lower punch 18. The inflating seal 24 around the upper punch 22 ensures that the accelerant gas is retained in the mould space 16.

The product material is pressed to a specific pressure depending on the material recipe and type. The material includes a binder which in all of the following examples is sodium silicate in liquid form. The binder is cured by exposing the pressed material to carbon dioxide at specified pressures and time duration, prior to removal from the mould space. The pressure and duration of exposure to carbon dioxide gas depends on the thickness of the material and the material permeability.

The green compact following removal from the mould space 16 is subsequently fired at required parameters for the material. Any reject compacts at any point are returned for recycling in the process.

The product material is initially prepared as follows. The glass is coarsely crushed and contaminants may be removed. The glass is then primary milled and contaminants again may be removed. The glass is then secondary milled and then passed through a series of vibrating screens to provide fractions of required sizes. Oversize glass is returned to secondary milling.

Example One

A colour sorted glass with a particle size of less than 2mm was mixed with 2% liquid sodium silicate and pressed at a pressure of 30.9 MPa in the apparatus loto a thickness of 65mm. Carbon dioxide gas was fed into the space 16 following pressing at 2 Bar pressure for 5 seconds.

The green compact was ejected from the space 16 and fired at a rate of 30°C per minute to a peak temperature of 690°C with a dwell of 30 minutes, and a subsequent cooling rate of 3°C per minute.

This produced a material with the appearance of a buff brick which had water absorption of 9% and a compressive strength of 65 N/mm2.

Example Two

A cathode ray tube glass with a particle size of less than 2mm was mixed with 2% liquid sodium silicate and pressed at a pressure of 61.8 Mpa in the apparatus 10 to a thickness of 50mm and carbon dioxide gas was fed into the space 16 under similar conditions as for example one.

The green compact was ejected from the space 16 and fired at a rate of 30°C per minute to a peak temperature of 630°C with a dwell of 30 minutes, and a subsequent cooling rate of 3°C per minute.

This produced a material with the appearance of a grey paver which had water absorption of 10% and a modulus of rupture of 9.5 MPa.

Example Three

A 70:30 mixture of less than 2mm colour blended container glass and less than imm cathode ray tube glass, was mixed with 2% sodium silicate binder. This was pressed to a thickness of 50mm and carbon dioxide gas was fed into the space 16 under similar conditions as for example one. The green compact formed was fired at similar heating and cooling rates to a peak temperature of 670°C for thirty minutes. This produced a pastel green paver with water absorption of 11% and a modulus of rupture of 10 MPa.

Example Four

A 50:50 mixture of colour sorted (brown and colourless) container glasses was mixed with 3% sodium silicate and pressed at 30.9 MPa to a 10mm thickness. Carbon dioxide was introduced as for example one.

The green compact was fired with 30°C per minute heating and 3°C per minute cooling rates to a peak temperature of 690°C and a dwell at peak temperature of thirty minutes. The material obtained was surface ground and provided a material with an appearance of yellow and white marble, with water absorption of 6.1% and a modulus of rupture of 16.9 MPa.

Example Five

A less than imm colour blended glass was mixed with a blue pigment and then 3% sodium silicate. This was pressed to a thickness of 5mm at 61.8 MPa and carbon dioxide was introduced as in example one. This was fired with 30°C per minute heating and 3°C per minute cooling rates to a peak temperature of 720°C and a peak temperature dwell of 30 minutes. This produced a material with a blue slate appearance, water absorption of 2.3% and a modulus of rupture of 17.8 MPa.

There are thus described methods, and materials produced by such methods, providing a wide range of uses for recycled glass .

This process provides a novel method for producing commercial building products, from these novel glass raw materials.

The process intentionally uses solely glass(es) as the principal product structural material to: i) reduce the amount of binder required, because the glass is non-absorbent; ii) permit firing the product at a low temperature, because glasses begin to soften at relatively low temperature; iii) permit rapid heating of the product during firing, because the glass does not exhibit endothermic reactions during heating (which introduce thermal barriers to heat transfer); iv) reduce the energy required to raise the temperature of the product during firing, because glasses possess relatively low specific heat capacity and no endothermic reactions;

The glass raw material is intentionally milled to a relatively course size to: i) reduce milling energy consumption; ii) reduce wear on components of the milling equipment; iii) reduce the binder component requirement, by minimizing the surface area of the milled glass; iv) produce the required texture and pore size, promoting durability in the final product.

The products are intentionally compacted and then gassed under pressure whilst still in the press, to: i) reduce the magnitude of shrinkage during firing, though elimination of porosity during pressing; ii) reduce the maturing temperature and increase final strength, through elimination of porosity during pressing; iii) reduce the binder requirement, by increasing intimacy of particle contact; iv) simplify the hardening process, by facilitating gassing through existing standard press components; v) allow the rapid hardening of the product before removal from the mould box, to increase press production output.

A process which can totally recycle 100% of its own final product and product from ay stage of the process, as its own glass feedstock.

The use of the inorganic sodium silicate binder provides a number of advantages. Firstly, relatively small proportions of this material are required, and this is a non volatile material which can thus be handled without the requirement for fume extraction and the like. During firing the sodium silicate is incorporated into the material. Therefore this binder and also the materials which have also already been fired at a higher temperature, produce very few emissions during firing. The sodium silicate once cured by carbon dioxide provides sufficient rigidity to the materials to be handled up to and during firing. The low proportions of sodium silicate mean that the materials can be fired immediately following pressing without any requirement for drying or other processing.

The materials formed can be readily pressed into required shapes to make products such as interior or exterior bricks, pavers, blocks, cladding products, or garden ware.

Various other modifications may be made without departing from the scope of the invention. For example other materials and parameters or a mixture of those described above can be used. The surface of the compact can be coloured prior to firing by the application of a suitable colourant using for example conventional techniques of spraying, atomisation, brushing or printing etc., and particularly screen printing. It is to be realised that reject material or product can at any time be recycled in the process. If required the surface of the compact can be processed prior to firing by brushing, compressed air or glass blasting, with any removed material being returned into the process. Following firing the material can be finished by edge or surface grinding, surface polishing or cutting.

Whilst endeavouring 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

1. A method of making a building product material, the method including forming a compact of a product material, the product material including particulate recycled glass and an inorganic binder, and firing the compact.

2. A method according to claim 1, characterised in that the product material includes greater than 95% recycled glass.

3. A method according to any of claims 1 and 2, characterised in that the recycled glass is colour sorted.

4. A method according to any of the preceding claims, characterised in that the recycled glass is obtained from one or more of: container glass such as bottles or jars; glass used in cathode ray tubes; vehicle windscreen or window glass; flat plate glass.

5. A method according to any of the preceding claims, characterised in that the product material includes a mixture of one or more different types of recycled glass.

6. A method according to any of the preceding claims, characterised in that the recycled glass in the product material has a particle size of less than 4mm.

7. A method according to any of the preceding claims, characterised in that the recycled glass is crushed prior to formation of the compact.

8. A method according to claim 7, characterised in that the recycled glass is milled following crushing.

9. A method according to claims 7 or 8, characterised in that contaminants are removed during and/or after crushing and/or milling.

10. A method according to any of the preceding claims, characterised in that the recycled glass is coloured by the addition of a colouring material which is in the form of metallic oxides, pigments, or stains.

11. A method according to claim 10, characterised in that the recycled glass is mixed with the colouring material prior to formation of the compact.

12. A method according to any of the preceding claims, characterised in that the inorganic binder is cured during or following formation of the compact but prior to firing.

13. A method according to any of the preceding claims, characterised in that the inorganic binder comprises sodium silicate.

14. A method according to claim 13, characterised in that the sodium silicate is in liquid form.

15. A method according to claims 13 or 14, characterised in that the sodium silicate is cured by carbon dioxide gas.

16. A method according to claim 15, characterised in that the carbon dioxide gas is introduced at a pressure of between 1 and 4 bar.

17. A method according to claims 15 or 16, characterised in that the carbon dioxide gas is introduced for a time period of between one and twenty seconds.

18. A method according to any of the preceding claims, characterised in that less than 3.5% inorganic binder is included.

19. A method according to claim 18, characterised in that less than 2.5% inorganic binder is included.

20. A method according to any of the preceding claims, characterised in that the pressing pressure to form the compact is in the range 15.4 to 61.8 MPa.

21. A method according to any of the preceding claims, characterised in that the compact is formed by pressing the product material in a mould space.

22. A method according to claim 21 , characterised in that the inorganic binder is cured following pressing of the compact, but whilst the compact is still in the mould space.

23. A method according to claim 15 or any of claims 16 to 22 when dependent on claim 15, characterised in that a perforated punch, other permeable item, or inlet into the mould space, is provided through which carbon dioxide is passed to enter the compact.

24. A method according to any of the preceding claims, characterised in that one or more surfaces of the compact are profiled.

25. A method according to claim 24 when dependent on claim 21 , characterised in that the compact is profiled by using any of, a profiled punch, a profiled mould, or a profiled former provided in the mould space.

26. A method according to any of the preceding claims, characterised in that a surface of the compact is treated prior to firing by any of brushing, compressed air or glass blasting.

27. A method according to claim 21 or any of claims 22 to 26 when dependent on claim 21 , characterised in that a different material is provided just near a surface of the compact by initially filling the mould space with the different material.

28. A method according to claim 21 , or any of claims 22 to 27 when dependent on claim 21 , characterised in that a different material is provided just near a surface of the material by finally filling the mould space with the different material.

29. A method according to any of the preceding claims, characterised in that a surface of the compact is decorated.

30. A method according to claim 29, characterised in that the decoration is achieved by spraying, atomisation, brushing, and/or printing and in particular screen printing.

31. A method according to any of the preceding claims, characterised in that the compact is finished following firing by any of edge grinding, surface grinding, surface polishing and/or cutting.

32. A method according to any of the preceding claims, characterised in that product material rejected during formation is recycled in the method.

33. A method according to any of the preceding claims, characterised in that firing takes place at a peak temperature of between 600 and 1100°c.

34. A method according to any of the preceding claims, characterised in that firing takes place at a peak temperature dwell of between five and sixty minutes.

35. A building product material made by a method according to any of the preceding claims.

36. A method of making an article, the method comprising using a method according to any of claims 1 to 35 with a mould space of a required shape to form the article.

37. An article made by the method of claim 36.

38. An article as claimed in claim 37, characterised in that the article comprises a building product including any of interior/exterior bricks, pavers, blocks, cladding or garden ware.

39. A method of making a building product material, the method being substantially as hereinbefore described.

40. A building product material substantially as hereinbefore described.

41. An article substantially as hereinbefore described.

42. 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.