GB2441313A

GB2441313A - Method and plant for forming a concrete building product

Info

Publication number: GB2441313A
Application number: GB0617284A
Authority: GB
Inventors: Claude Stock
Original assignee: Lafarge Roofing Technical Centers Ltd
Current assignee: Lafarge Roofing Technical Centers Ltd
Priority date: 2006-09-01
Filing date: 2006-09-01
Publication date: 2008-03-05
Also published as: GB0617284D0; WO2008025984A1; WO2008025984B1

Abstract

A cementitious composition containing at least water, aggregate and cement, is mixed and fed into the moulding cavity 40 of a mould 7, where at least the surface 36, 38 of the cavity 40 is formed of a concrete releasing polymer to prevent the adhesion of the cementitious composition thereto. Surrounding the moulding cavity 40 is a hollow space 42 which contains a static heat-control liquid 34 that allows the cementitious composition to cure without the application of heat. The product (e.g. concrete roof tiles) is then de-moulded from the mould 7 and a top coating is applied on the upper surface of the product. A suitable plant includes a mixing station (2), a moulding station (4) (figure 2 - not shown), a curing station (26), a demoulding station (8) (figure 3 - not shown) and a coating station.

Description

METHOD AND PLANT FOR FORMING A CONCRETE BUILDING PRODUCT

Field of the invention

This invention is concerned with a method for the manufacture of building products and a plant for effecting the method for the manufacture of the building products, especially concrete roof tiles.

Background of the invention

A conventional practice for the manufacture of concrete roof tiles is described in GB 1352627, where the tiles are manufactured by an extrusion method, in which a stiff concrete mortar is fed from a hopper onto a series of tile pallets passing beneath the hopper where the mortar is formed on the pallets by extrusion between the pallets and an overlying roller and slipper.

A principal drawback of forming roof tiles by an extrusion method is that the shape and configuration of the upper surface of the extruded roof tile is dictated by the cross-section of the extrusion rollers and slippers that are conventionally used for their production. Thus, it is not possible to provide tiles with a headlock for increasing the rain-tightness thereof when the tiles are assembled on a roof. Also, tiles with exotic and aesthetic shapes cannot be produced with the known extrusion process. This presents a serious commercial disadvantage as the demand for roofing products with such shapes is strongly increasing in many countries.

In order to overcome or mitigate the disadvantages described above, casting processes were developed. Casting of concrete roof tiles facilitates the choice of shape and configuration for the upper surface in use of the concrete roof tiles made by this method.

However, whether the tiles are formed by extrusion or by casting, the surface finish is very rough. Therefore, the surface of the tiles uppermost in use is coated with pigmented coating compositions in order to reduce the roughness of said surface, and/or enhance the surface finish and the aesthetic appeal of the finished product and/or improve the weather resistance thereof.

Generally, such a casting method involves mixing a cementitious composition comprising water, aggregate and cement, feeding the cementitious composition into a metal mould, allowing the cementitious composition to cure in the mould to form a cast concrete building product and de-moulding the cast concrete building product from the mould.

To prevent the adhesion of the cementitious composition to the surface of the mould cavity, that surface may be sprayed with a release agent.

Known casting processes can be distinguished in two types: those using re-usable moulds and those using lost moulds.

A casting process for roof tiles using re-usable moulds is described in EP 0437672, in which process a series of haif-moulds is formed into a gang mould so that a plurality of roof tiles can be cast at one time. Due to the surface smoothness of the haif-moulds the cast roof tiles receive a much smoother surface than extruded roof tiles.

However, there are two serious disadvantages in such a process. Firstly, the haif-moulds need to be cleaned and provided with a release agent after each casting process in order to allow a proper shaping and de-moulding of cured roof tiles. Secondly, it is not possible to apply surface coatings to the surfaces of the cured roof tiles because any residual presence of the release agent will prevent a proper adhesion of the surface coating. Application of a surface coating is essential to resist the hazards of inclement weather conditions and for the supply of roof tiles with different surface colours and finishes.

WO 03/008166 describes a manufacturing process for concrete bodies which prevents the complicated handling and treatment of re-usable moulds by using lost moulds. The ruoulds are made from a material, e.g. moulding sand, which can be aggregated by compression and subsequently broken up.

Moulds made from such a material have a rough surface and, consequently, the cast concrete bodies will also have a rough surface necessitating the application of a surface coating thereto.

Metal moulds have a high thermal capacity so that the heat released during the hydration process is quickly lost. In order to prevent this, the metal moulds need to be heated and kept at a temperature between 40 -50C during the curing process. This costs time and energy.

Summarising, it is a fact that none of the roof tile manufacturers have managed to launch a cast roof tile in the market regardless of the increasing demand for different shapes of tiles and the existence of casting processes. This is because they are not able to provide roof tiles with surface coatings capable of resisting the hazards of inclement weather conditions.

It appears that one reason for the difficulty to coat the roof tiles is because the surfaces of the roof tiles contain residua of the release agent, which serves to weaken the tile surface layer that may prevent penetration of the coating material.

It is therefore an object of the present invention to provide a method f or the casting of concrete building products in which the aforesaid disadvantages are overcome and which in particular facilitates a high flexibility in the shaping of the products and provides excellent surface qualities on visible surfaces.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of forming a concrete building product comprising: (i) mixing a cementitious composition comprising water, aggregate and cement; (ii) feeding the cementitious composition into the moulding cavity of a mould; (iii) allowing the cementitious composition to cure in the mould to form a cast concrete building product; Cv) de-moulding the cast concrete building product from the mould; and (iv) applying a top coating on the upper surface of the S cast building product, characterised in that at least the surface of the moulding cavity is formed of a concrete releasing polymer to prevent the adhesion of the cementitious composition thereto.

According to a second aspect of the invention there is provided a plant for forming a concrete building product comprising: (1) a mixing station for admixing a cementitious composition comprising water, aggregate and cement; (ii) a moulding station for feeding the cementitious composition into the moulding cavity of a mould and for allowing the cementitious composition to cure in the mould to form a cast concrete building product; (iii) a de-moulding station for dc-moulding the cast concrete building product from the mould; and (iv) a coating station for applying a top coating on the upper surface of the cast building product, characterised in that at least the surface of the moulding cavity is formed of a concrete releasing polymer to prevent the adhesion of the cementitious composition thereto.

The cementitious composition is preferably fed into the moulding cavity at a temperature above ambient, such as between 15 C and 35 C. During the hydration process the temperature increases to 40 -50 C which enables one to avoid the need to provide additional heat.

Thus, the cementitious composition is preferably allowed to cure without the application of any further heat thereto. This avoidance of heating may be enabled by using a concrete releasing polymer having a suitable heat conductivity. Thus the selection of the mould material has not only to consider concrete releasing properties but also heat conductivity.

The concrete releasing polymer preferably comprises polyethylene, polypropylene or more preferably polyoxymethylene. For example, the concrete releasing polymer is advantageously polyoxymethylene or less preferably is selected from (i) a composition of polyoxyniethylene with calcium carbonate, such as about 20% by weight calcium carbonate; and (ii) a composition of polyoxymethylene with wollastonite, such as about 30% by The thermal expansion of the preferred concrete releasing polymer used for the mould is up to 10 times higher than that of the concrete body. Consequently there would be a risk that, upon cooling, the mould stretches the concrete body so that it cracks. This effect may be partly alleviated by providing hollow spaces in the mould adjacent the moulding cavity, advantageously the concrete releasing polymer needs to have a certain degree of heat-conductivity in order to allow the heat to enter hollow spaces of the mould to prevent a critical thermal expansion.

Alternatively or additionally, the avoidance of heating may be enabled by a heat-control liquid, such as water, or a water-based liquid, adjacent the moulding cavity. This may be achieved, in a preferred embodiment of the invention, where the mould comprises hollow spaces, adjacent the moulding cavity, for retaining a heat-control liquid therein. The heat will be absorbed by the heat-control liquid placed in the hollow spaces of the mould.

The heat-control liquid retains the heat, so that no further heat has to be applied during the curing process. Thus, the heat-control liquid is preferably static within hollow spaces of the mould while the cementitious composition is allowed to cure.

In effecting the method provided by the present invention, the mould is filled under pressure or by gravity and the filled mould is conveyed to the curing zone.

Preferably, the cementitious composition is allowed to cure in the moulding cavity for a period of from 5 hours to 24 hours, such as approximately 3 hours. Compared with casting processes using metal moulds, this curing time is shorter and no additional heat needs to be supplied.

Conveniently, the method of admixing the cementitious composition includes the addition of an air entraining agent and/or a super-plasticiser.

In a preferred embodiment of the invention, prior to being fed into the moulding cavity, the ingredients of the cementitious composition are mixed at least party in a partial vacuum. Thus the mixing station of the plant may comprise a vacuum mixer. The benefit of using a partial vacuum during mixing of the constituents, and especially after admixing the super-plasticiser, is that the amount of entrained air is controlled to provide the building product with the required freeze / thaw resistance.

Thus the cementitious composition is formed, for

example, by:

a) mixing in a first step water, sand, pigment, fly ash, cement and an air entraining agent under atmospheric pressure; and, b) adding a super-plasticiser to the cementitious composition, which is mixed thereafter in a second step in a partial vacuum.

The cementitious composition may be mixed in the second step under a partial vacuum of between 240 and 320 mBar. In this manner a cementitious composition having a Ford Cup flow of between 35 and 90 seconds, preferably between 40 and 60 seconds, can be obtained.

Preferably, the mixed cementitious composition has the property of a slump test of between 160 and 220 mm.

In one convenient method provided by the present invention, after de-moulding, the cured building products are conveyed to the coating zone for applying a top coating.

The top coating may comprise a water based emulsion paint.

In a preferred embodiment, at least the upper surface of the cast building product is heated before the top coating is applied.

After the application of the top coating the cured building products are conveyed to a drying zone in which the top coating is heated to reduce the tendency for the cured building products to be damaged during packaging.

Subsequent to de-moulding the building product, the mould may be cleaned and re-used for forming a further such building product, for example the mould is cleaned with high pressure water.

The building products may be a roof tile or fittings therefor.

The moulds may be formed in such a manner that they may be assembled into a stack to form a gang mould with the mould cavities being formed between each two adjacent moulds in the stack. Each mould may be formed in two parts, preferably by injection, the parts being subsequently joined together to form the hollow space for the heat-control liquid. The parts can be joined together by welding or gluing.

Thus, a plurality of moulds, arranged in the gang mould, are conveniently provided for the simultaneous moulding of an appropriate number of building products between each pair of adjacent moulds of the gang. When moulding the building products, the moulds are preferably orientated on end within the gang mould.

Conveniently, means are provided at the de-moulding station for rotating the gang mould, for example through 90 degrees, to orientate the moulds and the cured building products in a substantially horizontal condition for de- moulding, and the cured building products are each de-moulded together with a next in line below mould, the de-moulding station preferably comprising separation means for separating the cured building products from their respective half -moulds.

The plant may further comprise conveyor means for conveying the separated cured building products to the coating station and the separated moulds to a cleaning station whereat the moulds are prepared for a subsequent moulding operation.

The invention will now be further described, purely by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagrammatic illustration of part of a gang mould for use in the present invention.

Figure 2 is diagrammatic representation of mixing and moulding stations of the invention and, Figure 3 is a diagrammatic representation of cured cementitious product and mould separation station and product preparation, coating and heat treatment zones of the invention.

Referring to Figure 1, there are shown two moulds 7a, 7b of a series of moulds arranged in a gang for the simultaneous production of twenty-four concrete tiles.

Each mould is formed polyoxymethylene to prevent the adhesion of the cementitious composition thereto.

Each mould is formed in two parts 58, 56 by injection which parts are welded together to define a hollow space 42 there-between. A port, not shown, is provided for the inlet of a heat-control liquid 34 such as static water to the hollow space.

The upper outer surface 36 and the lower outer surface 38 of each mould are of such a shape that when two such moulds are stacked in a gang, a moulding cavity 40 having the shape of the roof tile T to be formed, is defined between them. A port, not shown, is provided for the inlet of cementitious composition into the moulding cavity.

For the sake of simplification the moulding cavity shown in Figure 1 will produce a roof tile having flat parallel upper and lower surfaces, although more complex shapes are clearly possible. Part 44 of the upper outer surface and part 46 of the lower outer surface of each mould are so shaped as to provide the tile formed in the mould with an overlock 60 and an underlock 62.

After moulding, the formed roof tile is recovered by demoulding, i.e. by separating mould 7a from mould 7b.

Referring to Figures 2 and 3, there is shown a plant for forming concrete roof tiles T. A mixing station 2 is provided for admixing a cementitious composition. The mixing station 2 is of conventional design and includes a vacuum mixer 16 wherein the constituents of a cementitious composition are admixed.

The cementitious composition is formed by mixing in a first step water, sand (of 0.3 mm to 3 mm grain size), pigment, fly ash, cement and an air entraining agent under atmospheric pressure. A super-plasticiser is then added to the cementitious composition, which is mixed thereafter in a second step in a partial vacuum of 280 mBar. The cementitious composition so formed has a Ford Cup flow of 50 seconds and a slump test of 200 mm.

The benefit of using a partial vacuum during mixing of the constituents, and especially after admixing the super-plasticiser, is that the amount of entrained air is controlled to give a required consistency to the admixed cementitious composition.

A moulding station 4 is provided, having provision for locating a succession of gang-moulds 6, each of which comprises a series of moulds 7 for the simultaneous production of twenty-four concrete tiles T. The moulding station is provided with funnels, not shown, through which a cementitious composition is fed simultaneously and under pressure into the twenty-four mould cavities defined by the moulds 7, such as cavity 40 of Figure 1. The cementitious composition is fed into the moulding cavities at room- temperature, approximately 18 C. At this time the gang-mould 6 is orientated so that the moulds 7 are positioned on end and thus, the cavities formed by the moulds 7 are also orientated so that the concrete roof tiles T are cast in a vertical plane.

Although it is described herein that the cementitious composition is fed into the mould cavities under pressure, in a modified method the cernentitious compositions may be fed under gravity.

-10 -From the moulding station 4, the gang-mould 6 is conveyed to the curing area 5 where the concrete roof tiles T are allowed to cure for 8 hours. The cementitious composition is allowed to cure without the application of heat thereto.

When the concrete roof tiles T are fully cured in their respective moulds 7, the gang-mould 6 is conveyed to an orientating station, not shown, where it is rotated through 90 degrees to orientate the moulds 7 and the cast concrete roof tiles T in a substantially horizontal position. This reorientation of the moulds 7 and roof tiles T facilitates the ease with which the tiles T may be separated from the moulds 7.

A de-moulding station 8 is provided for de-moulding the cast concrete roof tiles T from the moulds 7.

Thereafter, the moulds 7 are conveyed to the cleaning station 10 where they are cleaned with high pressure water at a cleaning station 10 for preparing gang-moulds 6 for successive casting operations, i.e. the rnoulds are re-used for forming further such roof tiles.

At the same time, the cast concrete roof tiles T are placed on a conveyor 20 with their upper sides in use uppermost, the tiles T being conveyed to surface preparation zone 12 where the cured roof tiles T are each subjected to a surface preparation operation and provided with surface coatings to at least their upper surface in use on a roof.

The tiles are conveyed in turn through: (i) the heating zone 22 where the tiles are selectively warmed prior to having a primer coat applied thereto (by "selective warming" in this context we mean that at least those surfaces of the concrete roofing tiles which are to receive the primer coating are heated), (ii) the first coating zone 24 where a primer coat of a water based epoxy primer coat is applied to the at least the upper surface in use of the roof tile T, the primer coat being capable of cross-linking with the cement rich surface of the roof tile to provided a receptor surface -11 -for a top coat, (iii) through the first curing zone 26 for effecting cross-linking between the cementitious body of each roof tile T and the primer coat, (iv) the heating zone 27 where the primer coated concrete roof tiles are selectively heated to a temperature of 60 C before application of a surface coating thereto, (v) the second coating zone 28 where a surface coating of water based emulsion paint is applied onto the primer coat, (vi) the second curing and drying zone 30 where the surface coating of water based emulsion paint is cross-linked with the water based epoxy primer coat and in which the top coating is heated to reduce the tendency for the cured roof tiles T to be damaged during packaging, and (vii) to the stacking arid packaging station 14 where the coated concrete roof tiles T are stacked and packaged for storage and eventual distribution.

Claims

-12 -

CLAIMS

1. A method of forming a concrete building product comprising (i) mixing a cementitious composition comprising water, aggregate and cement; (ii) feeding the cementitious composition into the moulding cavity (40) of a mould (7); (iii) allowing the cemerititious composition to cure in the mould (7) to form a cast concrete building product; (v) de- moulding the cast concrete building product from the mould (7); and (iv) applying a top coating on the upper surface of the cast building product, characterised in that at least the surface (36, 38) of the moulding cavity (40) is formed of a concrete releasing polymer to prevent the adhesion of the cementitious composition thereto.

2. A method according to claim 1, wherein the cementitious composition is allowed to cure without the application of heat thereto.

3. A method according to claims 1 to 3, wherein a heat-control liquid (34) surrounds the moulding cavity.

4. A method according to claim 3, wherein the heat-control liquid (34) comprises water, or a water-based liquid.

5. A method according to claim 3 or 4, wherein the heat-control liquid (34) is static within hollow spaces (42) of the mould (7) while the cementitious composition is allowed to cure.

-13 - 6. A method according to any preceding claim, wherein the cementitious composition is fed into the moulding cavity (40) at a temperature of between 15C and 35C.

7. A method according to any preceding claim, wherein the cementitious composition is allowed to cure in the moulding cavity (40) for a period of from 5 hours to 24 hours.

8. A method according to any preceding claim, wherein, prior to being fed into the moulding cavity, the ingredients of the cementitious composition are mixed at least party in a partial vacuum.

9. A method according to claim 8, wherein the cementitious composition is formed by: a) mixing in a first step water, sand, pigment, fly ash, cement and an air entraining agent under atmospheric pressure to form a precursor composition; and b) adding a super-plasticiser to the precursor composition, which is mixed thereafter in a second step in a partial vacuum.

10. A method according to claim 9, wherein the cementitious composition is mixed in the second step under a partial vacuum of between 240 and 320 mBar.

11. A method according to any preceding claim, wherein the cementitious composition has a Ford Cup flow of between 35 and 90 seconds, preferably between 40 and 60 seconds.

12. A method according to any preceding claim, wherein the mixed cementitious composition has the property of a slump test of between 160 and 220 mm.

-14 - 13. A method according to any preceding claim, wherein the cured building products are conveyed to a coating zone for applying a top coating.

14. A method according to any preceding claim, wherein the top coating comprises a water based emulsion.

15. A method according to any preceding claim, wherein at least the upper surface of the cast building product is heaLed before the top coating is applied.

16. A method according to any preceding claim, wherein the cured building product is subsequently conveyed to a drying zone (30) in which the top coating is heated to reduce the tendency for the cured building product to be damaged during packaging.

17. A method according to any preceding claim, wherein subsequent to de-moulding the building product, the mould (7) is cleaned and re-used for forming a further such building product.

18. A method according to claim 17, wherein the mould (7) is cleaned with high pressure water.

19. A method according to any preceding claim, wherein the building product is a roof tile (T).

20. A method according to any preceding claim, wherein the surfaces of the mould (7) defining the moulding cavity (40) are not treated with a release agent prior to feeding the cementitious composition into the moulding cavity.

-15 - 21. A plant for forming a concrete building product comprising (1) a mixing station (2) for admixing a cementitious composition comprising water, aggregate and cement; (ii) a moulding station (4)for feeding the cementitious composition into the moulding cavity (40) of a mould (7) and for allowing the cementitious composition to cure in the mould (7) to form a cast concrete building product; (iii) a de-moulding station (8) for de-moulding the cast concrete building product from the mould (7); and (iv) a coating station (24) for applying a top coating on the upper surface of the cast building product, characterised in that at least the surface (36, 38) of the moulding cavity (40) is formed of a concrete releasing polymer to prevent the adhesion of the cementitious composition thereto.

22. A plant according to claim 21, whereby the mixing station (2) comprises a vacuum mixer (16) 23. A plant according to claim 21 or 22, whereby the concrete releasing polymer comprises polyoxymethylene.

24. The plant according to claim 21, wherein the concrete releasing polymer is polyoxymethylene.

25. A plant according to any one of claims 21 to 24, whereby the mould (7) is made of a material comprising polyoxyrnethylene.

26. A plant according to any one of claims 21 to 25, wherein the mould (7) comprises hollow spaces (42), adjacent the moulding cavity, for retaining a heat-control liquid (34) therein.

-16 - 27. A plant according to any one of claims 21 to 26, a plurality of said moulds (7) are provided, assembled into a stack to form a gang mould (6) with the mould cavities (40) being formed between each two adjacent moulds in the stack.

28. A plant according to claim 27, whereby each mould is formed in two parts (56, 58), preferably by injection, and the parts being subsequently joint together to form the hollow space for the heat-control liquid (34).