GB2416327A - Method of producing a shaped concrete product - Google Patents

Abstract

A method for producing a shaped concrete product e.g. a hard landscaping product such as flagstones, paving slabs and edging comprises the steps of combining an aggregate of mainly recycled blast furnace material, a binder, optional additional elements and an excess of water sufficient to create a flowable slurry; passing the slurry to a shaping zone whereat a shaped intermediate may be fabricated by either wet casting, wet pressing or semi dry pressing and then curing the shaped concrete product. Later embodiments relate to a method for producing a two layer hard landscaping product and a hard landscaping or other shaped concrete product precursor.

Description

CONCRETE PRODUCT AND METHOD OF MANUFACTURE

The invention relates to a method for producing a shaped concrete product such as a hard landscaping product, to a shaped concrete product such as a hard landscaping product produced thereby and to a facility for the production thereof.

Shaped concrete products are often used in hard landscaping and similar applications, both as a practical feature, and to add interest and/ or be decorative in nature. Hard landscaping products typically include paving slabs, flagstones and edging. Traditionally such products were created from natural stone. Alternatives using reconstituted stone or concrete have become more popular. Concrete hard landscaping products are available in a wide range of colours, shapes, styles and thicknesses at a fraction of the price of natural 1 5 stone.

Shaped concrete hard landscaping and like products of are manufactured from dry ingredients including aggregate and binder such as cement in familiar manner, although usually on a smaller scale than bulk concrete for construction or the like. The aggregate and binder may be combined with additives such as pigment or other additives to give processibility and/or desired finished properties. Traditionally the aggregate used in this process is quarried natural aggregate of various grades including gravel and sand. These are combined with water and the mixture is moulded to the desired shape and cured to produce the end product.

As will be familiar, for a given formulation of dry ingredients, and in particular a given level of binder there is an optimum level of hydration for maximum strength in the cured product. However, this optimum level of hydration does not give an optimally processable intermediate. Concrete formulations and fabrication processes thus become a compromise between considerations for a workable intermediate, and considerations for a strong product.

For shaped concrete products for hard landscaping and the like, three principal approaches have been developed.

In a first alternative, dry ingredients are mixed with an excess of water (that is, with a water content above the optimum strength point). This produces a Plowable, workable and conveniently handled wet intermediate mixture, which can readily be fabricated into the desired shape. However the amount of water used is critical as it affects the strength of the final product. The wet intermediate product has a water content significantly above the optimum level for optimum strength in cured product.

Two approaches producing two distinct wet processes will be familiar. In the first, water level is reduced significantly toward the optimum level prior to curing by generation of a hydraulic pressure in the wet mixture, typically using an external press. The process is usually known as wet pressing. In the second process, usually known as wet casting, the water is not driven off before curing but more binder is added to the mix. Some reduction of water level will occur in practice during curing, for example through evaporation, but wet casting is in essence a compromise solution to produce adequate strength in the cured product, in which water level above optimum is tolerated and a greater quantity of binder is used instead.

In a third approach, usually called semi-dry pressing, the dry ingredients are combined with a controlled amount of water intended to be sufficient merely to hydrate the mixture to (or more typically just below) optimum hydration levels before shaping and pressing. This process produces an end product of high strength, since it involves from the outset careful control of the water content. However, the material is harder to manipulate as a product is formed.

It is sometimes necessary to add additional substances during forming to provide flowability or mouldability, and semi-dry processes are not always suitable for all types of aggregate or fabricated product.

Natural aggregate is traditionally graded into three main categories; coarse medium and fine grade, sometimes referred to as filler. Sand is an example of fine grade natural aggregate. Natural aggregate used in the manufacture of hard landscaping products usually comprises a combination of all three grades of material.

The problem with using natural aggregate is that it is a non-sustainable source of aggregate, and quarried aggregate is relatively expensive. These problems create the need to find a source of sustainable or recycled aggregate material to replace quarried aggregate in the manufacture of such products.

Hard landscaping products comprising recycled materials are available commercially. However, there are a number of reasons why the use of recycled materials from previously fabricated concrete products might be limited. First, there are the collection and processing issues which always limit the practicality of recycled material use. Second, there are issues concerning the control of material composition, particle size and shape and the like. For these and other reasons, recycled material use is not widespread, and the greenest' product currently on the market is believed to comprise only 41% recycled material.

There is thus a general desire to source and/or develop a process to allow use of an effective substitute for natural, newly-quarried aggregate in such products. We have now surprisingly found that by adapting current processes recycled blast furnace material can be used as an aggregate substitute to create an aesthetically pleasing hard landscaping product containing a substantial proportion of such blast furnace material, such that a substantial proportion of the aggregate content of the hard landscaping product is from a source other than a new quarried source.

Accordingly in a first aspect of the invention there is provided a method for producing a shaped concrete product such as a hard landscaping product comprising the steps of combining aggregate, binder and optional additional agents with an excess quantity of water sufficient to create a flowable slurry, passing the slurry to a shaping zone whereat a shaped intermediate is fabricated in suitable wet processing manner, and curing the shaped intermediate to produce a shaped concrete product, wherein at least the major part of the aggregate comprises recycled blast furnace material.

The process is thus a wet process, in which a workable slurry is created by addition of water to a level above the optimum hydration level. The wet process may be a process in which a shaped intermediate is fabricated and cured with the excess water content retained, that is, it may be a wet casting process. Binder content would be formulated accordingly. However, in a preferred embodiment, the wet process is a process in which a shaped intermediate is further treated by the step of reduction of the water content to a level more closely approaching optimal hydration level for the binder/aggregate combination, for example by wet pressing, prior to curing.

Blast furnace waste material from the steel making industry is available in vast supplies. It is currently used in the construction trade as a bulking agent, but so far this material has not been used extensively in the hard landscaping industry to produce a finished product. Whilst not strictly a recycled material in the context of fabricated concrete, it is therefore nonetheless a currently unused by-product of an industrial process which would otherwise be a waste material, and hence confers equivalent environmental benefits, in that it can replace, at least in part, newly-quarried aggregate in the binder/aggregate mix, provided the necessary process modifications are made in accordance with the present invention.

Blast furnace waste materials are available in huge quantities, can easily be graded into size ranges suitable for applications in substitution for aggregates, and can be sourced in large quantities from a single site. This makes their use much more practical as a non-quarried aggregate alternative than is the case for recycled concrete waste.

Blast furnace materials have not hitherto been used to manufacture hard landscaping products for several reasons. In particular, recycled blast furnace materials have an angular, flaky grain shape and when mixed it does not align, flow or pack together as readily as natural aggregates. The material doesn't flow using water levels normally employed in wetprocess hard landscaping production lines and presses.

It is well known in the art that water content is absolutely critical in determining the structural properties of the finished product. For any given aggregate/binder composition there will be an optimum hydration level at which the structural integrity of the finished product is maximised, and that at higher water levels the structure can be compromised.

For various well known reasons, excess water fabrication techniques such as wet casting and wet pressing are widely used to give a flowable and conveniently handled intermediate mixture during fabrication. However, it is established that this excess must be limited.

First, in both wet pressing and wet casting, it is well established that an excess above the levels conventionally used can produce segregation problems as the ingredients segregate during forming of the product, for example during vibration to fill a shaped would. The result is an inferior cured product of inadequate structural consistency. This limits the amount of water that can be added. Second, in wet pressing it is likely to become progressively harder to reduce water to approach optimum levels as initial levels are increased, and there is always likely to be some excess water left.

Thus, any excess water process is a compromise between achieving satisfactory flowability during fabrication and achieving satisfactory strength in the finished product. There is a huge technical prejudice in the art against any process modification which would increase water levels during excess water fabrication, since this would inherently be expected to reduce structural integrity in the finished product andlor lead to segregation issues and/or make the fabrication step involving removal of water more difficult and expensive.

For wet processes in accordance with the invention, the recycled blast furnace materials must be combined with sufficient quantity of water to create a Plowable slurry. At normal water levels any substantial blast furnace material content in the aggregate is found to render the slurry difficult to work at the shaping stage, and such a formulation would be rejected. It is believed that this is attributable to the much more angular shape and texture of the particles.

In accordance with the process of the invention it has been found that a Plowable slurry is achievable, but substantially more water must be used than in conventional concrete wet processes to overcome the problems faced due to the shape and texture of the material. An excess of perhaps 10 to 20% over the quantity of water traditionally viewed as the maximum sensible for a conventional excess water concrete fabrication process involving conventional quarried aggregate needs to be considered. In the context of concrete fabrication, this is a substantial excess, and would normally not be countenanced by those experienced in concrete fabrication processes, since it would be considered to make segregation problems during fabrication highly likely, and to be generally detrimental to finished product strength..

However, it has been surprisingly found that such a level of excess is less of a problem in relation to compositions where a significant part of the aggregate is formed by recycled blast furnace waste material rather than by conventional quarried or otherwise obtained aggregate of a conventional nature. Even at such water levels, it is found that an adequate fabricated product with satisfactory structural integrity can be produced without undue difficulty, and without segregation during forming.

Whilst the invention is not limited by any particular theory, it is believed that the expected segregation effect is mitigated by the greater porosity of the blast furnace material particles over conventional aggregates. Initial water levels are raised sufficiently to cause the mixture to flow, but as the form and cure stages proceed at least some of this excess becomes tied up by absorption into the pores within the blast furnace material particles. The expected worst effects of the excess water on the forming stage and on the cured product are mitigated.

To achieve these greater levels of excess water in the wet mixture, preferably the solid and water mixture prepared in accordance with the above method comprises water in an amount 12 to 15% by weight when a wetpressing process is used. As will be familiar, a greater excess of water may be tolerated with wet-casting, and a wet-casting process conveniently comprises water in an amount 14 to 20% by weight. In either instance, this is a significant increase in water compared to conventional concrete processing methods using an excess of water.

Recycled blast furnace material also contains iron particles that are a by- product of the steel manufacturing process. Iron particles present in a finished hard landscaping product would cause surface staining, discolouration and flaws. The difference in the coefficient of thermal expansion between the iron particles and the bulk material in the product may cause hairline cracks. Iron particles in a finished product can also pose a health and safety hazard as sparks can be generated when such products are cut. For these reasons it is difficult to produce an aesthetically pleasing finished hard landscaping product using materials with appreciable iron content.

It is thus preferable to remove iron particles from the recycled blast furnace materials prior to combination with water to avoid all the undesirable features outlined above. In accordance with an embodiment of the invention, this necessary step is also built into the process, in that the blast furnace material is passed through at least one magnetised zone to remove iron particles prior to combining with water.

To remove the iron, the blast furnace material is passed through at least one magnetized iron segregation zone. The blast furnace material preferably passes through several magnetized iron segregation zones in order to remove substantially all the iron from the blast furnace material prior to combining the with water. The magnetized iron segregation zone may comprise any suitable arrangement of magnets to remove the iron. Preferably the material is passed over at least one magnetised drum on a suitable conveyer belt.

The aggregate ingredient may comprise an amount of quarried natural aggregate combined with blast furnace material. Preferably aggregate ingredient comprises at least 50% blast furnace material by weight, more preferably more than 70%, more preferably the aggregate is substantially all blast furnace material.

Blast furnace material can be graded into three main categories in a similar way to natural aggregate. Fine grade material is sometimes referred to as filler or blast furnace dust. Coarse blast furnace material includes the largest sized particles of approximately lOmm in size. Blast furnace material used in the method of the invention comprises a combination of all three grades of material.

The dry ingredients are preferably combined in the range 80 to 90% by weight aggregate to 10 to 20% binder by weight.

The binder may comprise ordinary Portland cement (OPC). Alternatively, processed Ground Granulated Blastfurnace Slag, known as GOBS, can be used as a cement replacement. Preferably the binder comprises OPC and GOBS in the range O to 20% GGBS by weight and 80 to 100% OPC by weight.

The dry ingredients may be combined with colourant for aesthetic purposes.

Preferably colourant is iron oxide. Preferably colourant is present in the range 0.3 to 1% by weight of dry ingredients.

The dry ingredients may be combined with other additives to give improved processibility properties and/or desired finished properties. Such additives may include additives designed to modify the behaviour of the composition during fabrication, for example plasticisers and the like to modify flowability of the wet mixture, andlor additives to provide modifications to the properties of the finished product, such waterproofing. Preferably additives are present in an amount not more than 5%, preferably not more than 1% by weight of dry ingredients.

Recycled blast furnace material is very abrasive compared to conventional l 5 aggregate. The abrasive nature of the material causes damage to mixers used in conventional hard landscaping product manufacturing facilities. To overcome this any mixers, moulds and presses are preferably provided with liners to protect from the abrasive particles.

After combining with water the resulting slurry is passed to a fabrication zone to be formed into a suitable shape prior to curing. This step preferably comprises filling a suitably shaped mould with wet mixture. Even filling of the shaped mould may be facilitated by vibration and/ or application of pressure.

The mixture may be processed by a wet casting process in which the excess water is essentially retained for the curing stage, but is preferably further treated by removal of water, for example being wet pressed, prior to curing.

Standard wet presses must be modified to include deeper mould carriers to accommodate the large amount of water present in the slurry. For example moulds are 25 - 30 mm deeper than conventional wet-press moulds.

In accordance with a preferred embodiment of the method, a mixture comprising excess water is prepared as hereinbefore described. The mixture is passed to a fabrication zone and transferred to a suitable mould to be formed to the desired shape; compression is applied to the shaped mixture in the mould to reduce the level of excess water to more closely approach the optimum hydration level for the mixture. Any suitable press such as a hydraulic press may used in familiar manner. A fabrication pressure of suitable known level is applied to squeeze water out of the material mixture in the mould. The shaped structure may be removed from the mould for handling, for example to be taken to a curing zone for curing.

IS In a particularly preferred embodiment, the method is a method for fabricating generally planar structures, and for example generally rectangular planar structures, such as flagstones, paving slabs and the like, and comprises transferring wet mixture into a suitably shaped mould and removing the excess water therefrom in the manner hereinbefore described. In particular, excess water is removed by application of pressure. For example, the process is carried out on a three stage wet press processor, comprising a rotating processing table having three suitably and equivalently sized mould features, the rotating table successively transferring each mould feature from a first filling stage where wet material is applied to a second pressing stage where compression is applied to drive off excess water to a third ejection stage where the formed flag or slab is ejected for subsequent handling and processing.

Whilst hard landscaping products manufactured from recycled blast furnace materials are perfectly suitable for most applications, there is the occasion where finer, higher quality finishes are required for aesthetic reasons.

As a refinement to the method as hereinbefore defined there is provided a method for producing a two-layer hard landscaping product comprising a face layer and a backing layer wherein the face layer comprises fine, high quality aggregate and the backing layer comprises blast furnace material as an aggregate substitute. The method comprises the initial steps of mixing a face layer mixture comprising combining higher quality natural aggregate with binder and water and transferring to a mould in a thin layer, the face layer is then subjected to a first compression in order to prevent mixing, a backing layer comprising recycled blast furnace materials, binder and water is then added to the mould and the two layers are then subjected to a second compression at a higher pressure in order to produce the finished product.

In particular, the method is a refinement of the three stage process carried out above, and is carried out on a five stage processor, comprising a rotating processing table having five suitably and equivalently sized mould features rotating past five process stages successfully comprising a first fill to fill the mould feature to the desired surface depth with a first, high quality material, a first press to apply the necessary firming pressure to the first fill to prevent mixing, a second fill to apply the wet mixture intended to comprise the majority of the body of the flag or slab, a second press to apply a higher pressure to remove the excess water, and a final ejection zone as above described.

By fabricating a hard landscaping product in this way, more expensive, traditional aggregates can be used to create a thin surface, while the rest of the product comprises recycled aggregate material as hereinbefore defined.

With a two-layer hard landscaping product the face layer can be subsequently shot-blasted to provided a textured surface without detriment to the finish of the product.

Blast furnace materials as above described can also be used as aggregate replacement in semi-dry processes. In a second aspect of the invention there is provided a method for producing a shaped concrete product such as a hard landscaping product combining the steps of combining aggregate, binder and additional agents with a sufficient quantity of water to approach optimum hydration level and passing to a fabrication zone to shape the product using a semi-dry press, wherein at least the major part of the aggregate comprises recycled blast furnace material. Again the blast furnace material is preferably passed through at least one magnetised zone to remove iron particles prior to combining with water.

It is possible to use water from a basic supply in this way. Nevertheless, since the shaped concrete fabricator would tend to desire aggregates which can be used in all three processes, and indeed might combine more than one process in a plant, he would tend strongly to prefer materials that can be used for wet and semi-dry processes also.

However, it has been found that this apsect of the invention is particularly effectively practiced if water produced as a byproduct of wet pressing of mixtures including blast furnace material is used. Thus, in a refinement of the method of the second aspect, the dry ingredients are mixed with water which has been recycled after removal during a wet press method of the first aspect of the invention.

The high alkalinity of the waste water is believed to increase the effectiveness of a given quantity of binder. For this reason, use of recycled water is also strongly to be preferred for a wet casting process in accordance with the first aspect of the invention. Thus, in a refinement of the wet casting method of the first aspect of the invention, the dry ingredients are mixed with water which has been recycled after removal during a wet-press method of the first aspect of the invention.

This illustrates a further advantage of the invention as the excess water employed in the wet press method of the invention can be recycled without further chemical processing and combined with dry ingredients for pressing in a semi-dry press or wet cast without further chemical processing.

Recycling of water in this manner is obviously an environmental advantage.

However a further advantage of recycling the waste water in this manner is that as the waste water is alkaline, curing times for products produced in the semi-dry press or wet cast are improved and/ or binder levels can be reduced.

Preferably the excess water removed during a wet press process is treated to remove fine particles, preferably via a settlement process, prior to its use in a semi-dry or wet cast process.

Conveniently, an integrated plant can be provided with a facility for wet pressing of mixtures in accordance with the invention, a facility for semi-dry pressing and/ or wet casting of mixtures in accordance with the invention, and a means to recycle water from the facility for wet pressing for use in the facility for semi-dry pressing and/ or wet casting.

The dry ingredients may be combined with colourant for aesthetic purposes.

Preferably colourant is iron oxide. Preferably colourant is present in the range 0.3 - 1% by weight of dry ingredients.

In a further aspect of the invention there is provided a hard landscaping product obtained by the method as hereinbefore defined.

In a further aspect of the invention there is provided a hard landscaping product comprising 80-90% aggregate by weight, at least the major part of which is recycled blast furnace material, not more than 5% and preferably not more than 1% additives, and the balance save for incidental impurities is binder.

In a further aspect of the invention there is provided a hard landscaping or other shaped concrete product precursor material suitable for wet pressing or wet casting comprising a slurry comprising excess water, aggregate, binder and additional agents, wherein at least the major part of the aggregate comprises recycled blast furnace material.

In a further aspect of the invention there is provided a dry mixture suitable for combining with water to form a hard landscaping product precursor material suitable for pressing or casting as hereinbefore defined.

In a further aspect of the invention there is provided apparatus for production of a two-layer hard landscaping product in the form of a three or five station wet press as described in connection with the preferred embodiments of the method.

The invention is now illustrated in non limiting manner with reference to the following examples of suitable composition ranges and to the following figures. Where used herein it will be understood that references to "dry" ingredients are to ingredients "dry" in the sense used in the art. It will be understood, for example, that "dry" aggregates retain some residual moisture, up to 2 to 3% by weight, especially when stored outside.

Example 1: Composition for Wet Pressing Coarse recycled blast furnace material 90 - l OO Kg Medium recycled blast furnace material 75 - 90 Kg Recycled blast furnace dust 240 - 260 Kg OPC 55-65Kg GGBS 4 - 6 Kg The above dry ingredients were combined with approximately 60 litres of water and the resulting slurring was transferred to a 3 station wet press to produce paving slabs.

Example 2: Composition for Wet Casting Coarse recycled blast furnace material 180 - 200 Kg Medium recycled blast furnace material 200 - 220 Kg Recycled blast furnace dust 240 - 260 Kg OPC 120- 135 Kg GGBS 17 - 24 Kg The above dry ingredients were combined with approximately 90 litres of water and the resulting slurring was wet cast to produce paving slabs.

Example 3: Composition for Semi-dry Pressing Coarse recycled blast furnace material 180 - 220 Kg Medium recycled blast furnace material 160 - 200 Kg Recycled blast furnace dust 375 - 425 Kg OPC 140 -160 Kg The above dry ingredients were combined with approximately 30 litres of water and the resulting mixture was transferred to a semi-dry press to produce paving slabs or paving blocks.

Figure l Figure l illustrates a five station wet press for fabrication of a two-layer hard landscaping product in accordance with an especially preferred embodiment of the method.

The press consists of five moulds (1) on a rotatable table (2). At the first station (A) the mould is filled with a thin layer of face mix. The table is then rotated so this mould is transferred to the second station (B). At B the face layer is subjected to a first compression. The table is then rotated so this mould is transferred to the third station (C). At Cthe mould is filled with backing mix. The table is then rotated so this mould is transferred to the fourth station (D). At D the contents of the mould are subjected to a second compression at a higher pressure than the first. The table is then rotated so this mould is transferred to the fifth station (E). At E the two-layer product is ejected from the mould.

Figure 2 Figure 2 is a flow chart which illustrates an example of a plant combining wet pressing with other processes.

The recycled blast furnace material is passed through at least one magnetized zone before being weighed into the wet press mixer. Binder and additives are weighed into the mixer and excess water is added and the contents are mixed to create a flowable slurry. The slurry is then passed to a wet press fabrication zone to produce a hard landscaping product.

Excess water removed in the fabrication zone is then passed to a water treatment zone where the water is treated to remove fine particles via a settlement process. This water is then added to a semi-dry or wet cast mixer containing fresh recycled blast furnace material, binder and additives. The semi-dry mix is then passed to a semi-dry press fabrication zone and/or the wet mix is passed to a wet cast zone to product the hard landscaping product.

The excess alkalinity of the recycled water improves the curing efficiency of the other two processes.

Claims (1)

1. A method for producing a shaped concrete product such as a hard landscaping product comprising the steps of combining aggregates binder and optional additional agents with an excess quantity of water sufficient to create a Plowable slurry, passing the slurry to a shaping tone whereat a shaped intermediate is fabricated in suitable wet processing manner, and curing the shaped intermediate to produce a shaped concrete product, wherein at least the major part of the aggregate comprises recycled blast furnace material.

. 2. A method in accordance with Claim 1 wherein the shaped intermediate ë.

A. .. is further treated by the step of reduction of the water content to a level .e more closely approximating optimal hydration level for the .

15 binder/aggregate combination prior to curing. :.

A.' . 3. A method in accordance with Claim 2 wherein the step ol reduction of In the water content is carried out by wet pressing.

2() 4. A method in accordance with any preceding claim wherein, to achieve a Plowable slurry, an excess of water of at least 10% over the conventional optimum for a wet process is used.

5. A method in accordance with any preceding claim wherein the shaped intermediate is fabricated by wet pressing.

6. A method in accordance with Claim 5 wherein the solid and water mixture comprises water in an amount of 12 to 15% by weight. \

7. A method in accordance any one of Claims I to 4 wherein a wet casting process is used.

8. A method in accordance with Claim 7 wherein the solid and water mixture comprises water in an amount 14 to 20% by weight.

9. /\ method in accordance with any preceding claim further comprising the step of removing iron particles from the recycled blast furnace material prior to combination with water.

10. A method in accordance with Claim 9 wherein the blast furnace . material is passed through at least one magnetized iron segregation ë - . zone in order to remove substantially all the iron from the blast furnace ë material. . .

11. A method in accordance with Claim 10 wherein the magnetized iron . segregation zone comprises an arrangement of at least one magnetised .. drum on a suitable conveyer belt over which the material may be passed 12. A method in accordance with any preceding Claim wherein the dry ingredients are combined in the range 80 to 90% by weight aggregate to 20% by weight binder.

13. A method in accordance with Claim 12 wherein the aggregate comprises at least 50% recycled blast furnace material by weight.

14. A method in accordance with Claim 12 or Claim 13 wherein the binder comprises a mixture of ordinary Portland cement and processed Ground Granulated F3lastfurnace Slag in the respective ratios of 80 to 100% and O to 20% by weight.

15. A method in accordance with any preceding Claim wherein the mixture is passed to a fabrication zone and transferred to a suitable mould to be formed to the desired shape; compression is applied to the shaped mixture in the mould to reduce the level of excess water to more closely approach the optimum hydration level for the mixture.

16. A method in accordance with any preceding Claim being a method for fabricating generally rectangular planar structures, comprising the further step of transferring wet mixture into a suitably shaped mould ë A. .. and removing the excess water therefrom by wet pressing. .e .

15 17. A method in accordance with Claim 16 wherein the process is carried .

out on a three stage wet press processor, comprising a rotating processing table having three suitably and equivalently sized mould . features, the rotating table successively transferring each mould feature from a first filling stage where wet material is applied to a second pressing stage where compression is applied to drive off excess water to a third ejection stage where the formed flag or slab is ejected for subsequent handling and processing.

18. A method for producing a two-layer hard landscaping product comprising a face layer and a backing layer wherein the face layer comprises fiec, high quality aggregate and the backing layer comprises blast furnace material as an aggregate substitute, the method comprising the initial steps of mixing a face layer mixture comprising combining higher quality natural aggregate with binder and water and transferring to a mould in a thin layer, the face layer then being subjected to a first compression in order to prevent mixing, a backing layer comprising recycled blast furnace materials, binder and water then being added to the mould and the two layers then subjected to a second compression at a higher pressure in order to produce the finished product.

19. A method in accordance with Claim 18 carried out on a five stage processor, comprising a rotating processing table having five suitably and equivalently sized mould features rotating past five process stages successfully comprising a first fill to fill the mould feature to the : .. desired surface depth with a first, high quality material, a first press to ë apply the necessary firming pressure to the first fill to prevent mixing, a second fill to apply the wet mixture intended to comprise the majority 15 of the body of the flag or slab, a second press to apply a higher pressure ë to remove the excess water, and a final ejection zone as above . - described. ë

. 20. A hard landscaping or other shaped concrete product precursor material suitable for wet pressing or wet casting comprising a slurry comprising excess water, aggregate, binder and additional agents, wherein at least the major part of the aggregate comprises recycled blast furnace material.

21. A dry mixture suitable for combining with water to form a hard landscaping product precursor material in accordance with Claim 2O7 the dry mixture comprising 80 to 90% by weight aggregate to 10 to 20 % by weight binder, wherein at least the major part of the aggregate comprises recycled blast furnace material.