This invention relates to a new method of continuously casting concrete by extruding the concrete from a fixed or moving mould. The extruded concrete may contain prestressed reinforcing or other inclusions which are added during the extrusion process.

Concrete casting is a well known art and is used generally where there is a need for a number of identical products to be manufactured. Examples of such products are concrete stormwater pipes, concrete interlocking panels used for earth reinforcement, concrete railway sleepers, and in some cases, pre-cast concrete water tanks.

However, each of the above mentioned products is formed entirely by casting in the usual sense in which a mould is formed and filled with concrete and the mould broken only when the concrete is set so that the product can be removed.

Problems exist with this method in that it is time consuming, firstly in the time required to fill the mould and appropriately seal it, and then to later re-open the mould and remove the concrete product and make suitable preparations for the next casting operation, and secondly in respect of the time required for concrete to set and cure. The time taken in filling and stripping the mould adds to the cost of the final product.

Techniques for the production of concrete such as slipforming and related methods of continuous casting are highly developed based on the conventional hardening rates for normal concretes. A typical time for initial set is about four hours arid the rate of strength development thereafter is relatively slow so that the product is usually not self-supporting.

It is an object of the present invention to substantially overcome, or ameliorate, the above mentioned problems through provision of a continuous concrete casting method by extrusion.

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Recent developments in cement chemistry now mean that sufficiently strong hardened concretes can be achieved within, say fifteen to thirty minutes of mixing. Not only does rapid set occur at times which can be predetermined by appropriate cement formulation but reasonable strengths can be achieved. Strength gains of the order of 1 MPa within 30 minutes from mixing for example, can be reliably achieved. Such concretes have opened new prospects for the production of reinforced concrete using an extrusion technique.

In accordance with the present invention there is disclosed a method of continuous concrete casting by extrusion comprising the steps of:

Supplying concrete to a mould having open ends, and forcing the concrete into the other end of the mould where it passes through and thereby acquires the shape of the mould, subjecting the concrete within the mould to predetermined high compression pressures, and other physical and chemical parameters so as to permit substantial hardening within the mould prior to exiting from the other open end of the mould as self supporting hardened concrete.

Preferably, a means of reinforcement is provided with the concrete being supplied to the mould so as to provide reinforcement for the hardened concrete. This reinforcement may be prestressed.

Also, the mould can be adapted to move in concert with the concrete. This can be performed preferably with a conveyor-type mould structure.

Composite material can be fed into the extrusion device in the form of fabricated layers or paste to bind with the concrete mix during the extrusion process, providing many of the attributes described later.

Also preferably, the physical conditions within the mould can be selected, for example the speed of throughput, temperature, pressure, time, humidity, and chemical processing. Changes in these parameters can accelerate curing and yield

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the high strength required to meet product specifications. Mould walls may be perforated to perform the dewatering process, which assists in the prevention of shrinkage and cracks, and to allow other treatments such as steam curing etc. to be applied as required.

The apparatus for performing the extrusion is also disclosed.

A number of embodiments of the present invention will now be described with reference to the drawings.

Fig. 1 is a schematic representation of a mould structure; (also referred to as an

"extrusion machine"). Fig. 2 illustrates the mould and extruded concrete product;

Fig. 3 is a view similar to Fig. 1 but showing an arrangement by which the thickness of the concrete being extruded can be varied;

Fig. 4 shows a wedge shaped extruded concrete product;

Fig. 5 shows a concrete product with a curved cross-section; Fig. 6 shows a configuration for production of large concrete storage containers;

Figs. 7 to 11 show various product shapes that can be achieved using the present invention;

Fig. 12 illustrates an alternative mould structure;

Fig. 13 shows a section of a multiple wave profile product formed by the apparatus shown in Fig. 12;

Fig. 14 shows a multiple wave profile extruded concrete product;

Fig. 15 shows an alternative mould structure (extrusion machine) with moving mould walls;

Fig. 16 shows a wall extruded on top of an existing wall by a mould having 3 walls;

Fig. 17 shows a ground slab being extruded by a mould having 3 walls;

Fig. 18 shows the sub-base in a trench, being extruded at the same time as the pipe is being extruded;

Fig. 19 shows the sub-base being extruded at the same time as the top slab is

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extruded. The mould has 4 walls;

Fig. 20 shows a schematic view of a mould having tapered walls to reduce friction forces;

Fig. 21 shows a schematic view of a mould having sliding sheets or belts, for the purpose of managing the friction forces. Sliding sheets may rotate like a conveyor belt;

Fig. 22 shows a schematic view of a mould for extruding composite materials at the same time as the concrete mix is extruded;

Fig. 23a shows a cross section of a composite product having cables as the core and concrete as the protective cover. Also a longitudinal section of a product having a different concrete core and concrete cover is shown in Fig. 23b;

Fig. 24 shows a schematic view of a mould having a series of vanes which act as a guide to distribute the concrete mix;

Fig. 25 shows a perforated cubic mould used for sampling of the mix. Some pressure is applied to extract additional water. The sample is strength tested in compression;

Fig. 26 shows a schematic view of the equipment used for prestressing the reinforcement;

Fig. 27 shows a cross section of a T-beam with the reinforcing rod bonded into the concrete;

Figs. 28a to 281 show examples of products that may be mass produced by extrusion.

Figs. 29a to 29j show examples of products that may be extruded on-site.

Referring to Fig. 1, a mould structure 1 is shown which is formed by two parallel plates 2 and 3 each having flanged ends 4 and 5 respectively. Together, the flanged ends 4 and 5 mate with a feeder 6 which permits concrete 15 to be fed into the mould 1.

Also provided are rolls 7 and 8 of reinforcing wire, fabric or mesh which is introduced via holes or slots 9 and 10 between the feeder 6 and the flanged ends 4,5. A pair of guides 13 and 14 are located in the compression zone adjacent to

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the flanged ends 4 and 5 respectively to position the mesh 7 and 8 at an appropriate depth within the concrete mix 15. Lubrication points 16 and 17 are also provided to ease the sliding movement of cast concrete. Lubrication points can be scattered through the mould walls as required:

The concrete mix 15 is pressurised such that it is compressed between the two plates (walls) 2 and 3. The pressure can be maintained by a pump or other suitable mechanisms. As the concrete 15 passes between the plates 2 and 3, it is acted upon by a number of physical, thermal and chemical parameters so as to ensure adequate hardening of the product such that, when the concrete 18 exits the mould 1 , it is in a substantially hardened and therefore self supporting state. The cast concrete product 18 can then be supported by props if required (not illustrated) to ensure retention of shape whilst hardening is completed. Physical parameters that can be controlled depend upon the length a of the mould 1 as seen in Fig. 2, and the speed at which the concrete 18 exits from the mould 1. The process also utilises a predetermined combination of mixtures such as cement,

Water, aggregate, metal fibres (optional), chemicals and other substances known in the art. Various temperatures, pressures and speed of throughput are used to achieve predetermined results such as production rate, appropriate strength, and so on. If required, accelerated curing can be achieved by utilising hot air, microwave ovens or steam in the known manner. Such a process lends itself to the ready application of computerised process control and automation.

The extrusion pressure obviates the need for vibration as a means of achieving concrete compaction in many circumstances.

In addition to the embodiments shown in Figs. 1 and 2, the width can be varied using overlapping plate sections which can slide across each other and thereby vary the width of the mould 1.

In the embodiment shown in Fig. 3, each of the plates (walls) 2 and 3 are connected to a number of hydraulic rams 19 which operate to vary the distance

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between the plates 2 and 3 and accordingly, the thickness of the concrete product 18 produced. Such a configuration is useful in the production of a variety of different shell thicknesses, as well as concrete wall sections where generally a greater thickness is required at the base of the wall than at the top. As an alternative to the rams 19, a number of adjustable clamps (not illustrated) can be used to achieve the same effect.

Such an arrangement is shown in Fig. 4 where a wedged profile 20 is shown. In this configuration, the plates 2 and 3 are angled towards each other so as to produce the appropriate profile.

Another arrangement is shown in Fig. 5 where a curved profile 21 is produced. In this configuration, the plates 2 and 3 are curved along the width of the mould 1.

Turning now to Fig. 6, an arrangement which provides for the production of a cylindrical shape, such as that used in a water tower, is shown. A rotating base 22 or rail (not illustrated) is provided upon which a mould 23 is provided at a constant position with respect to the rotating base 22. The mould 23 is curved to match the curvature desired and the concrete mix 15 is input in the manner corresponding to Figs. 1 and 3. When the concrete product 24 exits from the mould 23 - it rests upon, and is carried out by the rotating base 22. This provides means for continuous cylindrical profiles to be extruded.

In an alternative configuration (not illustrated) which can be used for large structures, such as water towers, the concrete product 24 stays with no relative movement to the base, and the mould 23 is moved to provide continuous casting. This method may be applied to the extrusion of water towers, domes... etc. The concrete mix 15 is input to one end of the mould 23 and is then extruded out of the other end.

It is apparent that a combination of the configurations of Figs. 4, Fig. 5 and Fig. 6

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can provide for the production of cylindrical or conical casting having a variable profile. An example of such a profile is shown in Fig. 7 where a conical shape 25, is illustrated in which both the length and the width of the mould 1 can have curved sections.

It is apparent from the foregoing that a variety of products and cross-sectional shapes which are axi-symmetric, helical or having other prismatic three dimensional profiles can be produced by the extrusion method. Such products as a standard pipe 26 as seen in Fig. 8, a curved hollow section 27 as seen in Fig. 9, a channel section 28, as seen in Fig. 10, and a girder section 29 as seen in Fig. 11 may be produced. Such profiles, and many others, have applications in the production of pipes, sewerage systems, building roofing members, ceilings and load bearing walls. Figs. 28 and 29 show some examples of products that may be extruded in mass production operations or in on-site applications.

Turning now to Fig. 12, an alterative arrangement of a mould 30 is shown which provides for the production of a curved or waved profile product 46 as seen in Fig. 13. In Fig 12, the mould 30 comprises two parallel plates 31 and 32 which are connected by hinges 33 and 34, respectively, to the feeder plate portions 35 and 36. In this manner, the feeder remains in a fixed position for the extrusion of the concrete mix to the interior of the mould 30 between the plates 31 and 32.

As also seen in Fig. 12, the plates 31 and 32 are connected by a push rod 37 and fixing pins 40 and 41. The fixing pins 40, 41 permit the plates 31 and 32 to pivot whilst maintaining a parallel disposition. At each end of the push rod 37, flat end pieces 38 and 39, respectively are provided which are arranged to contact cam ^' s 42 and 43 respectively. The cams 42 and 43 are rotated by a common drive but are displaced by 90 degrees. This causes corresponding displacement of the push rod 37 which causes a reciprocating pivotal motion, or pendulum-like motion, of the plates 31 and 32. It will be apparent to those skilled in the art that such a motion, when applied in proportion to the speed of concrete mix passing between the plates 31 and 32 will provide a waved profiled concrete product 46 as seen in Fig. 12.

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A further extension of the embodiment shown in Fig. 12 is to provide cammed movement in the vertical plane in addition to providing cammed movement in the horizontal plane (as in Fig. 12). Such a configuration can be achieved by replacing the plates 31 and 32 with a series of interconnected sliding plates operated by a series of cams arranged in both vertical and horizontal planes. It will be apparent to those skilled that an appropriate arrangement of cams and plates can permit the formation of a multiple wave profile concrete product 48 as seen in Fig. 14. Furthermore, it will be apparent that each of the sections A-A and B-B as seen in Fig. 14 will substantially correspond to the waved profile shown in Fig. 13.

The concrete product 48 of Fig. 14 provides an increased strength and load bearing capability over that of a flat sheet of concrete and is therefore suitable for wider spans. Also, the profile shown in Fig. 14 can be combined with other profiles such as those of Figs. 8 to 11 if required.

The concrete product 48 of Fig.14 can also be produced with the same principles explained in the earlier pages, but with another modified version of mould 1 as shown in Fig. 15. The plates 2 and 3 of the mould 1 of Fig. 1 are transformed to a series of the blades 51 and 52 of the mould 50 as shown in Fig. 15. ( erforation may be required to assist the dewatering process - not shown).

Blades 51 and 52 are assembled on the conveyors 53 and 54 and have a motion parallel to the centre line of the mould 50 and to each other.

The concrete mix 15 is pressurised and enters through the feeder 6 into the mould 50 and is carried forward by the motion of the blades 51 and 52 until the hardened or partially cured concrete 18 exits the mould 50.

In this modified version, the mould 50 can produce three dimensional shapes such as corrugated sheets etc. The blades can have different cross sections, with respect to each other, to produce corrugations or other patterns in three

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dimensions. Each blade is required to have a similar shaped border to the adjacent blade to ensure that there is no gap between the blades and that there is a continuous flow of extruded material. There are no appreciable friction forces between the mix 15 and the blades 51 and 52.

Each of the parallel opposite blades can act as a discrete mould to enable continuous production of discrete elements.

The speed of the process is controlled by the rate at which the concrete mix 15 is fed between the blades 51 , 52 thereby causing the blades to move forward. Alternatively, the process speed can be controlled by motors or brakes which cause motion of the conveyors 53 and 54 at a predetermined speed.

The conveyors 53 and 54 can follow curved paths which produce products with an overall or global curvature. The blades 51 and 52 can also accept different irregular cross sections and profiles, in the horizontal and vertical planes and varieties of profiles can thereby be produced as well as those shown in Figs. 4 to 11. Fig. 15 shows a mould 50 with curved sections in both the horizontal and vertical planes which will produce the product 48 as shown in Fig. 14.

The high compression forces within the mould can not only overcome the friction forces between the mix and the mould walls, but can also cause dewatering of the cast mix, to achieve and control the required low water/cement ratio, which subsequently results in a faster setting, less shrinkage, higher strength, cohesion and reduced permeability.

Perforation of the mould walls may be carried out so that there are varying numbers/diameters of holes per unit area, and these holes may spread over different sections of the mould, where the compression and dewatering occurs (compression zone). This would mostly happen within the initial sections of the mould. The perforations shall be designed to allow liquid extraction only. Holes of varying numbers/diameters may also be required through the mould, for the

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purpose of fast curing (steam curing) and/or other types of treatment.

In the cases where the movable mould 55 in Figs. 16,17, 18 and 19 moves during the casting and the product remains in a constant position, then one or more walls (partially or completely) may be replaced with a prepared surface. (The term "wall" is used for all of the areas exposed to concrete as it passes through the mould). For example, the panel 72 which is cast on top of the existing panel 65, or the ground slab 73 which is extruded with the mould 55 having 3 walls.

In another version used for extrusion of products such as a pipe 81 in a trench, or a top slab 82 (see Figs. 18 and 19), concrete 74 is extruded underneath of the pipe 8 I/slab 82 at the same time as the pipe 81/top slab 82 is extruded, to provide a good foundation 74 (sub-base).

Moderate tapering (widening) of the later sections of the mould walls 2 and 3 in Fig. 20 may be introduced to reduce and bring friction forces within the required limits.

As shown in Fig. 21, sliding sheets 56 or belts of suitable materials (to be perforated when required) like stainless steel shims... etc, can be incorporated to serve as an intermediate between the mix 15 and the mould walls 2 and 3. The sheets or belt will move forward with the mix for the purpose of managing and controlling of the friction forces. The belt may also be used for other purposes such as; applying coatings (by immersing the belt in coating material or rubbing coating material onto the belt while it is rotating outside the mould), or texturing and providing the desired smoothness or three-dimensional pattern (which may ^' penetrate the full depth of the product) on the concrete surface. The sliding sheets 56 will rotate (like a conveyor belt) around the longitudinal sections of the mould. There are options for lubrication between the belt 56 and the mould walls 2,3 and also between the mix 15 and the belt 56 if required. Belts can cover the whole length of the mould walls, or can be fed through the slots 81 and 82 provided within and following the compression zone. There are no substantial friction

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forces between the mix 15 and the belt 56, also between the belt 56 and the mould walls 2 and 3, although some friction force could be created by restraining the belt movement (if required).

The speed of the belt 56 may be independently controlled so that every possibility between full sliding of the mix 15 relative to the belt 56 and no movement of the mix 15 relative to the belt 56 is encompassed.

Introduction of products which form a composite section 75 can be achieved in different ways as shown in Fig 22. Materials 57, 58 already fabricated (like shims) or in the form of paste, could be fed or extruded through the slots 77, 78, 79 and 80, to bond with the concrete mix 15 and become a permanent part of the product 75. Materials 57, 58 may be added / extruded in layers and go through the subsequent stages, during the extrusion process.

In another version, a mould with one slot or multiple slots 77, 78, 79 and 80 can be used for production of other building materials (other than concrete), where the constituent materials have to be fed in the form of a paste or a paste and fabricated layers. Gypsum panels may be produced in this way (not illustrated).

Addition of the layers can have many important benefits, both in terms of material properties and the function that the product is designed for. Some of the attributes are as follows;

- To act as reinforcement, to resist tension and shearing forces, and to increase strength and durability.

To protect and preserve the product against corrosion, abrasion, and other physical and chemical hazards. To act as waterproofing. - To act as an insulation layer.

To provide patterns and textures, also to give a better appearance to the

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finished product.

To assist the curing process by keeping moisture inside, thus preventing cracks.

To act as a lubricant to allow management of the friction forces between the mould and the concrete.

To incorporate a coating, paint or other surface treatment.

Materials that may be used cover a wide range including steel, aluminium, other metals, wrapped enamelled papers, fabrics, plastics, adhesives, paints, chemicals which may be applied in the form of a paste, sheets or semi-hardened materials such as rubber.

Materials can be applied as a temporary measure to assist in manufacture of the extruded concrete, e.g. controlling friction, or accelerating setting and curing, providing patterns and textures to the product surfaces.

Materials can be applied as shown in Fig. 23a, to act as the core 59 of a product (e.g. cable), with concrete 60 to act as the cover. Also a section consisting of concrete (or other material) layers having different characteristics may be produced, e.g. light density concrete 61 as the core surrounded by a layer of heavier density concrete 62 as the shield as shown in Fig. 23b.

The incorporation of the reinforcement into the product can be carried out using rods, wires, wire-mesh (woven wire - mesh for conical shapes), sheet material, synthetic or other fibres (cut in pieces or being continuously fed within the mix or fed separately like rods), plastics or a combination of the above materials during the extrusion process. The reinforcement may be selected from both metals and non-metallic materials (e.g. steel fibres, synthetic polystyrene, glass fibre.).

Prestressing may be applied to the reinforcement, by utilising one of the following methods (or combinations of these methods);

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Utilising the principle that materials elongate when exposed to heat. By heating up the reinforcement (by electrical or other means), the reinforcement may be elongated to the extent required during the extrusion process. Well established relationships between temperature and elongation exist for metal bars and wires and so extensions can be easily calculated.

Applying resistance forces between the compressed reinforced mix and the reinforcement feeder utilising a tensioning device as a means of pretensioning the reinforcement during the extrusion process, utilising an expansive concrete which will increase in volume during curing thus causing prestress in the reinforcement.

Referring to Fig. 26 the forward driving force resulting from the pumping pressure or other prime mover can be utilised to induce a tensile force or longitudinal prestress in the reinforcement 84 (which is bonded to the hardened concrete 85). The prestress is achieved by providing a braking action (tensioning device) on the drum containing the rolls 7 and 8 from which the reinforcement plays out. Fig. 27 shows a T section containing the reinforcing rod 64.

The concrete mix 15 can be fed through a series of vanes 63 into the mould 83, as shown in Fig. 24 which act as a guide, ensuring uniform distribution of the concrete mix across the cross-section.

Mould design and manufacture may incorporate some of the above features or combinations of these features.

The output from the process may consist of either continuous or discrete elements. This can be achieved by feeding non-binding elements at the end of extruding one product and before extruding the next (non-adhesive pastes may be fed between two discrete products during the extrusion process).

The perforated cubic mould 71 can be fabricated in a similar fashion to those used in practice for measuring the strength of concrete mixes 15. Fig. 25 shows the

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mould 71 which has a slightly greater height than the ones used in practice. This is to compensate for the volume change due to dewatering through the holes 84 during the compression process. After final setting of the test material and stripping of the mould 71 , the cubic sample 76 will be strength tested by compression. This method presents a simple solution for testing the suitability of the cementitious material to be used in the extrusion process.

Figs. 28a to 281 show the examples of products that can be mass produced by manufacturers and precast industries. Civil engineering examples are; Fig. 28a; pipes in standard diameters and lengths, Fig.28b; culverts and channels, Fig. 28c; manholes, Fig. 28d; arches of any size and curvature. Building industries examples are; Fig. 28e; beams of different cross-sections, Fig. 28f; masonry blocks, Fig. 28g; roof tiles, Fig. 28h; corrugated sheets, panels, facades, bearing walls, ceilings, Fig.28i; steps, Fig. 28j; helical shapes, Fig.28k; boxes of different configurations, Fig.281; railway sleepers. Figs. 29a to 29j show the examples of products that can be produced on-site by builders and contractors. Mining industry examples are; Fig. 29a; arches and linings .for tunnels. Civil engineering examples are; Fig. 29b; pipes laid in trenches continuously, Fig. 29c; culverts and channels (lean concrete extruded under slab as slab is extruded), Fig. 29d; manholes, Fig. 29e; tank farms. Building industries examples are; Fig. 29f; roof tiles in strips or in one piece, Fig. 29g; roof ceilings, Fig. 29h; domes, Fig. 29i; columns, walls (straight and curved), fences, Fig. 29j; ground slabs. The extrusion machine 1, 23, 30, and 50 described above may be manufactured in any size so as to suit the particular product which is to be extruded. Machines could be manufactured to carry out in-situ extrusion. An example of the use of such a device is in multi-storey building construction where concrete can be pumped to the particular floor under construction. Extrusion machines are capable of extruding floors, walls, domes and the like.

The foregoing describes only a number of the embodiments of the present invention, and modifications, obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.

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