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Title:
METHOD OF MANUFACTURING A COMPLETE INSULATED HIGH STRENGTH CONCRETE ELEMENT HAVING A SUPERIOR SURFACE, AS WELL AS A HIGH STRENGTH CONCRETE ELEMENT MANUFACTURED BY SAID METHOD
Document Type and Number:
WIPO Patent Application WO/2013/010545
Kind Code:
A1
Abstract:
Method of manufacturing a high strength concrete element in a main mould (1), where the main mould (1) comprises at least two mould surfaces (2,3,4), where said at least two mould surfaces (2,3,4) are arranged at relative angles between 15° and 165° relative to each other where one mould surface (3) is substantially horizontal, comprising the steps of: • - spraying an outer skin layer (20) of reinforced high strength concrete mix against the mould sides (2,3,4); • - pouring a first backfilling (30) of a high strength concrete against the substantially horizontal surface (3) covered by the outer skin (20) • - placing an insulation layer (40) in the still wet backfilling (30) • - pouring a second backfilling (30') of a high strength concrete in the space between the insulation (40) and the outer skin layer (20) and the first backfilling concrete (30) • - allowing the outer skin layer (20) and the backfillings (30,30') to harden and chemically react hydraulically or pozzolanically together, to form one monolithic layer, where the insulation (40) is connected to the now hardened backfilling (30,30'); • - removing the mould (1).

Inventors:
SERWIN BO (DK)
JOERGENSEN KAJ ERIK (DK)
BRO KARSTEN (DK)
Application Number:
PCT/DK2012/050258
Publication Date:
January 24, 2013
Filing Date:
July 06, 2012
Export Citation:
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Assignee:
CONNOVATE APS (DK)
SERWIN BO (DK)
JOERGENSEN KAJ ERIK (DK)
BRO KARSTEN (DK)
International Classes:
B28B1/00; B28B1/32; B28B1/52; B28B13/02; B28B19/00; B28B23/00; B32B13/04; E04C2/288
Domestic Patent References:
WO2006088364A12006-08-24
WO2007147178A22007-12-21
Foreign References:
FR2580981A11986-10-31
EP0000837A11979-02-21
US20090283208A12009-11-19
Other References:
None
Attorney, Agent or Firm:
PATRADE A/S (Aarhus C, DK)
Download PDF:
Claims:
Claims

1. Method of manufacturing a high strength concrete element in a main mould, where the main mould comprises at least two mould surfaces onto which an outer cement- based skin layer is sprayed, where said at least two mould surfaces are arranged at relative angles between 15° and 165° relative to each other where one mould surface is substantially horizontal, comprising the steps of:

spraying an outer skin layer against the mould sides where said outer skin layer is a reinforced high strength concrete mix, said outer skin layer having a thick- ness of between 2 mm to 10 mm;

pouring a first backfilling of a high strength concrete against the substantially horizontal surface covered by the outer skin , said backfilling having a layer thickness between 10 mm and 100 mm

placing an insulation layer in the still wet backfilling, where the insulation is ar- ranged a distance away from the other mould surfaces corresponding to the layer thickness of the backfill;

pouring a second backfilling of a high strength concrete in the space between the insulation and the outer skin layer and the first backfilling concrete allowing the outer skin layer and the backfillings to harden and chemically react hydraulically or pozzolanically together, to form one monolithic layer, where the insulation is connected to the now hardened backfilling;

removing the mould.

2. Method according to claim 1, wherein the high strength concrete in the backfilling is not vibrated, but cast as a self compacting high performance concrete wet-in-wet with the skin layer.

3. Method according to claim 1, wherein the mould comprises three mould surfaces onto which the outer skin layer is sprayed, where said three mould surfaces are ar- ranged at relative angles between 15° and 165° relative to each other.

4. Method according to claim 1 or 3, wherein the high strength concrete in the backfilling is not vibrated, but cast as self compacting high performance concrete after the skin layer has hardened, securing the wet-in-wet condition due to a special hydrau- lic/pozzolanic activator applied to the inner surface of the skin layer.

5. Method according to any preceding claim characterized in that the backfill concrete covers the insulation layer.

6. Method according to any preceding claim, wherein the concrete for the outer skin layer comprises an additive, making it possible to spray and let the high strength concrete remain in situ when spraying vertically up and horizontally against the mould where said additive is selected from one or more of the following:polymers like Axilat PAV 29, or a Si02 Nanosilica.

7. Method according to claim 1, wherein before the moulds are removed a further back plate mould for casting a back plate is prepared by spraying an outer skin layer against the back plate mould where said outer skin layer is a high strength concrete mix, said outer skin layer having a thickness of between 2 mm to 10 mm; pouring a backfilling of a high strength concrete, having a layer thickness between 10 mm and 100 mm and optionally forcing an insulating material provided with cut out channels into the backfilling thereby creating concrete ribs extending into the insulating material; placing the back plate mould up side down on the main mould.

8. Method according to claim 1, wherein before the moulds are removed, a further backfilling is poured over the insulation, such that the backfilling connects with the backfilling and outer skin layers wet in wet or alternatively where an insulating strip or part of the insulation layer extends to the mould side, separating the first or secondly poured backfill from the last backfill, and where the insulation layer optionally on the upper surface is provided with cut out grooves.

9. Method according to claim 1 or 8, wherein before the moulds are removed a further back plate mould for casting a back plate is prepared by spraying an outer skin layer against the back plate mould where said outer skin layer is a high strength concrete mix, said outer skin layer having a thickness of between 2 mm to 10 mm.

10. Method according to any preceding claim wherein the manufacturing process for the manufacture of a concrete panel comprises a number of stations:

- a first station where the concrete casting moulds are prepared and assembled,

- a second station where the skin layer of high strength concrete is sprayed onto a front side mould in a layer thickness of between 2 and 10 mm;

-a third station where the first backfill is poured into the mould;

- a fourth station where insulation, and optionally reinforcement, shear connectors and anchors and/or mounting/lifting devices are arranged in the wet backfill concrete;

- a fifth station where the concrete panel is cured and de-moulded

- a sixth storage station for the finished cured concrete panels.

11. A method according to claim 10 wherein further stations are arranged between the fifth and sixth stations, where at least one or more of the following are present:

- a station impregnating or surface treating the front side of the panel with an agent, is arranged where the agent is selected among one or more of the following agents: liquid silicone impregnating agent, nano surface treatment like Contec F3 Nanosealer, Acrylic sealers like Contec F2 or chemically reacting sealers like Contec Fl surface hardener, acid staining, water repellent agent, colouring agent etc.;

- a concrete panel drying station optionally comprising an autoclave;

- a polishing and/or grinding station finishing edges and surfaces

12. The method according to any preceding claim wherein the insulation is selected from one or more of the following: aerated concrete, insulating concrete using lightweight aggregates like expanded clay or alike, mineralwool, glasswool, rockwool, pa- perwool, expanded polystyrene, polyurethane foam.

13. The method according to any preceding claim wherein in the outer skin layer concrete an aggregate is mixed in or said aggregate is arranged in the mould prior to spraying of the outer skin layer, where said aggregate comprises one or more of the following in a granulated form : tile, slate, glass, metal, or other mineral materials.

14. The method according to claim 11 where the outer skin layers surface after de- moulding and at least partly curing, is polished, sanded, grinded or otherwise abrasively treated to expose the aggregate. 15. High strength concrete element comprising insulation manufactured according to any of claims 1 to 14.

Description:
Method of manufacturing a complete insulated high strength concrete element having a superior surface, as well as a high strength concrete element manufactured by said method.

The present invention discloses a method of manufacturing a high strength concrete element having a superior surface, high structural strength and insulating properties, as well as a high strength concrete element manufactured by said method.

Casting a three or more sided concrete structure with unique and superior surfaces on all sides is a challenging and almost impossible task, which normally asks for extreme flow (i.e. low viscosity) in the concrete material combined with high vibration to avoid air bubbles and trapped air in the surface. Normally this type of casting is followed by finishing and/or repair works on the visible surfaces in order to achieve an acceptable evenly smooth surface, free of air voids.

Alternatively the concrete structure must be assembled from a number of separate panels, all cast with the visible surface horizontally and downwards, in order to avoid voids and other irregularities.

With the first procedure the repairs/finishing work will be visible and over time the repaired areas will not be as durable as the integrally cast areas, leading to damage and further repairs.

With the second procedure the separate panels have to be assembled, leaving seams or cracks between panels, which require special constructions to leave them moisture tight etc. For both procedures the aesthetic result is not pleasing, and will in most instances require finishing work or surface treatment, for example paint or the like. The difficult tasks described above become even more complicated when the panels are to be insulated, as the insulation needs to be held in place while the concrete elements are assembled and finished. Particularly in situations where constructions are three- dimensional, as is the case for corners and the like, fitting the insulation and the ele- ment in the correct position in the construction is challenging.

Consequently it is an object of the present invention to provide a method and a panel, which alleviates these disadvantages.

The invention addresses this by a method of manufacturing a high strength concrete element comprising the steps of:

spraying an outer skin layer against the mould sides where said outer skin layer is a reinforced high strength concrete mix, said outer skin layer having a thickness of between 2 mm to 10 mm;

pouring a first backfilling of a high strength concrete against the substantially horizontal surface covered by the outer skin , said backfilling having a layer thickness between 10 mm and 100 mm

placing an insulation layer in the still wet backfilling, where the insulation is arranged a distance away from the other mould surfaces corresponding to the layer thickness of the backfill;

pouring a second backfilling of a high strength concrete in the space between the insulation and the outer skin layer and the first backfilling concrete allowing the outer skin layer and the backfillings to harden and chemically react hydraulic or pozzolanically together, to form one monolithic layer, where the insulation is connected to the now hardened backfilling;

removing the mould.

The present invention in this manner demonstrates a method, by which, all surfaces independent of position horizontally or vertically as well as upwards or downwards curved, both convex or concave as well as planar will achieve the same perfect void free surface quality in a High Performance Concrete on all surfaces, due to the advantages of the spraying technique. Spraying concrete against a mould provides a very smooth, homogeneous, and dense surface. This is further improved when using high performance high strength concrete in that the high strength concrete from the outset is more dense and compact and when sprayed onto a surface, becomes even more compact and dense, thereby providing a very compact and smooth finish.

By achieving the perfect surface by shotcreting High Performance Concrete or Glassfi- bre Reinforced High Performance spraying techniques against the front mould the backfilling material, between the sprayed surface and the insulation placed against the back mould can further more be chosen to be of the same high quality High Performance Concrete as the surface or an even stronger and outstanding Ultra High Performance Concrete to achieve slim constructions with extreme strength. The backfilling may also be a more traditional concrete. For concave or circle segment surfaces gravity will naturally cause the backfill to flow down to the deepest point and therefore not be evenly distributed along the surface of the concrete element. In these instances the insulation will be manufactured with the same shape as the interface surface between the backfill and the insulation such that as the insulation is forced into the wet back fill, the pressure will distribute the back fill along the back side of the outer skin layer such that a substantially even backfill layer thickness will be achieved due to the pressure provided by the insulation.

By further securing cohesion between the spray-layer and the backfill, i.e. avoiding the presence of a boundary layer whereby a monolithic concrete structure is achieved, a strong panel is obtained.

The provision of the backfill layer in time for the two fractions (the sprayed layer and the backfill) to react hydraulically or pozzolanically, shall be understood such that the binder acts across the interface/boundary layer between the two fractions as these ma- terials are compatible such that the reaction, i.e. strength building process is the same for both fractions. When performed correctly, the interface between the two layers will only be detectable due to differences in density, and possibly strength if one or the other is selected with a different strength. There will be no zone where the materials are prone to delaminate due to the difference in the manner in which the materials are placed in the mould or built into the panel. Microscopic tests indicate that the chemical reactions appears homogeneously across the interface, when the method is carried out correctly.

The strong backfilling material is furthermore perfect for anchors, shear connectors, profiles etc. to be cast into this material, making outstanding properties and using the full potential of these. As the insulation is placed in the backfill the fasteners and/or shear connectors needs to project through the insulation as they are embedded in the backfilling, and needs to be accessible on the free side of the insulation, when the element is to be mounted or further processed. As the first spray layer is very thin, and the viscosity is adjusted such that the outer skin layer may adhere to the mould during the casting process, it is necessary to cast the backfilling in a more conventional manner, i.e. taking into account the effect of gravity.

For this purpose, the horizontal part of the mould is used in order to pour a first back- filling having the desired layer thickness. After pouring of the first backfilling, an insulation layer is placed in the wet back filling where the insulation layer has a distance to adjacent mould sides which already are covered by the outer skin layer. When a second backfill layer is placed, the insulation, which have just been arranged on the first backfill will have the effect of a mould side such that the second backfill will fill spaces not horizontal, between the back side of the outer skin placed/shotcreted on the mould surfaces and the insulation. In this manner a three-dimensional concrete element is manufactured where the outer surfaces are angled relative to each other.

The second backfill layer will therefore fill the space between the insulation and the sidewall of the mould, and as the second backfill concrete is substantially poured wet in wet with the first backfill, the entire backfill layer will act as one monolithic structure together with the outer skin layer. Preferably, the compressive strength of the high strength concrete is between 80 and 200 MPa. At these strengths very strong panels are achieved, and due to the presence of fibers, at least in the outer skin layer, which is sprayed on, a high degree of ductility is also achieved, together with a perfect finished surface.

In a further advantageous embodiment the backfilling is not vibrated, but cast as self compacting concrete wet-in-wet with the skin layer.

Since the surface quality is already optimized, the backfilling concrete can be cast without vibration as a self compacting concrete or traditional concrete both vertically and horizontally. This is a dramatic advantage specifically to the size, dimension and strength of the mould, which normally must be extremely strong due to the heavy vibrations imparted to the mould in order to compact the concrete. In most cases only heavy steel moulds can be used for this kind of casting, whereas simple wooden or plastic mould can be used when casting without vibration, as is the case with the present invention.

Even when the skin layer has hardened either partly or completely, it is possible to secure conditions similar to wet-in-wet conditions due to a special hydraulic/pozzolanic activator applied to the inner surface of the skin layer, making it possible to cast the backfill concrete at a later stage, and still achieve a monolithic construction. The same additive may in an alternative embodiment of the invention be added to the free side of the backfill in order to be able to place the insulation at a later stage as well. The concrete for the outer skin layer may comprise an additive, making it possible to spray and let the high strength concrete remain in situ when spraying vertically up and horizontally against the mould.

Preferred products to serve as additive in this procedure can be either polymers like Axilat PAV 29 or alternatively a Si02 Nanosilica like Aerosil Fumed Silica from

Evonik Degussa GmbH to adjust the consistency and stability of the Ultra High Performance Concrete perfectly. In a further advantageous embodiment of the invention the mould comprises three mould surfaces onto which the outer skin layer is sprayed, where said three mould surfaces are arranged at relative angles between 15° and 165° relative to each other. When having three mould surfaces relatively complex corner constructions become possible. It should, however, in this context be noted that when within the present description the term mould surface is used, it is to be understood that that is the main surface part of a mould side. In practice a mould surface will also include side limitations such that in theory any mould surface will be delimited by side surfaces arranged substantially orthogonal to the mould surface. However, for the understanding of the invention the term mould surface shall be construed as meaning a major surface.

In a still further advantageous embodiment of the invention the backfill concrete covers the insulation layer.

In this manner it is possible by this simple process to manufacture a complete insulated concrete panel having superior characteristics in a single working method where the surface due to the use of spraying high strength concrete having superior surface characteristics has a surface providing the panel with very good resistance against the influ- ences of the environment, and where the back fill concrete provides the structural stability surrounding a core of insulation providing the insulating properties of the panel.

In a still further advantageous embodiment of the invention the method foresees that before the moulds are removed a further back plate mould for casting a back plate is prepared by spraying an outer skin layer against the back plate mould where said outer skin layer is a high strength concrete mix, said outer skin layer having a thickness of between 2 mm to 10 mm; pouring a backfilling of a high strength concrete, having a layer thickness between 10 mm and 100 mm and optionally forcing an insulating material provided with cut out channels into the backfilling thereby creating concrete ribs extending into the insulating material; placing the back plate mould up side down on the main mould. This method step may in a further advantageous embodiment be modified by providing that before the moulds are removed, a further backfilling is poured over the insulation, such that the backfilling connects with the backfilling and outer skin layers wet in wet or alternatively where an insulating strip or part of the insulation layer extends to the mould side, separating the first or secondly poured backfill from the last backfill, and where the insulation layer optionally on the upper surface is provided with cut out grooves, or in a still further advantageous embodiment of the invention that before the moulds are removed a further back plate mould for casting a back plate is prepared by spraying an outer skin layer against the back plate mould where said outer skin layer is a high strength concrete mix, said outer skin layer having a thickness of between 2 mm to 10 mm.

With these embodiments it is foreseen that also the back side of the panel is provided with the superior characteristics achieved with the spraying technique of a high- strength concrete such that the entire panel both on the front and back side has the unique characteristics achievable with the invention as described above. By using a back plate mould and the characteristics of the outer skin layer being able to adhere to the mould side it is possible to create a construction which is made wet in wet all the way from the outer skin layer being the front layer to the outer skin layer being the back layer and in between having back fills cast wet in wet around for example an insulation core such that a finished panel having superior surface characteristics is achieved.

The manufacture of concrete structures/panels using the method above may be industrialized as set out in a further advantageous embodiment wherein the manufacturing process for the manufacture of a concrete panel comprises a number of stations:

- a first station where the concrete casting moulds are prepared and assembled, where said mould at least comprise a front side mould and a rear part mould;

- a second station where the skin layer of high strength concrete is sprayed onto a front side mould in a layer thickness of between 2 and 10 mm;

-a third station where insulation, and optionally reinforcement and anchors and/or mounting/lifting devices are arranged in the rear part mould;

- a fourth station where the rear part of the mould is positioned and fastened relative to the front side mould; - a fifth station where the backfill concrete is entered into the cavity between the outer skin layer and the rear part mould;

- a sixth station where the concrete panel is cured and de-moulded

- a seventh storage station for the finished cured concrete panels.

By arranging the production in this manner a rational, controllable and fast manufacturing process is achieved. By further adding work stations arranged between the sixth and seventh stations further advantages are achieved, where at least one or more of the following stations are present:

- a station impregnating or surface treating the front side of the panel with an agent, is arranged where the agent is selected among one or more of the following agents: liquid silicone impregnating agent, nano surface treatment like Contec F3 Nanosealer, Acrylic sealers like Contec F2 or chemically reacting sealers like Contec Fl surface hardener, acid staining, water repellent agent, coloring agent etc.;

- a concrete panel drying station optionally comprising an autoclave;

- a polishing and/or grinding station finishing edges and surfaces

The insulation being an important element of the invention is selected among one or more of the following: aerated concrete, insulating concrete using lightweight aggre- gates like expanded clay or alike, mineralwool, glasswool, rockwool, paperwool, expanded polystyrene, polyurethane foam, vacuum insulation.

In a still further advantageous embodiment of the invention an aggregate is mixed in the outer skin layer concrete or said aggregate is arranged in the mould prior to spray- ing of the outer skin layer, where said aggregate comprises one or more of the following in a granulated form : tile, slate, glass, metal, or other mineral materials.

In this manner it becomes possible to provide the outer skin layer with added features. For example when granulated tile or slate is added to the outer skin layer, especially when it is arranged in the mould prior to spraying of the outer skin layer, the finished concrete panel will have a surface with the characteristics of tile or slate. This may be advantageous both for aesthetic reasons and in order to fit in with surrounding constructions, but also from a wear point of view it might provide advantages. In a still further advantageous embodiment the outer skin layer surface after demoulding and at least partly curing, is polished, sanded, grinded or otherwise abrasively treated to expose the aggregate. By further working the concrete panel surface, for example by polishing, sanding, grinding or otherwise abrasively treating the surface in order to remove part of the outer skin layer in order to expose the added aggregate a wide variety of surfaces becomes possible. For example if a granular glass material has been added it will be possible in a combined sanding and polishing process to achieve a surface which is ex- tremely smooth provided with any durable colour as any other glass construction. The same is true if a metal is added, for example stainless steel granules whereby it will be possible to create a concrete construction having a stainless steel look-alike surface.

Due to the inventive method of manufacture the concrete panels may be provided with specific and exceptional aesthetic properties in the outer skin layer a constructive reinforced and highly ductile layer behind the outer skin layer, for example by incorporating reinforcement in the shape of a net or discreet fibres in the backfill whereas other layers having special features such as for example a carbonization retarding layer or the like may be initiated. In this context, however, it should be noted that the high strength concrete mix due to its density will have a very high carbonization retarding property and furthermore as the carbonization is initiated it will due to the reactions between the C02 in the atmosphere and the concrete materials have a self-retarding/breaking effect such that carbonization will only reach a few tenth of millimeters into the outer skin layer.

The advantages of manufacturing a complete element, i.e. an element having the desired outer characteristics such as color, texture, weather-proof ness (grace the dense outer skin layer), structural strength provided by the backfill concrete optionally comprising reinforcement either as traditional reinforcement or in the shape of fibres, where the structural backfill is in monolithic contact with the outer skin layer, where the element may furthermore be in a 3D shape, and comprising the desired insulation integral with the rest of the panel, provides a simple completion of a building structure, as when the element is mounted in it's correct position, the work is done. Furthermore as all element-work is carried out under factory conditions a very high degree of quality, consistency and finish may be achieved, such that the final result, becomes substantially perfect. The invention is also directed to a concrete panel manufactured according to the inventive method disclosed above.

The invention will now be explained with reference to the accompanying drawing wherein:

Fig. 1 illustrates the outer mould of a three sided panel onto which the sprayed skin layer is applied.

Fig. 2 illustrates the final three sided panel after casting.

Fig. 3 illustrates the mould principle with an outer and inner mould to work as platform for the outer sprayed skin (Outer mould) and mould to be mounted before casting the back filling High Performance Concrete (Inner mould) A gap to cast the back filling concrete is situated in the top of the mould.

Fig. 4 illustrates a concrete panel cast in the mould depicted in fig 3.

Detailed description

Turning to fig. 1 an outer mould 1 having three planar sides 2, 3, 4 is illustrated. The mould 1 is suitable to be sprayed upon. Due to the composition of the concrete sprayed onto the mould, the concrete panel's side facing the mould (typically the exterior side of the panel) will have a surface substantially corresponding to the mould. Therefore if the mould surface is very smooth - which is achievable with plastics or steel, the panels' surface will be very smooth.

In this manner using high strength concretes both when spraying and when backfilling a very strong and monolilthic panel is obtained. Prior to pouring the bacfill concrete 22, in one embodiment of the invention reinforcement 23, anchors, bolts,and other desired features can be arranged in the mould. When pouring the backfill concrete 22, these features will be cast in with the backfill concrete, as illustrated in fig. 2.

Fig. 2 illustrates a semi-finished panel 7 according to the invention. The panel comprises an outer skin 20 containing fibres 24, where the outer skin consists of a high performance concrete sprayed onto a mould, as described above. A backfill 22 - also high performance or ultra high performance self-compacting comcrete, also optionally containing fibres 24' and reinforcement 23 is positioned behiond the outer skin layer. Typically the backfill layer will have a thickness between 50 and 150 mm dependeing on the intended aplication.

In figure 3(a)-(f) is in "cartoon form" illustrated the procedure of manufacturing a concrete panel according to the invention.

In figure 3(a) a cross section through a mould 1 having a bottom 3 and two side surfaces 2, 4 is illustrated. The mould is ready and is illustrated by the dashed lines in figure 3(b) a thin layer of shotcrete 20 is applied to the size of the mould 1.

While the shotcrete is still in its unhardened state, a first backfill layer 30 of selfcompacting concrete 30 is added in the bottom of the mould. The shotcrete 20 has a thickness of 5-10 millimeters whereas the backfill layer 30 has a thickness of approx. 30-40 millimeters in this particular embodiment. While the backfill concrete layer 30 has not set, an insulation member 40 is placed in the still wet backfill concrete layer 30 as illustrated in figure 3(d). Between the insulation and the sides 2, 4 of the mould 1 is provided a space corresponding to the thickness of the backfill layer which is desirable along the sides of the mould. In the following step as depicted in figure 3(e) further backfill concrete 30' is placed inside the mould. In this particular embodiment enough backfill concrete 30' is filled inside the mould such that the insulating element 40 will be completely covered with a backfill concrete. In other embodiments, however, the backfill concrete may only be filled into the mould to a level even with the backside 40' of the insulation element.

In figure 3(f) the concrete panel 100 according to the invention has been removed from the mould 1 and the concrete element 100 is provided with three smooth surfaces 2',

3', 4' having the surface characteristics of the shotcrete 20 initially applied to the inside of the mould 1 as described above with reference to figure 3(b).

In other embodiments the backside of the insulation 40' may be provided with a shotcrete layer where the shotcrete has been applied to a second mould (not illustrated) and thereafter wet-in- wet applied to the backfill concrete 30' and the backside of the insulation 40'. In this manner a concrete element having shotcrete mouldsides on all four sides may be achieved. Turning to figure 4 a special embodiment is illustrated where a close-up of a section of a concrete panel according to the invention is illustrated. In this particular embodiment a granular aggregate 50 has been introduced against the mould surface 2, 3, 4 prior to applying the shotcrete layer 20. After the shotcrete layer is applied the backfill 30 is applied as illustrated with reference to figure 4(a).

After being allowed to set, i.e. the shotcrete 20 and the backfill 30 have hardened, the mould is removed as illustrated with reference to figure 4(b). Hereby a surface having exposed a special aggregate 50 and partly shotcrete 20 will be the exterior surface of the concrete panel.

By treating the exposed surface of the concrete panel, for example by a grinding and polishing process, a surface as illustrated with reference to figure 4(c) is achieved, namely a surface having a very smooth and even surface structure with exposed aggregate 50 which aggregate 50 is held in place by the shotcrete 20 and the backfill 30. By selecting the granular aggregate 50, for example as being granular glass, stainless steel, tile or slate the surface will appear with a special aesthetic presentation, but still retain the good physical characteristics of the inventive concrete element according to the invention, namely the very high strength shotcrete providing a dense and maintenance free surface with the structural strength partly provided by the shotcrete, but also by the backfill 30. The manner in which to treat the surface 50' naturally depends on the selection of granular aggregate 50, but typically a sanding/grinding process followed by a polishing or impregnation process will provide an aesthetically pleasing surface.

For the sake of illustration the figures described above does not contain all details pertaining to the moulds, casting equipment etc, but only schematically illustrates the principles of the present invention. In the figures mainly cross-sections through the moulds and panels are illustrated.