The present invention discloses a method of manufacturing a high strength concrete plate member having a superior surface, as well as a high strength concrete panel 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 re- quire finishing work or surface treatment, for example paint or the like. 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 plate member comprising the steps of:

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

- secondly backfilling with a high strength concrete vertically and/or horizontally, having a layer thickness between 10 mm and 100 mm

allowing the two layers to harden and chemically react hydraulically or poz- zolanically together, to finally form one monolithic layer;

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 High Performance Concrete on all surfaces.

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 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. By further securing cohesion between the spray-layer and the backfill, i.e. avoiding the presence of a boundary whereby a monolithic concrete structure is achieved, a strong panel is obtained. The strong backfilling material is furthermore perfect for anchors, profiles etc. to be cast into this material, making outstanding properties and using the full potential of these.

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 layer between the two fractions as these materials 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 se- lected 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 appear homogeneously across the interface, when the method is carried out correctly. In a further preferred embodiment 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 high strength concrete in the backfilling is not vibrated, but cast as self compacting high performance concrete wet-in-wet with the skin layer.

Since the surface quality is already optimized, the back filling High Performance Con- crete can be cast without vibration as a self compacting High Performance Concrete both vertically and horizontally. This is a dramatic advantage to the size 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 se- curing 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.

In a further advantageously embodiment of the invention 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.

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.

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;

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

-an optional third station where insulation, reinforcement and anchors and/or mount- ing/lifting devices are arranged in the mould;

- a fourth station where a 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:

- 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 invention is also directed to a concrete panel manufactured according to the tive method disclosed above. The invention will now be explained with reference to the accompanying drawing wherein: illustrates the outer mould of a three sided panel onto which the sprayed skin layer is applied.

illustrates the final three sided panel after casting,

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.

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 the mould surface is very smooth - which is achievable with plastics or steel, the panels' surface will be very smooth.

Jumping to fig 3 further illustrates an embodiment. The outer mould is in this embodiment four sided 2',3', 5, 6. The inner mould 10 is arranged such that the space between the two mould parts , 10 provides space for the concrete panel to be casted. Before the inner mould 10 is positioned the outer concrete skin layer 20 is sprayed against all outer mould 1 surfaces. Typically the layer thickness is between 2 and 10 mm and preferably containing fibres, in order to provide the hard but brittle concrete with high ductility.

After having sprayed the outer skin layer 20, the inner mould 10 is positioned as illustrated. Along an upper edge an openeing 21 is provided, through which the back fill concrete 22 is poured. The back fill concrete is a self-compacting concrete, whereby vibrating the mould is not neccessary in order to achieve a monolithic structure. The back fill concrete will flow into the mould and occupy the space not taken up by the outer skin layer.

In this manner using high strength concretes both when spraying and when backfilling very strong and monolilthic panel is obtained.

Prior to pouring the bacfill concrete 22 and positioning the inner mould 10,

reinforcement 23, anchors, bolts, insulation 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. 4.

Fig. 4 illustrates a 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. 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.