CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority from South African provisional patent application number 2014/01 124, and PCT patent application number PCT/IB2014/063295 both of which are incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to prefabricated heat insulated structural building panels and, more particularly, although not exclusively, to prefabricated heat insulated building panels that can be employed as a complete wall section extending along at least a part of a side of a building or in the alternative is floor panels or ceiling panels. The invention also relates to assemblies of such building panels to form buildings, especially but not exclusively, domestic dwellings. It is envisaged that composite prefabricated heat insulated structural building panels according to the invention can be made to comply with standards applicable to low energy consumption types of buildings such as those termed "Passive House Standard" in Germany or "code level 6 HLP buildings" in the United Kingdom. This would typically be achieved by an appropriate selection, dimensioning and configuration of the various layers making up the thickness of the insulated structural building panel.

In this specification and the term "panel" should be given a broad meaning that includes a substantially completed longitudinal section of a wall as well, a facade for a wall, a floor panel, a ceiling panel and a roof panel.

BACKGROUND TO THE INVENTION

Structural insulated building panels are a composite building material consisting of an insulating layer that may be in the form of a continuous or more commonly semi-continuous insulating core attached to at least one structural layer and often sandwiched between two structural layers, for example. The structural layers can be oriented strand board, plywood, cement that is often reinforced with fibres to form cement composites, magnesium oxide board, or sheet metal. The core can be polyurethane foam, expanded polystyrene foam, extruded polystyrene foam, polyisocyanurate foam, or composite honeycomb. Structural insulated building panels can be used for many different applications, such as wall, roof, floor and foundation systems. The sizes of structural insulated building panels that are presently available are typically 300, 600, 900 or 1 ,200 mm wide and 2.4, 2.7 or 3 metres long with the length of the panel extending up the height of the relevant wall and the upright edges of adjacent panels being joined at regular intervals either directly to each other or, more commonly, to interposed skeletal frame members. Roof structural insulated panels may have a length of 6 metres or more. Presently available building panels are either not loadbearing or have limited loadbearing characteristics such that they need to be at least partially supported by a structural frame or beam that is typically made of steel, concrete, timber or a composite. On the practical side, smaller building panels make transportation to an erection site and handling easier whilst the use of the largest possible building panels generally creates a building having better thermal insulation properties. Structural insulated building panels are typically available in thicknesses ranging from about 100 mm to about 300 mm. Conventional structural insulated building panels do not, however, exhibit favourable properties for use in external applications and appreciable negative properties reveal themselves in practice. Structural insulated building panels are commonly made of oriented strand board panels laminated onto a rigid foam core made of moulded polyurethane foam, expanded polystyrene, or extruded expanded polystyrene. Other materials can be used in place of the oriented strand board, such as plywood, pressure treated plywood for below-grade foundation walls, steel, aluminium, cement board and even exotic materials such as stainless steel. Some structural insulated building panels use fibre-cement or plywood sheets for the panels, and agricultural fibre, such as wheat straw, for the insulating core. One component currently used in structural insulated building panel construction is an upright spline or connector piece between adjacent structural insulated building panels. Dimensional lumber is commonly used but creates thermal bridging which lowers insulation values. To maintain higher insulation values through the spline, manufacturers use insulated lumber, composite splines, mechanical locks, overlapping oriented strand board panels, or some other methods that may be proprietary. Depending on the method selected, other advantages such as full nailing surfaces or increased structural strength may become available.

Although structural insulated building panels have been available for many years, their use has been limited in that in the configurations and systems that have been made commercially available to date, their use has been associated with high cost in relation to the advantages being achieved. Some of the disadvantages have been their lack of financial appeal as well as their lack of aesthetic appeal. In order to achieve a desirable level of thermal and acoustic insulation, more and more complex floor, wall, ceiling and roof structures have been developed. The complexity is required in order to achieve the required structural integrity; required thermal properties; required acoustic properties; required waterproofing; required fire rating and a target minimum lifespan of the structure. It hardly needs to be mentioned that not only is the thermal insulation responsible for heating and cooling costs of a finished building but also for any accompanying dissipation of heat and associated carbon footprint.

Applicant is aware of certain technical trials that have taken place with building panels using as a structural base particle wood boards without the use of frames. However, as far as applicant is aware, the required structural strength is only achieved with a considerable weight of the panels and the panels exhibit inadequate thermal insulation.

There is thus an ongoing need to try and accommodate target requirements of a building, especially a target thermal insulation requirement, whilst simplifying on-site construction and labour requirements. There is also a need for alternative construction of components that exhibit desirable structural and thermal properties.

In what follows, the expression CNC (computer numerical controlled) forming machine is intended to include various different machines each of which has cutting or abrading tools appropriate to the material to be cut, shaped, abraded or reamed and that are moved in response to action of a controlling computer. The type of machine will clearly be appropriate to treatment of the prefabricated structural building panel or a component thereof and will typically involve the use of a gantry straddling a support for a work piece with either the gantry or a work piece on the support being movable so that effective working of the work piece can take place across its entire width and along its length. Thus, in the instance that the prefabricated structural building panel is made of wood or a substance that can be worked using woodworking tools or any combination of wood and such substances, the expression would extend to a suitable woodworking machine. In other instances in which the prefabricated structural building panel or a component thereof is made of a harder material, the type of machine may employ a laser or a water jet cutter, for example. Simply by way of example, a suitable type of CNC forming machine may be an appropriate model of a machine of the type made by HUNDEGGER MACHINENBAU GmbH of Germany and sold as one of their panel cutting machines.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at any priority date of this application.

Also in what follows, the term "vertical" means a direction that is intended to be vertical in the erected condition of the prefabricated structural building panel assembly and the term "horizontal" means a direction that is intended to be horizontal in the erected condition of the prefabricated structural building panel assembly in spite of the fact that the relevant components may adopt many other orientations during manufacture, storage and transport. It is recorded that Ultra High Performance Concrete (UHPC) is identified as a potential material for use as cladding or as the outer surface of a fagade produced according to my PCT patent application number PCT/IB2014/063295 from which the present application claims partial priority. UHPC is characterized by being a fibre-reinforced cement composite material with compressive strengths in excess of 150 MPa, possibly exceeding 250 MPa and even possibly ranging up to about 600 MPa. UHPC generally includes as constituent materials fine-grained sand, quartz flour, silica fume, plasticizers, small fibres that have in the past been of steel but are believed to more recently include organic fibres such as carbon fibres, special blends of high-strength cement, usually Portland cement, and a curing agent that is typically water. UHPC does not include any larger aggregate particles.

The term high performance concrete (HPC) for the purposes of this specification means any concrete reinforced with fibres that may be glass fibres and wherein the HPC has a compressive strength in the range of from about 30 MPa to about 80 MPa, preferably in the region of about 50 MPa. Advantages of HPC include enhanced compressive strength; ease of placement; compaction without segregation; long-term mechanical properties and long life in severe environments. it will be quite apparent to one of ordinary skill in the art as to what compositions of both UHPC and HPC will be appropriate for the purposes set forth in this specification.

Throughout the specification and claims unless the content requires otherwise the word 'comprise' or variations such as 'comprises' or 'comprising' are to be understood as implying the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention there is provided a prefabricated composite structural layer suitable for inclusion in a prefabricated structural wall panel assembly or a fagade for a building wherein the structural layer has an ultra-high performance concrete (UHPC) layer permanently bonded to at least one layer of high performance concrete (HPC) to form a laminated construction including the UHPC layer and the layer of HPC permanently bonded thereto. Further features of this first aspect of the invention provide for the UHPC layer to be bonded to the first HPC layer by moulding uncured HPC directly in contact with uncured UHPC so that cement in the two layers forms a continuous cementitious matrix and the two layers are bonded together by the resultant cured cement; in the alternative, for the UHPC and HPC layers to be individually made and cured followed by subsequent lamination using adhesive between the two layers; for the UHPC layer to be configured as an outermost UHPC layer in which case it may embody weather resisting or self-cleaning compounds such as may be exhibited by an effective amount of titanium dioxide (Ti0 ₂ ) being included in the outermost layer as a pigment and as a catalyst for decomposing at least some unwanted environmentally deposited compounds and pollutants; and for the prefabricated composite structural layer to be cut and trimmed to a desired size of a completed prefabricated building panel assembly in which it is to be integrated.

Still further features of the first aspect of the invention provide for the size of the prefabricated composite structural layer to correspond to the dimensions of a completed prefabricated building panel assembly in which it is to be embodied; for prefabricated structural building panel assembly to be a wall panel assembly wherein the length of the prefabricated structural building panel assembly is in excess of two, three, four or more times the height of the prefabricated building panel assembly; and for at least one complete access aperture for one or more closures selected from a door, a window or other closure for an access aperture to be provided through the prefabricated structural layer so as to fall fully within the length of a prefabricated structural building panel assembly embodying it.

In accordance with a second aspect of the invention there is provided a method of making a prefabricated composite structural layer as defined above wherein the structural layer has an ultra-high performance concrete (UHPC) layer permanently bonded to at least a layer of high performance concrete (HPC) to form a laminated construction including the UHPC layer and the inner layer of HPC bonded thereto, the method including the steps of casting a layer of either UHPC or HPC concrete onto a flat mould surface; whilst in the cast layer is still uncured, casting a layer of the other of UHPC or HPC concrete directly onto the first cast layer of UHPC or HPC concrete so that the uncured cement of each of the two layers are in intimate contact with each other and form a continuous cementitious matrix, and allowing the prefabricated composite structural layer to cure. A further feature of the second aspect of the invention provides for the prefabricated composite structural layer to be cured whilst being pressed in a vacuum press; for a plurality of prefabricated composite structural layers to be stacked one on top of the other with one or more suitable release sheets being interposed between adjacent prefabricated composite structural layers so that a stack of two or more prefabricated composite structural layers can be cured in a single vacuum press at the same time; and for one or more additional layers of ultra-high performance concrete (UHPC) to be positioned on an opposite surfaces of an HPC layer with optional additional layers of HPC being bonded to an opposite surface of the UHPC layer; for reinforcing of the UHPC layers to include fibres made from carbon, glass, one or more polymers or a mixture of two or more different fibres; and for reinforcing of the high performance concrete (HPC) layers to include fibres made from carbon, glass, one or more polymers or a mixture of two or more different fibres.

In accordance with a third aspect of this invention there is provided a prefabricated structural building panel assembly for forming at least a section of a wall, floor, ceiling or roof of a building, the building panel assembly having a prefabricated composite structural layer as defined above as an outermost layer with the UHPC layer outermost wherein the prefabricated structural building panel assembly has at least one continuous or discontinuous heat insulating layer therein forming a part of the composite construction of the prefabricated structural building panel assembly.

Further features of the third aspect of the invention provide for the heat insulating layer to be in the form of at least one heat insulating layer located on the inside of at least one prefabricated composite structural layer and in many cases between two spaced parallel structural layers; for the heat insulating layer to comprise a layer of self-supporting insulating material such as a suitably rigid thermally insulating foam material that is preferably a closed cell foam material; for the heat insulating layer to be a discontinuous heat insulating layer having zones of rigid heat insulating material located in multiple parallel cavities extending vertically between spaced vertical transverse on-edge panels or strips that may be of a structural panel material with transverse horizontal on-edge panels forming top and bottom boundaries to the prefabricated structural building panel assembly; for transverse horizontal on-edge panels to form top and bottom boundaries to access apertures through the prefabricated structural building panel assembly; and for the prefabricated structural building panel assembly to optionally include a sound insulating layer such as in the form of multiple elastic spacers between two layers of the panel, and especially between a structural layer and another layer, the elastic spacers optionally assuming the form of elastomeric strips.

Still further features of the third aspect of the invention provides for a series of parallel grooves or rows of projections such as truncated pyramids or cones to be provided for forming spaces for enabling heat collecting fluid such as air or liquid antifreeze mixtures to flow and collect or deliver thermal energy as it flows through the spaces; in the case of grooves or other elongate spaces for the grooves or rows of projections to be orientated to be generally vertical in use; for there to be transverse manifold spaces at upper and lower ends thereof; and for the prefabricated structural building panel assembly to be configured to form part of a geothermal storage system.

The prefabricated structural building panel assembly is preferably surface finished on at least the outer surface and is formed from different materials bonded together to form what becomes a unitary or monolithic wall, floor, ceiling or roof panel having at least one structural layer according to the invention bonded to a foamed heat insulating material and by on-edge transverse panels or strips of suitable material.

The bonding of the plurality of layers to each other as may be necessary, including a layer of cladding if it is separately provided, may be conducted using interposed adhesive layers. Adhesive can be interposed between layers and in order to secure the transverse on-edge panels or strips that surround apertures and volumes of foam insulation and to the composite outermost structural layer. Still further features of the third aspect of the invention provide for the periphery of each aperture in a wall panel to be provided with a window or door frame as the case may be, attached to the prefabricated building panel at factory level as a part of the prefabrication process; and for the multiple layers of the prefabricated structural building panel assembly to be selected to be workable by a CNC forming machine.

Still further features of the third aspect of the invention provide for the prefabricated structural building panel assembly to embody plumbing, electrical and communications services built into the prefabricated structural building panel with termination formations being accessible from the appropriate surface of the prefabricated structural building panel assembly such as electrical outlet sockets, water pipe connection sockets and communications terminal points; and for an operatively upper edge of the prefabricated structural building panel to be configured for direct engagement by a roof span. In accordance with a fourth aspect of the invention there is provided a method of making a prefabricated structural building panel assembly as defined above, the method comprising the steps of forming a first prefabricated layer having a length and a transverse dimension, cutting or trimming the prefabricated layer to a required size and forming any required apertures using a CNC forming machine; locating a plurality of on-edge transverse panels or strips against an inner surface of the first prefabricated layer to form multiple parallel cavities with transverse on- edge transverse panels or strips forming terminal boundaries of the prefabricated structural building panel assembly and also, in the case of apertures, upper and lower boundaries of the one or more access apertures for closures selected from a door, a window or other closure for an access aperture through the prefabricated structural building panel assembly; introducing heat insulating material into selected cavities to form a heat insulating layer, located between the on-edge transverse panels or strips; and securing a second prefabricated layer cut or trimmed to have dimensions corresponding to those of the first prefabricated layer and any aligned apertures for forming window or door openings through the completed prefabricated structural building panel assembly; wherein at least one of the prefabricated layers is a prefabricated composite structural layer as defined above.

Further features of the fourth aspect of the invention provide for the panel to have a series of parallel grooves or rows of projections such as truncated pyramids or cones forming spaces for enabling heat collecting fluid such as air or liquid antifreeze mixtures to flow; in the case of grooves or other elongate spaces provided in wall panels for the grooves or rows of projections to be orientated to be generally vertical in use; for there to be transverse manifold spaces at upper and lower ends thereof in which instance at least the second prefabricated layer is made as defined above with the UHPC layer outermost; for the other of the first and second prefabricated layers to also be a prefabricated composite structural layer as defined above; for any additional cladding to be bonded to the outermost surface of the UHPC layer as may be required in order to obscure the exposed surface of the UHPC layer and provide a more aesthetically appealing outer surface to the prefabricated structural building panel assembly; and for window or door frames that surround apertures in the building panels to be installed at factory level.

The layer of heat insulating material may be introduced by introducing a reaction mix into voids between the on-edge transverse panels or strips for forming rigid foamed heat insulating material that becomes permanently bonded to the surfaces of the structural layer or layers and the on-edge transverse panels or strips which can be used as a part of a mould or as a mould liner in the production process. The invention also provides a prefabricated structural building panel assembly for forming at least a section of a wall, floor, ceiling or roof of a building, the building panel assembly having an outer prefabricated composite structural layer configured to receive solar energy in use, at least one continuous or discontinuous inner heat insulating layer forming a part of the composite construction of the prefabricated structural building panel assembly, and a series of parallel grooves or rows of projections forming spaces for enabling heat collecting fluid to flow through the panel between the prefabricated composite structural layer and the heat insulating layer so as to collect or deliver thermal energy as it flows through the grooves or spaces. It will be understood that air channels for the purpose of providing one or more channels for ducting air into or out of a building constructed using the prefabricated structural building panel assemblies of this invention or, alternatively, a space between a pair of closely adjacent parallel on-edge transverse panels or strips may be left open for that purpose. Similarly, channels can be formed for the subsequent introduction of service ducts for water, electricity, and communications cable. Alternatively, service ducts for water, electricity, and communications cables may be provided in any of the cavities with the insulation being formed therein afterwards to envelop the services or communications pipes, ducts or cables.

In accordance with a fifth aspect of the invention there is provided a prefabricated building or module comprising a plurality of prefabricated structural building panel assemblies as defined above joined together and provided with a floor and ceiling or roof, or both.

In order that various aspects of the invention may be more fully understood one embodiment as well as some variations thereof now follow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a schematic elevation of a wall of a hypothetical dwelling that has been constructed using prefabricated structural building panels according to the invention;

Figure 2 is an enlarged elevation of the wall illustrated in Figure 1 showing the internal arrangement of on-edge transverse panels or strips relative to the windows and doorway; Figure 3 is the same as Figure 2 but showing the outer surface of the same part of the wall;

Figure 4 is a schematic section through part of a first prefabricated structural layer of a wall such as is illustrated in Figure 3;

Figure 5 is a schematic sectional view through part of a pair of structural layers during manufacture;

Figure 6 is a schematic section through part of a prefabricated wall assembly showing one prefabricated structural layer as shown in Figure 4 with the addition of the on-edge transverse panels or strips against an inner surface of the prefabricated structural layer;

Figure 7 is the same as Figure 6 but showing the addition of a rigid foam heat insulating layer in the voids between on-edge transverse panels or strips and showing the surface of the heat insulating layer machined to provide multiple parallel grooves in its exposed surface;

Figure 8 shows an area of grooved insulation in which the grooves communicate between transverse manifold grooves;

Figure 9 is the same as Figure 7 but showing the addition of a second and outer prefabricated structural layer and schematically illustrates a window frame in situ;

Figure 10 is the same as Figure 9 but of a variation of the invention in which the heat insulating material is devoid of parallel grooves and in which an air exchange duct formed in the rigid foam heat insulating material is shown;

Figure 1 1 is the same as Figure 10 but showing an additional variation of the invention;

Figure 12 is a schematic section through part of a prefabricated wall assembly that is an alternative to that illustrated in Figure 9; and,

Figure 13 is a schematic section through a part of a floor panel made according to the invention. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the production of prefabricated structural building panel assemblies according to the invention as described hereinafter, use may be made of a CNC forming machine that for the purpose of materials that are appropriately workable may be a comprehensive woodworking type of machine or, in other instances, may use other suitable working tools such as laser or water jet cutters.

In any event, the CNC forming machine may be of the general type sold by HUNDEGGER MACHINENBAU GmbH of Germany as one of their range of panel cutting machines. This type of machine may typically have a gantry bridging a feed path for large panels that may have a range of sizes of up to a present day maximum of about 3300 millimetres wide and, depending on various limiting factors, the ability to process panels having a length of up to 12,000 millimetres and longer.

The limits mentioned above are not to be considered as limitative in any way on the scope of the invention but they do satisfy the requirements of the current invention of providing the facility for processing prefabricated self-supporting structural building panel assemblies that may be designed to support loads of more than one storey of a building as may be appropriate. The building panels may have a width corresponding to the total height of a standard single storey of a building (of the order of 2,600 millimetres for a single storey building and of the order of 3,000 millimetres or more for a multi-storey building) and a practical length of up to 12,000 millimetres which may be sufficient for the whole length of a wall of a small building and that corresponds in that instance to from 4 to 5 times the height of the wall.

It is also to be noted that the length of 12,000 millimetres is considered to be a practical working upper limit in view of the fact that any prefabricated structural building panels longer than that would likely need special transport permits and possibly vehicular escorts for transport along public roads to an erection site and such added requirements may raise the cost of a final building unduly.

The gantry of the woodworking machine would typically support various working tools including, but not limited to, one or more chain saws, laser or water jet cutters that are able to cut at all angles; one or more milling or grinding machine heads with the ability of forming contours and shapes using up to 5-axes; drill heads capable of drilling a wide range of diameters of holes in many directions and recesses as well as countersinking recesses. Such a machine can be constructed such that panels can be cut, milled, drilled and labelled under computer numerical control. Referring now to the drawings, and especially to Figures 1 to 3, the invention is applied in this particular instance to a prefabricated structural building panel assembly (1 ) for forming a wall of a building, generally indicated by numeral (2) in Figure 1 , which may be a dwelling constructed using multiple prefabricated structural building panels. The building panels may have a height of about 2,600 millimetres and a length of approximately 12,000 millimetres that can be designed to constitute one entire wall of the building or a substantial part of it.

The prefabricated structural building panel has a construction that will become quite apparent from a description of its manufacture that is carried out in accordance with the second aspect of the invention as follows.

As provided by the first aspect of the invention, a prefabricated composite structural layer (3) suitable for inclusion in a prefabricated structural panel assembly or in a fagade for a building wherein the structural layer has an ultra-high performance concrete (UHPC) layer (4) reinforced with carbon fibres, glass fibres, one or more polymer fibres or a mixture of two or more different fibres with the layer being permanently bonded to a first layer (5) of high performance concrete (HPC) reinforced with carbon fibres, glass fibres, one or more polymer fibres or a mixture of two or more different fibres in a laminated construction.

The prefabricated composite structural layer (3) is preferably made according to the second aspect of the invention wherein the ultra-high performance concrete (UHPC) layer (4) is cast onto a flat mould surface (6) treated with a suitable release agent and whilst that layer is still uncured, casting the layer (5) of the HPC concrete directly onto the uncured cast layer of UHPC concrete so that the uncured cement of each of the two layers is in intimate contact with each other and form a continuous cementitious matrix. A stack of further prefabricated composite structural layers may be separated from each other by a release sheet (7) to enable the simultaneous curing of the plural prefabricated composite structural layers in a vacuum press, for example, indicated by numeral (8) in Figure 5, and allowing the prefabricated composite structural layers to cure in a kiln in the usual manner.

The cost of the UHPC reinforced predominantly with carbon fibres layer is currently more than the cost of the HPC layer reinforced predominantly with glass fibres and it is estimated that for the purposes of this embodiment of the invention the UHPC layer could be of the order of 3 mm thick and the HPC layer could be of the order of 7 mm thick. The target thicknesses will only be determined after significant further testing and research. Clearly other thicknesses will apply depending on the properties of the concretes and the strengths to be achieved of the structural layers as well as overall cost factors. Also, one or more additional layers of ultra-high performance concrete (UHPC) may be positioned on an opposite surface of an HPC layer with optional additional layers of HPC being bonded to the additional UHPC layer. In this way cement in adjacent layers forms a continuous cementitious matrix and the layers are bonded together by the resultant cured cement.

The entire layering process may be carried out or using travelling discharge hoppers (9) moving over the surface of the mould and discharging the liquid or semiliquid cementitious mix onto the mould surface or onto an immediately subjacent layer of cementitious material or a separating release sheet. The prefabricated outermost structural layer described above may, when all of the layers are in place, be cured using the vacuum press in well-known manner followed by any treatment in a suitable kiln or the like.

A substantially identical prefabricated composite structural layer may be made for use as the inside of a composite prefabricated structural wall panel assembly that is described further below.

The UHPC layer, or at least the first layer thereof is configured as an outermost UHPC layer in which case it preferably embodies self-cleaning components such as an inclusion of an effective amount of titanium dioxide (Ti0 ₂ ) in the outermost layer to serve primarily as a catalyst for combatting at least some unwanted environmentally deposited compounds and pollutants. Through nanotechnology in the use of small particles of Ti0 ₂ , the envelope may be made to be self-cleaning and UHPC structures have been expected to have a maintenance free lifespan of more than 100 years. The prefabricated composite structural layers made as described above are cut and trimmed to a desired size of a completed prefabricated building panel assembly in which it is to be integrated with access apertures for windows (1 1 ) and at least one access aperture for a doorway (12) being cut in the prefabricated composite structural layer. Turning now to the third aspect of this invention, and with particular reference to Figures 6 to 9 of the drawings, a prefabricated structural building panel assembly (1 ) as described above has a first prefabricated composite structural layer (3) that is to form an inside surface of the final wall panel assembly has it's outermost layer with the UHPC layer facing downwards in the mould so as to form the finished inside surface of the wall panel assembly. A plurality of on- edge transverse panels or strips (13) of UPC material are adhesively bonded to the inner surface of the UPC layer of the prefabricated layer to form multiple parallel cavities (14) extending vertically with respect to the final height of the prefabricated structural building panel assembly. Longitudinal on-edge transverse panels or strips (15) are bonded to the prefabricated composite structural layer to form upper and lower boundaries of the prefabricated structural building wall panel assembly. Additional longitudinal on-edge transverse panels or strips (16) are bonded to the prefabricated composite structural layer to form upper and lower boundaries to the window apertures (1 1 ) and door aperture (12).

This arrangement leaves cavities or voids between the on edge transverse panels or strips into which heat insulating material is introduced to form a heat insulating layer (17). The layer of heat insulating material may be introduced by introducing a reaction mix into voids between the on-edge transverse panels or strips for forming rigid foamed heat insulating material that becomes permanently bonded to the surfaces of the structural layer or layers and the on-edge transverse panels or strips which can be used as a part of a mould or as a mould liner in the production process. At this stage the partially made wall panel can be treated in a CNC forming machine to form a series of parallel grooves (18) extending up the height of the wall panel and that may be interconnected at top and bottom by transverse manifold grooves (19). It is to be noted that because the rigid foam bonds to the surface of the structural layers and on- edge transverse panels or strips it adds to the rigidity and structural strength of the building panel assembly.

Thereafter, a second prefabricated layer cut or trimmed to have a height and length corresponding to those of the first prefabricated layer and aligned apertures for forming window or doorways through the completed prefabricated structural building panel assembly is secured in position to the upper free edges of the on-edge transverse panels or strips. In this instance because of the location of the grooves, the second prefabricated layer forms the outermost layer and its outermost UHPC layer forms the outermost surface of the building panel assembly.

The finished appearance of a UHPC may not be sufficiently aesthetically pleasing for some people. It typically has a look similar to smooth porcelain. In some cases a cladding material, such as wood panels may be glued and vacuum pressed to the UHPC panel. Any additional cladding (21 ) may be bonded to the outermost surface of the UHPC layer as may be required in order to obscure the exposed surface of the UHPC layer and provide a more aesthetically appealing outer surface to the prefabricated structural building panel assembly, as shown in Figure 10. Any window or door frames (22) that are typically channel shaped and surround the apertures may also be installed at factory level if it is convenient and cost effective to do so. It should be noted that UHPC/ HPC panels are regarded as being completely water and vapour proof. Therefore, no mould should develop as by foaming out the inside of the panels all air is replaced by closed cell foam. Both polyurethane and closed cell polystyrene foam are currently proposed although the polyurethane is a more effective insulator at the present time. The prefabricated structural building panel assembly is preferably surface finished on at least the outer surface at factory level and is formed from different materials bonded together to form what becomes a unitary or monolithic wall panel having at least one structural layer according to the invention bonded to a foamed heat insulating material and on-edge transverse panels or strips of suitable material.

The parallel grooves in the prefabricated structural building panel assembly need only be provided in respect of panels the will receive solar energy in use for enabling air or other heart transfer fluid such as antifreeze to flow and collect or deliver thermal energy as it flows in the grooves. The prefabricated structural building panel assembly may be configured to form part of a geothermal storage system.

Of course, as indicated above, the prefabricated structural building panel assembly may embody plumbing, electrical and communications services built into it at factory level.

Also, in instances in which the wall is not to be used as a thermal collector, the grooves can be omitted entirely as shown in Figure 10. Figure 10 also illustrates the presence of an air channel (25) for the purpose of ducting air into or out of a building constructed using the prefabricated structural building panel assemblies or to or from a geothermal storage facility.

In the instance that the heat insulating material is to be introduced and set in situ in spaces or voids without the presence of any grooves the heat insulating material can be introduced into the spaces by way of holes (20) through the peripheral transverse on edge panels (13, 15) or strips.

Figure 1 1 illustrates a variation in which the inner prefabricated structural panel (26) is made without an outer layer of UHPC. There are numerous ways in which the structural building panel assembly constructed as described above can be varied or supplemented in different ways.

Figure 12 illustrates a variation of the invention in which grooves (31 ) are provided but in this instance both the inner and outer surfaces of the grooves are made up of HPC as it is less likely to be adversely affected by pollutants in the heat exchange fluid passing through the grooves. As shown, the inner layer (32) of HPC has a moulded or machine grooved panel (33) adhesively secured to it or, alternatively, suitably moulded onto it to form a permanent bond between the two HPC layers. In this instance the wall panel is provided with an additional UHPC layer (34) on the inside of the grooved HPC layer.

Figure 13 illustrates the application of the invention to a floor panel that could, in the alternative, also be used as a floor, ceiling or even a roof panel. In this instance the prefabricated structural building panel is provided with a floor covering (35) on its outermost surface and may optionally be provided with a second grooved structure (36) on its under surface for the purposes of accommodating sound insulating material. The grooves are preferably shaped so that soundwaves are effectively neutralised.

It should be noted that there are perceived to be major advantages in the construction described above in spite of the fact that ultra-high performance concrete (UHPC) reinforced with carbon fibres is very expensive and high performance concrete (HPC) reinforced with glass fibres or polymeric fibres also currently costs three to four times the cost of conventional concrete. UHPC has a compression strength of more than 150 MPa and up to 600MPa; HPC has a compression strength of about 50MPa, whilst normal concrete has a compression strength of only about 5MPa. The thicknesses of the layers mentioned above should be adequate to provide a prefabricated structural building panel of the type described. It is envisaged that implementation of the invention may result in radically reduced construction periods and construction costs with the possibility of organizing that finished building panels are delivered just-in-time for fast-track assembly and building erection. Labour input can be reduced by as much as 80% and the use of thinner walls without sacrificing any structural properties can provide up to 20% more usable space for any given building footprint. It is possible to incorporate in the building envelope a bioclimatic heating and cooling system and to comply with ZeroEnergy construction standard.

The invention provides an adaptable and durable structural system with low embodied C0 ₂ content and is aimed at maximising the envelope value, including improved aesthetics, acoustic and lightning comfort, and quality of indoor environment. A building erected using prefabricated structural building panel assemblies according to the invention can comply with the energy performance standards such as the international ZeroEnergy standard.

Numerous variations may be made to the examples of the invention described above without departing from the scope hereof.