WO1999051829A1

WO1999051829A1 - Pre-cast concrete walling system

Info

Publication number: WO1999051829A1
Application number: PCT/AU1999/000234
Authority: WO
Inventors: Phillip Boot
Original assignee: Phillip Boot Holdings Pty. Ltd.
Priority date: 1998-04-07
Filing date: 1999-03-31
Publication date: 1999-10-14
Also published as: MY114848A; CN1108424C; CN1296542A; TR200002908T2; AR014822A1; KR20010042467A; ID27587A

Abstract

The invention concerns a pre-cast concrete panel comprising two skins and a non-concrete spacer element disposed between the two skins. A series of ducts extend through the spacer element and connectors extend through the ducts between the two skins. A series of channels are also defined in the two opposed faces of the spacer element and concrete supporting ribs extend along the channels and support the skins. The concrete connectors and ribs are formed monolithically, i.e. cast in one piece, although in some embodiments the connectors may be discontinuous in their length at or near their centre with the two halves of the connector joined by an insulated structural tie extending into the two halves of the connector. The skins may be cast in concrete at the same time as the ducts or ribs or alternatively may comprise a preformed board. The specification also discloses a battery casting method of vertically moulding such building panels.

Description

PRE-CAST CONCRETE WALLING SYSTEM

Field of the Invention

The present invention relates to a pre-cast concrete walling system. In particular the invention provides a large prefabricated light weight concrete wall panel and methods of making such a panel. The panels of the present invention may be load bearing or non load bearing and suitable for use in low cost single storey or multiple storey building construction.

Background of the Invention

There are many types of lightweight concrete walling systems in existence. The term "lightweight" when used to describe concrete, refers to concrete weighing no more than 1,400 kg/m³, which is still veiy dense. Existing lightweight concrete walling systems, include solid walls made from lightweight materials or walls or wall panels which are made hollow which include cast in "concrete voids" that reduce the content of concrete and hence reduce the overall density of the panel. The term "concrete void" as used herein, implies an absence of concrete with the space occupied by either air or a non-concrete filler. The present invention relates to improvements in the "concrete void" type of lightweight concrete walling.

There are two types of "concrete void" walling systems. There are the solid types that support the skin, i.e. the face of the wall panel, in which the solid material sometimes acts as an insulator, and hollow types that are cast in as lost or removed form work.

Insulation is a major consideration for a society which has a responsible energy policy, and seeks to make energy efficient buildings, hence most building elements now utilise an insulative material as the concrete void. However, insulation is usually only of any real value when used for the external walling of the building in areas where the temperature external of the building fluctuates to levels that are not comfortable to live in. The majority of walling in residential dwellings is internal walling which requires little of no insulation and the use of insulated panels for internal walling to a large extent wastes the value of the insulation used. Materials which are typically used as insulation, include expanded polystyrene and polyurethane. The use of such materials as concrete voids serves a dual purpose both providing insulation and also reducing the weight of the walling element. However, such materials have very low melting temperatures and present almost no resistance to heat at elevated temperatures as is required for fire ratings. Also in some cases such insulating materials can be more expensive than the materials they replace, particularly in developing countries where the raw materials required to manufacture such insulating materials, are quite expensive relative to building materials.

Many existing walling systems, use a rigid insulation material to support wall surfaces in a sandwich type construction in which the skins of the wall are bonded to the insulating material.

As is well understood, walls can perform two basic functions. The first function is to act as the sides of a room also known as the walling function. Many internal non-loading bearing walls perform only that function. Structural load bearing walls support roof and upper floor loads, resist horizontal forces, this being the structural function, as well as acting as the sides of the rooms (the walling function). There are various considerations which have to be taken into account when trying to reduce the weight of walling and save on material costs. It is obviously desirable to make the wall element skin thickness as thin as possible and if the wall is to have an overall thickness of over a 100 mm the two wall surface skins will have to be separated by another element and still remain connected.

When making thin concrete wall sections, reinforced with a steel mesh fabric, because of the size of the steel mesh fabric, it is very difficult to reduce the wall section below 25 mm. The use of fibre reinforcing makes it possible to reduce the thickness of the wall section further, however the thin wall section (which may be between 8 to 45 mm thick, most preferably 12 to 35mm) will need to be supported by some other element both during the manufacturing and hardening process and afterwards. The distance the wall skin can effectively span between support elements depends on the thickness of the skin and is quite limited without any additional support. This factor is further highlighted when using a pre-manufactured cementitious board when the wall section thickness may be as low as 4mm.

A further problem, is that the two wall skins must be connected to each other to give each other enough strength to perform the walling function. However, at the locations where the two skins are connected, high stress zones occur depending on the span between the connecting support. In most cases, this problem is addressed by bonding the wall skins to the "concrete void" and secondly by connecting the two skins with a series of vertical studs or very slender vertical columns. It is known to cast the two wall skins separately and bond the two cast skins together at a later time. However, this is a very difficult process particularly with large structural prefabricated wall panel skins which can be 8 meters long by 3 meters by 10-25 mm thick and may include window and door openings, since the thin fragile pre-cast skin members require extreme care in handling prior to being joined. Further, the connectors/spacers are not homogeneous with the skins and this can lead to long term delamination and areas of high stress in the vicinity of the connectors. Such stresses can cause unsightly cracking. Thus, this type of system is only suitable for vary small modular type non structural panels. The second problem with this system is that separately casting skins is a very inefficient use of mould space and such systems require twice the mould surface area that a monolithically cast system would require to produce a panel of the same size.

The present invention seeks to alleviate the problems of the prior art and provide pre-cast lightweight walling system which can weigh less in wall volume than 800 kg/m³.

Summary of the Invention

Thus in a first aspect of the present invention there is provided a concrete building panel having :- two skins comprising concrete faces, or boards; at least one lightweight non-concrete spacer element disposed inside the building panel between the two faces, the lightweight spacer element defining a plurality of spaced apart ducts extending therethrough and a series of channels which extend away from ends of the duct to an adjacent duct; concrete connectors projecting through the ducts connecting the skins; and concrete supportive ribs formed in the channels wherein the ribs and connectors define a support structure for the two skins.

The support structure is very strong and robust in all directions and is moulded monolithically i.e. components are cast at the same time. The grid pattern and size of the ribs and connectors is dictated by the shape of the spacer element and may be varied by varying the pattern and size of the channels defined by the spacer element. The pattern can be square rectangular or triangular. The ribs can run in at least two co-planar directions, such as vertical and horizontal, preferably in three or four. The majority, in some structures all, of the intersections between ribs will occur at the connectors, in others the majority will occur at the connectors.

The ribs are sized to suit various applications including structural and may be of different size in the same spacer element. They may be reinforced with fibre, fibre rod, or steel rod or sometimes both rod and fibre. Viewed with the panel oriented horizontally, it is preferred that the channels defined in the spacer element radiate away both outwardly towards another duct and also upwardly from the central part of the duct towards the skin such that a tangent to the ribs intersects the plane of the skin at an angle, typically 30 to 60 degrees. It is preferred that the core of the ducts are shaped having radially expanded or bell-shaped ends where the duct meets the skin.

It is preferred that the sectional shape of the ducts is generally flower shaped with "petals" defined where the ends of the channels intersect the duct. In a preferred embodiment a concrete perimeter beam extends around the whole of or part of the perimeter of the panel.

In one embodiment the concrete connectors are discontinuous in their length at or near their centre. The two halves of the connector are joined at or near their centre by an insulated structural tie extending towards and into the two halves of the connector, and extending towards and into, or being connected to, the concrete ribs.

In one embodiment the skins are formed by boards which comprise fibre reinforced sheet material, and are typically cementitious.

However the strength of the support structure is enhanced many times by moulding it integrally with concrete surface skins.

Thus in a related aspect, the present invention also provides a method for making a building panel comprising providing a mould having a base and sides placing a lightweight non-concrete spacer element defining a plurality of spaced apart ducts inside the mould on a layer of concrete placed therein; vibrating or agitating and pushing the spacer element into the concrete so as to encourage any air entrapped under the spacer to escape around the space or through the ducts to the surface of the concrete and to force concrete into the ducts and channels; pouring additional concrete over and around the spacer element to fill the mould; finishing the surface of the concrete to a suitable texture for the wall; and allowing the panel to cure.

It is preferred that the panel is covered when it is allowed to cure.

The rate of agitation/vibration is preferably quite low, typically a half to 5 Hz, most preferably 1 Hz. The amplitude of the vibration of the panel may be as much as 5 to 20 mm, preferably around 10 mm.

The panel may of course be formed with more than one non-concrete spacer element and the mould may define spaces for doors, windows and the like and during the moulding process all the structural elements can be reinforced where necessary.

In an alternative method, casting could be carried out with the sides of the panel vertically oriented. The spacer element would have to be solid or, if hollow, have internal supports to avoid collapse due to the hydrostatic pressures and vibrations. The degree of internal support could be graduated to suit the relative changing values of the hydrostatic pressure in the vertical casting method.

The invention also provides non-concrete spacer element for use in making the building panel of the present invention defining sides and two opposed faces, at least one, preferably radially expanded, duct extending through the panel from one face to the other and a series of channels extending along each face of the panel away from the duct.

Typically the spacer element will include a number of ducts with the channels extending between adjacent ducts.

Throughout this specification "non-concrete" includes cementitious products with a high air content.

The spacer element is preferably hollow and made in two typically identical halves which are then joined together and sealed to form the spacer.

Suitable materials for the non-concrete spacer include gypsum and plaster, wood pulp and wood products, high impact styrene, expanded polystyrene, any waste products bonded together even any suitable porous material with the outer surface sealed to prevent concrete penetration during concrete casting, or any suitable plastics or cementitious material.

If the void is to be manufactured of a material which has a good fire rating, glass reinforced gypsum plaster and foamed gypsum plaster or foamed portland cement are preferred.

The minimum sectional area midway along the ducts at their centre is about 125mm² with the preferred sectional area being about 1250mm². It is preferred that the ducts are spaced apart in a square grid pattern at between 100 to 500 mm apart.

Brief Description of the Drawings

Specific embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which:- Figure 1 is an elevation of a non-concrete spacer element or void former;

Figure 2 is a cross section on lines II-II of Figure 1;

Figure 2a is an enlarged section on lines Ila-IIa of Figure 1;

Figure 2b is an enlarged section on the centre of a duct. Figure 3 shows a rear elevation of one half of a hollow void element with internal supports;

Figure 4 shows a section on line VI of Figure 3;

Figure 5 shows a section on line V of Figure 3;

Figure 6 is an elevation of a wall spacer; Figure 7 is a plan view of the wall spacer shown in Figure 6;

Figure 8 is a elevation of a load bearing panel embodying the present invention;

Figure 9 is a side elevation of the load bearing panel of Figure 8;

Figure 10 is an elevation of a battery casting assembly embodying the present invention;

Figure 11 is an overall plan view of a battery casting assembly working area;

Figure 12 shows an elevation of a mould batteiy embodying the present invention; Figure 13 is a section on lines XIII-XIII shown in Figure 12;

Figure 14 is a section on lines XIV-XIV shown in Figure 12; Figure 15 is a side elevation of a first lower cell divider locater; Figure 16 is a side elevation of a second lower cell divider locater; Figure 17 shows a floor plate; Figure 18 is a side elevation of a cell divider Figure 19 shows the underside of the cell divider shown in Figure 18;

Figure 20 illustrates a spacer element tied to a panel base board with a restraint strap;

Figure 21 shows an edgeboard;

Figure 22 is a enlarged cross-section on XXII-XXII of Figure 21; Figure 23 is an elevation illustrating cell framing for the panels;

Figure 24 illustrates an edgeboard seal; and Figure 25 shows an top cell divider locater.

Detailed Description of Preferred Embodiments Referring to the drawings, Figures 1 to 2 illustrate a solid non-concrete spacer element 10, or concrete void former 10. As shown, the spacer element is generally square in plan view although it could be rectangular. A series of ducts 12 extend from one face 10A of the former to the other face 10B. The ends of the ducts are radially expanded/bell-shaped. A series of channels, including vertical channels 14, horizontal channels 16, and diagonal channels 18 are defined in the faces 10A and 10B of the spacer element.

The sectional area of the ducts at their narrowest part is approximately 1250 mm², the channels are rounded and are approximately 25 mm deep and have a cross-sectional area of approximately 600mm², but may vary from 8mm to 40mm deep with their cross-sectional area varying from 65mm² to 1600mm².

As will be described later on in this specification, the spacer element is used in a process for vertical casting of a concrete building panel, in an arrangement in which the channels 14 are oriented vertically. Although in the embodiment shown in Figure 1, all the channels 14, 16 and 18 are the same size, it would be possible to vary the size of the channels to facilitate the casting process, for example the vertical channels 14 could be made larger to facilitate concrete flow. Selected channels, for example vertical channels 14 on matching opposite sides of the spacer element could also be enlarged to become structural members and incorporate steel or fibre rod reinforcing whilst other channels could remain smaller. In some situations enlarged reinforced ribs could partially or completely replace structural members 52 and 54 shown in Figure 8 and discussed below.

As shown in figure 2a the channels are bell-shaped in section so that in the finished panel described below they blend smoothly with the skins avoiding sharp edges where stresses can propagate. As seen in figure 2 the ribs as well as radiating outwardly in the plane of the surface of the spacer element from one duct to another also curve and radiate outwardly from the central area of the ducts so that a tangent T to the channel surface shown in Figure 2 intersects the plane of the surface of the spacer element at an angle. The channels may also extend through the spacer element as shown in Figure 2 showing a generally C-shaped connection defined by channel portions 16a and 16b linked by centre portion 16c so that in section through the central area of the duct resembles a flower head, with each of the channels defining a petal. It is also possible to use a hollow or partially hollow spacer element 10 shown in Figures 3 to 5. Figure 3 is a rear view of one half 20 of a hollow spacer element 10. The front view is the same as the spacer element shown in Figure 1. Where the various channels 14, 16 and 18 are formed, the material is extended to define coplanar flat ridges 22. These are coplanar with the rear perimeter edges 24. Thus when two halves 30 are joined together rear face to rear face, the ridges 22, 24 on each half will bear on each other and can be glued together. The spacer element formed encloses a series of generally triangular hollows 26.

Because the ridges 24 to meet and bear on each other internally, when the two halves of the spacer element are joined together, this increases the strength of the void and also allows the void to be cut along the horizontal, or vertical channels where the material is solid.

The ridges are not essential except where the spacer element needs to be stronger to resist pressure. They may be discontinuous so that they only bear partially: this can be adjusted to suit the degree of pressure that is to be resisted. In some cases the ridges can be deleted or the spacer element may be graduated from continuous ridges to partial ridges or no ridges in one building panel.

If desired, and with or without ridges, the hollow portions 26 and any other hollow parts may be partially or completely filled with waste material to strengthen the spacer element against collapse under pressure. Figures 6 and 7 illustrate a plastic wall spacer 30 which is used to space the spacer elements 10 from the walls of a mould if the surface skins are to be made of concrete. The wall spacer comprises a plate on one side of which there are four pins 32 which can be pushed into a spacer element to secure the wall spacer to the spacer element and on the other side of the plate the element defines a tip or protrusion 34 whose height "h" is 12 mm high, but may vary between 8 and 45mm.

Figures 8 to 9 illustrate a load bearing panel 50 which may be formed using spacer elements 10. The panel has a perimeter beam 52 (reinforced with solid steel rod, not shown), which extends around the perimeter of the panel. There are also a series of four steel reinforced columns 54, spaced 600 mm apart. Disposed between the walls and the columns 54 are a series of spacer element assemblies (each one made from three spacer elements such as are shown in Figure 1 joined together). The faces or skins 58 of the panels are 12 mm thick concrete and define wall surfaces which are interconnected internally by a series of small horizontal connectors 60 (formed by the ducts 12 in the spacer). A series of supporting ribs 62 interconnect the horizontal connectors 60, the ribs being formed by the channels 14, 16, 18 in the spacer element. Non-load bearing panels in which the panel includes a single spacer element assembly made up from a large number of conjoined spacer elements and has no load bearing columns, apart from those which form part of an optional perimeter beam may also be made. A semi-load bearing panel might also be provided in which only a single load-bearing column is provided. Figures 10 and 11 give an overall view of a vertical battery casting apparatus which can be used to form panels as shown in Figure 8. Before describing the apparatus in detail, there follows a brief, and somewhat simplified, overview of the principals behind the vertical battery casting system. Referring to Figure 11, the system requires a flat concrete platform located on the ground approximately 12 m wide and a minimum of 20 m long. Rails 102 and 104 are set into the concrete platform. A large gantry crane 106 runs on rails 102. A small gantry crane 108 runs on rails 104. The panels are manufactured in a mould battery, generally indicated at 110 which, as is described in more detail below, is made up from a number of components including side frames 112 and cell dividers 114. The mould 10

assembly includes a heavy steel base frame 116. The cell dividers are oriented vertically and panels are moulded in battery style in between pairs of adjacent cell dividers 114. A concrete panel curing rack 118 is located adjacent base plate 116. A heavy steel base frame 116B is located on the concrete platform between the rails 104 spaced approximately 8 m from frame 116 A. The battery casting operation for making the panels 50 is preferably based on the principal of moving the mould/casting position every two or four cycles, although the battery mould could be stationary. Thus, the battery casting mould is first assembled on frame 116A and prepared for casting with the spacer element assemblies located inside the series of moulds defined between the cell dividers 114. Concrete is poured into the cells until they are filled, vibrating if necessary. The concrete panels are then allowed to harden in the mould until they can be moved. The small gantry crane 108 is then used to remove one of the side frames 112, and position it on the second frame 116B. The cell divider which was located adjacent that side frame is then carried by the small gantry crane into a cell divider cleaning area 120 located between the frames 116A and 116B, cleaned and re-positioned on base plate 116B. Edge boards, seals and blockouts are then removed from around the exposed panel 50 and the large gantry crane 106 moves that panel to the concrete panel curing rack 118. The process is repeated until the mould is completely reassembled on base 116B and all the concrete panels 50 are positioned on the rack 118.

While the concrete panels 50 are curing on the curing rack 118 it is then possible to use the mould to manufacture a second set of concrete panels. After those panels have cured, the panels are then moved to a curing rack adjacent the base 116B. In a two cycle system, the bases would then be moved by industrial roller skates (not shown) or other means approximately 8 m in one direction along the rails where the two cycle operation described above is repeated. Alternatively, it is possible to use a larger gantiy crane, and have concrete panel curing racks 118 either side of the base frames in which case the mould can be reassembled on base 116A and the concrete panels formed in that third moulding operation are transferred to the empty rack on the other side of the mould. The mould is reassembled on base 116B and a fourth set of panels made and stored on the last empty rack. The bases can then be moved and the four cycle operation described above repeated. 11

After another set of four panels has been made, the bases can then be moved to a new position again, or back to the original position, depending on how many days storage of concrete panels is required. If desired, after the completion of several moves in one direction, the mould could be moved sideways and a new line of production commenced. Alternatively, the empty base frame 116 can be moved temporarily to allow loading of the panels 50 onto transport vehicles and then moved back again for the mould to be reassembled.

In projects which have roads, provided that roads are reasonably level, the mould could continue to move along the road in one continuous production line with the panels being deposited adjacent to the areas where buildings are to be constructed. Mobile cranes could then directly lift the products into the building thus eliminating any transport requirements.

With the system described above, enough curing time for the panel can be allowed for the panel to be taken directly from where it was made to where it is to be installed. This clearly increases the efficiency of the process as handling of large concrete panels is an awkward and time consuming process, particularly in developing countries where sophisticated materials handling apparatus and infrastructure is not normally available. By moving the mould, space is left near the concrete curing rack 118 for loading panels 50 onto vehicles. This can be done using the large gantry crane 106, when that crane is not being used for disassembling a mould.

There now follows a detailed description of the mould assembly and concrete pouring process. The assembled mould battery, is illustrated in Figures 12 to 14.

Components of the mould battery are illustrated in the later numbered drawings. Base frame 116 is located at the base of the mould battery. That frame is best seen in Figure 14. It is made from three smaller steel frames 150, 152 and 154. Frame 154 is identical to frame 150. Each frame consists of two parallel heavy duty steel I-beam girders fixed on top of two similar parallel I-beam girders 158. A bracing beam 160 extends between two diagonally opposite corners where the beams intersect. The parallel beams 158 project to one side only of the frame elements 150 and 154 and to both sides of the frame element 152. Additional bracing 160 is installed between adjacent frame elements to strengthen the frame. 12

Cell divider locaters 170, 172 are then fixed to the steel base 116. Cell divider locater 170 (refer Figure 15) comprises an elongate steel plate on which is positioned nine upwardly projecting blocks 174. The blocks are generally rectangular in plan and upper parts of the blocks define sloping walls which extend as far as a flat rectangular top. A series of holes 176 are formed in the cell divider for bolting the cell divider to the base frame 116. Cell divider locater 172 is much shorter than cell divider 170 and only defines one block 174. In use, the cell divider locater 170 is used for locating nine cell dividers, to form eight cells for moulding panels. If an additional cell divider locater 172 is disposed either side of cell divider locater 170, it is possible to mould an additional two panels as shown in Figure 13. The lower cell divider locaters are aligned with and bolted to the members 156 of the base frame 116. Thus six locaters 170 and twelve locaters 172 are required. Next steel floor plates 180 shown in Figure 22 are positioned on top of base frame 116 between the lower cell divider locaters. The width of the floor plates is the same as the distance between the edges of the girders 156. Side frames 112 which are positioned on either side of the base frame 156. The side frames are made of steel girders and have to be strong enough to transfer the hydrostatic pressure which occurs during moulding, to the base frame 116. When the mould battery assembly is being assembled, one of the two side frames is installed after the floor plates have been positioned. The other is installed towards the end of the assembly procedure. Bolts 192 depend from the base of the side frame and slot into corresponding holes provided in the base plate. The upper end of the frame defines two trapezoidal plates 194 each of which includes a through hole 196 for lifting the side frame using the gantry crane. The upper part of the frame also defines a series of six upstanding cylindrical projections 198 which, as is described later, are used for mounting a top cell divider locater 250.

After the first side frame 112 has been fixed to the base frame 116, a first cell divider 114 is attached to the side frame. As is shown in Figures 18, the cell divider comprises two plates 202 is welded to each side of a support frame. On each side of the cell divider there is a straight hook 210. A series of horizontally oriented slots 212 are defined in the top of the cell divider. As shown in Figure 19, the base of the cell divider defines six rectangular slots 214 which are configured to receive the blocks 174 of the lower cell divider locaters. 13

Next a bottom panel base board 220 is installed, which comprises an elongate metal plate having downturned edges. The board 220 defines the base of the mould. As shown in Figure 20, restraint straps 222 extend between the board 220 and the steel floor plate 180. After installation of board 220, sealant is then applied to the joints and edge board seals 240 are attached to the edge boards 230 (see Figure 24). The edge board seal has angled tip portions 242. Because of the angle of the tip portions, hydrostatic pressure P acting on the seal tends to force the tip portions against the cell dividers and thus, the greater the pressure, the better is the seal.

An edge board is shown in Figure 21 and 22. Each edge board comprises two elongate metal tubes 232 having a annular rectangular cross- section joined together by a series of plates 234. Near the middle of the edge boards an annular socket 236 is provided for receiving a prop. Depending cylindrical plugs 238 are provided at the base of the edge boards. As shown in Figure 23, the cell dividers are slotted into the bottom panel base board 220 using plugs 238. Figure 23 shows an arrangement in which two concrete panels are cast end to end rather than a single concrete panel extending along the entire length of the mould. Next blockouts are installed where window and door openings are desired.

Release agent is applied to the surface of the cell divider, the base board 220 and the edge board seal 240.

Next the spacer element assembly is attached to base boards 220 by restraint straps 222. During the moulding process, after concrete is poured into the mould the lightweight spacer elements would rise up if they were not restrained by straps 222 each of which has to take up to a one tonne force. The spacer element assemblies comprise a number of spacer elements such as are shown in Figure 1 or Figure 4 joined together in one block such as is shown in Figure 9 or Figure 10 for ease of handling. Typically, the spacer element assembly will be graduated, in other words the spacer elements which are located near the top of the mould will be hollow and the spacer elements which are located towards the bottom will be solid so as to resist the greater hydrostatic pressures. The spacer elements towards the middle of the panel might be hollow but partially infilled. If the skins are made of fibre reinforced sheet material, they are attached to the spacer element and installed at this stage. 14

The next step is the installation of reinforcing rods if and where required such as around the perimeter, along any spaces where columns 54 are to be located, and above doorways or windows, and along the channels 14, 16 or 18 if needed. Next releasing agent is applied to one surface of a second cell divider

114 and that second cell divider is positioned over the next lower cell divider locater 170. The operation is then repeated until all cell dividers, edge boards, edge board seals, restraint straps, spacer elements, reinforcing and the like are located in position. Next top cell divider locaters 250 shown in Figure 25 are positioned on top of the mould. Each top cell divider locater has eleven depending projections 252 spaced along the base of the top cell divider locater. At each end of the cell divider locater is a plate 254 which defines a hole 256 which is received on one of the projections 198 on the side frame 112. Six top cell divider locaters in all, are used. The depending projections 252 slot between the members 232 of the edge boards 230. The spacer element assemblies are then tied to the top cell divider locaters to position them in the mould. When the mould is assembled as shown in Figure 16, concrete is then poured in the top of the mould. The concrete mix should be made of up of least Portland cement, fine aggregate, such as sand, a superplasticising high range water reducing agent and water. Preferably the mixture would include fibre such as polypropylene or steel and in some but not all applications, a coarse aggregate to reduce the water/cement ratio and increase the strength The coarse aggregate's size depends on the thickness of the skin of the faces of the panels (where the skins are concrete). If the wall spacer shown in Figures 7 and 8 is used, the thickness would be 12 mm, and the coarse aggregate could be up to 8 mm in diameter. If the skin were made 15 mm thick, course aggregate up to 10 mm diameter could be used. In the case where a thin board is used as a skin and the channels are small, the large aggregate would be omitted from the mix design.

The mould or concrete may be vibrated during the filling operation, as necessary.

The concrete panels are then allowed to initially harden. After the concrete panels have sufficiently hardened, the mould battery is then disassembled and the components, other than the steel base moved as described above with reference to Figures 12 to 14. It is necessary to cut the 15

strapping 222 to remove the bottom panel base board 220 from the concrete panel.

Typically the mould battery described above will consist of ten cells approximately 6 to 7 m long and up to 3 m high. One or more concrete panels can be made in each cell. The thickness of the panel can be varied between 50 mm to 200 mm in which case less cell dividers are required to complete the battery configuration. A normal ten cell configuration could vary between six cells and 20 cells in extreme cases.

The advantages of the moving vertical casting method described above compared with static horizontal casting, are as follows:

• smaller casting area;

• less distance for material and worker movement;

• less worker skills as no finishing skills are required;

• products need not be covered during initial hardening to prevent moisture loss;

• accelerated curing due to containment of heat of hydration without moisture loss;

• lower overall capital expenditure - less depreciation costs;

• onsite production, plant does not require cover or a building; • plant relocation can be achieved within days;

• moving battery mould means that the product is stored immediately on demoulding and only has to be loaded onto transport, this means less product handling;

• by using two bases, the speed of battery mould reassembly is improved.

The panel of the present invention could also be made by a horizontal moulding process, although a vertical moulding is much preferred.

For horizontal moulding, the process of making the panel commences with the treatment of a flat horizontal mould surface with a release agent to facilitate de moulding of the panel.

Edge boards define the perimeter and depth of the panel and are placed in position on the mould surface. Edge boards also define any doorways or windows extending through the panel.

Concrete is then poured into the mould and spread evenly in the mould up to approximately half of the depth of the edge boards. 16

The concrete is preferably made up of portland cement, small coarse aggregate and sand. The mix should be quite plastic as it will be required to flow around and into the channels on the spacer element 10. The water/cement ratio is important to prevent unsightly cracking. One or more spacer elements 30 are then placed on top of the leveled concrete and since the voids are very light, they have to be pushed and worked or vibrated down into the concrete until they are in the correct position. Typically the spacer elements are vibrated at approximately 1 Hz and an amplitude of around 10 mm. This assists the concrete to be forced up into the channels 18 and also through the ducts 12, and at the same time forces any entrapped air around the former surface or through the ducts 12 so that the channels 18 are filled with concrete. The spacer element is pushed into the mould until it is at the correct depth in the mould i.e. approximately 10 to 12 mm from the horizontal mould surface, depending on the intended thickness of the skin, which will depend on inter alia, the size of the aggregate, and the quantity of reinforcing material if any, used in the skin.

Steel reinforcing rods are then placed in the perimeter of the mould between the edge boards and the former if a perimeter beam is required and in any other structural member of the panel which may require reinforcing. The remaining concrete is then poured over the top of the former to fill the mould. The surface is then screed off and finished to a suitable texture. The panel is covered, allowed to cure and then lifted from the mould. Covering the panel prevents excessive moisture evaporation and helps prevent cracking.

When extra structural members like vertical studs/columns, horizontal beams or windows and doorways are required, the spacer elements are cut to size or assembled to suit the panel configuration.

Whether made by vertical casting or horizontal casting, the overall shape of the building panel, the pattern of ribs joining of the ducts to the skins by radially expanded bell-shaped portions perform the following functions:

1. They form a monolithic moulded concrete shape around the ducts that strengthens and reinforces the highly stressed area where the two wall skins are joined to each other by the columns, by forming a series of ribs around the former inside the wall cavity. 17

2. The radially expanded ends of the ducts and the ribs prevent the propagation of cracks in the skin by increasing the skin depth at the rib sections so that the thinnest part of the skin is always bordered by the sectionally deeper ribs, this helps prevent and arrest crack development.

3. The completed panel is virtually hollow except for the perimeter beam, if used, the small horizontal columns and any other solid structural members. This allows easy access for services within the wall cavity having only to penetrate the thin concrete skin of the wall and the soft spacer element 30.

The spacer element may be formed of any suitable moulded material such as gypsum, plaster, wood pulp, wood products, high impact styrene, expanded polystyrene, foamed cement, a suitable plastics material or even waste material which can be moulded to the desired shape of the former. In cases where the building panel has to have a high fire rating, glass reinforced gypsum plaster and foamed gypsum plaster having a varying thickness to suit the desired fire rating are preferred.

Insulation may be inserted into the hollows of the spacer element 30. Alternatively, the element 30 may be manufactured of an insulative material having a wall thickness which when combined with the hollows of the element 30 supplies the degree of insulation required.

In a variant, for cold or hot climate countries, the ducts 12 are blocked off approximately midway along their length with a layer of insulating material. The two halves of the connector are then separated by the insulating layer and must be structurally joined by a structural tie element. The tie element is preferably made from a material with poor thermal conductivity for example a reinforced plastic The tie element will project through the insulating layer into the bell-shaped where it is securely anchored and embedded in concrete. The shape of the structural tie element can vary from a cylindrical tube to an X-shape or star shape. If the shape of the element is a star shape the number of points in the star are related to and will correspond to the number of channels or ribs that are that are intersecting at the connector as each point or projection on the star will project and anchor into each rib. These projections will be perforated or corrugated to enable adequate bonding of the projection into the rib. In addition the insulating layer must seal off the duct at the minimum sectional 18

area i.e. at the midway along the length of the connector, if the structural tie element is of a circular or tubular design then the duct, the insulating layer or the tube must be shaped to fit and seal the minimum sectional area of the duct where it is divided into two as is the case with all tie elements. The part of the tubular tie projecting into the bell shape of the connector will also have perforations to enable thin reinforcing rods to be inserted to structurally anchor the connectors and the ribs to the tie. The structural tie must assume approximately the same structural functional role as if the connector was continuous from skin to skin. Concrete is a good conductor of heat and the solid pillars of concrete formed by the ducts would transmit cold temperatures through the wall, forming cold spots. The insulating layer prevents this.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.