EP0000837A1

EP0000837A1 - Load bearing wall panels and method of manufacture thereof

Info

Publication number: EP0000837A1
Application number: EP7878300249A
Authority: EP
Inventors: Graeme John Tilly
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-08-15
Filing date: 1978-08-15
Publication date: 1979-02-21
Also published as: AU520177B2; AU3881978A

Abstract

A load beaming wall panel and method of manufacture thereof, the panel comprising a non-load bearing core and a layer of load bearing fibrous concrete material (33) located on each face, each layer being substantially impervious to moisture, and the thickness of each layer is less than the thickness .of the core.

A method of forming said panel comprising spreading a layer of fibrous concrete onto a base of a mould, laying blocks of the core material onto the exposed surface of the fibrous concrete and forcing said blocks into intimate contact with said fibrous concrete until it has set, applying a second layer of fibrous concrete between and over the blocks and allowing it to set.

The base of the mould may be flexibleto take on a curved configuration to form curved panels.

Description

It is an established practice to construct buildings by means of panels cast from concrete or like cementitious material. However in the past such panels have presented significant problems which detract from the advantage of being able to produce them under factory-like conditions and then transport them to the site for erection. In the case of monolithic panels which are formed completely from concrete the major problem resides in their weight and the inherent problems of transport to the site and erection of the panels.
An alternative panel to the monolithic panel has been the incorporation of a lightweight core between two layers of concrete. Where the core has been required to support a portion of the load an the panel it has been found that the density of the core has to be relatively high and the weight advantage is not significant. Where the core is hot intended to be of a load bearing nature the concrete layers which are reinforced by continuous reinforcing are required to have a total thickness at least equal to that of the monolithic panels.
In such cases the incorporation of the continuous reinforcing such as reinforcing rods and reinforcing mesh into the panel mould presents significant difficulties in ensuring that none of the reinforcing is located such that it will be exposed at the surface of the panel and is properly located in the mould.
Further alternative panels utilise a lightweight non load bearing core with a non load bearing skin of any suitable waterproof material, and a load supporting structure incorporated in the panel such as steel framing. The difficulties of such panels resides in the existence of the internal framing of the lead supporting structure and the proper location of such prior to the forming of the lightweight core.
It is the object of this invention to provide building panels which can be manufactured under factory-like conditions and transported to the building site.
It is a further object of this invention to provide panels which can support the normal loads exerted on the walls of a building but is of reduced mass in comparision to monolithic panels formed of concrete or like cementitious materials and does not incorporate a load supporting frame or structure.
It is a further object of this invention to provide a panel which in its construction does not require the arranging of continuous reinforcing material in a mould prior to the addition of concrete in the mould.
In one form the invention resides in a load bearing wall panel comprising a relatively lightweight non load bearing core and a layer of load bearing fibrous concrete material located on each face thereof, each layer being substantially impervious to moisture, the thickness of said layers being less than the thickness of the core.
According to a preferred feature of the invention at least one web is provided between the layers wherein said web provides resistance to shear forces exerted between said layers.
According to a further preferred feature of the invention the panel is provided with webs at its top and bottom surfaces interconnecting said layers wherein said webs serve in distributing the loads thereon.
It is a further preferred object of this invention to provide panels which can have an attractive texture or pattern cast onto one face of the panel.
The invention will be more fully understood in the light of the following description of one specific embodiment. The description is made with reference to the accompanying drawings of which:-

Fig. 1 is a sectional end elevation of the mould and support therefor in which the panel of the embodiment is formed;
Figs. 2A, 2B, 2C and 2D show the steps of formation of the panels;
Figs. 3A and 3B are sectional elevations through a panel on completion of formation of the first and second layer of fibrous concrete respectively in the mould showing the provision for the formation of a window opening in the panel;
Figs. 4A and 4B are sectional side and end elevations respectively of the top of a panel showing the provision of the load distributing member formed thereat; and
Figs. 5A, 5B, 5C, 5D and 5E are sections of the mould and panel showing the stages in the construction of curved sandwich panels.

The embodiment is directed to a wall panel having a non-load bearing lightweight core with a relatively thin skin formed at each major face of the core, where the skins are formed of fibrous concrete and is load supporting. Each skin of the panel is interconnected by a plurality of parallel webs interconnecting their inner faces and formed of the same material as the skins.
The core of the embodiment comprises a plurality of spaced parallel blocks of rigid polystyrene foam having a thickness determined by the nature of the application, and the degree of sound and thermal insulation required of the panel.
The skins are formed of a fibrous concrete which is formed from a mixture of sand and portland cement having a preferred ratio of between 1.5:1 and 2.5:1. In addition a quantity of pozzolanic material is added to the mixture to increase the strength of the final product and decrease its susceptibility to permeability. The water to cement ratio is preferably 0.29:1 and should not exceed 0.4:1 in order that the final mixture has a final slump of between 60 and 120 mm.
The steel fibres are incorporated with the concrete mixture in a ratio of fibres to concrete of between 0.02:1 to 0.06:1. The steel fibres are formed from mild steel wire although corrosion resistant metals can be used if such is desired. The fibres of the embodiment have enlarged ends and a length of between 14 mm and 25 mm and a thickness of betweenO.3mm and 0.5mm.
The fibres may be incorporated with the concrete mixture at the time of mixing of the sand, cement and water. Alt- . ernatively if the concrete mixture is to be applied by spraying or like methods the fibres can be blown onto the surface with the concrete.
Each skin is interconnected by parallel webs formed of fibrous concrete which extend the full height of the panel. The webs are formed by spacing the blocks of foam forming the core to provide moulding space between the blocks. Such webs serve in tying the skins together and resisting shear forces which may be exerted on the panel between the skins.
The dimensions of the panel are limited by the transportation limitations in moving the panels-from the factory to the site. At present the maximum limitations are a length 13 metres and a breadth of 5 metres. It is envisaged however that panels can be fabricated which are to extend the full length of the side of a house. The thickness of the panel can vary to suit the application and similarly the thickness of each skin is determined by the proposed loading for the panel. In the case of a single storey building the thickness of each skin could be as low as 5 mm for light duty panels and 10 mm for the load bearing walls of a single storey building.
The engineering principle of the panel resides in the fact that the two skins share the compressive load and are separated to achieve a high modulus of section to resist buckling. The webs interconnecting the skins serve to ensure that the two skins act as a single structural member. The degree of separation of the skins will depend on the ratio of transverse to vertical loading proposed for the panel and the degree of sound and thermal properties desired for the panel and may vary between 9 mm to 300 mm. However for normal building structures a separation of 30 mm would be adequate for internal walls and 50 mm for external walls.
A panel was constructed according to the embodiment having a height of 2.7 metres and thickness of 71 mm with a skin thickness of 10 mm at each side of a core of rigid polystyrene foam core 51 mm thick. The weight of such a panel was 58 kg/m² while the loading capacities were 10 KN/m² transverse pressure and a vertical loading of 50 KN/m of wall length.
The method of manufacture of the panels is shown in the accompanying drawings. The mould for the panel comprises a base plate 11 mounted to a frame 13 which is supported on a plurality of flexible pedestals 15. The pedestals comprise a base 17 fixed to the factory floor and a resilient flexible mounting 19 fixed to the base 17. The interconnection between the mounting and the frame comprises a hinge arrangement. As a result of the pedestal mounting the frame is capable of vertical movement and a pivotal movement. The underneath of the frame is connected to at least one eccentric vibrator 21 which impart an oscillatory action on the frame 13 on the pedestals 15. Such vibrations permit compaction of the concrete as it is introduced into the mould.
To give the exterior face of the panel a textured finish a moulded liner 23 is laid on the base plate. The moulding surface of the liner can be formed to any suitable texture (eg. a brick wall). To support the edges of the panel during moulding,shuttering 27 is fixed around the perimeter of the proposed panel. Such shuttering may be textured to conform with the liner 23 or may be covered with a corresponding liner.
The liner has laid over it by spraying or screeding (as shown in Figure 2A) a layer 25 of a finishing mixture in order that an attractive finish is produced on the resultant panel. The layer need only be slightly thicker than the depth of the deepest indentation of the liner. The layer can be formed from a high quality white or pigmented cement. Compaction of the layer is achieved by vibrating the base plate 11 by means of the eccentric vibrators 2₁. The layer is also trowelled onto the shutter at the edges of the panel.
The first skin of fibrous concrete 29 is introduced onto the mould from a hopper mounted above the mould and intend- ded to traverse the length of the mould (see figure 2B). The hopper is constructed such that the width of the opening can be adjusted according to the width of the proposed panel. On placement of the fibrous concrete 29 onto mould it is compacted by the action of the eccentric vibrators 21 (which can also be mounted to the hopper delivering the fibrous concrete). Prior to the setting of the first layer 29 of fibrous concrete,the blocks of rigid foamed polystyrene are placed on the layer in spaced relation to provide for transverse parallel spaces between the blocks. In the case of the embodiment the spacings are 20 mm. Steel fibres are sprinkled onto the wet surface of the fibrous concrete between the blocks and the first layer of fibrous concrete is allowed to set. During the setting process a heavy plate 31 (see Fig. 2C) is placed over the blocks to force them into intimate bonding relationship with the first layer. If desired conduits 1A and service pipes may be located in the space between the blocks. If it is desired to post-tension the panel by ties between the roof plate and the foundations,conduits 2A for such tensioning cables may be located in the spaces between the blocks.
On the completion of the setting of the first layer 29 of fibrous concrete, the heavy plate 31 is removed and a further layer 33 is deposited from the hopper into the mould and is screeded and compacted over the foam blocks and into the spaces between the blocks (see Fig . 2D). If desired, the top layer can be smooth trowelled ready for painting or may be treated to provide a textured surface. Prior to the setting of the further layer 33, tie bars 34 are pressed into the upper face of the panel around the edges to facilitate fixing the panel to the foundations or to adjoining walls.
On completion of the setting of the further layer 33,the panel is removed from the mould and is transferred to a curing chamber. To remove the panel, one side of the frame 13 supporting the base plate 11 is raised while the other side hinges on the pedestals 15 supporting that side and the panel is transferred to a trolley which supports the panel upright. The raising of the one side of the mould can be achieved by neans of a crane or suitable hydraulic jacks.
To facilitate late handling of the panel and the distribution of load o to the panel, the top and bottom of the panel may be forme with a continuous web 35 interconnecting the two skins (see Figs. 4). The web 35 has located within it a length f continuous reinforcing 37 such as reinforcing mesh loated throughout the length. In addition the web has cast therein a series of spaced attachment means 39 such as thr aded sockets. The attachment means facilitate the lifting of the panel on completion of the setting process, when transporting the panels to the building site and locating the panel in position on the foundations. In addition, the web 35 serves in distributing the loads exerted on the panel in position by the roof structure of the building.
The method of formation of window and accessway spaces through the panel is shown at figure 3. Prior to the formation of the initial layer 25 of finishing material and the first layer 29 of fibrous concrete a blanking piece 41 is located in the mould on top of the liner 23 at the desired position of the window or accessway. The sides of the blanking piece may be textured in conformity with the texture of the liner 23 in order that on the completed panel there is some continuity of the panel finish. In the formation of the further layer 33 of fibrous concrete a deeper blanking piece 41A or box with a closed top, is located in the window space and the further layer is screeded around the blanking piece to the height thereof. The blanking pieces may be suitably contoured at their edges to support and locate a window frame.
Figures 5A to 5E illustrate a method of forming panels of the embodiment into a curved configuration. The mould comprises a flexible base plate 43 having rigid vertical shuttering 44 at either end and flexible vertical shuttering 47 at each side. The base plate is supported at each end as is the base plate of the mould of figure 1 upon resilient pedestals 45 via hinge pins pivotally received on the pedestals. The mounting of at least one of the hinge pins to the base plate is such as to permit longitudinal sliding movement of the hinge pin on the base plate. The portion of the base plate is supported by a series of spaced transverse pins 49 mounted in side plates 48 which are located at each side of the base plate. The vertical location of each pin in the side plates is variable due to the existence of a plurality of vertically spaced apertures in the side plates. An inflatable bag 55 is located under neath the base plate between each pedestal such that on pedestal inflation the bag supports the base plate 43 in the horizontal position. By further inflation of the bag the base plate can be curved upwardly and the pins relocated to accept some of the loading on the bag. Alternatively by deflation of the bag 55 and relocation of the pins 49 the base plate can be caused to curve downwardly.
In forming the panel the base plate is initially positioned such that it is horizontal and the initial finishing layer and first layer 52 of fibrous concrete is applied to it to form a thin skin. Blocks of core material 55 are positioned on the layer while still wet and are pressed into place by a heavy plate. The layer is then compacted by means of vibrators 46 and allowed to set.
After the initial set of the first layer the second layer of fibrous concrete is applied between and over the blocks of core material and it is compacted by vibration. While the second layer is still fluid the weight of the base plate is taken by the inflatable bag, the pins 49 are withdrawn and the bag is inflated or deflated to give the desired curvature of the panel. On reaching the desired curvature the pins are reinserted. During the bending of the base plate the first layer flexes because it has not fully cured and because it is maintained thin enough to flex and the second layer conforms to the curvature because it is still wet. The panel remains in the mould until it has cured sufficiently to be removed.
It is possible to utilise a number of inflatable bags in order that a panel of complex curvature can be produced. or to control the manner of curvature by restraining the bending of the base plate at predetermined positions by leaving some of the pins 49 restraining the base plate in position while inflating or deflating the bag.
In addition the provision of a reinforced web at the top and bottom of the panel with attachment means as shown at figures 4A and 4B is also applicable to curved panels together with the provision of window spaces and like access apertures.
It should be appreciated that the scope of the invention is not to be limited to the scope of the panel and the method of forming panels disclosed in the above description of the embodiment.
In particular the light weight non load bearing core may be formed of any one of the following:-

1. Rigid polystyrene foam.
2. Rigid polyurethane foam.
3. Concrete having an aggregate formed of foamed polystyrene beads or like material.
4. Foamed concrete.
5. Rice husks or straw in a binding medium.
6. Q-cells or micro balloons in a resin or cement binder.
7. Expanded aggregate in a cement binder.

In addition the web may be formed of the following:-

1. Light gauge rolled steel sections.
2. Welded mesh placed between blocks of core materials or embedded in webs of fibrous concrete.
3. Strips of expanded metal.
4. Rigid plastic extrusions such as tubes, the surface of which has been roughened to give an adequate bond with the skins.
5. Fibrous concrete.

Claims

1. A load bearing wall panel comprising a non-load bearing core and a layer of load bearing fibrous concrete material located on each face, each layer being substantially impervious to moisture, and the thickness of each layer is less than the thickness of the core.

2. A load bearing wall panel as claimed at claim 1 wherein each layer of fibrous concrete is interconnected by a plurality of spaced parallel webs, said webs providing resistance to shear forces exerted between the layers of fibrous material.

3. A load bearing wall panel as claimed at claim 2 wherein the web is formed of fibrous concrete moulded integrally with one layer and bonded to the other layer.

4. A load bearing wall panel as claimed at anyone of claims 1, 2 or 3 wherein the upper and lower edge of the panel is formed with an upper web interconnecting the two layers and extending the full length of the panel, said upper web being formed of fibrous concrete and provided with continuous reinforcing extending the full length of the web, and being provided with a plurality of spaced .attachment means embedded in it.

5. A load bearing wall panel as claimed at anyone of the preceding claims wherein the ratio of sand to cement in the mixture falls within the range from 1.5:1 to 2.5:1 and the mixture has a quantity of pozzolanic material added thereto.

6. A load bearing wall panel as claimed at anyone of the preceding claims wherein the water to cement ratio of the mixture varies between 0.25:1 and 0.4:1.

7. A load bearing wall panel as claimed at any one of the preceding claims wherein the ratio of steel fibres to concrete in the fibrous concrete mixture varies between 0.02:1 and 0.06:1.

8. A load bearing wall panel as claimed at any one of the preceding claims wherein the thickness of each layer of fibrous concrete therein varies between 5 mm and 20 mm for panels used with single storey buildings.

9. A load bearing wall panel as claimed at anyone of the preceding claims wherein windows and accessways are formed within the panel.

10. A load bearing wall panel as claimed at anyone of the preceding claims wherein service conduits and ducts are provided in the lightweight core and/or the webs.

11. A load bearing wall panel as claimed in anyone of the preceding claims as dependant on claim 2 wherein each web is associated with a conduit for the accommodation of a post tensioning cable to extend through the panel when in position.

12. A load bearing wall panel as claimed at anyone of the preceding claims wherein at least one face of the panel is provided with a patterned or textured surface cast into the surface of the panel.

13. A load bearing wall panel as claimed at anyone of the preceding claims wherein the panel is curved about an axis parallel to the transverse axis of the panel.

14. A load bearing wall panel as claimed at claim 13 wherein one layer is under stress.

15. A method of forming load bearing wall panels having a non-load bearing core and a layer of load bearing fibrous concrete material on each face where each layer is substantially impervious to moisture and the thickness of each layer is less than the thickness of the core, said method comprising spreading a layer of fibrous concrete onto the base of a mould, laying blocks of the core material onto the exposed surface of the fibrous concrete and forcing said blocks into intimate contact with said fibrous concrete until it has set, applying a second layer of fibrous concrete between and over the blocks and allowing it to set.

16. A method as claimed at claim 15 wherein the base of the mould is configured to a desired pattern and prior to the application of the fibrous concrete thereto a layer of high quality finishing cementitious material is applied thereto.

17. A method as claimed at claim 15 dr 16 wherein the base of the mould is flexible and is pivotally supported at each end by fixed supports, the portion of the base plate between the supports being supported by at least one inflatable member whereby the portion of the base can be configured, stops being provided at the sides of the base to maintain the base plate in the configuration determined by the inflatable members; wherein the layers of fibrous concrete and the blocks of non core material are applied to the base when horizontal, the base is caused to take on a curved configuration after the first layer has set and the second layer is still unset, and allowing the second layer to set in the curved configuration.

18. A method of forming a load bearing panel substantially as herein described with reference to the accompanying drawings.

19. A load bearing wall panel substantially as herein described with reference to the embodiment.