GB2486723A

GB2486723A - Shuttering

Info

Publication number: GB2486723A
Application number: GB1021915.2A
Authority: GB
Inventors: Alastair Seaton
Original assignee: Cordek Ltd
Current assignee: Cordek Ltd
Priority date: 2010-12-23
Filing date: 2010-12-23
Publication date: 2012-06-27
Anticipated expiration: 2030-12-23
Also published as: EP2655762A2; GB2486723B; ES2686552T3; EP2655762B1; WO2012085570A2; GB201021915D0; WO2012085570A3

Abstract

Shuttering for use in casting a slab/beam over a substrate comprises a hollow support structure including a plurality of spaced apart support walls 7, 8 defining cells 6 therebetween. The support structure is able to be placed on the substrate to support the slab/beam during casting and is formed with its spaced apart walls by a moulding process. The cells 6 are of a substantially hexagonal shape. The shuttering allows upward movement in the substrate, e.g. clay heave, to be accommodated the collapsible nature of the support walls 7, 8, 9

Description

Shuttering

Technical Field

This invention relates to shuttering for use, particularly in the construction industry, in casting slabs or beams over a substrate, to a method of manufacturing such shuttering and to a method of casting a slab/beam over a substrate.

The invention relates, more especially, to shuttering for use in casting floor slabs or ground beams over a substrate in which upward movement is expected. The upward movement may, for example, be caused by heaving movement in a clay substrate; this is a common cause of such movement, but other factors may also cause such movement. A floor slab or ground beam cast directly on such a substrate would be at risk of cracking or breaking as a result of excessive upward movement in the substrate applying an upward force on the slab or beam, but the risk can be substantially reduced if the slab or beam can be spaced from the substrate to enable such upward movement to be accommodated.

Background of the Invention

Traditional approaches to casting slabs or beams over a substrate in which movement, particularly heaving movement, is expected have included shuttering which is intended to be destroyed by moisture emanating from the substrate or introduced deliberately after the slab has been cast. This known form has the disadvantage that it can be destroyed prematurely by moisture from other sources, for example by rainwater. A further disadvantage of this known form is the production of methane gas following its destruction by moisture.

Another established approach involves the use of shuttering which comprises a support surface on which material is cast, and a support structure of cellular construction located between the support surface and a substrate in which movement is expected. The support structure, which is made of expanded polystyrene supports the weight of the cast material but under a predetermined, higher, compressive force will fail. Shuttering of this nature is disclosed in both GB 2206637 and GB 2241976 and has proved successful commercially. Large blocks of expanded plastics material are formed and then cut into sections of the required size. As a result of this process the sections of expanded plastics material used to construct the support structure may not be of uniform density. A support structure assembled from such sections may then have characteristics (for example, maximum load prior to failure) that are not uniform across the assembled structure. Furthermore, the characteristics of a first support structure panel can differ from that of a second panel which is nominally identical to the first. Such variations can be disadvantageous, especially if it is desired to have only a small gap between the load that the shuttering can safely bear without collapse and the load at which the shuttering is required to have failed.

In GB 2390390 and GB 2417283 shuttering of the kind just described is modified by moulding it from expanded polystyrene. Shuttering formed in this way can be made with more uniform characteristics resulting in a more consistent and predictable performance of a given product of given dimensions. Such moulded products are currently manufactured and sold by the Applicants under the trade marks CELLOORE and CELLEORM. Moulding products of this kind is challenging and GB 2390390 and GB 2417283GB describe moulding procedures that make it feasible to mould such products cost effectively. A particular issue that has to be addressed is the feeding of polystyrene beads into the mould and to all parts of the support structure.

In the embodiments illustrated in GB 2390390 and GB 2417283 and in the equivalent commercial products, the support structure comprises a multiplicity of four-sided cells bounded by a first set of walls extending across the structure in a first direction and a second set of walls extending across the structure in a second direction perpendicular to the first. It is challenging to feed material into the walls during the moulding process.

A support structure of the kind described above has a first supporting condition, in which it is manufactured, in which it can accommodate a given loading with very little compression of the material. The depth of the support structure of the product in this condition is referred to herein as the depth (D) of the support structure in the first supporting condition. The maximum loading at which the support structure is assured of remaining in the first supporting condition is referred to in commercial products as the "Safe Load" and during casting of a slab or beam this Safe Load should not of course be exceeded. The support structure also has a second failed condition, in which the walls have failed. The minimum loading at which this is assured of having occurred is referred to in commercial products as the "Fail Load". As the loading on the product increases from zero towards the Safe Load, so its resistance to compression is maintained, but, at some stage after the loading exceeds the Safe Load, the resistance of the product to compression stops increasing and even reduces until the product is much reduced in depth. At some much reduced depth the product willagain increase its resistance to compression and there is a reduced depth at which the load that has to be applied to cause yet further reduction in depth exceeds the Fail Load.

That reduced depth is therefore the depth that the support structure has at the Fail Load and is referred to herein as the depth Cd) of the support structure in the second failed condition. As will be understood it is a simple matter to apply a test load to a product to establish the Safe Load and the Fail Load and also to establish the depth of the support structure in both the first supporting condition and the second failed condition.

Products of the kind referred to are used in a variety of applications and those different applications require

different specifications of product. For a given

application, there are two main kinds of variable to be specified: one is the amount of upward movement that the product is required to accommodate; the other is the value of the Safe Load that the product is required to accommodate, with the Fail Load preferably being only slightly higher than the Safe Load.

In current commercially available standard products the amounts of upward movement accommodated are 50mm, 100mm and 150mm. The more movement that is required to be accommodated, the greater the depth of product required in order that the difference in depth between the depth (ID) of the support structure in the first supporting condition and the depth (d) of the support structure in the second failed condition is equal to the amount of upward movement to be accommodated. In commercial products that embody the invention of GB 2390390 and GB 2417283 the support structure for accommodating an upward movement of 50mm has a depth of about 95mm, a support structure for accommodating an upward movement of 100mm has a depth of about 170mm and a support structure for accommodating an upward movement of 150mm has a depth of about 245mm.

In the products just described, typical Safe Loads and Fail Loads are: a Safe Load of 2OkN/m2 and a Fail Load of 3OkN/m2; a Safe Load of l5kN/m2 and a Fail Load of 22kN/m2; a Safe Load of lOkN/rn2 and a Fail load of l5kN/m2; a Safe Load of 8kN/m2 and a Fail Load of l2kN/m2. The Safe and Fail Loads are controlled primarily by adjusting the density of the supporting structure.

When using shuttering of the kind referred to, it is of course necessary to provide a space below the level of the slab to accommodate the shuttering and in many cases that will mean that an additional amount of excavation of the substrate is required. That extra excavation often involves extra cost.

It is an object of the invention to provide improved shuttering for use, in the construction industry, in casting slabs or beams over a substrate, to provide an improved method of manufacturing such shuttering and to provide an improved method of casting a slab/beam over a substrate

Summary of the Invention

According to a firtht aspect of the invention there is provided shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure including a plurality of spaced apart support walls defining cells therebetween, the support structure being able to be placed on the substrate to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and the cells are of a substantially hexagonal shape.

We have found that providing a moulded support structure made of expanded plastics material and with cells of a substantially hexagonal shape, rather than the usual rectangular shape, has special advantages. A feature of a hexagonal structure is that each intersection of walls involves only three walls, rather than four in a rectangular structure. We have found that the positions at which walls intersect tend to be more resistant to failing than positions midway between intersections; this impedes the provision of a supporting structure of uniform characteristics across its area. By reducing the number of walls from 4 to 3, however, that cause of non-uniformity is very significantly reduced. When making the support structure by moulding, there are obvious advantages in providing rectangular cells; as explained in GB 2390390 and GB 2417283, such moulding is difficult and in accordance with the teaching in those documents, alternate supporting walls defining the rectangular cell are slightly inclined in opposite directions to the vertical, to facilitate moulding. With a hexagonal cellular structure, that option is not available, deterring a skilled person from trying a hexagonal structure.

Each substantially hexagonal cell may have the shape of a regular hexagon but in a preferred embodiment of the invention each cell has the shape of an irregular hexagon.

Preferably the cell has some symmetry: more particularly, it is preferred that at least one pair of opposite walls of each substantially hexagonal cell are substantially parallel to one another. The shuttering is preferably a panel of rectangular shape and, in that case, one pair of substantially parallel walls preferably extend substantially parallel to shorter end edges of the panel.

Said one pair of substantially parallel walls may be spaced apart by a distance less than the spacing of the other opposite walls of the substantially hexagonal cell. The difference in spacing is preferably small, and preferably less than 10%. Preferably, all three pairs of opposite walls are substantially parallel to one another; it should be understood, however, that even in this case the hexagonal shape need not be that of a regular hexagon. In a regular hexagon, each interior angle is 120 degrees. In the present invention, the interior angles of the hexagonal cells are preferably not all the same but preferably lie in the range of 110 to 130 degrees.

The support structure preferably has a first supporting condition in which the depth of the support structure is D and a second collapsed condition in which the depth of the support structure is d, wherein d is less than 0.38D. By providing a support structure in which the depth of the structure reduces to less than 0.38D of its original depth upon failure it becomes possible to provide an arrangement in which the amount of excavation required to provide a support structure capable of accommodating a given upward movement of a substrate is reduced, thereby reducing the cost of using the shuttering according to the invention. For example in a possible example of the invention described below, a support structure able to accommodate about 150mm of upward movement has depth D in a first supporting condition of about 215mm and a depth d in a second failed condition of about 65mm. This reduction of depth represented by d being equal to about 0.30D may be contrasted to current commercially available shuttering of the same kind where to accommodate the same 150mm of movement the supporting structure has a depth D in a first supporting condition of 245mm and a depth d in the failed condition of 95mm.

Preferably, in shuttering embodying the invention, d is less than 0.36D and more preferably d is less than 0.33D. It should be noted, however, that it is also within the scope of the broadest aspect of the invention for d to be greater than 0.38D. In such a case it is preferable, but not essential, that d is less than 0.45D and,more preferably, less than 0.4D.

Preferably, shuttering embodying the invention has relatively thin walls. When moulding shuttering it is generally desirable to provide thick walls in order to facilitate introduction of material into the walls during the moulding process. In the present invention, however, it is preferred to ignore that general teaching and to employ relatively thin walls and accept the difficulties that arise as a result. The walls are preferably less than 15mm thick and more preferably less than 13.5mm thick.

Preferably all the walls are of the same thickness but it is within the scope of the invention for the walls to be of -10 -varying thickness and in that case a minority of the walls may have a thickness greater than the preferred upper ranges given above.

In a typical process for moulding a product from expanded polystyrene the raw material employed is non-expanded beads of polystyrene. Such non-expanded beads typically have a diameter of the order of 1mm. The beads are then steamed to cause them to expand and the degree of expansion at this stage can be controlled according to the density of the expanded polystyrene material required for the final product. The size of the bead after this first stage of expansion for products that might be suitable for the present invention is likely to be in the range of 2mm to 10mm and the expanded beads have to be introduced into the mould cavity. Whilst if the expanded bead size is only 2mm, the size is fairly immaterial, when a product of relatively low density, providing relatively low Safe and Fail Loads is required, the bead size has to be relatively big. For a larger expanded bead size, it can immediately be seen that there is a significant difference between moulding a wall having a thickness of 16.5mm and a wall having any less thickness. In general the wall thickness is preferably at least twice the expanded bead size. In embodiments of the invention described below, the walls have a thickness of only 13mm. As already indicated, in the preferred embodiments of the invention, the teaching towards the use of walls much thicker than 10mm to facilitate moulding is ignored and thinner walls are -11 -employed. Various techniques may then be used to make it feasible to mould even relatively low density products and these are referred to elsewhere in this specification.

The actual depth 0 selected for the support structure in the first supporting condition depends apon the amount of upward movement of the substrate that is required to be accommodated. In one example where about 150mm of upward movement is to be accommodated by the shuttering, the depth D of the support structure in the first supporting condition is in the range of 200mm to 220mm and the depth d of the support structure in the second collapsed condition is more than 140mm less than the depth D in the first supporting condition. In another example where about 100mm of upward movement is to be accommodated by the shuttering, the depth D of the support structure in the first supporting condition is in the range of 140mm to 160mm and the depth d of the support structure in the second collapsed condition is more than 95mm less than the depth 0 in the first supporting condition. In another example where about 50mm of upward movement is to be accommodated by the shuttering, the depth D of the support structure in the first supporting condition is in the range of 70mm to 80mm and the depth d of the support structure in the second collapsed condition is more than 45mm less than the depth 0 in the first supporting condition.

The Safe and Fail Loads of the shuttering for given dimensions of the support structure can be adapted by selecting an appropriate density of the expanded plastics -12 -material. In examples of the support structure, the Safe Load varies between about 7kN/m2 and about 24kN/m2 while the Fail Load varies between about lOkN/m2 and about 30kN/m2.

Some examples of pairs of Safe/Fail loads, all in kN/m2, are 7/10, 9/13, 13/18, 17/23 and 24/30. Thus the Safe Load is typically about three quarters of the Fail Load. Prefer-ably the Safe Load is at least 70% of the Fail Load.

The size and shape of the cells is preferably uniform across the support structure. The shuttering may be a panel of rectangular shape and in that case the longest dimension of the hexagonal cells in a direction parallel to the short sides of the panel and measured between mid-points of the walls defining the cells is preferably in the range of 195mm to 205mm. Preferably this is the separation of opposite corners of each hexagonal cell. The spacing of the centres of cells, measured in a direction parallel to the short sides of the panel, is preferably in the range of 140mm to 160mm and more preferably about 150mm. A panel may have an overall length of 2400mm and an overall width of 1200mm; with the dimensions just mentioned the structure can be cut lengthwise at intervals of about 150mm to provide the same repeating cellular structure, for example to provide pieces of shuttering, each of appropriate cross-section, and of 450mm width, or of 600mm width. When hexagonal cells are of the width indicated above, if they were a regular hexagonal shape, the loads that the structure could accommodate would be reduced because of the size of the cells. It is therefore preferred that the -13 -spacing of the centres of the cells measured in a direction parallel to the long sides of the panel is in the range of 150mm to 160mm and more preferably about 155mm. A centre-to-centre spacing.widthwise of about 150mm and lengthwise of 155mm is achieved by having hexagons with three pairs of parallel sides, one pair being aligned with the widthwise direction and having interior angles for the hexagon of about 114 degrees for one pair of smaller angles and of about 123 degrees for two pairs of larger angles.

The plane of each support wall is preferably approximately vertical. Although the provision of vertical walls could be seen as making moulding difficult, as explained elsewhere, we have found a satisfactory method of moulding such a structure.

In an especially advantageous form of the invention the walls are recessed in the regions of at least some of their intersections. Preferably the recesses are formed during the moulding process but it is also possible to form them by removing material after moulding. The recesses may be provided at the top and/or bottom of the support structure. The recesses preferably define passageways between adjacent cells in the support structure. A recess may define a passageway between only two adjacent cells, or, as in a preferred embodiment, between three adjacent cells. It is already known to provide such passageways away from the intersections of the walls to allow drainage, for example of water, from one cell to another. The provision of passageways at the intersections of the walls -14 -also serves that purpose but is able additionally to serve two other purposes: firstly, it facilitates moulding of thin walls and, secondly, it facilitates an even collapse of the supporting structure when it fails. A brief explanation of how those advantages are achieved will now be given.

A difficulty when moulding thin walls is the small physical size of the openings in the mould between opposite portions of the mould defining the space into which material has to be introduced to form the mould. The size is greatest at the intersection of walls and it is therefore preferred to introduce material into the mould cavity at that position. By providing a recess at the intersection, a bigger space is created in which to provide a point for introducing material into the mould cavity.

As already described, an advantage of making the support structure by moulding is that a more consistent product can be obtained and of course this is advantageous in facilitating prediction of the load at which the structure fails. We have found, however, that in the case of a support structure that does not employ recesses at the intersections of the walls, those intersections represent regions of increased resistance to failure and consequently there is a tendency for the structure to behave non-uniformly as the load on it is increased beyond the Safe Load. By providing the recesses, the forces on the support structure from the slab/beam and/or the substrate are no -15 -longer applied directly at the intersections and so more uniform collapse of the structure can be achieved.

Usually the support structure is open on its top face and the shuttering further comprises a top sheet of material on the top of the support structure. The sheet may be placed loosely on top of the support structure but preferably is attached to the support structure, for example by adhesive. Similarly the shuttering may further comprise a bottom sheet of material on the bottom of the support structure. That sheet is preferably also attached to the support structure, for example by adhesive. The sheet or sheets of material may be of any suitable form but may comprise a polypropylene sheet which may be fluted or may comprise a sheet of expanded polystyrene with a thin sheet of polypropylene on the outside. When the sheet comprises a polypropylene sheet alone, it may be 5mm to 10mm thick.

As described above the use of a support structure that has walls less than 15mm thick and yet is moulLded is a special and advantageous feature and can be employed in shuttering that is not in accordance with the first aspect of the invention, for example, because the support structure does not define cells of substantially hexagonal shape. Accordingly, in a second aspect of the invention there is provided shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure including a plurality of spaced apart support walls, the support structure being able to be placed on the substrate -16 -to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and is moulded from expanded plastics material, and wherein the thickness of the walls is less than 15mm.

Similarly the use of a moulded support structure that has intersecting walls that are recessed at some or all intersections is a special and advantageous feature and can also be employed in shuttering that is not in accordance with the first aspect of the invention, for example, because the support structure does not define cells of substantially hexagonal shape. Accordingly, in a third aspect of the invention there is provided shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure including a plurality of spaced apart support walls which intersect with one another, the support structure being able to be placed on the substrate to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and is moulded from expanded plastics material, and wherein the walls are recessed at intersections.

When in use a 1ab or beam is cast on shuttering of the invention, a structure is formed with the shuttering below. Accordingly, the invention also provides a structure including a slab or beam cast on shuttering of the first second or thiird aspects of the invention.

-17 -The present invention further provides a method of manufacturing shuttering for use in casting a slab/beam over a substrate, the method including the step of moulding a support structure from expanded polystyrene material to provide shuttering of the first second or third aspects of the invention.

The method may further include the step of introducing material into the mould at locations cdrresponding to intersections of the support walls.

Different mouids are required to mould shuttering of different depths and it is desirable to have as few moulds as possible. The depth of the shuttering can, if desired, be increased by placing one support structure of the invention on top of another. Such an arrangement may be desirable if an especially large amount of upward movement of a substrate is expected. In order to form shuttering of relatively small depth, the method of the invention may include the step of cutting the moulded product into two halves along a plane partway between the top and bottom of the support structure. If the moulded product is cut midway between the top and bottom of the support structure, then both halves may be employed for shuttering of relatively small depth.

During the moulding, a substantially hexagonal cell in the support structure is preferably created by the combination of a first mould portion inserted into the cell from one side of the support structure and a second mould portion inserted into the cell from the opposite side of -18 -the support structure. The first and second mould portions preferably have complementarily inclined confronting faces that come together in the middle of a hexagonal cell when the expanded plastics material is introduced into the mould. The inclination is preferably only a few degrees.

In that case the mould portions are naturally slightly tapered and it becomes much easier to produce a hexagonal cell with vertical sides of constant thickness.

The method preferably further includes the step of securing a top sheet over the support structure.

Especially when moulding support structures of relatively low density, it may be desirable to use non-expanded beads of a smaller size than are conventionally used for building products made of expanded polystyrene, in order that the size of the expanded beads introduced into the mould are not too large.

The present invention still further provides a method of casting a slab/beam over a substrate, the method including the step of placing shuttering according to any of the first second or third aspects of the invention on the substrate, and casting the slab/beam on the top of the shutte ring.

The substrate may rise after casting of the slab/beam and the shuttering may then fail. Thus excess upward pressure on the slab/beam is avoided.

It will be appreciated that the shuttering of the first, second and third aspects of the invention are closely related and that therefore essential or preferred -19 -features of one aspect of the invention may, unless indicated otherwise or clearly inappropriate, be incorporated into another. Similarly the shuttering of the invention and the methods of the invention as described herein are closely related. Thus,' features described above in respect of the shuttering may be incorporated into the methods of the invention and vice versa.

Brief Description of the Drawings

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is an end view of a shuttering panel embodying the invention, Fig. 2 is a bottom plan view of the bottom of'the shuttering panel, Fig. 3 is an enlarged bottom plan view of part of the shuttering panel, Fig. 4 is a vertical section illustrating the panel in use, Fig: 5 is the same vertical section but shows the arrangement after the support structure has partly collapsed, and Fig. 6 is an isometric view of part of the supporting structure of the panel, showing a modification of the panel in which there are recesses at intersections of the walls.

-20 -

Detailed Description of Embodiments

The shuttering panel 1 shown in Figures 1 and 2 comprises a hollow support structure 2 and a top sheet 3.

The top sheet 3 has a pair of long sides 4 and a pair of short sides 5. The top sheet 3 is formed from any suitable material. It may, for example, be heavy duty polypropylene sheet or a sheet of expanded polystyrene topped with a thin sheet of polypropylene. The support structure may be bonded to the top sheet in any suitable manner, for example by an impact adhesive.

The hollow support structure 2 comprises a plurality of support walls which together define a multiplicity of hexagonal cells 6. Each hexagonal cell is bounded by a pair of opposite walls 7 which extend parallel to one another and parallel to the short sides 5 of the panel, a pair of opposite walls 8 which define an angle, in this particular example an angle of about 123 degrees, to the waiis 7, and a pair of opposite walls 9 which define an angle, in this particular example again an angle of about 123 degrees, to the walls 7. Thus the angle defined between the walls 8 and 9, where they intersect is about 114 degrees. The plane of each of the walls 7, 8 and 9 is perpendicular to the plane of the top sheet 3. The support walls 7, 8 and 9 are of a uniform thickness in order to obtain more uniform performance characteristics across the hollow support structure.

-21 -The size and shape of the hexagonal cells 6 is uniform across the support structure. In a particular example of the invention, each of the walls 7, 8 and 9 is of 13mm thickness.

The hollow support structure 2 is formed in its hollow form by a moulding process, from expanded plastics material. In the embodiment shown the support structure is mouided from expanded polystyrene. By forming the hollow support structure by moulding rather than cutting the required hollow shape from a block of material, it is possible to mould a structure which is devoid of any bulky regions of solid material and consequently it is possible to obtain more uniform characteristics of the expanded plastics material throughout the structure.

Figure 3 shows the support structure in greater detail and shows a repeating portion of the structure. Some typical dimensions of the cellular structure are marked in Figure 3. A spacing Si between intersections of the walls 8 and 9 on opposite sides of a cell is marked. Also marked is the spacing S2 between opposite wails 7. In a particular example of the invention, *the spacing Si is about 200mm and the spacing S2 is about 155mm, measured in each case between the middies of the walls 7, 8 and 9.

Also marked in Figure 3 is a spacing 53 which is the centre-to-centre spacing of the ceils in a widthwise direction and a spacing S4 which is the centre-to-centre spacing of the cells in a lengthwise direction. In the particular example of the invention shown the spacing S3 is -22 -about 150mm and the spacing S4 is the same as S3 and therefore about 155mm.

The manner in which the shuttering panel 1 is used in laying a floor slab of a building is Illustrated in Figures 4 and 5. The normal surface level of the substrate 10 is shown, as is one of the piles 11 that are sunk into the substrate to support the building. A conventional ground beam 12 of reinforced concrete extends along the top of a line of piles 11, to support one of the walls of the building between which a suspended floor slab is to be constructed.

The substrate over which the floor slab is to be constructed is excavated to the required depth and the surface of the substrate is made level. Shuttering panels 13, each as shown in Figures 1 to 3, are then laid edge to edge to cover the prepared surface completely. The joins between adjacent panels are covered over, for example with a formwork tape. Full size panels may be cut to ensure the prepared surface is completely covered.

The bottom of the hollow support structure rests on the prepared surface. In Figure 4 the support structure is shown in its first supporting condition occupying a depth D. Conventional steel reinforcement (not shown) for the suspended floor panel is then secured over the panels 13, and is spaced slightly above the tops of the panels by conventional spacers (not shown) . Concrete is then laid over the support panels 13 and vibrated in the normal way.

When the top surface of the concrete has been finished, for example by tamping, the concrete is left to cure.

During the laying and initial curing process, the concrete is supported by the panels 13 but, as the concrete cures, the floor slab 14 becomes self-supporting between the walls.

If heaving movement occurs in the substrate, a vertical compressive force is exerted on the support walls 7, 8 and 9. Initially creep occurs in the expanded polystyrene material and, if the hea\ring movement of the substrate is extensive, the support walls 7, 8 and 9 begin to compress. If the compressive force on the support walls 7, 8 and 9 is such that it exceeds a predetermined limit, the moulding will fail. The resistance of the support walls 7, 8 and 9 to further compression will actually reduce and thus the resistance to further heaving movement reduces. Of course, if the heaving movement were to continue beyond the amount that the shuttering is designed to accommodate, the resistance to heaving movement would then increase beyond the original resistance level. Figure shows the situation where there has been some heaving movement but not as much as the shuttering is designed to accommodate. Thus Figure 5 shows the support structure as it is collapsing and occupying a depth d'. If no heaving movement of the substrate occurs to bring about the failute of the support walls 7, 8 and 9, the shuttering panel 1 and in particular, the hollow support structure 2, will remain intact.

-24 -It is also possible to use shuttering of the *type above to provide support on which a ground beam 12 is cast.

In this case, panels of a different size are likely to be required. Typically, shuttering panels for use in casting ground beams have a width in the range 300mm to 1200mm and, mOst commonly 450mm and 600mm.

Shuttering of the type above can be used in many situations in which concrete slabs or beams are cast over a substrate, for example, under reinforced suspended ground ancL basement floors, piled beams and piled rafts. The support structure of the shuttering can compress and collapse under the load from the substrate, caused for example by swelling clay or ground heave, and allows movement and pressure release to occur. The hollow support structure 2 of the shuttering panel also serves to insulate the concrete and thus accelerates the curing of the concrete, especially in cold weather.

The dimensions of the hollow support structure are determined by the mould. The hollow support structure is produced in sections which are typically 2.4m long and l.2m wide. When the top sheet 3 comprises simply a single polypropylene sheet, it will typically have a thickness of the order of 5mm to 10mm. When the top sheet 3 comprises a layer of expanded polystyrene on top of which there is a polypropylene sheet it may have a thickness of the order of 50mm.

The dimensions referred to above for the cells of the support structure and the overall dimensions of the panel -25 -described above are particularly advantageous as the most commonly used widths, 450mm and 600mm, can be easily cut from the moulded panel. Sections of support structures of these widths are generally used to support ground beams rather than cast floor slabs. The full size moulded support structure panel may be cut using a saw or a hot wire. In the case of a beam of 600mm in width, the full size panel is cut, using hot wires, into two sections. The panel is cut parallel to the long sides 4.

The thickness, spacing and/or height of the support walls 7, 8 and 9 can be varied, having regard to the conditions under which the walls are required to fail and bearing in mind that a change in the thickness and number of walls will alter the surface area over which the walls contact the substrate.

The support structure 2 is moulded in one piece directly in the shape shown in Figures 1 to 3. Since the support structure 2 is devoid of any bulky regions, all of it is close to a surface of the mould during the moulding process and it is therefore possible to achieve a very good uniformity throughout the structure 2 of the density of the expanded material forming the structure. In order to create the cells with vertical walls of constant thickness, mould portions are introduced into the cell space from opposite sides. For each cell, one half of the cell is filled by a mould portion introduced from one side and one half is filled from a mould portion introduced from the other side. The mould portions meet at a plane that is -26 -inclined to the vertical so that each mould portion is tapered towards its leading end. Thus the mould portions can be introduced into the cells with clearance between them, only coming together along their interface when they reach their fully inserted positions. Similarly, when they are withdrawn after moulding, they can be moved apart in directions inclined to the adjacent moulded walls with a componerxt of the movement away from the walls.

The shuttering panel shown in Figures 1 to 3 can, if required, be modified further by adding a bottom sheet similar to the top sheet which is locatable between the support structure and the substrate. This bottom sheet may be made out of a sheet of a suitable riqid material similar to that of the top sheet: it may, for example, also be expanded polystyrene. The surface may be bonded to the hollow support structure, for example by an impact adhesive.

Figure 6 illustrates an especially advantageous modification to the support structure 2. In the modification, the walls 7, 8 and 9 are recessed at their intersections to create recesses 20. Figure 6 shows the recesses at the tops of the walls 7, 8 and 9, but it should be understood that similar recesses may be providedat the bottoms of the walls. The recesses define passageways that provide fluid commuhication between adjacent cells, with all three cells adjoining an intersection being in communication with one another via the passageways. In addition to providing passageways for fluid communication, the recesses also have the advantage of reducing the extent to which compressive loads on the structure are borne by the intersecting portions of the walls 7, 8 and 9, and of defining a relatively large space in a mould for an injector through which mould material can be injected into the walls 7, 8 and 9 during moulding.

It is desirable to provide the shuttering described above as a range of products to cover different applications, according to the Safe Load that the product 10. is required to bear and the amount of upward movement of the ground that the product Is required to accommodate.

Some particular examples of products that may be made available are set out below.

In all the examples the shuttering is of the kind described above with reference to Figs. 1 to 3 and the support structure has the dimensions referred to above.

Example 1

In the first example the depth D of the walls 7, 8 and 9 when first moulded is about 215mm. The support structure 2 is moulded from expanded polystyrene having a density of about 2Okg/m3 and this results in shuttering with a Safe Load of 9kN/m2 and a Fail Load of l3kN/m2. When in testing, the Fail Load of l3kN/m2 is applied, the support structure 2 reduces in depth by about 150mm to a depth d of about 65mm.

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Example 2

In the second example the depth 0 of the walls 7, 8 and 9 when first moulded is about 150mm. The support structure 2 is moulded from expanded polystyrene having a density of about 30kg/rn3 and this results in shuttering with a Safe Load of l7kN/m2 and a Fail Load of 23JcN/m2. When in testing, the Fail Load of l7kN/m2 is applied, the support structure 2 reduces in depth by about 100mm to a depth d of about 50mm.

Example 3

In the third example the depth D of the walls 7, 8 and 9 when first moulded is about 150mm. The support structure 2 is moulded from expanded polystyrene having a density of about l8kg/m3. The shuttering is then cut in half by a hot wire to provide shuttering of depth about 75mm and this results in shuttering with a Safe Load of 7kN/m2 and a Fail Load of IOkN/m2. When in testing, the Fail Load of lOkN/m2 is applied, the support structure 2 reduces in depth by about 50mm to a depth d of about 25mm.

Where in the foregoing description, integers or

elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

Claims

-30 -Claims: 1. Shuttering for use in casting a slab/beam over a substrate, compriäing a hollow support structure including a plurality of spaced apart support walls defining cells therebetween, the support structure being able to be placed on the substrate to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and the cells are of a substantially hexagonal shape.
2. Shuttering according to claim 1, in which each substantially hexagonal cell has the shape of an irregular hexagon.
3. Shuttering according to claim 2, in which at least one pair of opposite walls of the substantially hexagonal cell are substantially parallel to one another.
4. Shuttering according to claim 3, in which the shuttering is a panel of rectangular shape and one pair of substantially parallel walls extend substantially parallel to shorter end edges of the panel.
5. Shuttering according to claim 4, in which said one pair of substantially parallelwalls are spaced apart by a distance less than the spacing of the other opposite walls of the substantially hexagonal cell.
6. Shuttering according to any of claims 3 to 5, in which all three pairs of opposite walls are substantially parallel to one another.

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7. £huttering according to any preceding claim, in which the interior angles of the hexagonal cells lie in the range of 110 to 130 degrees.
8. Shuttering according to any preceding claim, in which the walls have a thickness of less than 15mm.
9. Shuttering according to any preceding claim, in which the walls have a thickness of less than 13.5mm.
10. Shuttering according to any preceding claim, in which the support structure has a first supporting condition in which the depth of the support structure is D and a second collapsed condition in which the depth of the support structure is d, wherein d is less than 0.38D.
11. Shuttering according to any preceding claim, in which the size and shape of the cells is uniform across the support structure.
12. Shuttering according to claim 11, in which the shuttering is a panel of rectangular shape and the longest dimension of the hexagonal cells in a direction parallel to the short sides of the panel and measured between mid-points of the walls defining the cells is in the range of 195mm to 205mm.
13. Shuttering accordingto any preceding claim, in which the plane of each support wall is approximately vertical.
14. Shuttering according to any preceding claim, in which the walls are recessed in the regions of at least some of their intersections.
15. Shuttering according to claim 14, in which the recesses define passageways between adjacent cells.

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16. Shuttering according to claim 14 or 15, in which the recesses are provided at the top and/or bottom of the support structure.
17. Shuttering according to any preceding claim, further comprising a top sheet of material on the top of the support structure.
18. Shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure including a plurality of spaced apart support walls, the support structure being able to be placed on the substrate to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and is moulded from expanded plastics material, and wherein the thickness of the walls is less than 15mm.
19. Shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure including a plurality of spaced apart support walls which intersect with one another, the support structure being able to be placed on the substrate to support the slab/beam during casting, wherein the support structure is formed with its spaced apart walls by a moulding process and is moulded from expanded plastics material, and wherein the walls are recessed at intersections.
20. Shuttering substantially as herein described with reference to the accompanying drawings.
21. A structure including a slab or beam cast on shuttering according to any preceding claim.

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22. A method of manufacturing shuttering for use in casting a slab/beam over a substrate, the method including the step of moulding a support structure from expanded polystyrene material to provide shuttering according to any of claims 1 to 20.
23. A method according to claim 22, including the step of introducing material into the mould at locations corresponding to intersections of the support walls.
24. A method according to claim 22 or 23, in which during the moulding a hexagonal cell in the support structure is created by the combination of a first mould portion inserted into the cell from one side of the support structure and a second mould portion inserted into the cell from the opposite side of the support structure.
25. A method according to claim 24, in which the first and second mould portions have complementarily inclined confronting faces that come together in the middle of a hexagonal cell when the expanded plastics material is introduced into the mould.
26. A method according to any of claims 22 to 25, including the step of cutting the moulded product into two halves along a plane partway between the top and bottom of the support structure.
27. A method according to any of claims 22 to 26, further including the step of securing a top sheet over the support structure.
28. A method of casting a slab/beam over a substrate, the method including the step of placing shuttering according to any of claims 1 to 20 on the substrate, and casting the slab/beam on the top of the shuttering.
29. A method according to claim 28, in which the substrate rises after casting of the slab/beam and the shuttering fails.
30. A method of manufacturing shuttering for use in casting a slab/beam over a substrate, the method being substantially as herein described with reference to the accompanying drawings.
31. A method of casting a slab/beam over a substrate, the method being substantially as herein described with reference to the accompanying drawings.