GB2486722A

GB2486722A - Collapsible shuttering

Info

Publication number: GB2486722A
Application number: GB1021914.5A
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: EP2907924B1; EP2655749B8; EP2907924B2; WO2012085569A2; WO2012085569A3; EP2655749B1; ES2603081T3; GB201021914D0; GB2486722B; EP2907924A1; EP2655749A2; ES2536642T3; ES2603081T5

Abstract

Shuttering for use in casting a slab/beam over a substrate comprises a hollow support structure 2 defining a multiplicity of four-sided cells (8, 9 Figure 4) bounded by a first set of walls 6 extending across the structure in a first direction and a second set of walls 7 extending across the structure in a second direction transverse to the first direction. The support structure is placed on the substrate to support the slab during casting. The support structure is formed by a moulding process using expanded plastics material. The structure has a first supporting condition (Figure 6)in which the depth of the support structure is D, and a second collapsed condition (Figure 7)in which the depth of the support structure is d, wherein d is less than 0.38D. The shuttering may feature recesses which define passageways between adjacent cells.

Description

Shuttering for use in the construction industry

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 sudh 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 thay 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 CELLCORE and CELLFORM. 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, 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 will again 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 (d) 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 (0) 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 2417Z83 th&upbItH 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 1OkN/m2 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 a method of casting a slab/beam over a substrate

Summary of the Invention

According to a first aspect of the invention there is provided shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure defining 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 transverse to the first direction, 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 has a first supporting condition in which the depth of the support structure is 0 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 0.38 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 0 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 0.300 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 0 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 0.360 and more preferably d is less than 0. 33D.

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 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 embodiments of the invention described below, the wails 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 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 D selected for the support structure in the first supporting condition depends upon 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 D in the first supporting condition. In another example where about 50mm of upward movement is to be accommodated by the shuttering, the depth C of the support structure in the first supporting condition is in the range of 70mm to -10 - 80mm and the depth d of the support structure in the second collapsed condition is more than 45mm less than the depth D in the first supporting condition.

The Safe and Pail Loads of the shuttering for given dimensions of the support struature can be adapted by selecting an appropriate density of the expanded plastics 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 about3OkN/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.

Whilst it is within the scope of the invention for the first and second directions in which the walls extend to be at an angle significantly away from 90 degrees, it is preferred that the second direction is perpendicular to the first direction.

The spacing of adjacent walls is preferably uniform across the structure, preferably in the case of both sets of walls. The spacing of walls in one of the sets of walls may be the same as or different from the spacing in the other of the two directions. In a preferred arrangement of the invention the centre-to-centre spacing of adjacent walls in one of the sets of walls is in the range of 148mm to 152mm. In that same arrangement or in another arrangement, the centre-to-centre spacing of adjacent walls in one of the set of walls is in the range of 158mm to -11 - 162mm. In an embodiment of the invention described below, the spacing of the first set of walls is in the range of 148mm to 152mm and the spacing of the second set of walls is in the range of 158mm to 162mm. A spacing of about 150mm is especially suitable for a support structure that may be cut to form shuttering for beams that are 600mm wide or 450mm wide or of any other width that is an integral number of 150mm widths.

Preferably, the planes of the support walls, whilst approximately vertical, are angled to the vertical, preferably at an angle in the range of 0.5 to 5 degrees to the vertical; in an embodiment described below, the angle is about 1.3 degrees to the vertical, and larger inclinations are acceptable. Preferably, adjacent walls are angled in opposite directions, so that whilst one cell tapers in one direction through the thickness of the support structure the adjacent cells taper in the opposite direction. As explained below, such an arrangement facilitates moulding of the support 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, -12 -between three adjacent cells or, as in a preferred embodiment, between four 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 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 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 iith 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 moulded 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 comprise four-sided cells or because d is not less than 0.380. Accordingly, in a second aspect of -14 -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 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 intersection 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 comprise four-sided cells or because d is not less than 0.38D. 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/bean 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.

In the first aspect of the invention described above, d is less than 0.38D, but we have already indicated that it -15 -is within the scope of the second and third aspects of the invention for d to be greater than 0.380. In a variation of the first aspect of the invention, d may be less than 0.45D or less than 0.40.

When in use a slab 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 third aspects of the invention.

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 corresponding to intersections of the support walls.

Different moulds 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 -16 -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.

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 shuttering.

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 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 -17 -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 a side view of a shuttering panel constructed in accordance with the invention, Fig. 2 is a view in the direction of arrow A, of the bottom sheet of the shuttering panel in Fig. 1, Fig. 3 is an enlarged side view of the shuttering of Fig. 1, Fig. 4 is an enlarged view of a section of the bottom sheet of the shuttering panel in Fig. 1, Fig. 5 is an isometric view of a hollow support structure forming part of the shuttering panel, Fig. 6 is a iertica1 section illustrating the panel in use, Fig. 7 is the same vertical section but shows the arrangement after the support structure has partly collapsed, and Fig. 8 is an isometric view of part of the structure of Figure 5, showing recesses at intersections of the walls.

-18 -

Detailed Description of Embodiments

When describing embodiments of the invention, it is convenient to begin with a general description of the shuttering and thereafter describe certain particular examples of the invention and the special features that are particular to the present invention.

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 6,7. The plane of each wall is substantially perpendicular to the plane of the top sheet 3. In this particular embodiment the support walls 6,7 whilst substantially perpendicular, are angled to the vertical at an angle of the order of one degree. Some of the support walls, referenced 6, run parallel to the long sides 4 of the top sheet, while the remaining support walls, referenced 7, run in a direction substantially parallel to the short sides of the top sheet 3 and therefore perpendicular to the long sides and to th walls 6. The support walls 6 extend continuously along the -19 -length of the top sheet 3 and the support walls 7 extend continuously across the width of the top sheet 3. The support walls are of a uniform thickness in order to obtain more uniform performance characteristics across the hollow support structure.

The support walls are spaced apart substantially regularly in both directions such that the support walls define cells 8,9. The cells 8,9 defined by the support walls 6,7 are approximately square in plan.

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 moulded 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.

Figures 3 and 4 show the support structure in greater detail. As a result of the moulding process the cells 8,9 defined by the support walls 6,7 taper slightly between the top sheet 3 and the bottom of the hollow support structure 2. In Figures 3 and 4, the angling of the substantially perpendicular support walls has been exaggerated. Some of the cells, referenced 8, defined by the support walls 6,7 have a larger cross section at the bottom of the hollow support structure 2 than at the top of the support -20 -structure 2. The remaining cells, referenced 9, have a smaller cross section at the bottom of the hollow support structure 2 than at the top of the support structure. The distance between adjacent walls 6,7 varies as a function of displacement from the top sheet 3 towards the substrate in a direction perpendicular to the plane of the top surface of the support structure. This tapered cell structure enables simple release of the moulded hollow support structure from the mould.

The manner in which the shuttering panel 1 is used in laying a floor slab of a building is illustrated in Figures 6 and 7. 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 5, 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 6 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 6,7. Initially creep occurs in the expanded polystyrene material and, if the heaving movement of the substrate is extensive; the support walls 6,7 begin to compress. If the compressive force on the support walls 6,7 is such that it exceeds a predetermined limit, the moulding will fail. The resistance of the support walls 6, 7 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 7 shows the situation where there has been some heaving movement but -22 -not as much as the shuttering is designed to accommodate.

Thus Figure 7 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 break-up of the support walls 6,7 the shuttering panel 1 and in particular, the hollow support structure 2, will remain intact.

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 and 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. Other dimensions of the shuttering will be described in more detail below with reference to some particular examples. In the examples the centre-to-centre spacing of the walls 6 is 150mm and the centre-to-centre spacing of the walls 7 is 160mm.

The dimensions referred to are particularly advantageous as the most commonly used widths, 450mm to 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, number, height and/or layout of the support walls 6,7 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. For example, the size of the cells defined by the walls can be decreased by increasing the number of shorter support walls 7 and/or increasing the number of longer support walls 6.

-24 -The support structure 2 is moulded in one piece directly in the shape shown for example in Figure 5.

Alternate cells are formed by projecting parts of appropriate halves of the mould and the tapering of the cells assist the withdrawal of the mould halves from the support structure after moulding. 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.

The shuttering panel shown in Figures 1 and 2 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 rigid 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 8 illustrates an especially advantageous modification to the support structure 2. In the modification, the walls 6 and 7 are recessed at their intersections to create recesses 20. Figure 8 shows the recesses at the tops of the walls 6 and 7, but it should be understood that similar recesses may be provided at the bottoms of the walls. The recesses define passageways that provide fluid communication between adjacent cells, with -25 -all four 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 6 and 7, and of defining a relatively large space in a mould for an injector through which mould material can be injected into the walls 6 and 7 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 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 7 and the support structure has the following dimensions: Centre-to-centre spacing of walls 6: 150mm Centre-to-centre spacing of walls 7: 160mm Thickness of walls 6 and 7: 13mm Thickness of top sheet 3: 10mm

Example 1

In the first example the depth D of the walls 6 and 7 when first moulded is about 215mm. The support structure 2 is moulded from expanded polystyrene having a density of about 19kg/rn3 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.

Example 2

In the second example the depth D of the walls 6 and 7 when first moulded is about 150mm. The support structure 2 is moulded from expanded polystyrene having a density of about 28kg/rn3 and this results in shuttering with a Safe Load of l7kN/m2 and a Fail Load of 23kN/m2 When in testing, the Fail Load of 23kN/rn2 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 6 and 7 when first moulded is about 150mm. The support structure 2 is moulded from expanded polystyrene having a density of about 22kg/rn3 The structure is then cut in half by a hot wire to provide two structures of depth about 75mm and this results in shuttering with a Safe Load of l3kN/rn2 and a Fail Load of l8kN/rn2. When in testing, the Fail Load of l8kN/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 -27 -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

-28 -Claims: 1. Shuttering for use in casting a slab/beam over a substrate, comprising a hollow support structure defining 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 transverse to the first direction, 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 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.
2. Shuttering according to claim 1, in which the walls have a thickness of less than 15mm.
3. Shuttering according to claim 1 or 2, in which the walls have a thickness of less than 13.5mm.
4. Shuttering according to any preceding claim, in which 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.
5. Shuttering according to any preceding claim, in which the depth D of the support structure in the first -29 -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 90mm less than the depth D in the first supporting condition.
6. Shuttering according to any preceding claim, in which 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 D in the first supporting condition.8. Shuttering according to claim 1 or 2, in which the second direction is perpendicular to the first direction.9. Shuttering according to any preceding claim, in which the spacing of adjacent walls of the support structure is uniform across the structure.10. Shuttering according to claim 9, in which the centre-to-centre spacing of adjacent walls in one of the sets of walls is in the range of 148 to 152mm.11. Shuttering according to claim 9 or 10, in which the centre-to-centre spacing of adjacent walls in one of the sets of walls is in the range of 158 to 162mm.12. Shuttering according to any preceding claim, in which the plane of each support wall is approximately vertical but is angled to the vertical.13. Shuttering according to claim 12, in which the plane of each support wall is angled to the vertical at an angle in the range of 0.5 to 5 degrees.-30 - 14. Shuttering according to claim 12 or 13, in which adjacent walls are angled in opposite directions.15. Shuttering according to any preceding claim, in which the walls are recessed in the regions of at least some of their intersections.16. Shuttering according to claim 16, in which the recesses define passageways between adjacent cells.17. Shuttering according to claim 15 or 16, in which the recesses are provided at the top and/or bottom of the support structure.18. Shuttering according to any preceding claim, further comprising a top sheet of material on the top of the support structure.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, 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.20. 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 -31 -spaced apart walls by a moulding process and is moulded from expanded plastics material, and wherein the walls are recessed at intersections.21. Shuttering substantially as herein described with reference to the accompanying drawings.22. A structure including a slab or beam cast on shuttering according to any preceding claim.23. 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 21.24. A method according to claim 23, including the step of introducing material into the mould at locations corresponding to intersections of the support walls.25. A method according to claim 23 or 24, including the step of cutting the moulded product into two halves along a plane partway between the top and bottom of the support structure.26. A method according to any of claims 23 to 25, further including the step of securing a top sheet over the support structure.27. 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 21 on the substrate, and casting the slab/beam on the top of the shuttering.-32 - 28. A method according to claim 27, in which the substrate rises after casting of the slab/beam and the shuttering fails.29. 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.30. A method of casting a slab/beam over a substrate, the method being substantially as herein described with reference to the accompanying drawings.