GB2417283A

GB2417283A - Collapsible shuttering for use in casting slabs or beams

Info

Publication number: GB2417283A
Application number: GB0520952A
Authority: GB
Inventors: Alastair Seaton
Original assignee: Cordek Ltd
Current assignee: Cordek Ltd
Priority date: 2002-07-02
Filing date: 2002-07-02
Publication date: 2006-02-22
Anticipated expiration: 2022-07-02
Also published as: GB0215288D0; GB0520952D0; GB2390390B; GB2417283B; GB2390390A

Abstract

Shuttering for use in casting a slab/beam (14) over a substrate (10) comprises a hollow support structure (2) which supports the slab/beam during casting. The hollow support structure (2) is made from expanded plastics material and is formed, in its hollow form, by a moulding process. The arrangement of shuttering requires a sheet of material (3, Fig 1) placed on top of the hollow support structure 2. Preferably, the support structure is made from expanded polystyrene.

Description

24 1 7283 - 1 - The invention relates to shattering for use, in the

construction industry, in casting slabs or beams over a substrate and to a process for producing said shattering.

The invention relates, more especially, to shattering for use in casting floor slabs or ground beams over a substrate in which movement, particularly heaving movement, is expected. A floor slab or ground beam cast directly on such a substrate (for example, clay) would be at risk of cracking or breaking as a result of excessive movement in substrate, but the risk can be substantially reduced if a void can be provided, between the floor slab or beam and the substrate, into which this movement can take place.

A known approach to casting slabs or beams over such a substrate involves a form of support structure or shattering onto which the slab/beam can be cast, the support structure being of a temporary nature so that it will in the course of time, leave a void between the substrate and the cast floor slab or beam, which is then self supporting.

Traditional approaches to casting slabs or beams over a substrate in which movement, particularly heaving movement, is expected have included shattering 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.

An alternative traditional form of shattering is that which is intended to be compressed by upward movement of the substrate. Shuttering of this type is intended to take up movement of the substrate and thereby - 2 - prevent damage to the cast slab or beam but, in practice it is difficult to ensure that a damaging load is not applied to the cast slab or beam if the substrate heaves.

A more recent approach involves the use of shattering which comprises a support surface on which material is cast, and an assembled support structure of cellular construction located between the support surface and a substrate in which movement, particularly heaving movement, is expected. The support structure supports the weight of the cast material but under a predetermined compressive force will break up. Usually the support structure is assembled using expanded plastics material.

Shuttering of this nature is disclosed in both British Patent No. 2206637 and British Patent No. 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 shattering can safely bear without collapse and the load at which the shattering is required to have collapsed.

It is an object of the present invention to provide a shattering structure for use in casting slabs or beams, which enables disadvantages of the known structures to be overcome.

The present invention provides shattering for use in casting a slab/beam over a substrate, comprising a hollow support structure locatable on the substrate to support the slab/beam during casting, wherein the hollow support structure is formed in its hollow form by a moulding process and is moulded from expanded plastics material.

The support structure is such that it will support the weight of the cast material but will fail under a greater load.

By forming the hollow support structure by moulding, rather than by cutting the required hollow shape from a block of material, it becomes 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. That in turn enables there to be a smaller difference between the load that the shattering can safely bear without collapse and the load at which the shattering is required to have collapsed than with a product manufactured and assembled from blocks.

The expanded plastics material from which the support structure is moulded is preferably expanded polystyrene.

The support structure of the shattering may be such that it breaks up under a predetermined force, such as that due to heaving movement of the substrate.

In an embodiment of the invention described herein, the support structure comprises a plurality of spaced apart support walls which may define cells.

The cells defined by the spaced-apart support walls may be of a generally cuboidal form. The plane of each support wall is preferably substantially perpendicular to a top and/or bottom surface of the supporting structure. - 4 -

It should be noted, however, that in a particularly preferred embodiment of the invention the planes of the support walls, whilst substantially perpendicular, are angled to the perpendicular, for example, at an angle of about 1.3 degrees to the vertical, and larger inclinations are acceptable. Preferably, successive 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.

The distance between adjacent support walls is preferably uniform across the structure in each of two mutually perpendicular directions; the spacing in one of those two directions may be the same as or different from the spacing in the other of the two directions. In an especially preferred arrangement of the invention the centre-to-centre spacing of the walls in one direction is in the range of 140 mm to 150 mm and the centre-to-centre spacing of the walls in the other direction is in the range of 148 mm to 158 mm. In an embodiment of the invention, the centreto-centre spacing is about 144 mm in one direction and about 153 mm in the other direction.

A spacing of about 153 mm is especially suitable for a support structure that is 1220 mm (4 ft) wide and also makes it easy to cut the structure down to two that are 600 mm wide or two that are 450 mm wide, that being advantageous for use in casting beams of 450 mm width or 600 mm width.

Preferably the spaced-apart support walls are of substantially constant thickness. That facilitates accurate prediction of the support structure.

Preferably the spaced-apart support walls are of constant thickness. - 5

The dimensions of each support wall may be such that under the predetermined force, the support wall begins to fail, flexes and then breaks up. Additionally, the support walls may have, in the direction perpendicular to the surface of the support structure, comparatively good compressive strength and comparatively low transverse flexural strength. To assist in obtaining the comparatively low transverse flexural strength, the transverse dimension of each support wall may be small in comparison with its dimension in the direction perpendicular to the top surface of the support structure (i.e. the height of the support structure when the.

shattering is in use); the ratio is preferably in the range from 1:2 to 1:15. The spacing between the support walls may be large in comparison with the transverse dimension of the support walls; the ratio is preferably in the range from 1:2 to 1:15.

Advantageously, the support structure is formed from a material in which creep occurs when the structure is subjected to sufficiently high compressive load.

Usually the support structure is open on its top face and the shattering further comprises a sheet of material over the top of the support structure. The sheet may be placed loosely on top of the support structure but preferably is attached to the structure.

Similarly the shattering may further comprise a sheet of material over the bottom of the support structure and that sheet is preferably attached to the structure. The sheet or sheets of material are preferably of rigid material.

The depth of the shattering 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 heave is expected.

The present invention further provides a method of moulding a support structure of shattering for use in casting a slab/beam over a substrate, wherein the support structure is moulded from expanded plastics material.

The support structure may comprise a plurality of spaced- apart walls which may define cells and may be formed of expanded polystyrene. The structure may also include any of the other features described above.

The present invention also provides a method of casting a slab/beam over a substrate, comprising the steps of locating shattering as defined above on the substrate to provide a supporting surface for cast material, and casting the slab/beam over the surface.

Advantageously, under the predetermined compressive force the support structure is compressed, begins to fail and collapses; the collapse of the support structure allows the structure heaving substrate to move upwards.

The present invention also provides a method of casting a slab/beam over a substrate, including the steps of locating shattering as defined above on the substrate to provide a supporting surface for cast material and casting the slab/beam over the surface, in which the support walls flex under a predetermined compressive force, such as that due to heaving movement of the substrate, and thereafter break up.

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 shattering panel constructed in accordance with the invention. 7

Fig. 2 is a view in the direction of arrow A, of the bottom sheet of the shattering panel in Fig. 1 Fig 3. is an enlarged side view of the shattering of Fig. 1 Fig. 4 is an enlarged view of a section of the bottom sheet of the stuttering panel in Fig. 1 Fig. 5 is a perspective view of a hollow support structure forming part of the shattering panel.

Fig. 6 is a vertical section illustrating the panel in use.

Fig. 7 is the same vertical section but shows the arrangement after the support structure has collapsed.

The shattering panel 1 shown in figures 1 and.2 comprises a hollow support structure 2 and a rigid top sheet 3.

The rigid top sheet has a pair of long sides 4 and a pair of short sides 5. The top sheet 3 is formed from any suitable rigid 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 about 1.3 degrees. Some of the 8 - 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 sides to the short sides of the top sheet 3. The support walls 6 extend continuously along the 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 structure 2. The remaining cells, - 9 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 support walls 6,7 have a comparatively good compressive strength in a direction perpendicular to the plane of the top sheet 3 and a comparatively low transverse flexural strength and, as indicated by figures 1 to 5, are comparatively thin for their height and are also thin in comparison with the distance between them.

The manner in which the shattering 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 sheet of the hollow support structure rests on the prepared surface. - 10

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 flex. If the compressive force on the support walls 6,7 is such that it exceeds a predetermined limit, the expanded polystyrene will flex no further and fails. The support walls 6,7 break up progressively. This is the situation illustrated in figure 7. The walls 6,7 are designed to ensure that they break up before the heaving movement in the substrate causes any upward movement in the cast slab. Following the break up of the support walls 6,7 the resistance of the shattering panel to load is negligible and any subsequent movement of the substrate within the design limits of the shattering may take place without affecting the slab. Unless otherwise destroyed, if no heaving movement of the substrate occurs to bring about the break-up of the support walls 6,7 the shattering panel 1 and in particular, the hollow support structure 2, will remain intact.

It is also possible to use shattering of the type above to provide support on which a ground beam 12 is - 11 cast. In this case, panels of a different size are likely to be required. Typically, stuttering panels for use in casting ground beams have a width in the range 450mm to 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 shattering compresses and collapses 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 shattering panel also serves to insulate the concrete and thus accelerates the curing of the concrete, especially in cold weather. Insulation is also provided, following the collapse of the shattering, by the layer of polystyrene rubble on the substrate and this can be useful, particularly underneath a floor slab.

The characteristics of the support structure are determined by the density of the expanded polystyrene from which it is moulded. Thus by varying the density the characteristics of the support structure can be altered in a controlled manner. Expanded polystyrene, when use with the dimensions specified below for the walls 6,7 has good compressive strength in the plane of the wall but a low transverse flexural strength. The dimensions of the hollow support structure are determined by the mould. The hollow support structure is produced in sections which are typically 2440mm long and 1220mm wide. The spacing of the support walls 6, 7 is such that the sections may be easily cut into widths that are commonly used. The thickness of the top sheet 3 is., typically, within the range of from 5mm to 60mm. The - 12 walls 6 have a centre-to-centre spacing in the range of from 148mm to 158mm, the walls 7 have a spacing in the range from 140mm to 150mm. The support walls 6,7 are typically from lOOmm to 300mm high and from lOmm to 40mm thick. In the panel shown in figures 1 to 4, the walls 6,7 are 180mm high and 16.5mm thick. The walls 6 are spaced apart a distance, between centres of adjacent cells, of approximately 144mm and the walls 7 are spaced apart at a distance, between the centres of adjacent cells, of approximately 153mm.

The dimensions of the hollow support structure shown in figures 1 to 4 are particularly advantageous as the most commonly used widths, 450mm to 600mm, can be easily cut from the moulded panel. Sections of support structure 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 three sections. The panel is cut parallel to the long sides 4 and a middle section 20mm in width is removed from the panel, leaving two sections 600mm in width and 2440mm in length.

However, 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 break up 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. Alternatively, or in addition, the shape of the cells could be altered. Generally, the ratio of - 13 thickness of the support walls to the spacing between them (ie the spacing between centres) should be within the range of from 1:2 to 1:15.

The height of the support walls 6,7 is determined by the required depth of the void between the cast concrete slab and the substrate. The void between the cast concrete slab and the substrate should be sufficient to accommodate the expected substrate movement (which can be determined by soil analysis) together with the depth of the expanded polystyrene rubble. A particular height, of say 180mm, may not be suitable in all cases and could, when appropriate, be reduced or increased. The uniform nature of the moulded hollow support structure makes it possible to stack hollow support structure panels if a greater depth is needed. The height of the walls also determines, for particular expanded plastics material, the maximum permissible thickness of the walls if they are to break up in a reliable manner when a predetermined heaving movement occurs in the substrate. Generally the ratio of the thickness of a support wall to its height should be within a range from 1:2 to 1:15.

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 shattering panel shown in figures 1 and 2 can, if required, be modified further by adding a bottom sheet - 14 slmilar 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. -

Claims

Claims 1. Shuttering for use in casting a slab/beam over a substrate,

comprising a hollow support structure, open on its top and bottom face and a sheet of material over the top of the support structure, the support structure being locatable on the substrate to support the slab/beam during casting, wherein the support structure is formed in its hollow form by a moulding process and is moulded from expanded plastics material.
2. Shuttering according to claim 1 in which the expanded plastics material is expanded polystyrene.
3. Shuttering according to claim 1 or 2 in which under a predetermined compressive force, such as that due to heaving movement of the substrate, the support structure will break up.
4. Shuttering according to claim 1 or 2 which is such that under a predetermined compressive force, such as that due to heaving movement of the substrate, the support structure is compressed, begins to fail and collapses.
5. Shuttering according to any preceding claim in which the support structure comprises a plurality of spaced- apart support walls.
6. Shuttering according to claim 5 in which the plurality of spaced-apart support walls define cells.
7. Shuttering according to claim 6 in which the cells defined by the spaced-apart support walls are of generally cuboidal form.
8. Shuttering according to any of claims 5 to 7, in which the plane of each support wall is substantially perpendicular to a top and or bottom surface of the supporting structure. - 16
9. Shuttering according to claim 8, in which the planes of the support walls are angled to the perpendicular.
10. Shuttering according to claim 9, in which the planes of the support walls are at an angle of about 1.3 degrees to the vertical.
11. Shuttering according to claim 9 or claim 10, in which successive walls are angled in opposite directions.
12. Shuttering according to any of claims 5 to 11, in which the distance between adjacent support walls is uniform across the structure in each of two mutually perpendicular directions.
13. Shuttering according to claim 12, in which the centre-to-centre spacing of the walls in one of the directions is in the range of 140 mm to 150 mm.
14. Shuttering according to claim 12 or 13, in which the centre-to-centre spacing of the walls in one of the directions is in the range of 148 to 158 mm.
15. Shuttering according to any one of claims 5 to 14, in which the support walls are of constant thickness.
16. Shuttering according to any one of claims 5 to 15, in which the dimensions of each support wall are such that under a predetermined force, such as that due to heaving movement of the substrate, the support wall flexes under the said predetermined force and thereafter breaks up.
17. Shuttering according to any one of claims 5 to 15 in which the dimensions of each support wall are such that under a predetermined compressive force, such as that due to heaving movement of the substrate, the support wall flexes under the predetermined compressive force and thereafter fails.
18. Shuttering according to any one of claims 5 to 17, in which the spaced-apart support walls have, in the direction perpendicular to the top surface of the support structure, comparatively good compressive strength and comparatively low transverse flexural strength.
19. Shuttering according to any one of claims 5 to 18 in which a transverse dimension of each support wall is small in comparison with its height.
20. Shuttering according to claim 19, in which the ratio of the transverse dimension of each support wall to its height is within the range from 1:2 to 1:15.
21. Shuttering according to any one of claims 5 to 17 in which a transverse dimension of each support wall is small in comparison with the spacing of the support walls.
22. Shuttering according to claim 21, in which the ratio of the transverse dimension of each support wall to the spacing of the support walls is within the range of from 1:2 to 1:15.
23. Shuttering according to any preceding claim, in which the support structure is formed from a material in which creep occurs when the structure is subjected to a compressive load.
24. Shuttering according to any preceding claim, in which the sheet of material is attached to the support structure.
25. Shuttering according to any preceding claim, further comprising a sheet of material over the bottom of the support structure.
26. Shuttering according to claim 24 or 25 in which the sheet or sheets of material are of rigid material.
27. A method of moulding a support structure according to any one of claims 1 to 26 for use in casting a slab/beam over a substrate, wherein the support structure is moulded from expanded plastics material.
28. A method of casting a slab/beam over a substrate, including the steps of locating shattering on the substrate, the shattering being according to any of claims 1 to 26, to provide a supporting surface for cast material, and casting the slab/beam over the surface.
29. A method according to claim 28 wherein the support structure thereafter breaks up under a predetermined compressive force, such as that due to heaving movement of the substrate, to form a void between the slab/beam and the substrate.
30. A method of casting a slab/beam according to claim 28 wherein the support structure thereafter fails and collapses under a predetermined compressive force, such as that due to heaving movement of the substrate.
31. A method of casting a slab/beam over a substrate, including the steps of locating shattering on the substrate, the shattering being according to any of claims 5 to 22, or any of claims 23 to 26 when dependent upon claim 5, to provide a supporting surface for cast material, and casting the slab/beam over the surface, in which the support walls flex under a predetermined compressive force, such as that due to heaving movement of the substrate, and thereafter break up.
32. A method of casting a slab/beam over a substrate, including the steps of locating shattering on the substrate, the shattering being according to any of claims 5 to 22 or any of claims 12 to 26 when dependent upon claim 5, to provide a supporting surface for cast material, and casting the slab/beam over the surface, in which the support walls fail and collapse under a predetermined compressive force, such as that due to heaving movement of the substrate.
33. A method according to any of claims claim 28 or 32 further including the step of breaking up the support structure of the shattering, at least partly, to form a void between the cast slab/beam and the substrate.