WO1991014828A1

WO1991014828A1 - Compressed material and uses and methods for the use thereof

Info

Publication number: WO1991014828A1
Application number: PCT/GB1991/000456
Authority: WO
Inventors: Louis Obermeister; Keith Fendall Murray
Original assignee: Louis Obermeister
Priority date: 1990-03-27
Filing date: 1991-03-26
Publication date: 1991-10-03
Also published as: ZA912330B; AU7584191A; GB2269838B; GB2269838A; GB9006795D0; EP0596875A1; GB9319864D0

Abstract

Resilient closed-cell cellular sheets, for example similar to air-bubble packaging material, are used as a mould void filler for casting concrete floors, as heave-relief means under buildings, roads and other structures, and in situations where geotextiles are of use. The cellular material may be formed into self-supporting panels (15) comprising superimposed cellular sheets (16) bonded together, and preferably provided with at least one outer skin (18). The panel (15) may be precompressed to increase its rigidity. Such panels may also be used as structural elements.

Description

COMPRESSED MATERIAL AND USES AND METHODS FOR THE USE THEREOF

This invention relates to a compressed material and use and methods for the use thereof. Particularly, but not exclusively, the invention relates to a compressed material for use in building and civil engineering applications.

Embodiments of the invention can be used, JLnter alia in the building of structures, for example domestic and commercial buildings, roads, railways, runways, pavements, walkways etc.

Embodiments of the invention can also be used in the casting of materials to form structures, in particular but not exclusively in the casting of concrete, for example to form floors, roofs, and/or walls of building

Known materials for use in the above applications often lack one or more desirable characteristics, which must be sacrificed in favour of other considerations.

The present invention sets out to provide a versatile

SUBSTITUTESHEET material which can be manufactured and/or adapted to assume combinations of physical characteristics which are particularly suitable to cope with the conditions of use of the material. Particularly, the invention sets out to provide a material which can have, for example, its compressibility, its density, its stiffness, its permeability to liquids and gasses, its resistance to structural damage, its resistance to structural decay, its resistance to damp, its propensity to retain its shape, its thermal conductivity, its ability to transmit light and its ability to resist noise and vibration selected and provided so as to best suit the conditions in which the material will be used.

According to a first aspect of the invention there is provided a material comprising at least one sheet-like element having a plurality of closed fluid-containing cells with flexible cell walls, and means maintaining the fluid pressure within the cells greater than the ambient pressure outside the cells whereby the cell walls are under permanent tensile stress.

The invention also provides a compressed layer comprising a sheet-like element of closed-cell cellular form and a sheet-like skin element superimposed thereon and held thereagainst to form a self-supporting body, e. g. , a panel, block, slab, sheet, curvilinear shell or other configuration. The invention further provides a plurality of compresse layers, each layer comprising a sheet-like element of closed-cell cellular form, the sheet-like elements bein superimposed upon one another and held together to form a self-supporting body, e. g. , a panel, block, slab, sheet, curvilinear shell or other configuration.

The invention can be regarded as residing in compressed stressed-skin materials.

Preferably the said body is a panel or sheet.

The cells will in general be bubbles formed by a skin o skins of flexible but not necessarily extensible material, for example plastics film and/or metal foil.

In general, the cells are at internal pressures above atmospheric pressure. Alternatively or in addition, the pressure outside the cells may be maintained below ambient pressure.

A roportion of the cells may contain sub-ambient pressures, to help to draw outer surfaces of the panels or other bodies together under the ambient pressure; the proportion may be for example be 1: 2 to 1: 5 sub-ambient : normal-pressure cells.

The pressures in the cells will depend on temperature, which may be different at the point of use from the point of manufacture, enabling the body to have different properties when made, when transported, and when installed.

In one embodiment of the invention the self supporting panel further comprises a material which interleaves adjacent sheet-like elements.

Preferably said sheet-like element of closed-cell cellular form comprises a plurality of fluid-filled pockets; "fluid" herein includes gels and pastes as well as gases, vapours and liquids. The pockets contain gas, such as air, for example, or other gas, or a liquid, gel or paste, or any combination of these, at above atmospheric pressure. This pressure would normally be introduced during manufacture, by the manner of introducing the fluid and/or by mechanically deforming and constraining the element(s). Preferably said superimposed sheet-like elements are bonded to one another adhesively or by solvent welding or other welding ( e. g. laser welding) so as to be held together and form the aforesaid self-supporting panel .

The cell walls may be made of or include a material of rel atively hi gh tensile strength e. g. , " Kevlar" to increase the value of internal pressure that can be sustained.

Advantageously the sel f-supporting panel comprises a skin of puncture-resistant material surmounting the superimposed sheet-like elements on at least one face. Preferably the superimposed sheet-like elements are disposed between and adhesively bonded to upper and lower skins of puncture-resistant material.

I f said skins are j oined to one another (e. g. by interconnecting edge strips or by welding together adj acent edge portions of the upper and lower skins ) , the superimposed sheet-like elements may be held together by (and between) the skins and these materials need not be adhesively or otherwise bonded to one another.

Preferably one or each of said skins comprises thermall bonded fibres - advantageously a geotextile material, e. g. manufactured by Exxon Chemical Geopolymers Limited under the Trade Mark "TERRAM". Skins of other geotextile materials, in particular woven goetextiles, can be used. Geotextiles and other puncture-resistant materials (which may include plastics, metals, and metal-piastics laminates) are stiff (high E value) and have excellent tensile strength, making panels with such skins suitable for applications in which the panels span distances, for example as part of a shuttering, ceiling, roof, dome or arch.

Panels used for spanning must also be able to resist internal compressive stresses at the face from which load is applied, that is to say, the upper face when used as part of a ceiling or the like. It may therefore be advantageous to provide, on at least one face of the panel, a layer of material providing compressive strength, for example a layer of wood-based material, which may be in laminated form. Alternatively, the layer providing compressive strength may be or include plastics, plaster, fibres, cementitious material, or board, or compressive strength may be provided by impregnating with resin a fabric skin or layer, such as the previously mentioned geotextile materials and the like. It may be desirable to provide a compression-resistant load spreading skin or layer on both faces of the panel, so that the panel does not have a "right" and "wrong" face; this will make the panels easier to use, particularly when installed on site by relatively unskilled labour. Such panels are suitable for any application involving bending.

Panel materials in accordance with the first aspect of the invention may be formed by compressing a layer or a plurality of layers of closed-cellular material so that the fluid within the cells is under excess pressure. By this means, it is possible to produce a board-like material which stiffens with increased applied pressure.

Such boards have numerous uses, not restricted to structural and civil engineering uses. With suitable stressed skins they can be used for example to manufacture:

a) Hardcore substitute. b) Roof structures (including vaults) with or without structural framework; in this case, at least the outer skin may be of a weather-resistant material, or a weather-resistant outer skin may be added. c) Lighting panels; closed-cell materials of the kind with which the invention is concerned are commonly translucent, and can therefore be used for natural and artificial lighting. d) Light weight panelling for doors, partitions, advertising screens etc. e) Shuttering for casting concrete. f) Floors, roof decks, ceilings, external and internal walls, flooring and other underlays. g) Furniture padding on frames or fra eless furniture, h) Panelling, hulls, bulkheads, decking, internal structures, superstructures etc. for aircraft, motor vehicles, boats, and lighter-than-aircraft i) Leisure: beach and camping use, for example mattresses, rafts. j ) Packaging and packing. k) Thermal and acoustic insulation boards.

1) Vibration isolation boards for mechanical plant and audio amplifiers where the present materials can achieve minimal sound transmission through fastening means compressing the layers of cellular material; to reduce the transmission of different sound frequencies bubbles of varying sizes and pressures could be incorporated..

The board may be provided with frames. Materials for civil engineering and structural uses will be under precompression such as to be relatively hard and rigid. For furniture, and upholstery the degree of pre-compression, or the pressure in the cells, will be lower to provide softer and more flexible materials.

For use in circumstances in which the panels may be subjected to bending, compression-resistant outer skin may be added at least on that face of the panel which will become concave (that is, in compression under bending load), for example by a layer of laminated or other wood-based material and/or by resin impregnation of an outer layer made from a compression resistant material e. g. , fibre glass. Preferably, both faces are made compression-resistant.

Board materials in accordance with the invention can be made fire-resistant. For example, individual cells may contain fire-retardant material. The cell walls may incorporate fire-retardant additives. The panels may have fire-retardant outer skins. The boards have very little mass of material.

Materials in accordance with the invention can be used, as already mentioned, as underlays for roads and runways, or as part of a sub-formation for railway tracks. In these applications, the present materials can be used in a manner similar to what are known as geotextiles, acting as a separator and also absorbing shear stresses acting horizontally outwards, thereby increasing the vertical loading which can be applied before substantial vertical deformation occurs.

In marine and aviation applications, the present materials have the advantage of a very high rigidity in relation to weight, and excellent weather resistance. These qualities are also valuable for the other purposes (a)-(l) already listed.

The board material translates compressive stresses into tensile stresses in the cell walls and thereby the panel stiffens under load. To ensure that all of the cell walls are in tension at all times and the boards are relatively firm to the touch, the cells may be pre-compressed so that the enclosed fluid is under pressure.

It may be desirable to provide means for mechanically pulling and holding the outer surfaces of the panel material together to enhance stiffness, for example to enable the material to be used for the construction of roof decks, floors, partitions, doors, shuttering and temporary structures where a greater degree of compression would be an advantage. The structure can be designed to retain the pressurised fluid or release it under appropriate conditions.

The structure may be unsurfaσed or covered with materials ranging from flexible materials to rigid materials. The structure may also be interleaved with such materials.

Air bubble film may be employed in embodiments of all aspects of the invention, including those described below.

It is known to use air bubble film which is relatively impervious to pressurised air; the air in the bubbles is at atmospheric pressure and the material is provided in flexible sheets in rolls for use in the packaging industry. This film may be laminated at the crowns of the bubbles to a single layer of plain film.

It is also known to use air bubble film which is not so relatively impervious to pressurised air. Such bubble film is converted into a flexible product which is consequently soft for thermal insulation, vapour barrier, or damp proofing, consisting of two layers of air bubble film laminated together with aluminium foil each side. This product is provided in relatively thi sheets in rolls for use in the building industry and is prone to damage by short term deflation, puncture or general handling.

In order to embody the present invention, one or more resilient closed cell sheets, for example similar to air bubble film packaging material, are arranged in one or more layers and compressed to create a structure with inherent stiffness greater than that of the uncompressed air bubble film. In order to place the film in layers, several sheets may be laid one upon another, a single sheet may be rolled upon itself, a single sheet may be folded in an alternating or zig-zag fashion or otherwise, or a combination of these arrangements may be employed. The pressure in the bubbles may be retained by adhesive or mechanical means.

The bubble film utilised in accordance with any aspect of the invention may be compressed by placing a firm level surface across the crowns of the bubbles, and applying pressure to cause the bubbles to deform into oblate spheroids which may come into contact with each other.

The sizes of the bubbles can be constant or can vary within a particular structure. Advantageously the or each of the cellular elements comprises a sheet of air-bubble packaging material, e. g. that manufactured by Sealed Air Ltd. under the Trade Mark "AirCap", or a similar material. The material may be barrier sealed and may comprise barriers of any suitable thickness or density.

As described above, the invention is not restricted to the use of air as a filling for the bubbles, cells or pockets. The pockets may be filled with any suitable fluid. For example, it may be desirable to fill the pockets with helium in order to reduce the density of the structure. Alternatively, the pockets may be filled with water or other liquid in order to make the structure more rigid.

If the cellular layers are asymmetrical (i.e., bubbles on one side, flat on the other), adjacent layers may be arranged with the bubbles sides facing and so that the positions of the bubbles correspond so that bubbles from separate layers contact in a crown to crown fashion, alternatively the layers may be arranged so that bubbles from one layer are located in interstices between bubbles in another layer, or the bubbles may relate in a random fashion. Alternatively bubbles of one layer may face the flat face of an adjacent layer. The film can be selected to conform to a wide variety of design criteria such as the required strain properties, the fluid pressure to be retained in the pressurised oblate spheroid cells during storage and use, the properties of any other intermediate laminations, the compressive tensile properties of any puncture resistant skins, and the properties of any other facings. The film might also be metallised for thermal insulation purposes. In the same structure, there may be variations of thickness and/or fluid pressure in any layer.

The cells themselves may be made from any suitable material. The above-described bubble films are generally made from plastics materials, and such a construction will often be adequate for the present invention. However, it is preferred to form the cells or bubbles from high-grade polyethylene instead of the conventional low-grade polyethylene. Conventional plastics bubble walls may lose pressure with age. This may be advantageous, for example if the present materials are to be used as anti-heave or void-forming materials as described below. If long-term stability is essential, barrier-sealed plastics films or other impervious cell wall materials can be used. In some instances it may be desirable that the skin of the cells is inextensible and for this purpose metal foil, for example, may be employed to form the cell structure or may be added to a plastics cell structure or a plastics cell structure may be metallised.

It is also possible to interleave a matrix material between layers of a structure, or even between cells in a particular sheet. Where a matrix is thus provided, it can serve to limit the sideward deformation of the cells. In certain situations, the matrix will be in compression whilst the cells are in tension. As a result, the structure is very strong in relation to its weight. This property finds many useful applications in the construction of buildings. In particular, when the material is used in foundation work, e. g. , for heave relief or void formation, the matrix provides enhanced stability, ensuring that the material remains reliably at the required depth.

The matrix may be compressible or incompressible. The matrix will help to maintain the pressure of the fluid in the bubbles.

The matrix may be applied as a liquid, slurry or paste which subsequently sets. The application of the matrix can be performed during manufacture of the structure. Alternatively, the matrix can be applied when the structure is in situ on site, thereby allowing the customisation of structural components. Further aspects of the invention will now be described with reference to various applications of the invention. All aspects of the invention described below may make use of the first aspect of the invention, described above. However, it should be understood that they are not limited only to the use of that first aspect of the invention.

It is known, in building a structure upon ground liable to upward and/or sideward heave forces, to provide heave relief means between the ground and the structure. One known form of such heave relief means comprises a rigid layer of fibre-board material bonded on either side of a paper egg-crate hexagonal or rhomboid structure all of which degrades or rots rapidly when water is piped in or rots progressively due to take up of moisture from the soil and/or the atmosphere (e.g. due to rain), thereby providing a void between the ground and the structure. The degree of overall rotting cannot accurately be predicted, and will depend upon the amount of oxygen present. Because the product is made from organic material, anaerobic conditions will lead to the production of methane, which can be dangerous. The said rigid layer panels used are heavy, laborious to cut, and need to be stored in dry surroundings - all difficulties on building sites. Another form of heave relief means comprises sheets of expanded polystyrene, this does not provide a void between the ground and the structure, but it does provide a compressible layer where a proportion of the ground heave is transmitted to the structure. The polystyrene sheets are fragile in handling and due to limited compressibility, usually have to be provided to a considerable depth (or sheet thickness) with consequential expense.

According to a second aspect of the present invention there is provided heave relief means for use in building a structure upon ground liable to impart upon the structure forces due to heave of the ground, said heave relief means being in the form of a deformable layer for disposal between the ground and the structure, characterised in that said deformable layer comprises at least one resilient, closed cell, cellular element of sheet-like form that is compressible by said heave forces.

According to a third aspect of the invention there is provided a method of building a strcture upon ground liable to impart to the structure forces due to heave of the ground, said method including the step of providing heave relief means in the form of a deformable layer between the ground and the structure, characterised in that said deformable layer comprises a resilient, closed-cell cellular element of sheet-like form that is compressible by said heave forces. They can either provide a void or protective compressile layer between the ground and the structure.

The ground heave may be accommodated by stretching of the skins of the cells as the cells change shape, especially if these are bubbles as described above, without significant transmission of pressure to the structure.

Preferably, the cellular element comprises a plurality of fluid-filled pockets which may contain gas, such as air, for example, or some other gas, or even a liquid, gel or paste at above atmospheric pressure. This pressure would normally be introduced during manufacture.

In one embodiment of the second and third aspects of the invention, the deformable layer has a puncture resisting skin on one of its faces.

The heave forces will usually be upward forces on a slab or associated ground beam base and sideways forces on associated ground beam sides.

The working weight of the wet reinforced concrete causes a relatively small deformation of the said deformable layer. The said pockets deflate further due to the significantly greater increased pressure caused by ground heave and the permeability of the film and its capacity to stretch. Advantageously said pockets are individually sealed and relatively temporary.

Advantageously a plurality of said cellular elements of sheet-like form are provided as a series of superimposed layers.

The upper and/or lower surface of the deformable layer may comprise or be covered with a puncture-resistant material with high tensile strength for example a woven or non-woven fabric or other skin materials described hereinabove. Apart from the said deflation of the pockets, the layer may be so designed that either of its surfaces will be or can be punctured, or degraded by a chemical agent, in the event of ground heave, to allow fluid to escape from the pockets so that they can collapse to provide space to accommodate the ground heave or the protection can be achieved by σomprssion only of the fluid. Where a plurality of superimposed layers are provided, each of the layers may be designed to be capable of sustaining a puncture through its entire thickness, to enable adjacent inner layers to be punctured and allow fluid to escape from the inner layers. Another aspect of the invention relates to the casting of concrete and like materials.

In buildings and other constructions the load-bearing capacity of a reinforced concrete floor, particularly a suspended floor, is determined primarily by the thickness of the concrete between the upper and lower planar surfaces of the floor. This thickness, if constant, necessitates large volumes of concrete and consequent expense and weight loading on the building' s foundations. Past attempts to provide slabs of thinner thickness with integral depending ribs have necessitated the use of expensive or impractical materials for the void fillers (which are either left cast-in integrally with the slab or are removable therefrom for re-use).

According to a fourth aspect of this invention there is provided a void filler for use in casting concrete (or other mouldable or settable building composition) in which at least part of a surface of the configuration to be cast is determined by a surface of the said void filler, characterised in that said void filler comprises at. least one precompressed layer provided by a closed-cell, cellular element. According to a fifth aspect of the invention there is provided a method of casting concrete or other settable building composition, in which at least part of a surface of the configuration to be cast is determined by the surface of a void filler, characterised in that said void filler comprises at least one compressible layer provided by a resilient, closed-cell, cellular element.

Where the casting is to form the floor or wall of a building, it may be pre-cast or, if preferred, cast in situ.

Preferably said cellular element comprises a plurality of fluid-filled pockets formed between two membranes, the said pockets containing air, some other gas, liquid, gel, paste or a combination of these under pressure.

Preferably a plurality of void fillers are provided in the mould laterally spaced from one another to provide a castellated cross-sectional shape for at least one surface of the casting.

Advantageously said pockets are individually sealed and relatively permanent or impermanent according to requirement. Preferably the void filler comprises a plurality of said cellular elements provided as a series of superimposed layers.

By way of non-limiting example, embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a schematic cross-sectional view through the ground floor (i.e. the floor at ground level) of a building comprising a reinforced concrete slab and supporting ground beam.

Figure 2 is a similar view through a modified form of ground floor slab, having a somewhat castellated cross-section.

Figure 3 is a schematic cross-section through a mould in which concrete is being cast using an embodiment of the present invention.

Figure 4 is an underneath perspective view of one form of a floor for a building cast using the embodiment described with reference to Fig 3, and

Figure 5 is a similar view of another form of a floor for a building cast using the embodiment described with reference to Fig 3. The floor 10 illustrated in Fig 1 is for the ground floor of a building and comprises a slab 12 of reinforced concrete, e. g. 200mm thick, supported by the ground 14 via the compressible layer, and when cured by lateral supports. The ground 14 is compacted or otherwise consolidated and, as usual (particularly with clay) would be subject to movement-inducing heave forces as the clay' s water content changes following completion of the constructional work or due to the effects of trees, particularly their removal. To avoid such heave forces being transmitted directly to the concrete slab 12 and supporting beams 12A and potentially moving and cracking (or otherwise damaging) the slab Ϊ2 and supporting beams 12A and any building elements supported thereby, a self-supporting compressible panel 15, e. g. 50mm thick, is interposed between the slab 12, and supporting beams 12A, and the consolidated ground 14.

The panel 15 comprises a plurality of, e. g. four or five, layers 16 of a closed-cell air-bubble sheet material. Each of the panel' s sheets 16 comprises a plurality of air-bubble pockets closely adjacent one another and formed between two membranes of polyethylene coextruded with nylon to seal each pocket against egress of the pressurised air of the bubbles during storage of the panels and during their use under the working load of wet reinforced concrete. The bubbles may be of 12.7mm nominal height and of 31.75mm nominal diameter. Preferably the material employed is similar to that already well-known (in single sheet form) for packing purposes and manufactured by Sealed Air Limited under the Trade Mark "AirCap", but is designed to allow the escape of the air under the significantly high pressure exerted by the weight of the reinforced concrete and the action of ground heave forces.

In one arrangement the sheets or layers 16 of the panel

15 are adhesively bonded to one another by an adhesive, the uppermost (and preferably also the lowermost) sheet

16 being covered and similarly bonded to an outermost skin 18 of a puncture-resistant material. The or each skin 18 is preferably formed of thermally bonded fibres, e. g. a geotextile fabric such as that manufactured by Exxon Chemical Geopolymers Limited under the Trade Mark "TERRAM" and/or, on the upper surface, of a rigid material.

In another arrangement the sheets or layers 16 of the panel 15 are not bonded to one another but are held together within an envelope formed by the outermost skins 18 which are either interconnected by edge strips or have their overlying edges welded to one another. In the latter case, a single length of skin material of double width can be folded over to encapsulate the layers 16 so that edge welding need only be performed along one side or face of the panel 15.

In yet another arrangement the sheets 16 need not be preformed into a self-supporting panel 15 at all. Instead the sheets 16 are laid in situ as individual layers, either loosely one upon the other or adhesively bonded one to the other (with or without the outermost skin 18) by, say, an adhesive. This is performed prior to casting the slab 12 in situ.

In any of said Fig 1 arrangements, the sheets 16 provide necessary ground heave relief and a measure of thermal insulation between the ground and the cast concrete, and in addition serve to provide a damp-proof membrane.

In the embodiment of Fig 2, the concrete slab 22 is likewise cast in situ, but in this instance is formed with integral strengthening ribs 23 extending longitudinally and/or transversely of the slab. Such a castellated cross-sectional shape, which allows for a thinner concrete slab to be provided, can be obtained by casting the concrete directly upon a pre-positioned array of individual panels 25, each formed similarly to the aforesaid panel 15 (but of smaller area), and fixed an continuous array of panels 25A leaving these panels 25A in position to absorb the stress or strain resulting from heave in the ground 24 that, prior to casting, is consolidated or compacted beneath the slab 22 and the panels 25. The panels 25 and 25A also provide thermal insulation between the ground and the cast concrete, and in addition provide a measure of moisture transfer resistance in the manner of a damp-proof membrane.

Methods of casting concrete using embodiments of the invention are shown in Figs. 3 to 5.

The mould 40 of Fig 3 has a flat base wall 41 upon which a plurality of void filler panels 45, e. g. rectangular, are disposed in side-by-side, equi-spaced relation. The panels of this array are all of similar dimensions and disposed longitudinally and/or transversely of the mould 40. Each of the panels 45 comprises a plurality of, e. g. four or five, layers of a resilient, closed-cell, air-bubble sheet material, each such sheet comprising a plurality of air-bubble pockets closely adjacent one another and formed between two membranes of polyethylene coextruded with nylon to seal each pocket against egress of the pressurised air of the bubbles during storage of the panels and their use under the working load of wet reinforced concrete and except under the significantly high pressure exerted by the action at ground heave forces, generally as described above in relation to panels 15 in Fig. 1, and 25 and 25A in fig.2.

The air-bubble sheets need not be pre-formed into a self-supporting panel. Instead they can be laid in sit as individual layers, either loosely one upon the other or adhesively bonded one to the other on site (with or without the outermost skins).

Concrete is poured into the mould 40 over, and in between, the array of panels 45 so that it will set and form the floor as a rigid concrete slab 32 having stiffening ribs 33 depending from the major area lower surface 37 of the slab. These stiffening ribs 33 deriv from concrete entering the interstices between adjacent panels 45 in the mould. They enable the height of .the slab between upper surface 39 and the said lower surfac 37 to be substantially less than that of a conventional constant thickness flooring slab of equivalent rigidity or load-bearing capacity.

It will be appreciated that the pattern provided by the stiffening ribs 33 is derived from the initial pattern formed in the mould 40 by the array of panels 45. Wher these are of elongated rectangular shape, the resultant floor 32 has a castellated cross-sectional form substantially as shown in Fig. 4 in which the ribs run transversely (or longitudinally). Where the panels 45 are of square shape, the resultant floor 32 has a castellated cross-sectional form substantially as shown in Fig. 5 in which the ribs run both transversely and longitudinally. The panels may be any other shape. Each of these floors may be provided in a building with the same panels 45, or with other panels, retained within the cavities formed by the ribs 33, such panels providing a background for suitable facing materials and a measure of thermal and/or sound insulation. Alternatively the panels 45 may be removed and the underside of the suspended floor left in its castellated form.

It will be appreciated that other slab-like items (such as walls and the like) may be cast in a mould in a similar manner to that described above for the floor 32. It will also be appreciated that for casting concrete for roads, runways, pavements, walkways and the like, the mould "wall" supporting one or more panels 45 is provided by the ground or by a continuous array of further panels 45 or by a layer of material thereon, e.g. a particulate "blinding" material. Where used to create voids, the material can be removed by heating, burning or chemical means. To form extended areas of material, particularly for use as mould void fillers, two or more panels or slabs of the pocketed fluid-filled material may be fastened together side by side, or on top of each other, for example by means of tape.

Panels or slabs of the material can be heat-formed to desired shapes, for example as used as mould void formers.

Other embodiments of the present invention will be apparent to those skilled in the construction art and all such embodiments are to be deemed within the scope of the present invention. For example, the skin covering the upper (and preferably also the lower) surface of each panel 45 may alternatively be provided of a rigid material, or may indeed be omitted. Embodiments of the invention will find applications in many areas, particularly, but not exclusively, those of structure forming, cushioning, void forming, damp proofing, light transmission, thermal and acoustic insulation, fire retarding. Embodiments can easily be made to have a low mass and a high buoyancy.

Claims

1. A material comprising at least one sheet-like element having a plurality of closed fluid-containing cells with flexible cell alls , and means maintaining the fluid pressure within the cells greater than the ambient pressure outside the cells whereby the cell walls are under permanent tensile stress.

2. The material claimed in claim 1 in which the cells are at super-atmospheric internal pressure.

3. The material claimed in claim 1 or 2 in which sub -atmospheric pressure is maintained outside the cells.

4. A compressed layer comprising at least one sheet-like element of closed-cell cellular form and a sheet-like skin element superimposed thereon and held thereagainst to form a self-supporting body.

5. A plurality of compressed layers, each layer comprising a sheet-like element of closed-cell cellular form, the sheet-like elements being superimposed upon one another and held together to form a self-supporting body.

6. A self supporting body according to claim 4 or 5, further comprising a material which interleaves ad acent elements .

7. A self-supporting body according to Claim 4, 5 or 6 wherein said superimposed sheet-like elements are bonded to one another adhesively or by solvent welding or other ( e. g. laser) welding so as to be held together and form the aforesaid self-supporting body.

8. A self-supporting body according to any one of Claims 4 to 7, having a skin of puncture-resistant material.

9. A self-supporting body according to any one of Claims 4 to 8, wherein the superimposed sheet-like elements are disposed between upper and lower skins of puncture-resistant material.

10. A self-supporting body according to Claim 9, wherein the said skins are j oined to one another by inter-connecting edge strips, and the superimposed sheet-like elements are held together by (and between) the s ins.

11. A self-supporting body according to Claim 9, wherein the said skins are j oined to one another by welding together adj acent edge portions of the upper and lower skins, and the superimposed sheet-like elements are held together by (and between) the skins .

12. A self-supporting body according to any one of Claims 8 to 11, wherein one or each of said skins comprises thermally bonded fibres .

13. A self-supporting body according to any one of Claims 8 to 12, wherein one or each of the said skins comprises a geotextile material.

14. A self-supporting body according to any one of Claims 4 to 13, wherein the or each cellular element comprises a sheet of air-bubble packaging type material .

15. A self-supporting body as claimed in claim 14 in which the bubbles are barrier-sealed

16. A self-supporting body according to any of Claims 4 to 15, in which the said layers are under pre-compression.

17. A self-supporting body as claimed in any of the preceding claims in which the body is a panel.

18. A self-supporting body substantially as herein described with reference to the accompanying drawings.

19. Heave relief means for use in building a structure upon ground liable to impart upon the structure forces due to heave of the ground, said heave relief means being in the form of at least one deformable layer for disposal between the ground and the structure, characterised in that said deformable layer comprises a resilient, closed-cell cellular element of sheet-like form that is compressible by said heave forces.

20. Heave relief means according to claim 19, wherein said cellular element comprises a plurality of pockets formed between two membranes, the said pockets containing fluid under pressure.

21. Heave relief means according to Claim 20, wherein said two membranes are made of plastics material, and the said fluid comprises gas, liquid, gel or paste under pressure.

22. Heave relief means according to Claim 20 or 21, wherein said pockets are individually sealed.

23. Heave relief means according to any of claims 19 to 22 wherein a plurality of said cellular elements of sheet-like form are provided as a series of superimposed layers.

24. Heave relief means substantially as described with reference to Fig. 1 or Fig. 2 of the drawings.

25. A method of building a structure upon ground liable to impart to the structure forces due to heave of the ground, said method including the step of providing heave relief means in the form of a deformable layer between the ground and the structure, characterised in that said deformable layer comprises a resilient, closed-cell cellular element of sheet-like form that is compressible by said heave forces.

26. A method according to claim 25, wherein said heave relief means comprises the features of any one of claims 19 to 24.

27. A structure comprising heave relief means according to any one of claims 19^' to 24.

28. A structure according to Claim 27, constituting a road, runway, pavement, walkway or the like.

29. A structure according to Claim 27, constituting a building.

30. A void filler for use in casting concrete or other settable building composition in such a manner that at least part of a surface of the configuration to be cast is determined by the surface of said void filler, characterised in that said void filler comprises at least one compressed layer provided by a resilient, closed-cell, cellular element.

31. A void filler according to Claim 30 and wherein the void filler is for use in casting the floor or wall of a building, characterised in that the void filler is configured to allow the floor or wall is pre-cast away from its intended building location.

32. A void filler according to Claim 30 and wherein the void filler is for use in casting the floor or wall of a building, characterised in that the void filler is configured to allow the floor or wall to be cast in situ.

33. A void filler according to any one of Claims 30 to 32 wherein said cellular element comprises a plurality of pockets formed between two membranes, the said pockets containing fluid.

34. A void filler according to claim 33, wherein said membranes are made of plastics material, and the said fluid is gas, liquid or gel or paste under pressure.

35. A void filler according to Claim 33 or 34, wherein said pockets are individually sealed.

36. A void filler according to any one of Claims 30 to 35, wherein the said void filler comprises a plurality of said cellular elements provided as a series of superimposed layers.

37. A void filler according to any one of Claims 30 to 36, comprising a plurality of panels laterally spaced from one another to provide a castellated cross-sectional shape for at least one surface of the casting.

38. A void filler according to any one of Claims 30 to 37, wherein the or each cellular element comprises a sheet of air-bubble material.

39. A void filler according to claim 38 wherein said air-bubble material in barrier sealed.

40. A void filler substantially as described with reference to Fig. 3 and 4, or Fig. 5 of the drawings.

41. A method of casting concrete or other settable building composition, in which at least part of a surface of the configuration to be cast is determined by the surface of a void filler, characterised in that said void filler comprises at least one compressible layer provided by a resilient, closed-cell, cellular element.

42. A method according to claim 41 wherein the void filler comprises the features of any one of claims 30 to 40.

43. A pre-cast floor or wall for a building, said floor being cast by use of a void filler according to any one of Claims 30 to .40.

44. A building having at least one floor or wall formed by use of a void filler according to any one of Claims 30 to 40.

45. A road, runway, pavement, walkway or the like comprising concrete cast by use of a void filler according to any one of Claims 30 to 40.

46. A structure according to Claim 27, 28 or 29, the heave-relief means comprising one or more bodies as claimed in any one of Claims 4 to 18.

47. A void filler according to any of claims 30 to 40, the void filler comprising one or more bodies as claimed in any one of claims 4 to 18.

48. Heave relief means according to any of claims 19 to 24, the heave relief means comprising one or more bodies as claimed in any one of claims 4 to 18.