GB2254090A - Formwork for casting a beam - Google Patents

Abstract

A formwork element (10) for casting of a beam, comprises three longitudinally directed and mutually flexible sections (14) of substantially impervious material that are to form the two sides and bottom of the formwork, the sections being spaced apart laterally and interconnected by web portions (16) which permit flexure of the sections relative to one another and into a box-like form. The two side sections (14) comprise pockets for the retention of rigid panels (15a, 15b). The bottom section (14) may comprise a pocket for the retention of rigid panel (15c) or may comprise a unitary component of solid plastics material. One or more of said pockets (15a, 15b, 15c) may be fast with a plurality of compartments that are sealed (or are to be sealed during casting of the concrete), the compartments being opened to atmosphere manually or automatically - by biological, chemical or electrolytic degradation of a compartment wall or closure member - after the concrete has set thereby enabling the compartments to collapse and/or deform due to heave forces applied thereto. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO BUILDING DESCRIPTION This invention relates to building methods, to structures - particularly beam-supported structures (e.g. buildings, raised walkways and the like) - built by such methods, and to apparatus for use in building methods.

The formwork apparatus conventionally used for constructing cast beams and the like is assembled by nailing wooden side panels permanently to a base panel and, e.g. at approximately 600mm centres, externally applying vertical struts (usually strutted and raked back to the ground) to ensure that the side panels do not bulge outwards when the concrete is poured in to the beam-like form provided by the formwork apparatus. The construction of formwork apparatus in this way is very time consuming. Furthermore, where the formwork apparatus is for the casting of a ground beam, it cannot be readily re-used for the construction of other or of further similar beams.

Moreover, where the ground beam is to support a structure upon soil liable to upward heave forces, it is usually necessary to provide heave relief means between the soil and the beam.

One known form of such heave relief means comprises a rigid layer of fibre-board material which degrades or rots progressively as it takes up moisture from the soil and/or the atmosphere (e.g. due to rain). Prior to use, these boards need to be stored in dry surroundings - a difficulty on most building sites - and, to avoid premature decay due to the moisture content of the concrete ground water or rain they must be well-wrapped in plastic sheeting before the concrete is poured onto them. Moreover, the fibre-board panels in general use are heavy and expensive to buy and use - particularly when the need to wrap them in plastic sheeting is taken into account. Furthermore, during their intended rotting or decay, the fibre-board material often emits substantial quantities of methane - which not only has an unpleasant odour but is highly inflammable.Use of such fibre boards is thus dangerous. Such cellulose materials can also harbour dry rot or infestation particularly in damp poorly ventilated voids of the type required by their many specifications.

Another known form of such heave relief means is provided by one or more superimposed sheets of expanded polystyrene foam. However, due to their limited compressibility, such foam sheets usually have to occupy a considerable depth (or sheet thickness), with consequential expense. In any event, when the superimposed sheets are compressed they simply transmit onto the beam varying degrees of the uplift forces applied to them.

It is accordingly considered highly desirable to overcome the above-mentioned and/or other disadvantages associated with the prior art.

According to a first aspect of the present invention there is provided an element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising three longitudinally directed and mutually flexible sections of substantially impervious material that are to form the two sides and bottom of the formwork or shuttering, the sections being spaced apart laterally and interconnected by web portions which permit flexure of the sections relative to one another and into a box-like form.

Preferably in such an arrangement at least the two side sections comprise pockets retaining (or for the retention of) separate rigid panels - and in this case the pockets may be themselves flexible (until the panels are inserted therein), e.g. by being of the same flexible material as the webs - ideally being integral and unitary therewith.

According to a second aspect of this invention there is provided an element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising a sheet of flexible, substantially impervious material (e.g. polythene or other plastics sheeting material) having three longitudinally directed pockets therein to accomodate formwork panels that are to form the two sides and bottom of the shuttering, the three pockets being spaced apart laterally and interconnected by web portions of the sheet which permit flexure of the pockets (when accomodating said panels) relative to one another and into a box-like form.

Advantageously, the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel. Preferably the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel with an outer major face of said one panel generally contiguous with the side edge of the adjacent panel that adjoins to (or forms an arris with) the selvedge portion of the said adjacent panel.

Advantageously, and for use in the casting of a structure liable to the effect of heave, one or more (preferably all) of said three pockets are fast with a plurality of compartments that are sealed (or are to be sealed during casting of the concrete), an opening of the compartments to atmosphere being made after the concrete has set. Such an arrangement enables heave-moved ground material to be accomodated by the opened, and thus more readily compressible, compartments.

According to a third aspect of this invention there is provided a method of erecting formwork or shuttering for the casting of a beam, said method comprising the steps of: (a) providing formwork panels in the said pockets of an element according to the first or second aspect of this invention, (b) folding up the panel-containing element into the bottom and two sides of an elongate box-like form, and (c) interconnecting the upper edges of the two sides at longitudinally spaced intervals to assist in retaining the two side panels in vertical attitude.

According to a fourth aspect of this invention there is provided a method of casting a beam wherein the formwork or shuttering therefor is erected as an elongate box-like form by a method according to said third aspect of the invention, concrete is poured into the box-like form (after any necessary beam reinforcement rods have been placed therein) and, after the concrete has set, the pockets accomodating the two side panels are opened to permit removal of the two side panels.

The recovered or removed two side panels can thus be re-used in erecting formwork or shuttering for the casting of another beam (or of an additional longitudinal section of the same beam).

Where a ground beam is being cast utilising an element having its said pockets fast with the aforesaid initially sealed compartments, the sealed compartments may be opened after the concrete has set so that they can be subsequently impressed (or "deflated") very easily by any heave-moved ground material. The heave forces can thus be readily accomodated.

The panels may be of wood or, as is preferred, of cement-bonded particle board (e.g. such as that obtainable from C.P. Boards Limited, Manor Yard, Gt. Shefford, Berks.) that is formed by compressing and curing a mixture of cement and wood chip particles.

By way of example, embodiments of the present invention will now be described with reference to the accompanying drawings of which: Figure 1 is a side elevational view of an element embodying this invention and for use in the provision of formwork or shuttering for the casting of a beam, Figure 2 is a tranverse sectional view of a beam being cast utilising an element as shown in Figure 1, Figure 3 is a schematic illustration of a modification of the embodiment of Figures 1 and 2, and Figure 4 is a schematic perspective view of an element in another embodiment of this invention as arranged for the casting of a beam.

Figure 1 shows an element 10 for use in the provision of formwork or shuttering 20 (Fig 2) for the casting of a beam 25. The element 10 comprises a sheet 12 of a flexible, substantially impervious material, e.g. such as high density polythene or another suitable plastics sheeting material. The sheet 12 is provided with three longitudinally directed parallel pockets 14 of generally rectangular shape in plan view. These pockets in use accomodate formwork panels 15 that are to form the two sides 15a,15b and the bottom 15c of the shuttering 20. The three pockets 14 are spaced apart laterally and are interconnected by web portions 16 of the sheet, these web portions being contiguous with one major surface of the rectangular pockets. In the embodiment of Fig 1 these web portions are contiguous with the upper major surface of the pockets.The web portions 16 permit flexure of the pockets 14 (when accomodating the panels 15) relative to one another and into the box-like form 20 shown in Fig 2.

The transition from the arrangement shown in Fig 1 to that shown in Fig 2 is by folding side sections 15a,15b upwards and holding their upper edges at a fixed distance apart by means of transverse rods 26 provided at their ends with clips 28 engaging the upper edges of sections 15a and 15b, the rods being located at intervals along the length of the form 20.

By folding side sections 15a,15b in the opposite sense with respect to section 15c, an arrangement is obtained as that illustrated in Fig 3. In this, the web portions 16 are contiguous with the lower major surface of the pockets 14 and are dimensioned to permit a lower edge of each side panel 15a,15b to overlie a selvedge portion of the major surface of the adjacent bottom panel 15c, preferably with an outer major face of each side panel 15a,15b vertical and generally contiguous with the side edge of the adjacent bottom panel 15c.

The panels 15 may be of wood or, as is preferred, of a cement-bonded particle board (for example such as that obtainable from C.P. Boards Limited, Manor Yard, Gt.

Shef ford, Berks.) that is formed by compressing and curing a mixture of cement and wood chip particles. The element 10 may be supplied without the panels or with the panels already in situ in the pockets 14. In this latter case the pockets 14 may then be sealed to enclose the panels all round.

It will be appreciated that the spacing between the upper and lower major surfaces of each pocket 14 is sufficient to enable a panel 15 to be slid therein from one open end. The width of the sections 15a, 15b and 15c may be the same (e.g. between 400 to 600 mm) or may have the two side sections 15a,15b of one dimension wider or narrower than the width of the bottom section 15c. The element 10 may be provided in a range of lengths, e.g. 1 to 5 metre lengths, and may be provided with longitudinally projecting margins of the plastic material that can be heat or solvent welded (or simply taped or stapled) to the plastic material of an adjoining, similar element 10 - where a longer beam is to be cast.Alternatively, the pockets 14 of the side sections 15a,15b may be open at their long upper edges (opposite the side edges of bottom section 15c) to facilitate insertion of the side panels 15 therein.

The element 10 of Figs 1 to 3 can be used for the casting of a ground beam or of a raised beam that is to be supported on pillars, piles or cross-supports (in the manner of rafters). For use in the casting of a ground beam, the folded-up element 10 is supported upon one or more separate void-forming devices 35 (e.g. such as any one of those disclosed in my co-pending patent application filed simultaneously with the present application, or of those disclosed in either of my co-pending UK Patent Applns. Nos. 9102946.2 and 9106289.3 or in the patent applications claiming priority therefrom), the bottom section containing panel 15g resting directly on the void-forming device 35. Similar void-forming devices may be provided between each of the two side sections 15a,15b and the adjacent soil or ground substrate material.The purpose of such void-forming devices is to create a substantially incompressible void space between each panel 15 and the ground whilst the concrete for the beam is poured in and allowed to set, but thereafter to permit that space to contract under heave-induced forces and/or accomodate the substrate material that is moved by such forces.

After the concrete has set, the separate void-forming devices 35 at the two sides of the beam may be removed for re-use elsewhere (e.g. for further sections of the same beam 25 or for another beam).

Alternatively for a ground beam liable to be subjected to ground heave forces, each of the panels 15,15, and 15c may be associated on one or each face with one or more superimposed sheets of expanded polystyrene foam that are left in situ after the panels 15a,15b are removed from the side pockets 14 for use elsewhere.

The element 30 of Fig 4 is substantially similar to that of Figs 1 to 3 but is, however, particularly suited for use in the casting of a ground beam or other structure liable to the effect of heave. In the Fig 4 embodiment, one or more (preferably all three) of the pockets 14 is/are bonded, welded or otherwise joined fast with a plurality of compartments 24. The compartments 24 of bottom section 15c (and optionally also those fast with each of side sections 15a,15b) are each attached to and in communication with a long length of tubing 22 containing air at atmospheric or super-atmospheric pressure and sealed closed either by adhesive, plastics welding or by a valve device. The tubing may also serve to interconnect all the compartments 24 with one another.The walls of each compartment 24 are of polythene or other suitable plastics material and of a suficient thickness, e.g. lmm thick, as to be rigid but deformable, i.e. such that the compartments are self-supporting (even when open to atmosphere) but can be deformed or "deflated" by usual heave forces.

It will be appreciated that before casting a beam, formwork or shuttering is erected by (a) inserting formwork panels 15 into the pockets 14 (if the element 10 was not pre-supplied with such panels in situ) (b) folding up the panel-containing element into the elongate box-like form 20 composed of a panel-containing, or an integral, bottom 15c and two panel-containing sides 15a and 15, and (c) interconnecting the upper edges of two the sides 15a,15b at longitudinally spaced intervals by transverse rods 26 having clip-like terminations 28 by which to retain the two side panels 15a,15b in a vertical attitude spaced apart and parallel to one another.

Thereafter, any necessary beam-reinforcement rods or cage 32 are placed within the box-like form 20, and concrete is poured in. After the concrete has set to form the beam 25, the pockets 14 accomodating the two side panels 15a,15b are slit along their upper edge to permit removal of the two side panels 15a,15b. The latter can thus be re-used in erecting formwork or shuttering 20 for the casting of another beam (or an additional longitudinal section of the same beam 25).

Where a ground beam is being cast utilising an element 30 such as that of Figure 4, i.e. having its pockets 14 fast with the initially sealed compartments 24, then - after the concrete has set - the sealed compartments are opened to atmosphere, e.g. by opening the valve device or by cutting through the tubing 22 where it projects upwardly or laterally outwardly from the cast slab. Heave-moved ground material can then be accomodated by the compression or "deflation" of the now opened - and thus more readily compressible - compartments 24. In this way the effect of heave forces may be accomodated.

In one alternative construction, the lines 22 are filled with fluid, e.g. water, instead of air or some other gas.

In another alternative construction, the tubing 22 is omitted and each compartment 24 has at least part thereof biologically, electrolytically or chemically degradable.

Thus each compartment 24 may have a main body and a biodegradable or chemically degradable closure member such as a cap, plug or seal.

The cap, plug or seal can be of various forms but, in all arrangements co-operates with the body of the compartment 24 to seal it such that the sealed compartment is substantially incompressible, the material of the compartment body being such that the compartment is (in comparison) readily compressible when it is unsealed.

In one preferred arrangement, each compartment 24 has the form of a bottle blow-moulded of polyethylene teraphthalate (PET) plastics material to have a substantially parallelepiped form of approximate dimensions in the range 150mm x 200-300mm x 50-150mm and an externally-threaded neck 43 (Figs 5 and 6) leading to an open mouth, e.g. of about 50mm diameter. Such bottles can be produced with highly flexible walls of a thickness less than lmm yet, when filled with water and sealed by an internally-threaded closure member screwed onto the bottle's neck and mouth, are substantially rigid and can withstand an externally applied pressure of about 75 lbs/in2 without bursting or being excessively deformed.

In one simple construction the closure member 40 comprises a plastics material screw cap which has a small hole 41 in its bight wall 42 and a disc 44 of a water soluble material, e.g. sodium stearate (soap) sandwiched between that bight wall 42 and the mouth 46 of the compartment 24 to cover w and seal - the hole 41 (see Fig 5).

Alternatively (as shown in Fig 6), a cylindrical slug of the water soluble material, e.g. sodium stearate (soap), can be wedged into the tubular bore or hole 41 (or a tubular spout or nozzle protruding axially and outwardly of the cap's bight wall 42) so as to seal it. With either construction the water soluble material is initially sufficiently impervious as to effect sealing of the container but in a predictable or predetermined period of time, e.g. approximately 2 months, will dissolve sufficiently in the fluid within the bottle 24 so as to unseal from the cap and permit subsequent collapse of the compartment 24 under heave forces.

In another construction, the cap's tubular bore or hole 41 (or the tubular nozzle or spout protruding outwardly of the cap's bight wall 42) is fitted with a metallic insert 45 which, when exposed to fluid within the bottle compartment 24 effects a reaction causing decomposition. Such devices are considered very predictable as to the decomposition rate and it is thought can be produced to degrade (into an unsealing condition) within a day or two of a prespecified, short time period (e.g. 21 days, 2 months or 3 months).

The metallic insert 45 may comprise a cylindrical slug of a magnesium alloy - e.g. MAB1 obtainable from Castex Products Ltd - that is inserted as a close and tight sealing fit within the cap's tubular nozzle or spout 48.

After filling the compartment 24 with water, the cap 40 is screwed on tightly, the thus sealed compartment being located, with other similarly sealed compartments, between the trench susbstrate and the panels 15a, 15 and 15C. If desired, salt or another chemical compound, e.g. in a pervious sachet, may be inserted into the or each compartment 24 (prior to or subsequent to its being filled with water) to promote or assist in the chemical degradation process.The chemical degradation of the magnesium due to the salt water (saline solution) is thought to be as follows: Mg + 2NaCl = MgCl2 + 2Na 2Na + 2H2O = 2NaOH + H2 2NaOH + MgCl2 = Mg(OH)2 + 2NaCl In experiments it has been found that with a metal insert 45 as a 5mm diameter cylindrical slug of said magnesium alloy, a slug length of approximately 5mm will chemically degrade to a cap-open state in about 20 days, and that a slug length of approximately 3.5mm will chemically degrade to a cap-open state in about 10 days.

It will be appreciated that due firstly to the limited quantity of magnesium required for each slug 45 - which provides for the effective collapse of each compartment 24 by a degradation of an element far smaller than the entirety of the container - and secondly to the relatively large distances between the discrete compartments 24, the very small quantities of hydrogen gas liberated by the degradation process will be widely dissipated so that the risk of any hydrogen-induced fire or explosion is minimal if not zero.

In another preferred arrangement, each compartment 24 has the form of a bottle blow-moulded of polyethylene teraphthalate (PET) plastics material to have a substantially cylindrical form of approximately 150mm diameter and a length in the range 100-300mm, its externally-threaded neck, like the neck 43, leading to an open mouth, e.g. of about 50mm diameter. As illustrated in Fig 6, the separately-provided cap for this bottle-shaped compartment 24 is "over-sized" in that it has an outer diameter similar to that of the bottle and has an axial length corresponding substantially to the axial lenth of the bottle's neck 43 whereby, when the cap is fully screwed onto the bottle, the bottle-plus-cap provides a generally cylindrical formation of substantially uniform diameter throughout its length.

The "over-sized" cap of this arrangement can usefully serve as a support for the bottle - particularly when provided under the bottom section 15c of the element.

If required, with either said arrangement of cap and bottle, the cap can be shrink-wrapped to prevent pre-use attack by atmospheric moisture. In that case, the wrapping may be arranged such as to be automatically pierced when the cap 40 is screwed on to the compartment 24.

Also, with either of the aforesaid arrangements of the cap and bottle, a gas-producing chemical compound or mixture, e.g. in a pervious sachet (optionally the same sachet containing the salt), may be inserted into the or each compartment 24 - prior to or subsequent to its being filled with water - to increase the internal pressure within the compartment (e.g. to the order of 15psi) so that it is better able to support the loads thereon, e.g. due to the concrete and its associated reinforcements. For example, the gas-producing chemical compound or mixture may be a mixture of sodium bicarbonate and tartaric acid in powder or granular form.

As an alternative to filling the compartments 24 with water, they may be filled with gas (e.g. air) - optionally under pressure - and the degradation process may be effected by ground moisture alone.

It is envisaged that other chemically degradable devices may be provided in the cap including (but not limited to) constructions employing a molecular sieve or a sol-glass.

It will be appreciated that arrangements similar to those suggested above for the compartments 24 of Fig 4 can be readily applied to the separate void-forming devices 35 utilised with the formwork or shuttering 20 of Figs 1-3.

It will be further appreciated that the present invention is not restricted to the particular illustrated embodiments described above with reference to the drawings, but that other embodiments and modifications are to be deemed within the scope of the present invention as claimed.

For example, the initially-sealed compartments 24 may be filled with any suitable fluid - i.e. liquid or gas. If a gas (e.g. air) is employed, the latter may be at atmospheric pressure or, if desired, may be at an overpressure.

In another example of a modification to the illustrated embodiments, the bottom section 15c may be provided as a single thicker 'slab' of rigid plastics material rather than as a pocket for the insertion of a separate panel.

Such a thicker 'slab' would preferably have a plurality of integral reinforcement ribs extending laterally and/or longitudinally of the element.

The illustrated embodiments of the invention are thus particular examples in which the bottom section too comprises a pocket retaining or for the retention of a separate rigid panel.

In any event, it will be apparent that the webs 16 of the various above-described and illustrated embodiments of the invention act somewhat in the manner of a continuous "hinge" and when tensioned - as, for example, when the concrete is poured into the box-like form 20 - serve to prevent (or at least restrict) separation of the bottom section 15c away from the bottom edges of the two side sections 15a,15b.

Claims (25)

1. An element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising three longitudinally directed and mutually flexible sections of substantially impervious material that are to form the two sides and bottom of the shuttering, the sections being spaced apart laterally and interconnected by web portions which permit flexure of the sections relative to one another and into a box-like form.

2. An element according to Claim 1, wherein at least the two side sections comprise pockets for the retention of separate rigid panels.

3. An element according to either Claim 1 or Claim 2, wherein the bottom section too comprises a pocket for the retention of a separate rigid panel.

4. An element according to either Claim 1 or Claim 2, wherein the bottom section is itself a rigid, slab-like, panel unitary of solid plastics material connected to said web portions.

5. An element according to any one of Claims 2 to 4, wherein the pockets are themselves flexible (until the panels are inserted therein).

6. An element according to any one of Claims 2 to 5, wherein the pockets are of the same flexible material as the webs.

7. An element according to any one of Claims 2 to 6, wherein the pockets are integral and unitary with the webs.

8. An element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising a sheet of flexible, substantially impervious material having three longitudinally directed pockets therein to accomodate formwork panels that are to form the two sides and bottom of the shuttering, the three pockets being spaced apart laterally and interconnected by web portions of the sheet which permit flexure of the pockets (when accomodating said panels) relative to one another and into a box-like form.

9. An element according to any one of the preceding Claims, wherein the said impervious material comprises a sheet of polythene or other plastics sheeting material.

10. An element according to any one of Claims 2 to 9, wherein the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel.

11. An element according to any one of Claims 2 to 10, wherein the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel with an outer major face of said one panel generally contiguous with the side edge of the adjacent panel that adjoins to (or forms an arris with) the selvedge portion of the said adjacent panel.

12. An element according to any one of Claims 8 to 11 and for use in the casting of a structure liable to the effect of heave, wherein one or more (preferably all) of said pockets is/are fast with a plurality of compartments that are sealed - or are to be sealed during casting of the concrete - the compartments being opened to the environment after the concrete has set.

13. An element according to Claim 12, wherein the sealed compartments are maintained in a substantially rigid condition whilst the structure is being cast, but are thereafter unsealed to enable them to collapse and/or deform due to heave forces applied thereto.

14. An element according to Claim 12 or Claim 13, wherein said compartments are at least partially of a degradable material such that, after the structure has been built, the sealed compartments will become unsealed when the material degrades and they can then collapse, releasing the fluid therein.

15. An element according to Claim 14 wherein said degradable material comprises magnesium and said fluid comprises a saline water solution.

16. An element according to any one of Claims 2 to 15 and containing a panel within each of the said pockets.

17. An element according to Claim 16, wherein one or more of said panels is of wood.

18. An element according to Claim 16, wherein one or more of said panels is of cement-bonded particle board.

19. An element for use in the provision of formwork or shuttering for the casting of a beam, the element being substantially as herein described with reference to and/or as illustrated in the accompanying drawings.

20. A method of erecting formwork or shuttering for the casting of a beam, said method comprising the steps of: (a) providing formwork panels in the pockets of an element according to Claim 2, or to any one of Claims 3 to 7 when dependant from Claim 2, or to any one of Claims 8 to 19, (b) folding up the panel-containing element into the bottom and two sides of an elongate box-like form, and (c) interconnecting the upper edges of the two panelcontaining sides at longitudinally spaced intervals to assist in retaining the two side panels in vertical attitude.

21. A method according to Claim 20 and substantially as herein described with reference to the accompanying drawings.

22. A method of casting a beam wherein the formwork or shuttering there for is erected as an elongate box-like form by a method according to Claim 20 or Claim 21, concrete is poured into the box-like form (after any necessary beam reinforcement rods have been placed therein) and, after the concrete has set, the pockets accomodating the two side panels are opened to permit removal of the two side panels.

23. A method according to Claim 22, wherein the two recovered or removed side panels are re-used in erecting formwork or shuttering for the casting of another beam or for the casting of an additional longitudinal section of the beam.

24. A method according to Claim 22 or Claim 23 for casting a ground beam and utilising an element according to Claim 12 or to any one of Claims 13 to 17 when dependent from Claim 12, wherein said sealed compartments are opened after the concrete has set so that they can subsequently be readily compressed (or "deflated") by heave-induced forces in the ground material.

25. Each and every novel feature or novel combination of features disclosed herein and/or the principle(s) underlying that novel feature or combination of features.

25. A method according to Claim 24 and substantially as herein described.

26. Each and every novel feature or novel combination of features disclosed herein and/or the principle(s) underlying that novel feature or combination of features.

Amendments to the claims have been filed as follows l.An element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising three longitudinally directed and mutually flexible sections of substantially impervious material that are to form the two sides and bottom of the shuttering, characterised in that at least the two side sections comprise pockets for the retention of separate rigid panels, and in that the sections are spaced apart laterally and interconnected by web portions which permit flexure of the sections relative to one another and into a box-like form.

2. An element according to Claim 1, wherein the bottom section too comprises a pocket for the retention of a separate rigid panel.

3. An element according to Claim 1, wherein the bottom section is itself a rigid, slab-like, unitary panel of solid plastics material connected to said web portions.

4. An element according to any one of Claims 1 to 3, wherein the pockets are themselves flexible (until the panels are inserted therein).

5. An element according to any one of Claims 1 to 4, wherein the pockets are of the same flexible material as the webs.

6. An element according to any one of Claims 1 to 5, wherein the pockets are integral and unitary with the webs.

7. An element for use in the provision of formwork or shuttering for the casting of a beam, the element comprising a sheet of flexible, substantially impervious material having three longitudinally directed pockets therein to accomodate formwork panels that are to form the two sides and bottom of the shuttering, the three pockets being spaced apart laterally and interconnected by web portions of the sheet which permit flexure of the pockets (when accomodating said panels) relative to one another and into a box-like form.

8. An element according to any one of the preceding Claims, wherein the said impervious material comprises a sheet of polythene or other plastics sheeting material.

9. An element according to any one of Claims 1 to 8, wherein the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel.

10. An element according to any one of Claims 1 to 9, wherein the web portions are dimensioned to permit a side edge of one panel to overlie a selvedge portion of the major surface of an adjacent panel with an outer major face of said one panel generally contiguous with the side edge of the adjacent panel that adjoins to (or forms an arris with) the selvedge portion of the said adjacent panel.

11. An element according to any one of Claims 7 to 10 and for use in the casting of a structure liable to the effect of heave, wherein one or more (preferably all) of said pockets is/are fast with a plurality of compartments that are sealed - or are to be sealed during casting of the concrete - the compartments being opened to the environment after the concrete has set.

12. An element according to Claim 11, wherein the sealed compartments are maintained in a substantially rigid condition whilst the structure is being cast, but are thereafter unsealed to enable them to collapse and/or deform due to heave forces applied thereto.

13. An element according to Claim 11 or Claim 12, wherein said compartments are at least partially of a degradable material such that, after the structure has been built, the sealed compartments will become unsealed when the material degrades and they can then collapse, releasing the fluid therein.

14. An element according to Claim 13, wherein said degradable material comprises magnesium and said fluid comprises a saline water solution.

15. An element according to any one of Claims 1 to 14 and containing a panel within each of the said pockets.

16. An element according to Claim 17, wherein one or more of said panels is of wood.

17. An element according to Claim 17, wherein one or more of said panels is of cement-bonded particle board.

18. An element for use in the provision of formwork or shuttering for the casting of a beam, the element being substantially as herein described with reference to and/or as illustrated in the accompanying drawings.

19. A method df erecting formwork or shuttering for the casting of a beam, said method comprising the steps of: (a) providing formwork panels in the pockets of an element according to any preceding Claim, (b) folding up the panels-containing element into the bottom and two sides of an elongate box-like form, and (c) interconnecting the upper edges of the two panelscontaining sides at longitudinally spaced intervals to assist in retaining the two side panels in vertical attitude.

20. A method according to Claim 19 and substantially as herein described with reference to the accompanying drawings.

21. A method of casting a beam wherein the formwork or shuttering therefor is erected as an elongate box-like form by a method according to Claim 19 or Claim 20, concrete is poured into the box-like form (after any necessary beam reinforcement rods have been placed therein) and, after the concrete has set, the pockets accomodating the two side panels are opened to permit removal of the two side panels.

22. A method according to Claim 21, wherein the two recovered or removed side panels are re-used in erecting formwork or shuttering for the casting of another beam or for the casting of an additional longitudinal section of the beam.

23. A method according to Claim 21 or Claim 22 for casting a ground beam and utilising an element according to Claim 11 or to any one of Claims 12 to 18 when dependent from Claim 11, wherein said sealed compartments are opened after the concrete has set so that they can subsequently be readily compressed (or "deflated") by heave-induced forces in the ground material.

24. A method according to Claim 23 and substantially as herein described.