WO1993016237A1

WO1993016237A1 - Casting slabs or beams

Info

Publication number: WO1993016237A1
Application number: PCT/GB1993/000246
Authority: WO
Inventors: William Robert Oliver
Original assignee: Cordek Limited
Priority date: 1992-02-07
Filing date: 1993-02-05
Publication date: 1993-08-19
Also published as: GB9202640D0; DE69325259D1; ATE181123T1; GB2261002A; GB2261002B; AU3505493A; EP0625227A1; EP0625227B1

Abstract

A vented structure rests on a substrate (10) and comprises a shuttering element (1) including pillars (3) and an upper surface (9) which supports cast material in the form of a slab or beam. The pillars (3) are spaced from each other and provide passageways (6) allowing gas emerging from the substrate (10) to be vented safely away via a pipe (11).

Description

Casting Slabs or Beams

The invention relates to the casting of slabs or beams on a substrate, which may be the ground, and is especially concerned with allowing for the venting of any gases, for example methane or radon, that may seep through the substrate. More particularly, the invention provides a vented structure including a cast slab or beam, a method of casting a slab or beam over a substrate and a shuttering element for use in such a structure and method.

Problems have been experienced when building structures on certain sites from gas seeping through the ground, emerging underneath the structure and becoming trapped there. For example, when building on top of a land fill site it is common to find that substantial guantities of methane gas are seeping up through the ground as a result of vegetable matter in the ground decaying. If a slab is cast on such ground using conventional technigues then there is a risk of methane gas becoming trapped under the slab and, once a significant volume of gas has become trapped, there is a risk of an explosion. If a conventional building is built on ground through which radon gas is seeping, then there is a danger of that gas seeping up through the building and having a deleterious effect on anyone occupying the building. It is an object of the present invention to provide a vented structure in which gas emerging from a substrate on which the structure is supported can be vented safely away. It is a further object of the present invention to provide a method of casting a slab or beam over a substrate in which gas emerging from the substrate can be vented safely away. It is a still further object of the present invention to provide a shuttering element that is suitable for use in a structure or method of the kind defined above.

The present invention provides a vented structure supported on a substrate and comprising shuttering and material cast over the shuttering, the shuttering including an upper surface for supporting the cast material and a support structure resting on the substrate for supporting the surface in a position above and spaced from the substrate, the support structure including openings distributed across its bottom face and passage¬ ways providing a gas path across the support structure from the openings to a vent passage which extends from the support structure to a region from which gas is to be vented.

Any gas seeping through the substrate passes through the openings over the bottom face of the shuttering and then along the passageways in the shuttering to the vent passage at the downstream end of which it escapes, directly or indirectly, in a safe manner. Of course, it is possible, if desired, to collect any escaping gas and/or to treat the gas to make it safe.

The invention is applicable to a wide variety of structures and, whilst in the commonest case a continuous slab will be cast over the whole of the top of the support structure, that need not be the case since the top of the shuttering may be devoid of any openings and thereby itself provide a continuous barrier to any gas. Thus, the terms ^■■slab" and "beam" used in the present specification are to be given a wide meaning. While the shuttering may be assembled on site, it is preferable that it be preformed since that facilitates its use on site. The shuttering is preferably preformed in elements of a size that are readily transportable and therefore, for a typical structure, there are a plurality of preformed elements of shuttering placed side by side, with passageways in adjacent elements of shuttering communicating with one another.

It is possible to arrange for the vent passage to extend from any region of the shuttering, but for most applications it is preferable for the vent passage to extend from an edge of the shuttering.

The material for the slab or beam is preferably cast over the whole of the top of the shuttering and beyond the edges thereof. The vent passage preferably passes through the cast material.

Typically, the cast material is concrete although the invention may be employed using other materials. The support structure preferably includes a plurality of spaced apart support members. Preferably the spaced apart support members define a grid of intersecting passageways which are preferably arranged at right angles to one another. Preferably the space occupied by the passageways between the support members is at least as great as, and preferably more than twice as great as, the space occupied by the support members. Preferably the support members are regularly spaced across the shuttering. Preferably the shuttering comprises an upper slab portion, the top of which defines the upper surface of the shuttering and from the bottom of which extend a plurality of spaced apart support members. The support members are preferably in the form of pillars. The preferred arrangements defined above promote good support for the cast material combined with free movement of gas under the structure.

Preferably the openings over the bottom face of the support structure are defined by gaps between the ends of the supporting members. The ends of the supporting members are preferably free ends.

Preferably the portion of the shuttering defining the upper surface and the supporting structure are integral with one another.

Preferably the shuttering is formed from an expanded plastics material, preferably expanded polystyrene.

The substrate on which the shuttering rests will of course usually be the ground, which may have a layer of aggregate of some suitable kind as its top layer. The vent passage may be defined by a pipe which preferably extends up to a location spaced above the ground, preferably at least 3 m above ground level, at which location any gas vented through the passage passes into the atmosphere. The venting arrangement may rely only on a build up of pressure below the structure for venting or a forced venting arrangement may be employed. The forced venting arrangement may include a fan and/or it may be arranged to be operated by wind; for example, the top of the pipe may be provided with a cowl shaped such that wind blowing across the top of the pipe draws gas out of the pipe; such venting arrangements are known per se.

The present invention also provides a method of casting a slab or beam over a substrate, the method comprising the steps of placing shuttering on the substrate with an upper surface of the shuttering providing a support for the slab or beam and a support structure resting on the substrate and supporting the upper surface in a position above the substrate, and casting the slab or beam over the substrate, wherein the support structure includes openings distributed across its bottom face and passageways providing a gas path across the support structure from the openings to a vent passage which extends from the support structure to a region from which any gas emerging from the substrate is to be vented.

The method may further include the step of inserting a pipe defining at least a portion of the vent passage in working relationship to the shuttering before casting material over the shuttering to form the slab or beam. The casting of the material may serve to locate the pipe in position, or the pipe may be located by other means, for example, the pipe may be located in a support which is cast before the slab or beam and which is positioned under an edge of the slab or beam to support it. Preferably the vent passage is extended upwardly above the substrate to a level at least 3 m above ground level.

Preferably the step of placing shuttering on the substrate comprises placing a plurality of preformed elements of shuttering adjacent to one another with passageways in adjacent elements of shuttering communicating with one another.

Preferably the method further comprises the step of providing a barrier to cast material, before casting of the slab or beam, in the region of the junction of the vent passage and the support structure. Such a barrier, which may for example be formed from aggregate material laid in the region of the junction of the shuttering and the vent passage, prevents cast material from reaching the end of the vent passage and blocking it.

It should be understood that while the invention is primarily concerned with applications where it is known that gas is likely to seep through the ground and will then be vented, it may also be adopted where there is no perceived risk of such gas seepage, either in case there is such seepage or in order to vent the region under the slab or beam for some other purpose. The invention further provides a shuttering element suitable for use in a method as defined above, the shuttering element including an upper surface for supporting the cast material and a support structure for supporting the surface in a position spaced from a substrate on which the support structure is resting, the support structure including openings distributed across its bottom face and passageways providing gas paths spanning the support structure.

Preferably the shuttering element comprises an upper slab portion, the top of which defines the upper surface for supporting the cast material, and a plurality of spaced apart support members. Preferably the support members are spaced inwardly from the peripheral edge of the slab portion so that when two shuttering elements are placed side by side a passageway is formed between them and passageways in the two shuttering elements leading to the side-by-side edges are placed in communi¬ cation with one another via the passageway formed between the two elements. The shuttering element may incorporate any of the features of the shuttering defined above in relation to the vented structure.

By way of example an embodiment of the invention will now be described with reference to the accompanying drawings, of which:

Fig. 1 is a perspective view of an inverted shuttering element embodying the invention, Fig. 2 is a schematic underneath plan view of parts of two adjacent shuttering elements showing their interface, Fig. 3 is a sectional view of part of a vented structure embodying the invention, and Fig. 4 is a sectional view, similar to Fig. 3, of part of another vented structure embodying the invention. The shuttering element 1 shown in Fig. 1 comprises a slab portion 2 and a plurality of supporting members in the form of pillars 3 which, in the illustrated embodi¬ ment, are of sguare cross-section and are regularly spaced apart over the area of the slab portion and extend perpendicularly from the underneath face 4 of the slab. In Fig. 1 the width of each pillar 3 is referenced "w" , the length of each pillar is referenced "1", the spacing of adjacent pillars is referenced "s" and the depth of the slab portion 2 is referenced "d" .

The slab portion 2 and the pillars 3 are formed integrally and are made from expanded polystyrene. The spacing "s" of the pillars 3 is approximately the same as the width "w" of each pillar enabling pairs of shuttering elements to be cut out of a block of expanded polystyrene with little wastage of material: such a pair of elements are formed with the upper surfaces of their slab portions 2 defining opposite faces of the block and with their pillars 3 interlocking; in that way two elements can be formed from a block of depth 2d + 1. In a particular example of the invention the dimensions of the shuttering element are as follows: w = 150 mm, s = 150 mm, 1 = 200 mm and d = 100 mm. (It should be noted in this respect that, if Fig. 1 is to be regarded as drawn to scale, then the shuttering element shown in that Figure does not have the dimensions just referred to.) As can be seen in Fig. 1 the pillars 3 are spaced from the edges 4 of the slab portion 2. The pillars 3 have free ends 5 and the bottom of the element is therefore open with less than 50% of the bottom face occupied by the ends 5 of the pillars. A grid of intersecting passageways, comprising a first set of parallel passageways 6 aligned with arrow A and a second set of parallel passageways 7 at right angles to the passageways 6 and aligned with arrow B, are formed between the pillars 3. The pillars 3 occupy about one third of the space occupied by the passageways 6, 7.

Fig. 2 shows how shuttering elements of the kind shown in Fig. 1 can be laid adjacent to one another. Freguently adjacent shuttering elements will be aligned with one another but in Fig. 2 the elements are shown at the greatest possible misalignment in that the pillars 3A of element 1A are aligned with passageways 6B of element IB and the pillars 3B of element IB are aligned with passageways 6A of element 1A. Even in that case, however, it will be seen that the passageways of the element 1A communicate with those in the element IB via a passageway 8 which is formed between the adjacent elements. Thus, in whatever way the shuttering elements are positioned side by side, the passageways in the elements will always be in communication and no special attention need therefore be paid to their laying.

In order to build a vented structure the ground is first levelled and any reguired layer of aggregate or the like laid to provide a level top surface. Shuttering elements of the kind shown in Fig. 1 are next placed on the ground in an array to provide the reguired area for a slab to be cast. If necessary the elements along edges of the array can be cut to provide the reguired size. Fig. 3 shows a sectional view of part of the structure showing a shuttering element 1 resting on ground 10, only part of the shuttering element being shown in Fig. 3. After the shuttering has been positioned on the ground a vent pipe 11 is positioned as shown in Fig. 3 and blinding 12 laid around the shuttering forming an inclined peripheral surface 13 over which to cast the slab. Any reguired reinforcement for the concrete slab to be cast is also put in position and the usual formwork installed defining the periphery of the slab. The slab is then cast: the upper surface 9 of the shuttering element 1 supports the cast material which also extends around the edge of the shuttering and, by virtue of the blinding 12, is formed with an inclined internal face matching the surface 13. Once the concrete has set, the formwork is removed and the structure is complete except that it may be desired to extend the vent pipe upwardly and/or provide some forced ventilation of the pipe.

As can be seen from Figs. 1 and 3 , any gas seeping up through the ground can pass into the support structure through any of the open areas between the free ends of the pillars 3 and be conveyed along the passageways 6 and the passageways 7 (see Fig. 1) extending perpendicular thereto until it reaches the open end 14 of the vent pipe 11; it can then pass through the pipe 11 and escape to atmosphere. Although the shuttering is able to support the weight of the slab itself it is not intended to support loads imposed on the slab in use; for example, the walls of a building may be supported on the slab. Such loads are taken by the peripheral portion 15 of the slab which rests on suitable foundations or piles (not shown) in the ground. In the arrangement shown in Fig. 3 and described above, the slab is formed with its own integral support beams (the peripheral portion 15). An alternative procedure, however, which is common in the industry is to cast the support beams first and thereafter cast a slab of constant thickness spanning the beams and the space(s) between them. In an embodiment of the invention applied to that alternative procedure, a vented structure whose edge region is as shown in Fig. 4 is produced: the beam 15A is cast in the conventional way using formwork as reguired, but with the addition of the pipe 11; shuttering elements 1 are then placed inside the beam 15A filling the space between that beam and other beam(s) defining the periphery of the slab; the slab 16 is then formed by material cast over the top of the shuttering elements 1 and the beams to provide the vented structure shown in Fig. 4.

Before casting material over the shuttering elements 1, a waterproof and/or gasproof membrane may be fitted over the elements 1; the concrete is then not cast directly onto the elements 1 and similarly is indirectly supported (via the membrane) , rather than directly supported, by the elements 1.

In the embodiment of the invention described above the pillars 3 are each of length 200 mm but they can be of various lengths. Preferably the length of the pillars 3 is in the range of 50 to 500 mm, the width of each pillar is in the range of 50 to 300 mm and the depth of the slab portion 2 of the element is in the range of 50 to 150 mm. While in the illustrated embodi¬ ment the pillars are of sguare cross-section, they may be of rectangular cross-section with each of the sides of the rectangle of length in the range of 50 to 300 mm, or indeed they may be of other shapes. Whilst in the preferred embodiment of the invention the element 1 is made of polystyrene, other expanded or non-expanded plastics materials may be used, or indeed other materials that are not plastics materials may be employed.

Claims

Claims :

1. A vented structure supported on a substrate and comprising shuttering and material cast over the shutter¬ ing, the shuttering including an upper surface for supporting the cast material and a support structure resting on the substrate for supporting the surface in a position above and spaced from the substrate, the support structure including openings distributed across its bottom face and passageways providing a gas path across the support structure from the openings to a vent passage which extends from the support structure to a region from which gas is to be vented.

2. A structure according to claim 1 in which the top of the shuttering is devoid of any openings.

3. A structure according to claims 1 and 2 in which the shuttering is preformed.

4. A structure according to claim 3 in which the shuttering comprises a plurality of preformed elements placed side by side, with passageways in adjacent elements of shuttering communicating with one another.

5. A structure according to any preceding claim in which the vent passage extends from an edge of the shuttering.

6. A structure according to any preceding claim in which the material for the slab or beam is cast over the whole of the top of the shuttering and beyond the edges thereof.

7. A structure according to any preceding claim in which the vent passage passes through the cast material.

8. A structure according to any preceding claim in which the support structure includes a plurality of spaced apart support members.

9. A structure according to claim 8 in which the spaced apart support members define a grid of intersecting passageways.

10. A structure according to claim 9 in which the intersecting passageways are arranged at right angles to one another.

11. A structure according to any one of claims 8 to 10 in which the space occupied by the passageways between the support members is at least as great as the space occupied by the support members.

12. A structure according to claim 11 in which the space occupied by the passageways between the support members is more than twice as great as the space occupied by the support members.

13. A structure according to any one of claims 8 to 12 in which the support members are regularly spaced across the shuttering.

14. A structure according to any preceding claim in which the shuttering comprises an upper slab portion, the top of which defines the upper surface of the shuttering and from the bottom of which extend a plurality of spaced apart support members.

15. A structure according to any one of claims 8 to 14 in which the support members are in the form of pillars.

16. A structure according to any one of claims 8 to 15 in which the openings over the bottom face of the support structure are defined by gaps between the ends of the supporting members.

17. A structure according to any one of claims 8 to 16 in which the ends of the supporting members are free ends.

18. A structure according to any preceding claim in which the portion of the shuttering defining the upper surface and the supporting structure are integral with one another.

19. A structure according to any preceding claim in which the shuttering is formed from an expanded plastics material.

20. A structure according to claim 19 in which the expanded plastics material is expanded polystyrene.

21. A structure according to any preceding claim in which the vent passage may be defined by a pipe which extends up to a location spaced above the ground.

22. A structure according to any preceding claim in which a forced venting arrangement is employed.

23. A vented structure substantially as herein described with reference to and as illustrated by the accompanying drawings.

24. A method of casting a slab or beam over a sub¬ strate, the method comprising the steps of placing shuttering on the substrate with an upper surface of the shuttering providing a support for the slab or beam and a support structure resting on the substrate and supporting the upper surface in a position above the substrate , and casting the slab or beam over the substrate, wherein the support structure includes openings distributed across its bottom face and passageways providing a gas path across the support structure from the openings to a vent passage which extends from the support structure to a region from which any gas emerging from the substrate is to be vented.

25. A method according to claim 24 further including the step of inserting a pipe defining at least a portion of the vent passage in working relationship to the shuttering before casting material over the shuttering to form the slab or beam.

26. A method according to claim 24 or 25 in which the vent passage is extended upwardly above the substrate to a level at least 3 above ground level.

27. A method according to any one of claims 24 to 26 in which the step of placing shuttering on the substrate comprises placing a plurality of preformed elements of shuttering adjacent to one another with passageways in adjacent elements of shuttering communicating with one another.

28. A method according to any one of claims 24 to 27 further comprising the step of providing a barrier to cast material, before casting of the slab or beam, in the region of the junction of the vent passage or support structure.

29. A method of building a vented structure according to any one of claims 1 to 23 using a method according to any one of claims 24 to 28.

30. A method of casting a slab or beam over a sub- strate, the method being substantially as herein described with reference to and as illustrated by the accompanying drawings.

31. A shuttering element suitable for use in a method according to any one of claims 24 to 30, the shuttering element including the upper surface for supporting the cast material and a support structure for supporting the surface in a position spaced from a substrate on which the support structure is resting, the support structure including openings distributed across its bottom face and passageways providing gas paths spanning the support structure.

32. A shuttering element according to claim 31 com¬ prising an upper slab portion, the top of which defines the upper surface for supporting the cast material, and a plurality of spaced apart support members.

33. A shuttering element according to claim 32 in which the support members are spaced inwardly from the peripheral edge of the slab portion so that when two shuttering elements are placed side by side a passageway is formed between them and passageways in the two

'shuttering elements leading to the side-by-side edges are placed in communication with one another via the passageway formed between the two elements.

34. A shuttering element substantially as herein described with reference to and as illustrated by Fig. 1 of the accompanying drawings.