AU2004203236A1 - Cavity former - Google Patents

Description

PA00 11 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Cavity former The following statement is a full description of this invention, including the best method of performing it known to us: CAVITY FORMER Field of the Invention This invention relates to concrete slabs and foundations. More specifically, the invention relates to an apparatus for forming a hollow cavity in a slab or foundation.

Background of the Invention The practice of using cavity formers as space filling members in the preparation of a concrete slab or foundation is an existing technique for reducing the amount of concrete required to form a slab or foundation. While the reduced concrete content in a slab having hollow cavities serves to reduce the cost of the slab, it also advantageously allows the slab to be built on unstable soil as expanding soils will flow into the formed cavities. Such cavities also assist the easy placement of electrical and plumbing conduits throughout the slab.

As the cavity formers must be sufficiently strong to support, firstly, the weight of workers when the formers are in place prior to a pour and, secondly, the load of wet concrete when it is poured, they are prefabricated remote from the building site in standard sizes and then delivered to the building site ready to be set in place prior to pouring of the concrete. Known cavity formers include multiple web reinforced cardboard or fibreboard boxes and so called pods of foamed polymeric material, for instance polystyrene.

Cardboard or fibreboard formers must have sufficient structural integrity to support the wet slab for a prescribed period, eg 3 hours, after a concrete pour, before they weaken through moisture absorption. Polystyrene overcomes this limitation, but it has the disadvantage that, when cut into smaller shapes for cavities of smaller sizes, large quantities of fine polystyrene particles are often generated. Such polystyrene particles present an environmental problem because they are easily scattered by a breeze. Furthermore, polystyrene pods do not disintegrate to more completely form the cavity and this presents a disposal and 004514581 2 environmental problem when the slab is partially or wholly demolished or reshaped. For these reasons, the use of polystyrene as a cavity former is being restricted in at least the United States.

It is an object of this invention to provide an improved cavity former which is of optimum versatility but retains the strength necessary to support the wet concrete during pouring and the weight of workers beforehand.

Summary of the Invention In accordance with the invention, it has been recognised that transport of cavity formers would be more convenient were the formers, collectively, to have a less voluminous state than their volume when ready for the concrete to be poured.

This less voluminous state is achievable by providing a suitable structural configuration which is stackable and which also enables the cavity former to meet the weight support requirements mentioned above. In a particularly advantageous application of the invention, such a structural configuration permits the formation of the cavity former from a degradable material.

The invention accordingly provides a cavity former for use in forming a cavity in a concrete slab, said cavity former comprising: a) a support member for supporting a predetermined weight of a person standing on the member or of wet concrete bearing down on the member until the wet concrete has cured sufficiently to support itself; and b) cover means detachably engageable with the support member for distributing said weight onto the support member and preventing flow of said concrete into the support member; wherein said support member is stackable with at least one other similar support member for transport, the stacked support members collectively defining a volume less than the summed volume of the separate support members.

004514581 3 The support member may be nestable with at least one other similar support member to provide said stackability.

Advantageously, the cavity former is made of a degradable material to facilitate disintegration of the cavity former over time to leave a cavity within the formed concrete slab. For example, the degradable material may be cardboard or fibreboard. If necessary, the cardboard or fibreboard may have a coating to slow the diffusion of moisture into the member and thereby prolong the weight bearing capacity of the member. In an embodiment, the support member comprises paper pulp without a coating and the cover means comprises cardboard or fibreboard having a coating for slowing moisture diffusion.

The cover means is may be configurable between a more compact state to facilitate transport of the cover means and an expanded state for engagement with the support member. Preferably, the cover means, in the more compact state, is a blank foldable to form a housing having a base, for receiving the support member, and having an integrally formed lid engageable with the support member for distributing said weight onto the support member.

The cavity former may include means for retaining the cover means in engagement with the support member. In an embodiment, the retaining means is provided by walls depending from said lid, which walls frictionally engage the base to retain the lid in engagement with the support member.

The member may comprise a top side surface complementary to an underside surface of the member. Open channels are preferably included in the member for receiving at least part of another support member to enable stacking of the members.

In an embodiment, the lattice arrangement is provided by an integrally formed matrix of cell walls, each cell wall having a V-shape in cross section, and wherein the matrix defines a plurality of cells. The structural strength of the support member may be improved by forming each cell with a floor on the same side of the support member as the channels 004514581 4 The channels may form a lattice arrangement to permit stacking of support members having non-identical configurations and having cell walls based on the same shape as the other support members in the stack.

Brief description of the drawings A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a cavity former in accordance with the present invention, laid out with reinforcing materials in preparation for wet concrete to be poured to form a concrete slab or foundation; Figure 2 is an isometric view of a cavity former of Figure 1 with the lid of the cover means open; Figure 3 is an isometric view of a support member of the cavity former in Figure 2; Figure 4 is an isometric view of the underside of the support member of Figure 3 with a floor formed in a cell; Figure 5 is a side elevation, in the direction A in Figure 3, showing two stacked support members, the second support member is shown in dashed lines; and Figure 6 is a plan view of a blank which is foldable to form the cover means of the cavity former of Figure 2.

Description of the preferred embodiment Figure 1 shows cavity formers 10 in accordance with the present invention arranged with reinforcing products, such as reinforcing bars 12 and reinforcement mesh 14 supported on bar chairs 16, in preparation for pouring of the concrete to form a slab or foundation. It will be appreciated that the wet concrete is poured 004514581 around and over the cavity formers such that the cured concrete slab has hollow sections in the shape of the cavity formers.

Referring now to Figure 2, the cavity former 10 has a cover means, in the form of housing 100, that comprises a lid 120 and base housing 160 attached together by a hinge such that the lid 120 can fold over a cellular structure which forms the support member, housed in the base housing 160. The lid 120 and base housing 160 are integrally formed in a flat blank 100' (Figure 6) to reduce the volume of the housing 100 for transport purposes.

The housing 100 and cellular structure 20 are made of degradable materials to ensure disintegration of the cavity former after the concrete slab has been formed. Such disintegration advantageously leaves a cavity in the formed concrete slab to accommodate unstable soils and to facilitate placement of electrical and plumbing conduits.

The cellular structure 20 is formed as an integral moulding of a suitable degradable material, for instance paper pulp, such that cell walls 30 define a square array of cells 36. The cell walls 30 have top edges 32 which collectively define a lattice on which the lid 120 rests when the cellular structure 20 is enclosed in housing 100. In this manner the weight bearing down on the lid 120 is distributed over top edges 32 of cell walls 30 for support by the cell walls 30. It will be appreciated that alternative cell wall 30 arrangements may be utilised to form cells 36 of different shapes and sizes. However, one advantage of discrete cells 36 is the potential for customized resizing of the cavity former 10 on the construction site as desired. This is because the cavity former 10 can be sectioned along any vertical plane without affecting the integrity of the remaining cells 36 to define a closed volume about which wet concrete can be poured to form a cavity of the desired shape in the subsequently formed concrete slab.

The cell walls 30 have an inverted V-shape to provide the cellular structure with a top side 40 and an underneath side 50 that are complementary. The underneath of each cell wall 30 includes a channel 34 (Figure 4) such that the underneath side 50 has a network of linked channels 34 into which a top side 004514581 6 of another cellular structure 20' (shown in dashed lines) is receivable for stacking (Figure In such arrangement, the stacked cellular structures 20 and collectively define a volume that is less than the sum total volume defined by the individual cellular structures 20 and 20' when separated.

For improved strength in the cellular structure 20, each cell 36 may be provided with a floor 38 (Figure 5) formed in the underneath side 50 of the cellular structure 20 to be surrounded by the channels 34.

It will be appreciated that the network of linked channels 34 permits stacking of cellular structures having different cell wall 30 configurations in each array, provided that the cell walls 30 are in the same relative alignment with and are based on the same cell wall shape as cellular structure The internal angle of the V-shape forming the cell walls 30 may be in the range of 15 400, but preferably in the range of 25 30'. In the cellular structure the cell walls 30 have an internal angle of 270 for optimal weight distribution throughout the cellular structure Referring now to Figure 6, the blank 100' for housing 100 comprises a lid panel 121 linked to a base panel 161 via an intermediate wall 140. Walls 122 extend along opposed sides of the lid panel 121 adjacent to the intermediate wall 140. A further wall 126 extends along an edge of the lid panel 121 opposite the intermediate wall 140. Wall 126 is provided with opposed tabs 128 having an arcuate shape and including a slot 132 to define a tongue 130.

The lid 120 is formed by folding the blank such that edges 136 and 134 of walls 122 and 126 meet. During this process, tongues 130 of tabs 128 are inserted through slots 124 formed in walls 122 thereby to secure the walls 122 and 126 in depending arrangement from lid panel 121.

The base housing 160 comprises a square base panel 161 having attached thereto opposed side walls 162 and end walls 164 extending along an edge of the base panel 161 opposite intermediate wall 140. The end wall 164 is formed as a 004514581 7 mirror image, including tabs 128, of wall 126 of the lid 120. Similarly, the intermediate wall 140 includes opposed tabs 142 formed identically to tabs 128.

Side walls 162 include slots 172 and 174 respectively formed near opposed ends of the walls 162 for receiving the tongues of tabs 142 and 166. Each wall 162 may further include a flange 180 including equally spaced cut-out portions 182. The cut out portions 182 are shaped and spaced to receive a cell wall 30 of the cellular structure The base housing 160 is formed by folding the blank 100' such that walls 162, 164 and 140 into an upstanding arrangement whereon the tongues of tabs 142 and 166 are inserted through slots 174 and 172 in walls 162. In this manner, the base housing 160 defines a tray for receiving the cellular structure Each flange 180 is folded inwardly of the base housing 160. A cellular structure 20 may then be inserted into the base housing 160 with one array of cell walls 30 registering the opposed cut out portions 182 formed in the flanges 180.

The cavity former 110 is then closed by folding the lid 120 over the cellular structure 20 such that depending walls 122 and 126 fit about and frictionally engage with walls 162 and 164 of the base when the lid panel 121 engages the top edges 32 of the cellular structure The cellular structure 20, enclosed within the housing 100, provides sufficient strength to withstand up to 50kPa from the weight of a person or of wet cement or concrete for up to 3 hours. The structure of the cavity former ensures that the structural integrity is retained over that period despite being made of a degradable material and despite the diffusion of moisture from the wet concrete into the housing 100 and cellular structure 20 which, over time, weakens them. Eventually the housing 100 and cellular structure 20 will disintegrate to leave a cavity in the slab.

A suitable degradable material in which to form the cavity former 10 may be, for instance, uniform corrugated cardboard having a coating which slows the diffusion of moisture into the cardboard. A suitable coating must, firstly, be sufficiently moisture resistant to slow moisture diffusion to an extent that enables 004514581 8 the cavity former to support the weight for up to 3 hours, i.e. until the concrete has sufficiently cured to be self supporting. Secondly, the coating must be substantially inert with the highly alkaline wet concrete. Finally, the coating must be able to withstand abrasions so that the integrity of the coating is not compromised in the event that particles in the wet concrete are ground against the coating, eg during pouring of the wet concrete or when a worker stands on the cavity former.

Examples of suitable coatings include plastics, either flexible or rigid, or paints, eg. rymild white, which is sprayed on and then cured by exposure to ultraviolet light.

In order to optimise costs, the cellular structure 20 may be formed integrally of low grade materials, eg. paper pulp, without a coating and the housing 100 may be formed of high grade paper materials, for instance cardboard or fibreboard, with a coating.

The cavity former 10 is generally rectangular, eg a square, but may equally be formed in any other polygonal shape as required that can form a more compact state. The preferred embodiments are square and have a side length in the range of 0.5 to 1.5m, but preferably 1.0 to 1.2m. They may be formed with a height in the range 150-400mm, but specifically may be fabricated with 175, 225, 300 or 375 mm heights.