AU2015238916A1 - Closed void former for inclusion in concrete slabs - Google Patents

Abstract

Void formers or "pods" used to expand masses of poured concrete provide a stiff enclosed body that resists reasonable deforming forces at least until the concrete has become sufficiently solid. The invention uses a minimum of materials in complementary and merged pairs of injection-moulded formed sheets; each pair forming one pod. The formed sheets have projecting, interlocking, spaced-apart formations acting as volume-enclosing elements. The pods replace expanded volume-occupying materials and can be cut down to fit a space. Alternating holes and formations allow the user to lay one sheet partially over another one, so that a given floor surface can be covered without having to cut any one frame apart, thereby minimising time. 200a 211 21K2 ~~t 7KNA' ~~~tA 214 5(4%t - wi 1/8~

Description

TITLE CLOSED VOID FORMER FOR INCLUSION IN CONCRETE SLABS FIRD: 5 The invention relates to objects known as void formers or pods or cores which are immersed in a poured concrete mass to reduce the amount of concrete used in construction of concrete slabs to form floors of buildings or other concrete surfaces. They create hollow internal voids that enhance structural strength for a given amount of concrete. DEFINITIONS 0 The word "pod" is used here as synonymous with "void former". It may be stackable prior to assembly on site. A concrete slab floor is also known as a "raft floor". "Cuboidal" is a term used in this document to refer to a solid having six rectangular faces - as distinct from a cube or cubic solid, which has six square faces. 5 A "formed sheet" is one half of a pod (as in Example 2) and carries "formations". The term "formed sheet" is not to be taken as necessarily meaning that the invention begins life as a flat sheet that is later deformed during manufacture; it is simply a convenient label. Each "pod" as herein described may receive a matching cover sheet, having similar dimensions as an upper surface of the pod. 20 BACKGROUND An established method for constructing a kind of concrete floor, sometimes called a "raft floor" a "rib-raft floor" or a "slab floor" for a building such as but not limited to a dwelling has a poured concrete mass formed into a particular shape comprising a deep, stiff array of criss-crossed vertical beams containing reinforcing steel that support a continuous floor surface. The beams 25 surround the exterior and run across the interior of the mass. The upper surface is unbroken because the upper edges of the beams are run together with a sufficiently strong horizontal sheet of the same poured mass of concrete, containing a reinforcing mesh supported up and into the horizontal sheet with bar stools, from a supporting surface. The vertical beams are separated by voids extending down to a substrate such as a damp course membrane laid upon compacted 1 30 gravel. The voids confine the poured concrete to the remaining spaces beneath a floor surface. After the concrete has hardened, the mechanical properties of the void formers are of no account. In the past, voids contain rigid blocks of expanded polystyrene or other plastics material. Sometimes the voids are hollow and are made of cardboard or plastics. In floors of this type, strength and stiffness of a given mass of concrete is increased by putting 5 the concrete into an "exoskeleton" provided with appropriate steel reinforcing. Use of concealed void formers to increase the external size of a given mass of concrete provides the reinforcing with greater strength by separating the steel bars with intervening concrete. Use of non-reusable void formers within the mass of concrete lowers both the costs and environmental impacts of construction by about halving the amount of concrete required. o PRORART Strong, waterproofed cardboard boxes have been used as void formers. More recently, dense grades of polystyrene foam blocks (expanded polystyrene) (geotech polystyrene) have been used widely. Polystyrene rafts formed to standard dimensions can efficiently form voids in poured concrete, but they are bulky to transport and disintegrate easily into non-biodegradable particles, 5 which are readily lost from vehicles or construction sites. NZ328098 describes a two piece former to form void spaces in concrete components. The two parts are not made of thin sheet material, do not define a cuboidal void and do not interlock together. PROBLEM TO BE SOLVED The problem is to balance the opposing requirements of low cost (minimised materials in an 50 easy-to-make shape) and sufficient strength for void formers. For transport and storage reasons it is desirable if a number of formers can be stacked together on top of, or inside each other. For fitting into non-standard or non-modular spaces it is desirable that the formers can be configured into particular shapes without loss of strength. The currently preferred option, polystyrene foam (expanded polystyrene) is an environmental 55 contaminant and its use has been prohibited in many localities, despite its useful thermal insulating properties. Disposal of excess polystyrene is increasingly expensive. Waste escaping from sites or vehicles is vigorously prosecuted. For example, in Australia there are penalties for littering a building site with pieces of expanded polystyrene. An alternative is needed. OBJECT 2 60 An object of the present application is to provide strong, stackable void formers for use in concrete construction, or at least to provide the public with a useful choice. SUMMARY OF INVENTION In a first broad aspect the invention provides a pod for use as a void former within concrete slabs, floors or foundations; wherein each pod has a rectangular top surface having a length and a 5 width, and a depth or thickness thereby defining a void having a cuboidal shape; the pod being comprised of two interconnected, formed sheets; at least one sheet having been made or formed in order to bear a plurality of stiff formations produced from one side of the top surface as a spaced-apart array; each formation enclosing a hollow centre or internal space within curved or polygonal sides; each formation having a length defining the depth of the void former, each 0 formation tapering to a narrower cross section away from the top surface. Preferably each pod is comprised of a pair of complementary shaped and formed sheets each having a surface and a length and a width and a selected thickness; the formation comprising a pattern of formations, each extended from the surface and having a consistent height; a thickness of the pod being determined by the height of the formations; the pod coming into existence when 5 said pair is assembled. Preferably each formation has tapered sides, ending in a base having a flat surface parallel to, but distanced from the surface of the sheet. Preferably, each formation has a tapered three-dimensional shape having a sectional outline selected from a range including circles, ellipses, and polygons having from three to twelve sides. 80 Optionally the sides of each formation include lengthwise corrugations or flutes thereby providing increased resistance against depression for a given amount of material. Alternatively each formation has inwardly sloping curved sides and ends in a curved dome; while each formed sheet also includes a concave receptacle alongside each formation in order to receive an end of a complementary formation when in use. 85 Preferably the formations are spaced apart and preferably they are placed in an alternating pattern such that when two identical formed sheets are overlaid but with the bases of the formations facing each other the formations will fit in between each other thereby providing a strong cuboidal shape - the pod - which is comprised of two, interconnected, formed sheets. In one option the top surface is square and has a 6 x 6 array of formations. 3 90 Preferably each pod provides a flat top surface having a length and a width conforming to a conventional modular dimension. Preferably a pod can be sawn across without degrading its strength in order to fit into a non modular space or to fit around an included pipe, duct, or other structure, since the strength of the pod is distributed amongst its formations. 5 Optionally, a plurality of formed sheets are pressed together with each formed sheet overlapping a part of two facing formed sheets and including a gap therebetween thereby creating a single large void former having overlapping or alternating top and bottom surfaces. Preferably each complementary sheet is identical, and, assuming the presence of the described tapered formations, is stackable for storage or transport as a stack of sheets in which the bases 0 are all directed in the same direction. Optionally the surface of each formed sheet in between the formations includes strengthening ribs providing the surface with greater stiffness. Preferably each pod is provided with a cover sheet for an upper or pour side of a pod as previously described in this section, the cover sheet having a length and width similar to that of 5 the pod; the cover sheet being placed over the pod in order to prevent concrete from invading the interior of the formations, thereby creating a three-layered entity. Optionally the cover sheet for a pod is comprised of a material selected from a range including plywood, plastics, cardboard, and the internally reinforced two-sheet plastics material known as "Corflute@". 10 Preferably the cover sheet for a pod is comprised of a moulded sheet including strengthening ribs and including engagement means capable of connecting to an underlying formed sheet of a pod. Optionally the cover sheet and the formed sheets are provided with a chamfer so that a concrete column extending from a mass of poured concrete past the pod and to a substrate below may be created, when pouring takes place, in the corners of each pod. 15 Optionally each pod is comprised of two sets of multiple formed sheets fitted together, so that the resulting multiple-layered void former has a greater inherent strength in its structure than a single, non-layered pair of formed sheets fitted together. Preferably at least one surface of any one formed sheet is provided with fastening means selected from a range including complementary clips, protrusions and matching sockets, lips, hook and 4 20 eye materials, barbs, and surfaces coated with adhesives, and corresponding surfaces of another sheet are provided with compatible receiving means, thereby locking the two sheets together. Preferably each formed sheet is made of a thermoplastics selected from a range including polyethylene, (PE), high-density polyethylene (HDPE) polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and alloys thereof. 5 Optionally, each formed sheet may be made of a moulded paper fibre; preferably treated so as to become waterproof. PREFERRED EMBODIMENT The description of the invention to be provided herein is given purely by way of example and is 0 not to be taken in any way as limiting the scope or extent of the invention. Any dimensions are purely illustrative. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Throughout this specification unless the text requires otherwise, the word "comprise" and 5 variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference. Reference to cited material or information cited in the text should not be understood as a concession that the 40 material or information was part of the common general knowledge or was known in New Zealand or in any other country. DRAWINGS Fig la: is a simplified drawing of the two parts of a two-piece or closed pod, using contour lines around or inside each of the formations to indicate shapes. This version includes 45 apertures through the flat parts of each sheet against the positions of mating formations. Fig 1b: is a simplified drawing of the two parts of an alternative two-piece or closed pod, using contour lines to indicate shapes. No apertures are included in this version. Fig 1c: is a diagrammatic cross-section through parts of a two-piece pod using egg-shaped formations. 5 50 Fig 2a: shows a perspective diagrammatic view of one half of the two-piece pod, facing upwards. Fig 2b: shows a detailed view of part of both halves of the two-piece pod, with the upper backing sheet 120a shown in outline only. Fig 2c: is a perspective view of a 6 x 6 array of formations in one half of a two-piece pod. Fig 2d: is a plan view of the Fig 2c pod part. 5 Fig 2e: is an elevation view of the Fig 2c pod part. Fig 3: shows a perspective view of the invention with formations facing downwards. (In this drawing the formation-less parts are shown empty.) Fig 4: (as Fig 4a and 4b) shows plan and perspective views of overlappable upwards facing formations. 0 Fig 5: (as Fig 5a and 5b) shows a variant of the invention with fasteners (0 and +) on formations and on backing sheets. Fig 6: (as Figs 6a, 6b, and 6c) illustrates a closely-interlocking pod variant having an octagonal base and a square top surface. Fig 7: provides a perspective view of four rectangular pods arranged to leave side channels and 5 a central hollow ready for pouring. Fig 8: (as Figs 8a and 8b) shows perspective and plan views of a square pod having chamfered corners, and a central hollow. INTRODUCTION 70 The invention comprises one or more void formers, herein called "pods". The invention is intended to provide a reliable enclosed volume which encloses a space and resists reasonable deforming forces, such as the weight of a standing person, before the concrete to be poured has become sufficiently solid. The designs described herein are intended to provide such resistance within an easily manufactured shape and while using a minimum of materials. The invention 75 uses complementary pairs of formed sheets that have projecting, interlocking formations - with or without actual fasteners or adhesives to clip them together. The formations act as volume enclosing elements. Pairs of formed sheets fitted together provides a volume, having a desirable capacity to resist compression from above, from flat sheets without resorting to volume occupying materials such as expanded polystyrene parts. Alternating holes and formations allow 6 BO the user to lay one sheet partially over another one, so that a given floor surface can be covered without having to cut any one frame apart, thereby minimising time. Inside a pod, the tips of the formations from one side are supported by the bases of the formations from the other side, adding to a resistance to deformation. Sheets can be formed using known techniques such as, but not limited to injection moulding of plastics. Paper fibre moulds may be used, especially if 5 waterproofed. SJMMARY Void formers or "pods" used to fill out masses of poured concrete provide a stiff enclosed body that resists reasonable deforming forces until the concrete has become sufficiently solid. The invention uses a minimum of materials in complementary and merged pairs of injection-moulded 0 formed sheets. The sheets have projecting, interlocking, spaced-apart formations acting as volume-enclosing elements and replace expanded volume-occupying materials. They can be cut down to fit a space. Alternating holes and formations allow the user to lay one sheet partially over another one, so that a given floor surface can be covered without having to cut any one frame apart, thereby minimising time. Paper fibre moulds may be used, especially if 5 waterproofed. EXAMPLE 1 The paired pod distributes the strength throughout the area of the bearing surface, so that the design can be made smaller or larger and retain the same average weight bearing capacity per )0 unit area. Each interlocked pod retains a reasonable strength even if sawn across, as it may be to fit into a restricted space. An example pod may be 0.2 to 0.5 metres high and occupy a modular space or a sub-multiple of a modular space 0.6 metres wide and 0.6 metres long, as required in order to fit into standard building dimensions. The reinforcing mesh position and strength is generally prescribed by building regulations. )5 As shown in Figs la and 1b, the paired pod example comprises an array of interlocking pods assembled on-site by flipping every second pre-shaped or formed sheet taken from a stack, pressing the two together so that the formations on one sheet fit in between the formations on the opposed sheet, and usually putting a sealing sheet over the top. A reinforcing mesh will be laid 7 over the tops of the pods and supported at a prescribed distance above the pod or covering sheet 0 upper surfaces by specifically placed bar-stool supports (see below). Figs la, lb and 2a diagrammatically show an individual "formed sheet" (200) or hemi-pod according to the invention, as would be provided for sale or shipped to a building site as one of a stack of identical sheets. An advantage of this invention over voluminous prior-art pods (such as expanded polystyrene) is that because the tapered formations (210) fit inside each other, a large 5 number of pods can be transported as a kit of parts in a small volume. Figs la and 2b suggests that material is deleted (as at 214) from the sheet of the pod (220) leaving apertures at the positions where formations would appear from adjoining sheets. This is purely an option, having the advantage of conserving material but perhaps weakening the structure. Fig 2b shows two such sheets fitted together, formation side to formation side, ready for 0 application of the sealing surface sheet (not shown) and then for covering with a pour of concrete. Each formation (210) in the examples so far has a cut-off tetrahedral shape with bevelled edges (215). Those bevels may be extended so as to make an octahedral shape, in accordance with optimisation of strength for a given thickness of plastics material. A hexagonal shape, a circular shape (in section) or other shape may be used, although not specifically drawn. 5 Each formation is open and hollow, having an opening (213) which can be clearly seen in Figs la, lb and 2b. The formed sheet (200) in Fig 2a comprises a flat, thin frame of standardised dimensions (such as 3 wide x 4 long units) which in use would be oriented down. The sheet (220) from which the formations arise carries alternating holes (225) and tetrahedral formations (210). 30 Fig 1c: is a diagrammatic cross-section through parts of a two-piece pod (242 and 243) in which the concept of an eggshell is used to provide the incremental oval volume-enclosing shapes (244, 245 and 246. This diagram may be evolved to better provide for stacking of like sheets, with each formation receiving a formation from an adjacent sheet. Each of the three oval shapes 244, 245 and 246 is mounted alternately on one sheet (242) or the other (243) or the other, so as to 35 maintain the identical nature of the sheets as previously described. The oval volume-enclosing formations of this version of the invention are half-egg-shaped oval bodies, importing the strength of an avian egg shell that, although being a brittle material is strong. As a mating surface, a concave matching depression 247 is preferably moulded on the inner surface of each empty space in order that the adjacent formation when in contact receives a force distributed 40 over an area, not a point. An alternative formation may comprise a sphere. 8 Fig 2c shows a moulded sheet having a 6 x 6 array of formations (210) extended to one side of a base plane 240. It will be noted from Figs 2c and 2d (a plan view) that each formation is separated from a neighbouring formation by a gap (225) which allows a formation from a corresponding sheet to slide in between, when the pod is assembled. The height of the formations 5 is indicated in Fig 2e as the distance between plane 230 and plane 240. It will be appreciated that optimisation of pod strength versus plastics amount may allow variations in shape, and variations in wall thickness, according to required strength. Unless a cover sheet is used, the downward facing formations will inevitably become filled with concrete. Although this option uses more concrete, it does provide a stronger floor and may be 0 preferred at times. It is usually desirable to block off the formations from being filled by applying a cover sheet, covering the upper surface. A cover sheet is selected from a range including plywood, plastics, cardboard, and may be comprised of the reinforced two-sheet plastics material known as "Corflute@", cut to size. Alternatively, a cover sheet can be moulded to suit each moulded sheet, having (a) a similar surface area, (b) ribbing for strength, and (c) 5 engagement means on one side that fit into at least some of the apertures that lead into the array of formations. Preferably the engagement means does not preclude stacking. Use of a cover sheet provides a three-layered protected pod. As for Example 1, the strength of each pod should be evaluated and made fit for purpose, so that the void will be maintained before a poured mass of concrete has set solid. The formations might 0 collapse when wet concrete is poured around them, since wet concrete is a heavy "fluid" and may have a head height of up to a metre in a raft floor for a residential building, tending to collapse the lower parts of the sides of a pod in place first. Pod collapse could also be caused when a worker is standing above and the concrete is not present, or not yet sufficiently cured. An advantage of the design is that the constructor can assemble a stronger pod from pairs of 55 sheets - taking a first two or more sheets from a supplied stack and fitting them against a second two or more sheets taken off the stack, thereby doubling the thickness of the plastics material over the customary amount. Optionally, fastening means such as a barb, hook, clip or adhesive can be included in any one formed sheet, using shapes well known in the plastics moulding arts, and a matched receiving 70 means is also included in the other formed sheet. Perhaps a separate sheet with receiving means for the fastener could then be laid on top of a double layer of the pods to fix these securely in place. See Fig 5a, showing a perspective view of upwards-facing pod units (200). Some pods 9 (210) have top surfaces (211) fitted with fastening means (510). The backing sheet (220) is fitted at some points with matched receiving means (520). Alternatively sticky tape could be applied to 5 maintain stability until after pouring is finished. In a further variant, formed sheets are pressed together in an alternating way with overlapping top and bottom surfaces; any one first sheet pressed against abutting halves of two second sheets, thereby creating "polypods" that cover a wide area. One sheet is cut into, or provided as two parts. 0 MATEALS Note that a finite element analysis of strength of a concrete slab using void formers of this type has not yet been carried out. Such an analysis can lead to an optimised pod design, in particular with reference to a total amount of a given plastics material required. The cost, including a cost of shaping, and a resulting strength of the selected plastics material is 5 an important aspect of Utility. The invention is able to use any thermoplastics including without limitation a selection from the following presently available range: polyethylene, (PE), high density polyethylene, (HDPE) polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). The plastics material may be virgin, or recycled, or a mixture, or may be an alloy of different plastics, always being in mind the requirement to stand up to use while 0 minimising cost. Fillers might be added. Colours might be added, to provide visual contrast at a worksite. Biologically sourced materials such as cellulose or the like, or paper fibre can be used since that is a renewable material. Pods in this Example may have corrugated walls and tops, much like corrugated roofing iron. Simple corrugations of the planar walls (and closed end) of each pod )5 would minimise the risk of collapse for a given load. Optimisation for any plastics material has not yet been carried out. See Figs 6a and 6b, showing perspective views of, respectively, downwards facing and upwards facing formation arrays (600). The combination of octagonal faces (610) and square faces (611) is shown. See also Fig 6c, showing detail of an upwards facing formation interlocking with a )0 downwards facing formation. Flat sides of upwards and downwards facing pods are at the same angle and fit closely against one another. Bevelled edges (615) enclose a gap between pods. The bottom edge has four longer sides, each the same width as an edge of the square top surface. In this case it is assumed that concrete in between the flat sides is not required. 10 PERIODIC CONCRETE COLUMNS BYPASSING THE PODS 5 One way to get an incremental pod size and provide vertical reinforcing in between ribs is to use an assembly of four rectangular pods laid out to cover a square shape and having a central hollow open to above and closed below by the substrate, which can become filled with concrete. See Fig 7, showing a perspective view of rectangular pods (701) arranged around a central hollow (710). Pods are arranged to leave channels (720) which can be filled with poured 0 concrete or, if made wider, can carry reinforcing iron rods. The larger and smaller sides are arranged to form central hollows which can fill with poured concrete. See Figs 8a and 8b. Octagonal pods (801) may include an internal reinforcement (802) formed in plastic which resists compression of the top surface. Pod sides are spaced to leave a central hollow (710) between any four adjacent pods. 5 BAR STOOLS Preferred bar stools, which are support devices used to hold a subsequently applied reinforcing mesh above the top surface of either the pod or the cover sheet, preferably have wide, round collars that spread any applied weight over a broader surface of the relatively frangible pod below. (Relative to pods made of expanded polystyrene foam). A spike, to penetrate the material 0 of the pod and cover sheet, is preferred and it may include a barb so that it will tend to stay in place during assembly of the reinforcing materials. Each bar stool can be made of plastic by injection moulding. RESULTS AND ADVANTAGES The two-part pods provide an easily laid void former. The cuboidal shape suits the requirements 25 of rib-raft floors. The shapes of the formers, being essentially formed flat sheets, allow minimisation of the amount of plastics used while maintaining the function of excluding concrete from inside the void spaces. Since both faces are identical, and since the formations are tapered, stacks of the pods can be stored and transported to a site in compacted form, and then spread about the site. 30 The optional covering surface is also stackable without lost space. Use of expanded polystyrene foam is avoided. Finally it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various 11 modifications, additions, known equivalents, and substitutions are possible without departing 5 from the scope and spirit of the invention as set forth in the following claims. 12

Claims (12)

1. A pod for use as a space-occupying void former within concrete slabs, floors or foundations; wherein each pod has rectangular top and bottom surfaces each having a 0 length and a width, and has a depth or thickness, thereby defining a void having a cuboidal shape; the pod being comprised of two interconnected, formed sheets each including a plurality of stiff formations produced from one side of a top surface having the length and the width as a spaced-apart array; each formation enclosing a hollow centre within curved or polygonal sides; each formation having a length defining the 5 depth of the void former, each formation tapering to a narrower cross section away from the top surface.

2. A pod as claimed in claim 1, wherein the formations on each formed sheet are spaced apart and placed in a regular alternating pattern such that when two formed sheets are overlaid with the formations upon a first sheet facing the formations upon a second sheet 0 and pressed together, the formations of the first sheet will fit in the spaces and lie beside the formations of the second sheet; the combination thereby providing a strong cuboidal pod.

3. A void former or pod as claimed in claim 2, wherein a plurality of formed sheets are pressed together with each formed sheet overlapping a part of each of two facing formed 5 sheets thereby creating a single large void former having overlapping top and bottom surfaces.

4. A stack comprised of a plurality of formed sheets each as claimed in claim 1, wherein the stack provides a compacted means for storage.

5. A cover sheet for an upper side of a pod as claimed in claim 1; the cover sheet having a 50 profile similar to that of the pod; the cover sheet being placed over the pod in order to prevent concrete from invading the interior of the formations, thereby creating a three layered protected pod.

6. A cover sheet for a pod as claimed in claim 5, comprised of a moulded sheet including strengthening ribs and including engagement means capable of connecting to an 55 underlying formed sheet of a pod. 13

7. A cover sheet for a pod as claimed in claim 5, comprised of a material selected from a range including plywood, plastics, cardboard, and the internally reinforced two-sheet plastics material known as "Corflute@".

8. A three-layered pod as claimed in claim 6 or in claim 7 wherein the cover sheet and the 0 formed sheets are provided with a chamfer so that a concrete column extending past the pod and to a substrate below may be created, when in use, in the corners of each pod.

9. A pod as claimed in claim 2 wherein each pod is comprised of two sets of multiple formed sheets fitted together, so that the resulting multiple layered void former has a greater inherent strength than a single pair of sheets fitted together. 5

10. A pod as claimed in claim 2 wherein at least one surface of any one formed sheet is provided with fastening means selected from a range including complementary clips, protrusions and matching sockets, lips, hook and eye materials, barbs, and surfaces coated with adhesives, and corresponding surfaces of another sheet are provided with compatible receiving means. 0

11. A pod as claimed in any previous claim, wherein each formed sheet is made of a thermoplastics selected from a range including polyethylene, (PE), high-density polyethylene (HDPE) polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and alloys thereof.

12. A pod as claimed in any of claims 1 to 11 inclusive, wherein each formed sheet is made 5 of a paper fibre. 14