US20110120036A1 - Environmentally Degradable Void Former - Google Patents
Environmentally Degradable Void Former Download PDFInfo
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- US20110120036A1 US20110120036A1 US12/952,309 US95230910A US2011120036A1 US 20110120036 A1 US20110120036 A1 US 20110120036A1 US 95230910 A US95230910 A US 95230910A US 2011120036 A1 US2011120036 A1 US 2011120036A1
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- slab
- void forming
- ground surface
- degradable material
- environmentally degradable
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
- E04B5/00—Floors; Floor construction with regard to insulation; Connections specially adapted therefor
- E04B5/43—Floor structures of extraordinary design; Features relating to the elastic stability; Floor structures specially designed for resting on columns only, e.g. mushroom floors
Definitions
- the present invention relates to a void forming apparatus and suspension system for a building/construction and in particular to an apparatus and method for creating voids under a structural concrete slab of a building/construction such that the building/construction is suspended above the ground and is able to withstand changes in the level of the underlying ground support.
- Buildings such as residential homes or commercial buildings, generally rely upon a solid footing to support the considerable weight of the structure.
- the footing generally provides a flat and level base upon which the building is supported, with the base being in communication with the underlying ground surface.
- Many modern buildings are built upon a flat, concrete slab that provides both a base for the structure as well as the bottom floor for the building.
- the concrete is typically placed over a prepared ground surface and is shaped to the desired dimensions to form the footings of the building. This may be achieved through laying pre-cast components of concrete, or through pouring wet concrete into a mould and allowing the concrete to set in position.
- Such concrete slabs consist of a system of structurally engineered concrete beams and platforms, which together form what is collectively referred to as a slab.
- a common problem with concrete slabs supported on a ground surface is that large areas of land available for residential development have soil profiles with high clay content. Such soil profiles are not considered stable, as the surface level of the soil can change as the moisture content of the soil changes. This is due to the volume of the soil being directly dependent upon the soil's moisture content. In particular, as the moisture content of the soil increases, the volume of the soil increases, resulting in the surface level of the soil changing. Such a phenomena causes uplifting of a concrete slab that may be supported on the surface of the soil. When this uplifting of soil occurs, the concrete slab formed on this surface is said to have “heaved”. With such soils, when their moisture content reduces, the soil reduces (shrinks or settles) in volume.
- the factors contributing to variations in soil moisture content, which generates such concrete slab movements, are various and complex. Some common factors include: natural moisture variations due to seasonal considerations such as wet and dry seasons; soil drying due to trees growing or being introduced into a zone of influence of the soil; soil wetting due to the removal of trees and other related flora such that previously drier soils re-hydrate resulting in the phenomena of “rebound” occurring in the soil; garden watering (or lack thereof) by owners/occupiers of a subject site; or a combination of any of these sources. Any or all of these factors can significantly alter the soil moisture content, resulting in a concrete slab deflecting or becoming damaged. This can result in damage to the super-structure supported on the slab, such as a residential dwelling or the like, requiring time-consuming and expensive corrective action.
- soil moisture content is not consistent and may vary across regions, resulting in further differential shrinking/swelling of the soil.
- construction areas have been chosen to avoid soils having a high clay content to reduce the occurrence of soil heave.
- areas which have previously been avoided such as beach/river frontages; steeply sloping hinterland areas beyond the coastlines; and the grazing plains (some of which are flood prone) which surround most cities and towns, are increasingly becoming the site for a variety of constructions and developments that have previously been considered unsuitable for such a soil base.
- a number of methods have been proposed to address the soil heave phenomena and to prevent highly expansive soils from damaging the structures supported on such soil. Typically, these methods are employed prior to construction and rely upon chemical treatment of the soil; engineered fill and compaction of the soil; and/or the formation of a void space beneath the concrete slab to accommodate expansion of the soil into these voids without damaging the structure.
- the present invention provides an apparatus for creating a void beneath a structural concrete slab, comprising:
- a body having a first surface adapted to support wet concrete for forming at least a portion of the concrete slab and a second surface adapted to contact a ground surface;
- the body is partly or fully formed of an environmentally degradable material, and wherein the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting, but thereafter degrades to create a cavity into which swelling ground can expand.
- the first surface is located remote from the second surface such that the at least a portion of the concrete slab is separated from the ground surface.
- the first surface and the second surface are separated by one or more wall members.
- the one or more wall members may extend from said first surface at a proximal end terminating at a distal end.
- the second surface of the body may define the distal end of the one or more wall members.
- the apparatus may comprise an enclosed form.
- the apparatus may include one or more cavities or may be a solid block of low density material or water degradable material or water soluble material or include a combination of these features.
- the body may include at least one cavity extending at least partially from the second surface toward the first surface.
- the at least one cavity may be open to the ground surface to accommodate any rise that may occur in the ground surface following positioning of the member beneath the slab, or may be closed by a continuous floor member in which case rise in the surface may be accommodated by degradation of at least part of the body.
- the at least one cavity may be formed by the one or more wall members and the first surface.
- the body may have a thin-walled cellular structure, which may be formed by thermoforming or vacuum forming
- One or more supporting struts may be provided within the cavity.
- the struts may extend from the first surface at a proximal end to the second surface at a distal end.
- the distal end of the struts may contact the ground surface to provide support to the first surface or may be supported on a floor member closing the cavity.
- the one or more struts may be regularly spaced within the cavity.
- the struts are deformable such that any rise of the ground surface into the cavity will cause deflection of the struts. Once the body begins to degrade, deflection or disintegration will occur when the ground level raises. The body is therefore preferably sacrificial, and will collapse rather than transmit ground movement to the slab.
- the present invention provides a system for creating a suspended structural concrete slab, comprising:
- each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface and the second end arranged to extend a position at or near said ground surface;
- At least one void forming element the or each void forming element being formed of an environmentally degradable material and being arranged to substantially cover a ground surface upon which the structural slab is to be placed and to define a surface onto which wet concrete for forming the structural slab is to be poured;
- said at least one pile member is adapted to support the structural slab above the ground surface such that said at least one void forming element is positioned between the structural slab and the ground surface;
- the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting.
- the present invention provides a method of forming a suspended structural concrete slab, comprising:
- each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface, and the second end arranged to extend to a position at or near said ground surface;
- each void forming element being formed of an environmentally degradable material and being arranged to substantially cover a ground surface upon which the structural slab is to be placed, the pile members extending above at least part of the surface formed by the at least one void forming element;
- the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting.
- the void forming elements may be formed by injection moulding, rotational moulding or vacuum moulding the environmentally degradable material.
- the environmentally degradable material may be adapted to be degraded by contact with water and/or soil.
- the environmentally degradable material may be a biodegradable polymer.
- the environmentally degradable material may be compostable.
- the environmentally degradable material may be formed from a manufactured biopolymer, such as a thermoplastic starch polymer (eg. the biopolymer sold under the trade name PlanticTM).
- the environmentally degradable material may be formed from PLA, Mater-bi, Biograde, or a range of biodegradable polyesters such as PHA, PBAT, or PBSA.
- a barrier may be provided between the environmentally degradable material and the structural slab.
- the coating may take the form of a film of moisture inhibiting material or a moisture inhibiting coating on the environmentally degradable material.
- a thickness of the environmentally degradable material may be selected to provide the environmentally degradable material with a desired structural longevity.
- the environmentally degradable material is preferably adapted to retain sufficient structural strength to support the concrete slab for at least 12 hours, more preferably at least 24 hours, and in some embodiments for at least 48 hours.
- the environmentally degradable material preferably has a density of more than 1 g/cm3, and more preferably between 1 g/cm3 and 2 g/cm3.
- the environmentally degradable material In a dry, undegraded, granular state, the environmentally degradable material preferably has a maximum tensile stress of between 10 MPa and 100 MPa, and more preferably between 15 MPa and 50 MPa. In a dry, undegraded, granular state, the environmentally degradable material preferably has a Young's Modulus of between 500 MPa and 5000 MPa, and more preferably between 500 MPa and 3000 MPa. The degradable material may degrade into a biocompatible component of soil underneath the concrete slab.
- the at least one void forming element is an apparatus according to the first aspect.
- the at least one void forming element may be arranged such that the second end of the at least one pile member extends therethrough.
- the pile members may engage the structural slab.
- the engagement may be in the form of a wider portion located in the upper part of the pile such that the concrete formed over the pile surrounds and engages the widened portion and a narrower portion beneath it.
- the wider portion may comprise a rod or bar extending horizontally through a hole in a vertical portion of the pile located above the lower extremity of the structural slab.
- the piles may be located in beam portions of the structural slab and the rod or bar may extend longitudinally of the beam portions.
- the at least one pile member is a screw pier foundation pile.
- the second end of the at least one pile member may be raised above the ground surface to a predetermined height.
- the pile members may be arranged in a grid to form a consistent and level array of loading points above the ground surface.
- the structural slab may be a concrete slab consisting of a plurality of platforms and beams.
- the structural slab may be supported above the ground surface by the beams receiving the second end of the at least one pile member.
- the depth to which the second ends of the piles are received by the beams is determined by the bearing capacity of the building/construction.
- the installed height of the pile member above the ground enables the second end of the pile members to penetrate to a desired depth into the beams of the structural slab.
- the piles are subsequently structurally connected to the concrete slab within the beam.
- FIG. 1 is a perspective view of a void forming and suspension arrangement of the present disclosure
- FIG. 2 is a cross sectional side view of the void forming and suspension arrangement of FIG. 1 , supporting a concrete slab;
- FIG. 3 is a plan view of the slab of FIG. 2 ;
- FIG. 4 is a perspective view of an embodiment of a spacer void forming element of the void forming arrangement of FIG. 1 ;
- FIG. 5 shows a plan view of a second embodiment of a spacer void forming element of the void forming arrangement of FIG. 1 ;
- FIG. 6 shows an elevation view of the embodiment of a spacer void forming element of FIG. 5 with a first height
- FIG. 7 shows an elevation view of the embodiment of a spacer void forming element of FIG. 5 with a second height
- FIG. 8 shows (a) plan, (b) elevation and (c) end elevation views of an embodiment of a shallow void forming element of the void forming arrangement of FIG. 1 ;
- FIGS. 9 a shows a underside perspective view of an alternative embodiment of the void forming elements of FIGS. 5-7
- FIG. 9 b shows a plurality of the void forming elements of FIG. 9 a grouped together in abutting relationship
- FIGS. 10 a and 10 b show underside perspective and cross-sectional views, respectively, of a further alternative embodiment of the void forming elements of FIGS. 5-7 .
- FIG. 1 A void forming and suspension system 10 in accordance with the present disclosure is shown in FIG. 1 .
- the void forming and suspension system 10 generally consists of a plurality of void forming elements 12 , 16 arranged to extend over a ground surface 22 upon which the building is to be constructed. As will become more apparent in the following description, the void forming system 10 functions to act as an interface between the ground surface 22 and a concrete slab 20 of the building to be constructed, while the slab is being formed. Once the slab 20 is formed and the wet concrete for forming the slab has hardened, the void forming system is superfluous and can be allowed to collapse, reducing the risk of swelling ground heaving the slab.
- a plurality of load bearing compression and tension piles 14 are driven, drilled, jacked, tied or otherwise fixed into the deeper soil or rock of high bearing capacity to provide stability to the structure which is to be built.
- the piles 14 may be in a variety of forms, such as screw piles which communicate directly with the load bearing ground beneath the ground surface 22 .
- the piles 14 perform in both tension and compression and are raised above the ground surface to a predetermined height.
- the piles are arranged in a grid to form a consistent and level loading region above ground upon which to found the beams of the finished concrete slab.
- the depth to which the piles 14 are installed is determined in relation to where they will achieve the engineered and designed bearing capacity for the said building/construction.
- the installed height of each pile 14 above ground will allow the end of the piles 14 to penetrate to an engineered depth into the finished beams of the concrete slab above.
- the piles 14 are subsequently structurally connected to the concrete slab within the beam. It will be appreciated that the size and shape of the slab can be readily adapted to suit the size and shape of the building to be constructed. As such, the placement location and number of piles 14 utilised is variable, though based on the relevant modular system engineered design for that project.
- void forming elements 12 are positioned over and around the piles 14 .
- the void forming elements 12 are in the form of elongate shallow members which may be designed to effectively absorb extreme ground movement in the short term, as well as allow the piles 14 to pass therethrough. In the long term, the void forming elements 12 will disintegrate due to their construction from environmentally degradable material, as discussed in detail below.
- the void forming elements 12 extend along the piles 14 , they are typically arranged in parallel rows in accordance with the specific design of the structure to be built. It will be appreciated that the arrangement as shown in FIGS. 1 to 3 represents a substantially rectangular footing wherein the piles are regularly spaced and positioned in rows and hence the void forming elements 12 extend in rows, however it will be appreciated that the footing structure may vary in accordance with the specific design of the building to be constructed.
- the spacer void forming elements 16 are in the form of elongate void former structures, which are also partially or fully formed of an environmentally degradable material and may also be deformable to accommodate short term movement of the ground surface. Over time, the spacer void forming elements 16 will degrade, due to contact with moisture or soil, and collapse, leaving the concrete slab 20 supported substantially entirely by the piles 14 .
- the spacer void forming elements 16 extend between each of the shallow void forming elements 12 , as shown, to provide an additional surface, elevated from the ground surface, offering a holistic void forming body upon which the concrete slab (platform regions and beams) can be placed. In this regard, the platform and beam regions of the concrete slab are supported upon the spacer void forming elements 16 and the shallow void forming elements 12 and are suspended from the ground surface upon placement.
- the void forming elements 12 , 16 are formed by injection moulding the environmentally degradable material.
- the environmentally degradable material is a biodegradable, manufactured biopolymer, preferably a thermoplastic starch polymer formulated for injection moulding.
- the material is also compostable under ambient conditions, such as those in a conventional vegetable waste compost environment.
- a suitable material is sold under the trade name PlanticTM.
- PlanticTM is renewable sourced biodegradable polymer made from non-genetically modified corn starch. Several forms of PlanticTM are available, some of which are water dispersible and/or injection mouldable.
- the environmentally degradable material In a dry, undegraded, granular state, the environmentally degradable material has a density of between 1 g/cm 3 and 2 g/cm 3 , a maximum tensile stress of between 15 MPa and 50 MPa, and a Young's Modulus of between 500 MPa and 3000 MPa.
- Other suitable environmentally degradable materials are PLA, Mater-biTM, BiogradeTM, or a range of biodegradable polyesters such as PHA, PBAT, or PBSA.
- the environmentally degradable material has a degradation rate appropriate to provide sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self supporting.
- the timeframe for the slab 20 to become self-supporting varies based on a number of factors, including the nature of the concrete mix for forming the slab, the weather conditions and the slab design. Typically, however, the slab will be self-supporting in around 24 hours.
- a barrier in the form of a plastic film, may be provided between the void forming elements 12 , 16 and the slab 20 to inhibit passage of moisture from the slab, especially in the first 24 hours after it has been poured.
- the barrier may take the form of a coating on the environmentally degradable material.
- the thickness of the environmentally degradable material may be selected to provide the desired structural longevity. After the slab has sufficiently cured, the degradable material degrades into a biocompatible component of soil underneath the concrete slab.
- the area upon which the void forming system is placed is prepared.
- Such preparation typically comprises excavating the site to form a level surface upon which the concrete is to be placed. Trenches can also be dug to position deep edge beams and the like to define the perimeter of the foundation to enable the piles 14 to be positioned as discussed above.
- the void forming elements 12 , 16 can be positioned as shown in FIG. 1 , for placement of the concrete.
- the environmentally degradable material of the spacer void forming elements 16 and the shallow void forming elements 12 can be readily shaped or cut to fit around plumbing pipes and the like, through the use of a hand or power saw. Generally, this may not be necessary as the spacer void forming elements 16 and shallow void forming elements 12 can be custom made and delivered to the building site to suit the building plans provided. It will be appreciated that whilst the void forming elements 12 , 16 of one embodiment of the invention are made from an environmentally degradable material, the void forming elements may be made in a variety of shapes and from a variety of materials to enable the void forming system 10 to perform its function, as will be appreciated below.
- reinforcing mesh and bar 18 may be placed over the void forming elements 12 , 16 to further reinforce the slab 20 .
- Such a mesh material may be particularly applicable if the concrete is to be poured over the void forming elements 12 , 16 to form the slab 20 .
- the slab 20 is fully supported above the surface of the soil 22 by the void forming elements 12 , 16 and piles 14 , thereby completely isolating the slab 20 from the ground soil 22 .
- the slab is suspended above the ground surface 22 , with the load of the structure being supported by the piles 14 which are in turn supported by the deeper soil or rock of high bearing capacity.
- the piles 14 have a direct/positive engagement with the slab 20 and the ground, thereby offering load bearing capacity for the concrete slab in both tension and compression.
- the engagement will typically be in the form of a wider portion located in the upper part of the pile such that the concrete formed over the pile surrounds and engages the wider portion and a narrower portion beneath it.
- the wider portion comprises a rod or bar 15 extending horizontally through a hole in a vertical portion of the pile located above the lower extremity of the structural slab.
- the piles are located in beam portions 13 of the structural slab and the rod or bar 15 extends longitudinally of the beam portions.
- FIG. 3 shows a plan view of one such slab arrangement 20 where the shallow void forming elements 12 are arranged to form two internal parallel beams which extend the length of the slab 20 .
- Perimeter beams 24 are also formed by placement of shallow void forming elements 12 about the perimeter of the site such that the parallel beams work in conjunction with the perimeter beams 24 to form a grid arrangement upon which the slab 20 is supported, separate from the ground surface.
- the size and shape of the slab 20 can be readily adapted to suit the size and shape of the building to be constructed.
- the void forming and suspension system 10 is a modular arrangement that can be easily assembled to accommodate a variety of sized and shaped slabs. In this regard, a variety of sizes are provided in both the void forming elements 12 , 16 to accommodate differing dimensions of the slab design and positions and lengths of the piles 14 to accommodate varying depths of soil penetrated to achieve the appropriate bearing capacities required.
- the void forming element 16 is in the form of a box-like element having four vertical side surfaces 26 and a top surface 28 .
- the surfaces 26 , 28 of the void forming element 16 are configured to interface with the concrete slab 20 in the manner as shown in FIG. 2 .
- the underside 30 of the void forming element 16 namely the side which is supported on the ground surface 22 , is open thereby providing a cavity within the void forming element 16 .
- the cavity is defined by the inner walls of the surfaces 26 , 28 , and in the embodiment as shown in FIG. 4 , represents a substantially rectangular space.
- a plurality of strut members 32 are provided within the cavity and extend from the inner surface of the top surface 28 to the ground surface 22 when the void forming element 16 is positioned thereon for use.
- the strut members 32 support the top surface 28 of the void forming element 16 along its length such that the top surface 28 is able to support the load of the reinforced concrete during placement of the slab 20 , as well as the load of workers or machinery used during the placement process.
- the shape of the struts 32 and their location within the cavity defines the strength of the void forming element. It will be appreciated that the arrangement and shape of the struts 32 can be altered in accordance to the specific construction.
- Such an arrangement of struts 32 provides structural integrity and enables the void forming elements 12 , 16 to carry higher loads without failing or disintegrating during the formation of the structural slab 20 .
- this configuration of walls and individual struts also provides an ability to cope with any soil heave that may occur over time as the struts and walls will collapse under pressure such that movement is not transmitted to the slab.
- the strut members 32 may be formed from an environmentally degradable material, such that, like the void forming elements 12 , 16 , the strut members 32 degrade over time.
- the strut members 32 may be shielded from moisture by a barrier such as a coating or plastic film, or be formed from an appropriate thickness of environmentally degradable material, in order to increase their structural longevity if required.
- a barrier such as a coating or plastic film
- the shallow void forming elements 12 may also be constructed in the same manner as the spacer void forming element 16 of FIG. 4 .
- the structure and material of the void forming elements 12 , 16 ensure that they degrade over time to leave cavities into which soil supporting the slab may expand without heaving the slab, with the void forming elements 12 , 16 preferably also being adapted to compress under load during the construction process without deforming or failing should ground swelling occur at this time.
- the soil is able to expand into the cavities remaining after degradation of the void forming elements 12 , 16 (and the struts 32 if formed from degradable material), where appropriate.
- the struts 32 are not degradable, since the void forming elements 12 , 16 are made from an environmentally degradable material, in the event of soil expanding into the cavities, the struts 32 break away from the body of the degraded void forming elements 12 , 16 to further accommodate the expanding soil.
- the void forming element 16 in this embodiment is in the form of a box-like element having four vertical side members 46 , 47 and a top platform member 49 forming the concrete supporting surface 48 .
- Lower portions 46 of the side walls are corrugated and while upper portions 47 of the side walls are corrugated on an inner surface and have the corrugations filled on the outer surface.
- the members 46 , 47 49 of the void forming element 16 are configured to interface with the concrete slab 20 in the manner as shown in FIG. 2 .
- the underside 30 of the void forming element 16 namely the side which is supported on the ground surface 22 , is open thereby providing a cavity within the void forming element 16 .
- the cavity is defined by the inner surfaces walls of the members 46 , 49 , and in the embodiment as shown in FIGS. 5 and 6 , again represents a substantially rectangular space, although in this instance with corrugated walls.
- FIG. 7 show an elevation of an alternative version of the spacer void forming element 16 having differing heights to that of FIG. 6 .
- the embodiments shown in elevation in FIGS. 6 and 7 are similar to one another.
- a plurality of strut members 42 are provided within the cavity and extend from the inner surface of the platform member 49 to the ground surface 22 when the void forming element 16 is positioned thereon for use.
- the strut members 42 provide support for the platform member 49 of the void forming element 16 along its length such that the top surface 48 is able to support the load of the reinforced concrete during placement of the slab 20 , as well as the load of workers or machinery used during the placement process.
- the shape of the struts 42 and their location within the cavity defines the strength of the void forming element.
- the struts have a substantially rectangular cross section with two opposing concave sides. It will be appreciated that the arrangement and shape of the struts 42 can be altered in accordance to the specific construction.
- FIG. 8 illustrates an embodiment of the structure of the shallow void forming element 12 .
- the shallow void forming element 12 in this embodiment is also in the form of a box-like element having four vertical side members 56 (in this case not corrugated) and a top platform member 59 forming the concrete supporting surface 58 .
- the height of the shallow void forming element 12 is preferably the same as the height of the corrugated lower portion 46 of the walls of the spacer void forming element 16 . Therefore the overall height of this shallow void forming element 12 is shorter than that of the spacer void forming elements 16 to allow the formation of concrete beams between the spacer void forming elements 16 .
- the members 56 , 59 of the shallow void forming element 12 are also configured to interface with the concrete slab 20 in the manner as shown in FIG. 2 .
- a single internal strut 52 is provided extending from the inner surface of the platform member 59 to the ground surface 22 when the void forming element 12 is positioned thereon for use and the strut 52 divides the internal space of the shallow void forming element into two cavities 60 .
- Each cavity is defined by the inner surfaces of walls of the members 56 , 59 and the strut 52 , and in the embodiment as shown in FIG. 6 , again represents a substantially rectangular space.
- FIGS. 9 a and 9 b show an alternative embodiment of the void forming elements 12 , 16 of FIGS. 5-7 , where corresponding reference numerals indicate corresponding features with corresponding functionality.
- the void forming elements 12 , 16 of FIGS. 9 a and 9 b include a thin-walled cellular base structure defined by a network of cell walls 70 formed by thermoforming or vacuum forming
- a solid top 72 is provided over the cellular base structure to support the curing concrete slab 20 .
- the top 72 may or may not be formed from the environmentally degradable material. It will be appreciated that a smaller amount of environmentally degradable material is required to be used to form the void forming elements of FIGS. 9 a and 9 b as compared to those of FIGS.
- FIGS. 9 a and 9 b may also assist in crumpling of the void forming elements 12 , 16 due to soil heave in situations where the void forming elements have not completely degraded.
- the void forming elements 12 , 16 of FIG. 9 a may be grouped together in abutting relationship to define a void form of a desired size for supporting a concrete slab during curing.
- FIGS. 10 a and 10 b show a further embodiment of the void forming elements 12 , 16 of FIGS. 5-7 .
- the embodiment of FIGS. 10 a and 10 b has many features in common with the embodiment of FIGS. 9 a and 9 b , where corresponding reference numerals indicate corresponding features with corresponding functionality.
- the void forming elements 12 , 16 of FIGS. 10 a and 10 b are formed by injection moulding the environmentally degradable material.
- Void forming elements 12 , 16 as shown in FIGS. 10 a and 10 b may be grouped together, as shown in FIG. 9 b , to define a void form of a desired size for supporting a concrete slab during curing.
- the void forming elements 12 , 16 may have a lattice construction, similar to an inverted milk crate.
- the top of the void forming elements 12 , 16 may be solid, or of lattice construction with an overlaying solid layer for supporting the curing concrete slab 20 .
- the void forming system is formed from a solid block of environmentally degradable material, which degrades over time due to contact with moisture and/or soil to leave a void into which swelling substrate ground can expand without heaving the slab 20 .
- the system described in the embodiment above comprises a concrete slab supported on deep footings, typically screw piles, drilled piles and piles designed for compression and/or tension.
- the slab is designed to be suspended between the deep footings and the void forming elements allow concreting to be easily accomplished during construction and serves as a compressible/crushable/degradable zone during the life of the slab as the underlying soil expands.
Abstract
There is disclosed herein a void forming and suspension system (10), which generally consists of a plurality of void forming elements (12, 16) arranged to extend over a ground surface (22) upon which the building is to be constructed. As will become more apparent in the following description, the void forming system (10) functions to act as an interface between the ground surface (22) and a concrete slab (20) of the building to be constructed, while the slab is being formed. Once the slab (20) is formed and the wet concrete for forming the slab has hardened, the void forming system degrades to create a cavity into which swelling ground can expand.
Description
- This application is related to Australian Provisional Patent Application No. 2009905738, the entire disclosure of which is incorporated herein by way of reference.
- The present invention relates to a void forming apparatus and suspension system for a building/construction and in particular to an apparatus and method for creating voids under a structural concrete slab of a building/construction such that the building/construction is suspended above the ground and is able to withstand changes in the level of the underlying ground support.
- Buildings, such as residential homes or commercial buildings, generally rely upon a solid footing to support the considerable weight of the structure. The footing generally provides a flat and level base upon which the building is supported, with the base being in communication with the underlying ground surface. Many modern buildings are built upon a flat, concrete slab that provides both a base for the structure as well as the bottom floor for the building. The concrete is typically placed over a prepared ground surface and is shaped to the desired dimensions to form the footings of the building. This may be achieved through laying pre-cast components of concrete, or through pouring wet concrete into a mould and allowing the concrete to set in position. Typically such concrete slabs consist of a system of structurally engineered concrete beams and platforms, which together form what is collectively referred to as a slab.
- A common problem with concrete slabs supported on a ground surface is that large areas of land available for residential development have soil profiles with high clay content. Such soil profiles are not considered stable, as the surface level of the soil can change as the moisture content of the soil changes. This is due to the volume of the soil being directly dependent upon the soil's moisture content. In particular, as the moisture content of the soil increases, the volume of the soil increases, resulting in the surface level of the soil changing. Such a phenomena causes uplifting of a concrete slab that may be supported on the surface of the soil. When this uplifting of soil occurs, the concrete slab formed on this surface is said to have “heaved”. With such soils, when their moisture content reduces, the soil reduces (shrinks or settles) in volume.
- Heaving and settling of soil due to moisture content change therein tends to occur at varying rates across the surface plane of the soil. This variance is termed differential movement. As a concrete slab being supported on the surface of such soil will heave and settle accordingly, this differential movement can result in a concrete slab supported on such a soil surface experiencing a variety of loading forces over the life of a building construction.
- The factors contributing to variations in soil moisture content, which generates such concrete slab movements, are various and complex. Some common factors include: natural moisture variations due to seasonal considerations such as wet and dry seasons; soil drying due to trees growing or being introduced into a zone of influence of the soil; soil wetting due to the removal of trees and other related flora such that previously drier soils re-hydrate resulting in the phenomena of “rebound” occurring in the soil; garden watering (or lack thereof) by owners/occupiers of a subject site; or a combination of any of these sources. Any or all of these factors can significantly alter the soil moisture content, resulting in a concrete slab deflecting or becoming damaged. This can result in damage to the super-structure supported on the slab, such as a residential dwelling or the like, requiring time-consuming and expensive corrective action.
- Typically, soil moisture content is not consistent and may vary across regions, resulting in further differential shrinking/swelling of the soil. Historically, construction areas have been chosen to avoid soils having a high clay content to reduce the occurrence of soil heave. However, as populations increase, more and more land having such high clay content soil is being used for development. In this regard, areas which have previously been avoided such as beach/river frontages; steeply sloping hinterland areas beyond the coastlines; and the grazing plains (some of which are flood prone) which surround most cities and towns, are increasingly becoming the site for a variety of constructions and developments that have previously been considered unsuitable for such a soil base.
- A number of methods have been proposed to address the soil heave phenomena and to prevent highly expansive soils from damaging the structures supported on such soil. Typically, these methods are employed prior to construction and rely upon chemical treatment of the soil; engineered fill and compaction of the soil; and/or the formation of a void space beneath the concrete slab to accommodate expansion of the soil into these voids without damaging the structure.
- Most void systems previously proposed have been arranged such that the beams of the concrete slab are placed between the void forming elements. Conventionally, the beam regions of the concrete slab do not have a void space and hence are more susceptible to soil heave.
- Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
- Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
- In a first aspect, the present invention provides an apparatus for creating a void beneath a structural concrete slab, comprising:
- a body having a first surface adapted to support wet concrete for forming at least a portion of the concrete slab and a second surface adapted to contact a ground surface;
- wherein the body is partly or fully formed of an environmentally degradable material, and wherein the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting, but thereafter degrades to create a cavity into which swelling ground can expand.
- In one embodiment, the first surface is located remote from the second surface such that the at least a portion of the concrete slab is separated from the ground surface. In one form, the first surface and the second surface are separated by one or more wall members. The one or more wall members may extend from said first surface at a proximal end terminating at a distal end. In this regard, the second surface of the body may define the distal end of the one or more wall members. Alternatively the apparatus may comprise an enclosed form. The apparatus may include one or more cavities or may be a solid block of low density material or water degradable material or water soluble material or include a combination of these features.
- The body may include at least one cavity extending at least partially from the second surface toward the first surface. The at least one cavity may be open to the ground surface to accommodate any rise that may occur in the ground surface following positioning of the member beneath the slab, or may be closed by a continuous floor member in which case rise in the surface may be accommodated by degradation of at least part of the body. The at least one cavity may be formed by the one or more wall members and the first surface.
- The body may have a thin-walled cellular structure, which may be formed by thermoforming or vacuum forming
- One or more supporting struts may be provided within the cavity. The struts may extend from the first surface at a proximal end to the second surface at a distal end. In this regard, the distal end of the struts may contact the ground surface to provide support to the first surface or may be supported on a floor member closing the cavity. The one or more struts may be regularly spaced within the cavity. In one form, the struts are deformable such that any rise of the ground surface into the cavity will cause deflection of the struts. Once the body begins to degrade, deflection or disintegration will occur when the ground level raises. The body is therefore preferably sacrificial, and will collapse rather than transmit ground movement to the slab.
- According to a second aspect, the present invention provides a system for creating a suspended structural concrete slab, comprising:
- at least one pile member, the or each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface and the second end arranged to extend a position at or near said ground surface; and
- at least one void forming element, the or each void forming element being formed of an environmentally degradable material and being arranged to substantially cover a ground surface upon which the structural slab is to be placed and to define a surface onto which wet concrete for forming the structural slab is to be poured;
- wherein said at least one pile member is adapted to support the structural slab above the ground surface such that said at least one void forming element is positioned between the structural slab and the ground surface; and
- wherein the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting.
- According to a third aspect, the present invention provides a method of forming a suspended structural concrete slab, comprising:
- installing at least one pile member, the or each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface, and the second end arranged to extend to a position at or near said ground surface;
- installing at least one void forming element, the or each void forming element being formed of an environmentally degradable material and being arranged to substantially cover a ground surface upon which the structural slab is to be placed, the pile members extending above at least part of the surface formed by the at least one void forming element; and
- pouring wet concrete to form the structural slab, whereby the structural slab is supported above the ground surface by the at least one pile member such that the at least one void forming element is positioned between the structural slab and the ground surface,
- wherein the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting.
- In embodiments of any of the first to third aspects above, the void forming elements may be formed by injection moulding, rotational moulding or vacuum moulding the environmentally degradable material. The environmentally degradable material may be adapted to be degraded by contact with water and/or soil. The environmentally degradable material may be a biodegradable polymer. The environmentally degradable material may be compostable. The environmentally degradable material may be formed from a manufactured biopolymer, such as a thermoplastic starch polymer (eg. the biopolymer sold under the trade name Plantic™). Alternatively, the environmentally degradable material may be formed from PLA, Mater-bi, Biograde, or a range of biodegradable polyesters such as PHA, PBAT, or PBSA. A barrier may be provided between the environmentally degradable material and the structural slab. The coating may take the form of a film of moisture inhibiting material or a moisture inhibiting coating on the environmentally degradable material. Alternatively, or in addition, a thickness of the environmentally degradable material may be selected to provide the environmentally degradable material with a desired structural longevity. The environmentally degradable material is preferably adapted to retain sufficient structural strength to support the concrete slab for at least 12 hours, more preferably at least 24 hours, and in some embodiments for at least 48 hours. In a dry, undegraded, granular state, the environmentally degradable material preferably has a density of more than 1 g/cm3, and more preferably between 1 g/cm3 and 2 g/cm3. In a dry, undegraded, granular state, the environmentally degradable material preferably has a maximum tensile stress of between 10 MPa and 100 MPa, and more preferably between 15 MPa and 50 MPa. In a dry, undegraded, granular state, the environmentally degradable material preferably has a Young's Modulus of between 500 MPa and 5000 MPa, and more preferably between 500 MPa and 3000 MPa. The degradable material may degrade into a biocompatible component of soil underneath the concrete slab.
- In one embodiment of the second aspect, the at least one void forming element is an apparatus according to the first aspect. The at least one void forming element may be arranged such that the second end of the at least one pile member extends therethrough.
- The pile members may engage the structural slab. The engagement may be in the form of a wider portion located in the upper part of the pile such that the concrete formed over the pile surrounds and engages the widened portion and a narrower portion beneath it. The wider portion may comprise a rod or bar extending horizontally through a hole in a vertical portion of the pile located above the lower extremity of the structural slab. The piles may be located in beam portions of the structural slab and the rod or bar may extend longitudinally of the beam portions.
- In another embodiment, the at least one pile member is a screw pier foundation pile. The second end of the at least one pile member may be raised above the ground surface to a predetermined height. Where more than one pile member is employed, the pile members may be arranged in a grid to form a consistent and level array of loading points above the ground surface.
- The structural slab may be a concrete slab consisting of a plurality of platforms and beams. The structural slab may be supported above the ground surface by the beams receiving the second end of the at least one pile member. The depth to which the second ends of the piles are received by the beams is determined by the bearing capacity of the building/construction. In this regard, the installed height of the pile member above the ground enables the second end of the pile members to penetrate to a desired depth into the beams of the structural slab. In this regard, the piles are subsequently structurally connected to the concrete slab within the beam.
- By way of example only, embodiments of the present disclosure are now described with reference to the accompanying drawings, in which:
-
FIG. 1 is a perspective view of a void forming and suspension arrangement of the present disclosure; -
FIG. 2 is a cross sectional side view of the void forming and suspension arrangement ofFIG. 1 , supporting a concrete slab; -
FIG. 3 is a plan view of the slab ofFIG. 2 ; -
FIG. 4 is a perspective view of an embodiment of a spacer void forming element of the void forming arrangement ofFIG. 1 ; -
FIG. 5 shows a plan view of a second embodiment of a spacer void forming element of the void forming arrangement ofFIG. 1 ; -
FIG. 6 shows an elevation view of the embodiment of a spacer void forming element ofFIG. 5 with a first height; -
FIG. 7 shows an elevation view of the embodiment of a spacer void forming element ofFIG. 5 with a second height; -
FIG. 8 shows (a) plan, (b) elevation and (c) end elevation views of an embodiment of a shallow void forming element of the void forming arrangement ofFIG. 1 ; -
FIGS. 9 a shows a underside perspective view of an alternative embodiment of the void forming elements ofFIGS. 5-7 , andFIG. 9 b shows a plurality of the void forming elements ofFIG. 9 a grouped together in abutting relationship; and -
FIGS. 10 a and 10 b show underside perspective and cross-sectional views, respectively, of a further alternative embodiment of the void forming elements ofFIGS. 5-7 . - A void forming and
suspension system 10 in accordance with the present disclosure is shown inFIG. 1 . - The void forming and
suspension system 10 generally consists of a plurality ofvoid forming elements ground surface 22 upon which the building is to be constructed. As will become more apparent in the following description, thevoid forming system 10 functions to act as an interface between theground surface 22 and aconcrete slab 20 of the building to be constructed, while the slab is being formed. Once theslab 20 is formed and the wet concrete for forming the slab has hardened, the void forming system is superfluous and can be allowed to collapse, reducing the risk of swelling ground heaving the slab. - Prior to positioning the void forming system as shown in
FIG. 1 , a plurality of load bearing compression and tension piles 14 are driven, drilled, jacked, tied or otherwise fixed into the deeper soil or rock of high bearing capacity to provide stability to the structure which is to be built. Thepiles 14 may be in a variety of forms, such as screw piles which communicate directly with the load bearing ground beneath theground surface 22. Thepiles 14 perform in both tension and compression and are raised above the ground surface to a predetermined height. In this regard, the piles are arranged in a grid to form a consistent and level loading region above ground upon which to found the beams of the finished concrete slab. - The depth to which the
piles 14 are installed is determined in relation to where they will achieve the engineered and designed bearing capacity for the said building/construction. The installed height of eachpile 14 above ground will allow the end of thepiles 14 to penetrate to an engineered depth into the finished beams of the concrete slab above. Thepiles 14 are subsequently structurally connected to the concrete slab within the beam. It will be appreciated that the size and shape of the slab can be readily adapted to suit the size and shape of the building to be constructed. As such, the placement location and number ofpiles 14 utilised is variable, though based on the relevant modular system engineered design for that project. - Following the positioning of the
piles 14 in accordance with the design of the structure to be built,void forming elements 12 are positioned over and around thepiles 14. Thevoid forming elements 12 are in the form of elongate shallow members which may be designed to effectively absorb extreme ground movement in the short term, as well as allow thepiles 14 to pass therethrough. In the long term, thevoid forming elements 12 will disintegrate due to their construction from environmentally degradable material, as discussed in detail below. As thevoid forming elements 12 extend along thepiles 14, they are typically arranged in parallel rows in accordance with the specific design of the structure to be built. It will be appreciated that the arrangement as shown inFIGS. 1 to 3 represents a substantially rectangular footing wherein the piles are regularly spaced and positioned in rows and hence thevoid forming elements 12 extend in rows, however it will be appreciated that the footing structure may vary in accordance with the specific design of the building to be constructed. - Between each of the rows of shallow
void forming elements 12, there are provided spacervoid forming elements 16. The spacervoid forming elements 16 are in the form of elongate void former structures, which are also partially or fully formed of an environmentally degradable material and may also be deformable to accommodate short term movement of the ground surface. Over time, the spacervoid forming elements 16 will degrade, due to contact with moisture or soil, and collapse, leaving theconcrete slab 20 supported substantially entirely by thepiles 14. The spacervoid forming elements 16 extend between each of the shallowvoid forming elements 12, as shown, to provide an additional surface, elevated from the ground surface, offering a holistic void forming body upon which the concrete slab (platform regions and beams) can be placed. In this regard, the platform and beam regions of the concrete slab are supported upon the spacervoid forming elements 16 and the shallowvoid forming elements 12 and are suspended from the ground surface upon placement. - The
void forming elements slab 20 to become self-supporting varies based on a number of factors, including the nature of the concrete mix for forming the slab, the weather conditions and the slab design. Typically, however, the slab will be self-supporting in around 24 hours. In order to slow the degradation rate of the environmentally degradable material, a barrier, in the form of a plastic film, may be provided between thevoid forming elements slab 20 to inhibit passage of moisture from the slab, especially in the first 24 hours after it has been poured. In other embodiments, the barrier may take the form of a coating on the environmentally degradable material. Alternatively, or in addition, the thickness of the environmentally degradable material may be selected to provide the desired structural longevity. After the slab has sufficiently cured, the degradable material degrades into a biocompatible component of soil underneath the concrete slab. - It will be appreciated that prior to setting and positioning the
void forming system 10 ofFIG. 1 , the area upon which the void forming system is placed is prepared. Such preparation typically comprises excavating the site to form a level surface upon which the concrete is to be placed. Trenches can also be dug to position deep edge beams and the like to define the perimeter of the foundation to enable thepiles 14 to be positioned as discussed above. Thevoid forming elements FIG. 1 , for placement of the concrete. - The environmentally degradable material of the spacer
void forming elements 16 and the shallowvoid forming elements 12 can be readily shaped or cut to fit around plumbing pipes and the like, through the use of a hand or power saw. Generally, this may not be necessary as the spacervoid forming elements 16 and shallowvoid forming elements 12 can be custom made and delivered to the building site to suit the building plans provided. It will be appreciated that whilst thevoid forming elements void forming system 10 to perform its function, as will be appreciated below. - Prior to placement of the
concrete slab 20, reinforcing mesh and bar 18 (as shown inFIG. 2 ), and/or steel fibres, may be placed over thevoid forming elements slab 20. Such a mesh material may be particularly applicable if the concrete is to be poured over thevoid forming elements slab 20. As is clearly evident inFIG. 2 , theslab 20 is fully supported above the surface of thesoil 22 by thevoid forming elements slab 20 from theground soil 22. In this regard, following setting/positioning of theslab 20 and construction of a building over theslab 20, the slab is suspended above theground surface 22, with the load of the structure being supported by thepiles 14 which are in turn supported by the deeper soil or rock of high bearing capacity. It will be appreciated that in this arrangement, thepiles 14 have a direct/positive engagement with theslab 20 and the ground, thereby offering load bearing capacity for the concrete slab in both tension and compression. The engagement will typically be in the form of a wider portion located in the upper part of the pile such that the concrete formed over the pile surrounds and engages the wider portion and a narrower portion beneath it. Preferably, the wider portion comprises a rod or bar 15 extending horizontally through a hole in a vertical portion of the pile located above the lower extremity of the structural slab. Preferably also, the piles are located inbeam portions 13 of the structural slab and the rod orbar 15 extends longitudinally of the beam portions. -
FIG. 3 shows a plan view of onesuch slab arrangement 20 where the shallowvoid forming elements 12 are arranged to form two internal parallel beams which extend the length of theslab 20. Perimeter beams 24 are also formed by placement of shallowvoid forming elements 12 about the perimeter of the site such that the parallel beams work in conjunction with the perimeter beams 24 to form a grid arrangement upon which theslab 20 is supported, separate from the ground surface. It will be appreciated that the size and shape of theslab 20 can be readily adapted to suit the size and shape of the building to be constructed. As such, the void forming andsuspension system 10 is a modular arrangement that can be easily assembled to accommodate a variety of sized and shaped slabs. In this regard, a variety of sizes are provided in both thevoid forming elements piles 14 to accommodate varying depths of soil penetrated to achieve the appropriate bearing capacities required. - Referring to
FIG. 4 , one embodiment of the structure of the spacervoid forming element 16 is shown. Thevoid forming element 16 is in the form of a box-like element having four vertical side surfaces 26 and atop surface 28. Thesurfaces void forming element 16 are configured to interface with theconcrete slab 20 in the manner as shown inFIG. 2 . Theunderside 30 of thevoid forming element 16, namely the side which is supported on theground surface 22, is open thereby providing a cavity within thevoid forming element 16. The cavity is defined by the inner walls of thesurfaces FIG. 4 , represents a substantially rectangular space. - A plurality of
strut members 32 are provided within the cavity and extend from the inner surface of thetop surface 28 to theground surface 22 when thevoid forming element 16 is positioned thereon for use. Thestrut members 32 support thetop surface 28 of thevoid forming element 16 along its length such that thetop surface 28 is able to support the load of the reinforced concrete during placement of theslab 20, as well as the load of workers or machinery used during the placement process. In this regard, the shape of thestruts 32 and their location within the cavity defines the strength of the void forming element. It will be appreciated that the arrangement and shape of thestruts 32 can be altered in accordance to the specific construction. Such an arrangement ofstruts 32 provides structural integrity and enables thevoid forming elements structural slab 20. However this configuration of walls and individual struts also provides an ability to cope with any soil heave that may occur over time as the struts and walls will collapse under pressure such that movement is not transmitted to the slab. Moreover, thestrut members 32 may be formed from an environmentally degradable material, such that, like thevoid forming elements strut members 32 degrade over time. Again, thestrut members 32 may be shielded from moisture by a barrier such as a coating or plastic film, or be formed from an appropriate thickness of environmentally degradable material, in order to increase their structural longevity if required. Whilst not shown, it will be appreciated that the shallowvoid forming elements 12 may also be constructed in the same manner as the spacervoid forming element 16 ofFIG. 4 . - It will be appreciated that the structure and material of the
void forming elements void forming elements FIG. 2 , the soil is able to expand into the cavities remaining after degradation of thevoid forming elements 12, 16 (and thestruts 32 if formed from degradable material), where appropriate. In embodiments where thestruts 32 are not degradable, since thevoid forming elements struts 32 break away from the body of the degradedvoid forming elements - Referring to
FIGS. 5 and 6 , a more preferred embodiment of the structure of the spacervoid forming element 16 is shown in plan and elevation respectively. Thevoid forming element 16 in this embodiment is in the form of a box-like element having fourvertical side members top platform member 49 forming theconcrete supporting surface 48.Lower portions 46 of the side walls are corrugated and whileupper portions 47 of the side walls are corrugated on an inner surface and have the corrugations filled on the outer surface. Themembers void forming element 16 are configured to interface with theconcrete slab 20 in the manner as shown inFIG. 2 . As with the previously described embodiment, theunderside 30 of thevoid forming element 16, namely the side which is supported on theground surface 22, is open thereby providing a cavity within thevoid forming element 16. The cavity is defined by the inner surfaces walls of themembers FIGS. 5 and 6 , again represents a substantially rectangular space, although in this instance with corrugated walls. -
FIG. 7 show an elevation of an alternative version of the spacervoid forming element 16 having differing heights to that ofFIG. 6 . In other respects the embodiments shown in elevation inFIGS. 6 and 7 are similar to one another. - A plurality of
strut members 42 are provided within the cavity and extend from the inner surface of theplatform member 49 to theground surface 22 when thevoid forming element 16 is positioned thereon for use. Thestrut members 42 provide support for theplatform member 49 of thevoid forming element 16 along its length such that thetop surface 48 is able to support the load of the reinforced concrete during placement of theslab 20, as well as the load of workers or machinery used during the placement process. In this regard, the shape of thestruts 42 and their location within the cavity defines the strength of the void forming element. In theFIG. 5 embodiment the struts have a substantially rectangular cross section with two opposing concave sides. It will be appreciated that the arrangement and shape of thestruts 42 can be altered in accordance to the specific construction. -
FIG. 8 illustrates an embodiment of the structure of the shallowvoid forming element 12. The shallowvoid forming element 12 in this embodiment is also in the form of a box-like element having four vertical side members 56 (in this case not corrugated) and atop platform member 59 forming theconcrete supporting surface 58. The height of the shallowvoid forming element 12 is preferably the same as the height of the corrugatedlower portion 46 of the walls of the spacervoid forming element 16. Therefore the overall height of this shallowvoid forming element 12 is shorter than that of the spacervoid forming elements 16 to allow the formation of concrete beams between the spacervoid forming elements 16. Themembers void forming element 12 are also configured to interface with theconcrete slab 20 in the manner as shown inFIG. 2 . A singleinternal strut 52 is provided extending from the inner surface of theplatform member 59 to theground surface 22 when thevoid forming element 12 is positioned thereon for use and thestrut 52 divides the internal space of the shallow void forming element into twocavities 60. Each cavity is defined by the inner surfaces of walls of themembers strut 52, and in the embodiment as shown inFIG. 6 , again represents a substantially rectangular space. -
FIGS. 9 a and 9 b show an alternative embodiment of thevoid forming elements FIGS. 5-7 , where corresponding reference numerals indicate corresponding features with corresponding functionality. Thevoid forming elements FIGS. 9 a and 9 b include a thin-walled cellular base structure defined by a network ofcell walls 70 formed by thermoforming or vacuum forming A solid top 72 is provided over the cellular base structure to support the curingconcrete slab 20. The top 72 may or may not be formed from the environmentally degradable material. It will be appreciated that a smaller amount of environmentally degradable material is required to be used to form the void forming elements ofFIGS. 9 a and 9 b as compared to those ofFIGS. 5-7 , which facilitates cost savings. The thin-walled construction of the void forming elements ofFIGS. 9 a and 9 b may also assist in crumpling of thevoid forming elements FIG. 9 b, thevoid forming elements FIG. 9 a may be grouped together in abutting relationship to define a void form of a desired size for supporting a concrete slab during curing. -
FIGS. 10 a and 10 b show a further embodiment of thevoid forming elements FIGS. 5-7 . The embodiment ofFIGS. 10 a and 10 b has many features in common with the embodiment ofFIGS. 9 a and 9 b, where corresponding reference numerals indicate corresponding features with corresponding functionality. As with the void forming elements ofFIGS. 5-7 and 9 a and 9 b, thevoid forming elements FIGS. 10 a and 10 b are formed by injection moulding the environmentally degradable material. Void formingelements FIGS. 10 a and 10 b may be grouped together, as shown inFIG. 9 b, to define a void form of a desired size for supporting a concrete slab during curing. - In yet further embodiments (not shown), the
void forming elements void forming elements concrete slab 20. - In other embodiments, not shown, the void forming system is formed from a solid block of environmentally degradable material, which degrades over time due to contact with moisture and/or soil to leave a void into which swelling substrate ground can expand without heaving the
slab 20. - It will be appreciated that the system described in the embodiment above comprises a concrete slab supported on deep footings, typically screw piles, drilled piles and piles designed for compression and/or tension. The slab is designed to be suspended between the deep footings and the void forming elements allow concreting to be easily accomplished during construction and serves as a compressible/crushable/degradable zone during the life of the slab as the underlying soil expands.
- It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above described embodiments without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Claims (20)
1. An apparatus for creating a void beneath a structural concrete slab, comprising:
a body having a first surface adapted to support wet concrete for forming at least a portion of the concrete slab and a second surface adapted to contact a ground surface;
wherein the body is partly or fully formed of an environmentally degradable material, and wherein the environmentally degradable material retains sufficient structural strength to support the structural slab until the concrete has cured sufficiently to be self-supporting, but thereafter degrades to create a cavity into which swelling ground can expand.
2. An apparatus according to claim 1 , wherein the environmentally degradable material is adapted to be degraded by contact with water and/or soil.
3. An apparatus according to claim 1 , wherein the environmentally degradable material is a biodegradable polymer.
4. An apparatus according to claim 3 , wherein the environmentally degradable material is a thermoplastic starch polymer.
5. An apparatus according to claim 1 , wherein the environmentally degradable material is formed from one of: PLA, Mater-bi, Biograde, and a biodegradable polyester.
6. An apparatus according to claim 1 , comprising a barrier between the environmentally degradable material and the structural slab.
7. An apparatus according to claim 1 , wherein the barrier comprises a film of moisture inhibiting material or a moisture inhibiting coating on the environmentally degradable material.
8. An apparatus according to claim 1 , wherein the body has a thin-walled cellular structure.
9. An apparatus according to claim 1 , wherein the environmentally degradable material is adapted to retain sufficient structural strength to support the concrete slab for at least 12 hours.
10. An apparatus according to claim 9 , wherein the environmentally degradable material is adapted to retain sufficient structural strength to support the concrete slab for at least 24 hours.
11. An apparatus according to claim 1 , wherein the environmentally degradable material has a maximum tensile stress of between 10 MPa and 100 MPa.
12. An apparatus according to claim 1 , wherein, in a dry, undegraded, granular state, the environmentally degradable material has a Young's Modulus of between 500 MPa and 5000 MPa.
13. An apparatus according to claim 1 , wherein the degradable material is adapted to degrade into a biocompatible component of soil underneath the concrete slab.
14. A system for creating a suspended structural concrete slab, comprising:
at least one pile member, the or each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface and the second end arranged to extend to a position at or near said ground surface; and
at least one void forming element in the form of the apparatus of any one of the preceding claims, the or each void forming element being arranged to substantially cover a ground surface upon which the structural slab is to be placed and to define a surface onto which wet concrete for forming the structural slab is to be poured;
wherein said at least one pile member is adapted to support the structural slab above the ground surface such that said at least one void forming element is positioned between the structural slab and the ground surface.
15. A system according to claim 14 , wherein the at least one pile member is of a type selected from the group consisting of: a screw pile, a driven pile, and a bored pile.
16. A system according to claim 14 , wherein the at least one void forming element is arranged such that the second end of the at least one pile member extends therethrough.
17. A method of forming a suspended structural concrete slab, comprising:
installing at least one pile member, the or each pile member having a first end and a second end, the first end adapted to be embedded into a ground surface to be in contact with load bearing ground beneath said ground surface, and the second end arranged to extend to a position at or near said ground surface;
installing at least one void forming element in the form of the apparatus of claim 1 , the or each void forming element being arranged to substantially cover a ground surface upon which the structural slab is to be placed, the pile members extending above at least part of the surface formed by the at least one void forming element; and
pouring wet concrete to form the structural slab, whereby the structural slab is supported above the ground surface by the at least one pile member such that the at least one void forming element is positioned between the structural slab and the ground surface.
18. A method according to claim 17 , wherein the at least one pile member is a screw pier foundation pile.
19. A method according to claim 18 , wherein the second end of the at least one pile member is offset from the ground surface by a predetermined distance.
20. A method according to claim 19 , where more than one said pile member is employed, the pile members being arranged in a grid.
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AU2009905738A AU2009905738A0 (en) | 2009-11-23 | Environmentally degradable void former | |
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WO2016077890A1 (en) * | 2014-11-20 | 2016-05-26 | Knew Pod Systems Pty Ltd | A building element |
AU2014265077A1 (en) * | 2014-11-20 | 2016-06-09 | Knew Pod Systems Pty Ltd | A Building Element |
US9771728B2 (en) | 2012-05-23 | 2017-09-26 | Dennard Charles Gilpin | Device for forming a void in a concrete foundation |
US9803329B1 (en) | 2016-06-09 | 2017-10-31 | King Saud University | Expansive soil resistant foundation system |
CN109403524A (en) * | 2018-09-10 | 2019-03-01 | 湖南工业大学 | Honeycomb type hollow sandwich panel ceiling for storied building and production method equipped with U-shaped steel composite structure |
US20210317670A1 (en) * | 2020-04-14 | 2021-10-14 | Voidform Products, Inc. | Modular Void Form Structure |
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US8834072B1 (en) * | 2012-01-26 | 2014-09-16 | William T Donald | Method for forming suspended foundations |
US10000938B2 (en) | 2012-05-23 | 2018-06-19 | Dennard Charles Gilpin | Concrete void forming method and device |
US9771728B2 (en) | 2012-05-23 | 2017-09-26 | Dennard Charles Gilpin | Device for forming a void in a concrete foundation |
JP2016524060A (en) * | 2013-06-11 | 2016-08-12 | ファビオ・パロディFabio PARODI | Formwork whose thickness is reduced by the load of on-site cast slab |
WO2014200364A1 (en) * | 2013-06-11 | 2014-12-18 | Fabio Parodi | Formwork of reducing thickness due to loading of slab cast in-situ |
AU2014265077B2 (en) * | 2014-11-20 | 2017-03-02 | Knew Pod Systems Pty Ltd | A Building Element |
AU2015207927A1 (en) * | 2014-11-20 | 2016-06-09 | Knew Pod Systems Pty Ltd | A building element |
AU2015207927B2 (en) * | 2014-11-20 | 2017-03-02 | Knew Pod Systems Pty Ltd | A building element |
AU2014265077A1 (en) * | 2014-11-20 | 2016-06-09 | Knew Pod Systems Pty Ltd | A Building Element |
WO2016077890A1 (en) * | 2014-11-20 | 2016-05-26 | Knew Pod Systems Pty Ltd | A building element |
US9803329B1 (en) | 2016-06-09 | 2017-10-31 | King Saud University | Expansive soil resistant foundation system |
CN109403524A (en) * | 2018-09-10 | 2019-03-01 | 湖南工业大学 | Honeycomb type hollow sandwich panel ceiling for storied building and production method equipped with U-shaped steel composite structure |
US20210317670A1 (en) * | 2020-04-14 | 2021-10-14 | Voidform Products, Inc. | Modular Void Form Structure |
Also Published As
Publication number | Publication date |
---|---|
AU2010246376B2 (en) | 2014-07-24 |
AU2010246376A1 (en) | 2011-05-19 |
AU2011201876B2 (en) | 2014-07-31 |
NZ589460A (en) | 2012-06-29 |
AU2011201876A1 (en) | 2011-05-19 |
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