A void former for concrete slabs

Abstract

A void former for use in a concrete slab including a precast bottom plate. The void former comprises a first hollow body with enclosed sides of the same height, an enclosed top portion and an open bottom portion, with the internal surface of the top portion including a plurality of integral reinforcement ribs, a means for embedding and anchoring the first hollow body to the precast bottom plate, and a means for ensuring the first hollow body is seated level on the precast bottom plate. The means for embedding and anchoring the first hollow body in turn comprises a plurality of L-shaped legs which project downwards from the periphery of the open bottom portion, and the means for seating and levelling the first hollow body comprise a plurality of tabs which extend laterally from the enclosed sides around the periphery of the open bottom portion.

Description

[0001] A VOID FORMER FOR CONCRETE SLABS

[0002] FIELD OF THE INVENTION

[0003] This invention relates to the field of building construction, specifically a void former for use in the formation of construction elements such as concrete slabs.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of precast concrete slabs in the construction of the floors of a building is well-known in the field of building construction, as is the use of void formers to create voids within the slab to reduce the volume of concrete that needs to be poured during the casting process by some 20 to 30% which in turn reduces the weight and thus the cost of a slab, while still maintaining the structural strength of the slab.

[0006] Examples of the void formers (which is also referred to as a cavity former) which are already known are those disclosed in the documents WO 2017 / 095263 A2, WO 2005 / 108701 Al, AU 2018202136 Bl, AU 2019101738 B4 and AU 2021286454 Al.

[0007] WO 2017 / 095263 A2 relates to a permanent formwork void former comprising a hollow body provided with a spatial position fixing means and including conical supporting feet and at least one box-like member in the shape of a truncated pyramid, which is open at the large base end and has channels at the corners and stiffening ribs for reinforcing the top side.

[0008] WO 2005 / 108701 Al discloses a cavity former for forming one or more cavities in a concrete slab, and includes a hollow body about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity.

[0009] AU 2018202136 Bl relates to a shortenable void former for use in making ferroconcrete objects such as slab floors comprising a shaped body having a volume and usually an open base that is moulded plastic. AU 2019101738 B4 relates to a void forming module including at least one hollow body with at least one upper surface and a lower abutment perimeter, and at least one shaped support extending from the at least one upper surface and terminating at a level coplanar with the lower abutment perimeter.

[0010] AU 2021286454 Al relates to a void filling system for use in forming a concrete slab, comprising a hollow void former having a body comprising four side walls, a top wall and an open bottom, the void former configured to be separated into multiple hollow sections.

[0011] All of the above examples of void formers are made from a suitable plastic or a thermoplastic by injection moulding. Notably, all of these examples have elaborate multi-part structural features which are complex. Examples of the elaborate features are the internal legs or supports present in several of the previously described void formers which may be integral with or separately provided, continuous flanges, heavy internal ribbing and even mechanical features for aligning or locking multiple void formers placed adjacent each other.

[0012] While such structural features are undoubtedly useful, they are also conceivably more expensive to manufacture and in turn purchase, due to the higher cost associated with the tooling of the injection moulds by virtue of the elaborate mechanical design, the number of unique parts and greater amount of raw material used in their manufacture.

[0013] In view of the rising cost of building materials, it is desirable and an objective of the present invention to provide an alternative void former that is simpler, more material efficient to manufacture and thus more cost-effective without compromising the structural strength of the concrete slab.

[0014] SUMMARY OF THE INVENTION

[0015] In a first aspect, the invention provides a void former for use in a concrete slab including a precast bottom plate.

[0016] The void former comprises a first hollow body with enclosed sides of the same height, an enclosed top portion and an open bottom portion, wherein the internal surface of the top portion includes a plurality of integral reinforcement ribs, a means for embedding and anchoring the first hollow body to the pre-cast bottom plate of the concrete slab, and a means for ensuring the first hollow body is seated level on the pre-cast bottom plate of the concrete slab.

[0017] The means for embedding and anchoring the first hollow body comprises a plurality of L-shaped legs which project downwards from the periphery of the open bottom portion.

[0018] The means for seating and levelling the first hollow body comprises a plurality of tabs which extend laterally from the enclosed sides around the periphery of the open bottom portion.

[0019] In the void former according to the first aspect of the invention, the enclosed sides have a thickness of 2.0 mm + / - 0.1 mm.

[0020] In the void former according to the first aspect of the invention, the L-shaped legs preferably have a length of 20.0 mm.

[0021] Alternatively, the plurality of L-shaped legs are preferably integral to the first hollow body.

[0022] As a further alternative, the plurality of tabs are also preferably integral to the first hollow body.

[0023] In the void former according to the first aspect of the invention, the enclosed top portion of the first hollow body preferably has an external surface with edges that are filleted / rounded / curved.

[0024] In the void former according to the first aspect of the invention, the first hollow body preferably has a square frustum shape with the enclosed sides converging upwards or inclined relative to the open bottom portion.

[0025] Alternatively, the enclosed sides of the first hollow body converge or are inclined at an angle of 106.05° relative to the open bottom portion.

[0026] In the void former according to the first aspect of the invention, the first hollow body is preferably made from a polymeric material. As an alternative, the polymeric material used may be recycled polypropylene.

[0027] In the void former according to the first aspect of the invention, the enclosed top portion of the first hollow body is capable of receiving a second hollow body with enclosed sides, an enclosed top portion and an open bottom portion which corresponds to the enclosed top portion of the first hollow body, for extending the height of the void former.

[0028] In the void former according to first aspect of the invention, the plurality of integral reinforcement ribs preferably comprise a longitudinal reinforcement rib and a latitudinal reinforcement rib which intersect in the centre of the internal surface of the enclosed top portion of the first hollow body.

[0029] In the void former according to the first aspect of the invention, the second hollow body is preferably made from a polymeric material.

[0030] Alternatively, the polymeric material may be recycled polypropylene.

[0031] In a second aspect, the invention provides a precast concrete bottom plate with an upper surface and a lower surface, longitudinal and latitudinal edges and having a thickness in the range of 50 to 100 mm.

[0032] The precast concrete bottom plate comprises a first reinforcement mesh that is embedded within the bottom plate, a plurality of lattice girders along the longitudinal length of the bottom plate with the lower chords of each lattice girder attached to the reinforcement mesh and embedded within the bottom plate and the upper chord protruding from the upper surface of the bottom plate, a plurality of L-shaped dowels with one end attached to the reinforcement mesh and embedded within the bottom plate and another end protruding from the longitudinal edges of the bottom plate, and a plurality of the void former according to the first aspect of the invention embedded and anchored on to the upper surface of the bottom plate.

[0033] In the precast concrete bottom plate according to the second aspect of the invention, the plurality of void formers embedded and anchored on to the upper surface of the bottom plate are preferably positioned on either side of each lattice girder along the longitudinal length of the bottom plate. Additionally, the precast concrete bottom plate according to the second aspect of the invention may include one or more post-tensioning ducts positioned longitudinally and latitudinally along the length and width of the upper surface of the concrete bottom plate.

[0034] The precast concrete bottom plate according to the second aspect of the invention may form part of a concrete slab which also comprises a second reinforcement mesh seated on top of the bottom plate and is attached to the upper chord of the plurality of lattice girders protruding from the upper surface of the bottom plate, and a concrete top layer cast over the steel reinforcement mesh and the bottom plate.

[0035] The use of the void former according to the first aspect of the invention in a precast concrete bottom plate according to the second of the invention for use in the fabrication of concrete slabs alleviate the problem of the increasing cost of construction materials without sacrificing structural strength and integrity.

[0036] DESCRIPTION OF THE DRAWINGS

[0037] The invention is illustrated, though not limited by the following description of the embodiments that is being given by way of example only, with reference to the accompanying drawings in which:

[0038] Figure 1A illustrates in the perspective view the void former for use in a concrete slab according to the first aspect of the invention.

[0039] Figure IB illustrates in the plan view the void former for use in a concrete slab according to the first aspect of the invention.

[0040] Figure 1C illustrates a sectional view of the void former for use in a concrete slab according to the first aspect of the invention taken along line A-A of the plan view.

[0041] Figure ID illustrates another sectional view of the void former for use in a concrete slab according to the first aspect of the invention taken along line B-B of the plan view. Figure 2A illustrates in the perspective view the height extender for the void former for use in a concrete slab according to the first aspect of the invention.

[0042] Figure 2B illustrates in the plan view the height extender for the void former for use in a concrete slab according to the first aspect of the invention.

[0043] Figure 2C illustrates in the side view the height extender for the void former for use in a concrete slab according to the first aspect of the invention.

[0044] Figure 2D illustrates a sectional view of the height extender for the void former for use in a concrete slab according to the first aspect of the invention taken along line A-A of the plan view.

[0045] Figure 3A illustrates in the perspective view the height extender of Figures 2A to 2D in use with the void former for use in a concrete slab according to the first aspect of the invention.

[0046] Figure 3B illustrates in the plan view the height extender of Figure 2A to 2D in use with the void former for use in a concrete slab according to the first aspect of the invention.

[0047] Figure 3C illustrates a sectional view of the height extender of Figure 2A to 2D in use with the void former for use in a concrete slab according to the first aspect of the invention taken along line A-A of the plan view.

[0048] Figure 3D illustrates a sectional view of the height extender of Figure 2A to 2D in use with the void former for use in a concrete slab according to the first aspect of the invention taken along line B-B of the plan view.

[0049] Figure 4A illustrates in the perspective view, a precast concrete bottom plate with a plurality of the void former according to the first aspect of the invention on its upper surface.

[0050] Figure 4B illustrates in exploded view format, the perspective view of the precast concrete bottom plate illustrated in Figure 4A. Figure 5 illustrates in the perspective view, a cast concrete slab with a plurality of the void former according to the first aspect of the invention on its upper surface of the precast concrete bottom plate.

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] Figures 1A to ID illustrate a void former 1 for use in a concrete slab according to the first aspect of the invention, in the perspective view, plan view and sectional views.

[0053] The void former comprises a first hollow body 10 with enclosed sides 11 of the same height, an enclosed top portion 12 and an open bottom portion 13, a means for embedding and anchoring the first hollow body 10 to the precast bottom plate of the concrete slab and a means for ensuring the first hollow body 10 is seated level on the precast bottom plate of the concrete slab.

[0054] The enclosed sides 11 have a thickness of 2.0 mm with a tolerance of + / - 0.1 mm which is sufficiently thin to give the first hollow body a degree of flexibility and to allow for coring works to be easily carried out on the concrete slab to facilitate the installation of conduits, plumbing, electrical ducting and the like.

[0055] The means for embedding and anchoring the first hollow body 10 is in turn comprised of a plurality of L-shaped legs 14 that project downwards from the periphery of the open bottom portion 13 of the first hollow body 10.

[0056] The purpose of the plurality of L-shaped legs 14 is to embed and anchor the first hollow body 10 to the upper surface of a precast concrete bottom plate, so that the void former 1 is able to support a load without deforming or cracking after it has been embedded on a concrete bottom plate.

[0057] This is accomplished by the fact that when each L-shaped leg 14 is embedded in and anchored to the precast concrete bottom plate, a resistive force will exist between the L-shaped legs 14 and the surrounding concrete after the concrete has cured. When there is a point load on the slab, the force exerted downwards will be distributed and spread over the entire surface of the enclosed sides 11 and the enclosed top portion 12 of the first hollow body 10. The force exerted downwards creates a resultant force which is then counteracted by the resistive force that exists between the L-shaped legs 14 and the surrounding concrete. This is similar to how a simple arch bridge supports a load. A simple arch bridge is anchored at each end of the span which are connected to one another by an arch rib, and when there is a load across the span of a simple arch bridge, the effect of the load is transferred to and distributed to the arch ribs. In the void former according to the first aspect of the invention, the enclosed sides 11 and the enclosed top portion 12 of the first hollow body 10 taken in combination are the equivalent of an arch rib of a simple arch bridge, while the L-shaped legs 14 is the equivalent of an anchoring point at both ends of the arch rib.

[0058] Since a precast concrete bottom plate generally has a thickness of between 50 mm to 100 mm depending on the structural requirement of a construction project, the length of the L-shaped leg in the void former according to the first aspect of the invention is preferably 20 mm.

[0059] In Figures 1A and IB, the void former 1 is illustrated as having an L-shaped leg 14 at each corner of the first hollow body 10 and another L-shaped leg 14 in the middle of each enclosed side 11, which in essence means that the L-shaped legs 14 are spaced apart at uniform intervals. The number of L-shaped legs 14 incorporated is more a function of cost and the invention is by no means limited to the configuration shown and described here. For example, it is possible to include more L-shaped legs which are spaced apart at different intervals without impacting the effectiveness of the invention.

[0060] Finally, the means for seating and levelling the first hollow body 10 on the bottom plate of the concrete slab comprises of a plurality of tabs 15 that protrude or extend laterally from the enclosed sides 11 around the periphery of the open bottom portion 13 to the first hollow body 10.

[0061] The purpose of the plurality of tabs 15 is to ensure that a first hollow body 10 embedded on the upper surface of a precast concrete bottom plate is kept level with the upper surface of the bottom plate, by serving as a visual indicator. Once the first hollow body 10 is embedded on the upper surface of the precast concrete bottom plate, as long as the plurality of tabs 15 are visible, it means that the first hollow body 10 is in fact level with the upper surface of the precast concrete bottom plate. Typically, the objective is to ensure the thickness of the concrete top layer that is cast over the enclosed top portion of a void former is 75 mm. A concrete top layer with a thickness of 75 mm will suffice to withstand the punching sheer resulting from a point load acting on the concrete slab, such as the tyre of a vehicle parked on the concrete slab. Therefore, any void formers which are unevenly embedded will result in the thickness of the top layer being inconsistent, hence the need to ensure that the void formers are embedded level on the precast concrete bottom plate.

[0062] By ensuring that each of the plurality of void formers are embedded level on the upper surface of the precast concrete bottom plate, the plurality of levelling tabs 15 provides a simple solution to the problem of ensuring that the freshly poured concrete on the precast concrete bottom plate sets with an even thickness, simply by visual observation and without requiring any specialized tools and jigs.

[0063] The advantage of using a plurality of levelling tabs 15 as opposed to a continuous flange around the periphery of the open bottom portion 13, is that the plurality of levelling tabs 15 are still able to provide the same effect as a continuous flange while having the advantage of being more material efficient and cheaper to tool.

[0064] In Figures 1A and IB, the void former 1 is illustrated as having a levelling tab 15 between each pair of L-shaped legs 14. The number of levelling tabs 15 incorporated is a function of cost and the invention is by no means limited to the configuration of levelling tabs shown and described here. For example, it is possible to include more levelling tabs that are spaced apart at different intervals without impacting the effectiveness of the invention.

[0065] The void former 1 according to the first aspect of the invention is manufactured by injection moulding, with the plurality of L-shaped legs 14 and plurality of levelling tabs 15 being formed integrally with the first hollow body 10 during manufacture.

[0066] However, the invention is not limited to this configuration, and it is conceivable that the first hollow body 10 could be manufactured without the plurality of L-shaped legs 14 and / or the plurality of tabs 15. The L-shaped legs 14 and levelling tabs 15 may in fact be manufactured as separate pieces that are attached to the first hollow body 10 by means of mounting clips or slots. This allows L-shaped legs and levelling tabs of different lengths to be incorporated should there be a need for such.

[0067] As shown in Figures 1A to ID, the first hollow body 10 has a square frustum shape with the enclosed sides 11 converging upwards or inclined relative to the open bottom portion 13. The enclosed sides 11 of the first hollow body 10 are inclined specifically at an angle of 106.2° relative to the open bottom portion 13, to enable the void former 1 according to the first aspect of the invention to support a point load of 100 kg without deformation or cracking by ensuring that the resultant force of a given point load that is pressing downwards on the enclosed top portion 12 of the first hollow body 10 does not exceed the resistance force acting on the L-shaped legs 14 when the void former 1 is embedded in a precast concrete bottom plate.

[0068] The enclosed top portion 12 of the first hollow body 10 has an external surface with edges that are filleted (i.e., rounded or curved) to aid in the flow of freshly poured concrete during the casting of the top layer of a concrete slab. The filleted edge of the external surface also enables a plurality of the void former 1 to be easily stacked up to save space during transportation or storage, since the first hollow body 10 is able to receive through its open bottom portion 13 another identical first hollow body 10.

[0069] As can be seen in the sectional views of the void former 1 in Figures 1C and ID, the internal surface of the top portion 12 of the first hollow body 10 includes an integral longitudinal reinforcement rib 16 and an integral latitudinal reinforcement rib 17 which intersect on the centre of the internal surface of the enclosed top portion to increase the stiffness of the enclosed top portion 12 which will eventually have to bear the weight of the top layer of a concrete slab, and thereafter the weight of any human or vehicle traffic when the construction is completed.

[0070] Since the void former 1 according to the first aspect of the invention is manufactured by injection moulding, the longitudinal reinforcement rib 16 is formed as an integral structure on the internal surface of the top portion 12 of the first hollow body 10.

[0071] Although the void former 1 of the first aspect of the invention is shown in Figures 1A to ID and also described here as having a single longitudinal reinforcement rib 16 and a single latitudinal reinforcement rib 17, the invention is clearly not limited to such a configuration. It is conceivable that additional longitudinal and / or latitudinal reinforcement ribs may be incorporated in a further embodiment of the invention to increase the stiffness of the first hollow body 10, and thus its load bearing capacity.

[0072] As an example, the first hollow body 10 of the void former 1 according to the first aspect of the invention having a square frustum shape preferably has an enclosed top portion 12 with an area of 0.4 m x 0.4 m and an open bottom portion 13 with a 'footprint' of 0.47 m x 0.47 m.

[0073] The void former 1 according to the first aspect of the invention is made from a polymeric material that is well suited for injection moulding. An example of a suitable polymeric material would be polypropylene (PP), and as an economy and ecological measure, recycled polypropylene may be used due to its widespread usage for disposable containers, bottles and packaging material.

[0074] The suitability of the use of recycled polypropylene is by virtue of its mechanical properties, specifically a tensile strength at break of 18 MPa, at 23 °C, which means that it has the ability to withstand a maximum tensile or compressive load of 18 MPa (which equals to 18 N / mm2) before it deforms and breaks.

[0075] For a concrete slab with a concrete top layer having a thickness of 75 mm utilising the hollow body 10 having an open bottom portion 13 with a 'footprint' of 0.47 m x 0.47 m and enclosed sides 11 inclined at angle of 106.2° relative to the open bottom portion 13, based on the assumption that concrete has an average density of 2,500 kg / m3, the downward force, F acting on the first hollow body 10 is calculated as below.

[0076] F = 0.075 x 0.47 x 0.47 x 2500 = 0.414 kN

[0077] The resultant, Ri of the downward force, F acting on the first hollow body 10 is calculated as below.

[0078] Ri = 0.414 cosine 16.05° = 0.40 kN Since the tensile strength at break for polypropylene is 18 N / mm2, the resistance by each L- shaped leg 14 assuming a length of 20 mm and a width of 25 mm is calculated as below.

[0079] 18 N / mm2x 20 mm x 25 mm = 9.0 kN

[0080] This is greater than the resultant force, Ri of 0.40 kN and validates the ability of the first hollow body 10 to withstand the weight of a 75 mm thick layer of concrete by virtue of the resistance of each L-shaped leg 14 anchored onto the bottom plate of the concrete slab.

[0081] The void former 1, as illustrated in Figures 1A and IB and described here, comprises a total of 8 L-shaped legs which will suffice to bear a 6,000 kg load (such as a vehicle parked on the concrete slab) which will exert a downward force of 60 kN. This downward force when distributed over the 8 L-shaped legs equates to each L-shaped leg bearing a load of 7.5 kN, and the resultant, Fb of the downward force acting on the hollow body is calculated as follows.

[0082] Fb = 7.5 cosine 16.05° = 7.1 kN

[0083] This clearly does not exceed the resistance by each L-shaped leg which was previously calculated as 9.0 kN, thus, validating the hollow body's ability to withstand a 6,000 kg load.

[0084] Since it is envisaged that the void former 1 according to the aspect of the invention will be manufactured in a solitary and standard size as an economy measure, should a construction work require thicker concrete slabs which in turn require taller cavities to be formed within the slab, the height of the void former according to the first aspect of the invention may be easily increased by means of a height extender 2.

[0085] Figure 2A illustrates in the perspective view the height extender 2 for the void former 1 for use in a concrete slab according to the first aspect of the invention.

[0086] The height extender 2 comprises a second hollow body 20 with enclosed sides 21, an enclosed top portion 22 and an open bottom portion 23, with the shape and dimensions of the open bottom portion 23 of the second hollow body 20 corresponding to the shape and dimension of the enclosed top portion 22 of the first hollow body 20 so that it is capable of being received over the enclosed top portion 22 of the first hollow body 20.

[0087] As with the void former 1 according to the first aspect of the invention, the enclosed sides 21 also have a thickness of 2.0 mm with a tolerance of + / - 0.1 mm.

[0088] In order for the height extender 2 to correspond to and be capable of being received by the void former 1, the height extender 2 also has a square frustrum shape with the enclosed sides 21 of the height extender 2 also being inclined at an angle of 106.2° relative to the open bottom portion 23.

[0089] As with the void former 1 according to the first aspect of the invention, the enclosed top portion 22 of the second hollow body 20 also has an external surface with edges that are filleted to aid in the flow of freshly poured concrete during the casting of the top layer of a concrete slab. The filleted edges of the external surface also enables a plurality of the height extender 2 to be stacked up for transportation or storage, since the second hollow body 20 is able to receive another identical second hollow body 20 through its open bottom portion 23.

[0090] Similarly, the height extender 2 is also made by injection moulding from a polymeric material such as polypropylene. Consequently, the height extender may also be made from recycled polypropylene.

[0091] Figures 3A to 3D illustrate how the height extender 2 is used with the void former 1 according to the first aspect of the invention.

[0092] The height extender 2 is simply stacked on top of the void former 1 according to the first aspect of the invention as shown in Figures 3A to 3D. Since the shape and dimensions of the open bottom portion 23 of the second hollow body 2 correspond to the shape and dimensions of the enclosed top portion 12 of the first hollow body 10, the second hollow body 20 will be firmly seated on top of the first hollow body 20, thus extending the height of the void former 1.

[0093] Since the enclosed sides 11 of the first hollow body 10 and the enclosed sides 21 the second hollow body 20 are both inclined at the same angle (i.e., 106.2° relative to their respective open bottom portions), when the height extender 2 is stacked on the void former 1, the enclosed sides of the combined structure form a continuous and uninterrupted surface as can be seen in Figures 3A to 3D.

[0094] While the void former 1 and its height extender 2 are both shown and described here as having a square frustum shape, the present invention is certainly not limited to only this shape. The void former 1 and its height extender 2 may have a circular frustum shape in another embodiment of the invention, so long as the enclosed sides are inclined at the angle of 106.2° relative to their open bottom portions.

[0095] The void former 1 according to a first aspect of the invention (and its height extender 2, where required), are utilized in the fabrication of concrete slabs which essentially comprises a precast concrete bottom plate and a layer of reinforcement mesh, upon which a concrete top layer is poured and formed. The void former 1 and its height extender 2 are introduced during the fabrication of the concrete slab and is a component of the precast concrete bottom plate.

[0096] Figure 4A illustrates a precast concrete bottom plate 4 according to a second aspect of the invention that makes use of the void former 1 according to the first aspect of the invention, in the perspective view. Figure 4B is an exploded view of the precast concrete bottom plate 4 of Figure 4A which more clearly shows the individual components which the precast concrete bottom plate comprises of.

[0097] The precast concrete bottom plate 4 according to the second aspect of the invention is essentially a conventional concrete bottom plate 40 which includes an upper surface 40a, a lower surface 40b, longitudinal edges 40c and latitudinal edges 40d and may be fabricated with a thickness of 50 to 100 mm depending on the user's requirement.

[0098] The precast concrete bottom plate 4 according to the second aspect of the invention comprises the following components: i) a reinforcement mesh 41 that is embedded within the bottom plate 40, ii) a plurality of lattice girders 42 positioned along the longitudinal length of the bottom plate 40 with the lower chords of each lattice girder attached to the reinforcement mesh 41 and embedded within the bottom plate 40 and the upper chord protruding from the upper surface 40a of the bottom plate 40, iii) a plurality of L-shaped dowels 43 which function as shear connectors with one end attached to the reinforcement mesh 41 and embedded within the concrete bottom plate 40 and another end protruding from the longitudinal edges 40c of the bottom plate 40, and iv) a plurality of the void former 1 according to the first aspect of the invention that are embedded and anchored on to the upper surface 40a of the concrete bottom plate 40.

[0099] Additionally, the precast concrete bottom plate 4 may include post-tensioning if required. This is accomplished through the inclusion of post-tensioning ducts 44a, 44b which are positioned longitudinally and latitudinally along the length and width of the upper surface of the concrete bottom plate 40.

[0100] During the fabrication of the precast concrete bottom plate 4, the reinforcement mesh 41, plurality of lattice girders 42 and plurality of L-shaped dowels 43 are welded together to form the internal structure of the precast concrete bottom plate 40 before concrete is poured.

[0101] Thereafter, the plurality of void formers 1 according to the first aspect of the invention are anchored to the reinforcement mesh 41 and embedded on the upper surface 40a of the concrete bottom plate 40 before the concrete sets. The plurality of levelling tabs 15 on each void former 1 serves as a visual indicator to ensure that each void former 1 has in fact been embedded at the same level on the upper surface 40a of the concrete bottom plate 40.

[0102] In the event a concrete slab of greater thickness is required, a height extender may be utilized with the void former to form taller cavities.

[0103] The plurality of void formers are positioned in a matrix or array dictated by the positions of the plurality of lattice girders 42 to ensure that the cavity formed by each void former are evenly distributed and / or spaced apart.

[0104] Should post-tensioning be required, a plurality of post-tensioning ducts 44a, 44b may then be anchored on the upper surface 40a of the pre-cast concrete bottom plate 40, longitudinally and latitudinally along the length and width of the upper surface of the concrete bottom plate 40, between the rows and columns of the array of void formers 1.

[0105] Figure 5 illustrates a perspective view of a concrete slab (5) fabricated from the precast concrete bottom plate 4 according to the second aspect of the invention.

[0106] The concrete slab 5 essentially comprises: i) a precast concrete bottom plate 4 according to the second aspect of the invention, ii) a second reinforcement mesh 45 that is seated on top of the precast concrete bottom plate 4, and iii) a concrete top layer 51 of the desired thickness that is cast over the steel reinforcement mesh 45 and the precast concrete bottom plate 4.

[0107] The second reinforcement mesh 45 is attached to the upper chord of the lattice girders 42 which protrudes from the upper surface 40a of the pre-cast concrete bottom plate 40 and will eventually be embedded in the concrete top layer 51 when the concrete to form the top layer 51 is poured over the precast concrete bottom plate 4 and second reinforcement mesh 45 according to the required thickness.

[0108] As can be seen from the foregoing, the present invention provides an effective solution to the rising cost of construction materials by way of a void former that is simple in design and material efficient, while maintaining good structural strength and possessing features which aid in the fabrication of concrete slabs of consistent thicknesses.

[0109] The present invention is not limited to what has been disclosed here, as the description serves only to exemplify the invention and further modifications are readily apparent without departing from the scope of the invention.

Claims

CLAIMS1. A void former (1) for use in a concrete slab including a precast bottom plate, said void former comprising: a first hollow body (10) with enclosed sides (11) of the same height, an enclosed top portion (12) and an open bottom portion (13), wherein the internal surface of the enclosed top portion includes a plurality of integral reinforcement ribs (16, 17), a means for embedding and anchoring the first hollow body (10) to the precast bottom plate of the concrete slab, and a means for ensuring the first hollow body (10) is seated level on the precast bottom plate of the concrete slab, characterized in that the means for embedding and anchoring the first hollow body (10) comprise a plurality of L-shaped legs (14) which project downwards from the periphery of the open bottom portion (13), and the means for seating and levelling the first hollow body (10) comprise a plurality of tabs (15) which extend laterally from the enclosed sides around the periphery of the open bottom portion (13).

2. The void former (1) according to claim 1, wherein the enclosed sides have a thickness of 2.0 mm + / - 0.1 mm.

3. The void former (1) according to claim 1 or claim 2, wherein the L-shaped legs (14) have a length of 20.0 mm.

4. The void former (1) according to any preceding claim, wherein the plurality of L-shaped legs (14) are integral to the first hollow body (10).

5. The void former (1) according to any preceding claim, wherein the plurality of tabs (15) are integral to the first hollow body (10).

6. The void former (1) according to any preceding claim, wherein the enclosed top portion (12) of the first hollow body (10) has an external surface with edges that are filleted / rounded / curved.

7. The void former (1) according to any of the preceding claims, wherein the first hollow body (10) has a square frustum shape with the enclosed sides (11) converging upwards or inclined relative to the open bottom portion (13).

8. The void former (1) according to claim 6, wherein the enclosed sides (11) of the first hollow body (10) converge or are inclined at an angle of 106.05° relative to the open bottom portion (13).

9. The void former according to any of the preceding claims, wherein the plurality of integral reinforcement ribs comprise a longitudinal reinforcement rib (16) and a latitudinal reinforcement rib (17) which intersect in the centre of the internal surface of the enclosed top portion (12) of the first hollow body (10).

10. The void former (1) according to any of the preceding claims, wherein the first hollow body (10) is made from a polymeric material.

11. The void former (1) according to claim 9, wherein the polymeric material is recycled polypropylene.

12. The void former (1) according to any of the preceding claims, wherein the enclosed top portion (12) of the first hollow body (10) is capable of receiving a second hollow body (20) with enclosed sides (21), an enclosed top portion (22) and an open bottom portion (23) which corresponds to the enclosed top portion (12) of the first hollow body (10), for extending the height of the void former.

13. The void former (1) according to claim 12, wherein the second hollow body (20) is made from a polymeric material.

14. The void former (1) according to claim 13, wherein the polymeric material is recycled polypropylene.

15. A precast concrete bottom plate (4) with an upper surface (40a) and a lower surface (40b), longitudinal edges (40c) and latitudinal edges (40d) and having a thickness in the range of 50 to 100 mm, wherein the pre-cast concrete bottom plate comprises: a first reinforcement mesh (41) embedded within the bottom plate (40); a plurality of lattice girders (42) along the longitudinal length of the bottom plate (40) with the lower chords of each lattice girder attached to the reinforcement mesh (41) and embedded within the bottom plate and the upper chord protruding from the upper surface of the bottom plate; a plurality of L-shaped dowels / shear connectors (43) with one end attached to the reinforcement mesh (41) and embedded within the bottom plate (40) and another end protruding from the longitudinal edges (40c) of the bottom plate; and a plurality of the void former (1) according to any of claims 1 to 14 are anchored to the reinforcement mesh 41 and embedded on the upper surface (40a) of the bottom plate (40).

16. The precast concrete bottom plate (4) according to claim 15, wherein the plurality of void formers (10) embedded and anchored on to the upper surface (40a) of the bottom plate (40) are positioned on either side of each lattice girder (42) along the longitudinal length of the bottom plate (40).

17. The precast concrete bottom plate (4) according to claim 15 or claim 16, wherein one or more post-tensioning ducts (44a, 44b) positioned longitudinally and latitudinally is included along the length and width of the upper surface (40a) of the bottom plate (40).

18. A concrete slab (5) comprising: a precast concrete bottom plate (4) according to any of claims 15 to 17; a second reinforcement mesh (45) seated on top of the concrete bottom plate (4) and attached to the upper chord of the plurality of lattice girders (42) protruding from the upper surface (40a) of the bottom plate (40); and a concrete top layer (51) cast over the steel reinforcement mesh (45) and the precast concrete bottom plate (4).

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