AU2017202029A1 - Improvements in concrete slab construction - Google Patents

Abstract

Disclosed is an apparatus (10, 10', 10", 10"') for forming an underside of a concrete slab (100), including beam portions (100b) of the slab and the underside of a main portion (100a) of the slab. The apparatus comprises a top (12) for forming the underside of the main portion (100a) of the slab, sidewalls (14) extending downwardly and outwardly from the top for forming the beam portions (100b) of the slab, and a base (15) at an opposite end of the sidewalls to the top, the base being adapted for bearing on a substrate (200) on which the concrete slab is to be formed. The apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 20mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: (i) the space between the adjoining sidewalls at a distance of 100mm above the base is greater than or equal to the space between the adjoining sidewalls at a distance of 30mm above the base, and (ii) the space between the adjoining sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base.

Description

"Improvements in concrete slab construction"

Cross-Reference to Related Applications [0001] The present application claims priority from Australian Patent Application No 2016901153 filed on 29 March 2016, the content of which is incorporated herein by reference.

Technical Field [0001] The present disclosure relates to improvements in concrete slab construction and, more particularly, to a forming apparatus for concrete ground slabs, along with a system utilising the forming apparatus. A method of forming concrete ground slabs is also disclosed, as is a concrete ground slab. The forming apparatus, system, method and concrete ground slab have been developed primarily for use on reactive soils and will be described hereinafter with reference to this application. However, the forming apparatus, system, method and concrete ground slab may also be employed on non-reactive soils.

Background [0002] When a concrete slab is in contact with the ground, it can be subjected to extremely high uplift forces as a result of ground heave. The problem of ground heave is particularly prevalent in areas of highly reactive soil, where the soil volume changes significantly between periods of wet and dry weather.

[0003] Known systems for forming concrete ground slabs seek to resist extremely high uplift forces by providing additional beams underneath the slab and/or increasing beam depth to increase the structural capacity of the slab. Typically, known slabs are provided with rectangular beams that are in direct contact with the substrate. In areas of higher soil reactivity, the spacing of the beams must be reduced and the depth and size of steel reinforcement of the beams must also be increased, resulting in significantly increased slab costs.

[0004] Several methods are conventionally used for forming the beams underneath ground slabs. One of the methods involves excavating trenches for forming the beams prior to pouring the slab. Another method involves placing rectangular blocks of polystyrene or other material (often referred to as “waffle pods”) over the substrate, leaving spaces between the blocks at positions where the beams are to be formed, and pouring the slab over the blocks. The waffle pod method is often preferred as it avoids the need for trench excavation, which can be expensive and time consuming. However, both methods suffer from the problem that the entire underside of the slab and beams is in contact with the substrate, thereby exposing the slab and beams to extremely high uplift forces in situations of ground heave.

[0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification 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 disclosure as it existed before the priority date of each claim of this application.

Summary [0006] 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.

[0007] Throughout this document, unless the context clearly implies otherwise, the term “form” is to be taken to mean a “support or mould”, as in terms of a concrete form, and the term “forming” is to be similarly construed unless the context clearly implies otherwise.

[0008] In a first aspect, there is provided an apparatus for forming an underside of a concrete slab, including beam portions of the slab and the underside of a main portion of the slab, the apparatus comprising: a top for forming the underside of the main portion of the slab; sidewalls extending downwardly and outwardly from the top for forming the beam portions of the slab; and a base at an opposite end of the sidewalls to the top, the base being adapted for bearing on a substrate on which the concrete slab is to be formed, wherein the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 20mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the adjoining sidewalls at a distance of 100mm and/or 200mm above the base is greater than or equal to the space between the adjoining sidewalls at a distance of 30mm above the base, and the space between the adjoining sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base.

[0009] In an embodiment, the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 30mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the sidewalls at a distance of 100mm and/or 200mm above the base is greater than or equal to the space between the sidewalls at a distance of 30mm above the base, and the space between the sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base, such as being a space of between around 20mm and around 70mm, or of around 50mm.

[0010] In embodiments, the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 30mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the sidewalls at a distance of 100mm above the base is less than 200mm or less than 150mm or less than 100mm or less than 90mm or less than 80mm or less than 70mm, but greater than or equal to the space between the sidewalls at a distance of 30mm above the base, and the space between the sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base, such as being a space of between around 20mm and around 70mm, or of around 50mm.

[0011] In embodiments, the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 30mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the sidewalls at a distance of 200mm above the base is less than 400mm or less than 300mm or less than 200mm or less than 150mm or less than 100mm or less than 90mm, but greater than or equal to the space between the sidewalls at a distance of 30mm above the base, and the space between the sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base, such as being a space of between around 20mm and around 70mm, or of around 50mm.

[0012] In embodiments, the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 40mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base, such as with a space of between around 50mm and 60mm or of around 55mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the sidewalls at a distance of 100mm above the base is less than 200mm or less than 150mm or less than 100mm or less than 90mm or less than 80mm or less than 70mm, but greater than or equal to the space between the sidewalls at a distance of 30mm above the base, and the space between the sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base, such as being a space of between around 20mm and around 70mm, or of around 50mm.

[0013] In embodiments, the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 30mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base, such as with a space of between around 50mm and 60mm or of around 55mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the sidewalls at a distance of 200mm above the base is less than 400mm or less than 300mm or less than 200mm or less than 150mm or less than 100mm or less than 90mm, but greater than or equal to the space between the sidewalls at a distance of 30mm above the base, and the space between the sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base, such as being a space of between around 20mm and around 70mm, or of around 50mm.

[0014] The apparatus may have a cavity extending from the base toward the top for creating a void between the slab and the substrate inside the apparatus. The sidewalls may have a thickness of between around 1mm and around 60mm, or between around 1mm and around 50mm, or between around 1mm and around 40mm, or between around 1mm and around 30mm, or between around 1mm and around 20mm, or between around 1mm and around 10mm, or between around 1mm and around 5mm, or of around 3mm. The base may comprise a rim, which may extend outwardly from the sidewalls. The surface area of the rim for engaging the substrate may be less than about Vi, or less than about 2/5 or less than about 1/3 of the area enclosed by an outer perimeter of the rim. In embodiments where the area enclosed by the outer perimeter of the rim is at least 180,000 mm , the surface area of the rim for engaging the substrate may be less than about 2/5 or less than about 1/3 of the area enclosed by an outer perimeter of the rim. In embodiments where the area enclosed by the outer perimeter of the rim is less than 180,000 mm , the surface area of the rim for engaging the substrate may be less than about V2 or less than about 2/5 or less than about 1/3 of the area enclosed by an outer perimeter of the rim. At least one post may extend from the top and terminate substantially at the level of the base. The at least one post may comprise a single post extending substantially perpendicularly from the centre of the top. The post may taper from a first end associated with top to a second end associated with the base and may have a X-shaped transverse cross section so as to define transversely extending vanes. The vanes may have a width of less than 30mm and in some embodiments of around 20mm. In other embodiments, the post may be tubular and may have a circular, oblong or square transverse cross section. The post may be hollow and may have an opening at its top end.

[0015] The rim may extend laterally from the sidewalls and be configured to overlap the rim of an adjoining said apparatus. The rim may comprise engagement formations for engaging corresponding engagement formations on an adjoining said apparatus. The engagement formations may be configured to space the sidewalls of adjoining said apparatuses at a predetermined fixed distance apart (i.e. the engagement formations do not allow the adjoining apparatuses to be spaced apart at different distances). The predetermined fixed distance, measured at a distance of 30mm above the base, may be less than around 70mm or may be around 55mm. The engagement formations may, for example, comprise ribs, tongue and groove formations, dovetail formations, or projections and corresponding slots.

[0016] Reinforcement raising formations may extend from the rim on at least two sides of the apparatus to elevate reinforcement placed on the raising formations above the rim to provide a predetermined thickness of concrete cover between the reinforcement and the rim. In embodiments where a cross-section through the apparatus in a plane parallel to the plane of the base is substantially rectangular, the reinforcement raising formations may be provided on two adjacent sides of the apparatus.

[0017] Intersecting perpendicular grooves may be provided in the top for locating reinforcement for the underside of the top portion of the slab. Reinforcement raising formations may be provided in the grooves for elevating the reinforcement above a base of the grooves to provide a predetermined thickness of concrete cover between the reinforcement and the base of the grooves.

[0018] The top may slope towards the sidewalls, and may for example be domed, to facilitate flow of uncured concrete over the top and down the sidewalls.

[0019] The apparatus may be polygonal in a cross-section taken through the apparatus in a plane parallel to the plane of the base. In some embodiments, for example, the cross-section may be triangular, oblong, square, pentagonal, or hexagonal.

[0020] The base may define a rectangular footprint for the apparatus. In some embodiments, the base may define a square or oblong footprint for the apparatus. In some embodiments, the footprint may be approximately 900mm by 900mm. In other embodiments, the footprint may be approximately 600mm by 600mm, 900mm by 300mm, or 300mm by 300mm. The distance between the top and the base (i.e. the height of the apparatus) may be between around 100mm and around 500mm. The apparatus may be provided in a range of heights for use in different applications. For example, the apparatus may be provided in a height of between around 250mm and around 450mm, in a height of between around 150mm and around 250mm, and in a height of between around 100mm and around 150mm.

[0021] The apparatus may be formed from a plastics material, and ideally from a recyclable plastics material. The apparatus may alternatively be formed from any other suitable material.

[0022] In a second aspect, there is provided a system for forming a concrete slab, the concrete slab comprising a main area and a perimeter area extending around the main area, the system comprising: a plurality of apparatuses according to the first aspect above, comprising: a first group of the apparatuses placed side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first group, wherein the sidewalls of adjoining said apparatuses of the first group define at least part of a form for internal beam portions of the slab.

[0023] The first group of the apparatuses may be placed to form an underside of the main area of the slab and a second group of the apparatuses may be placed around the first group of apparatuses to form an underside of the perimeter area of the slab, the apparatuses of the second group being placed side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first and second groups, and the apparatuses of the second group having a height less than those of the first group so as to provide a greater slab depth in the perimeter area of the slab, the greater slab depth defining a perimeter beam of the slab. In some embodiments, the second group of apparatuses may not necessarily be placed around the first group of apparatuses to form a perimeter beam but may be placed at locations corresponding to the locations of piers installed in the substrate under the slab to provide an increased slab thickness above the piers.

[0024] Openings may be provided in the apparatuses to receive the tops of piers installed in the substrate under the slab. The openings in the first group of apparatuses may be provided at a grid spacing of between 2000mm and 4000mm, and in some embodiments at a spacing of around 2700mm. The openings in the second group of apparatuses may be provided at a spacing of between 1000mm and 3000mm, and in some embodiments at a spacing of around 1800mm. The tops of the piers may be mechanically connected to the slab to resist relative movement between the slab and piers. For example, a fastener may extend from the tops of the piers for casting into the slab to tie the slab to the piers. In some embodiments, the piers are screw piers, but other piers, such as concrete or timber piers, or steel piles, may alternatively be used. The piers may be embedded in the substrate a distance of greater than or equal to 0.75 Hs (where Hs is the depth of soil suction change).

[0025] The apparatuses may be placed side by side such that a space of around 50mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses.

[0026] In embodiments where the base of the apparatuses comprises a rim, the space between the sidewalls of adjoining apparatuses may be set by abutting or overlapping the rims of the apparatuses.

[0027] The apparatuses may be formed from a plastics material, and ideally from a recyclable plastics material. Alternatively, the apparatuses may be formed from any other suitable material.

[0028] Edge forms may be provided for closing a space between an outermost ring of said apparatuses and an adjoining structure such as side forms for the slab. The edge form may be reconfigurable to facilitate its use in closing spaces of different sizes.

[0029] A rebate edge form may also be provided for positioning adjacent an outer edge of the slab to support an external wall of a building formed on the slab. The rebate edge form may include a projection for casting into the slab to secure the rebate edge form to the slab.

[0030] In a third aspect, there is provided a method of forming a concrete slab, the concrete slab comprising a main area and a perimeter area extending around the main area, the method comprising: providing a plurality of apparatuses according to the first aspect above; and placing a first group of the apparatuses side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first group to define a form for internal beam portions of the slab.

[0031] The first group of the apparatuses may be placed to form an underside of the main area of the slab and a second group of the apparatuses may be placed around the first group of apparatuses to form an underside of the perimeter area of the slab, the apparatuses of the second group being placed side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first and second groups, and the apparatuses of the second group having a height less than those of the first group so as to provide a greater slab depth in the perimeter area of the slab, the greater slab depth defining a perimeter beam of the slab. In some embodiments, the second group of apparatuses may not necessarily be placed around the first group of apparatuses to form a perimeter beam but may be placed at locations corresponding to the locations of piers installed in the substrate under the slab to provide an increased slab thickness above the piers.

[0032] Openings may be provided in the apparatuses to receive the tops of piers installed in the substrate under the slab. The openings may be formed by removing a portion of the apparatuses, such as by cutting or punching a hole in the tops of the apparatuses. The openings in the first group of apparatuses may be provided at a grid spacing of between 2000mm and 4000mm, and in some embodiments at a spacing of around 2700mm. The openings in the second group of apparatuses may be provided at a spacing of between 1000mm and 3000mm, and in some embodiments at a spacing of around 1800mm. The tops of the piers may be mechanically connected to the slab to resist relative movement between the slab and piers. In some embodiments, the piers may be screw piers, but other piers, such as concrete or timber piers, or steel piles, may alternatively be used. The piers may be embedded in the substrate a distance of greater than or equal to 0.75 Hs (where Hs is the depth of soil suction change).

[0033] The apparatuses may be placed side by side such that a space of around 50mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses.

[0034] In embodiments where the base of the apparatuses comprises a rim, the space between the sidewalls of adjoining apparatuses may be set by abutting or overlapping the rims of the apparatuses.

[0035] Also disclosed is an apparatus for forming an underside of a concrete slab, including beam portions of the slab and the underside of a main portion of the slab, the apparatus comprising: a top for forming the underside of the main portion of the slab; sidewalls extending downwardly from the top to define an open base, the base having a peripheral rim for engaging a substrate on which the concrete slab is to be formed, the sidewalls and rim are adapted to provide a form for beam portions of the slab; and a cavity extending from the base toward the top for creating a void between the slab and the substrate inside the apparatus; wherein the surface area of the rim for engaging the subgrade is less than Vi, or in some embodiments less than or equal to around 2/5 or 1/3, of the area enclosed by an outer perimeter of the rim.

[0036] In embodiments where the area enclosed by the outer perimeter of the rim is at least 180,000 mm , the surface area of the rim for engaging the substrate may be less than about 2/5 or less than about 1/3 of the area enclosed by an outer perimeter of the rim. In embodiments where the area enclosed by the outer perimeter of the rim is less than 180,000 mm , the surface area of the rim for engaging the substrate may be less than about Vi or less than about 2/5 or less than about 1/3 of the area enclosed by an outer perimeter of the rim.

[0037] Also disclosed herein is a concrete ground slab comprising: a main portion; and beam portions extending from an underside of the main portion, each of the beam portions tapering in thickness from their top adjacent the slab to terminate in a relatively narrow base for bearing on a substrate on which the concrete slab is formed or is to be installed, wherein the thickness of the beam portions is between around 20mm and around 70mm at a distance of 30mm above the base, wherein the thickness of the beam portions at a distance of 100mm and/or 200mm above the base is greater than or equal to the thickness of the beam portions at a distance of 30mm above the base, and wherein the thickness of the beam portions at the base is less than or equal to the thickness of the beam portions at a distance of 30mm above the base.

Brief Description of Drawings [0038] Embodiments of the presently disclosed apparatus, system and method will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an isometric view of an embodiment of an apparatus for forming a concrete slab in accordance with the present disclosure;

Figure 2 is a plan view of the forming apparatus of Fig. 1;

Figure 3 is a front view of the forming apparatus of Fig. 1;

Figure 4 is a right side view of the forming apparatus of Fig. 1;

Figure 5 is a left side view of the forming apparatus of Fig. 1;

Figure 6 is an underside view of the forming apparatus of Fig. 1;

Figure 7 is a cross-sectional view taken along line 7-7 of the forming apparatus of Fig. l;

Figure 8 is an enlarged view of area B of Fig. 5;

Figure 9 is an enlarged view of area C of Fig. 7;

Figure 10 is an isometric view of four of the forming apparatuses of Fig. 1 connected together;

Figure 11 is a front view of the forming apparatuses of Fig. 10;

Figure 12 is an enlarged view of area B of Fig. 11;

Fig. 13 is a perspective view of a pier cover plate for use with the forming apparatuses of Figs. 1-12;

Fig. 14 is a schematic cross-sectional view taken vertically through a concrete slab forming system incorporating forming apparatuses as shown in Figs. 1-12 and the pier cover plate of Fig. 13;

Fig. 15 is an isometric view of another embodiment of an apparatus for forming a concrete slab in accordance with the present disclosure;

Fig. 16 is a plan view of the forming apparatus of Fig. 15;

Fig. 17 is a cross sectional view taken along line 17-17 of Fig. 16;

Fig. 18 is an isometric view of another embodiment of an apparatus for forming a concrete slab in accordance with the present disclosure;

Fig. 19 is an isometric view of another embodiment of an apparatus for forming a concrete slab in accordance with the present disclosure;

Fig. 20 is an isometric view of a system comprising an edge form used with the forming apparatuses of Figs. 15-19;

Fig. 21 is a side elevational view of the system of Fig. 20;

Fig 22 is an isometric view of a system comprising a rebate edge form used with the forming apparatuses of Figs. 15-19;

Fig. 23 is a plan view of the rebate edge form of Fig. 22;

Fig. 24 is an end elevational view of the rebate edge form of Fig. 22;

Fig. 25 is a cross-sectional view taken vertically through a concrete slab forming system incorporating forming apparatuses as shown in Figs. 15-19 and edge forms as shown in Figs. 2024;

Fig. 26 is a plan view of the concrete slab forming system of Fig. 25; and Fig. 27 is an isometric view of another embodiment of an apparatus for forming a concrete slab in accordance with the present disclosure.

Description of Embodiments [0039] Referring to the drawings, and initially to Figs. 1-9, there is shown an embodiment of an apparatus 10 for forming an underside of a concrete slab. The apparatus 10 comprises a top 12 and sidewalls 14 extending downwardly from the top 12 to define an open base 15. The base 15 has a peripheral rim 16 for engaging a substrate 200 on which the concrete slab 100 is to be formed. In the illustrated embodiment, the apparatus 10 is square in a cross-section taken in a plane parallel to the plane of the base 15 and rim 16.

[0040] As shown in Fig. 14, the top 12 is adapted to provide a form for the underside of the main portion 100a of a concrete slab 100, and the sidewalls 14 and rim 16 are adapted to provide a form for beam portions 100b of the slab. A cavity 300 is defined in the forming apparatus 10 and extends from the base 15 toward the top 12, such that, in use, the cavity 300 defines a void between the slab 100 and the substrate 300.

[0041] The surface area of the rim 16 for engaging the substrate 200 is less than 1/3 of the area enclosed by an outer perimeter of the rim. As shown in Figs. 10-12, the rim 16 comprises engagement formations, in the form of ribs 16a, for connecting adjoining apparatuses 10 together when their rims 16 are overlapped. By virtue of the rims 16 being overlappable, the less than 1/3 rim area to enclosed area ratio is maintained.

[0042] When their engagement formations 16a are engaged, the sidewalls 14 of adjoining apparatuses 10 are spaced at a predetermined fixed distance apart (i.e. the engagement formations 16a do not allow the adjoining apparatuses to be spaced apart at different distances). The predetermined fixed distance, measured at a distance of 30mm above the base 15, is 50mm. At a distance of 200mm above the base 15, the sidewalls 14 are spaced apart by around 100mm or less. In the embodiment of Figs. 1-9, the gradient of the sidewalls becomes flatter near the base 15, such that the sidewalls 14 are spaced apart by around 50mm or less adjacent the base.

[0043] The sidewalls 14 taper outwardly from the top 12 to the base 15. This taper facilitates stacking of the apparatuses 10.

[0044] The present inventors have found that the rim 16 and sidewall 14 configurations described above significantly reduce the uplift forces that would otherwise be transferred to the slab 100 as a result of ground heave by limiting the contact area between the apparatus 10 and subgrade 200, which promotes shearing of the subgrade 200 at its points of contact with the apparatus 10 as it heaves upwardly and swells into the cavity 300.

[0045] In the embodiment shown in Figs. 1-12, a supporting formation, in the form of a step 14s, is provided in the sidewalls 14 for supporting a pier cover plate 50, as shown in Figs 13 and 14.

[0046] The rim 16 is square shaped in plan view. When the apparatuses 10 are connected with their rims 16 overlapping as shown in Figs. 10-12 and 14, they have a centre-to-centre spacing of 600mm x 600mm. In other embodiments, the apparatuses 10 may be smaller or larger so as to provide centre-to-centre spacings smaller or larger than 600 mm x 600 mm, such as, for example, a centre-to-centre spacing of 900mm x 900mm. As shown in Figs. 7 and 9, reinforcement raising formations 16b extend from the rim 16 on two adjacent sides of the apparatus 10 to elevate steel reinforcing bars to provide a predetermined thickness of concrete between the reinforcing bars and the rim 16. Intersecting perpendicular grooves 12a are provided in the top 12 for locating steel reinforcing bars for the underside of the top portion of the slab 100. Reinforcement raising formations may be provided in the grooves 12a for elevating the steel reinforcing bars above a base of the grooves to provide a predetermined thickness of concrete between the reinforcing bars and the base of the grooves 12a.

[0047] The top 12 is domed to facilitate flow of uncured concrete over the top and down the sidewalls 14. Different heights of apparatus 10 are provided to facilitate varying the thickness of the slab 100 at certain locations. For example, taller apparatuses 10 can be placed under the main portion of the slab and shorter apparatuses 10 under the perimeter portion of the slab, so as to create a greater slab thickness in the perimeter portion relative to thickness of the main portion, thereby defining a perimeter beam. In the embodiment shown in Figs. 1-12, the apparatus has a height of 300mm. Despite having different heights, the 600mm length and 600mm width of the apparatuses 10 may be maintained. However, in some embodiments, apparatuses 10 of other lengths and widths may be provided.

[0048] The apparatus 10 is formed from a recyclable plastics material. However, the apparatus may alternatively be formed from any other suitable material. The tapered walls 14 of the apparatus 10 allow a plurality of apparatuses 10 of the same size to be stacked one on top of another in a compact nested arrangement for storage and transport.

[0049] As shown in Fig. 14, when the apparatuses 10 are laid out on a site ready for pouring a concrete slab 100, they define a system 500. A first group of the apparatuses 10 are laid out their rims 16 overlapping each other such that the sidewalls 14 and rims 16 of these adjoining apparatuses define a form for beam portions 100b of the slab. A second group of the apparatuses 10 are laid out with their rims 16 spaced apart to define a space S therebetween through which a connection can be formed between the slab 100 and a pier 400 embedded in the substrate 200.

For internal piers, the space S is 600mm x 600 mm and for perimeter piers, the space S is 300 mm x 600 mm.

[0050] When laid out in this manner, the area of the apparatuses 10 engaging the substrate 200 is less than 1/3 of the area of the slab 100. The present inventors have found that this arrangement significantly reduces uplift forces applied to the slab 100 if the substrate 200 heaves, and also promotes shear failure of the heaving substrate 200.

[0051] Pier cover plates 50 are supported on the steps 14s on the sidewalls 14 of the second group G2 of the apparatuses 10 to close the spaces S and define a form for a portion of the slab 100 above the piers 400. Pier cover plates 50 of 600 mm x 600 mm are provided for closing spaces above internal piers and pier cover plates of 300 mm x 600 mm are provided for closing spaces above perimeter piers. A fastener 60 extends from a top end of each pier 400 and through the pier cover plate 50 for casting into the slab 100 to tie the slab to the pier to resist relative movement between the slab and pier.

[0052] The pier cover plates 50 are ideally formed from a plastics material. However, they may also be formed from plywood or other materials of appropriate strength.

[0053] Figs. 15-17 show another embodiment of the forming apparatus 10’, which has many features in common with the embodiment of Figs. 1-9, where corresponding reference numerals indicate corresponding features with corresponding functionality. In the apparatus 10’ of Figs. 15-17, however, a post 20 extends perpendicularly and centrally from the top 12, through the cavity 300, and terminates at the level of the base 15 so as to engage the substrate 200 in use.

The post 20 supports the top 12 and therefore allows apparatus 10’ to be provided in greater lengths and/or widths whilst still allowing the apparatus to be formed with relatively thin walls and yet be strong enough to support the weight of operators walking on the apparatus as well as the weight of the slab. Apparatus 10’ is 900mm long and 900mm wide and has a wall thickness of approximately 3mm. The post 20 is X-shaped in transverse cross-section to define transversely extending vanes having a thickness of 20mm. The post 20 tapers from its top end to its base end. The post 20 is also hollow, being closed at its base end and open at the top. The hollow and tapering post 20, along with the tapered walls 14 of the apparatus 10’, allow a plurality of apparatuses 10’ of the same size to be stacked one on top of another in a compact nested arrangement for storage and transport. Also, in apparatus 10’, there is a relatively short transition length between the sidewalls 14 and the rim 16, rather than the relatively longer smoothly curving transition between the sidewalls 14 and rim 16 in apparatus 10. The rim 16 in apparatus 10’ has a width of around 50mm and the sidewalls extend from the rim 16 at an angle of around 105 degrees. Accordingly, the space between the sidewalls 14 of adjoining apparatuses 10’ is around 50mm at the base 15, around 55mm at a height of 30mm above the base and around 67mm at a height of 100mm above the base. Instead of ribs 16a, the engagement formations take the form of projections 16c that are engageable in slots 16d located at the inward ends of the reinforcement raising formations 16b. As with apparatus 10, apparatus 10’ may also be provided in a range of heights to facilitate varying the thickness of the slab 100 at certain locations. The embodiment of apparatus 10’ shown in Figs. 15-17 has a height of 300mm, but it can also be formed, for example, in heights of 215mm and 130mm.

[0054] Fig. 18 shows another embodiment of the forming apparatus 10”, which is identical to the forming apparatus 10’ of Figs. 15-17 apart from having a length of 900mm and a width of 300mm to facilitate its use at edge regions of the slab where a gap of less than 900mm x 900mm is available between an adjoining apparatus 10’ and the slab edge. Again, apparatus 10” may be provided in a range of heights to facilitate varying the thickness of the slab 100 at certain locations. The illustrated embodiment of apparatus 10” has a height of 300mm, but it can also be formed in heights of 215mm and 130mm.

[0055] Fig. 19 shows another embodiment of the forming apparatus 10”’, which is identical to the forming apparatus 10’ of Figs. 15-17 apart from having a length of 300mm and a width of 300mm to facilitate its use at edge regions of the slab where a gap of less than 900mm x 300mm is available between an adjoining apparatus 10’, 10” and the slab edge, and, due to its smaller span, omitting post 20. Again, apparatus 10” ’ may be provided in a range of heights to facilitate varying the thickness of the slab 100 at certain locations. The illustrated embodiment of apparatus 10’” has a height of 300mm, but it can also be formed in heights of 215mm and 130mm.

[0056] Figs. 20 and 21 show an edge form 70 for closing a space SI between an outermost ring of the apparatuses 10, 10’, 10”, 10’” and an adjoining structure, such as edge boards 600 for the slab 100. The edge form 70 includes a base 72 adapted to engage the outer edge of the rims 16 of the apparatuses 10, 10’, 10”, 10’”, a sidewall 74 extending from the base 72 at an obtuse angle and terminating in a top 76 that engage the top of edge boards 600. The edge form 70 can be flexed to adjust the angle between the base 72 and the sidewall 74 so as to configure the edge form for closing spaces SI of various widths. The edge form 70 has a thickness of between approximately 2mm and approximately 20mm so as to maintain the limited the contact area with the substrate 200 and promote shear failure of heaving substrate 200 to reduce transmission of uplift forces to the slab 100, as discussed above. In other embodiments, the base 72 may be configured to overlap the top or underside of the rims 16 so as not to increase the contact area with the substrate 200 at all.

[0057] Figs. 22-24 show a rebate edge form 80 for positioning adjacent an outer edge of the slab 100 to support an external wall 700 of a brick-veneer building formed on the slab. The edge form 80 comprises a sidewall 84 adapted to engage the outer edge of the rims 16 of the apparatuses 10, 10’, 10”, 10’” and extend vertically alongside the outer edge of the slab 100. A plurality of anchoring projections 86 extend from one of the major surfaces of the sidewall 84 for being cast into the slab 100 to fasten the edge form 80 to the slab. A wall support 88 extends perpendicularly from the opposite major surface of the sidewall 84 to provide a platform for laying brickwork 704 of the wall. The wall support 88 is provided at a position elevated from the base of the sidewall 84 to ensure that the brickwork 704 is correspondingly elevated above the level of the substrate 200. Strengthening elements 89 extend between the sidewall 84 and the wall support 88 to strengthen the wall support 88 for carrying the weight of the brickwork 704. The sidewall 84 has a width of 20mm so as to maintain the limited the contact area with the substrate 200 and promote shear failure of heaving substrate 200 to reduce transmission of uplift forces to the brickwork 704. In other embodiments, a base flange may extend from the lower end of the sidewall 84 to overlap the top or underside of the rims 16 so as not to increase the contact area with the substrate 200 at all.

[0058] Fig. 27 shows an alternative embodiment of the apparatuses 10’, 10”, 10’” of Figs. 1519, that is substantially identical thereto except for the rectangular rims 16 being replaced with V-shaped rims 16’. The point of the V-shaped rims 16’ faces downwardly to bear on the substrate in use, thereby further reducing the contact area between the apparatuses and the substrate.

[0059] Figs. 25 and 26 show a concrete slab forming system 500 incorporating forming apparatuses 10’, 10”, 10”’ as shown in Figs. 15-19 and edge forms as shown in Figs. 20-24. The cross-section shown in Fig. 25 is taken along line 25-25 of Fig. 26. A first group of apparatuses 10’ with a height of 300mm or 215mm, depending on the shrink-swell reactivity of the substrate 200, is placed to form an underside of the main area 100a of the slab 100. A second group of apparatuses 10’, 10”, 10”’ with a height of 130mm may be placed around the first group of apparatuses to form an underside of the perimeter area of the slab 100 and thereby create a perimeter beam 100c of the slab. Whilst not shown in Figs. 25 and 26, apparatuses 10’, 10”, 10’” with a height of 130mm may also be provided in spaced apart rows under the main area 100a of the slab to create internal beams if desired. The rims 16 of all of the apparatuses 10’, 10”, 10’” are overlapped and engaged such that a space, having a width of around 50mm or less measured at a distance of 30mm above the bases 15, is provided between the sidewalls 14 of adjoining apparatuses to form beam portions 100b of the slab 100. The space between the sidewalls 14 at a distance of 200mm above the bases 15 is greater, being around 100mm or less. As a result, the beam portions 100b have corresponding thicknesses of around 50mm and around 100mm at distances of 30mm and 200mm, respectively, above their bases.

[0060] Openings are cut or punched, or in some embodiments may be pre-formed, in the tops 12 of some of the apparatuses 10’, 10”, 10’” to receive the shafts of screw piers 400 installed in the substrate 200 under the slab 100, as shown in Figs. 25. The piers 400 are embedded in the substrate 200 a distance of greater than or equal to 0.75 Hs (where Hs is the depth of soil suction change). The piers 400, and therefore the openings in the respective apparatuses, are provided at a grid spacing of around 2700mm under the main area 100a of the slab and, in embodiments comprising a perimeter beam, at a spacing of around 1800mm under the perimeter beam 100c. In some embodiments, apparatuses 10’, 10”, 10’” with a height of 130mm may be placed above the pier locations to provide an increased slab thickness above the piers 400. A fastener 60 extends from the tops of the piers 400 for casting into the slab 100 to tie the slab to the piers to resist relative movement therebetween. In other embodiments, the fastener 60 may be omitted and the tops of the piers 400 may have a profile that promotes engagement between the piers 400 and the slab 100.

[0061] It will be appreciated that although the elements of the presently disclosed system 500 are placed on the substrate 200, the system 500 performs similarly to a suspended and tied-down slab system. Importantly, the shape/profile of the forming apparatuses 10, 10’, 10”, 10’”, along with those of edge forms 70 and 80, is specifically configured to allow upward heave of reactive substrate materials, such as clay, whilst significantly reducing transmission of the heave forces to the concrete slab 100 and/or building wall 700 constructed above the substrate 200 by promoting shear failure of the heaving substrate.

[0062] It will be appreciated that the illustrated system 500 does not require rectangular concrete beams to be formed and constructed directly onto/into/over the clay substrate 200. Accordingly, significant time reductions can be achieved with the illustrated system compared with conventional slab construction systems due to not having to excavate/form up or otherwise construct internal and perimeter beams as required with conventional techniques. Moreover, significantly less concrete is required to form a slab 100 using the illustrated system 500, due to the relatively narrow and tapered shape of the internal beams 100b, and since the thickness of the main portion 100a of the slab can be reduced compared to that required with conventional slabs for reactive soils, which must be able to withstand significant uplift forces.

[0063] The illustrated system 500 can be used for all substrate reactivity conditions and therefore effectively eliminate cost disparity between different sites. Accordingly, the illustrated system 500 allows builders to provide a standardised slab cost regardless of substrate reactivity.

[0064] Other advantages of the illustrated system 500 include: • faster construction • less reinforcing steel • reduction in waste • all elements recyclable • all elements made from recycled materials • small carbon footprint in manufacture, delivery, construction and demolition • no negative environmental impacts from material • post slab construction remains full-life cycle recyclable/renewable • less transport costs • compatible with all standard current slab construction methods • less specialised skills required than current systems • suits residential, commercial and industrial applications • improved long term performance/serviceability compared to conventional systems [0065] 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. Examples of possible variations and/or modifications include, but are not limited to: • the engagement formations 16a having a different form, such as being tongue and groove formations or dovetail formations, or projections and corresponding slots; • the supporting formation 14s may alternatively be a projection or groove in the sidewalls 14; • the apparatus 10, 10’, 10”, 10’” may be triangular, oblong, pentagonal, hexagonal, or other polygonal shape in a cross-section taken through the apparatus in a plane parallel to the plane of the base 15; • the sidewalls 14 may be corrugated; and/or • the post 20 of apparatus 10’, 10”, 10’” may have a different transverse cross-sectional shape, such as circular, oblong or square.

Claims (28)

1. CLAIMS:

   1. An apparatus for forming an underside of a concrete slab, including beam portions of the slab and the underside of a main portion of the slab, the apparatus comprising: a top for forming the underside of the main portion of the slab; sidewalls extending downwardly and outwardly from the top for forming the beam portions of the slab; a base at an opposite end of the sidewalls to the top, the base being adapted for bearing on a substrate on which the concrete slab is to be formed, wherein the apparatus is configured such that when two said apparatuses are placed side by side with a space of between around 20mm and around 70mm between their adjoining sidewalls at a distance of 30mm above the base: the space between the adjoining sidewalls at a distance of 100mm above the base is greater than or equal to the space between the adjoining sidewalls at a distance of 30mm above the base, and the space between the adjoining sidewalls at the base is less than or equal to the space between the sidewalls at a distance of 30mm above the base.
2. 2. An apparatus according to claim 1, wherein the space between the adjoining sidewalls at a distance of 200mm above the base is greater than or equal to the space between the adjoining sidewalls at a distance of 100mm above the base.
3. 3. An apparatus according to claim 2, wherein the space between the adjoining sidewalls at a distance of 200mm above the base is greater than the space between the adjoining sidewalls at a distance of 100mm above the base.
4. 4. An apparatus according to any one of claims 1 to 3, wherein the space between the adjoining sidewalls at a distance of 100mm above the base is greater than the space between the adjoining sidewalls at a distance of 30mm above the base.
5. 5. An apparatus according to any one of the preceding claims, wherein the space between the adjoining sidewalls at the base is less than the space between the adjoining sidewalls at a distance of 30mm above the base.
6. 6. An apparatus according to any one of the preceding claims, wherein the space between the adjoining sidewalls at the base is between around 50mm and around 70mm.
7. 7. An apparatus according to any one of the preceding claims, wherein the space between the adjoining sidewalls at a distance of 30mm above the base is between around 30mm and around 70mm.
8. 8. An apparatus according to any one of the preceding claims, wherein the space between the adjoining sidewalls at a distance of 100mm above the base is less than 200mm or less than 150mm or less than 100mm or less than 90mm or less than 80mm or less than 70mm.
9. 9. An apparatus according to any one of the preceding claims, wherein the space between the adjoining sidewalls at a distance of 200mm above the base is less than 400mm or less than 300mm or less than 200mm or less than 150mm or less than 100mm or less than 90mm.
10. 10. An apparatus according to any one of the preceding claims, comprising a cavity extending from the base toward the top for creating a void between the slab and the substrate inside the apparatus.
11. 11. An apparatus according to claim 11, wherein the sidewalls have a thickness of between around 1mm and around 10mm.
12. 12. An apparatus according to claim 10 or claim 11, wherein the base comprises a rim for engaging the substrate, wherein a surface area of the rim that engages the substrate, in use, is less than about Vi of the area enclosed by an outer perimeter of the rim.
13. 13. An apparatus according to claim 12, wherein the surface area of the rim that engages the substrate, in use, is less than about 2/5 of the area enclosed by the outer perimeter of the rim.
14. 14. An apparatus according to claim 12, wherein the surface area of the rim that engages the substrate, in use, is less than about 1/3 of the area enclosed by the outer perimeter of the rim.
15. 15. An apparatus according to any one of claims 12 to 14, wherein the rim extends laterally from the sidewalls and is configured to overlap the rim of an adjoining said apparatus.
16. 16. An apparatus according to any one of claims 12 to 15, wherein the rim comprises engagement formations for engaging corresponding engagement formations on an adjoining said apparatus.
17. 17. An apparatus according to claim 16, wherein the engagement formations are configured to space the sidewalls of adjoining said apparatuses at a predetermined fixed distance apart.
18. 18. An apparatus according to any one of claims 10 to 17, comprising at least one post extending from the top and terminating substantially at the level of the base.
19. 19. An apparatus according to any one of the preceding claims, comprising one or more grooves in the top for locating reinforcement for the underside of the top portion of the slab.
20. 20. An apparatus according to any one of the preceding claims, wherein the base defines a rectangular footprint for the apparatus.
21. 21. An apparatus according to claim 20, wherein the footprint is approximately 900mm by 900mm, or approximately 600mm by 600mm, or approximately 900mm by 300mm, or approximately 300mm by 300mm.
22. 22. An apparatus according to any one of the preceding claims, wherein the distance between the top and the base is between around 100mm and around 500mm.
23. 23. An apparatus according to claim 22, wherein the distance between the top and the base is between around 250mm and around 450mm, or between around 150mm and around 250mm, or between around 100mm and around 150mm.
24. 24. A system for forming a concrete slab, the concrete slab comprising a main area and a perimeter area extending around the main area, the system comprising: a plurality of apparatuses according to any one of the preceding claims, comprising: a first group of the apparatuses placed side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first group, wherein the sidewalls of adjoining said apparatuses of the first group define at least part of a form for internal beam portions of the slab.
25. 25. A system according to claim 24, wherein the first group of the apparatuses is placed to form an underside of the main area of the slab and a second group of the apparatuses is placed around the first group of apparatuses to form an underside of the perimeter area of the slab, the apparatuses of the second group being placed side by side such that a space of less than around 70mm, measured at a distance of 30mm above the bases, is provided between the sidewalls of adjoining apparatuses of the first and second groups, and wherein the apparatuses of the second group have a height less than those of the first group so as to provide a greater slab depth in the perimeter area of the slab, the greater slab depth defining a perimeter beam of the slab.
26. 26. A system according to claim 24, wherein a second group of the apparatuses is placed at locations corresponding to the locations of piers installed in the substrate under the slab to provide an increased slab thickness above the piers.
27. 27. A system according to any one of claims 24 to 26, wherein openings are provided in at least some of the apparatuses to receive the tops of piers installed in the substrate under the slab.
28. 28. A concrete ground slab comprising: a main portion; and beam portions extending from an underside of the main portion, each of the beam portions tapering in thickness from their top adjacent the slab to terminate in a relatively narrow base for bearing on a substrate on which the concrete slab is formed or is to be installed, wherein the thickness of the beam portions is between around 20mm and around 70mm at a distance of 30mm above the base, wherein the thickness of the beam portions at a distance of 100mm above the base is greater than or equal to the thickness of the beam portions at a distance of 30mm above the base, and wherein the thickness of the beam portions at the base is less than or equal to the thickness of the beam portions at a distance of 30mm above the base.