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Title:
APPARATUS FOR DISPLACING A VOLUME OF CONCRETE IN A CONCRETE SLAB
Document Type and Number:
WIPO Patent Application WO/2019/050476
Kind Code:
A1
Abstract:
An apparatus for displacing a volume of concrete in a concrete slab, including a main body defining an outer peripheral surface shaped to displace a volume of concrete in the slab, wherein the main body section includes foamed concrete having a reduced density when compared with the concrete of the concrete slab.

Inventors:
CHAILLAN GILLES ALAIN MARIUS (SG)
Application Number:
PCT/SG2018/050440
Publication Date:
March 14, 2019
Filing Date:
August 30, 2018
Export Citation:
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Assignee:
DRAGAGES SINGAPORE PTE LTD (SG)
International Classes:
E04B5/32; B28C5/38; E04C2/06
Domestic Patent References:
WO2006050665A12006-05-18
Foreign References:
CN102518243A2012-06-27
CN104074294A2014-10-01
CN101358478A2009-02-04
JP2005076183A2005-03-24
US20120200004A12012-08-09
Attorney, Agent or Firm:
DAVIES COLLISON CAVE ASIA PTE. LTD. (SG)
Download PDF:
Claims:
Claims Defining the Invention

1. An apparatus for displacing a volume of concrete in a concrete slab, including a main body defining an outer peripheral surface shaped to displace a volume of concrete in the slab, wherein the main body section includes foamed concrete having a reduced density when compared with the concrete of the concrete slab.

2. The apparatus claimed in claim 1, wherein the foamed concrete is formed by mixing cement slurry with foam that is formed in a foam generator.

3. The apparatus claimed in claim 1 or 2, wherein the foamed concrete is formed by an admixture for stabilising the mix formed around the bubbles.

4. The apparatus claimed in any one of claims 1 to 3, wherein the apparatus further includes a plurality of legs for elevating the main body above a floor surface of slab formwork so that concrete can fill a space created therebetween.

5. The apparatus claimed in claim 4, wherein the plurality of legs include said foamed concrete.

6. The apparatus claimed in claim 4, wherein the plurality of legs include said concrete so as to provide a homogenous material bottom layer in the concrete slab.

7. The apparatus claimed in any one of claims 1 to 6, being formed from a mould in upper and lower shells.

8. The apparatus claimed in any one of claims 4 to 7, including a viewing hole extending through the main body for allowing an inspection of a space therebelow. 9. A method for forming a concrete slab including a plurality of the apparatus claimed in any one of claims 1 to 8 positioned therein, the method including the steps of:

(a) positioning a bottom array of reinforced metal bars in a slab formwork;

(b) positioning respective ones of said apparatus in the slab formwork over the bottom array; (c) positioning a top array of reinforced metal bars in the slab formwork over said apparatus; and

(d) pouring concrete into the slab formwork so as to form the concrete slab. 10. The method claimed in claim 9, wherein the step of pouring the concrete includes the steps of:

(a) pouring an initial volume of concrete into the formwork so as to secure the apparatus in position; and

(b) pouring a second volume of concrete up to a predetermined height of the concrete slab.

11. A concrete slab formed from the method steps claimed in claim 9 or claim 10.

12. A concrete slab including a plurality of the apparatus claimed in any one of claims 1 to 8 positioned therein :

(a) a bottom array of reinforced metal bars;

(b) respective ones of said apparatus positioned over the bottom array; (c) a top array of reinforced metal bars positioned over the said apparatus; and

(d) concrete poured around the bottom array, the apparatus and the top array so as to form the concrete slab.

Description:
APPARATUS FOR DISPLACING A VOLUME OF

CONCRETE IN A CONCRETE SLAB

Technical Field of the Invention

The present invention relates to an apparatus for displacing a volume of concrete in a concrete slab. The present invention also relates to a method for forming a concrete slab. The present invention also relates to a concrete slab. Background of the Invention

Concrete slabs are horizontal structures which are typically used to construct floors and ceilings of a building. Reinforced concrete slabs, in particular two way slabs, are advantageous as they are stiffer than classic mono directional ribbed slab. Additionally, they have less deflection therefore allowing for thinner thicknesses. Advantageously, two way slabs do not require additional beams due to their capacity for stress distribution. This allows for greater architectural flexibility, a simpler structural design and more logical and rational reinforcement usage. Because of the aforementioned advantages, there has been an interest in developing the technology further. In particular, efforts to reduce the weight of the slabs have been of interest. Voided slabs provide an improvement resulting in lighter slabs which amplifies the benefit of this structural system. Additionally, it enables the implementation of longer spans and improves the seismic behaviour of the whole building. It is also more economically beneficial to implement compared to traditional systems.

Voided slabs are typically implemented by introducing displacement blocks which occupy the space around the neutral axis of the flexural elements. These blocks displace concrete material in areas where the concrete's mechanical capabilities are under used. As the displacement blocks do not serve any structural purpose, they are typically made of lightweight material which is compatible with the in situ concrete and steel, typically used for slab construction. Typically, displacement blocks (or void formers) are procured from established specialist manufacturers. These void formers consist of shells made of recycled plastics or polystyrene foam. However, these materials are typically petroleum based which create issues with respect to fire resistance. Additionally, at the end of the life of the building, the recycling of the slab is difficult due to the use of these materials.

It is generally desirable to overcome or ameliorate one or more of the above mentioned difficulties, or at least provide a useful alternative.

Summary of the Invention

According to the present invention, there is provided an apparatus for displacing a volume of concrete in a concrete slab, including a main body defining an outer peripheral surface shaped to displace a volume of concrete in the slab, wherein the main body section includes foamed concrete having a reduced density when compared with the concrete of the concrete slab.

According to the present invention, there is also provided a method for forming a concrete slab including a plurality of the apparatus claimed in any one of claims 1 to 8 positioned therein, the method including the steps of:

(a) positioning a bottom array of reinforced metal bars in a slab formwork;

(b) positioning respective ones of said apparatus in the slab formwork over the bottom array;

(c) positioning a top array of reinforced metal bars in the slab formwork over said apparatus; and

(d) pouring concrete into the slab formwork so as to form the concrete slab.

In certain embodiments, the above-mentioned step of pouring the concrete includes the steps of:

(a) pouring an initial volume of concrete into the formwork so as to secure the apparatus in position; and

(b) pouring a second volume of concrete up to a predetermined height of the concrete slab. According to the present invention, there is also provided a concrete slab formed by the above-mentioned method steps.

According to the present invention, there is also provided a concrete slab including a plurality of the apparatus claimed in any one of claims 1 to 8 positioned therein :

(a) a bottom array of reinforced metal bars;

(b) respective ones of said apparatus positioned over the bottom array; (c) a top array of reinforced metal bars positioned over the said apparatus; and

(d) concrete poured around the bottom array, the apparatus and the top array so as to form the concrete slab.

Brief Description of the Drawings

Preferred embodiments of the present invention are hereafter described, by way of non-limiting example only, with reference to the accompanying drawing in which :

Figure 1 is a top perspective view of an exemplary embodiment of a displacement block;

Figure 2 is a bottom perspective view of an exemplary embodiment of a displacement block;

Figure 3 is a side view of an exemplary embodiment of a displacement block;

Figure 4 is a section view of an exemplary embodiment of a displacement block;

Figure 5 is a top view of an exemplary embodiment of a displacement block;

Figure 6 is a side view and perspective view of another embodiment of a displacement block;

Figure 7 is a side view and perspective view of another embodiment of a displacement block;

Figure 8 is a side view and perspective view of another embodiment of a displacement block;

Figure 9 is a side view and perspective view of another embodiment of a displacement block;

Figure 10 is a section view of an exemplary embodiment of a voided slab system; Figure 11a shows a step in an exemplary method of forming a voided slab system; Figure l ib shows another step in an exemplary method of forming a voided slab system;

Figure 11c shows another step in an exemplary method of forming a voided slab system;

Figure l id shows another step in an exemplary method of forming a voided slab system; and

Figure l ie shows the final step in an exemplary method of forming a voided slab system. Detailed Description of Preferred Embodiments of the Invention

Embodiments of the invention provide an apparatus and method for displacing concrete in areas where the concrete's mechanical properties are under utilized. Using embodiments of the invention, the overall weight of the structure can be reduced thereby requiring less structural support.

Displacement Block 10

As particularly shown in Figures 1 to 5, a preferred embodiment of the invention is embodied by a displacement block 10. The displacement block 10 includes a main body section which defines an outer peripheral surface shaped to displace a volume of concrete, for example concrete in a concrete slab. The displacement block includes foamed concrete which has a reduced density when compared with the density of the displaced concrete of the concrete slab.

The normal density of concrete to form the structural sections of the slab is 2400 kg/m 3 compared to the reduced density of the foamed concrete of between 100 to 300 kg/m 3 , for example. The above-mentioned normal density concrete is made of 400 kg of cement, 650 kg of sand, 1250 kg of gravel, 180 L of water and plasticizing admixture resulting in a compression resistance of 35 to 40 MPa. The foamed concrete is made of 250 kg of cement, 950 L of foam, 130 L of water and network former admixture resulting in a compression resistance of 1 to 3 MPa. Of course, other materials and combinations of proportions of the materials can be used to form concrete and foamed concrete. The main body of displacement block 10 is made of two half shells; the top shell 14 and the bottom shell 16 as shown in Figures 1 and 2.

The sides of the shells 14 and 16 are slopping as shown in Figure 3. For example, the area of the top surface of bottom shell 16 is larger than the bottom surface of bottom shall 16. Additionally, the surface of the bottom of top shell 14 is larger than the surface of the top of top shell 14.

In some embodiments, the bottom of the displacement block 10 is supported by a plurality of legs 18 for elevating the main body above a floor surface of slab formwork so that concrete can fill a space created therebetween. Preferably, four legs 18 are coupled to the bottom shell 16 at the four corners of the shell as shown in Figures 1 and 2. The legs 18 function to provide support to the main body of displacement block 10. Additionally, the legs 18 allow the main body to be elevated above the bottom rebar layer 404. The legs 18 also permit the placing of a concrete layer that protects the rebar in the lowest part of the slab.

In some embodiments, the top shell 14 and the bottom shell 16 contain a central hole 12, or viewing hole, through the centre of the displacement block 10 as shown in Figures 1, 2, 4 and 5. The central hole 12 can be used as a visual mean of control that in situ concrete has filled up the entire volume below the displacement block 10. In some cases where the concrete was poured from the sides of the displacement block 10, it may be found later on that the bottom of the displacement block 10 has not been filled completely with concrete. The central hole 12 will allow more concrete to be poured through the central hole 12. However, it is anticipated that the displacement block 10 may not contain a central hole 12.

Additionally, the shape of the displacement block 10 is not limited by the embodiment shown in the figures. As particularly shown in Figures 1 to 5, the shape of the displacement block 10 was established to facilitate the prefabrication process. In particular, the chamfered corners, sloping slides and central hole 12 were provided to enable easy removal of the displacement block 10 from the fabrication mould. In some embodiments, the main body is provided by a single shell instead of a top shell and a bottom shell. Dimensions

As particularly shown in figures 6 to 9, embodiments of the invention can constitute various heights as required by the structural design. The desired height of the displacement block 10 may be established by a structural design study that defines the overall voided slab thickness together with the built up of normal weight concrete that is structurally required at the top and bottom sections of the slab and remaining slab core extent where the displacement block 10 may be implemented. This can be achieved by fixing the height of the bottom shell 16, as particular shown in Figures 6 to 9, i.e. D7 is 160mm, for example. Displacement blocks 10a, 10b, 10c and lOd have varying total heights, D5a, D5b, D5c and D5d, by varying the height of the top shell 14, D6a, D6b, D6c, D6d. The dimensions of the displacement blocks 10a, 10b, 10c and lOd are shown in the table below.

In some embodiments, the particular geometry configuration of the displacement block 10 allows a range of concrete voided two way slabs to be compliant with Eurocode (EC2 5.3.1 (6)). EC2 imposes geometrical restrictions on the dimensions of the in situ and displacement blocks 10 so as to apply the same design method as a monolithic slab instead of having to justify all the discrete elements such as top and bottom flanges (in situ concrete part on top and below the displacement blocks 10) or ribs (i.e. element between two blocks). Material Properties

Advantageously, embodiments of the displacement block 10 are made using foamed concrete (also referred to as "Foamcrete"). In some embodiments, all the parts of the displacement block 10, top and bottom shells 14, 16 and the plurality of legs 18, are made with foamed concrete. In other embodiments, only the top and bottom shells 14 and 16 are made with foamed concrete whilst the plurality of legs 18 are made of normal weight concrete for providing a homogenous material layer at the bottom of the slab.

Foamed concrete is a cement slurry (e.g. cement mixed with water) and foam. The foam is formed by using compressed air within a foam generator. Foam concrete is then made by mixing the cement slurry in a mixer pan, for example, with the foam that was formed by the foam generator.

In some embodiments, a network former admixture is added to the cement grout to stabilize the slurry that is formed around the foam bubbles in order to achieve higher mechanical resistance. An example of a network former admixture that can be used is LithoFoamĀ® SL 200-L by Luca Industries International GmbH which is an alkali resistant foam-forming agent based on highly-active, foam-forming proteins. Another example of a network former admixture is foaming agent, Isocem S/L by Isoltech which is a foaming agent for cellular concrete including natural surfactants mixed with plant-based raw materials. Of course, other types of admixture can be used. In some embodiments, the foam is entrained in the plastic grout. As the foamed concrete mix does not necessitate sand or gravel, all aggregates are completely substituted by microscopic foam bubbles. These bubbles allow a low material density to be achieved. Using foamed concrete results in the displacement block 10 being highly compatible with normal density concrete which is typically used to form the structural framing of the floor. Additionally, the microscopic foam bubbles in the grout matrix results in enhanced thermal and acoustic insulation. Foamed concrete is also not sensitive to fire unlike petroleum based materials. In addition, foamed concrete may enhance the thermal insulation properties to the structure. Further, foamed concrete does not affect the protection of the steel rebar as it does not compromise the concrete cover. As concrete foam has similar properties to normal weight concrete, the rebar protection against fire and corrosion will be compromised by the use of embodiments of the invention.

Fabrication

The fabrication of the displacement blocks 10 is performed in plastic or steel face molds, for example. The monolithic molds are filled with fresh foamed concrete material. In some embodiments, the displacement block 10 is being formed from a mould in upper and lower shells. After a predetermined amount of time for allowing the foamed concrete to harden, the displacement blocks 10 are removed from the molds. The molds are then cleaned and oiled to be ready for the next fabrication batch and the process is repeated for as many times as required. The entire displacement block 10 can be formed from a mold in upper and lower shells.

In some embodiments, the displacement blocks 10 are fabricated on site. This will reduce storage capacity and minimize transportation of the high volume - low mass elements.

In other embodiments, the displacement blocks 10 are fabricated in a mixing plant, for example in a fully automatized site mixing plant where all the ingredients are stored.

Method of Forming Voided Slab System 300

A voided slab system 400 as particularly shown in Figure 10 can be formed by method 300. As particularly shown in Figures 11a, l ib, 11c, l id and l ie, method 300 is for forming a concrete slab including a plurality of displacement blocks 10 positioned therein, the method including the steps of:

(a) positioning a bottom array 404 of reinforced metal bars 405 in a slab formwork 410;

(b) positioning respective ones of the displacement block 10 in the slab formwork 410 over the bottom array 404;

(c) positioning a top array 402 of reinforced metal bars 405 in the slab formwork 410 over the displacement block 10; and

(d) pouring concrete 408 into the slab formwork 410 so as to form the concrete slab 400.

In some embodiments, the method 300 above further includes the steps of:

(a) pouring an initial volume of concrete into the formwork so as to secure the displacement block 10 in position; and

(b) pouring a second volume of concrete up to a predetermined height of the concrete slab 400.

Method 300 forms a concrete slab 400. The concrete slab 400 concrete slab including a plurality of the displacement blocks 10 positioned therein :

(a) a bottom array 404 of reinforced metal bars 405;

(b) respective ones of the displacement block 10 positioned over the bottom array 404;

(c) a top array 402 of reinforced metal bars 405 positioned over the displacement block 10; and

(d) concrete 408 poured around the bottom array 404, the displacement block 10 and the top array 402 so as to form the concrete slab 400.

The first step of the method 300 includes locating a slab formwork 410 as shown in Figure 11a. The slab formwork 410 is for forming a slab in a predetermined shape as dictated by the shape of the slab formwork 410.

The next step of the method 300 includes positioning a bottom rebar layer 404, including of an array of reinforcing bars 405 or rebars, on the surface of the slab formwork 410 as shown in Figure l ib.

The method further including the step of positioning a plurality of displacement blocks 10 on the surface of the slab formwork 410 and over the bottom rebar layer 404 as shown in Figure 11c. The placement of the displacement blocks 10 on the slab formwork 410 is determined by the bending moments and shear forces calculated on the floor slab. In some embodiments of the displacement block 10, the main body includes a plurality of legs for elevating the main body above a floor surface of slab formwork so that concrete can fill a space created therebetween. As shown in Figure l id, a top rebar layer 402, including another array of reinforcing bars 405, is placed on top of the plurality of displacement blocks 10. The displacement block 10 being used as spacer for the positioning of the top rebar layer 402 at a predetermined elevation. As discussed in the preceding section, the height of the main body i.e. D5, defines the distance between the bottom rebar layer 404 and the top rebar layer 406 and can be adjusting in the fabrication process.

Concrete 408 is then poured into the slab formwork 410 as shown in Figure l ie. The central hole 12 or viewing hole extends through the main body of the displacement block 10. The central hole 12 allows inspection of a space between the bottom shell 16 and the slab formwork 410 to be viewed from above the top shell 14. The viewing hole 12 can be used to determine if concrete 408 has completely filled the space between the bottom surface of the slab formwork 410 and the bottom surface of the shell 16 of displacement block 10. Concrete 408 may also be poured into the central hole 12. In some embodiments of the method 500, the concrete 408 can be poured in two stages. The first stage involves a first concrete section of 100 mm thickness, for example. The first concrete section is first poured to secure the positioning of the displacement blocks 10. This is particularly useful to counter the uplift force due to the low density of the displacement block 10 when submerged in concrete with a higher density. The second stage can take place whilst the first section is hardening whereby the remaining section of concrete 408 can be casted. The central hole 12 is used as a visual check to verify that the in situ concrete has filled up the entire space below the displacement block 10. As particularly shown in Figure 10, the dimensions, for example, are as follows:

Dl 700mm;

D2 180mm;

D3 320mm;

D4 70mm; and D5 = 460mm.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention

In this specification and the claims that follow, unless stated otherwise, the word "comprise" and its variations, such as "comprises" and "comprising", imply the inclusion of a stated integer, step, or group of integers or steps, but not the exclusion of any other integer or step or group of integers or steps.

References in this specification to any prior publication, information derived from any said prior publication, or any known matter are not and should not be taken as an acknowledgement, admission or suggestion that said prior publication, or any information derived from this prior publication or known matter forms part of the common general knowledge in the field of endeavour to which the specification relates.