GB2482196A

GB2482196A - A multilayer lightweight concrete slab

Info

Publication number: GB2482196A
Application number: GB1012411.3A
Authority: GB
Inventors: Timothy John Page; Brian Richard Page
Original assignee: Page Concrete & Steel Ltd
Current assignee: Page Concrete & Steel Ltd
Priority date: 2010-07-23
Filing date: 2010-07-23
Publication date: 2012-01-25
Anticipated expiration: 2030-07-23
Also published as: GB201012411D0; GB201012894D0; GB2482196B

Abstract

A multilayer lightweight concrete slab (10) comprises three layers wherein the intermediate layer (35) is less dense than the outer layers (30,40). The outer layers (30,40) may pre-stressed and all three layers may be tied together. The intermediate layer may comprise foamed concrete and the slab may comprise further layers. The slab is suitable for flooring and walling applications and may be extruded.

Description

A CONCRETE SLAB

The present invention relates generally to a concrete slab and particularly to a multi-layer slab with particular physical properties.

Concrete is a construction material composed of cement (typically Portland cement) and other cemetitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravels or crushed rocks such as limestone or granite, plus a fine aggregate such as sand), water, and chemical additives. Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together and eventually creates a stone-like material. Concrete is a widely used material with various applications such as pavements, pipes, architectural structures, foundations, roads, bridges and parking structures. S...

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:. There are a variety of considerations when determining the nature of concrete slabs * . which should be used. One important consideration is weight, which can be * considerable. Hollow core slabs (also known as voided slabs or hollow core planks) have been developed and are typically used in the construction of floors in multi-storey buildings. These are pre-cast slabs of concrete with tubular voids extending the full length of the slab. The benefit of these structures is that they are lightweight compared to solid slabs. However, the problem with hollow core slabs is that the voids can fill up with water over time and they are poor sound insulators.

The present invention seeks to address the problems with known concrete slabs.

According to a first aspect of the present invention there is provided a concrete slab comprising a first layer of concrete having a first density, a second intermediate layer of concrete having a second densily and a third layer of concrete having a third density, the second density being less than the first and third densities.

The present invention provides the benefits of a solid slab together with the lightweight properties of a hollow core slab. By providing the intermediate layer of reduced density the weight of the slab can be significantly reduced, whilst the inclusion of the first and third layers retains the physical properties required for the slab to function as a load-bearing structure.

The first layer may comprise a base layer and the third layer may comprise a cap layer so that, in effect, a sandwich is formed with the intermediate layer flanked by the first and third layers. One or more further layers may be provided, some or all of which may comprise concrete. S.. * S S..

The first and third densities may be substantially the same. However, it is also possible for the first and third densities to be different. *

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* At least one of the layers may be pre-stressed. Concrete is strong in compression, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail.

Pre-sfressing is a method for overcoming concrete's inherent weakness in tension. Pre-stressing tendons (for example high tensile steel cables or rods, glass fibre or plastic fibre) are incorporated into the structure of the layer and subsequently used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the slab would otherwise experience due to a bending load. In some embodiments only the first and/or third layers are pre-stressed and in other embodiments only the first layer is pre-stressed.

At least Iwo of the layers may be tied together. In some embodiments all three layers are tied together. Any suitable method for tying the layers together may be used, including hystools which advantageously can be obtained in continuous lengths.

The second layer may comprise foamed concrete. Foam or foamed concrete is cement-bonded material manufactured by blending a very fluid cement paste (slurry) and then injecting stable, pre-formed foam into the slurry. The volume of slurry to foam dictates the density of the foam concrete.

The slab may be completely or partially pre-manufactured or completely or partially produced on-site. At least one of the layers may be pre-cast and/or at least one of the layers may be poured-in-place. For example, the first and second layers may be pre-cast and supplied to a site where the third layer is added in situ. * *** * *

The density of the intermediate layer may be in the range 100 to 200 kg/rn3, for example in the range 200 to 1600 kg/m3 and more specifically in the range 300 to 600 * kg/m3. S.. * **

The density of the first and/or third layers may be in the range 1500 to 2500 kg/rn3, for example in the range 2000 to 2400 kg/rn3.

The thickness of the layers may be in the range 25 mm to 500 mm. The thickness of each layer may be different to each other or the thickness of at least two of the layers may be substantially the same.

A strip of dense (for example in the region of 2400 kg/rn3) concrete may be provided on one or more of the layers, such as the intermediate layer. For example on the middle layer a strip may be provided on the ends and/or sides. Such strips may be used in slabs for apartment buildings across the ends of the planks or down the edge where load-bearing block walls are to be built up off the flooring slab to take another floor above, so the slab does not crush under the weight. The strip may be in the range of 50 to 250mm wide, for example in the region of 100mm wide.

There are many types of concrete available, created by varying the proportions of the main ingredients. The mix design used for slabs of the present invention will depend on the type of structure being built, how the concrete will be mixed and delivered, and how it will be placed to form this structure. By varying the proportions of materials, or by substitution for the cernentitious and aggregate phases, the finished slab can be tailored to its application with varying strength, density, or chemical and thermal resistance properties.

Fine and coarse aggregates will typically make up the bulk of the concrete mixture for each layer. Sand, natural gravel and crushed stone are mainly used for this purpose. *S..

Recycled aggregates (from construction, demolition and excavation waste) may be used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash, may also be used. * **

Chemical admixtures for one or more layer (in the form of powder or fluids) may be added to the concrete to give them certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages will be less than 5% by mass of cement, and will be added to the concrete at the time of batching/mixing. Common types of admixtures that may be used in one or more of the layers are as follows.

Additives which may be used in one or more layer include: -accelerators (such as CaCl2 and NaCI)to speed up the hydration (hardening) of the concrete: -retarders (such as sugar, sucrose, sodium gluconate. glucose, citric acid, and tartaric acid) to slow the hydration of concrete; -air entrainments to add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concretes durability: -plasticisers/superplasticisers (water-reducing admixtures) to increase the workability of plastic or fresh concrete, allowing it be placed more easily, with less consolidating effort. Typical plasticizers are liginsulfate, polyol type.

Alternatively, plasticisers may be used to reduce the water content of a concrete (and have been called water reducers due to this application) while maintaining workability. Such treatment improves its strength and durability characteristics. Superplasticisers (high-range water-reducing admixtures) are a class of plasticisers which have fewer deleterious effects when used to significantly increase workability. Representative superplasticisers are sulfonated *1** * : * naphthalene formaldehyde condensate, sulfonated rnelamine, formaldehyde condensate, and acetone formaldehyde condensate. More advanced * * superplasticizers are polycarboxylate types: and *** * -pigments to change the colour of one or more layers, for aesthetic or colour-coding purposes; * 20 -corrosion inhibitors may be used to minimise the corrosion of steel and steel bars in layers; -pumping aids may be added to improve pumpability, thicken the paste, and reduce separation and bleeding.

Inorganic materials that also have pozzolanic or latent hydraulic properties and may be used in layers of the slab. These very fine-grained materials may be added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements). For example, fly ash, ground granulated blast furnace, silica fume and high reactivity metakaolin.

The slab of the present invention may be provided as a flooring slab or a walling slab.

According to a further aspect of the present invention there is provided a building structure incorporating one or more slabs as described herein.

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings. in which: Figure 1 is a perspective view of a floor comprising three concrete slabs formed according to the present invention one of which is shown in cut away form: Figure 2 is a section of one of the slabs of Figure 1: S... * . S...

Figure 3 is a section of a slab formed according to an alternative embodiment; * S * . Figure 4 is a section of a partially formed slab according to an alternative embodiment

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::; shown in a pre-cast state; Figure 4b is a section of the slab of Figure 4 shown with a further concrete layer introduced on-site; and Figure 5 is a section of a slab formed according to an alternative embodiment.

Referring first to Figure 1 there is shown a floor generally indicated 10 and composed of three elongate concrete slabs or planks 15, 20, 25. In this embodiment the slabs 15, 20, are substantially identical to each other, although in other embodiments floors made up of slabs which are different to each other are possible.

The slab 25 is shown in cut away form to illustrate its construction as also shown in more detail in Figure 2.

The slab 25 comprises three parallel layers arranged one on top of the other. The layers comprise: a first or base layer 30; an intermediate or second layer 35 and a cap or third layer 40.

The outer layers 30, 40 are formed from dense concrete with a density of approximately 2400 kg/rn 3. In contrast, the middle layer 35 is formed from lightweight foamed concrete with a density of approximately 400 kg/rn 3.

The first layer 30 is provided with a plurality of spaced, longitudinal tensioning rods 45 which allow this layer to be pretensioned. * I ***I

*...: 15 The layers 30, 35, 40 are tied together using a string of tie members 50. * * **

* . The slab 25 may be formed by any convenient method such as extrusion or moulding, **. *

::; with the rods 45 and ties 50 inserted during the production process.

* 20 Some of the benefits of the slab 25 are as follows. Slabs of this type can provide comparable spans to hollow core flooring but without the drawbacks. They are easier to manufacture without fluctuations in thickness particularly when compared to polystyrene core planks. With top reinforcement lifting with a forklift is possible and counter levers are possible. In other embodiments (not shown) cast-in lifting loops are provided which facilitate quicker and easier placement than existing hollow core slabs.

The constituents of the concrete layers 30, 35, 40 can be varied to suit particular circumstances. Expensive production equipment is not required unlike hollow core plank production.

Referring now to Figure 3 there is shown a slab 125 formed according to an alternative embodiment. The slab 125 comprises first and third layers 130, 140 which are formed from the same type of concrete and are approximately the same thickness. The density of the layers 130, 140 is greater than the layer 135.

Referring now to Figure 4a there is shown a slab 225 formed according to an alternative embodiment. The slab comprises a base layer 230 and an intermediate layer 235. The slab is cast in this form and transported to a site for installation. When the slab 225 is in place, a cap layer 240 is cast on top of the intermediate layer 235 as shown in Figure 4b.

Referring now to Figure 5 there is shown a slab 325 formed according to an alternative embodiment. *.SS * . *..*

The slab comprises a base layer 330, an intermediate layer 335 and a cap layer 340.

The intermediate layer 335 is formed from concrete having a density which is lower than * . that of either the cap later 340 or the base layer 330. In this embodiment the base layer **. *

** ** * 330 is formed from concrete having a density greater than both the intermediate layer 335 and cap layer 340. * 20

Beneath the base layer 330 is a sub-base which is formed from concrete having a greater density than the layer 330. On the top side of the cap 340 is a cover layer 360, which in this embodiment is formed from a plastics (i.e. non-concrete) material.

Claims

CLAIMS1. A concrete slab comprising a first layer of concrete having a first density, a second, intermediate layer of concrete having a second density and a third layer of concrete having a third density, the second density being less than the first and third densities.
2. A slab as claimed in Claim 1, in which the first layer comprises a base layer.
3. A slab as claimed in Claim 1 or Claim 2, in which the third layer comprises a cap layer.
4. A slab as claimed in any of Claims I to 3, in which the slab comprises one or more further layers. * SS

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5. A slab as claimed in Claim 4, in which the further layers comprise concrete.. * * * ***
6. A slab as claimed in any preceding claim, in which the first and third densities are substantially the same. * S. *. .

* *. 20 * S.
7. A slab as claimed in any preceding claim in which at least one of the layers is prestressed.
8. A slab as claimed in Claim 7, in which only the first and/or third layers ore prestressed.
9. A slab as claimed in Claim 7, in which only the first layer is prestressed.
10. A slab as claimed in any preceding Claim, in which at least two of the layers are tied together.
11. A slab as claimed in any preceding Claim, in which the second layer comprises foam concrete.
12. A slab as claimed in any preceding claim, in which at least one of the layers is pre-cast.
13. A slab as claimed in any preceding claim, in which at least one of the layers is poured-in-place.
14. A slab as claimed in any preceding claim, in which the density of the intermediate layer is in the range 100 to 2000 kg/m. S...IS..... * .
15. A slab as claimed in any preceding claim, in which the density of the * : intermediate layer is in the range 200 to 1600 kg/m 3, *.. * * S

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16. A slab as claimed in any preceding claim, in which the density of the * 20 intermediate layer is in the range of 300 to 600 kg/m 3.
17. A slab as claimed in any preceding claim, in which the density of the first and third layers is in the range 1500 to 2500 kg/rn.
18, A slab as claimed in any preceding claim, in which the density of the first and third layers is in the range 2000 to 2400 kg/rn 3.
19. A slab as claimed in any preceding claim, in which the thickness of the layers is in the range 25mm to 500mm.
20. A slab as claimed in any preceding claim, in which the thickness of each layer is different to each other.
21. A slab as claimed in any of Claims ito 19, in which the thickness of at least two of the layers is substantially the same.
22. A concrete slab substantially as hereinbefore described with reference to. and as shown in, the accompanying drawings.
23. A flooring slab comprising a slab as claimed in any preceding claim.
24. A walling slab comprising a slab as claimed in any of Claims 1 to 22. S... * S*.... 15
25. A building structure incorporating one or more slabs as claimed in any preceding claim. S.. * S. * S * *. S. * S * S S *.AAmendments to the claims have been made as follows:CLAIMS1. A multilayer lightweight concrete slab comprising a first layer of concrete having a first density, a second, intermediate layer of concrete having a second density and a third layer of concrete having a third density, the second density being less than the first and third densities, in which only the first and/or third layers are prestressed and in which all three layers are tied together.2. A slab as claimed in Claim 1, in which only the first layer is prestressed.3. A slab as claimed in Claim 1 or Claim 2, in which the layers are parallel and arranged one on top of the other.4. A slab as claimed in Claim 1, in which the first layer comprises a base layer.5. A slab as claimed in Claim I or Claim 2, in which the third layer comprises a cap layer.6. A slab as claimed in any of Claims 1 to 3, in which the slab comprises one or more further layers.S*5I*** * S 7. A slab as claimed in Claim 4, in which the further layers comprise concrete. S. * S * S..8. A slab as claimed in any preceding claim, in which the first and third densities are substantially the same. S. S S S* * **9. A slab as claimed in any preceding Claim, in which the second layer comprises foam concrete.10. A slab as claimed in any preceding claim, in which at least one of the layers is pre-cast.11. A slab as claimed in any preceding claim, in which at least one of the layers is poured-in-place.12. A slab as claimed in any preceding claim, in which the density of the intermediate layer is in the range 100 to 2000 kg/rn 3.13. A slab as claimed in any preceding claim, in which the density of the intermediate layer is in the range 200 to 1600 kg/rn 3.14. A slab as claimed in any preceding claim, in which the density of the intermediate layer is in the range of 300 to 600 kg/rn.15. A slab as claimed in any preceding claim, in which the density of the first and third layers is in the range 1500 to 2500 kg/rn 3.16. A slab as claimed in any preceding claim, in which the density of the first and third layers is in the range 2000 to 2400 kg/rn 3. * SS* S.... * S17. A slab as claimed in any preceding claim, in which the thickness of the layers is in the range 25mm to 500mm.18. A slab as claimed in any preceding claim, in which the thickness of each layer is * different to each other.19. A slab as claimed in any of Claims 1 to 17, in which the thickness of at least two of the layers is substantially the same.20. A concrete slab substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.21. A flooring slab comprising a slab as claimed in any preceding claim.22. A walling slab comprising a slab as claimed in any of Claims I to 20.23. A building structure incorporating one or more slabs as claimed in any preceding claim.II..... * I ** ***** * I ** * I * I.. * I* * * * I.. I I. I * * I * II