DE20304239U1 - Lightweight concrete mixture containing sand, cement and low density component also contains plasticizer based on polycarboxylate ether and stabilizer - Google Patents

Abstract

Dry lightweight concrete mixture containing sand, cement and a low density component also contains plasticizer(s) based on polycarboxylate ether and stabilizer(s). An independent claim is also included for the lightweight concrete mix made from this dry mixture and water.

Description

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Pumpable lightweight concrete and dry mix for it Scope of the invention

The invention relates to a dry or mixed lightweight concrete mixture consisting of at least sand, cement and a low-density component, in particular granulated blast furnace pumice or preferably expanded clay grains, and optionally fly ash and/or limestone powder.

Background of the invention

Such lightweight concrete mixtures are well known and have the advantage over normal concrete of lower bulk density, lower weight, reduced thermal conductivity and yet good heat storage capacity, whereby this lightweight concrete can also be waterproof after mixing, pouring and setting.

However, processing is particularly difficult when this lightweight concrete has to be transported over a long distance after mixing because it cannot be pumped or can only be pumped with difficulty. This is due to

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because the very light expanded clay grains have a tendency

O to separate from the rest of the prepared mixture and

for example, to float up and deposit on the walls of a pumping line, while the finer but heavier components such as sand and ^cement can be moved more easily through the corresponding pumping line, together with the mixing water.

It is therefore necessary for such lightweight concrete mixtures to be constantly stirred and moved after mixing and

' should be processed as directly as possible at the point of mixing, for example by pouring it into the appropriate formwork.

If such lightweight concrete is to be transported by pumps, relatively large-volume piston pumps must be used, which are themselves expensive and require that the lightweight concrete is pumped from the outset in a controlled consistency that requires a high pump pressure.

The task is therefore to create a lightweight concrete mixture of the type mentioned above that can be pumped more easily and also allows the use of continuously operating pumps, for example screw pumps.

General description of the invention

To achieve this object, the lightweight concrete mixture defined at the outset comprises at least one polycarboxylate ether-based superplasticizer and at least one stabilizer as additional mixture components.

The superplasticizer makes the lightweight concrete mixture so fluid that it can be pumped very easily.

also with a screw pump. The stabilizer prevents the

Q Separation, so that the expanded clay grains, which are easily floating, no longer separate from the mixture, _ but remain in the desired manner within the mixture ^&ohgr; and are pumped along, so that even at the end of a pumping line the desired mixed lightweight concrete mixture arrives largely homogeneous.

It should also be mentioned that the pumpability can be further improved if the mixture contains one or more pore formers. Tests have shown that such air-entraining agents also contribute to the stabilization of the expanded clay grains. This therefore fulfills a dual function by further reducing the bulk density of the lightweight concrete and also reducing the risk of segregation.

Detailed description of the invention

Where the percentages given below are in weight, these refer to the mixture of cement, sand, low density component and (where present) limestone filler and/or fly ash.

Polycarboxylate ethers are flow agents known as superplasticizers, in which polycarboxylates with polyether-like side chains (usually mixtures of polymers of different molecular sizes) are present. In a possible preferred variant of the invention, these can be present in a proportion of 0.01 to 0.5% by weight, in particular, for example, from 0.02 to 0.2% by weight.

Stabilizers used are in particular those based on alkyl cellulose, such as methyl cellulose, in a proportion that

for example in a preferred lightweight concrete mixture in

a proportion of 0.005 to 0.2, preferably 0.01 to 0.1 wt.

%, or based on bentonite, which can be present, for example, in a preferred embodiment in a proportion of 0.05 ^ω to 0.5, preferably 0.01 to 0.3 wt. %, or mixtures thereof. The stabilizer or stabilizers are incorporated into the mixture in powder form in a preferred embodiment of the invention.

In addition, in a possible preferred embodiment of the invention

' Lightweight concrete contains one or more air-entraining agents, for example in a proportion of 0.0001 to 0.2, in particular for example from 0.0003 to 0.1% by weight. Substances which form a stable microfoam in the lightweight concrete are used as air-entraining agents, for example resin soaps or resins or in particular fatty alcohol sulfates, or also mixtures of two or more of these components.

The proportion of cement in a possible preferred lightweight concrete mixture according to the invention can be, for example, 20 to 50% by weight, with a range of 25 to 45% by weight representing a possible particularly preferred variant. For example, Portland cement (CEM I) is used.

The proportion of sand, in particular a natural sand (which can also contain gravel or consist only of gravel of a corresponding grain size), for example with a grain size of less than 5 mm, e.g. in a conceivable preferred embodiment of the invention from 0 to 4 mm, can for example be 20 to 80 wt.% in a possible preferred lightweight concrete mixture according to the invention, with a range of 30 to 70 wt.% representing a possible particularly preferred variant.

The proportion of low density components, especially expanded clay,

for example with a grain size of less than 8 mm, e.g.

In a conceivable preferred embodiment of the invention, the thickness of the concrete can range from 0 to 5 mm, for example in a possible preferred lightweight concrete mixture according to the invention, from 5 to 25% by ^weight , with a range of from 8 to 20% by weight representing a possible particularly preferred variant.

If desired, limestone powder (limestone filler) and/or fly ash can also be added, each in a

' possible proportion, for example, from 0 to 20 wt.%, with a proportion of 0 to 15 wt.% representing a possible particularly preferred variant.

A prepared lightweight concrete mixture contains a dry mixture as described above and also water in usual proportions, for example in a possible preferred embodiment in a proportion of 8 to 22, in particular 10 to 20 percent by weight based on the dry mass.

Examples:

The following examples illustrate the invention without limiting it:

5 Example 1: Lightweight concrete LB 25 (bulk density 1.6):

Components Proportion (wt.% based on
dry mix) Cement CEM I 3 2.5 R 22 Cement CEM I 52.5 R 12 Natural sand 0-4 mm 45 Expanded clay 0-5 mm 1 2 Limestone filler 4

Fly ash 5 Polycarboxylate ether 0.04 Fatty alcohol sulfate 0.0015 Bentonite 0.05 Methyl!cellulose 0.02

Example 2: Lightweight concrete LB 15 (bulk density 1.4)

Components Proportion (wt.% based on
dry mix) Cement CEM I 32.5 R 21 Cement CEM I 52.5 R 10 Natural sand 0-4 mm 46 Expanded clay 0-5 mm 14 Limestone filler 5 Fly ash 4 Polycarboxylate ether 0.04 Fatty alcohol sulfate 0.002 Bentonite 0.05 Methylcellulose 0.02

/ Expectations

Claims (12)

1. Dry lightweight concrete mixture, consisting of at least sand, cement and a low density component, characterized in that the lightweight concrete mixture has as additional mixture components at least one polycarboxylate ether-based flow agent and at least one stabilizer. 2. Dry lightweight concrete mixture according to claim 1, characterized in that it contains fly ash and/or limestone powder as further mixture components. 3. Dry lightweight concrete mixture according to one of claims 1 or 2, characterized in that the low density component consists of pumice or preferably expanded clay grains. 4. Dry lightweight concrete mixture according to one of claims 1 to 3, characterized in that it additionally contains an air-entraining agent, in particular a fatty alcohol sulfate. 5. Dry lightweight concrete mixture according to one of claims 1 to 4, characterized in that an alkyl cellulose, in particular methyl cellulose, or bentonite, or a mixture of two or more of these stabilizers, is provided as stabilizer. 6. Dry lightweight concrete mixture according to one of claims 1 to 5, characterized in that, based on the mixture of cement, sand, low-density component and, if present, limestone powder and/or fly ash, the cement is present in a proportion of 20 to 50% by weight, the sand in a proportion of 20 to 80% by weight, the low-density component, in particular expanded clay grains, in a proportion of 5 to 25% by weight, the limestone powder in a proportion of 0 to 20% by weight, fly ash in a proportion of 0 to 20% by weight, a first stabilizer in a proportion of 0.005 to 0.2% by weight, a second stabilizer in a proportion of 0.05 to 0.5% by weight, a polycarboxyl ether as a flow agent in a proportion of 0.01 to 0.5% by weight, and an air entraining agent in a proportion of 0.0001 to 0.2% by weight. 7. Dry lightweight concrete mixture according to one of claims 1 to 5, characterized in that, based on the mixture of cement, sand, low-density component and, if present, limestone powder and/or fly ash, the cement is present in a proportion of 25 to 45% by weight, the sand in a proportion of 30 to 70% by weight, the low-density component, in particular expanded clay grains, in a proportion of 8 to 20% by weight, the limestone powder in a proportion of 0 to 15% by weight, the fly ash in a proportion of 0 to 15% by weight, a first stabilizer in a proportion of 0.01 to 0.1% by weight, a second stabilizer in a proportion of 0.01 to 0.3% by weight, a polycarboxyl ether as a flow agent in a proportion of 0.02 to 0.2% by weight, and an air entraining agent in a proportion of 0.0003 to 0.1% by weight. 8. A dry cement mixture according to any one of claims 1 to 7, wherein the cement is Portland cement. 9. Dry cement mixture according to one of claims 1 to 8, wherein the sand has a grain size of 0 to 4 mm. 10. Dry cement mixture according to one of claims 1 to 9, wherein the low density component, in particular expanded clay grains, has a grain size of 0 to 5 mm. 11. Prepared lightweight concrete mixture comprising a mixture of a dry lightweight concrete mixture according to one of claims 1 to 10 and water. 12. Prepared lightweight concrete mixture according to claim 11, wherein the water content, based on the weight of the dry mixture, is 10 to 20 wt.%.