DE29822087U1 - Building material mixture with at least two powdered flour particles - Google Patents

Description

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PATENT AND LAW FIRM Patent Attorney Djpl.-Ing. H. Schmitt

SCHMITT, MAUCHER & BORJES PateS Attorney at Law H. Börjes-Pestalozza

Maxit Holding GmbH Dreikönigstrasse 13

Kettengasse 7a D-79102 Freiburg i. Br.

79206 Breisach

Telephone (07 61) 70 67 73 Fax (07 61) 70 67 76

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"G 98 638 M

Mr/hae

Building material mixture with at least two powdery flour components

The invention relates to a building material mixture for producing flowing screed, plaster, concrete or the like, with at least two powdered flour grain components, namely cement and a powdered filler, and optionally with a further powdered flour grain component such as fly ash, furthermore with sand and/or gravel, wherein a flow agent can be mixed into the building material mixture in the dry state or when mixed with liquid.

Such building material mixtures are known in different compositions and mixing ratios. In particular, such building material mixtures for flow screed based on anhydrite have been known for a long time. In recent years, alpha hemihydrate has been used as a binding agent alongside anhydrite. Such gypsum-bound flow screeds are characterized not only by their easy installation but also by minimal deformation during drying, so that relatively large areas can be laid without joints. However, due to the moisture sensitivity of gypsum, they are essentially limited to indoor areas, i.e. the inside of buildings. They are not suitable for permanently wet areas and/or areas outside buildings. This results in the disadvantage that, depending on the building, at least two different types of screed are required to produce the screed.

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Products or building material mixtures are required, namely gypsum-bound flow screed, which is valued for its easy workability, and conventionally composed and applied cement screed for permanently wet areas and outdoor areas.

Numerous attempts have been made to produce cement-based flow screeds, i.e. building material mixtures of the type mentioned above, which avoid the disadvantages mentioned above:

^ EP 0 427 064 B1 describes a hydraulic binding agent for the production of flowing screed, among other things. The key factor here is the use of low-aluminate cements (C ₃ A content < 3%) in combination with calcium sulfate alpha hemihydrate and finely divided silica. This is intended to prevent the formation of ettringite. According to example 2, this should enable a screed without expansion joints both indoors and outdoors.

DE 44 10 130 C1 describes a cement screed that is supposed to be crack-free and whose binding agent consists of a combination of Portland cement and a reactive calcium sulphate component

in order to form the maximum possible amount of ettringite. ^ It is important that after hardening there is an excess of calcium sulfate dihydrate in order to ensure the stability of the ettringite formed.

DE 44 10 850 C2 describes a process for producing a binding agent for hydraulically setting flowing screeds, whereby this binding agent is to consist of a mixture of calcium sulfate, ground granulated blast furnace slag and alumina cement and/or fused alumina cement. This is intended to cause the ettringite to form at the beginning of the hardening process, so that it has no damaging effect.

From DE 195 01 074 A1 the use of citric acid, tartaric acid

or their salts for expansion cements in a mixture of gypsum, Portland cement and alumina cement, whereby the organic acids or their salts are intended to ensure that the ettringite formation is completed before the formation of the cement phases begins.

EP 0 573 036 B1 describes the use of polypropylene glycol as a shrinkage-reducing additive. Although an improvement in the shrinkage is achieved compared to mixtures without this additive, the absolute value of a shrinkage of 0.7 mm/m after 28 days is still too high for practical use in floating screed constructions.

Similarly, the use of alkanediols to reduce shrinkage is known from EP 0 308 950 BI. Acceptable shrinkage values of 0.43 mm/m after 28 days are only achieved with a water-cement ratio of 0.5 in the mixture. This is achievable in laboratory tests, but not in practice.

According to DE 44 14 999 A1, shrinkage compensation is to be achieved by adding a substance in dissolved form to the mortar, which precipitates when the building material dries out

fe and therefore requires a larger volume than in dissolved form.

DE 33 28 898 describes a dry mix for a screed, whereby the use of calcium sulphate or expanding cements to compensate for shrinkage, i.e. ettringite formation, is proposed with regard to possible cracking.

The systems described above are all complicated multi-component systems as far as the binding agent or agents are concerned. The individual components of the respective mixtures must be precisely coordinated with one another. Except for construction chemical products, these systems have not yet been used on a significant scale. One of the reasons for this is the strong temperature dependence of the

Swelling properties during ettringite formation as well as a clear dependence on the amount of mixing water.

Use as low-shrinkage concrete or cement screed is therefore ruled out, since at the time of concreting or laying of screed, such buildings usually cannot be heated.

DE 295 18 306 U1 describes a self-levelling cement screed based on Portland cement and hard coal fly ash,

^ whereby water-cement ratios of 0.35 to 0.65 must be observed. However, with a water-cement ratio of 0.35 the material is very difficult to work with, while with a water-cement ratio of 0.65 shrinkage cracks and dishing have been observed even in small areas. In the middle range, with a water-cement ratio of 0.5, field sizes of a maximum of 30 m ² without joints are possible in practice.

This corresponds to the field sizes that are also used for conventional cement screeds. With larger field sizes, cracks must be expected. Another disadvantage is that the flow agent for this cement flow screed can only be added to the truck mixer at the construction site, which results in a loss of time due to the additional mixing time required.

The invention is therefore based on the object of creating a building material mixture of the type mentioned at the beginning, with which a flowing screed, plaster or cement-based concrete can be produced which has a reduced crack formation, thus enabling larger field sizes without joints. In particular, low-shrinkage cement-based mortars or concretes should be made possible which - apart from the sulphate carriers already present in the cement for setting control - do not contain calcium sulphate and are therefore easy to produce and safe to use. In the practical range, with water-cement values of, for example, 0.5, 0.6 to 0.8, a drying shrinkage of only approx. 0.3 mm/m should occur, thus enabling a field size of, for example, 200 m ² without

Joints are made possible.

The above object is essentially achieved according to the invention in that the building material mixture mentioned at the outset is characterized in that the weight proportions of the individual grain fractions of the powdered flour grain components of the total mixture are each the same size up to a size of about 0.1 mm to 0.4 mm, so that in the logarithmic representation of the weight percentages of these flour grain components over their increasing size distribution, a linear or largely linear progression is given.

Tests have shown that with such an adjustment of the fine mixture components or fine grain fractions, after mixing the mixture and adding a flow agent in the plastic state, initially no or only very slight shrinkage occurs because the mass automatically compacts itself almost optimally, which in the case of conventional concrete must be achieved by using vibrators. It has also been shown that during the subsequent drying process only relatively little shrinkage takes place and, above all, hardly any cracks occur, even if the mixed building material mixture - for example as a flowing screed - is applied or laid over large areas of, for example, 100 m ² or even 200 m ² without joints .

Shrinkage is understood to mean the deformation of a screed, mortar or concrete in the first few hours after mixing and spreading, while the mixed mass is still plastic. Surprisingly, it was found that, for the same extent of drying shrinkage, the susceptibility to cracking of such a component made of mortar or concrete or of the building material mixture according to the invention is lower the lower the shrinkage in this first phase of setting. It was already known that very high shrinkage values in the first few days of applying a layer of screed, mortar or concrete lead to the formation of cracks in components, namely to so-called early shrinkage cracks, but for the first time

The present invention establishes a connection between the degree of shrinkage and the formation of cracks during the subsequent drying of components and thus shrinkage.

It is assumed that strong shrinkage during the setting of the building material or mortar mass disrupts the interlocking of the crystals that are forming in the cement matrix. Although this cannot be recognized macroscopically as a crack - except in the case of very high shrinkage values - since the mass is still plastic, the 0 structure that is forming in this area is disrupted.

^ When drying shrinkage occurs much later, cracks then form at these weak points, which is now avoided by the invention by keeping the shrinkage very small or largely avoiding it.

For particularly good compaction of the mixed building material due to the powdery fine grain components, it is advantageous if the grain size of the fine grain components is optimized to a grain size of equal to or smaller than about 0.2 mm. Even with grain sizes of the fine grain components of about 0.1 mm to about 0.4 mm, the gaps between the sand and gravel components are well filled, which is even more effective with the optimization of the fc grain size mentioned above.

It is expedient if the quantities and weight proportions of the other components such as sand, gravel or the like are selected in accordance with DIN 1045. In an advantageous manner, there is no need to deviate from the conventional technique with regard to the predominant quantities of the mixture components. The invention lies rather in selecting the fine or fine grain proportions in the manner mentioned in order to be able to produce surprisingly large areas of flowing screed or plaster and still achieve a largely crack-free finish.

A further embodiment of the invention may consist in that

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the building material mixture contains quicklime as a further powdered fine grain component in the form of burnt lime in the fine grain size up to 0.4 mm, in particular up to about 0.2 mm, and the proportions of this quicklime component are adapted to the proportions of the other fine grain components in such a way that a linear or largely linear progression is given in the logarithmic representation. This means that after the possible initial slight shrinkage of the mixed and discharged, still plastic building material mixture, an expansion occurs before the final drying process begins, so that the aforementioned

^ Shrinkage in the plastic phase is fully or partially compensated or, in some cases, even slightly overcompensated. Within certain limits, such overcompensation can be advantageous, especially for large-area processing, because tests have shown that if the preceding shrinkage in the plastic phase is overcompensated, the formation of cracks in the drying phase is minimal.

The flow agent added to the building material mixture or to the mixing liquid can consist of melamine-formaldehyde polycondensates and/or condensed naphthalene sulfonates and/or lignin sulfonates and/or condensed phenol-formaldehyde polymers and/or

fc carboxylated polyethers. Thus, the flow agent,

selected and adapted depending on the building material mixture.
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Furthermore, the building material mixture can contain setting retarders or setting accelerators in a manner known per se.

The invention also relates to a method for producing a building material mixture which, together with mixing liquid, produces flowing screed, plaster or concrete, wherein sand and/or gravel is mixed in a dry state with at least two powdered fines components, namely cement and a powdered filler, optionally at least one further powdered fines component such as fly ash.

The task mentioned at the beginning can be solved by first determining the grain size distribution in the cement - for example with a laser granulometer - and then grinding and classifying the fractions of the fine grain or fine grain components, i.e. the filler(s) and/or the fly ash, in such a way that the grain size distribution complements the grain size distribution of the cement in such a way that the mixture of these fines or fine grain components of cement and filler and/or fly ash in the finest grain range up to a size of about 0.1 mm to 0.4 mm grain size results in a constant grain size distribution. It has been shown that when mixing a

* With such a building material mixture, compaction occurs practically automatically, because the fine grains present in the appropriate distribution can practically automatically fill the gaps between the components with larger grain sizes. This 5 means that in the still plastic phase, only a slight shrinkage occurs, so that in the later drying phase, the risk of cracks forming is also significantly reduced.

The optimization of the fine grain proportions is preferably carried out up to a grain size of less than or equal to 0.2 mm in terms of their weight proportion, i.e. the fine grain proportions are mixed in with a grain size of up to 0.2 mm.

In this case, quicklime in fine grains up to 0.4 mm, especially up to 0.2 mm, can be added to the mixture as an additional fine grain or fine grain portion and the weight proportions of the individual grain fractions of this total mixture of fine grain portions can be adjusted so that a linear or largely linear progression is created in the logarithmic representation of these weight proportions of all fine grain portions in the fine grain range. This quicklime portion can ensure that after an initial slight shrinkage of the still plastic building material mixture, an expansion occurs before the final drying process begins, so that the shrinkage in the plastic phase is fully or partially compensated or possibly even overcompensated, which reduces the risk of

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the risk of cracking in the subsequent drying process is greatly reduced.

A flow agent, for example melamine-formaldehyde polycondensates and/or condensed naphthalene sulfonates and/or lignin sulfonates and/or condensed phenol-formaldehyde polymers and/or carboxylated polyethers, can be added to the dry mix or the mixing liquid. A conventional flow agent made from one or more known substances can therefore be used and adapted to the respective building material mixture in order to optimize it.

^ Furthermore, one or more setting retarders or setting accelerators can be added to the building material mixture in a known manner. The mixture components that are larger than the grain size of the fine grain or powder grain components, in particular sand and/or gravel, can be added according to the rules of concrete technology, for example according to DIN 1045.

Especially when combining one or more of the features and measures described above, a cement screed can be laid crack-free in a field size of up to 200 m ² by meeting the following requirements:

fe Water requirement: 11 - 12 %

Flow: 2 2 - 25 cm

Fresh mortar weight: 2.10 - 2.20 g/cm ³

Shrinkage: max. - 0.1 mm/m

Sources: max. + 0.2 mm/m

Drying shrinkage: max. - 0.4 mm/m

An analogous application is possible for concrete or cement mortar.

The invention is explained in more detail below by means of examples and with the aid of diagrams belonging to these examples:

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Example 1:

A cement screed was set up in such a way that the grain distribution of the fine grain portions is constructed or composed as shown in the diagram in Fig.1. The particle size is shown on the X-axis in logarithmic increase and the respective portion in weight percent is shown on the Y-axis. Below the diagram, individual particle sizes, their associated total portion and their respective individual portion are shown again in the form of a table. Accordingly, a fine grain portion with the particle

^ size 1 micron a total content of 4.3 weight percent is present.

The next largest particle size applied, 1.5 microns, is present with an individual proportion of 1.7%, so that of the fine grain fractions of a particle size of 1 micron and 1.5 microns, a total of 5 percent by weight is present, etc. The largest particle size in Fig. 1 is 192 microns, i.e. slightly less than 0.2 mm, and components in this particle size make up 3% of the total fine grain fraction of a building material mixture.

According to the diagram in Fig. 2, this leads to a maximum shrinkage of 0.04 mm/m, followed by swelling and then to a drying shrinkage after 1000 hours of 0.33 mm/m.

The maximum swelling value is used as the 0-reference value for the drying shrinkage.

A cement screed adjusted in this way, in which the weight proportions of the individual grain fractions of the powdered flour grain portions of the total mixture are each approximately equal from almost 0 to about 0.1 mm, leads to a largely linear curve in the diagram according to Fig.1, which, like the ideal grain size distribution in Fig.1, is set with a dashed line in comparison to the actual curve.

In practice, a cement screed prepared in this way has been laid without joints and without cracks up to a field size of 200 m ²

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remained.

Example 2:
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The building material mixture for a cement screed according to Example 2 was adapted with regard to the grain distribution in the flour grain area even closer to the ideal grain distribution according to the dashed line in the diagram in Fig.1 and Fig.3, as can also be seen from the table below the diagram in Fig.3.

^ also the respective individual portion better matches the ideal horizontal dashed line of an ideal respective portion of the different particle size compared to the example in Fig.1 is somewhat improved.

This leads to a shrinkage and contraction behavior according to the diagram in Fig.4, i.e. the initial shrinkage is practically avoided and after 1000 hours a drying shrinkage of only 0.29 mm/m was measured compared to the largest swelling value.

In practice, this cement screed, like that in Example 1, also remains crack-free up to a field size of 200 ^m2 , even with difficult geometries.

Comparison example:

For clarification, a building material mixture for a cement screed was adjusted in the comparative example according to the diagram in Fig. 5 so that the grain distribution of the powder grains with a size of up to 0.2 mm has a course that deviates greatly from the distribution according to the invention, which is illustrated by the large deviation of the actual distribution curve from the ideal dashed line.

5 According to the diagram in Fig.6, this initially leads to a maximum

Shrinkage of 0.2 mm/m in the plastic phase, so that the subsequent swelling practically only leads back to the initial value, from which a drying shrinkage of also 0.33 mm/m was measured after 1000 hours, again related to the maximum swelling as a zero reference value.

In practice, this cement screed shows a clear cracking, although the drying shrinkage is approximately the same as that of the example according to Fig.1 and 2. Since in both examples the same cement, the same flow agent and

^ the same other recipe ingredients were used unchanged, with the exception of the fineness of the filler used, the same value for drying shrinkage was obtained as expected, but due to the different distribution of the particle sizes of the individual flour grain components, there was a different behavior in terms of crack formation, according to which in example 1 the absence of cracks was achieved with a field size of 200 m ² , whereas in the comparison example crack formation occurred due to the unfavorable distribution of the individual proportions of the flour grain components.

This shows that, for the same extent of drying shrinkage fc, the crack susceptibility of the component made from the building material mixture is lower the lower the shrinkage at the beginning in the still plastic phase.

In a building material mixture for the manufacture of flowing screed in particular, but also plaster, concrete or the like, which contains several powdered flour grain components and in each case cement and a powdered filler, the weight proportions of the individual grain fractions of the powdered flour grain components of the total mixture up to a size of about 0.1 mm to about 0.4 mm and expediently in a size of 0.001 mm to 0.2 mm are each approximately the same size, so that in the logarithmic representation of the weight percentages of these flour grain components over their increasing

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Size distribution is largely linear. If there is too great a deviation from this linear progression, excessive shrinkage occurs in the first plastic phase and thus cracks form in the subsequent drying phase, at least for a larger field size.

Expectations

Claims (6)

1. Building material mixture for producing flowing screed, plaster, concrete or the like, with at least two powdery fine grain components, namely cement and a powdery filler, and optionally with a further powdery fine grain component such as fly ash, furthermore with sand and/or gravel, wherein a flow agent can be added to the building material mixture in the dry state or when mixed with liquid, characterized in that the weight proportions of the individual grain fractions of the powdery fine grain components of the overall mixture are each approximately the same up to a size of approximately 0.1 mm to 0.4 mm, so that in the logarithmic representation of the weight percentages of these fine grain components over their increasing size distribution, a linear or largely linear progression is given. 2. Building material mixture according to claim 1, characterized in that the optimization of the grain size of the flour grain components takes place up to a grain size of equal to or smaller than about 0.2 mm. 3. Building material mixture according to claim 1 or 2, characterized in that the quantity and weight proportions of the further components such as sand, gravel or the like are selected according to DIN 1045. 4. Building material mixture according to one of claims 1 to 3, characterized in that it contains, as a further powdered fine grain component, quicklime in the fine grain size up to 0.4 mm, in particular up to about 0.2 mm, and the proportions of this quicklime component are adapted to the proportions of the other fine grain or fine grain components in such a way that a linear or largely linear progression is given in the logarithmic representation. 5. Building material mixture according to one of claims 1 to 4, characterized in that the flow agent mixed into the building material mixture or which can be mixed with the mixing liquid consists of melamine-formaldehyde polycondensates and/or condensed naphthalene sulfonates and/or lignin sulfonates and/or condensed phenol-formaldehyde polymers and/or carboxylated polyethers. 6. Building material mixture according to one of claims 1 to 5, characterized in that it contains setting retarders or setting accelerators.