EP4271660A1 - Hydraulically bound multilayer panel - Google Patents

Abstract

The invention relates to a method for producing a hydraulically bound multilayer panel comprising at least one facing layer and at least one core layer. The method has the following steps: a. introducing a flowable facing mixture into a mold, said facing mixture containing at least the following components: i. an facing glue containing at least 1. a hydraulic binder and 2. water; and ii. an aggregate, said aggregate having an average diameter d50 which is greater than or equal to 100.0 µm, determined according to ISO 13320:2009 and/or EN 12620, whereby an facing mixture layer is formed; b. introducing a dried to earth-moist core mixture into the mold, wherein the core mixture contains at least the following components: i core glue containing at least 1. a hydraulic binder, 2. a fine material, said fine material having an average diameter d50 of up to 100.0 µm, determined according to ISO 13320:2009, and 3. water; and ii. an aggregate, said aggregate having an average diameter d50 which is greater than 100.0 µm, determined according to ISO 13320:2009 and/or EN 12620; whereby a core mixture layer is formed, and c. compressing the facing mixture layer together with the core mixture layer in the mold in order to form a hydraulically bound multilayer panel which can be directly stripped and which comprises at least one facing layer and at least one core layer, wherein water contained in the facing mixture layer is partly or completely pressed into the core mixture layer.

Description

Hydraulically bonded multilayer board

The invention relates to a method for producing a hydraulically bound multi-layer board with at least one facing layer and at least one core layer, and a multi-layer board produced using the method.

Background of the Invention

Multi-layer panels of the type mentioned at the outset are known in principle and are used, for example, as floor coverings, including for outdoor applications such as gardens and terraces.

Basic requirements for concrete slabs are regulated in EN 1339 and the national application standards DIN EN 1339 and ÖNORM EN 1339. With regard to the load-bearing capacity, a certain flexural strength or a minimum breaking load determined in the flexural test is required. Large-format products in particular usually have to meet a minimum requirement for the characteristic flexural strength of at least 5.0 MPa and the characteristic breaking load of at least 7 kN. It should be noted here that the strength values that are actually required depend heavily on the actual size of the panel and that special load conditions must be taken into account, especially for lengths > 600 mm. The dimensions of the panels according to EN 1339 are limited. These are as follows: (1) Minimum panel thickness according to ÖNORM EN 1339: 4 cm ± 1 mm; (2) total length: < lm; and (3) total length to thickness ratio: > 4.

In addition to the requirements for load-bearing capacity, requirements for durability must also be met. The finished products should have very good weather resistance (weathering according to DIN EN 1338/DIN EN 1339 < 50 g/m ² ) and/or adequate abrasion resistance (abrasion according to DIN EN 1338/1339 < 20 mm).

In addition, there are requirements regarding the limitation of deformation (concave deformation of the panels < 2.0 mm) due to creep, shrinkage and thermal deformation. The board must be optimized in terms of porosity and capillarity in such a way that it has a high resistance to contamination (no capillary suction and/or very low water absorption < 1.0% according to DIN EN 1338/1339).

Floor tiles that meet the above minimum requirements can be manufactured using different production techniques. These include the casting process, wet pressing process, vibratory pressing process, hammer mill process and the hermetic process.

According to the current status, it is possible to produce multi-layer panels economically using the hermetic process. The hermetic process is mostly used for the production of two-layer terrace and pavement slabs, as well as large-format slabs for public spaces and buildings in high quality and density. Thin single-layer panels for interior use and building cladding can also be manufactured using the hermetic process.

The visible layer facing upwards or outwards is referred to as the facing layer, the non-visible layer facing downwards or inwards is referred to as the core or backfill layer. Both the facing layer and the core layer must meet the requirements of the manufacturing process. The facing layer is first made flowable so that after filling it fills the corners of the formwork and can even begin to level out. Leveling can be supported by vibrating or pressing on attachment distribution plates. The core layer, on the other hand, is usually produced dry to earth-moist and is usually applied to the facing layer with a layer thickness that is as homogeneous as possible using a filling funnel and a slider. By pressing both layers, in which excess water is pressed from the facing layer into the core layer and a strong compression is also carried out, the production process results in a stable multi-layer panel that can be stripped immediately and that can be removed using vacuum lifting devices and stored on pallets. Products manufactured using the hermetic process are characterized by a special surface quality that is well suited for further processing by means of grinding, brushing and blasting. In addition, the hermetic process can be used to produce a stable and storable product that can be stripped immediately.

According to the current status, floor panels from a thickness of 30 mm up to an edge length of 400 mm and from a thickness of 40 mm with an edge length of up to 800 mm can be manufactured using the hermetic process. However, large-format, thin multi-layer panels which have a larger edge length/thickness ratio cannot be produced, or cannot be produced satisfactorily, with previous production techniques. In particular, the mechanical properties and thus the usability of such large-format, thin multi-layer panels are often unsatisfactory.

It is therefore an object of the invention to provide an improved method with which, in particular, large-format, thin multi-layer boards that can be stripped directly can also be produced.

Description of the invention

The above object is achieved by a method for producing a hydraulically bound multi-layer board with at least one facing layer and at least one core layer, the method comprising the following steps: a. Introduction of a free-flowing facing mixture into a mold, the facing mixture containing at least the following components: i. containing at least

1. hydraulic binder and

2. water; such as 11. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm; whereby a facing mixture layer is formed; b. Introduction of a dry to earth-moist core mixture into the mould, the core mixture containing at least the following components: i. containing glue at least

1. hydraulic binder,

2. Extremely fine material, where the extremely fine material has an average diameter d50 determined according to ISO 13320:2009 of up to 100.0 μm, and

3. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm; thereby forming a core mixture layer, and c. Pressing the facing mixture layer with the core mixture layer in the mold to form a hydraulically bound, directly strippable multi-layer panel with at least one facing layer and at least one core layer, the water contained in the facing mixture layer being pressed partially or completely into the core mixture layer.

Within the meaning of the invention, directly strippable is understood in particular to mean that the multi-layer board can be removed from the mold immediately or shortly after pressing, for example by means of vacuum lifting, and/or has a strength that enables further processing and storage without formwork.

With the method according to the invention, a multilayer board can be produced which can have an edge length/thickness ratio of more than 20 and is nevertheless distinguished by a high characteristic flexural strength and/or a high characteristic breaking load. The advantages of the manufacturing process according to the invention are particularly evident in the case of large-format products. In particular, it is possible with the method according to the invention to produce multilayer panels with edge lengths of more than 800 mm and/or thicknesses of less than 40 mm, in particular thicknesses of 25 to 35 mm. Surprisingly, it was found that multi-layer panels produced by the method according to the invention have a high load-bearing capacity and serviceability despite the higher edge length-to-thickness ratio and are outstandingly suitable for use as floor coverings, especially for outdoor applications.

In order to produce a large format multi-layer board that meets all minimum floor covering requirements, conventional pressing methods use layers of core mixture, which after pressing have a void content, so the degree of compaction is less than 1.0. A degree of compaction of less than 1.0 is necessary for good compression of the water from the face mix layer into the core mix layer. A high degree of compaction would lead to excess water being able to form at the edge of the panels after the pressing process. With a high degree of compaction in the core mix layer, there is also the risk that the excess water from the facing mix layer cannot penetrate to the underside of the core mix layer. As a result, layers with different water contents can form in the core mixture layer, which would lead to uneven or incomplete activation of the hydraulic binder in the core mixture layer and to a deterioration in the mechanical properties of the multilayer board. In addition, core mixtures that have a high fines content and low water content can lead to problems in the mixing process, such as insufficient dispersion of the fines, clumping and dust formation. In addition, an insufficiently mixed core concrete can be problematic with regard to the compactibility as well as the subsequent hardened concrete properties.

The present invention now provides a manufacturing process in which the face and core mix layers optimally cooperate to produce a multilayer board with an optimized packing density and water requirement.

Without being bound to any particular theory, the interaction of the very fine material contained in the core size with the additive contained in the core size appears to be essential for the process according to the invention. Fines with a mean diameter d50 smaller than the mean diameter d50 of the hydraulic binder fill the interstices of the binder particles instead of void water. Very fine materials with an average diameter d50 similar to a binder do not fill the gaps, but still have a lower water requirement than the binder. Fines with an average diameter d50, which is higher than the diameter d50 of the hydraulic binder, but not more than 100 μm, and aggregate with an average diameter d50, which is higher than 100 μm, presumably reduce the density of the mixture when the excess water is pressed out from the face mix layer, which favors injecting the water from the face mix layer into the core mix layer.

Contrary to expectations, the proportion of fines in the core glue mixture does not impair sufficient pressing of the excess water from the face mix layer into the core mix layer. On the contrary, the core mixture used in the process according to the invention has an optimum water/powder ratio, which enables excellent processability of the core mixture and strength and durability of the multilayer boards.

The core mixture contains at least the following components: i. containing glue at least

1. hydraulic binder,

2. Extremely fine material, where the extremely fine material has an average diameter d50 determined according to ISO 13320:2009 of up to 100.0 μm, and

3. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm.

By placing the core mix in the mold, a layer of core mix is formed.

When introduced into the mould, the core mixture has a dry to earth-moist consistency. When introduced into the mold, the core mixture preferably has a consistency of at most consistency class Fl according to DIN 1045-2 and/or EN 206. According to DIN 1045-2, consistency class Fl has a slump of < 340 mm and a stiff consistency, whereas the higher consistency classes F2 to F6 have larger slumps and softer or more flowable consistencies. A preferred embodiment of the invention provides that the core mixture layer before pressing according to step c. a consistency of maximum consistency class Fl according to DIN 1045-2 and/or EN 206.

The core mix layer is formed by placing a dry to semi-dry core mix in a mold, the core mix containing at least core glue and aggregate. According to a preferred embodiment of the invention contains the Core mixture, based on the total dry weight of the core mixture, at least 450 kg/m ³ , in particular 450 to 1250 kg/m ³ , more preferably 600 to 1250 kg/m ³ core glue.

finest fabric

According to the invention, the core glue contains very fine material. Very fine material within the meaning of the invention is material which has an average diameter d50, determined according to ISO 13320:2009, of up to 100.0 μm. “Mean diameter” within the meaning of this invention is always to be understood as meaning the mean diameter d50 determined according to ISO 13320:2009.

According to the invention, the core glue can contain very fine material with an average diameter of 1.0 to 100.0 μm. In a preferred embodiment, the core size contains fines with an average diameter d50 determined according to ISO 13320:2009 of 1.0 to 100.0 μm in an amount of 5 to 45% by volume, based on the total volume of hydraulic binder contained in the core size and fines.

An advantageous further development provides that the core glue contains very fine material which has an average diameter d50, determined according to ISO 13320:2009, which is smaller than the average diameter d50, determined according to ISO 13320:2009, of the hydraulic binder contained in the core glue . This ultra-fine material fills the interstices of the hydraulic binder particles instead of what is known as cavity water, which means that a higher packing density and reduced water requirements can be achieved. In addition, such a fine material can replace part of the hydraulic binder, which in the case of a cement replacement can lead to a reduced clinker content with a lower efflorescence potential.

According to a preferred embodiment of the invention, the core size contains fines with a mean diameter that is smaller than the mean diameter of the hydraulic binder in an amount of 5 to 45% by volume based on the total volume of hydraulic binder and fines contained in the core size . In another version the core glue contains fines with a mean diameter that is smaller than the mean diameter of the hydraulic binder in an amount of 5 to 45% by volume based on the total volume of the hydraulic binder and the fines of the core size.

The very fine material contained in the core glue particularly preferably has an average diameter d50, determined according to ISO 13320:2009, of from 1.0 to 30.0 μm, preferably from 1.0 to 5.0 μm. In a preferred embodiment, the core glue contains very fine material with an average diameter d50, determined according to ISO 13320:2009, of 1.0 to 30.0 μm in an amount of 5 to 45% by volume, based on the total volume contained in the core glue hydraulic binder and fines. The core glue particularly preferably contains very fine material with an average diameter d50, determined according to ISO 13320:2009, from 1.0 to 5.0 μm in an amount from 5 to 20% by volume, in particular from 8 to 15% by volume. related to the total volume of hydraulic binder and fines contained in the core glue.

It has also proven to be advantageous if the core glue contains ultrafine material with an average diameter d50, determined according to ISO 13320:2009, of 30.1 to 100.0 μm in an amount of 0 to 45% by volume, in particular from 0 to 25 % by volume, based on the total volume of hydraulic binder and fines contained in the core size. In a preferred embodiment, the core glue has fines with an average diameter of 30.1 to 100.0 μm in an amount of 0% by volume.

According to the invention, the very fine material can be a rock aggregate, in particular a rock aggregate based on quartz and/or limestone.

An advantageous further development provides that the ultra-fine material contains at least one inert powdered rock, preferably an inert powdered rock selected from the group consisting of limestone, dolomite and quartz, or a combination thereof. In one embodiment, the core glue contains inert rock flour Feinststoff in an amount of 5 to 45 % by volume, in particular from 20 to 45% by volume, based on the total volume of hydraulic binder and fines contained in the core glue.

Furthermore, it is preferably provided that the very fine material contains at least one hydraulically active material. In one embodiment, the superfine contains at least one hydraulically active, synthetically produced substance and/or one hydraulically active natural substance. Preferably, the fines contain at least one hydraulically active material selected from the group consisting of blast furnace slag, microsilica and fly ash, or a combination thereof. In a particularly preferred embodiment of the invention, the very fine material contains microsilica. The finest material particularly preferably consists of a hydraulically active material, in particular microsilica. The core size particularly preferably contains hydraulically active fines, in particular microsilica, in an amount of 5 to 20% by volume, in particular 8 to 15% by volume, based on the total volume of hydraulic binder and fines contained in the core size.

In a preferred embodiment, the finest material (a) contains inert rock powder selected from the group consisting of limestone powder, dolomite powder and quartz or a combination thereof in an amount of 10 to 25% by volume, based on the total volume of hydraulic binder contained in the core size and Fines and (b) hydraulically active material selected from the group consisting of blast furnace slag, microsilica and fly ash, or a combination thereof, in an amount of 8 to 15% by volume based on the total volume of hydraulic binder and fines contained in the core size.

In a particularly preferred embodiment, the superfine consists of (a) inert rock powder selected from the group consisting of limestone powder, dolomite powder and quartz or a combination thereof in an amount of 10 to 25% by volume, based on the total volume of hydraulic material contained in the core glue binder and fines and (b) hydraulically active material selected from the group consisting of blast furnace slag, microsilica and fly ash, or a combination thereof (especially microsilica) in an amount of 8 to 15% by volume, based on the total volume of hydraulic binder and fines contained in the core size. binder

For the purposes of this invention, hydraulic binders are any binders that form strength-forming hydrate phases with the addition of water and, if appropriate, other components. It is preferably provided that the hydraulic binder in step a. and/or step b. is selected from the group consisting of cement, hydraulically active additives, latent hydraulic or pozzolanic additives, silicate binders, or a combination thereof.

For the purposes of this invention, hydraulic binders are also to be understood as meaning geopolymeric binders. Geopolymeric binders are, in particular, slag-based geopolymeric binders, rock-based geopolymeric binders, fly ash-based geopolymeric binders (i.e. alkali-activated fly ash and/or slag/fly ash-based), aluminum silicate binders (alkali-activated aluminum silicates) and ferro-sialate-based geopolymeric binder. Such geopolymeric binders are fundamentally known and familiar to the person skilled in the art. Geopolymeric binders can be used either as the sole hydraulic binder or in combination with other hydraulic binders, especially in combination with cement.

Furthermore, it is preferably provided that the hydraulic binder in step a. and/or step b. is selected from the group consisting of cement, fly ash, microsilica, blast furnace slag, natural or artificial pozzolan, geopolymers, metakaolin, calcined clays, or a combination thereof.

According to a particularly preferred embodiment of the invention, the hydraulic binder in step a. and/or step b. Cement. The cement can be from the group consisting of the classes CEM I and CEM IVA according to EN 197-1, or a combination thereof.

It is advantageous if the core glue contains at least 350 kg/m ³ , in particular 350 to 1000 kg/m ³ , in particular 500 to 1000 kg/m ³ , based on the total dry weight of the core mixture, of hydraulic binder. It is furthermore preferably provided that the core glue contains hydraulic binder, in particular cement, in an amount of 60 to 95% by volume, in particular from 65 to 80% by volume, based on the total volume of hydraulic binder and fines contained in the core glue , contains.

According to the invention, the facing glue contains at least a hydraulic binder and water. It is preferably provided that the facing glue, based on the total dry weight of the facing mixture, contains 350 to 1000 kg/m ³ , in particular 500 to 1000 kg/m ³ , of hydraulic binder.

The face glue and the core glue can contain the same or different hydraulic binders. In a preferred embodiment of the invention, the end glue and the core glue contain the same hydraulic binder. In a particularly preferred embodiment, the hydraulic binder of the face glue and the core glue is cement, in particular a cement selected from the group consisting of classes CEM I and CEM IVA according to EN 197-1, or a combination thereof.

An advantageous development of the method according to the invention provides that the front glue contains hydraulic binder, in particular cement, in an amount of 40 to 91% by weight, in particular 50 to 70% by weight, based on the total dry weight of the front glue.

The core mix also contains aggregate with an average diameter d50, determined according to ISO 13320:2009 and/or EN 12620, greater than 100.0 μm. Preferably, the aggregate has an average diameter that is larger than the average diameter of the hydraulic binder. This has the advantage that the additive improves the compressibility of the core mixture when the excess water is pressed out of the face mixture layer and/or promotes the pressing of the water out of the face mixture layer into the core mixture layer.

According to a preferred embodiment of the method according to the invention, it is provided that the aggregate contained in the core mixture is a mixture containing organic and/or inorganic substances, wherein the organic and/or inorganic substances are optionally selected from the group consisting of coarse rock flour, including mineral aggregate Aggregate according to EN 12620, ceramics, glass, synthetic fibres, natural fibers and biological components, in particular grass, or a combination thereof. Furthermore, it is preferably provided that the aggregate contained in the core mixture is a rock aggregate according to EN 12620, preferably a rock aggregate according to EN 12620 based on quartz, basalt, granite, lime, lime chips or mixtures thereof. It is also preferred that the aggregate contained in the core mixture and/or facing mixture is an aggregate according to EN 12620, which has an average diameter of 0.101 mm to 5.000 mm, in particular 0.125 mm to 5.000 mm, preferably 0.250 mm to 5.000 mm.

According to a preferred embodiment of the invention, a mixture is used as the aggregate, the composition of which is optimized by means of methods for determining the optimal grading curve in such a way that a minimum cavity for aggregate mixtures with a very small particle size that is larger than the average diameter d50 is determined according to ISO 13320:2009, of the hydraulic binder. water binding mean value

In one embodiment, the core mixture introduced into the mold before pressing according to step c. a water binder average value (W/B) of 0.10 to 0.40, preferably 0.12 to 0.20, based on the ratio of water to the sum of hydraulic binder and fines with an average diameter of 1.0 to 100 .0 pm, in particular from 1.0 to 30.0 pm.

If the water content is too low, it can have a negative effect on later strength. The W/B value in the core concrete should therefore not be too low after grouting. Accordingly, it is preferred that the core mixture introduced into the mold after pressing according to step c. has an average water-binding value of 0.20 to 0.45, preferably 0.21 to 0.28, based on the ratio of water to the sum of hydraulic binder and fines with an average diameter d50 determined according to ISO 13320:2009 of 1.0 to 100.0 pm, in particular from 1.0 to 30.0 pm. In a particularly preferred embodiment, the core mixture introduced into the mold after the pressing in step c. an average water binding value of 0.22 to 0.24.

The method according to the invention provides that water is pressed from the face mixture layer into the core mixture layer. As a result, the W/B value of the layer of facing mixture is generally lower after pressing than before pressing. Conversely, the W/B value of the core mix layer is usually higher after pressing than before pressing. It is further provided that the core mixture introduced into the mold before pressing according to step c. has an average water-binding value that is the same as or lower than the average water-binding value of the facing mixture introduced into the mold before pressing according to step c.

In a particular embodiment, the core mixture introduced into the mold before pressing according to step c. an average water binding value that deviates by 15% or less from the facing mixture introduced into the mold before pressing according to step c), based on the average water-binding value of the facing mixture introduced into the mold before pressing according to step c). This design is particularly advantageous if UHPC concrete (ultra high performance concrete) is used as the facing layer.

According to a preferred embodiment of the invention, the step b. The core mixture used is characterized by a relatively high degree of glue saturation (LSG). The LSG is a measure of the degree to which the cavity specified by the aggregate is filled with binding agent. It can be calculated using the following formula (1):

LSG . Degree of glue saturation [-]

VL glue volume (percentage of water and fines < 100pm per m ³ concrete) [m ³ /m ³ ] VG.HP void content of the aggregate mixture 100pm in the pressed state [m ³ /m ³ ]

VG,H,P can be calculated as follows:

Vc.H.p voids content of aggregate mixture 100 µm in compacted state [m ³ /m ³ ]

VG, _P -- measured volume of aggregate mixture 100pm in compacted state [m ³ ]

Vc.id-- idealized volume of aggregate mixture > lOOum without considering air volume [m ³ ]

The press test with the hermetic press to determine the void content VG, _P can be carried out as follows: • Amount of aggregate > 100 pm is poured into a press mold (eg laboratory hermetic press) and distributed as evenly as possible using a steel ruler or similar.

• The filled quantity of aggregates is then pressed with 20 MPa for 10 s.

• Then the distance hi between the top edge of the mold and the top edge of the panels is measured at each of the 4 corners of the mold. The actual volume of the pressed plate VG, _P is then determined with this.

The idealized volume of the aggregate mix > lOOum without considering the

air volume [m ³ ] (Vc.id) can be calculated as follows:

Theoretically, an LSG of 1 would be an ideal-typical state in which there is a maximum packing density. However, this maximum packing density is not usually achieved in practice, since in addition to a proportion of air voids, which can be assumed to be 1.0 to 1.5% by volume, the degree of compression or compressibility plays an important role . A significant increase in the strength of the multilayer panel in the hardened state can be achieved by increasing the LSG of the core mixture. However, increasing the LSG to values above 1.1 is disadvantageous for common core compounds, as this leads to a reduction the flexural strength of the multilayer panel. It has now been found that the method according to the invention enables a further increase in the characteristic flexural strength, specifically up to an LSG of the core mixture of around 1.5. As a result, greater strength can be achieved than was possible with known multi-layer panels.

In a preferred embodiment, the amount of core glue contained in the core mixture is calculated in such a way that a degree of glue saturation for the core mixture, calculated according to formula (1), from 1.0 to 1.5, preferably from 1.1 to 1.4, results.

glue layer thickness

A further advantage of the invention is that a high degree of compaction and/or a high packing density can be achieved even with a low glue layer thickness (LSD) of the core glue layer. Glue layer thickness (LSD) is the calculated LSD that results after pressing according to formula (2):

LSD . Glue thickness [um/

VL .... volume of glue (volume of fines (largest particle size < 100 m) and water) [m ³ /m ³ ]

VG.HP voids content of aggregate mix > 100 m in compacted state [m ³ /m ³ ] m _g mass of aggregate mix > 100 µm per m ³ of concrete [kg/m ³ ]

SG .... Specific surface of the aggregate > 100pm [m ² /kg ³ ]

When calculating the specific surface area of the aggregates SG, the grain shape of the aggregates (compact factor) and the grading curves of the aggregates are taken into account. In a preferred embodiment, the amount of core glue contained in the core mixture is calculated in such a way that a glue layer thickness, calculated according to formula 2, is at most 30.0 μm, in particular at most 20.0 μm or from 3.0 to 20.0 μm , for the core glue layer.

end-mix

The in step a. The end-mixture used in the process according to the invention contains at least the following components: i. containing at least

1. hydraulic binder, and

2. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm.

It is essential that the face mix has a soft to flowable consistency. In a preferred embodiment, the face mixture layer has, before the pressing according to step c. a consistency of at least consistency class F5 according to DIN 1045-2 and/or EN 206, in particular a consistency according to one of the consistency classes F5 or F6.

According to a preferred embodiment of the invention, it is further provided that the facing mixture, based on the total dry weight of the facing mixture, contains 450 to 1250 kg/m ³ , in particular 600 to 1250 kg/m ³ , of facing glue.

It is not mandatory that the endpaper contains fines. However, it is preferred that the end glue contains very fine material as a further component, in particular very fine material with an average diameter d50, determined according to ISO 13320:2009, of up to 100.0 μm. According to a preferred embodiment of the invention, the face size contains fines with an average diameter of 1.0 to 100.0 gm in an amount of 5 to 50% by weight, preferably 15 to 45% by weight, in particular 20 to 45% % by weight based on the total dry weight of the end face glue.

An advantageous further development also provides that the end glue contains very fine material which has an average diameter d50, determined according to ISO 13320:2009, which is smaller than the average diameter d50, determined according to ISO 13320:2009, of the hydraulic binder and preferably in an amount of 5 to 50%, more preferably 15 to 45%, and most preferably 20 to 45% by weight based on the total dry weight of the face size.

Provision is also preferably made for the end glue to contain very fine material with an average diameter d50, determined according to ISO 13320:2009, of 1.0 to 30.0 gm, in particular 1.0 to 5.0 gm, in particular in a quantity from 5 to 50% by weight, preferably from 15 to 45% by weight, in particular from 20 to 45% by weight, based on the total dry weight of the endsize.

In a further embodiment of the invention, the face glue contains inert rock dust as the finest substance.

More preferably, the face size contains hydraulically active fines, in particular microsilica, in an amount of 5 to 20% by volume, in particular 8 to 15% by volume, based on the total volume of hydraulic binder and fines contained in the face size.

The in step a. The facing mixture used in the process according to the invention also contains additive. The aggregate that is suitable for the core mix is basically also suitable for the facing mix. The aggregate in the face mix has an average diameter that is greater than the average diameter of the hydraulic Binder, in particular greater than 100.0 pm. In a preferred embodiment of the invention, the aggregate contained in the facing mixture has an average diameter of 0.101 mm to 5.000 mm, in particular 0.125 mm to 5.000 mm or 0.250 mm to 5.000 mm.

According to a preferred embodiment of the invention, it is further provided that the aggregate contained in the facing mixture is a rock aggregate, in particular a rock aggregate based on quartz, basalt, granite, lime, lime chips or mixtures thereof. It is also advantageous if the aggregate contained in the facing mixture is a rock granule with an average diameter of 0.101 mm to 5.000 mm, in particular 0.125 mm to 5.000 mm or 0.250 mm to 5.000 mm.

It is also advantageous if the aggregate is a mixture containing organic and/or inorganic substances, with the organic and/or inorganic substances optionally being selected from the group consisting of coarse rock flour, mineral aggregate including aggregate according to EN 12620, ceramics, glass, synthetic fibers , natural fibers and biological components, in particular grass, or a combination thereof.

According to a particularly preferred embodiment, the aggregate is a mixture whose composition is optimized using methods for determining the optimal grading curve in such a way that there is a minimum cavity for aggregate mixtures with a micro-grain that is larger than the average diameter d50, determined according to ISO 13320:2009, of the hydraulic binder.

The facing mixture preferably contains at least the following components: i. containing at least

1. hydraulic binder, 2. Superfine material, wherein the superfine material has a mean diameter d50, determined according to ISO 13320:2009, which is at most 100.0 μm, and

3. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or EN 12620 that is greater than 100.0 μm;

With regard to the ingredients of the face mix, in particular with regard to hydraulic binder, ultra-fine material, aggregate and additives, unless otherwise stated, the above information, in particular that stated above in connection with the core mixture, applies accordingly.

According to a preferred embodiment of the method according to the invention, the facing mixture introduced into the mold before the pressing according to step c. a water binding average value (W/B) of at most 0.60, preferably at most 0.40, preferably from 0.20 to 0.40, based on the ratio of water to the sum of hydraulic binder and fines with a mean diameter of 1.0 to 100.0 pm, in particular from 1.0 to 30 pm.

Process steps of the method according to the invention

The steps a. and b. of the process according to the invention can be carried out in the order given (first step a., then step b.) or in the reverse order (first step b, then step a.). In the former case, the dry to earth-moist core mixture is applied in the mold to the flowable facing mixture layer that has already formed. This is the norm. However, it is also possible, although less preferred, to pour the dry to earth-moist core mixture into the mold first bring in and then apply the flowable facing concrete mixture to the core mixture layer.

Both the core mix and the face mix can also contain one or more additives according to EN 934. The use of suitable additives, which on the one hand improve the dispersion and wetting of the hydraulic binder, especially cement, and additives during the mixing process and on the other hand can reduce the frictional forces between the fine material components, can have a positive effect on the processing and compaction capacity.

In a preferred embodiment, the core mixture and/or the facing mixture contains 0.01 to 3.0% by weight, based on the total dry weight of the hydraulic binder, of additives according to EN 934 as a further component. The additive is preferably selected from the group consisting of plasticizers, superplasticizers, stabilizers, air entraining agents, accelerators, retarders, shrinkage modifiers and sealants, or a combination thereof. The core mixture and/or the facing mixture preferably contains 0.01 to 3.0% by weight, based on the total dry weight of the hydraulic binder, of superplasticizer as a further component. The flow agent is preferably selected from the group consisting of surfactants, particularly naphthalene sulfonates and/or lignin sulfonates, and dispersing agents, particularly melamine resins, polycarboxylates and polycarboxylate ethers, or a combination thereof. According to a particularly preferred embodiment, a polycarboxylate, polyaryl ether or polycarboxylate ether is used as flow agent.

When pressing according to step c. of the method according to the invention, water contained in the face mixture layer is partially pressed into the core mixture layer. According to a preferred embodiment of the invention, the pressure during pressing according to step c. at least 0.5 N/mm ² , in particular at least 10 N/mm ² , preferably at least 15 N/mm ² . The pressing preferably takes place according to step c. with a pressing time of 5 to 60 seconds, in particular 5 to 40 seconds or 5 to 15 seconds. The pressing according to step c. can take place in one pressing process or in at least two consecutive pressing processes with the same or different intensity. The pressing is preferably provided in a pressing process. According to a particularly preferred embodiment of the invention, the pressing takes place according to step c. in a hermetic press.

According to a further embodiment, the invention relates to a hydraulically bonded multi-layer panel which can be produced or is produced by the method according to the invention.

The hydraulically bound multilayer board according to the invention can have any dimensions. Preferably, the multilayer board according to the invention is a relatively large-sized hydraulically bonded multilayer board, for example a multilayer board having a length of at least 300, 400, 500, 600, 700 or 800 mm. In a particularly preferred embodiment, the hydraulically bound multilayer board according to the invention has a length of 800 to 1200 mm.

The hydraulically bound multilayer board according to the invention can have all the usual square dimensions and is not limited to large-format multilayer boards. However, the advantages of the invention are particularly evident in the production of large-format multilayer boards. The hydraulically bound multilayer board according to the invention preferably has an area of at least 0.16 m ² , in particular from 0.18 to 1.44 m ² , 0.32 to 1.44 m ² , 0.18 to 0.83 m ² or 0 .32 to 0.83 m ² . Particularly preferred is a hydraulically-bonded multilayer board having an area of 0.32 to 1.44 m ² .

The hydraulically bonded multilayer board of the present invention is not limited in thickness and may have any thickness. However, the advantages of the invention are particularly evident in the production of relatively thin multi-layer boards. Accordingly, preference is given to a hydraulically bonded multi-layer panel which has a thickness of at most 40.0 mm, in particular from 15.0 to 40.0 mm.

The hydraulically bound multi-layer board according to the invention also has a relatively high degree of compaction. The degree of compaction (VG) is the ratio between the calculated maximum raw density of the mixture of an idealized board without air and the measured raw density of the board produced after the pressing process. The degree of compaction is calculated in particular according to formula (3):

VG ₌ PFB d PFB

VG... degree of compaction [-]

PFB, id. Calculated, theoretical maximum raw density of the mixture when fresh (without air) [kg/m ³ ]

PFB measured raw density of the board after the pressing process [kg/m ³ ]

In a preferred embodiment, the core mixture layer has a degree of compaction, determined according to formula (3), of from 0.93 to 0.99, in particular from 0.97 to 0.99.

The hydraulically bound multilayer board according to the invention is also characterized by a relatively high packing density of the core mixture layer. Packing density is to be understood as meaning the packing density of all solids in the core layer mixture in the pressed state. In particular, the packing density can be calculated as follows:

PD _p ..packing density of all solids of the core layer mixture in the pressed state [-

VF,id... idealized volume of all solids in the core layer mixture without considering the air volume [m ³ ]

V _p measured volume of the core layer mix of the pressed boards without water [m ³ ] In a preferred embodiment, the core mixture layer has a packing density, determined according to formula (4), of 0.75 to 0.85, in particular 0.78 and 0.83.

It is also advantageous that the hydraulically bound multilayer panel has a characteristic flexural strength, determined according to DIN EN 1339 after 7 days of hardening, of more than 7.5 N/mm ² , in particular at least 8.5 N/mm ² and particularly preferably of at least 10.0 N/mm ² .

The invention is described in more detail below using exemplary embodiments.

examples

A. Core and end face glue

Various core and end face glue compositions were developed and tested. For this purpose, the water requirement at the saturation point (V _w , _s /V _p ) and the water binding mean value at the saturation point (w _s /p) were determined.

1. Core Glue

2. endpaper

Vw, _s /Vp means the water requirement of the powder (or of the very fine material in the context of this invention) at the saturation point. For this purpose, the method according to Marquardt I., described in Marquardt I: A mixture concept for self-compacting concrete on the basis of the volume parameters and water requirements of the starting materials, dissertation, University of Rostock, 2001, is adopted and adapted for the present application. For this purpose, a certain amount of the dry powder was put into a mixer that is able to record changes in the mixing energy input or its power consumption. Then water was mixed in continuously at a constant rotational speed and the amount of water added was continuously measured using a flow meter. The peak of the mixer's power consumption, which corresponds to the maximum shear resistance, indicates when the saturation point has been reached. The mixture becomes "earth-moist".

The water content in the mixture can be given at any time i, usually as "volumetric water powder ratio" (V _w ,i/V _p ). At the saturation point, this corresponds to the water demand at the saturation point (V _w , _s /V _p ). w _s /b means the water binding average value at the saturation point and it relates to the ratio of water to the sum of hydraulic binding agent and fines within the meaning of the invention.

A lower V _w ,s/V _p or w _s /b value indicates a lower void content or higher packing density. By filling the cavity between the binder particles, which would otherwise have to be filled with cavity water, less water is required to achieve comparable compactibility and strength.

The solid glue compositions described above are particularly well suited for their use in the production process according to the invention. This is because the core size compositions according to the invention give the core mixture layer of the multilayer board excellent compressibility and strength with reduced water requirements. The face size compositions of the present invention impart excellent workability, strength and durability to the face layer of the multilayer board.

B. Production of a multilayer board

A multilayer board was produced from the facing and core mixtures given above as follows:

Example 5

end-mix

166.9 kg/m ³ CEM I 42.5 R, kg/m ³ 241 CEM I 52.5 N were mixed with 137.1 kg/m ³ dolomite flour 0.0-0.3 mm, 161.8 kg/m ³ Quartz fine sand 0.0-0.5 mmF12, 529.2 kg/m ³ Granite fine sand (0.1-1.0 mm), 147.3 kg/m ³ Limestone chips (0.1-0.6 mm), 219.4 kg/m ³ limestone chippings (0.6-1.2 mm) and 361.5 kg/m ³ limestone chippings (1.5-3.0 mm) in an Eirich mixer 8L (5L effective volume) mixed for 60 seconds at 200 rpm. Then 31.2 kg/m ³ limestone powder (0.5 - 3.0 pm; d50 = 1.2 pm) and 31.2 kg/m ³ mineral plasticizer (1.0 - 25 pm; d50 = 4.5 pm) added and mixed for 120 seconds at 200 rpm. Then 270.8 kg/m ³ water and 3.77 kg/m ³ superplasticizer based on polycarboxylate ether were added and mixed for 120 seconds at 200 rpm. Finally the entire mixture was mixed for 120 seconds at 200 rpm. The face mix obtained in this way had a slump of 345 mm after 7 minutes, which corresponds to a flowable consistency.

core mix

779.9 kg/m ³ of cement CEM I 42.5 R were mixed with 251.3 kg/m ³ of quartz powder (100-200 μm), 703.6 kg/m ³ of fine limestone sand (0.3-0.8 mm ) and 310.2 kg/m ³ basalt 1-3 mm mixed in an Eirich mixer 8L (5L effective volume) for 60 seconds at 150 rpm. Thereafter, 126.09 kg/m ³ of water and 3.86 of flow agent based on polycarboxylate ether were added and mixed at 150 rpm for 60 seconds. Then 218.4 kg/m ³ quartz powder (2.0-100.0 pm; d50 = 15 pm) and 101.4 kg/m ³ RW quartz powder (2.0-100.0 pm; d50 = 5 pm) were added and 120 see mixed at 150 rpm. Finally 14.01 kg/m ³ water was added and mixed for 60 seconds at 150 rpm. A flowable core mixture was obtained.

Insertion and pressing

The prepared flowable facing mixture was introduced into an 800 mm 400 mm large hermetic press mold of the OCEM laboratory sliding table press 100 to type and distributed as evenly as possible in the mold. The layer thickness of the face mix after filling in the mold (ie, the thickness of the face mix layer) was about 6 mm. The prepared earth-moist core mix was then applied to the facing mix layer in a layer that was as homogeneous as possible (approx. 29 mm) using a funnel and a squeegee. The core mix layer and the face mix layer were pressed together in the hermetic press at a pressure of about 15.0 MPa for about 10 seconds. The multilayer panel obtained was demoulded immediately after pressing. The W/B value of the core mix layer was 0.159, the W/B value of the face mix layer was 0.664.

After pressing, the core mixture layer had a layer thickness of 24 mm, and the facing mixture layer had a layer thickness of 6 mm. The total thickness of the obtained

Multilayer board was 30 mm. Despite its relatively low thickness, the multi-layer panel had a characteristic flexural strength, determined according to DIN EN 1339 after 7 days of hardening, of 10.9 N/mm ² and was characterized by excellent load-bearing capacity and outstanding serviceability.

Claims

patent claims 1. A method for producing a hydraulically bound multi-layer board with at least one facing layer and at least one core layer, characterized in that the method comprises the following steps: a. Introduction of a free-flowing facing mixture into a mold, the facing mixture containing at least the following components: i. containing at least 1. hydraulic binder and 2. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm; whereby a facing mixture layer is formed; b. Introduction of a dry to earth-moist core mixture into the mould, the core mixture containing at least the following components: i. containing glue at least 1. hydraulic binder, 2. Extremely fine material, where the extremely fine material has an average diameter d50 determined according to ISO 13320:2009 of up to 100.0 μm, and 3. water; as well as ii. Aggregate, the aggregate having a mean diameter d50 determined according to ISO 13320:2009 and/or according to EN 12620 greater than 100.0 pm; thereby forming a core mixture layer, and c. Pressing the facing mixture layer with the core mixture layer in the mold to form a hydraulically bound, directly strippable multi-layer panel with at least one facing layer and at least one core layer, the water contained in the facing mixture layer being pressed partially or completely into the core mixture layer. 2. The method as claimed in claim 1, characterized in that the core glue contains very fine material with an average diameter d50 determined according to ISO 13320:2009 of 1.0 to 100.0 μm in an amount of 5 to 45% by volume, based on the total volume of hydraulic binder and fines contained in the core glue. 3. The method according to claim 1 or 2, characterized in that the core glue contains very fine material which has a mean diameter d50, determined according to ISO 13320:2009, which is smaller than the mean diameter d50, determined according to ISO 13320:2009, of the hydraulic binder contained in the core glue. 4. The method according to any one of the preceding claims, characterized in that the very fine material contained in the core glue has an average diameter d50, determined according to ISO 13320:2009, from 1.0 to 30.0 μm, in particular from 1.0 to 5.0 μm , having. 5. The method according to any one of the preceding claims, characterized in that the core glue contains very fine material with an average diameter d50, determined according to ISO 13320:2009, of 30.1 to 100.0 μm in an amount of 0 to 45% by volume, in particular from 0 to 25% by volume, based on the total volume of hydraulic binder and fines contained in the core size. 6. The method according to any one of the preceding claims, characterized in that the core glue consists of very fine material with an average diameter d50, determined according to ISO 13320:2009, from 1.0 to 30.0 μm in an amount of 5 to 45% by volume, based on the total volume of hydraulic binder and fines contained in the core glue. 7. The method according to any one of the preceding claims, characterized in that the core glue contains very fine material with an average diameter d50, determined according to ISO 13320:2009, of 1.0 to 5.0 μm in an amount of 5 to 20% by volume, in particular from 8 to 15% by volume, based on the total volume of hydraulic binder and fines contained in the core size. 8. The method according to any one of the preceding claims, characterized in that the end glue contains fines as a further component, in particular fines with an average diameter d50, determined according to ISO 13320:2009, of up to 100.0 μm. 9. The method according to any one of the preceding claims, characterized in that the end glue contains very fine material which has an average diameter d50, determined according to ISO 13320:2009, which is smaller than the average diameter d50, determined according to ISO 13320:2009, of the hydraulic binder. 10. The method according to any one of the preceding claims, characterized in that the end glue contains very fine material with an average diameter d50, determined according to ISO 13320:2009, of 1.0 to 30.0 μm, in particular 1.0 to 5.0 μm . 11. The method according to any one of the preceding claims, characterized in that the fines in step a and / or step b. contains at least one inert rock dust, preferably an inert rock dust selected from the group consisting of limestone, dolomite and quartz, or a combination thereof. 12. The method according to any one of the preceding claims, characterized in that the fines in step a. and/or b. contains at least one hydraulically active substance, in particular a hydraulically active natural or synthetically produced substance. 13. The method according to claim 12, characterized in that the hydraulically active substance is selected from the group consisting of blast furnace slag, microsilica and fly ash, or a combination thereof. 14. The method according to any one of the preceding claims, characterized in that the core glue, based on the total dry weight of the core mixture, contains 350 to 1000 kg/m ³ , in particular 500 to 1000 kg/m ³ , hydraulic binder. 15. The method according to any one of the preceding claims, characterized in that the face glue, based on the total dry weight of the face mixture, contains 350 to 1000 kg/m ³ , in particular 500 to 1000 kg/m ³ , hydraulic binder. 16. The method according to any one of the preceding claims, characterized in that the hydraulic binder in step a. and/or step b. is selected from the group consisting of cement, hydraulically active additives, latent hydraulic or pozzolanic additives, silicate binders, or a combination thereof. 17. The method according to any one of the preceding claims, characterized in that the hydraulic binder in step a. and/or step b. is selected from the group consisting of cement, fly ash, microsilica, blast furnace slag, natural or artificial pozzolan, geopolymers, metakaolin, calcined clays, or a combination thereof. 18. The method according to any one of the preceding claims, characterized in that the hydraulic binder in step a. and/or step b. Cement is, in particular, a cement selected from the group consisting of classes CEM I and CEM IVA according to EN 197-1, or a combination thereof. 19. The method according to any one of the preceding claims, characterized in that the core glue hydraulic binder, in particular cement, in an amount of 60 to 95 vol. %, in particular from 65 to 80% by volume, based on the total volume of hydraulic binder and fines contained in the core glue. 20. The method according to any one of the preceding claims, characterized in that the core mixture, based on the total dry weight of the core mixture, contains 450 to 1250 kg/m ³ , in particular 600 to 1250 kg/m ³ , of core glue. 21. The method according to any one of the preceding claims, characterized in that the amount of core glue contained in the core mixture is calculated in such a way that a degree of glue saturation for the core mixture, calculated according to formula 1 given in the description, is from 1.0 to 1. 5, especially from 1.1 to 1.4. 22. The method according to any one of the preceding claims, characterized in that the amount of core glue contained in the core mixture is calculated in such a way that a glue layer thickness, calculated according to formula 2 given in the description, of at most 30.0 μm, in particular at most 20.0 µm, or from 3.0 to 20.0 µm, for the core size layer. 23. The method according to any one of the preceding claims, characterized in that the facing mixture, based on the total dry weight of the facing mixture, contains 450 to 1250 kg/m ³ , in particular 600 to 1250 kg/m ³ , of facing glue. 24. The method according to any one of the preceding claims, characterized in that the introduced into the mold core mixture prior to pressing according to step c. has a water binding average value (W/B) of 0.10 to 0.40, preferably 0.12 to 0.20, based on the ratio of water to the sum of hydraulic binding agent and fines with an average diameter d50, determined according to ISO 13320 :2009, from 1.0 to 100.0 pm, especially from 1.0 to 30.0 pm. 25. The method according to any one of the preceding claims, characterized in that the core mixture introduced into the mold after the pressing according to step c. has an average water-binding value of 0.20 to 0.45, in particular 0.21 to 0.28 or 0.22 to 0.24, based on the ratio of water to the sum of hydraulic binder and fines with an average diameter d50 according to ISO 13320:2009 from 1.0 to 100.0 μm, in particular from 1.0 to 30.0 μm. 26. The method according to any one of the preceding claims, characterized in that the layer of facing mixture before pressing according to step c. has a consistency of at least consistency class F5 according to DIN 1045-2 and/or EN 206. 27. The method according to any one of the preceding claims, characterized in that the core mixture layer before pressing according to step c. a consistency of maximum consistency class Fl according to DIN 1045-2 and/or EN 206. 28. The method according to any one of the preceding claims, characterized in that the core mixture and / or the facing mixture as a further component of 0.01 to 3.0 wt -%, based on the total dry weight of the hydraulic binder, contains additives according to EN 934, wherein the admixture is optionally selected from the group consisting of plasticizer, superplasticizer, stabilizer, air entraining agent, accelerator, retarder and sealant, or a combination thereof. 29. The method according to claim 28, characterized in that the additive according to EN 934 is a flow agent, in particular a flow agent selected from the group consisting of surface-active substances, in particular naphthalene sulfonates and/or lignin sulfonates, and dispersing substances, in particular melamine resins, polycarboxylates and polycarboxylate ethers, or a combination thereof, in particular polycarboxylate, polyacrylic ether and/or polycarboxylate ether. 30. The method according to any one of the preceding claims, characterized in that the additive contained in the core mixture and / or facing mixture is a mixture containing organic and / or inorganic substances, wherein the organic and / or inorganic substances are optionally selected from the group consisting of Coarse rock flour, mineral aggregate including aggregate according to EN 12620, ceramics, glass, synthetic fibres, natural fibers and biological components, in particular grass, or a combination thereof. 31. The method according to any one of the preceding claims, characterized in that the aggregate and/or finest material contained in the core mixture and/or the facing mixture is an aggregate according to EN 12620. 32. The method according to claim 31, characterized in that the aggregate and/or finest material contained in the core mixture and/or the facing mixture is a rock grain according to EN 12620 based on quartz, basalt, granite, lime, lime chips or mixtures thereof. 33. The method according to claim 31 or 32, characterized in that the aggregate contained in the core mixture and/or facing mixture is an aggregate according to EN 12620 which has an average diameter d50, determined according to ISO 13320:2009, from 0.101 mm to 5.000 mm, in particular from 0.125 mm to 5.000 mm. 34. The method according to any one of the preceding claims, characterized in that the aggregate contained in the core mixture and / or facing mixture is a mixture whose composition is optimized by means of methods for determining the optimal grading curve so that a minimal cavity for aggregate mixtures with a micro-grain that is larger than the mean diameter d50, determined according to ISO 13320:2009, of the hydraulic binder. 35. The method according to any one of the preceding claims, characterized in that the introduction of the core mixture into the mold according to step b. by applying the core mixture to the step a. formed flowable facing mixture layer takes place. 36. The method according to any one of the preceding claims, characterized in that the pressure during pressing according to step c. at least 0.5 N/mm ² , in particular at least 10 N/mm ² or at least 15 N/mm ² . 37. The method according to any one of the preceding claims, characterized in that the pressing according to step c. with a pressing time of 5 to 60 seconds, in particular 5 to 40 seconds or 5 to 15 seconds. 38. The method according to any one of the preceding claims, characterized in that the pressing according to step c. takes place in at least two consecutive pressing processes with the same or different intensity. 39. Hydraulically bonded multilayer panel, producible by a method according to any one of claims 1 to 38. 40. Hydraulically bound multilayer board according to claim 39, characterized in that the hydraulically bound multilayer board has a length of at least 300, 400, 500, 600, 700 or 800 mm, in particular from 800 to 1200 mm. 41. Hydraulically bound multi-layer panel according to claim 39 or 40, characterized in that the hydraulically bound multi-layer panel has an area of at least 0.16 m ² , in particular from 0.18 to 1.44 m ² , 0.32 to 1.44 m ² , 0.18 to 0.83 m ² , or 0.32 to 0.83 m ² . 42. Hydraulically bound multilayer board according to one of claims 39 to 41, characterized in that the hydraulically bound multilayer board has a thickness of at most 40.0 mm, in particular from 15.0 to 40.0 mm. 43. Hydraulically bound multilayer panel according to one of claims 39 to 42, characterized in that the core mixture layer has a degree of compression, determined according to formula 3 given in the description, of 0.93 to 0.99, in particular 0.97 to 0.99 , having. 44. Hydraulically bound multilayer board according to one of claims 39 to 43, characterized in that the core mixture layer has a packing density, determined according to formula 4 given in the description, of 0.75 to 0.85, in particular of 0.78 and 0.83 , having. 45. Hydraulically bound multi-layer board according to one of claims 39 to 44, characterized in that the multi-layer board has a characteristic flexural strength, determined according to DIN EN 1339, after 7 days of hardening, of more than 7.5 N/mm ² , in particular of at least 8 5 N/mm ² .