EP4164996A1

EP4164996A1 - Core-facing concrete element, method for the production of same, and use of latent hydraulic or pozzolanic binder in the core layer

Info

Publication number: EP4164996A1
Application number: EP22743781.1A
Authority: EP
Inventors: Guido Volmer; Michael Metten
Original assignee: Metten Technologies & Co Kg GmbH
Current assignee: Metten Technologies & Co Kg GmbH
Priority date: 2021-06-30
Filing date: 2022-06-30
Publication date: 2023-04-19
Also published as: DE102021116928A1; CA3224132A1; IL309729A; CN117751094A; WO2023275267A1

Abstract

The invention relates to a concrete element comprising a concrete core layer and a concrete facing layer, wherein: the concrete element is obtained by compressing and curing a concrete core layer mixture in contact with a concrete facing layer mixture; the concrete core layer mixture contains a latent hydraulic core binder and/or a pozzolanic core binder, water, a granular core material and an alkali core curing agent; the concrete facing layer mixture contains a latent hydraulic facing binder and/or a pozzolanic facing binder, water, a granular facing material and an alkali facing curing agent; and the concrete element has a compressive strength in accordance with DIN EN 12390-3, in particular DIN EN 12390-3:2019-10, measured after 28 days, of less than 120 N/mm2. The invention also relates to a method for producing the concrete element and to the use of a latent hydraulic binder and/or pozzolanic binder together with an alkali curing agent to produce the concrete core layer in the concrete element.

Description

CORE-FACING CONCRETE ELEMENT, PROCESS FOR ITS MANUFACTURE AND USE OF LATENT HYDRAULIC OR PUZZOLANIC BINDER IN THE CORE LAYER

The invention relates to a concrete element comprising a core concrete layer and a facing concrete layer, the concrete element being obtained by compacting and curing a core concrete layer mixture in contact with a facing concrete layer mixture, the core concrete layer mixture and the

Face concrete layer mixture each contain a latent hydraulic binder and / or a pozzolanic binder, water, a granular material and an alkaline hardening agent. The invention also relates to a method for producing the concrete element according to the invention.

Concrete elements such as concrete blocks, concrete slabs, concrete wall elements or concrete steps are often used because of their durability and lower price compared to stones, slabs or steps made of natural stone. Concrete elements are usually made using cement as a binder.

Various methods were developed to enable a decorative appearance of the concrete elements. For this purpose, among other things, pigment and/or natural stone aggregates and/or sands are usually added in order to color and refine the concrete element.

Concrete elements containing cement sometimes have the problem that over time they show whitish spots on the surface, so-called efflorescence. Furthermore, the color of colored concrete blocks may fade. Both effects seem to arise from the formation of lime. The whitish spots on the surface are attributed to lime efflorescence, which is formed by the reaction of calcium hydroxide transported to the surface with carbon dioxide. It is assumed that the color fading is caused, among other things, by the fact that the Pigment that has settled on the cement particles for coloring is slowly being coated by the forming calcium carbonate. In this way, the color impression of the pigment is slowly lost.

Alternative binders to cement are known. An example of such alternative binders is based on the chemical building blocks S1O2 in combination with Al2O3. Examples of such binders include latent hydraulic binders and pozzolanic binders. These are also often referred to as "geopolymers". For example, EP 1 236702 A1 describes a building material mixture containing water glass and a latently hydraulic binder. EP 1236 702 A1 proposes using the building material mixture as mortar or spatula.

The production of concrete elements such as concrete blocks, concrete slabs, concrete wall elements or concrete steps places special demands on the concrete mixture used, especially in comparison to fresh concrete. In the production of concrete elements, it is desirable to achieve the highest possible stability of the not yet hardened concrete blocks after as short a time as possible reach so that they can be packed as quickly as possible. An additional requirement for the products, which have a facing concrete and core concrete layer, is a high bond strength in order to prevent the facing concrete layer from delaminating from the core under load and weathering. The bond tensile strength can be used as a measure of the stability against delamination of the facing concrete layer from the core concrete of the concrete elements. If the bond strength of the concrete elements is not high enough, the facing concrete layer and core concrete can separate under load (delamination) or tear apart as soon as the formwork is removed. Thus, the concrete elements can be used for a broader range of uses if they are designed with a sufficiently high bond strength.

WO 2021/047875 A1 describes concrete elements comprising a core concrete layer and a facing concrete layer, with the facing concrete layer containing a latent hydraulic binder and/or a pozzolanic binder. the However, WO 2021/047875 A1 does not describe that latent hydraulic binders and/or pozzolanic binders are also used in the core concrete layer.

Concrete elements are exposed to various types of attack over their service life, which causes the concrete elements to corrode. In addition to physical corrosion, for example due to frost and de-icing salt, chemical corrosion, including the alkali-silica reaction as a driving attack, is also an important form of corrosion. The alkali-silicic acid reaction occurs in particular with alkali-rich binders in combination with alkali-sensitive aggregates such as e.g.

greywacke up. These alkali-sensitive aggregates are rarely found in a facing concrete layer, for which higher-quality aggregates are usually used, but are mostly used for the core concrete layer. Therefore, there have been no efforts to date to use alkali-rich binders such as geopolymers in the core concrete layer, as this would have led to problems with the alkali-silica reaction due to the alkali-susceptible aggregates. In addition, the latent hydraulic binders and the pozzolanic binders in combination with the hardeners required for this are more expensive than cement-bound binders. Therefore, a conventional, i. H. cement-bound core concrete layer.

As part of the development of the present invention, it was found that concrete elements with a cement-bound core concrete layer and a facing concrete layer, which contains latent hydraulic binders and/or pozzolanic binders as binders, have a lower composite adhesive tensile strength under otherwise comparable manufacturing conditions and components than concrete elements in which both layers are cement-bound.

The object of the invention was therefore to provide aesthetically pleasing concrete elements that change their appearance less over time, less are susceptible to chemical corrosion, in particular the alkali-silica reaction, and can be produced economically. In particular, concrete blocks should be provided which show less staining and/or less tendency to soiling on the surface and/or less color fading and/or have a sufficiently high tensile bond strength, in particular a sufficiently high composite bond strength. A further object of the invention is to provide concrete elements with a reduced CO2 balance.

Further tasks result from the following explanations and some of them are listed below.

All or some of these objects are solved according to the invention by the concrete element according to claim 1 and the method according to claim 22.

Advantageous refinements of the invention are specified in the dependent claims and are explained in detail below.

The invention provides a concrete element, comprising a core concrete layer and a facing concrete layer, the concrete element being obtained by compacting and curing a core concrete layer mixture in contact with a facing concrete layer mixture, the core concrete layer mixture containing a latent hydraulic core binder and/or a pozzolanic core binder, water, a granular core material and contains an alkaline core hardening agent, with the facing concrete layer mixture containing a latent hydraulic facing binder and/or a pozzolanic facing binder, water, a granular facing material and an alkaline facing hardening agent, with the granular facing material passing through a sieve of 35.5 wt 99.5 wt Compressive strength DIN EN 12390-3, in particular DIN EN 12390-3: ^2019-10 , measured after 28 days, of less than 120 N/mm2.

Surprisingly, it has been shown that concrete elements comprising a core concrete layer and a facing concrete layer, the concrete element being obtained by compacting and curing a core concrete layer mixture in contact with a facing concrete layer mixture, the core concrete layer mixture containing a latent hydraulic core binder and/or a pozzolanic core binder, water, a granular core material and contains an alkaline core hardening agent and wherein the facing concrete layer mixture contains a latent hydraulic facing binder and/or a pozzolanic facing binder, water, a granular facing material and an alkaline facing hardening agent, the granular facing material having a sieve passage of 35.5% by weight with a screen aperture of 2 mm up to 99.5% by weight and with a sieve aperture of 0.25 mm a sieve passage of 2.5% by weight to 33.5% by weight, based in each case on the total weight of the granular facing material, its decorative properties change only slowly, if at all, and can be produced economically. In particular, the aforementioned concrete elements have a sufficiently high bond strength. This allows a wide range of uses for the concrete elements. Furthermore, these concrete blocks show at most a slow fading of the colors and little or no staining on the surface. In addition, the concrete blocks according to the invention show good resistance to the alkali-silica reaction. Finally, these concrete elements also have a good CO2 balance.

Without wishing to be bound to a specific scientific theory, this appears to be due to the fact that the use of latent hydraulic binders and/or pozzolanic binders in the core concrete layer and in the facing concrete layer increases the bond strength between the core concrete layer and the facing concrete layer, with the susceptibility to chemical Corrosion, in particular of the core concrete layer, is not significantly increased. Apparently, the use of latent hydraulic binder and/or pozzolanic binder both in the facing concrete layer and in the core concrete layer improves the bond strength between these two layers. Furthermore, the use of latent hydraulic binders and/or pozzolanic binders does not seem to cause the concrete elements to lose their decorative properties, or they do so only slowly. This seems to be caused by the fact that the concrete elements according to the invention contain less CaO than the concrete elements that usually contain a lot of cement. It has also been found that the use of a granular material which, with a sieve aperture of 2 mm, passes through a sieve of 35.5% by weight to 99.5% by weight and with a sieve aperture of 0.25 mm, passes through a sieve from 2.5% by weight to 33.5% by weight, when using latent hydraulic binders and/or pozzolanic binders, good tensile adhesion strengths can be achieved in the facing concrete layer itself. Although concrete elements could be produced with granular material with larger diameters, they showed poorer tensile strength in the facing concrete layer. Without wishing to be bound by any scientific theory, the improved bond strength could be due to the fact that the components of the granular material with rather smaller diameters have a smaller mean distance from one another. As a result, any shorter chains of the latent hydraulic binder and/or pozzolanic binder can link the components of the granular material with one another, which improves the mechanical properties and in particular the tensile strength of concrete elements that have not yet hardened.

The core concrete layer mix can also be referred to as core concrete mix. The facing concrete layer mix can also be referred to as facing concrete mix. The core concrete layer can also be referred to as the core layer. The facing concrete layer can also be referred to as a facing layer.

The granular material can also be referred to as aggregate.

The concrete elements that have not yet hardened can also be referred to as green concrete elements.

The bond strength can be determined on concrete blocks with a certain test age, for example 28 days. Concrete elements according to the invention preferably have a bond strength of 1 MPa and more after 28 days. The bond strength can be measured in particular according to the DAfSt guideline "Protection and repair of concrete components", Part 4, Section 5.5.11, 2001.

With a sieve aperture of 2 mm, the granular facing material preferably passes through the sieve from 42.5% by weight to 99.5% by weight, more preferably from 56.5% by weight to 98.5% by weight, particularly preferably from 72.5% by weight to 97.5% by weight, and with a sieve aperture of 0.25 mm a sieve passage of from 2.5% by weight to 27.5% by weight, more preferably from 2 .5% by weight to 22.5% by weight, more preferably from 2.5% by weight to 21.5% by weight, particularly preferably 2.5% by weight to 8% by weight or 11.5% by weight to 21.5% by weight, and with a sieve aperture of 0.125 mm a sieve passage of 0.1% by weight to 12.5% by weight, more preferably of 0.3 wt% to 10.0 wt%, more preferably from 0.3 wt% to 7.5 wt%, most preferably 0.3 wt% to 5.0 wt%, based on the total weight of the granular facing material. It has been found that granular facing material with the above-mentioned screen passages can produce concrete elements with good adhesive tensile strength in the facing layer with the screen hole widths mentioned.

With a sieve aperture of 8 mm, the granular core material expediently has a throughput of 42.5% by weight to 99.5% by weight, preferably 56.5% by weight. % to 98.5% by weight, more preferably from 72.5% by weight to 97.5% by weight and, with a screen aperture of 0.5 mm, a screen passage of 7.5% by weight to 39 5% by weight, preferably from 13.5% by weight to 37.5% by weight, particularly preferably from 25.5% by weight to 37% by weight, or from 14.5% by weight % to 24.5% by weight, in each case based on the total weight of the granular core material.

According to one embodiment, the grain size distribution of the granular core material is finer than the grading curve A16 and coarser than the grading curve C16, preferably finer than the grading curve B16 and coarser than the grading curve C16. According to a further embodiment, the grain size distribution of the granular core material is finer than the grading curve A8 and coarser than the grading curve C8, preferably finer than the grading curve A8 and coarser than the grading curve B8. The above grading curves correspond to the specifications of DIN 1045.

It has been found that granular core material with the above-mentioned screen passages and the screen hole sizes mentioned can result in concrete elements with good adhesive tensile strength in the core concrete layer.

The sieve passes specified above for the two sieve hole widths of the granular facing material can be combined with one another as desired. The screen passes specified above for the two screen hole sizes of the granular core material can be combined with one another as desired.

The granular facing material can also have a particle size of from 1.59 to 3.62, preferably from 1.61 to 3.17, particularly preferably from 1.61 to 2.55. The granular core material may also have a grading of from 1.97 to 4.61, preferably from 2.27 to 3.82. The grading number is a characteristic value for the grain composition of a rock aggregate, determined as the sum of the residues on the sieves of the standardized test sieve set in %, divided by 100. The grain composition is determined according to DIN EN 12620:2008-07 paragraph 4.3 of the The test sieve set is the sieve set according to DIN EN 933-2:2020-09 and the sieves meet the requirements of DIN ISO 3310-1:2017-11.

The granular facing material preferably has a graded grain composition. The granular core material preferably has a graded granular composition. A graded grain composition has, in particular, components with different grain sizes.

The granular facing material can be contained in different amounts in the facing mixture. The facing mixture preferably contains 55% by weight to 80% by weight, preferably 60% by weight to 75% by weight, more preferably 60% by weight to 72% by weight, of the granular facing material on the total weight of the face mix. The front mixture can particularly preferably contain 60% by weight to 65% by weight, in particular 60 to 64% by weight, of the granular front material, based on the total weight of the front mixture. The front mixture can particularly preferably also contain 67% by weight to 72% by weight of the granular front material, based on the total weight of the front mixture.

The granular core material can be contained in different amounts in the core mixture. The core mixture preferably contains 60% by weight to 95% by weight, preferably 65% by weight to 92.5% by weight, more preferably 70% by weight to 90% by weight, particularly preferably 74% by weight % to 79% by weight of the granular core material, based on the total weight of the core mixture.

In addition to the components mentioned above, the face mixture can also contain other components, for example a face filler. The preliminary mixture preferably contains 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, more preferably 5% by weight to 18% by weight, even more preferably 5 to 15% by weight. -%, more preferably 5% by weight to 10% by weight, particularly preferably 6 % by weight to 8 % by weight of a face filler, based on the total weight of the face mixture.

With a sieve aperture size of 0.025 mm, the facefiller preferably passes through the sieve from 63% by weight to 99% by weight, preferably from 68% by weight to 99% by weight, more preferably from 90% by weight to 99% by weight Wt 67% by weight, particularly preferably from 61% by weight to 66% by weight, based on the total weight of the facefiller.

In addition to the components mentioned above, the core mixture can also contain other components, for example a core filler. The core mixture preferably contains 1% by weight to 40% by weight, preferably 10% by weight to 30% by weight, more preferably 12.5% by weight to 30% by weight, particularly preferably 15% by weight. -% to 27.5% by weight, based on the total weight of the core mixture, of a core filler.

With a sieve aperture of 0.025 mm, the core filler preferably passes through the sieve from 63% by weight to 99% by weight, preferably from 68% by weight to 99% by weight, more preferably from 90% by weight to 99% by weight Wt 67% by weight, particularly preferably from 61% by weight to 66% by weight, based on the total weight of the core filler.

The screen passes specified above for the two screen hole widths of the facefiller can be combined with one another as desired. The screen passes specified above for the two screen hole sizes of the core filler can be combined with one another as desired. It has been found that through the use of facing and/or core fillers with the above-mentioned screen passed through with the specified screen hole widths, the adhesive tensile strengths in the facing concrete layer and/or in the core concrete layer, in particular of concrete elements that have not yet hardened, can be further improved. In particular, through the combined use of a granular facing and/or core material and a facing and/or core filler with the aforementioned sieve passed through the specified sieve hole widths, optimal results are achieved in terms of tensile strength in the facing concrete layer and/or in the core concrete layer. Furthermore, as a result, the facing mixture can also be adjusted in such a way that the decorative properties of the concrete element do not change or change only very slightly.

Different materials can be used as endface fillers. The face filler is preferably selected from the group consisting of ground rock, preferably classified ground rock, ground limestone, preferably classified ground limestone, and mixtures thereof.

What was said above for the face filler applies accordingly to the core filler.

With the fillers mentioned above, decorative concrete elements with a wide range of uses can be produced economically, the decorative properties of which do not fade or fade only slowly.

Latent hydraulic facing binder and/or pozzolanic facing binder can be contained in different amounts in the facing mixture. The preliminary mixture preferably contains 15% by weight to 40% by weight, preferably 20% by weight to 30% by weight, more preferably 20% by weight to 24% by weight or 26% by weight to 29 % by weight, particularly preferably 22% by weight to 24% by weight, of latent hydraulic facing binder and/or pozzolanic facing binder, based on the total weight of the facing mixture. Accordingly, the preliminary mixture can also contain only 15% by weight to 40% by weight, preferably 20% by weight to 30% by weight, more preferably 20% by weight to 24% by weight or 26% by weight up to 29% by weight, particularly preferably 22% by weight to 24% by weight, based on the total weight of the facing mixture, of latent hydraulic facing binder and no pozzolanic facing binder. The preliminary mixture can also contain only 15% by weight to 40% by weight, preferably 20% by weight to 30% by weight, more preferably 20% by weight to 24% by weight or 26% by weight to 29% by weight, particularly preferably 22% by weight to 24% by weight, based on the total weight of the facing mixture, of pozzolanic facing binder and no latent hydraulic facing binder.

Latent hydraulic core binder and/or pozzolanic core binder can be contained in different amounts in the core mixture. The core mixture preferably contains 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight, of latent hydraulic core binder and/or pozzolanic core binder, based on the total weight of the core mixture.

Correspondingly, the core mixture can also contain only 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight, based on the total weight of the core mixture, of latent hydraulic core binder and no pozzolanic core binder. The core mixture can also contain only 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight, based on the total weight of the core mixture, of pozzolanic core binder and no latent hydraulic core binder.

It has been found that the resulting concrete elements do not have sufficient strength in the facing or core concrete layer when using less than 10% by weight of latent hydraulic binder and/or pozzolanic binder. On the other hand, the use of more than 50% by weight of latent hydraulic binder and/or pozzolanic binder is uneconomical. Various substances can be used as latent hydraulic facing binders. The molar ratio of (CaO+MgO):SiO 2 in the latent hydraulic facing binder is preferably from 0.8 to 2.5, preferably from 1.0 to 2.0. Latent hydraulic facing binders with a molar ratio of (CaO + Mg0):Si02 in the above range harden well.

Advantageously, the latent hydraulic facing binder is selected from the group consisting of slag, blast furnace slag, preferably blast furnace slag, in particular ground blast furnace slag, electrothermal phosphorus slag, steel slag and mixtures thereof. More preferably, the latent-hydraulic facing binder is blast furnace slag, in particular ground blast furnace slag.

Bottom ash can either be industrial bottom ash, i.e. waste products from industrial processes, or synthetic bottom ash. The latter is preferred since industrial slag is not always present in constant quantity and quality. Blast furnace slag, particularly blast furnace slag, is an example of slag.

Ground blast furnace slag varies in fineness and particle size distribution depending on its origin and the type of treatment. The fineness has an influence on the reactivity. The Blaine value in particular can be used as a measure of the fineness. The ground blast furnace slag preferably has a Blaine value of from 200 to 1000 m ² kg ¹ , more preferably from 450 to 650 m ² kg ¹ .

Electrothermal phosphorus slag is a waste product of electrothermal phosphorus production. Electrothermal phosphorus slag is less reactive than blast furnace slag and contains about 45 to 50 wt% CaO, about 0.5 to 3 wt% MgO, about 38 to 43 wt% S1O2, about 2 to 5 wt% .-% Al2O3 and about 0.2 to 3 wt .-% Fe2Ü ₃ and fluorides and phosphates. Steel slag is a waste product of steel production and can vary considerably in its composition.

The molar ratio of (CaO+MgO):SiO 2 in the latently hydraulic binder is particularly preferably from 0.8 to 2.5 and the latently hydraulic binder is selected from the aforementioned substances.

What was said above for the latent hydraulic facing binder applies accordingly to the latent hydraulic core binder.

Various materials can be used as pozzolanic facing binders. Preferably, the pozzolanic facing binder is selected from the group consisting of amorphous silica, precipitated silica, fumed silica, microsilica, glass flour, fly ash such as lignite fly ash or bituminous coal fly ash, metakaolin, natural pozzolans such as tuff, trass or volcanic ash, natural and synthetic zeolites, and mixtures thereof. Most preferably, the pozzolanic binder prefix is amorphous silica.

The amorphous silica preferably shows no crystallinity in a powder diffractogram. Preferably, glass flour is also considered to be amorphous silica. The amorphous silicon dioxide advantageously has an S1O2 content of at least 80% by weight, preferably at least 90% by weight. Precipitated silicon dioxide is obtained industrially preferably by precipitating water glass. Depending on how it is produced, precipitated silicon dioxide can also be referred to as silica gel. Fumed silica is produced by reacting chlorosilanes such as silicon tetrachloride in an oxyhydrogen flame. Fumed silica is amorphous S1O2 powder with a particle diameter of 5 to 50 nm and a specific surface area of 50 to 600 m ² g- ¹ . Microsilica is a by-product of silicon or ferrosilicon production and contains large amounts of amorphous S1O2 powder. The particles have a diameter of about 0.1 μm. The specific surface is in the range of 15 to 30 m ² g- ¹ .

Fly ash is formed, for example, during combustion in coal-fired power plants. According to WO 2008/012438 A2, class F fly ash contains less than 8% by weight, preferably less than 5% by weight, of CaO.

Metakaolin is formed by dehydration of kaolin. While kaolin releases physically bound water in the temperature range of 100 to 200 °C, the collapse of the lattice structure and the formation of metakaolin (AI2S12O7) take place in a range of 500 to 800 °C. Pure metakaolin preferably contains about 54% by weight S1O2 and about 46% by weight Al2O3.

What was said above for the pozzolanic facing binder applies accordingly to the pozzolanic core binder.

It has been found that with the aforementioned latent hydraulic and pozzolanic facing binders and core binders, concrete elements can be produced whose decorative properties do not fade or fade only very slowly and which have good bond strength with a good CO2 balance.

Various substances can be used as alkaline hardening agents. The alkaline preliminary curing agent is preferably selected from the group consisting of alkali metal oxides, alkali metal hydroxides, alkali metal carbonates, alkali metal silicates, alkali metal aluminates and mixtures thereof, preferably consisting of alkali metal hydroxides, alkali metal silicates and mixtures thereof.

Examples of alkali metal oxides are L12O, Na2Ü, K2O, (NHO and mixtures thereof. Examples of alkali metal hydroxides are LiOH, NaOH, KOH, NH4OH and mixtures from that. Examples of alkali metal carbonates are U2CO3, Na2CC> ₃ , K2CO3, (NFD^CCh and mixtures thereof. The ammonium ion is also listed due to its similarity to the alkali metal ions.

Conveniently, alkali metal silicates are selected from compounds having the empirical formula m S1O2 n M2O, where M is Li, Na, K or NFD or a mixture thereof, preferably Na or K. The molar ratio of m:n is from 0.5 to 3.6, preferably from 0.6 to 3.0, particularly preferably from 0.7 to 2.0. Water glass, in particular liquid water glass, more preferably liquid sodium and/or potassium water glass, has proven to be a particularly useful alkali metal silicate. Silicic acid, particularly hydrous silicic acid, is another useful alkali metal silicate.

The alkaline hardening agents mentioned above are preferably used as an aqueous solution. This facilitates dosing.

The hardening of the facing concrete layer can be adjusted well with the aforementioned alkaline facing hardening agents. Furthermore, these alkaline hardening agents show good compatibility with the other components in the mixture.

The alkaline hardening agent can be included in the mixture in different amounts. The preliminary mixture preferably contains 1% by weight to 15% by weight, preferably 1% by weight to 10% by weight, more preferably 3% by weight to 5% by weight, even more preferably 3.15% by weight. -% to 4.85% by weight, more preferably 3.25% to 3.65% by weight or 4.0% to 4.75% by weight, most preferably 4.25 % by weight to 4.75% by weight, very particularly preferably 4.25% by weight to 4.45% by weight, of the alkaline hardening agent set, based on the total weight of the mixture set. Good results are also obtained when the face mix contains from 3.25% to 3.65% by weight of the alkaline hardener head, based on the total weight of the face mix. It was found that the The facing concrete layer hardens too slowly when using less than 1% by weight of the alkaline hardening agent. If more than 15% by weight of alkaline hardening agent is used, hardening can start too quickly, so that the resulting facing concrete layer can no longer be compacted well.

Various substances can be used as alkaline core hardening agents. Preferably, the alkaline core hardener comprises at least one organic and/or at least one inorganic base.

Examples of inorganic bases are the alkaline preliminary hardeners mentioned above. Examples of organic bases are, in particular, amine bases such as ammonia and mono-, di- and trialkylamines, for example triethylamine.

The hardening of the core concrete layer can be adjusted well with the aforementioned alkaline core hardening agents.

The alkaline core hardening agent can be included in the mixture in varying amounts. The core mixture preferably contains from 0.1% to 15% by weight, preferably from 0.5% to 10% by weight, of the alkaline core hardening agent, based on the total weight of the core mixture.

According to the invention, the facing mixture contains water. The preliminary mixture preferably contains 1% by weight to 20% by weight, preferably 3% by weight to 15% by weight, more preferably 3% by weight to 7% by weight, even more preferably 3.5% by weight. -% to 6.5% by weight, more preferably 4.0% to 6.2% by weight, even more preferably 4.2% to 4.9% by weight, particularly preferred 4.2% to 4.8% by weight of water, based on the total weight of the face mix. Good results are also achieved when the face mixture contains 5.2% by weight to 6.2% by weight of water, based on the total weight of the face mixture. The core mixture preferably contains 1% by weight to 20% by weight, preferably 3% by weight to 15% by weight, more preferably 3% by weight to 10% by weight, of water, based on the total weight of the core mix.

In addition to the components described above, the facing mixture can also contain other ingredients. For example, the facing mixture can also contain one or more additives such as gravel, grit, sand, perlite, kieselguhr or vermiculite. Furthermore, the facing mixture can contain cement and/or one or more aggregates such as gravel, grit, sand, perlite, kieselguhr or vermiculite, and/or one or more additives selected from the group consisting of plasticizers, anti-foaming agents, water retention agents, dispersants, pigments, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheology additives.

The facing mixture can in particular contain up to 5% by weight or up to 10% by weight of cement. Alternatively, the facing mixture can in particular be free of cement. If the facing mixture is free of cement, concrete elements can be produced in particular, which have an advantageous carbon dioxide balance.

The facing mixture advantageously contains hardening regulators. Setting retarders and/or setting accelerators are particularly suitable as hardening regulators.

Likewise, the core mixture can in particular contain one or more aggregates such as gravel, grit, sand, perlite, kieselguhr or vermiculite. Furthermore, the core mixture can contain cement and/or one or more aggregates such as gravel, grit, sand, perlite, kieselguhr or vermiculite, and/or one or more additives selected from the group consisting of plasticizers, antifoam agents, water retention agents, dispersants, pigment, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheology additives. In addition, the core concrete layer can also have other aggregates. The core concrete layer preferably contains 1% by weight or more, preferably 5% by weight or more, more preferably 15% by weight or more, particularly preferably 17.5% by weight or more, of opal, flint, chalcedony and/or or greywacke. According to a preferred embodiment, the core concrete layer contains 5% by weight to 30% by weight, in particular 5% by weight to 20% by weight, of opal, flint, chalcedony and/or greywacke. It has been shown that the concrete elements can be produced economically by using these aggregates in these quantities, but the alkali-silicic acid reaction is not very pronounced.

According to one embodiment, the core concrete layer has a free alkali content of 1500 g/m ³ and more.

The core mixture can in particular contain up to 5% by weight or up to 10% by weight of cement. Alternatively, the core mix can be free of cement in particular. If the core mix is free of cement, concrete elements can be produced that have an advantageous carbon dioxide balance.

Advantageously, the core mixture contains setting regulators. Setting retarders and/or setting accelerators are particularly suitable as hardening regulators.

The properties of the facing mixture and/or the core mixture can be well controlled with the aforementioned additives. In particular, the hardening behavior can also be well controlled with the aforementioned additives.

The preliminary mixture preferably contains 0.1% by weight to 2% by weight, more preferably 0.4% by weight to 1.5% by weight, of additives, based on the total weight of the preliminary mixture. The facing mixture expediently contains 0.025% by weight to 0.097% by weight or 1.5% by weight to 2% by weight of setting retarder and/or setting accelerator. The core mixture preferably contains 0.1% by weight to 1% by weight, more preferably 0.3% by weight to 0.9% by weight, of additives, based on the total weight of the core mixture. The core mixture expediently contains 0.0225% by weight to 0.0975% by weight or 1.0% by weight to 1.9% by weight of setting retarder and/or setting accelerator.

The concrete element preferably has a compaction class according to the standard DIN 1045-2 C0 or C01. Preferably, the concrete element is a concrete block, a concrete slab, a concrete wall element or a concrete step.

Furthermore, the concrete element preferably has a compressive strength according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10, measured after 28 days, of less than 110 N/mm ² , preferably less than 100 N/mm ² , more preferably less than 85 N/mm ² , particularly preferably less than 82.5 N/mm ² .

Furthermore, the core concrete layer of the concrete element preferably 28 days after production has an adhesive strength, measured according to DAfSt guideline "Protection and repairs of concrete components", Part 4, Section 5.5.11, 2001, of 1.0 MPa or more, preferably 1.3 MPa or more, more preferably 1.5 MPa or more, particularly preferably 2.0 MPa or more.

The concrete element according to the invention is characterized by good bond strength. The concrete element preferably has a composite tensile strength 28 days after production, measured according to DAfSt guideline "Protection and repairs of concrete components", Part 4, Section 5.5.11, 2001, of 0.75 MPa or more, preferably 1.0 MPa or more, more preferably 1.15 MPa or more, even more preferably 1.3 MPa, particularly preferably 1.5 MPa or more. The adhesive tensile strengths can change, in particular, within the first three to four months after production of the concrete element, and in particular they can increase during this time.

The invention also provides a method for producing concrete elements according to the invention, comprising the steps of: a. Production of a facing composition containing as components i. granular end paper, ii. optional pigment, iii. optional filler, iv. water, v. latent hydraulic facing binder and/or pozzolanic facing binder, and vi. alkaline hardener, b. Mixing the front-end composition to obtain a front-end mixture, c. Preparation of a core composition containing as components i. granular core material, ii. water, iii. latent hydraulic core binder and/or pozzolanic core binder, and iv. alkaline core hardener, d. mixing the core composition to obtain a core blend, e. Filling the core mix and the facing mix into at least one mold, f. Compacting the core mix and the facing mix in the mold to obtain at least one green concrete element.

Preferably, the core mix and the face mix are compacted in at least one mold. Compacting can be done by stamping, pressing and/or vibration. When stamping, the concrete in the mold is preferably compacted by vibration for a period of 1 to 20 seconds, preferably 2.5 to 4.5 seconds. When stamping, the concrete can be compacted in the mold with a pressure of 1.0 MPa or less.

During pressing, the concrete in the mold is preferably compacted with a pressure of 125 MPa or more, more preferably 125 MPa to 250 MPa. During pressing, the concrete in the mold is compacted preferably for a period of 5 to 20 seconds, more preferably 5 to 10 seconds, with essentially no vibration. The process steps are preferably carried out in the order given above.

According to one embodiment, in step e. firstly the facing mixture is filled into the mold and then the core mixture is filled onto the facing mixture in the mold and then the facing mixture is compacted in contact with the core mixture in the mold.

According to a further embodiment, in step e. First the core mixture is filled into the mold and then the face mixture is filled onto the core mixture in the mold and the core mixture is then compacted in contact with the face mixture in the mold.

According to an alternative embodiment, in step e. the core mixture is not filled into a mold but pressed into a strand and the facing mixture is pressed into the strand together or subsequently and then in step f. the core mixture is compacted in contact with the facing mixture in the strand. The concrete elements are obtained from the strand by cutting it to size and placing it on form panels. Furthermore, the components of the face composition are advantageously dosed in the order given. The components of the core composition are expediently dosed in the order given. It has been found that when the components are added in the order given above, good processability of the face composition and/or the core composition is achieved. In addition, it has proven to be expedient if the components of the end-use composition are already mixed during dosing. The same applies to the core composition.

The above applies to the granular facing material, the granular core material, the facing filler, the core filler, the water, the latent hydraulic facing binder and/or the pozzolanic facing binder, the latent hydraulic core binder and/or the pozzolanic core binder, the alkaline facing hardening agent and the alkaline core hardening agent concrete element according to the invention said accordingly, in particular also with regard to the amounts of the components used.

Furthermore, the facing composition and/or the core composition can also contain the other components listed above, such as cement, aggregates, additives, setting retarders and/or setting accelerators. Advantageously, aggregates, additives, setting retarders and/or setting accelerators are metered in with the water or the optional pigment, preferably with the water.

In the method according to the invention it is possible to shape the surface of the concrete elements. According to one embodiment, a portion of a granulated material containing (a) a litter component with an average grain diameter of 0.1 to 5 mm in an amount of 65 to 95% by weight is preferred before compacting onto the facing mixture in the at least one form 75 to 85% by weight, and (b) binder in an amount of 5 to 35% by weight, preferred 15 to 25% by weight, based on the total composition of the granulated material.

By using the scatter component and the binder in these concentration ranges, good anchoring of the granular material on the surface of the concrete element can be achieved.

The person skilled in the art understands the average grain diameter to be that diameter at which there are the same number of grains with a larger and smaller diameter. The mean grain diameter can be determined, for example, by sieving.

In order to produce aesthetically particularly appealing concrete elements according to this embodiment of the method according to the invention, it has proven to be advantageous if the facing concrete layer has an optical property such as color or degree of gloss and the granulated material has an optical property deviating from this. This makes it possible, for example, to create flamed, veined or speckled surfaces that resemble the natural structure of natural stone.

According to this embodiment, the granulated material is preferably applied to the mixture by means of an application device. The application device can have at least one trickling device, a centrifugal disc, a paddle wheel, a throwing arm and/or a catapult, to which at least one portion of the granulated material is fed. These can move over the mold or next to the mold and they can also be fed different portions with different time intervals. In this way the granulated material can be applied evenly to the mixture. Furthermore, it has been found that the method according to the invention can be carried out particularly economically in this way. Advantageously, the application device has at least one dosing container containing granulated material with a dosing strip, the dosing container being guided over the mold at a uniform or non-uniform speed.

In this case, vibrations or jolts are preferably exerted on the dosing bar, which are carried out evenly and/or unevenly and/or intermittently.

Different finishing materials and/or different portions of finishing material can preferably be supplied to the dosing strip along its extension.

Furthermore, it has also proven to be advantageous if the dosing container is attached to the front edge of the dosing carriage for the concrete, preferably the facing concrete.

Possible configurations of an application device with at least one dosing container with a dosing strip are described, for example, in EP 2910 354 A1. An example of an application device with at least one dosing container with a dosing bar is a filling carriage with at least one chamber. The granulated material can be contained in this chamber. The filling carriage can also have two or more chambers separated by a partition. The mixture according to the invention is then advantageously contained in a first chamber of the filling carriage, and the granulated material is preferably contained in a second chamber. Other chambers may contain other granular materials with different properties, such as a different color. The filling carriage can be moved over a mold along a guide rail.

The chamber containing the granular material may include an applicator. The application element can be taken out of the chamber. The chamber may include one or more application members. The application element preferably has a perforated dosing plate with at least one, preferably several holes and a dosing element. The holes may be uniform or arranged in a pattern in the metering plate. The holes can have the same or different diameters. The metering plate can be flat or curved. The dosing plate can also be designed in the shape of a cylinder. The dosing plate can in particular form the dosing bar.

The dosing element can be designed in different ways. The dosing element can, for example, have a shaft to which vanes are attached and which can be rotated about the longitudinal axis of the shaft. The granular material is preferably located in the spaces formed by two vanes of the shaft and the associated portion of the metering plate. By rotating the shaft about its longitudinal axis, the blades push the granulated material through the holes of the metering plate, which is thereby applied to the mix. Such a dosing element is preferably used in connection with a curved dosing plate.

The dosing element can also be designed like a comb. In this case, the comb-like dosing element preferably rests movably on a flat dosing plate. The granulated material preferably lies between the tines of the comb on the metering plate. Moving the comb on the metering plate pushes the granulated material through the holes in the metering plate, which is thereby applied to the mix.

The dosing element can also be a perforated plate. The perforated plate preferably rests on a flat metering plate. The granulated material preferably lies in the holes of the perforated plate on the metering plate. By moving the perforated plate on the metering plate, the granulated material is forced through the holes of the metering plate, which is thereby applied to the mix. Finally, the dosing element can also be a freely movable element, which is preferably arranged inside a cylindrical dosing plate. The granular material is preferably also located inside the cylindrical metering plate. The freely movable element is able to use its own weight to push the granulated material through the holes in the dosing plate. By moving, in particular rotating, the cylindrical dosing plate, the granulated material is pushed through the holes in the dosing plate, which is thereby applied to the mixture.

The application element advantageously also includes other components such as an actuator with which the dosing element can be moved. The actuator can be connected to an electric motor, which can preferably be controlled by electronic control means. The application member may also include an actuator rod, a cam follower engaged with a cam, and/or a gear.

According to a preferred embodiment of the method according to the invention, the application device has at least one pipe socket, to which one or more portions of a granular material are fed and through which these are scattered, thrown, shot and/or dropped onto the facing concrete layer. A particularly good distribution over the mold results when the pipe socket end is designed in the manner of a nozzle.

Practical tests have shown that in the method according to the invention it also contributes to a good distribution if the ejection takes place by means of a prestressed, spring-loaded piston, the locking of which is suddenly released for throwing.

Preferably, the applicator can be moved over the mold and/or alongside the mold. It can have or achieve different movement speeds, with jerky movements also being advantageous. Depending on the size of the mold and depending on the color of the application device with granulated material, several and different devices can also be used for one mold so that the application is made more uniform or a special characteristic application pattern of the granulated material is achieved.

Baffles are preferably used in the application devices, since such disc wheels or limbs and also pipe sockets can have a greater spread.

Several portions of the granulated material can be ejected one after the other by the application devices, which can involve different granulated materials, as described above.

Preferably, the binder contained in the granular material is an inorganic binder such as cement, hydraulic lime, gypsum, slag, blast furnace slag, preferably blast furnace slag, in particular ground blast furnace slag, electrothermal phosphorus slag, steel slag, amorphous silica, precipitated silica, fumed silica, microsilica, glass flour, fly ash such as Brown coal fly ash or hard coal fly ash, metakaolin, natural pozzolana such as tuff, trass or volcanic ash, natural and synthetic zeolites or water glass or the binder contained in the granulated material is an organic binder such as plastic dispersions, acylate resins, alkyd resins, epoxy resins, polyurethanes, sol-gel resins or silicone resin emulsions. Such binders are particularly easy to handle in connection with concrete elements. In addition, they do not place any additional requirements on the process. Furthermore, such binders allow good anchoring of the granular material on the concrete element.

Depending on the desired visual impression of the concrete element, bedding components with different average grain diameters can be used. Thus, as a litter component, a litter component with a mean grain diameters of 0.1 to 1.8 mm can be used. Alternatively, a litter component with an average grain diameter of 1.2 to 5 mm can be used.

A litter component with an average grain diameter of 0.1 to 1.2 mm is preferably used.

The granular material can also contain small rock grains, so that different materials with different colors, grain sizes of semi-precious stones or precious stones or mica or metal chips or plastic particles or glass particles can be introduced into the surface or facing concrete layer. The granular material can also be any rock mixture.

It has proven to be particularly practicable in the method according to the invention if the litter component is or contains a rock mixture. This can be used to produce concrete elements that come very close to the appearance of natural stone.

In the method according to the invention, the litter component preferably contains at least material selected from the group consisting of semi-precious stones, precious stones, mica, metal chips, glass and plastic particles. Using these materials allows a very economical process.

In the method according to the invention, the granulated material can in particular have a graduated grain composition with a maximum grain diameter of 2 mm.

The surfaces and/or edges of the at least one green concrete element can be processed with brushes in the method according to the invention and thereby structured and/or roughened and/or smoothed and/or overhangs at the edges be processed. As a result, a decorative visual impression can be further enhanced.

Before, but preferably after compaction, an organic or inorganic agent, which is preferably colorless, can be applied to the surfaces of the concrete elements before or after curing. This involves impregnating, sealing or coating the concrete elements. In particular, a sealing and/or impregnating agent can be applied to the surface of the at least one green concrete element. Such an approach adds another protective layer to the concrete elements, which further increases the durability and lifespan of the concrete elements. This layer can also act as a stain guard and also prevent lime efflorescence.

The green concrete element is preferably cured in the method according to the invention in order to obtain a concrete element. After hardening, the concrete element is preferably processed by grinding, blasting, brushing and/or structuring the concrete element.

The present invention also relates to the use of latent hydraulic binders and/or pozzolanic binders, in particular as binders, together with alkaline hardening agents to produce a core concrete layer in a concrete element comprising a core concrete layer and a facing concrete layer connected thereto.

The statements made above regarding the concrete element according to the invention preferably apply accordingly to the concrete element.

The statements made above in relation to the latently hydraulic core binder preferably apply correspondingly to the latently hydraulic binder. This also applies to the amounts given above. The statements made above regarding the pozzolanic core binder preferably apply correspondingly to the pozzolanic binder. This also applies to the amounts given above.

For the alkaline hardening agent, the statements made above with regard to the alkaline attachment hardening agent and/or core hardening agent preferably apply correspondingly.

According to one embodiment, the core concrete layer contains granular core material, for which what was said above regarding the granular core material applies accordingly. This also applies to the amounts given above.

According to a further embodiment, the facing concrete layer contains granular facing material, for which the above applies correspondingly to the granular facing material. This also applies to the amounts given above.

According to a further embodiment, the facing concrete layer contains facing filler, for which what was said above about the facing filler applies accordingly. This also applies to the amounts given above.

According to a further embodiment, the core concrete layer contains core filler, for which what was said above about the core filler applies accordingly. This also applies to the amounts given above.

According to a further embodiment, the core concrete layer contains 1% by weight or more, preferably 5% by weight or more, more preferably 15% by weight or more, particularly preferably 17.5% by weight or more, opal, flint, Chalcedony and/or greywacke. According to a further embodiment, the core concrete layer contains 5% by weight to 30% by weight, in particular 5% by weight to 20% by weight, of opal, flint, chalcedony and/or greywacke.

The concrete element of the use according to the invention is preferably a concrete element according to the invention.

Non-limiting examples are given below for further explanation.

EXAMPLES

materials

For geopolymer layers

Front binder mixture: containing mainly latent hydraulic binder and pozzolanic binder.

Core binder mixture containing predominantly latent hydraulic binder and pozzolanic binder.

Granular facing material: 72.5% by weight passing through the sieve with a sieve hole size of 2 mm and 7.5% by weight passing through the sieve with a sieve hole size of 0.25 mm.

Granular core material: aggregate with a sieving rate of 98.8% by weight with a sieve aperture of 8 mm and 18.0% by weight of a sieving with a sieve aperture of 0.5 mm. Facefiller: rock flour with a sieve passage of 97% by weight with a sieve aperture of 0.025 mm and 63% by weight of a sieve with a sieve aperture of 0.015 mm.

Alkaline hardening agent: 75% silica.

Alkaline core hardener: 40% aqueous solution of an inorganic base. Pigment: metal oxide pigment.

Additive for the face mix: setting retarder/setting accelerator. If necessary, cement: Portland cement CEM I 42, 5R

Granular material: containing 80% by weight of small rock grains with an average grain diameter of 0.7 mm and 20% by weight of inorganic binder.

For conventional shifts

Core binder mixture: Portland cement CEM I 52, 5N

Granular core material: aggregate with a sieving rate of 98.8% by weight with a sieve aperture of 8 mm and 18.0% by weight of a sieving with a sieve aperture of 0.5 mm.

Core filler: rock flour with a sieve passage of 97% by weight with a sieve aperture of 0.025 mm and 63% by weight of a sieve with a sieve aperture of 0.015 mm. methods

The tensile strength is determined according to the DAfSt guideline "Protection and repairs of concrete components", Part 4, Section 5.5.11, 2001. A drilling depth of 30 mm and 5 mm is selected as a deviation. The bond strength of the core layer was determined by testing the underside. The attachment strength or bond strength is determined by examining the tear depth (tear location).

Example 1 Into a mixing tank were charged successively 76.0% by weight of granular core material, 5.3% by weight of water, 17.0% by weight of core binder mixture and 1.7% by weight of alkaline core hardening agent to prepare a core composition obtained, the above information being based on the total weight of the core composition. The core composition was then mixed in the mixing tank to obtain a core mixture. The core mixture obtained in this way was poured as a core concrete layer into forms of a mold board. 66.6% by weight of granular facing material, 1.1% by weight of pigment, 6.4% by weight of water, 21.6% by weight of facing binder mixture, 4.26% by weight of alkaline primer curing agent and 0.04% by weight of additive to obtain a primer composition, the above information being based on the total weight of the primer composition. The face composition was then mixed in the mixing tank to obtain a face mix. The face mix thus obtained was filled as a face concrete layer into the molds of the above mold board. The facing concrete layer had a base colour. Subsequently, the mixtures in the mold were compacted by stamping, whereby a green concrete element was obtained. No tearing apart of the green concrete element was observed during demoulding. After demoulding and curing, the concrete element had a measured adhesive tensile strength of at least 0.77 MPa (test age 7d) and of at least 1.15 MPa (test age 28d). The demolition was intentional. Thus, the bond strength is at least the measured 0.77 MPa (test age 7d) and at least 1.15 MPa (test age 28d). Furthermore, the concrete element had a compressive strength according to DIN EN 12390-3:2019-10 of 56.9 N/mm ² (test age 7d) and 60.8 N/mm ² (test age 28d).

In addition, the concrete element had an adhesive tensile strength in the core layer of

I.89 MPa (test age 10 d). After curing, optically appealing concrete elements were obtained. The concrete elements showed no noticeable fading or other deterioration in their decorative properties over a period of 6 months. Furthermore, over a period of 6 months there were no signs of chemical attack on the concrete elements, which could result from an alkali-silica reaction.

Example 2 Comparative Examples In example 2, a conventional, i.e. cement-based core was produced as the core. For this purpose, 79.6% by weight of granular core material,

II.0% by weight of cement, 5.2% by weight of water and 4.2% by weight of core filler are poured in and mixed. The core mixture obtained in this way was poured as a core concrete layer into forms of a mold board.

The facing mixture from Example 1 was then poured onto the core mixture in the molds of the mold board. The facing concrete layer had a base colour. Subsequently, the mixtures in the mold were compacted by stamping, whereby a green concrete element was obtained. No tearing apart of the green concrete element was observed during demoulding. After demolding and curing, the concrete element had a measured tensile strength of at least 0.41 MPa (test age 7d) and at least 0.75 MPa (test age 28d). The tear occurred in the composite layer. Thus, the measured bond strength is the composite bond strength. Furthermore, the concrete element had a compressive strength according to DIN EN 12390-3:2019-10 of 61.1 N/mm ² . Example 3 for comparative examples

First, a conventional core mix was produced as in Example 2 and filled into the molds of a mold board.

A facing mixture was then produced as in Example 1, with the difference that only 15.3% by weight of facing binder was used and an additional 6.3% by weight of cement was added. The thus obtained face composition was then mixed in the mixing tank to obtain a face mix. The face mix thus obtained was filled as a face concrete layer into the molds of the above mold board. The facing concrete layer had a base colour. Subsequently, the mixtures in the mold were compacted by stamping, whereby a green concrete element was obtained. No tearing apart of the green concrete element was observed during demoulding. After demoulding and hardening, the concrete element had a measured adhesive tensile strength of at least 0.26 MPa (test age 7d) and at least 0.28 MPa (test age 28d). The tear occurred in the composite layer. Thus, the measured bond strength is the composite bond strength.

example 4

Example 4 is identical to Example 1 except that 74.8% by weight granular core material, 5.5% by weight water, 17.9% by weight core binder mixture and 1.8% by weight alkaline core hardener for the core composition were filled. Before stamping, any portions of a granular material were scattered, thrown, shot and/or dropped onto the facing concrete layer identical to Example 1 that was then filled in using a pipe socket designed like a nozzle. The applicator could move over the form board so that all layers of facing concrete in the forms could be reached at will. A funnel was arranged above the pipe socket, in which the granulated material was filled. A device for opening and closing the lower hopper opening allowed any portion of the granulated material to be fed into the pipe socket. In principle, several funnels containing different granular materials can be arranged above the centrifugal disk in order to scatter, throw, shoot and/or drop different granular materials in different doses onto the surfaces of the facing concrete layers. The pipe socket could be moved at different speeds, including jerky movements. The height to the form board could also be adjusted and varied as desired, even while the granulated material was being applied. No tearing apart of the green concrete element was observed during demoulding. After demolding and curing, the concrete element had a measured tensile strength of at least 0.83 MPa (test age 7d) and at least 1.17 MPa (test age 28d). The demolition was intentional. The bond strength is thus at least the measured 0.77 MPa (test age 7d) and 1.15 MPa (test age 28d). Furthermore, the concrete element had a compressive strength according to DIN EN 12390-3:2019-10 of 67.0 N/mm ² (test age 7d) and 74.4 N/mm ² (test age 28d). In addition, the concrete element had an adhesive strength of 2.18 MPa in the core layer (test age 10 days).

As follows from the examples, a combination of geopolymer-based core and geopolymer-based facing results in very good bond strength (Examples 1 and 4). At the same time, these fully geopolymer-based concrete elements showed very good resistance to chemical corrosion.

The combinations of a conventional core with a facing layer based on geopolymers (Example 2] and with a hybrid facing layer made of geopolymers and cement (Example 3) showed poorer bond strengths.

Claims

P atentClaims

1. Concrete element comprising a core concrete layer and a facing concrete layer, the concrete element being obtained by compacting and curing a core concrete layer mixture in contact with a facing concrete layer mixture, the core concrete layer mixture containing a latent hydraulic core binder and/or a pozzolanic core binder, water, a granular core material and an alkaline core hardening agent , wherein the facing concrete layer mixture contains a latent hydraulic facing binder and/or a pozzolanic facing binder, water, a granular facing material and an alkaline facing hardening agent, with the granular facing material passing through a sieve of 35.5 wt. % to 99.5 wt % and with a sieve hole size of 0.25 mm has a sieve passage of 2.5 wt. % to 33.5 wt 12390 -3, in particular DIN EN 12390-3:2019-10, measured after 28 days, of less than 120 N /mm ² .

2. Concrete element according to claim 1, characterized in that the granular facing material with a sieve aperture of 2 mm has a sieve passage of 42.5 wt .-% to 99.5 wt .-%, more preferably from 56.5 wt .-% to 98.5% by weight, particularly preferably from 72.5% by weight to 97.5% by weight, and with a sieve aperture of 0.25 mm a sieve passage of from 2.5% by weight to 27.5% % by weight, more preferably from 2.5% by weight to 22.5% by weight, even more preferably from 2.5% by weight to 21.5% by weight, particularly preferably 2.5% by weight. -% to 8% by weight or 11.5% by weight to 21.5% by weight, and with a screen opening of 0.125 mm passing through a sieve from 0.1% by weight to 12.5% by weight, more preferably from 0.3% by weight to 10.0% by weight, more preferably from 0.3% by weight to 7.5% by weight, particularly preferably 0.3% by weight to 5.0% by weight, based on the total weight of the granular facing material, and/or that the granular core material has a screen opening of 8 mm Passthrough from 42.5% by weight to 99.5% by weight, preferably from 56.5% by weight to 98.5% by weight, more preferably from 72.5% by weight to 97.5% by weight % by weight and with a sieve aperture size of 0.5 mm a sieve passage of 7.5% by weight to 39.5% by weight, preferably from 13.5% by weight to 37.5% by weight , particularly preferably from 25.5% by weight to 37% by weight, or from 14.5% by weight to 24.5% by weight, based in each case on the total weight of the granular core material.

3. Concrete element according to one of claims 1 or 2, characterized in that the granular facing material has a grain size of 1.59 to 3.62, preferably from 1.61 to 3.17, particularly preferably from 1.61 to 2.55 and/or that the granular core material has a grading number of from 1.97 to 4.61, preferably from 2.27 to 3.82.

4. Concrete element according to one of the preceding claims, characterized in that the facing mixture contains 55% by weight to 80% by weight, preferably 60% by weight to 75% by weight, more preferably 60% by weight to 72% by weight %, particularly preferably 60% by weight to 65% by weight, in particular 60 to 64% by weight, or 67% by weight to 72% by weight, of the granular face material, based on the total weight of the Facing mixture, and/or that the core mixture is 60% by weight to 95% by weight, preferably 65% by weight to 92.5% by weight, more preferably 70% by weight to 90% by weight, particularly preferably 74% to 79% by weight of the granular core material, based on the total weight of the core mixture.

5. Concrete element according to one of the preceding claims, characterized in that the facing mixture contains 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, more preferably 5% by weight to 18% by weight %, more preferably 5 to 15% by weight, more preferably 5% by weight to 10% by weight, particularly preferably 6% by weight to 8% by weight, of a facefiller, based on the total weight of the facing mixture, and/or that the core mixture contains 1% by weight to 40% by weight, preferably 10% by weight to 30% by weight, more preferably 12.5% by weight to 30% by weight, particularly preferably 15% by weight to 27.5% by weight of a core filler, based on the total weight of the core mixture.

6. Concrete element according to claim 5, characterized in that the face filler with a screen hole width of 0.025 mm passes through the screen from 63% to 99% by weight, preferably from 68% to 99% by weight preferably from 90% by weight to 99% by weight, particularly preferably from 95% by weight to 99% by weight, and with a sieve aperture of 0.015 mm a sieve passage of 38% by weight to 73% by weight , preferably from 58% by weight to 67% by weight, particularly preferably from 61% by weight to 66% by weight, based on the total weight of the face filler, and/or that the core filler has a screen opening of 0.025 mm passing through the sieve from 63% by weight to 99% by weight, preferably from 68% by weight to 99% by weight, more preferably from 90% by weight to 99% by weight, particularly preferably from 95% by weight % to 99% by weight, and with a sieve aperture of 0.015 mm a sieve passage of 38% by weight to 73% by weight, preferably from 58% by weight to 67% by weight, particularly preferably from 61 % by weight to 66% by weight, based on the total weight weight of the core filler.

7. Concrete element according to one of claims 5 or 6, characterized in that the face filler is selected from the group consisting of mineral powder, preferably classified mineral powder, limestone powder, preferably classified limestone powder, and mixtures thereof, and/or that the core filler is selected from the group consisting of mineral powder, preferably classified mineral powder, limestone powder, preferably classified limestone powder, and mixtures thereof.

8. Concrete element according to one of the preceding claims, characterized in that the facing mixture contains 15% by weight to 40% by weight, preferably 20% by weight to 30% by weight, more preferably 20% by weight to 24% by weight % or 26% by weight to 29% by weight, particularly preferably 22% by weight to 24% by weight, of latent hydraulic facing binder and/or pozzolanic facing binder, based on the total weight of the facing mixture, and/or that the core mixture contains 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight, of latently hydraulic core binder and/or pozzolanic core binder, based on the total weight of the core mixture.

9. Concrete element according to one of the preceding claims, characterized in that the latent hydraulic facing binder is selected from the group consisting of slag, blast furnace slag, preferably blast furnace slag, in particular ground blast furnace slag, electrothermal phosphorus slag, steel slag and mixtures thereof, and/or that in the latent hydraulic facing binder the Molar ratio of (CaO + MgO): Si0 ₂ is from 0.8 to 2.5, preferably from 1.0 to 2.0, and / or that the latent hydraulic core binder is selected from the group consisting of slag, blast furnace slag, preferably blast furnace slag, in particular ground blast furnace slag, electrothermal phosphorus slag, steel slag and mixtures thereof, and/or that in the latent hydraulic core binder the molar ratio of (CaO+MgO):Si0 ₂ is from 0.8 to 2.5, preferably from 1.0 to 2.0 , amounts to.

10. Concrete element according to one of the preceding claims, characterized in that the pozzolanic facing binder is selected from the group consisting of amorphous silicon dioxide, precipitated silicon dioxide, pyrogenic silicon dioxide, microsilica, glass powder, fly ash such as lignite fly ash or coal fly ash, metakaolin, natural pozzolan such as tuff, trass or volcanic ash, natural and synthetic zeolites and mixtures thereof, and/or that pozzolanic core binder is selected from the group consisting of amorphous silicon dioxide, precipitated silicon dioxide, fumed silicon dioxide, microsilica, glass flour, fly ash such as lignite fly ash or coal fly ash, metakaolin, natural pozzolans such as tuff, Trass or volcanic ash, natural and synthetic zeolites and mixtures thereof.

11. Concrete element according to one of the preceding claims, characterized in that the alkaline hardening agent is selected from the group consisting of alkali metal oxides, alkali metal hydroxides, alkali metal carbonates, alkali metal silicates, alkali metal aluminates and mixtures thereof, preferably consisting of alkali metal hydroxides, alkali metal silicates and mixtures thereof, and/or that the alkaline core hardening agent comprises an organic and/or an inorganic base.

12. Concrete element according to one of the preceding claims, characterized in that the facing mixture contains 1% by weight to 15% by weight, preferably 1% by weight to 10% by weight, more preferably 3% by weight to 5% by weight %, more preferably 3.15% to 4.85% by weight, more preferably 3.25% to 3.65% by weight or 4.0% to 4% by weight, 75% by weight, particularly preferably 4.25% by weight to 4.75% by weight, very particularly preferably 4.25% by weight to 4.45% by weight, of the alkaline hardening agent, based on the total weight of the front mixture, and/or that the core mixture is 0.1% by weight to 15% by weight, preferably 0.5% by weight. % to 10% by weight of the alkaline core hardener based on the total weight of the core mixture.

13. Concrete element according to one of the preceding claims, characterized in that the facing mixture contains 1% by weight to 20% by weight, preferably 3% by weight to 15% by weight, more preferably 3% by weight to 7% by weight %, more preferably from 3.5% to 6.5% by weight, more preferably from 4.0% to 6.2% by weight, more preferably from 4.2% to 4.9% by weight or 5.2% by weight to 6.2% by weight, particularly preferably 4.2% by weight to 4.8% by weight, of water, based on the total weight of the facing mixture, and/or that the core mixture contains 1% by weight to 20% by weight, preferably 3% by weight to 15% by weight, more preferably 3% by weight to 10% by weight, water, based on the total weight of the core mix.

14. Concrete element according to one of the preceding claims, characterized in that the facing mixture has hardening regulators, in particular setting retarders and/or setting accelerators, and/or that the core mixture has hardening regulators, in particular setting retarders and/or setting accelerators.

15. Concrete element according to one of the preceding claims, characterized in that the facing mixture cement, in particular up to 5 wt .-% or up to 10 wt .-% cement, and / or one or more aggregates such as gravel, grit, sand, perlite , kieselguhr or vermiculite, and/or one or more additives selected from the group consisting of plasticizers, antifoam agents, water retention agents, dispersants, pigment, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheology additives, and/or that the core mixture contains cement, in particular up to 5% by weight or up to 10% by weight of cement, and/or one or more aggregates such as gravel, grit, sand, perlite, kieselguhr or vermiculite, and/or one or more Additives selected from the group consisting of plasticizers, antifoams, water retention agents, dispersants, pigments, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheology additives.

16. Concrete element according to one of the preceding claims, characterized in that the concrete element preferably has a compressive strength according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10, measured after 28 days, of less than 110 N/mm ² less than 100 N/mm ² , more preferably less than 85 N/mm ² , particularly preferably less than 82.5 N/mm ² .

17. Concrete element according to one of the preceding claims, characterized in that the core concrete layer of the concrete element 28 days after production has an adhesive strength, measured according to DAfSt guideline "Protection and repairs of concrete components", part 4, section 5.5.11, 2001, from 1, 0 MPa or more, preferably 1.3 MPa or more, more preferably 1.5 MPa or more, particularly preferably 2.0 MPa or more.

18. Concrete element according to one of the preceding claims, characterized in that the concrete element 28 days after production has a bond strength, measured according to DAfSt guideline "Protection and repairs of concrete components", part 4, section 5.5.11, 2001, from 0, 75 MPa or more, preferably 1.0 MPa or more, more preferably 1.15 MPa or more, even more preferably 1.3 MPa or more, particularly preferably 1.5 MPa or more.

19. Concrete element according to one of the preceding claims, characterized in that the core concrete layer contains 1% by weight or more, preferably 5% by weight or more, more preferably 15% by weight or more, particularly preferably 17.5% by weight. % or more containing opal, flint, chalcedony and/or greywacke.

20. Concrete element according to one of the preceding claims, characterized in that the concrete element is a concrete block, a concrete slab, a concrete wall element or a concrete step.

21. A method for producing a concrete element according to any one of claims 1 to 20, comprising the steps of: a. Production of a facing composition containing as components i. granular end paper, ii. optional pigment, iii. optional filler, iv. water, v. latent hydraulic facing binder and/or pozzolanic facing binder, and vi. alkaline hardener, b. Mixing the front-end composition to obtain a front-end mixture, c. Preparation of a core composition containing as ingredients i. granular core material, ii. water, iii. latent hydraulic core binder and/or pozzolanic core binder, and iv. alkaline core hardener, d. mixing the core composition to obtain a core blend, e. Filling the core mix and the facing mix into at least one mold, f. Compacting the core mix and the facing mix in the mold to obtain at least one green concrete element.

22. The method according to claim 21, characterized in that the components of the attachment composition are dosed in the order given.

23. The method according to any one of claims 21 or 22, characterized in that the core mixture is filled into the at least one mold before the facing mixture.

24. The method according to claim 23, characterized in that the core mixture is compacted before filling in the facing mixture.

25. The method according to any one of claims 21 to 24, characterized in that before compacting on the facing mixture in the at least one mold containing a portion of a granular material (a) a litter component with an average grain diameter of 0.1 to 5 mm in a amount of 65 to 95% by weight and (b) binder in an amount of 5 to 35% by weight based on the total composition of the granular material.

26. The method according to claim 25, characterized in that the binder contained in the granular material is an inorganic binder such as cement, hydraulic lime, gypsum or water glass or that the binder contained in the granular material is an organic binder such as plastic dispersions, acylate resins, alkyd resins, epoxy resins, Polyurethanes, sol-gel resins or silicone resin emulsions, and/or that a litter component with an average grain diameter of 0.1 to 1.8 mm or 1.2 to 5 mm is used as the litter component, and/or that the litter component is a rock mixture is or contains, or that the litter component contains at least material selected from the group consisting of semi-precious stones, precious stones, mica, metal shavings, glass and plastic particles.

27. The method according to claim 25 or 26, characterized in that the granulated material is applied by scattering or throwing, and/or that the granulated material is applied to the facing mixture by means of an application device is applied, the application device having at least one pipe socket, to which one or more portions of a granular material are fed and through which these are scattered, thrown, shot and/or dropped onto the concrete layer.

28. The method according to any one of claims 21 to 27, characterized in that the surfaces and/or edges of the at least one green concrete element are processed with brushes and thereby structured and/or roughened and/or smoothed and/or excess material at the edges is removed.

29. The method according to any one of claims 21 to 28, characterized in that a sealing and/or impregnating agent is applied to the surface of the at least one green concrete element.

30. The method according to any one of claims 21 to 29, characterized in that the green concrete element is cured to obtain a concrete element, wherein the concrete element is preferably processed after curing by grinding, blasting, brushing and / or structuring of the concrete element.

31. Use of latent hydraulic binder and/or pozzolanic binder, in particular as a binder, together with alkaline hardening agent for producing a core concrete layer in a concrete element comprising a core concrete layer and a facing concrete layer connected thereto.

32. Use according to claim 31, characterized in that the latent hydraulic binder is defined as the core binder in claim 9, and/or the pozzolanic binder is defined as the pozzolanic core binder in claim 10, and/or that the core concrete layer contains granular core material as in Claims 1 to 4 contains defined, and / or that the facing concrete layer contains granular facing material as defined in claims 1 to 4, and / or that the core concrete layer Contains core filler as defined in claims 6 and 7, and/or that the facing concrete layer contains face filler as defined in claims 6 and 7, and/or that the alkaline hardening agent is as defined in claim 11, and/or that the concrete element is characterized by at least a feature of claims 16, 18 or 20 is defined, and/or that the core concrete layer 1

% by weight or more, preferably 5% by weight or more, more preferably 15% by weight or more, particularly preferably 17.5% by weight or more, opal, flint, chalcedony and/or greywacke.