Concrete element and method for producing same

Abstract

The present invention relates to a concrete element comprising a core concrete layer and a face concrete layer, the concrete element being obtained by compressing and hardening a core concrete layer mixture in contact with a face concrete layer mixture, the core concrete layer comprising a latent hydraulic core binder and / or a pozzolanic core binder, water, a granular core material and an alkaline core hardener, the face concrete layer mixture comprising a latent hydraulic face binder and / or a pozzolanic face binder, water, a granular face material and an alkaline face hardener, the concrete element having a compressive strength measured after 28 days according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10 of 120 N / mm 2 It also relates to a method for producing the concrete element of the invention.

Description

[Technical field]

[0001] The present invention relates to a concrete element comprising a core concrete layer and a face concrete layer, said concrete element being obtained by compacting and hardening a core concrete layer mixture in contact with a face concrete layer mixture, said core concrete layer mixture and said face concrete layer mixture each containing a latent hydraulic and / or pozzolanic binder, water, a granular core material and an alkaline hardener. The present invention also relates to a method for producing the concrete element according to the invention. [Background technology]

[0002] Concrete elements such as concrete blocks, concrete slabs, concrete wall elements or concrete steps are often preferred over plates or steps made of natural stone due to their durability and low cost. Concrete elements are usually produced using cement as a binder.

[0003] Various methods have been developed to give concrete elements a decorative appearance. For this purpose, they are usually coloured and polished, in particular by adding pigments and / or natural stone aggregates and / or sand.

[0004] Cement-containing concrete elements can have the problem of developing whitish spots on the surface over time, the so-called efflorescence. Also, coloured concrete blocks can fade. Both effects are thought to be caused by the formation of lime. The whitish spots on the surface are thought to be due to lime efflorescence, which is formed by the reaction of calcium hydroxide brought to the surface with carbon dioxide. The fading is thought to be caused, among other things, by the fact that the pigments deposited on the cement particles for colouring are slowly coated with the calcium carbonate that is formed.

[0005] Alternative binders to cement are known. One such alternative binder is based on a combination of the chemical building blocks SiO2 and Al2O3. Such binders include, for example, latent hydraulic binders and pozzolanic binders. These are often called "geopolymers". For example, EP 1 236 702 A1 describes a building material mixture comprising sodium silicate and a latent hydraulic binder. EP 1 236 702 A1 shows the use of this building material mixture as a mortar or filler.

[0006] In the production of concrete elements such as concrete blocks, concrete slabs, concrete wall elements or concrete steps, the concrete mix used must meet special requirements, especially when compared to ready-mix concrete. When producing concrete elements, it is desirable to have as high a stability as possible for the concrete block that is not yet hardened after as short a time as possible so that it can be set as quickly as possible. As a further requirement, in products that include face and core concrete layers, a high bond strength is required to prevent the face concrete layer from peeling off from the core under load and weathering. The bond adhesion tensile strength can be used to measure the resistance of the face concrete layer to peeling off from the core concrete of the concrete element. If the concrete element does not have the required bond adhesion tensile strength, the face concrete layer and the core concrete may separate (peel off) or split under load when the formwork is removed. Therefore, if a concrete element is designed with a sufficiently high bond adhesive tensile strength, it can be used in a wider range of applications.

[0007] WO 2021 / 047875 A1 describes a concrete element comprising a core concrete layer and a face concrete layer, the face concrete layer comprising a latent hydraulic binder and / or a pozzolanic binder. However, WO 2021 / 047875 A1 does not indicate that a latent hydraulic binder and / or a pozzolanic binder is also used in the core concrete layer.

[0008] Over their service life, concrete elements are exposed to various attacks that cause corrosion of the concrete elements. In addition to physical corrosion, e.g. by frost and deicing salts, chemical corrosion, including the triggering attack alkali-silica reaction, is also an important form of corrosion. Alkali-silica reaction occurs especially in combination with alkali-rich binders and alkali-reactive aggregates, such as greywacke. These alkali-reactive aggregates are rarely found in the face concrete layers, where higher quality aggregates are usually used, but are mainly used in the core concrete layers. Therefore, attempts to use alkali-rich binders, e.g. geopolymers, in the core concrete layers have not been made so far, because they may cause problems of alkali-silica reaction due to the alkali-reactive aggregates. Furthermore, the combination of latent hydraulic and pozzolanic binders and the hardeners required for this is more expensive than cementitious binders. For this reason, conventional, i.e. cementitious core concrete layers are usually used as the core concrete layers.

[0009] In the course of the development of the present invention, it was found that concrete elements having a cementitious core concrete layer and face concrete layers containing latent hydraulic and / or pozzolanic binders have a lower bond adhesion tensile strength under otherwise equivalent production conditions and ingredients than concrete elements in which both layers are cementitious. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] European Patent Application Publication No. 1 236 702 A1 [Patent Document 2] International Application Publication No. 2021 / 047875A1 [Patent Document 3] International Application Publication No. 2008 / 012438A2 [Patent Document 4] European Patent Application Publication No. 2 910 354 A1 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0011] It was therefore an object of the present invention to provide an aesthetic concrete element that is less susceptible to changes in appearance over time, to chemical corrosion, in particular to alkali-silica reactions, and that can be produced economically. In particular, concrete blocks should be provided that have a less susceptible to staining and / or soiling of the surface and / or that have less discolouration and / or that have a sufficiently high tensile bond strength, in particular a sufficiently high tensile bond strength. Another object of the present invention is to provide a concrete element with a reduced CO2 footprint.

[0012] Further objects, some of which are listed below, will be obtained from the embodiments described hereinafter. [Means for solving the problem]

[0013] The present invention achieves all or part of these aims by means of a concrete element according to claim 1 and a method according to claim 22.

[0014] Advantageous embodiments of the invention are set forth in the dependent claims and are explained in detail below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention relates to a concrete element comprising a core concrete layer and a face concrete layer, said concrete element being obtained by compressing and hardening a core concrete layer mixture in contact with a face concrete layer mixture, The core concrete layer comprises a latent hydraulic core binder and / or a pozzolanic core binder, water, a granular core material, and an alkaline core hardener; The face concrete layer mixture comprises a latent hydraulic face binder and / or a pozzolanic face binder, water, a granular face material, and an alkaline face hardener, the passing fraction of the granular face material being between 35.5% and 99.5% by weight for a screen hole width of 2 mm and between 2.5% and 33.5% by weight for a screen hole width of 0.25 mm, based on the total weight of the granular face material, and the concrete element has a compressive strength measured according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10 after 28 days of at least 120 N / mm 2 To provide a concrete element having a thickness of less than 100 mm.

[0016] Surprisingly, it has been found that a concrete element comprising a core concrete layer and a face concrete layer, said concrete element being obtained by compressing and hardening a core concrete layer mixture in contact with a face concrete layer mixture, said core concrete layer containing a latent hydraulic core binder and / or a pozzolanic core binder, water, a granular core material, and an alkaline core hardener, said face concrete layer mixture containing a latent hydraulic face binder and / or a pozzolanic face binder, water, a granular face material, and an alkaline face hardener, said granular face material having a passing fraction of 35.5% to 99.5% by weight with a screen hole width of 2 mm and 2.5% to 33.5% by weight with a screen hole width of 0.25 mm, based on the total weight of said granular face material, changes its decorative properties only slowly, if at all, and can be produced economically. The above-mentioned concrete element in particular has a sufficiently high bond adhesion tensile strength, which allows the concrete element to have a wide range of applications. Furthermore, these concrete blocks will only fade slowly, if at all, and will show little or no surface staining. Furthermore, the concrete blocks according to the invention show good resistance to alkali-silica reactions. Finally, these concrete elements have a good CO2 footprint.

[0017] Without wishing to be bound by any particular theory, this may be due to the fact that the use of latent hydraulic and / or pozzolanic binders in the core and face concrete layers increases the bond tensile strength between the core and face concrete layers, but does not significantly increase the sensitivity to chemical corrosion, especially in the core concrete layer. Presumably, the use of latent hydraulic and / or pozzolanic binders in both the face and core concrete layers improves the bond tensile strength between these two layers. Furthermore, the concrete elements appear to lose their decorative properties only slowly or not at all due to the use of latent hydraulic and / or pozzolanic binders. This may be due to the fact that the concrete elements according to the invention contain a lower CaO content than concrete elements that usually contain a higher amount of cement. It was also found that the bond tensile strength of the face concrete layer itself is better with latent hydraulic and / or pozzolanic binders, by using granular materials with a passing fraction of 35.5% to 99.5% by weight for a screen hole width of 2 mm and 2.5% to 33.5% by weight for a screen hole width of 0.25 mm. It was also possible to produce concrete elements using granular materials with larger diameters, but the bond tensile strength of the face concrete layer was not as good in that case. Without wishing to be bound by any theory, the improved bond tensile strength may be due to the fact that granular materials with a significantly smaller diameter have a smaller average distance between their components. This means that shorter chains of latent hydraulic and / or pozzolanic binders are still able to bond the components of the granular material to each other, thereby improving the mechanical properties of the not yet hardened concrete elements, in particular the bond tensile strength.

[0018] The core concrete layer mixture is also called the core concrete mixture. The face concrete layer mixture is also called the face concrete mixture.

[0019] The core concrete layer is also called the core layer. The face concrete layer is also called the face layer.

[0020] The granular material is also called aggregate.

[0021] Concrete elements that have not yet hardened are also called green concrete elements.

[0022] The bond tensile strength can be measured on concrete blocks at a certain test age, for example 28 days. The concrete elements according to the invention preferably have a bond tensile strength of ≧1 MPa after 28 days. The bond tensile strength can in particular be measured in accordance with the DAfStb (German Committee for Reinforced Concrete) directive "Protection and repair of concrete components", Part 4, Section 5.5.11, 2001 (DAfSt Richtlinie "Schutz und instandsetzungen von Betonbauteilen").

[0023] Preferably, the passing fraction of the granular face material is between 42.5% and 99.5% by weight for a screen hole width of 2 mm, more preferably between 56.5% and 98.5% by weight, particularly preferably between 72.5% and 97.5% by weight for a screen hole width of 2 mm, and between 2.5% and 27.5% by weight, more preferably between 2.5% and 22.5% by weight, even more preferably between 2.5% and 21.5% by weight, particularly preferably between 2.5% and 8% by weight or between 11.5% and 21.5% by weight for a screen hole width of 0.25 mm, and between 0.1% and 12.5% ​​by weight, more preferably between 0.3% and 10.0% by weight, even more preferably between 0.3% and 7.5% by weight, particularly preferably between 0.3% and 5.0% by weight for a screen hole width of 0.125 mm. It has been found that a granular face material having the above mentioned pass fraction at the above mentioned screen hole widths results in concrete elements having good bond tensile strength at the face layer.

[0024] For convenience, the passing fraction of the granular core material is 42.5% by weight to 99.5% by weight, preferably 56.5% by weight to 98.5% by weight, more preferably 72.5% by weight to 97.5% by weight when the screen opening width is 8 mm, and 7.5% by weight to 39.5% by weight, preferably 13.5% by weight to 37.5% by weight, particularly preferably 25.5% by weight to 37% by weight or 14.5% by weight to 24.5% by weight when the screen opening width is 0.5 mm, based on the total weight of the granular core material.

[0025] According to one embodiment, in terms of particle size distribution, the granular core material exhibits a distribution that is finer than the grade curve A16 and coarser than the grade curve C16, preferably finer than the grade curve B16 and coarser than the grade curve C16. According to another embodiment, in terms of particle size distribution, the granular core material exhibits a distribution that is finer than the grade curve A8 and coarser than the grade curve C8, preferably finer than the grade curve A8 and coarser than the grade curve B8. The above grade curves meet the specifications of DIN 1045.

[0026] It has been found that a granular core material having the above mentioned passing fractions at the above mentioned screen hole widths results in concrete elements having good bond tensile strength in the core concrete layer.

[0027] The passing fractions of the above-mentioned granular face materials at the two screen opening widths can be combined with each other as required. The passing fractions of the above-mentioned granular core materials at the two screen opening widths can be combined with each other as required.

[0028] The gradation number of the granular face material may be between 1.59 and 3.62, preferably between 1.61 and 3.17, particularly preferably between 1.61 and 2.55. The gradation number of the granular core material may also be between 1.97 and 4.61, preferably between 2.27 and 3.82. The gradation number is a characteristic value of the particle composition of the aggregate and is determined as the sum of the residues (%) remaining on the screens of a standard test screening set divided by 100. The particle composition is determined in accordance with DIN EN 12620:2008-07, paragraph 4.3. The test screening set is a screening set in accordance with DIN EN 933-2:2020-09 and the screens meet the requirements of DIN ISO 3310-1:2017-11.

[0029] The particulate face material preferably has a classified particle composition.The particulate core material preferably has a classified particle composition.The classified particle composition includes components of various particle sizes.

[0030] The content of the granular face material in the face concrete layer mixture is not particularly limited. The face concrete layer mixture advantageously contains 55% to 80% by weight, preferably 60% to 75% by weight, more preferably 60% to 72% by weight of the granular face material, based on the total weight of the face concrete layer mixture. The face concrete layer mixture may particularly preferably contain 60% to 65% by weight, in particular 60 to 64% by weight of the granular face material, based on the total weight of the face concrete layer mixture. The face concrete layer mixture may also particularly preferably contain 67% to 72% by weight of the granular face material, based on the total mass of the face concrete layer mixture.

[0031] The content of the granular core material in the core concrete layer mixture is not particularly limited. The core concrete layer mixture advantageously contains 60% to 95% by weight, preferably 65% ​​to 92.5% by weight, more preferably 70% to 90% by weight, and particularly preferably 74% to 79% by weight of the granular core material relative to the total weight of the core concrete layer mixture.

[0032] In addition to the above mentioned components, the face concrete layer mixture may also contain other components, such as face fillers. The face concrete layer mixture preferably contains 1% to 30% by weight of face fillers, preferably 1% to 20% by weight, more preferably 5% to 18% by weight, even more preferably 5% to 15% by weight, even more preferably 5% to 10% by weight, and particularly preferably 6% to 8% by weight, based on the total weight of the face concrete layer mixture.

[0033] The passing fraction of the face filler is preferably 63% by weight to 99% by weight, preferably 68% by weight to 99% by weight, more preferably 90% by weight to 99% by weight, particularly preferably 95% by weight to 99% by weight, for a screen hole width of 0.025 mm, and 38% by weight to 73% by weight, preferably 58% by weight to 67% by weight, particularly preferably 61% by weight to 66% by weight, for a screen hole width of 0.015 mm, relative to the total weight of the face filler.

[0034] In addition to the above-mentioned components, the core concrete layer mixture may also contain other components, such as a core filler. The core concrete layer mixture advantageously contains 1% to 40% by weight of the core filler, preferably 10% to 30% by weight, more preferably 12.5% ​​to 30% by weight, particularly preferably 15% to 27.5% by weight, based on the total weight of the core concrete layer mixture.

[0035] The passing fraction of the core filler is preferably 63% by weight to 99% by weight, preferably 68% by weight to 99% by weight, more preferably 90% by weight to 99% by weight, and particularly preferably 95% by weight to 99% by weight, when the screen hole width is 0.025 mm, and 38% by weight to 73% by weight, preferably 58% by weight to 67% by weight, and particularly preferably 61% by weight to 66% by weight, when the screen hole width is 0.015 mm, relative to the total weight of the core filler.

[0036] The passing fractions of the above-mentioned particulate face materials at the two screen opening widths can be combined with each other as required. The passing fractions of the above-mentioned core filler materials at the two screen opening widths can be combined with each other as required.

[0037] It has been found that by using face and / or core fillers with the abovementioned pass-through fractions at the abovementioned screen hole widths, the bond tensile strength of the face and / or core concrete layers, in particular of the not yet hardened concrete elements, can be improved even further.

[0038] In particular, by using a combination of granular face material and / or granular core material with face filler and / or core filler at each of the abovementioned passage fractions of the abovementioned screen hole widths, optimal results are achieved in terms of the bond tensile strength of the face concrete layer and / or the core concrete layer, which in turn makes it possible to adjust the face concrete layer mixture in such a way that the decorative properties of the concrete element are little or not altered at all.

[0039] As face filler various materials can be used, the face filler being preferably selected from the group consisting of rock powder, preferably classified rock powder, limestone powder, preferably classified limestone powder, and mixtures thereof.

[0040] The above statements regarding the face filler apply equally to the core filler.

[0041] By using the face and core fillers described above, decorative concrete elements can be economically produced which have a wide range of applications and whose decorative properties do not fade or fade only slowly.

[0042] The content of the latent hydraulic face binder and / or pozzolanic face binder in the face concrete layer mixture is not particularly limited. Preferably, the face concrete layer 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 the latent hydraulic face binder and / or pozzolanic face binder, based on the total weight of the face concrete layer mixture.

[0043] It is therefore possible for the face concrete layer mixture to contain only 15% to 40% by weight, preferably 20% to 30% by weight, more preferably 20% to 24% by weight or 26% to 29% by weight, more preferably 22% to 24% by weight of latent hydraulic face binders, based on the total weight of the face concrete layer mixture, and no pozzolanic face binders. It is also possible for the face concrete layer mixture to contain only 15% to 40% by weight, preferably 20% to 30% by weight, more preferably 20% to 24% by weight or 26% to 29% by weight, more preferably 22% to 24% by weight of pozzolanic face binders, based on the total weight of the face concrete layer mixture, and no latent hydraulic face binders.

[0044] The content of the latent hydraulic core binder and / or the pozzolana core binder in the core concrete layer mixture is not particularly limited. Preferably, the core concrete layer mixture contains 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight of the latent hydraulic core binder and / or the pozzolana core binder relative to the total weight of the core concrete layer mixture.

[0045] Therefore, the core concrete layer mixture may also contain only 10% to 50% by weight, preferably 10% to 40% by weight, of a latent hydraulic core binder, based on the total weight of the core concrete layer mixture, and may not contain a pozzolanic core binder.The core concrete layer mixture may also contain only 10% to 50% by weight, preferably 10% to 40% by weight, of a pozzolanic core binder, based on the total weight of the core concrete layer mixture, and may not contain a latent hydraulic core binder.

[0046] It has been found that the resulting concrete elements do not have sufficient strength in the face or core concrete layers when using less than 10% by weight of latent hydraulic and / or pozzolanic binders, whereas using more than 50% by weight of latent hydraulic and / or pozzolanic binders is uneconomical.

[0047] Various materials can be used as the latent hydraulic face binder. The molar ratio of (CaO+MgO):SiO2 in the latent hydraulic face binder is preferably 0.8-2.5, more preferably 1.0-2.0. The hardening of the latent hydraulic face binder with the molar ratio of (CaO+MgO):SiO2 in these ranges is good.

[0048] The latent hydraulic face binder is advantageously selected from the group consisting of slag, blast furnace slag, preferably blast furnace sand, in particular ground blast furnace sand, electrolytic phosphorus slag, steel slag and mixtures thereof. The latent hydraulic face binder is more preferably slag sand, in particular ground slag sand.

[0049] The slag can be either industrial slag, i.e. waste material resulting from industrial processes, or synthetically produced slag. Synthetically produced slag is preferred, as industrial slag is not always available in consistent quantities and grades. Blast furnace slag, and especially slag sand, are examples of slag.

[0050] Crushed slag sand has different fineness and particle size distribution depending on the place of origin and the type of processing. Fineness influences reactivity. The Blaine value can be used in particular as a measure of fineness. The Blaine value of crushed slag sand is preferably 200-1000 m 2 kg -1 , more preferably 450 to 650 m 2 kg -1 It is.

[0051] Electrochemical phosphorus slag is a waste product resulting from the production of electrochemical phosphorus. Electrochemical phosphorus slag is less reactive than blast furnace slag and contains about 45-50% by weight CaO, about 0.5-3% by weight MgO, about 38-43% by weight SiO2, about 2-5% by weight Al2O3, and about 0.2-3% by weight Fe2O3, as well as fluorides and phosphates.

[0052] Steel slag is a waste product resulting from the production of iron and steel and has a diverse composition.

[0053] The molar ratio of (CaO+MgO):SiO2 in the latent hydraulic binder is particularly preferably 0.8 to 2.5, and the latent hydraulic binder is selected from the above-mentioned materials.

[0054] The above statements regarding the latent hydraulic face binders apply equally to the latent hydraulic core binders.

[0055] As the pozzolanic face binder, various materials can be used. The pozzolanic face binder is preferably 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 anthracite fly ash, metakaolin, natural pozzolans such as tuff, trass or volcanic ash, natural and synthetic zeolites, and mixtures thereof. In particular, the pozzolanic face binder is preferably amorphous silicon dioxide.

[0056] Amorphous silicon dioxide preferably does not show any crystallinity in the powder diffractogram. Glass powder is also preferably considered as amorphous silicon dioxide. The SiO2 content of amorphous silicon dioxide is advantageously at least 80% by weight, preferably at least 90% by weight. Precipitated silicon dioxide is preferably obtained industrially by precipitating sodium silicate. Depending on the type of production, precipitated silicon dioxide can also be called silica gel. Pyrogenic silicon dioxide is produced by reacting chlorosilanes, such as silicon tetrachloride, in an oxyhydrogen flame. Pyrogenic silicon dioxide has a particle size of 5-50 nm and a specific surface area of ​​50-600 m 2 g -1 It is an amorphous SiO2 powder.

[0057] Microsilica is a by-product resulting from the production of silicon or ferrosilicon and contains a large amount of amorphous SiO2 powder. The particle diameter is about 0.1 μm. The specific surface area is 15-30 m 2 g -1 The range is.

[0058] Fly ash is produced, 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.

[0059] Metakaolin is produced by dehydrating kaolin. Kaolin releases physically bound water at temperatures between 100-200°C, while the destruction of the lattice structure and the production of metakaolin (Al2Si2O7) occurs at temperatures in the range of 500-800°C. Pure metakaolin preferably contains about 54% SiO2 and about 46% Al2O3 by weight.

[0060] The above statements regarding the pozzolanic face binder apply equally to the pozzolanic core binder.

[0061] It has been found that the use of the above mentioned latent hydraulic and pozzolanic face and core binders makes it possible to produce concrete elements with no or only slow fading of decorative properties, good bond adhesion tensile strength and a good CO2 footprint.

[0062] Various materials can be used as the alkaline face hardener. The alkaline face hardener 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 from the group consisting of alkali metal hydroxides, alkali metal silicates and mixtures thereof.

[0063] Alkali metal oxides include, for example, Li2O, Na2O, K2O, (NH4)2O, and mixtures thereof. Alkali metal hydroxides include, for example, LiOH, NaOH, KOH, NH4OH, and mixtures thereof. Alkali metal carbonates include, for example, Li2CO3, Na2CO3, K2CO3, (NH4)2CO3, and mixtures thereof. Ammonium ion is also included because of its similarity to the alkali metal ion.

[0064] The alkali metal silicate is expediently selected from compounds having the empirical formula mSiO2·nMO, where M is Li, Na, K or NH4 or mixtures thereof, preferably Na or K. The molar ratio of m:n ranges from 0.5 to 3.6, preferably from 0.6 to 3.0, particularly preferably from 0.7 to 2.0. Sodium silicate, in particular liquid sodium silicate, more preferably liquid sodium silicate and / or liquid potassium silicate, has proven to be a particularly useful alkali metal silicate. Silica, in particular aqueous silica, is also a useful alkali metal silicate.

[0065] The alkaline face hardeners mentioned above are preferably used as aqueous solutions, which allows for easy dosing.

[0066] The hardening of the face concrete layer can be easily adjusted with the alkaline face hardeners mentioned above. Moreover, these alkaline face hardeners have good compatibility with other components in the face concrete layer mixture.

[0067] The content of the alkaline face hardener in the face concrete layer mixture is not particularly limited. Preferably, the face concrete layer mixture contains 1% to 15% by weight of the alkaline face hardener, preferably 1% to 10% by weight, more preferably 3% to 5% by weight, even more preferably 3.15% to 4.85% by weight, even more preferably 3.25% to 3.65% by weight or 4.0% to 4.75% by weight, particularly preferably 4.25% to 4.75% by weight, very particularly preferably 4.25% to 4.45% by weight. Good results are also obtained when the face concrete layer mixture contains 3.25% to 3.65% by weight of the alkaline face hardener, based on the total weight of the face concrete layer mixture. It has been found that when less than 1% by weight of the alkaline hardener is used, the hardening of the face concrete layer is too slow. If more than 15% by weight of alkaline hardener is used, hardening may commence prematurely, with the result that the resulting face concrete layer can no longer be adequately compacted.

[0068] As alkaline core hardeners various substances can be used, which preferably comprise at least one organic base and / or at least one inorganic base.

[0069] Inorganic bases include, for example, the alkaline face hardeners mentioned above. Organic bases include, inter alia, amine bases such as ammonia, as well as mono-, di- and trialkylamines.

[0070] The hardening of the core concrete layer can be easily adjusted with the alkaline core hardener mentioned above.

[0071] The content of the alkaline core hardener in the core concrete layer mixture is not particularly limited. The core concrete layer mixture preferably contains 0.1% by weight to 15% by weight, preferably 0.5% by weight to 10% by weight of the alkaline core hardener relative to the total weight of the core concrete layer mixture.

[0072] According to the invention, the face concrete layer mixture contains water. Preferably, the face concrete layer mixture contains 1% to 20% by weight of water, preferably 3% to 15% by weight, more preferably 3% to 7% by weight, even more preferably 3.5% to 6.5% by weight, even more preferably 4.0% to 6.2% by weight, even more preferably 4.2% to 4.9% by weight, very particularly preferably 4.2% to 4.8% by weight, based on the total weight of the face concrete layer mixture. Good results are also obtained if the face concrete layer mixture contains 5.2% to 6.2% by weight of water, based on the total weight of the face concrete layer mixture.

[0073] The core concrete layer mixture preferably contains water in an amount of 1% by weight to 20% by weight, preferably 3% by weight to 15% by weight, more preferably 3% by weight to 10% by weight, based on the total weight of the core concrete layer mixture.

[0074] In addition to the above-mentioned components, the face concrete layer mixture may also contain further components. The face concrete layer mixture may also contain one or more aggregates, such as, for example, gravel, grit, sand, perlite, diatomaceous earth or vermiculite. Furthermore, the face concrete layer mixture may contain cement and / or one or more aggregates, such as gravel, grit, sand, perlite, diatomaceous earth or vermiculite, and / or one or more additives selected from the group consisting of plasticizers, defoamers, water retention agents, dispersants, pigments, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheological additives.

[0075] The face concrete layer mixture may in particular contain up to 5% or up to 10% by weight of cement. Alternatively, the face concrete layer mixture may in particular be free of cement. If the face concrete layer mixture is free of cement, a concrete element with a particularly advantageous carbon dioxide footprint may be produced.

[0076] The facing concrete layer mixture advantageously contains a set regulator. In particular, set retarders and / or set accelerators may be considered as set regulators.

[0077] The core concrete layer mixture may also contain one or more aggregates such as gravel, grit, sand, perlite, diatomaceous earth, or vermiculite. Additionally, the core concrete layer mixture may contain cement and / or one or more aggregates such as gravel, grit, sand, perlite, diatomaceous earth, or vermiculite, and / or one or more additives selected from the group consisting of plasticizers, defoamers, water retention agents, dispersants, pigments, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents, and rheological additives.

[0078] Furthermore, the core concrete layer may also contain other aggregates. The core concrete layer preferably contains at least 1% by weight of opal, flint, chalcedony and / or greywacke, preferably at least 5% by weight, more preferably at least 15% by weight, particularly preferably at least 17.5% by weight. According to a preferred embodiment, the core concrete layer contains 5% to 30% by weight, in particular 5% to 20% by weight of opal, flint, chalcedony and / or greywacke. It has been found that by using these additives in such amounts the concrete elements can be produced economically, but the alkali-silica reaction is still less pronounced.

[0079] According to one embodiment, the free alkali content of the core concrete layer is 1500 g / m 3 That's all.

[0080] The core concrete layer mixture may in particular contain up to 5% or up to 10% by weight of cement. Alternatively, the core concrete layer mixture may in particular not contain cement. If the core concrete layer mixture does not contain cement, a concrete element with a particularly advantageous carbon dioxide footprint may be produced.

[0081] The core concrete layer mixture advantageously contains a set regulator. In particular, set retarders and / or set accelerators may be considered as set regulators.

[0082] The properties of the face concrete layer mixture and / or the core concrete layer mixture can be well controlled with the above-mentioned additives. In particular, the hardening behavior can also be well controlled with the above-mentioned additives.

[0083] The face concrete layer mixture preferably contains 0.1% to 2% by weight of additives, more preferably 0.4% to 1.5% by weight, based on the total weight of the face concrete layer mixture. The face concrete layer mixture expediently contains 0.025% to 0.097% by weight or 1.5% to 2% by weight of set retarders and / or set accelerators.

[0084] The core concrete layer mixture preferably contains 0.1% to 1% by weight of the additive, more preferably 0.3% to 0.9% by weight, based on the total weight of the core concrete layer mixture. The core mixture conveniently contains 0.0225% to 0.0975% by weight or 1.0% to 1.9% by weight of the set retarder and / or set accelerator.

[0085] The concrete elements preferably have a compaction class according to the DIN 1045-2 C0 or C01 standard. The concrete elements are preferably concrete blocks, concrete slabs, concrete wall elements or concrete steps.

[0086] Furthermore, preferably, the concrete element has a compressive strength measured after 28 days according to DIN EN 12390-3, in particular according to DIN EN 12390-3:2019-10, of at least 110 N / mm 2 Less than 100N / mm 2 Less than 85N / mm 2 Less than 82.5 N / mm 2 is less than.

[0087] Furthermore, preferably the core concrete layer of the concrete element has a tensile bond strength measured 28 days after production according to the DAfStb (German Commission for Reinforced Concrete) Directive "Protection and Repair of Concrete Components", Part 4, Section 5.5.11, 2001, of at least 1.0 MPa, preferably at least 1.3 MPa, more preferably at least 1.5 MPa and particularly preferably at least 2.0 MPa.

[0088] The concrete elements according to the invention are characterized by a good bond tensile strength, preferably the concrete elements have a bond tensile strength measured 28 days after production according to the DAfStb Directive "Protection and Repair of Concrete Components", Part 4, Section 5.5.11, 2001 of at least 0.75 MPa, preferably at least 1.0 MPa, more preferably at least 1.15 MPa, even more preferably at least 1.3 MPa, particularly preferably at least 1.5 MPa.

[0089] The bond tensile strength may vary, especially during the first 3-4 months after production of the concrete elements, and may even increase during this period.

[0090] The present invention also relates to a method for producing a concrete element according to the invention, comprising the steps of: a. preparing a face composition; The face composition comprises the following components: i. granular face material; ii. optionally a pigment; iii. optionally a filler; iv.Water, v. Latent hydraulic and / or pozzolanic face binders, and vi. Contains an alkaline face hardener; b. mixing the face composition to obtain a face concrete layer mixture; c. preparing a core composition; The core composition comprises the following components: i. a granular core material; ii.Water, iii. a latent hydraulic core binder and / or a pozzolanic core binder; and iv. Contains an alkaline core hardener; d. mixing the core composition to obtain a core concrete layer mixture; e. filling the core concrete layer mixture and the face concrete layer mixture into at least one form; and f. compacting said core concrete layer mixture and said face concrete layer mixture within said formwork to obtain at least one green concrete element.

[0091] Preferably, the core concrete layer mix and the face concrete layer mix are compacted in at least one formwork. Compaction can be achieved by poking, pushing and / or vibrating.

[0092] During compaction, the concrete is preferably compacted in the formwork by vibration for 1 to 20 seconds, preferably 2.5 to 4.5 seconds. During compaction, the concrete can be compacted in the formwork with a pressure of up to 1.0 MPa.

[0093] During compaction, the concrete is preferably compacted in the formwork at a pressure of at least 125 MPa, more preferably between 125 MPa and 250 MPa. During compaction, the concrete is preferably compacted in the formwork substantially without vibration for a period of 5 to 20 seconds, more preferably between 5 to 10 seconds. The steps of the method of the present invention are preferably carried out in the order specified above.

[0094] According to one embodiment, in step e, first the face concrete layer mixture is poured into the formwork, then the core concrete layer mixture is poured onto the face concrete layer mixture in the formwork, and then the face concrete layer mixture is compacted in contact with the core concrete layer mixture in the formwork.

[0095] According to another embodiment, in step e, first the core concrete layer mixture is poured into the formwork, then the face concrete layer mixture is poured onto the core concrete layer mixture in the formwork, and then the core concrete layer mixture is compacted in contact with the face concrete layer mixture in the formwork.

[0096] According to an alternative embodiment, in step e, the core concrete layer mix is ​​not poured into a formwork but pressed into the strands and simultaneously or subsequently the face concrete layer mix is ​​pressed into said strands. Then, in step f, the core concrete layer mix is ​​compacted in contact with the face concrete layer mix in said strands. Concrete elements are obtained from the strands by cutting to size and placing them on the formwork panels.

[0097] Furthermore, the components of the face composition are advantageously metered in the order listed above. For convenience, the components of the core composition are metered in the order listed above. It has been found that adding the components in the order listed above allows for good processability of the face composition and / or the core composition. It has also proven to be convenient if the components of the face composition are already mixed during metering. The same applies to the core composition.

[0098] For the granular face material, the granular core material, the face filler, the core filler, the water, the latent hydraulic face binder and / or pozzolanic face binder, the latent hydraulic core binder and / or pozzolanic core binder, the alkaline face hardener and the alkaline core hardener the statements made above for the concrete element according to the invention apply analogously, in particular also with regard to the amounts of the components used.

[0099] Furthermore, the face composition and / or the core composition may also comprise additional components as listed above, such as cement, aggregates, additives, set retarders and / or set accelerators, which are advantageously metered together with water or optional pigments, preferably with water.

[0100] The method according to the invention allows the design of the surface of a concrete element. According to one embodiment, a quantity unit of granular material containing, based on the total composition of the granular material, (a) 65-95% by weight, preferably 75-85% by weight, of litter components with an average particle size of 0.1-5 mm, and (b) 5-35% by weight, preferably 15-25% by weight, of binder is applied to the face concrete layer mixture in at least one formwork before compaction.

[0101] By using litter components and binders in such concentration ranges, the granular material can be better fixed to the surface of the concrete element.

[0102] The average particle size is understood by those skilled in the art to mean the diameter at which there are an equal number of larger and smaller particles. The average particle size can be determined, for example, by sieving.

[0103] With this embodiment of the method according to the invention, it has proven to be advantageous, particularly for producing aesthetic concrete elements, for the facing concrete layer to have optical properties, such as color or gloss, and for the granular material to have other optical properties, which makes it possible, for example, to produce flamed, striated or speckled surfaces that resemble the natural structure of natural stone.

[0104] According to this embodiment, the granular material is preferably applied to the mixture by an application device, which may comprise at least one dripping device, centrifugal disk, paddle wheel, rim and / or catapult, to which at least one portion of the granular material is supplied. These devices can move above or next to the formwork and can also supply different portion units at different intervals. In this way, the granular material can be applied uniformly to the mixture. It has also been found that the method according to the invention can be implemented particularly economically in this way.

[0105] The application device advantageously comprises at least one metered container containing the granular material and a metered strip, the metered container being guided over the mould at a uniform or non-uniform speed.

[0106] Uniform and / or irregular and / or intermittent vibrations or vibrational impacts are preferably applied to the metering strip.

[0107] Preferably, different finishing materials and / or different dosage units of finishing materials can be supplied to the metering strip along its extension.

[0108] It has furthermore proven to be advantageous if the weighing vessel is attached to the tip of a weighing carriage for concrete, preferably for face concrete.

[0109] Possible configurations of the application device with at least one metering container with a metering strip are described, for example, in EP 2 910 354 A1. An example of an application device with at least one metering container with a metering strip is a filling carriage with at least one chamber. The granular material may be accommodated in this chamber. The filling carriage may also have two or more chambers separated by a partition. In that case, the mixture according to the invention is advantageously accommodated in a first chamber of the filling carriage. The granular material is preferably accommodated in a second chamber. Further compartments may accommodate other granular materials with different properties, for example different colors. The filling carriage may move on the formwork along guide rails.

[0110] The chamber containing the particulate material may comprise an application element. The application element may be removable from the chamber. The chamber may comprise one or more application elements.

[0111] The application element preferably has a perforated metering plate with at least one, preferably several holes and one metering element. The holes can be arranged uniformly or 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 metering plate can also be cylindrical. The metering plate can in particular form a metering strip.

[0112] The metering element can be of different designs. It can, for example, comprise a shaft to which blades are attached that can rotate about the longitudinal axis of the shaft. The granular material is preferably placed in the space formed by the two blades of the shaft and the associated part of the metering plate. By rotating the shaft about its longitudinal axis, the blades force the granular material through the holes in the metering plate, whereby the granular material is applied to the mixture. Such a metering element is preferably used in combination with a curved metering plate.

[0113] The metering element can also be designed in the form of a comb. In that case, the comb-shaped metering element is preferably movably mounted on a flat metering plate. The granular material is preferably arranged between the teeth of the comb on the metering plate. By moving the comb over the metering plate, the granular material is forced through the holes in the metering plate, whereby the granular material is applied to the mixture.

[0114] The metering element may also be a perforated plate. The perforated plate is preferably placed on a flat metering plate. The particulate material is preferably placed in the holes of the perforated plate on the metering plate. By moving the perforated plate over the metering plate, the particulate material is forced through the holes of the metering plate, whereby the particulate material is applied to the mixture.

[0115] Finally, the metering elements can also be freely movable elements, which are preferably arranged inside the cylindrical metering plate. The granular material is also preferably arranged inside the cylindrical metering plate. The freely movable elements can, by their weight, force the granular material through the holes in the metering plate. By moving, in particular by rotating, the cylindrical metering plate, the granular material is forced through the holes in the metering plate, whereby the granular material is applied to the mixture.

[0116] The dosing element also advantageously comprises further components such as an actuator capable of moving the metering element. The actuator may be connected to an electric motor, which may preferably be controlled by electronic control means. The dosing element may also comprise an actuator rod, a cam follower engaging with a cam, and / or a gear wheel.

[0117] According to a preferred embodiment of the method according to the invention, the application device comprises at least one pipe socket, into which one or more portions of the granular material are fed and which are spread, dumped, sprayed and / or dropped onto the facing concrete layer via the pipe socket. A particularly good distribution over the entire formwork is obtained if the end of the pipe socket is designed like a nozzle.

[0118] Actual tests have shown that good distribution occurs when the discharge is performed by a prestressed spring-loaded piston which is instantly unlocked to dispense the granular material.

[0119] The applicator can preferably move above and / or next to the mould. The applicator can have or achieve different moving speeds, jerky movements are also advantageous. Depending on the size of the mould and the colour of the granular material in the applicator, several different devices can be used for one mould, allowing for a uniform application of the granular material or for the application to have a special characteristic appearance.

[0120] It is preferred to use baffle plates in the applicator, such as disc wheels or rims, or even pipe sockets, which allow for a wider distribution area.

[0121] Several dosage units of particulate material may be dispensed in succession by a plurality of applicators, each of which may be a different particulate material, as described above.

[0122] Preferably, the binder contained in the granular material is an inorganic binder, for example cement, hydraulic lime, gypsum, slag, blast furnace slag, preferably slag sand, in particular ground slag sand, electrolytic phosphorus slag, steel slag, amorphous silicon dioxide, precipitated silicon dioxide, pyrogenic silicon dioxide, microsilica, glass powder, fly ash, for example lignite fly ash or anthracite fly ash, metakaolin, natural pozzolans, for example tuff, trass or volcanic ash, The binders contained in the granular material are natural and synthetic zeolites or water glass or are organic binders, such as plastic dispersions, acrylate resins, alkyd resins, epoxy resins, polyurethanes, sol-gel resins or silicone resin emulsions. Such binders are particularly easy to handle with respect to the concrete elements. They also do not require any additional requirements in the method. Furthermore, they allow the granular material to be firmly fixed on the concrete elements.

[0123] Depending on the desired visual appearance of the concrete element, litter components of different average particle sizes can be used. The litter components can have an average particle size of 0.1-1.8 mm. Alternatively, litter components with an average particle size of 1.2-5 mm can be used.

[0124] Preferably, litter components having an average particle size of 0.1 to 1.2 mm are used.

[0125] The granular material can also contain small aggregates, so that various types of materials of various colors can be embedded in the surface or face concrete layer, including granules such as semi-precious stones, precious stones, mica, metal chips, plastic particles or glass particles. The granular material can also be any rock mixture.

[0126] It has proven particularly useful for the method according to the invention if the litter component is or contains a rock mixture, which allows the production of concrete elements that closely resemble the appearance of natural stone.

[0127] In the method according to the present invention, the litter component preferably contains at least one material selected from the group consisting of semi-precious stones, precious stones, mica, metal chips, glass particles and plastic particles. The use of these materials makes the method very economical.

[0128] In the method according to the invention, the particulate material may in particular have a classified particle composition with a particle size of less than 2 mm.

[0129] The surface and / or edges of at least one green concrete element can be treated with a brush in the method according to the invention, thereby structuring and / or roughening and / or smoothing and / or reducing the projections of the edges, which can further improve the decorative visual appearance.

[0130] Before the compaction step, but preferably afterwards, a preferably colorless organic or inorganic agent can be applied to the surface of the concrete element before or after hardening. This is done for waterproofing, sealing or coating of the concrete element. In particular, a sealing agent and / or a waterproofing agent can be applied to the surface of at least one green concrete element. Such a procedure adds an additional protective layer to the concrete element, which increases its durability and service life even further. This layer also serves the function of protecting against dirt and, in addition, can prevent lime efflorescence.

[0131] The green concrete elements are preferably hardened in the method according to the invention to obtain concrete elements. After hardening, the concrete elements are preferably treated by sanding, blasting, brushing and / or structuring.

[0132] The present invention also relates to the use of a latent hydraulic and / or pozzolanic binder, in particular as a binder, together with an alkaline hardener, for producing a core concrete layer of a concrete element comprising a core concrete layer and a face concrete layer joined to said core concrete layer.

[0133] Preferably, the above statements regarding the concrete element according to the invention apply analogously to the concrete element in said use.

[0134] Preferably, the above statements regarding the latent hydraulic core binder apply analogously to the latent hydraulic binder in this use, also with respect to the contents mentioned above.

[0135] Preferably, the above statements regarding the pozzolanic core binder apply analogously to the pozzolanic binder in this use, also including the above-mentioned contents.

[0136] Preferably, the above statements regarding the alkaline face hardener and / or alkaline core hardener apply equally to the alkaline hardener in this use.

[0137] According to one embodiment, the core concrete layer contains a granular core material, to which the above statements regarding the granular core material apply analogously, also with respect to the above-mentioned contents.

[0138] According to a further embodiment, the face concrete layer contains a granular face material, to which the above statements regarding the granular face material apply analogously, also with respect to the above-mentioned contents.

[0139] According to a further embodiment, the face concrete layer contains a face filler, to which the above statements about the face filler apply analogously. This also applies to the above-mentioned contents.

[0140] According to a further embodiment, the core concrete layer contains a core filler, to which the above statements about the core filler apply analogously, also with respect to the contents mentioned above.

[0141] According to a further embodiment, the core concrete layer contains at least 1% by weight of opal, flint, chalcedony and / or greywacke, preferably at least 5% by weight, more preferably at least 15% by weight, particularly preferably at least 17.5% by weight.

[0142] According to a further embodiment, the core concrete layer contains 5% to 30% by weight, in particular 5% to 20% by weight, of opal, flint, chalcedony and / or greywacke.

[0143] The concrete element in the use according to the invention is preferably a concrete element according to the invention. EXAMPLES

[0144] For further explanation, non-limiting examples are listed below. material Geopolymer layer

[0145] Face binder mixture: Based on latent hydraulic binder and pozzolanic binder.

[0146] Core binder mixture: Based on latent hydraulic binder and pozzolanic binder.

[0147] Granular face material: aggregate with a passing fraction of 72.5% by weight at a screen hole width of 2 mm and a passing fraction of 7.5% by weight at a screen hole width of 0.25 mm

[0148] Granular core material: Aggregate with a passing fraction of 98.8% by weight at a screen hole width of 8 mm and a passing fraction of 18.0% by weight at a screen hole width of 0.5 mm

[0149] Face filler: rock powder with a passing fraction of 97% by weight at a screen hole width of 0.025 mm and 63% by weight at a screen hole width of 0.015 mm

[0150] Alkaline Face Hardener: 75% Silica

[0151] Alkaline core hardener: 40% aqueous solution of inorganic base

[0152] Pigments: Metal oxide pigments

[0153] Face mix additives: set retarders / set accelerators Cement (optional): Portland cement CEM I 42.5R

[0154] Granular material: Contains 80% by weight of small aggregate with an average particle size of 0.7 mm and 20% by weight of inorganic binder. Traditional Layer Core binder mixture: Portland cement CEM I 52.5N

[0155] Granular core material: Aggregate with a passing fraction of 98.8% by weight at a screen hole width of 8 mm and a passing fraction of 18.0% by weight at a screen hole width of 0.5 mm

[0156] Core filler: rock powder with a passing fraction of 97% by weight at a screen hole width of 0.025 mm and 63% by weight at a screen hole width of 0.015 mm method

[0157] The bond tensile strength is determined according to the DAfStb Directive "Protection and Repair of Concrete Components", Part 4, Section 5.5.11, 2001. Deviation from this, drilling depths of 30 mm and 5 mm are chosen. The bond tensile strength of the core layer is determined by testing the underside. The face or bond bond tensile strength is obtained by evaluating the crack depth (crack location). Example 1

[0158] 76.0% by weight of the granular core material, 5.3% by weight of water, 17.0% by weight of the core binder mixture, and 1.7% by weight of the alkaline core hardener were successively poured into the mixing vessel to obtain a core composition. The above values ​​are based on the total mass of the core composition. The core composition was then mixed in the mixing vessel to obtain a core concrete layer mixture. The core concrete layer mixture thus obtained was poured into the moldboard form as the core concrete layer.

[0159] 66.6% by weight of the granular face material, 1.1% by weight of the pigment, 6.4% by weight of the water, 21.6% by weight of the face binder mixture, 4.26% by weight of the alkaline face hardener and 0.04% by weight of the additive were successively added to the further mixing vessel to obtain the face composition. The above information relates to the total mass of the face composition. The face composition was then mixed in the mixing vessel to obtain a face concrete layer mixture. The face concrete layer mixture thus obtained was poured into the form of the moldboard as the face concrete layer. The face concrete layer was of basic color. The core concrete layer mixture and the face concrete layer mixture were then compacted by tamping in the form, thereby obtaining a green concrete element. Based on the observation when the form was removed, the green concrete element did not split. After demolding and hardening, the bond tensile strength of the concrete element was measured to be at least 0.77 MPa (at 7 days of test material) and at least 1.15 MPa (at 28 days of test material). Cracks occurred in the face. The bond tensile strength is therefore at least 0.77 MPa (at 7 days of testing) and at least 1.15 MPa (at 28 days of testing). Furthermore, the compressive strength according to DIN EN 12390-3:2019-10 of the concrete element is 56.9 N / mm 2 (Test material age 7 days) and 60.8N / mm 2 (Test material age: 28 days).

[0160] Additionally, the bond tensile strength of the core layer of the concrete element was 1.89 MPa (at 10 days of testing). After hardening, the resulting concrete element was visually appealing. The concrete element showed no discernible discoloration or other deterioration in its decorative properties over a six month period. Additionally, there was no sign of chemical attack on the concrete element that could result from alkali-silica reaction over a six month period. Example 2 (Comparative Example)

[0161] 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, 11.0% by weight of cement, 5.2% by weight of water and 4.2% by weight of core filler were poured into a mixing vessel and mixed. The core concrete layer mixture thus obtained was poured into a moldboard form as the core concrete layer.

[0162] The face concrete layer mixture of Example 1 was then poured onto the core concrete layer mixture in the formwork of the moldboard. The face concrete layer was of basic color. The core concrete layer mixture and the face concrete layer mixture were then compacted in the formwork by tamping, thereby obtaining a green concrete element. Based on the observations upon removal of the formwork, the green concrete element did not split. After demolding and hardening, the bond tensile strength of the concrete element was measured to be at least 0.41 MPa (test age 7 days) and at least 0.75 MPa (test age 28 days). The cracks occurred in the composite layer. The measured bond tensile strength is therefore the bond bond tensile strength. Furthermore, the compressive strength according to DIN EN 12390-3:2019-10 of the concrete element was 61.1 N / mm 2 It was. Example 3 (Comparative Example)

[0163] First, a conventional core concrete layer mixture was produced as in Example 2 and poured into the moldboard form. Then, a face concrete layer mixture was produced as in Example 1, except that only 15.3 wt% of the face binder was used and 6.3 wt% of cement was further added. Then, the face composition was mixed in a mixing vessel to obtain a face concrete layer mixture. The face concrete layer mixture thus obtained was poured into the moldboard form as a face concrete layer. The face concrete layer was of basic color. Then, the core concrete layer mixture and the face concrete layer mixture were compacted by tamping in the form, thereby obtaining a green concrete element. Based on the observation when the form was removed, the green concrete element did not split. After demolding and hardening, the bond tensile strength of the concrete element was measured to be at least 0.26 MPa (at 7 days of test material) and at least 0.28 MPa (at 28 days of test material). The cracks occurred in the composite layer. Therefore, the measured bond tensile strength is the bond bond tensile strength. Example 4

[0164] Example 4 is the same as Example 1, except that 74.8% by weight of granular core material, 5.5% by weight of water, 17.9% by weight of core binder mixture and 1.8% by weight of alkaline core hardener were injected to form the core composition. Before compaction, the desired quantity unit of granular material was sprinkled, poured, sprayed and / or dropped using a pipe socket designed like a nozzle onto the face concrete layer poured into the formwork, the same as in Example 1. The applicator could move over the entire surface of the moldboard, so that all face concrete layers of the formwork could be reached as desired. A funnel through which the granular material was injected was installed above the pipe socket. Any quantity unit of granular material may be injected into the pipe socket by means of an opening and closing device arranged above the opening of the hopper. In principle, several hoppers containing different granular materials can be arranged on the centrifugal disk to sprinkle, pour, spray and / or drop different granular materials in different doses onto the surface of the face concrete layer. The pipe socket can be moved at various moving speeds, including jerky movements. The height position relative to the moldboard can also be adjusted and changed as necessary, even during application of the granular material. Based on observations upon removal of the formwork, the green concrete elements did not split. After demolding and hardening, the bond tensile strength of the concrete elements was measured to be at least 0.83 MPa (test age 7 days) and at least 1.17 MPa (test age 28 days). Cracks occurred in the faces. The bond bond tensile strength is therefore measured to be at least 0.77 MPa (test age 7 days) and 1.15 MPa (test age 28 days). Furthermore, the compressive strength according to DIN EN 12390-3:2019-10 of the concrete elements is 67.0 N / mm 2 (Test material age 7 days) and 74.4N / mm 2 The bond tensile strength of the core layer of the concrete element was 2.18 MPa (test age: 10 days).

[0165] As can be seen from the above examples, the combination of a geopolymer-based core and a geopolymer-based face results in very good bond tensile strength (Examples 1 and 4). At the same time, these geopolymer-only based concrete elements showed very good resistance to chemical attack.

[0166] The combination of a conventional core with a geopolymer-based face layer (Example 2) and a conventional core with a geopolymer-cement hybrid face layer (Example 3) showed poorer bond adhesive tensile strength.

Claims

1. A concrete element comprising a core concrete layer and a face concrete layer, said concrete element being obtained by compacting and hardening a core concrete layer mixture in contact with a face concrete layer mixture; the core concrete layer mixture contains a latent hydraulic core binder and / or a pozzolanic core binder, water, a granular core material, and an alkaline core hardener; the face concrete layer mix containing a latent hydraulic face binder and / or a pozzolanic face binder, water, a granular face material, and an alkaline face hardener; the pass-through fraction of the granular face material is 35.5% to 99.5% by weight for a screen opening width of 2 mm and 2.5% to 33.5% by weight for a screen opening width of 0.25 mm, based on the total weight of the granular face material; The concrete element has a compressive strength of 120 N / mm after 28 days, measured according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10. ２ Less than, concrete elements.

2. the pass-through fraction of the granular face material is 42.5% to 99.5% by weight, more preferably 56.5% to 98.5% by weight, particularly preferably 72.5% to 97.5% by weight for a screen opening width of 2 mm, and 2.5% to 27.5% by weight, more preferably 2.5% to 22.5% by weight, even more preferably 2.5% to 21.5% by weight, particularly preferably 2.5% to 8% by weight or 11.5% to 21.5% by weight for a screen opening width of 0.25 mm, and 0.1% to 12.5% ​​by weight, more preferably 0.3% to 10.0% by weight, even more preferably 0.3% to 7.5% by weight, particularly preferably 0.3% to 5.0% by weight for a screen opening width of 0.125 mm, relative to the total weight of the granular face material; and / or 2. The concrete element according to claim 1, wherein the passing fraction of the granular core material is 42.5% by weight to 99.5% by weight, preferably 56.5% by weight to 98.5% by weight, more preferably 72.5% by weight to 97.5% by weight, based on the total weight of the granular core material, when the screen hole width is 8 mm, and 7.5% by weight to 39.5% by weight, preferably 13.5% by weight to 37.5% by weight, particularly preferably 25.5% by weight to 37% by weight or 14.5% by weight to 24.5% by weight, when the screen hole width is 0.5 mm.

3. the particle size number of the granular face material is between 1.59 and 3.62, preferably between 1.61 and 3.17, particularly preferably between 1.61 and 2.55; and / or A concrete element according to claim 1 or claim 2, characterized in that the granular core material has a gradation number between 1.97 and 4.61, preferably between 2.27 and 3.

82.

4. the face concrete layer mixture contains 55% to 80% by weight, preferably 60% to 75% by weight, more preferably 60% to 72% by weight, particularly preferably 60% to 65% by weight, in particular 60-64% by weight or 67% to 72% by weight of the granular face material relative to the total weight of the face concrete layer mixture; and / or 2. The concrete element according to claim 1, wherein the core concrete layer mixture contains 60% to 95% by weight, preferably 65% ​​to 92.5% by weight, more preferably 70% to 90% by weight, and particularly preferably 74% to 79% by weight of the granular core material relative to the total weight of the core concrete layer mixture.

5. the face concrete layer mixture contains from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 5% to 18% by weight, even more preferably from 5% to 15% by weight, even more preferably from 5% to 10% by weight, and particularly preferably from 6% to 8% by weight of face filler, based on the total weight of the face concrete layer mixture; and / or 2. The concrete element according to claim 1, characterized in that the core concrete layer 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 core filler, based on the total weight of the core concrete layer mixture.

6. the pass-through fraction of the face filler is 63% to 99% by weight, preferably 68% to 99% by weight, more preferably 90% to 99% by weight, particularly preferably 95% to 99% by weight, for a screen hole width of 0.025 mm, and 38% to 73% by weight, preferably 58% to 67% by weight, particularly preferably 61% to 66% by weight, for a screen hole width of 0.015 mm, based on the total weight of the face filler; and / or 6. A concrete element according to claim 5, characterized in that the passing fraction of the core filler is 63% to 99% by weight, preferably 68% to 99% by weight, more preferably 90% to 99% by weight, particularly preferably 95% to 99% by weight, for a screen hole width of 0.025 mm, and 38% to 73% by weight, preferably 58% to 67% by weight, particularly preferably 61% to 66% by weight, for a screen hole width of 0.015 mm, relative to the total weight of the core filler.

7. the face filler is selected from the group consisting of rock powder, preferably classified rock powder, limestone powder, preferably classified limestone powder, and mixtures thereof; and / or 7. A concrete element according to claim 5 or claim 6, characterized in that the core filler is selected from the group consisting of rock powder, preferably classified rock powder, limestone powder, preferably classified limestone powder, and mixtures thereof.

8. the face concrete layer mixture contains 15% to 40% by weight, preferably 20% to 30% by weight, even more preferably 20% to 24% by weight or 26% to 29% by weight, and even more preferably 22% to 24% by weight of the latent hydraulic face binder and / or the pozzolanic face binder, based on the total weight of the face concrete layer mixture; and / or 2. The concrete element according to claim 1, wherein the core concrete layer mixture contains 10% by weight to 50% by weight, preferably 10% by weight to 40% by weight, of the latent hydraulic core binder and / or the pozzolanic core binder relative to the total weight of the core concrete layer mixture.

9. The latent hydraulic face binder is selected from the group consisting of slag, blast furnace slag, preferably slag sand, in particular ground slag sand, electrolytic phosphorus slag, steel slag, and mixtures thereof, and / or (CaO+MgO):SiO ２ is in the range of 0.8 to 2.5, preferably 1.0 to 2.0, and / or The latent hydraulic core binder is selected from the group consisting of slag, blast furnace slag, preferably slag sand, in particular ground slag sand, electrolytic phosphorus slag, steel slag, and mixtures thereof, and / or (CaO+MgO):SiO ２ 2. A concrete element according to claim 1, characterized in that the molar ratio of is in the range of 0.8 to 2.5, preferably 1.0 to 2.

0.

10. The pozzolanic face binder is preferably 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 anthracite fly ash; metakaolin; natural pozzolans, such as tuff, truss or volcanic ash; natural and synthetic zeolites and mixtures thereof; and / or 2. The concrete element according to claim 1, characterized in that the pozzolanic core 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 anthracite fly ash; metakaolin; natural pozzolans, such as tuff, truss or volcanic ash; natural and synthetic zeolites and mixtures thereof.

11. The alkaline face hardener 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 from the group consisting of alkali metal hydroxides, alkali metal silicates and mixtures thereof; and / or 2. The concrete element according to claim 1, wherein the alkaline core hardener comprises an organic base and / or an inorganic base.

12. the face concrete layer mixture contains from 1% to 15% by weight, preferably from 1% to 10% by weight, more preferably from 3% to 5% by weight, even more preferably from 3.15% to 4.85% by weight, even more preferably from 3.25% to 3.65% by weight or from 4.0% to 4.75% by weight, particularly preferably from 4.25% to 4.75% by weight, very particularly preferably from 4.25% to 4.45% by weight of the alkaline face hardener, based on the total weight of the face concrete layer mixture; and / or 2. The concrete element according to claim 1, wherein the core concrete layer mixture contains 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 concrete layer mixture.

13. the face concrete layer mixture contains from 1% to 20% by weight of water, preferably from 3% to 15% by weight, more preferably from 3% to 7% by weight, even more preferably from 3.5% to 6.5% by weight, even more preferably from 4.0% to 6.2% by weight, particularly preferably from 4.2% to 4.9% by weight or from 5.2% to 6.2% by weight, very particularly preferably from 4.2% to 4.8% by weight, based on the total weight of the face concrete layer mixture; and / or 2. The concrete element according to claim 1, wherein the core concrete layer mixture contains 1% to 20% by weight of water, preferably 3% to 15% by weight, more preferably 3% to 10% by weight of water, based on the total weight of the core concrete layer mixture.

14. the face concrete layer mixture comprises a set regulator, in particular a set retarder and / or a set accelerator; and / or 2. A concrete element according to claim 1, characterized in that the core concrete layer mix contains a set regulator, in particular a set retarder and / or a set accelerator.

15. the face concrete layer mixture contains cement, in particular up to 5% or up to 10% by weight of cement, and / or one or more aggregates such as gravel, grit, sand, perlite, diatomaceous earth or vermiculite, and / or one or more additives selected from the group consisting of plasticizers, antifoaming agents, water retention agents, dispersants, pigments, fibers, redispersible powders, wetting agents, impregnating agents, complexing agents and rheological additives; and / or 2. A concrete element according to claim 1, characterized in that the core concrete layer mix contains cement, in particular up to 5% or up to 10% by weight of cement, and / or one or more aggregates, such as gravel, grit, sand, perlite, diatomaceous earth or vermiculite, and / or one or more additives selected from the group consisting of plasticizers, antifoaming agents, water retention agents, dispersants, pigments, fibres, redispersible powders, wetting agents, impregnating agents, complexing agents and rheological additives.

16. The compressive strength of the concrete element measured after 28 days according to DIN EN 12390-3, in particular DIN EN 12390-3:2019-10, is 110 N / mm ２ less than 100 N / mm ２ less than 85 N / mm ２ less than 82.5 N / mm ２ 2. The concrete element according to claim 1, wherein the thickness is less than 1 / 2 mm.

17. 2. The concrete element according to claim 1, wherein the core concrete layer of the concrete element has a tensile bond strength, measured according to DAfStb (German Committee for Reinforced Concrete) directive "Protection and repair of concrete components", Part 4, Section 5.5.11, 2001, 28 days after production, of at least 1.0 MPa, preferably at least 1.3 MPa, more preferably at least 1.5 MPa, and particularly preferably at least 2.0 MPa.

18. 2. The concrete element according to claim 1, characterized in that the concrete element has a bond adhesion tensile strength, measured 28 days after production in accordance with the DAfStb (German Commission for Reinforced Concrete) Directive "Protection and Repair of Concrete Components", Part 4, Section 5.5.11, 2001, of at least 0.75 MPa, preferably at least 1.0 MPa, more preferably at least 1.15 MPa, even more preferably at least 1.3 MPa and particularly preferably at least 1.5 MPa.

19. 2. A concrete element according to claim 1, characterized in that the core concrete layer contains at least 1% by weight of opal, flint, chalcedony and / or greywacke, preferably at least 5% by weight, more preferably at least 15% by weight, particularly preferably at least 17.5% by weight.

20. 2. The concrete element according to claim 1, characterized in that the concrete element is a concrete block, a concrete slab, a concrete wall element or a concrete step.

21. 10. A method for producing a concrete element according to claim 1, comprising the steps of: a. preparing a face composition; The face composition comprises, as components: i. a granular face material; ii. optionally a pigment; iii. Optionally, a filler; iv. water, v. latent hydraulic and / or pozzolanic face binders, and vi. Contains an alkaline face hardener; b. mixing the face composition to obtain a face concrete layer mix; c. preparing a core composition; The core composition comprises, as components: i. a particulate core material; ii. water, iii. a latent hydraulic core binder and / or a pozzolanic core binder; and iv. Contains an alkaline core hardener; d. mixing the core composition to obtain a core concrete layer mix; e. filling the core concrete layer mixture and the face concrete layer mixture into at least one form; and f) compacting said core concrete layer mixture and said face concrete layer mixture within said form to obtain at least one green concrete element.

22. 22. The method of claim 21, wherein the components of the face composition are metered in the order set forth in claim 21.

23. 23. A method according to claim 21 or claim 22, characterized in that the core concrete layer mix is ​​filled into the at least one formwork before the face concrete layer mix.

24. 24. Use according to claim 23, characterized in that the core concrete layer mixture is compacted before the face concrete layer mixture is added.

25. 22. The method of claim 21, wherein one portion of granular material containing, based on the total composition of the granular material, (a) 65 to 95% by weight of a litter component having an average particle size of 0.1 to 5 mm, and (b) 5 to 35% by weight of a binder is applied to the face concrete layer mixture in the at least one formwork before compaction.

26. 26. The method according to claim 25, characterized in that the binder contained in the granular material is preferably an inorganic binder such as cement, hydraulic lime, gypsum or sodium silicate, or the binder contained in the granular material is an organic binder such as a plastic dispersion, an acrylate resin, an alkyd resin, an epoxy resin, a polyurethane, a sol-gel resin or a silicone resin emulsion, and / or the litter component has an average particle size of 0.1 to 1.8 mm or 1.2 to 5 mm, and / or the litter component is or contains a rock mixture, or the litter component contains at least one material selected from the group consisting of semi-precious stones, precious stones, mica, metal chips, glass particles and plastic particles.

27. 27. A method according to claim 25 or claim 26, characterized in that the granular material is applied by scattering or dumping, and / or the granular material is applied to the face concrete layer mix by an application device, the application device comprising at least one pipe socket, into which one or more portions of granular material are supplied and which are scattered, dumped, sprayed and / or dropped onto the concrete layer via the pipe socket.

28. 22. Method according to claim 21, characterized in that the surface and / or the edge of the at least one green concrete element is treated with a brush, thereby structuring and / or roughening and / or smoothing and / or reducing the projections of the edges.

29. 22. Method according to claim 21, characterized in that a sealant and / or waterproofing agent is applied to the surface of the at least one green concrete element.

30. 22. The method according to claim 21, characterized in that the green concrete elements are hardened to obtain concrete elements, which are preferably treated after hardening by sanding, blasting, brushing and / or structuring.