Method for producing a building material from porous igneous rock and using the building material as an aggregate in the production of concrete

Abstract

The invention relates to a method for producing a building material in which aggregate particles of porous igneous rock, in particular pumice, are wetted with a liquid component containing graphene oxide and silicon dioxide dispersed in water and subsequently, while in motion, contacted with a fine-grained component containing at least cement and finally dried or processed with a water-cement mixture in a mixer to form concrete. The invention further relates to a building material for producing concrete. The building material comprises aggregate particles of porous igneous rock, in particular pumice, and a coating containing cement, graphene oxide, and silicon dioxide, which is hydraulically hardened on a surface of the aggregate particles.

Description

[0001] The invention relates to a method for producing a building material from porous igneous rock, in particular pumice, and the use of the building material as an aggregate in the production of concrete, in particular lightweight concrete.

[0002] Although lightweight concrete's properties, particularly its superior thermal and acoustic insulation, meet significantly higher quality standards in the construction industry, it still accounts for far less than 10 percent of all buildings constructed with standard concrete. This is due to several factors. Lightweight concrete is a special type of concrete characterized by a lower density than conventional concrete. This lower density is achieved through the use of lightweight aggregates such as expanded clay, expanded glass, perlite, polystyrene, or pumice. However, the lightweight aggregates used to date have several drawbacks in the resulting lightweight concrete. For example, the use of expanded glass or expanded clay is no longer justifiable from an ecological perspective, as their production is particularly energy-intensive and releases substantial amounts of carbon dioxide.Lightweight concretes with expanded polystyrene as an aggregate have not gained widespread acceptance in the construction industry due to their low modulus of elasticity and high shrinkage rates. Furthermore, expanded polystyrene, also known under the trade name Styrofoam, has required separate disposal since 2018, meaning that the disposal of lightweight concretes containing polystyrene could also become problematic in the future.

[0003] Naturally occurring porous pumice is found worldwide and is easy to extract, which is why its use, particularly as a lightweight aggregate, is gaining importance in the construction industry. However, the use of porous aggregates presents several challenges. Generally, porous aggregates tend to absorb and retain water highly. The water that penetrates the pores negatively impacts the resulting concrete quality in several ways. For example, the water-cement ratio is disrupted by the porous aggregate's absorption during mixing, meaning that the water absorbed into the pores is unavailable for the hydraulic setting of the cement. Consequently, additional water must be added to the concrete mix. This additional water, which cannot be used for the hydraulic setting process, is referred to in the industry as "free water."Reducing the proportion of free water is a key objective in the production of lightweight concrete mixes. Therefore, the lower the proportion of free water in the concrete mix, the more durable the resulting concrete qualities. This also applies to the resulting concrete strength. The lower the mass ratio of water to cement in a concrete mix, the higher the strength of the bonded concrete.

[0004] Another aspect to consider regarding lightweight concretes with porous lightweight aggregates is their tendency to absorb water within the structural system. Over several years, this water absorption can lead to significant structural damage, the extent of which can vary depending on the prevailing climatic conditions. In regions with frequent freeze-thaw cycles, trapped water can cause the concrete structure to deteriorate. In warm, humid regions, there is a risk of biological growth, such as mold, which can have adverse health consequences.

[0005] When using natural pumice as a lightweight aggregate, the problem of unimpeded water penetration into the pores arises right at the extraction site, for example, through rainwater. Therefore, there is a desire to seal the surface of the porous rock grains in such a way that the tendency to absorb and retain water is reduced, both during storage and the subsequent production of the concrete mixes.

[0006] Several approaches are known to minimize the water absorption of porous lightweight aggregates. For example, various methods are used to seal the surfaces of granular pumice with coatings that typically have a hydrophobic effect, thus preventing water from penetrating the porous aggregate at its surface. A selection of known methods is listed below.

[0007] DE 10 2016 013 793 A1 describes a process for producing lightweight concrete from porous aggregates such as pumice, perlite, vermiculite, and expanded clay. According to the process, a highly viscous water-binder suspension is first prepared, into which the porous aggregates are subsequently incorporated. Immediately upon incorporation of the porous aggregates into the binder suspension, the pores of the aggregates are sealed by the viscous binder suspension, preventing water from penetrating the pores.

[0008] As shown in DE 10 2016 013 793 A1, the stability of the water-binder suspension, and thus its water retention capacity, can be achieved by activating the mineral surfaces of the mixture components. Furthermore, the stability of the suspension can be increased by additives such as bentonite and methylcellulose to such an extent that water migration from the suspension into the pores of the lightweight aggregate is prevented. The process requires high rotational speeds of the mixing tools to achieve the necessary activation of the mineral surfaces required for the stability of the binder suspension. This is a significant disadvantage of the process, as the comparatively high rotational speeds of the mixing tools result in high energy consumption.Furthermore, the high rotational speeds cause increased shear stresses, which also have a detrimental effect on the effectiveness of flow agent additives.

[0009] According to German patent application DE 203 4 449 A, porous igneous rocks are treated with slurries of pumice powder and cement, with the coated granules subsequently subjected to heat treatment at 600 °C to 1150 °C. This planned thermal post-treatment makes the process uneconomical and is also associated with high CO2 emissions.

[0010] DE 10 2010 047 673 A1 describes the production of an acoustic plaster made from volcanic eruptive rocks with cement, lime, and water glass in combination with a latent heat storage medium made of paraffin encapsulated with polymethacrylate. The compressive strength of the polymer-modified mineral plaster is below 5 N / mm². 2. The material is therefore not suitable for use in the manufacture of structural buildings.

[0011] German patent application DE 10 2013 019 681 A1 discloses a method for the hydrophobic surface coating of pumice using a liquid glass composition based on silicon dioxide. The resulting surface-sealed pumice, the coating process itself, and the use of the treated pumice, particularly in lightweight concrete, to reduce its water absorption and increase its resistance to weathering and environmental influences are described.

[0012] DE 197 35 063 A1 describes a process for producing coated aggregates for structural concrete. In this process, aggregates are coated with an outer layer in special mixing or granulating units, allowing their water absorption behavior and adhesion to the cement paste to be specifically influenced.

[0013] It is also known to coat the surfaces of natural pumice with polyester and / or polyurethane. It has been shown that the resulting lightweight concretes exhibit positive effects on creep and shrinkage behavior. However, the use of plastics is associated with increased costs and leads to undesirable boundary layers on the surfaces of the light-colored aggregates.

[0014] The methods shown for hydrophobizing porous aggregates use costly hydrophobizing agents and, in some cases, energy-intensive drying steps.

[0015] The invention is therefore based on the objective of making porous igneous rock, in particular pumice, accessible as a building material, especially as a lightweight aggregate, for the production of concrete, particularly lightweight concrete, while avoiding the known disadvantages. It is thus an objective to provide a method for producing a building material from porous igneous rock, in particular pumice. Furthermore, it is an objective to provide a building material from porous igneous rock, in particular pumice, and to enable the use of this building material as an aggregate in the production of concrete, in particular lightweight concrete.

[0016] The problem is solved by a method with the features according to claim 1. Further embodiments of the method are specified in the dependent claims.

[0017] The invention is based on the surprising finding that, when granules of igneous, porous igneous rocks, particularly pumice, are combined with water-dispersed graphene oxide and silicon dioxide as liquid components, and a hydraulic binder, primarily cement, following the sequence of the process described below, a durable, hard surface coating is formed. This coating reduces water penetration and allows water already present in the granules to escape. Due to the resulting semi-permeable coating, the coated granules are advantageously used as a building material, particularly for concrete production.

[0018] According to the inventive process, the porous surfaces of aggregate particles from a provided aggregate of porous igneous rock, in particular pumice, are wetted with a liquid component containing graphene oxide and silicon dioxide dispersed in water for the production of a building material. The wetted surfaces are then contacted, while in motion, with a fine-grained component containing at least cement, whereby the aggregate particles are coated by the adhering fine-grained component. Finally, according to a first alternative, the coated aggregate particles are dried so that they can be used later. According to a second alternative, the coated aggregate particles can be directly processed into concrete in a mixer with a provided water-cement mixture.

[0019] For the purposes of this invention, a porous igneous rock, or simply porous igneous rock, is understood to be a porous rock of magmatic origin. Pumice is a prime example. This rock can exhibit closed and corresponding pores.

[0020] The aggregate is provided from a porous igneous rock, preferably pumice, so that the aggregate contains porous particles. The aggregate can be provided by crushing the porous igneous rock, resulting in an aggregate that predominantly contains porous particles, although it is not excluded that the aggregate may also contain non-porous particles. It may be provided that the crushed aggregate is treated by suitable methods to reduce the proportion of non-porous particles or the fines content of the aggregate.

[0021] The liquid component is provided separately, with graphene oxide and silicon dioxide dispersed in water. The liquid component dispersion can be produced using concrete superplasticizers in high-speed mixers. The fine-grained component is provided in the form of a dry fine-grained powder and contains at least cement as a hydraulically setting binder. The fine-grained powder is preferably provided and used in such a way that it does not contain any particles with a particle size larger than 200 µm. Consequently, the particles of the fine-grained component are smaller than 200 µm. The process according to the invention can be carried out in three steps. In the first step, the aggregate particles of porous igneous rock, in particular pumice, are wetted with the provided liquid component so that the porous surface of the aggregate particles is moistened.The wetting must be carried out in such a way that the rock grains are moistened on all sides in order to ensure all-round adhesion of the fine grain component.

[0022] Immediately after wetting with the liquid component, the surface-moist rock particles are moved and contacted with the dry, powdered fine-grain component until the pores of the rock particles are covered. This moving contact ensures that the fine-grain component adheres to the moist surface of the rock particles, completely encasing them. The movement of the rock particles also helps to dislodge any dry or loose particles of the fine-grain component that do not bond with the coating. This contact of the porous rock particles with the fine-grain component ensures that almost all pores on the surface of the rock particles are sealed. The coated rock particles are then dried according to the first alternative of the process, resulting in a bulk material consisting of coated rock particles.Drying preferably occurs without additional energy input, for example, under ambient conditions. To protect against rainwater, a cover or storage in a building can be provided. The resulting building material consists of coated aggregates, which can be used as an additive in concrete production. Advantageously, these coated aggregates can be used as a substitute for sand and gravel in concrete production.

[0023] According to the second alternative of the process, the coated aggregates are directly fed into a concrete production process. In this process, the coated aggregates are mixed with a water-cement mixture in a mixer to produce concrete. The water-cement mixture used for further processing can be produced separately in a known manner and can contain additional additives that influence flowability or the concrete structure. The building material produced according to the second alternative is therefore concrete.

[0024] The aggregate can be provided by grinding or crushing. The aggregate is preferably provided in the form of rounded grains with a size ranging from 1 mm to 20 mm.

[0025] The building material is preferably produced according to the inventive method using aggregate provided from pumice stone. Compared to other types of porous rock, pumice stone, as a porous aggregate, is characterized by its low weight, relatively high grain strength, good thermal and acoustic insulation, and high fire resistance, thus offering ideal conditions for the production of masonry blocks, insulating plasters, lightweight mortars, and especially lightweight precast concrete elements for residential and commercial construction.

[0026] The wetting of the rock particles according to the first process step can be carried out in various ways. However, care should be taken to ensure that the rock particles do not become too wet. To guarantee this, the rock particles are preferably wetted by spraying with the liquid component, whereby the rock particles are advantageously in motion to achieve wetting from all sides and at the same time keep the exposure time in the spray mist to a minimum. Preferably, the liquid component is sprayed to achieve wetting of the rock particles made of porous igneous rock. Spraying allows the liquid component to be dispersed particularly finely, so that the rock particles are wetted with a very thin film of the liquid component.Spraying can be carried out, for example, on a pelletizing plate, where the moving aggregate particles are evenly contacted and wetted by the liquid component from all sides. For higher throughput, systems are suitable in which the aggregate particles are set in motion, for example by vibration, and conveyed past a stationary spraying unit by means of a conveyor belt.

[0027] The liquid component is preferably provided with a water content in the range of 80% to 85% by mass, a graphene oxide content in the range of 5% to 10% by mass, and a silicon dioxide content in the range of 5% to 15% by mass. For preparation, the graphene oxide particles, which are in powder form, and the silicon dioxide particles are dispersed in water. Immediately before wetting the aggregate, the liquid component, provided as a dispersion, can be re-homogenized by stirring with a high-speed mixer to obtain a uniform distribution of the dispersed particles. It has been shown that the dispersion of the graphene oxide can be facilitated by the use of concrete superplasticizers. Consequently, small amounts of a concrete superplasticizer can be used to prepare the liquid component.

[0028] Graphene oxide is an oxidized form of graphene. It is produced by the chemical oxidation of graphite, in which oxygen groups are bonded to the carbon atoms.

[0029] The liquid component can also be applied by spraying in a free-fall mixer, allowing the uncoated granules to be immersed in the liquid component. If direct further processing according to the second alternative of the procedure is carried out, the water content of the liquid component can be taken into account when preparing the water-cement mixture to maintain a desired water-cement ratio.

[0030] According to one embodiment, the fine-grained component can consist solely of cement, which is provided in powder form with particles smaller than 200 µm. According to another embodiment, the fine-grained component is provided and used as a mixture of cement and another substance.

[0031] It can therefore be provided that the fine-grained component consists of a mixture containing a proportion of cement and at least one further proportion of a substance selected from the group consisting of lime, ground igneous rock flour, in particular pumice flour, fly ash, blast furnace slag, fine sand, brick dust, trass, and concrete flour. It is important that the components used to provide the fine-grained component contain only particles smaller than 200 µm.

[0032] A significant advantage of using an additional proportion of partially pozzolanic rock flour lies in the subsequent formation of strong bonds between a binder matrix and the coating layer formed on the rock particles during the production of concrete mixes. Furthermore, the use of fine particles of igneous igneous rock generated on-site, i.e., during the development of open-pit mines, eliminates the need for costly disposal or storage of these particles. Thus, in addition to its cost-effective utilization, the use of these fine particles also solves an ecological problem, as these components would otherwise cause dust pollution in the landscape during wind and siltation of the areas during rain.Should the quantities of fine particles required for the provision of the fine-grained component not be sufficiently obtained during the exploitation of the deposits of magmatic eruptive rock, the required fine particles can also be provided by grinding rock grains of the magmatic eruptive rock.

[0033] Furthermore, it can be provided that the fine-grained component is additionally mixed with at least one additive acting as a liquefier and / or a pore-forming agent and / or a shrinkage reducer. The fine-grained component can thus contain at least one additive acting as a liquefier and / or a pore-forming agent and / or a shrinkage reducer.

[0034] The addition of a pore-forming additive can be used to create micropores in the coating. These micropores are not interconnected and are only present on the surface. They do not absorb water and can improve the workability of the coated aggregate particles in a concrete matrix that has not yet hydraulically set. Commercially available air-entraining agents can be used as pore-forming agents.

[0035] The fine-grained component applied to the rock particles should have a maximum average layer thickness of 2 mm. The fine-grained component can be applied by sprinkling it onto the surface-moist rock particles. Alternatively or additionally, the surface-moist rock particles can be rolled on a powder bed formed from the fine-grained component to apply the component and seal the surface pores.

[0036] According to an advantageous embodiment of the method according to the invention, it can be provided that the moisture content of the aggregate is determined before wetting, wherein a delivery quantity of the liquid component during wetting is adjusted depending on the moisture content of the aggregate.

[0037] It can be provided that the rock particles are additionally sprayed with a dispersion of water and silicon dioxide during coating. Alternatively or additionally, the rock particles can also be sprayed with a dispersion of water and graphene oxide during coating to facilitate the adhesion of the fine-grained component in particularly fractured areas of the rock particles. The additional spraying with the silicon dioxide dispersion and / or the graphene oxide dispersion can be carried out in short bursts and in small quantities to prevent excessive moisture absorption on the surface of the rock particles.

[0038] The drying time for the aggregate depends primarily on the composition of the fine aggregate component. If the fine aggregate component consists solely of cement, the coated aggregate should be dried for at least 24 hours. If other fine particles are present, the coated aggregate should be dried for a longer period. In this case, the aggregate should be dried for at least 72 hours to achieve sufficient water resistance and coating strength.

[0039] Alternatively, the release of the coated aggregates for further processing can be determined by a test. According to the test, the drying of the coated aggregates continues until the fines fraction of the bulk material, obtained after mechanical stress in a free-fall mixer, is less than 0.063 mm and less than 10% by mass. Such a test can be performed to assess the stability of the coating layers. Only stable coating layers can withstand the stresses of ongoing transport operations with wheel loaders, conveyors, or screening plants during stockpiling operations.

[0040] The process according to the invention enables the production of coated aggregates of porous igneous rock for use as a building material. The use of a building material produced according to the invention is particularly intended as an aggregate in the production of concrete, especially lightweight concrete. Lightweight concretes produced with the coated aggregates are particularly suitable for the production of concrete modules for residential and commercial construction.

[0041] It has been shown that concretes in which coated aggregates produced according to the inventive method are used as aggregate exhibit increased strength. Due to its low weight, the building material produced according to the inventive method is particularly suitable for the production of lightweight structural concretes. Compared to uncoated aggregates, coated aggregates produced according to the inventive method achieve water-cement ratios of less than 0.6 when used as aggregate in concrete mix designs. In contrast, uncoated porous aggregates usually require pretreatment with water, as the high absorption capacity of the porous rock material results in excessive water loss from the fresh concrete mix, causing the concrete mix to dry out quickly and thus impairing its workability.

[0042] The coating of the porous aggregate particles according to the invention results in lower water-cement ratios, leading to significantly higher strengths in the resulting lightweight concretes. Lightweight concretes with uncoated pumice aggregates typically exhibit strengths of less than 20 N / mm². 2 They are therefore only conditionally suitable for structural applications. In contrast, concretes that use the aggregates coated according to the invention as building material additives achieve compressive strengths of more than 30 N / mm². 2 and are therefore widely used in residential and commercial construction, especially for the production of wall and ceiling elements.

[0043] In addition to the increased compressive strength of concrete mixtures in which the aggregates coated according to the invention are used, the resulting concretes are also characterized by improved flexural strength, higher moduli of elasticity, and lower shrinkage. Furthermore, the inventive method allows rock flours that have previously been little used or considered waste, such as those generated during the extraction of igneous igneous rocks, to be used as a component in the fine aggregate.

[0044] The aggregate particles in this building material can range in size from 1 mm to 20 mm. This particle size range is advantageous for concrete production. However, larger granules of this building material can also be produced.

[0045] Further details, features and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments.

[0046] According to one embodiment of the process for producing a building material, a liquid component containing graphene oxide and silicon dioxide dispersed in water, and a fine-grained component consisting of dry, powdered cement are provided. The base for the building material is crushed aggregate of porous pumice, with the aggregate particles having a size ranging from 1 to 20 mm. In a first step, the aggregate particles are wetted with the liquid component. For this purpose, the liquid component is sprayed, and the aggregate particles are set in motion by the spray to achieve complete wetting. A vibrator, a mixer, or a pelletizing disc can be used to set the aggregate particles in motion.

[0047] Immediately after wetting, the surface-moist rock particles are brought into contact with the fine-grained component by sprinkling it on the particles, ensuring they are completely covered. Finally, the rock particles are dried for at least 24 hours under ambient conditions, protected from rainwater, allowing the resulting coating to set and harden.

[0048] In this context, "curing" does not refer to the completion of the coating reaching its maximum final strength. Curing time, as defined in the invention, is the period required to ensure sufficient coating strength for transport or further processing.

[0049] Alternatively, if the specified dosing sequence is followed, the coated aggregates can be used directly as an additive for concrete production in a concrete mixing plant without a drying step. For direct processing, the coated aggregates are mixed with a pre-mixed water-cement mixture in the concrete mixing plant.

[0050] Pelletizing discs are suitable for producing large quantities of coated aggregates, as their varying diameters offer a wide range to meet the desired production capacities. Production capacities with pelletizing discs range from 100 kg to 100 t per hour, thus making it possible to cover the respective quantity requirements. Specifically, the process involves conveying the round aggregates, which have a particle size of 1 mm to 20 mm, onto the rotating, inclined pelletizing disc using a conveyor system. The rotational speed and the inclination of the pelletizing disc determine the residence time of the aggregate on the disc. While the aggregates are in motion on the pelletizing disc, the liquid component is sprayed in one area, ensuring that the aggregates are coated on all sides.The fine-grained component is then preferably scattered in another area of ​​the pelletizing tray so that the rock particles come into contact with it. Due to the moistened surface, the powdered fine-grained component adheres to the rock particles. After the coated rock particles leave the pelletizing tray, the drying step takes place.

[0051] One advantage of the pelletizing disc is the adjustable inclination and the variable rotation speed, which, depending on the respective grain size of the rock particles, also achieves a separation effect, which facilitates the subsequent sieving of the required grain sizes.

[0052] Examples of materials and mixtures used for the liquid component and the fine-grained component are listed below.

[0053] The first example concerns the production of a pumice lightweight concrete LC 15 / 20 according to DIN EN 206 (concrete density between 1500 and 1700 kg / m³). 3 ), where untreated, i.e., uncoated, pumice aggregates are used as the aggregate. The second example also concerns the production of a pumice lightweight concrete LC 25 / 30 according to DIN EN 206 (concrete density between 1500 and 1700 kg / m³). 3 ), wherein, in contrast to Example 1, the building material according to the invention has been used as an aggregate. Example 1

[0054] Recipe variant A - uncoated pumice Cement CEM I 42.5 330 kg Pumice flour 130 kg Water 320 kg Graphs I 3.8 kg Graphs II 3.5 kg Sand 0 / 4 300 kg Pumice granules 700 kg Sika Polypropylene Fiber 4 kg

[0055] Concrete produced according to Example 1 achieves the following characteristic values: Density after production 1791 kg / m 3 Water / flour ratio 0,711 Compressive strength after 28 days 18,7 N / mm 2 Flexural strength 1,9 N / mm 2 E-module 12.5 N / mm Example 2

[0056] Pumice lightweight concrete LC 25 / 30 according to DIN EN 206, concrete density between 1500 and 1700 kg / m³ 3 with pumice aggregates coated according to the invention as a lightweight aggregate

[0057] A) Provision of the liquid component for 700 kg of pumice aggregate Water 70 kg Silicon dioxide (water glass) 5 kg Graphene III (graphene oxide dispersed in water) 5 kg

[0058] B) Provision of the fine grain component as a flour grain mixture cement 10 kg Pumice flour (grain size < 0.125 mm) 10 kg

[0059] Mixing formula for lightweight concrete per cubic meter Cement CEM I 42.5 320 kg Pumice flour 120 kg Water 180 kg Graphs I 3.8 kg Graphs II 3.5 kg Sand 0 / 4 300 kg Coated pumice rock grains 700 kg Sika Polypropylene Fiber 4 kg

[0060] The differences in the components cement, pumice powder and water compared to example 1 are compensated for by the quantities used in the encapsulation.

[0061] The additives Graphene I, Graphene II and Graphene III are graphene oxide dispersed in water.

[0062] Graphene I (Hard Graphene Durability) contains 40% to 70% by mass of graphene oxide dispersed in water, as well as 10% by mass of a superliquefier, for example polycarboxylate ether.

[0063] Graphene II: (Mechanic Graphene Fluid Retraction) contains 40% to 70% by mass of graphene oxide dispersed in water, as well as 10% by mass of a shrinkage reducer and 10% by mass of a superliquefier, for example polycarboxylate ether.

[0064] Graphene III: contains 40% to 70% by mass of graphene oxide dispersed in water.

[0065] In a particularly simple example of a mixture, graphene I and graphene II are replaced by graphene III, so that the mixture contains exclusively graphene III, that is, graphene oxide dispersed in water. The proportion of graphene oxide in the dispersions is 40% to 70% by mass. Graphene I, graphene II, and graphene III are available, for example, from the company Grahenano in Murcia, Spain.

[0066] A shrinkage-reducing admixture (SRA), such as that contained in graphene II, generally consists primarily of surfactants that lower the surface tension of water in concrete. This reduces capillary water loss, which in turn reduces concrete shrinkage. Specifically, shrinkage reducers often contain the following components: Glycol-based compounds: These substances, such as polyethylene glycol (PEG) or propylene glycol, are the main components of many shrinkage reducers. They act as surfactants and reduce the surface tension of water in the concrete. Alcohol-based compounds: Alcohols such as polyvinyl alcohol (PVA) can also be used. These substances act similarly to glycols by slowing down the drying of the concrete and thus reducing shrinkage cracking. Organic additives: Shrinkage reducers may also contain organic additives or surfactants that can further influence the tendency to shrink.

[0067] A dispersion of graphene nanofibers and graphene oxide in an acrylic base can also be used to provide the liquid component. In this process, the dispersion of graphene nanofibers and graphene oxide is dispersed in water. The acrylic base acts as a dispersing agent. A mixture of graphene nanofibers with an average diameter between 2 nm and 200 nm and a length of 10 nm to 200 nm can be added to the dispersion.

[0068] Concrete produced according to example 2 achieves the following characteristic values: Density after production 1700 kg / m 3 Water / flour ratio 0,56 Compressive strength after 28 days 33,3 N / mm 2 Flexural strength 3,2 N / mm 2 E-module 18.5 N / mm

[0069] The following is the process for direct further processing of the coated rock grains per 2.5 m³. 3 Concrete according to the second alternative, presented in bullet points:

[0070] Dosing sequence for a continuously running free-fall mixer (30 rpm) for 2.5 cubic meters of concrete 1. Pouring in liquid component A (175 +12.5+12.5) 15 sec. 2. Addition of pumice granules (175) 15 sec. 3. Stepwise dosing of the fine-grain component B with a slowly rotating free-fall mixer (50) 20 seconds 4. Homogenizing the mixture 60 sec. 5. Dosage of cement components from the formulation (825) 120 seconds 6. Dosage of pumice flour components from the recipe (247.5) 80 seconds 7. Dosage of water from the formulation (water from liquid component taken into account) Example calculation per 2.5 m 3 Concrete: Total recipe water 170 + 70 = 240 x 2.5 (600) 60 sec. Dosage of additives Graphene I and II (9.5 + 8.75) 10 sec. 8. Dosage of sand components from the formula = (1000) 15 sec. 9. Mixing 100 seconds 10. Mixer emptying 20 seconds

[0071] The total time for providing the coated pumice granules and producing the concrete is approximately 2.5 m. 3 Concrete takes 515 seconds.

Claims

[1] Method for producing a building material in which aggregates of a porous igneous rock, in particular pumice, are wetted with a liquid component containing graphene oxide and silicon dioxide dispersed in water and subsequently contacted in motion with a fine-grained component containing at least cement and finally dried or processed with a water-cement mixture in a mixer. [2] Method according to claim 1, characterized by , that the rock grains are wetted by spraying with the liquid component, whereby the rock grains are in motion. [3] Method according to claim 1 or 2, characterized by , that the liquid component is provided with a proportion of water in the range of 80 wt% to 85 wt%, a proportion of graphene oxide in the range of 5 wt% to 10 wt% and a proportion of silicon dioxide in the range of 5 wt% to 15 wt%. [4] Method according to any one of the preceding claims, characterized by , that the fine grain component contains particles with a particle size smaller than 200 µm. [5] Method according to any one of the preceding claims, characterized by , that as a fine-grained component a mixture containing a proportion of cement and at least one further proportion of a substance selected from the group consisting of lime, igneous rock flour, in particular pumice flour, fly ash, blast furnace slag, fine sand, brick flour, trass and concrete flour, is provided and used. [6] Method according to any one of the preceding claims, characterized by that the fine grain component is additionally supplied and used with at least one additive selected from a group containing polycarboxylate ethers, naphthalene sulfonates, lignosulfonates, melamine sulfonates and setting accelerators. [7] Method according to any one of the preceding claims, characterized by, that the moisture content of the aggregate is determined before wetting, whereby the amount of liquid component released during wetting is adjusted depending on the moisture content of the aggregate. [8] Method according to any one of the preceding claims, characterized by that the aggregate is provided by grinding or crushing. [9] Method according to any one of the preceding claims, characterized by that porous rock grains are used, which have a size in the range of 1 mm to 20 mm. [10] Method according to any one of the preceding claims, characterized by that the coated rock grains are dried for at least 24 hours. [11] Method according to any one of the preceding claims, characterized by, that the coated rock grains are dried until the fine fraction obtained after mechanical stress in a free-fall mixer is less than 0.063 mm and less than 10% by mass. [12] Use of a building material produced according to any one of claims 1 to 11 as an aggregate in the production of concrete, in particular for the production of lightweight concrete.