Apparatus and method for processing old concrete

Abstract

The invention relates to a method for processing old concrete, wherein the old concrete comprises cement stone and aggregate, in particular sand and / or gravel, wherein the method comprises the steps of grinding the old concrete in a grinding device (14), classifying the ground old concrete into at least two products (26, 28, 30) having different particle components in a classification device (18), characterized in that the grinding is carried out at a grinding pressure of less than 50 MPa. The invention also relates to a plant (10) for processing old concrete, comprising a grinding device (14) for grinding the old concrete, a classification device (18) for classifying the ground old concrete into at least two products (26, 28, 30) having different particle components, characterized in that the grinding device (14) is designed and configured such that the grinding of the old concrete is carried out at a grinding pressure of less than 50 MPa.

Description

[0001] The present invention relates to an apparatus and a method for processing old concrete.

[0002] In the production of concrete, construction sand or gravel is often used as aggregate. The demand for construction sand is very high worldwide and is still growing. It is estimated that 30 to 50 billion tons of sand and gravel are consumed worldwide per year. An alternative to construction sand is recycled concrete, which is fed back into the concrete production process in pulverized form. At present, the recycling strategy for old concrete is based on the production of low-grade aggregates, which are used, for example, for backfilling in road construction. EP 3 613 713 Al discloses a method for producing aggregates for concrete from old concrete. The old concrete is crushed and then classified into different particle sizes.

[0003] Compared to natural aggregates, such recycled aggregates have a higher porosity and thus also a higher water absorption and a lower bulk density. Here, the bulk density is largely dependent on the moisture level, resulting in a series of different problems in concrete production compared to natural aggregates. The actual effective water content is a decisive control variable for further optimizing the quality of the concrete, but has not been adjustable in a targeted manner so far and is largely unknown. Recycled aggregates are therefore evaluated to a certain extent as being inferior to natural aggregates.

[0004] Low-grade aggregates result in an increased water demand in concrete applications, whereby the setting behavior of the produced concrete is poorer than with natural aggregates. The particle size distribution, the porosity and the particle shape of the concrete aggregates have a considerable influence on the handling properties and the strength of the concrete.

[0005] It is therefore an object of the present invention to specify an apparatus and a method for processing old concrete, wherein the quality of the aggregates recovered from the processed old concrete is improved.

[0006] According to the invention, this object is achieved by the method and the apparatus of the invention.

[0007] According to a first aspect, a method for processing old concrete, wherein the old concrete comprises cement stone and aggregates, in particular sand and / or gravel, the method comprising: grinding the old concrete in a grinding device, and classifying the ground old concrete into at least two products having different particle fractions in a classification device, wherein the grinding is carried out at a grinding pressure of less than 50 MPa.

[0008] Optionally, the old concrete is pre-crushed in a crushing device before the grinding. The crushing device is, for example, a crusher or a mill. The particle size of the pre-crushed (optionally) old concrete discharged into the grinding device is, for example, from 50 mm to 100 mm.

[0009] Old concrete is understood to mean a hardened solid concrete which is obtained, for example, from the demolition of buildings. Old concrete comprises in particular cement stone fractions, hydraulic cement and a fraction of preferably natural sand or gravel which is used as aggregate in the production of concrete.

[0010] The grinding device is, for example, a roller mill. The roller mill preferably comprises a first grinding roller and a second grinding roller which are arranged opposite one another and can be driven in opposite directions, wherein a grinding gap is formed between the grinding rollers. The roller mill is preferably a high-pressure roller mill, wherein the grinding material is comminuted predominantly or completely by pressure. It is also conceivable that the pressure additionally generates shear stresses in the grinding gap. The degree to which the material is comminuted by impact stresses is negligible, if at all. The grinding pressure can preferably be adjusted in the grinding device. The grinding pressure is understood to mean the pressure which acts on the grinding material to be comminuted in the grinding gap. This is generated and adjusted, for example, by means of a hydraulic device on one of the grinding rollers.

[0011] A grinding pressure of less than 50 MPa ensures a comminution of the old concrete in which only the cement stone which connects the aggregate particles is comminuted, but not the aggregate particles. The shear stresses generate friction at the particle surfaces and targeted wear of the cement stone in the aggregate. The sand and gravel in the old concrete thus remain unchanged and the particle shape is not optimally destroyed.

[0012] According to a first embodiment, the grinding is carried out at a grinding pressure which is below the breaking limit of the aggregate of the old concrete. The pressure which acts on the old concrete is thus below the breaking limit of the aggregate, such as sand and gravel. This ensures that only the cement stone, which preferably has a lower breaking limit than the aggregate, is comminuted by the grinding device. The breaking limit of the aggregate is understood in particular to mean the average breaking strength of the aggregate, such as sand and / or gravel, at which the aggregate is comminuted, in particular by pressure. The compressive strength of the old concrete is preferably understood to mean the average compressive strength of the old concrete at which the old concrete is comminuted, in particular by pressure.

[0013] The grinding device is, for example, connected to an open / closed loop control device which is designed in such a way that it controls the grinding pressure of the grinding device in open / closed loop at a value of less than 50 MPa. For example, the old concrete is analysed with regard to the properties of the aggregate, consisting of sand and / or gravel, before the old concrete is discharged into the grinding device. Preferably, the breaking limit of the aggregate of the old concrete and / or the compressive strength of the old concrete is determined and transmitted to the open / closed loop control device. The open / closed loop control device is preferably designed in such a way that it controls the grinding pressure of the grinding device in open / closed loop depending on the breaking strength of the aggregate and / or the compressive strength of the old concrete.

[0014] Preferably, the grinding pressure of the grinding device is adjusted such that it is below the breaking strength of the aggregate and, in particular, above the compressive strength of the old concrete. Thereby it is achieved that the cement stone of the old concrete, which connects the particles of the aggregate to each other, is crushed and at the same time the aggregate is not damaged. The aggregate is preferably separated from the cement stone.

[0015] The grinding pressure is preferably adjusted such that it is below the breaking limit of the aggregate by about 2 MPa to 10 MPa, in particular 5 MPa.

[0016] The open / closed loop control device is to be understood as meaning a device which is designed for open-loop control and / or closed-loop control.

[0017] The grinding device comprises a roller mill with two grinding rollers which form a grinding gap between each other, the grinding of the old concrete taking place with different rotational speeds of the grinding rollers relative to each other. This produces a shear gradient, which generates friction on the surface of the aggregate and thus leads to a targeted wear of the cement stone by the aggregate particles.

[0018] According to a further embodiment, the particle size distribution of the ground old concrete is determined and the grinding pressure of the grinding device is controlled in an open / closed loop manner depending on the determined particle size distribution. The particle size distribution of the old concrete is determined, for example, by visual inspection, for example on site or in-line, wherein, for example, the amount of old concrete is checked with different sieve sizes.

[0019] Preferably, a measuring device for determining the particle size distribution of the ground old concrete is provided between the grinding device and the sorting device. The measuring device is preferably connected to the open / closed loop control device, wherein the grinding pressure is controlled in an open / closed loop manner depending on the determined particle size distribution.

[0020] For example, the determined particle size distribution is compared with a predetermined limit value or limit range and the grinding pressure is increased or decreased in the event of a deviation from the limit value or limit range. Preferably, the grinding pressure is increased if the determined particle size distribution exceeds the predetermined limit value or limit range. Preferably, the grinding pressure is decreased if the determined particle size distribution is below the predetermined limit value or limit range.

[0021] According to a further embodiment, the particle size distribution is determined by an optical measuring device. The optical measuring device is, for example, a camera which is arranged such that it can capture the particle sizes of the ground old concrete and transmit them to, for example, an image evaluation system. For example, the measuring device is arranged above the sieve and captures the particle sizes on the sieve. The particle sizes determined by the camera, in particular the image evaluation system, are transmitted to the open / closed loop control device.

[0022] The ground old concrete is classified in a classification device into at least two products with different particle fractions, wherein a first product has a particle fraction with a particle size of 2 mm to 31.5 mm, in particular 2 mm to 16 mm, preferably 4 mm to 16 mm; and a second product has a particle fraction with a particle size of 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm. The products are preferably used as aggregates in a subsequent production of concrete. To this end, the products can be fed to a further classification device in order to, for example, produce a particle fraction which meets the requirements according to DIN EN 12620.

[0023] For example, the ground old concrete is further classified in a classification device into a third product with a particle fraction with a particle size of less than 0.15 mm. The third product, in particular with accumulated cement stone, is preferably subsequently used in a process for producing cement, in particular calcination to form cement clinker, wherein the cement stone is reactivated.

[0024] According to a further embodiment, the classification of the ground old concrete comprises sieving the ground old concrete in a sieving device and / or screening at least a portion of the ground or sieved old concrete in a screening device.

[0025] The classification device preferably comprises a sieving device and / or a screening device. The screening device is preferably located downstream of the sieving device. This makes it possible for the ground old concrete to be classified in several steps, thereby reliably generating different particle fractions.

[0026] According to a further embodiment, the sieving device comprises at least two sieves, wherein the ground old concrete is classified into at least three different particle fractions. The sieving device preferably comprises at least two, preferably three, four or more sieves. In particular, the sieves are arranged one after the other in series and have different aperture sizes. To this end, the sieves of the sieving device are preferably arranged one above the other, such that the material flows through the sieves by gravity. Preferably, the ground old concrete is sieved in the sieving device into a first particle fraction with a particle size of 2 mm to 16 mm, in particular 4 mm to 16 mm, a second particle fraction with a particle size of greater than 16 mm, and a third particle fraction with a particle size of less than 2 mm, in particular less than 4 mm. Preferably, the second particle fraction is fed to a grinding device and re-ground. In particular, the amount of material of the second particle fraction is determined by a measuring device and transferred to an open / closed loop control device.

[0027] Preferably, the grinding pressure of the grinding device is controlled in an open / closed loop manner depending on the determined amount of the second particle component. For example, the determined amount is compared to a predetermined limit value or limit range, and the grinding pressure is increased or decreased in case the amount deviates from the limit value or limit range. In particular, the grinding pressure is increased if the determined amount exceeds the limit value or limit range. In particular, the grinding pressure is decreased if the determined amount is below the limit value or limit range.

[0028] Preferably, the material of the third particle component having a particle size of less than 2 mm, in particular less than 4 mm, which is sieved in the sieving device, is fed to the screening device.

[0029] According to another embodiment, the sieved old concrete is classified in the screening device into a first particle component having a particle size of 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm, and a second particle component having a particle size of less than 0.15 mm. The screening device comprises, for example, dynamic and / or static screens. The dynamic screen comprises, for example, a rotatable bar cage, wherein particles exceeding a certain particle size are excluded at the outer circumference of the rotating bar cage and leave the dynamic screen through a coarse material outlet, wherein particles entering the bar cage leave the dynamic screen through a fine material outlet.

[0030] In the static screen, the coarse material screening is preferably carried out by means of impact and guiding devices. Parameters influencing the separation behavior of the static screen comprise, for example, the design of the flow elements, in particular the incidence angle of the guiding vanes of the flow elements and the flow velocity, as well as the number of flow elements in the static screen.

[0031] According to another embodiment, the sieved old concrete is classified in the screening device into a first particle component having a particle size of 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm, and a second particle component having a particle size of less than 0.15 mm.

[0032] According to another embodiment, the classified, in particular sieved and / or screened, old concrete having a particle component having a particle size of 0.15 mm to 16 mm, in particular 0.15 mm to 4 mm or 2 mm to 16 mm or 4 mm to 16 mm, is fed to a jig and separated according to the density of the old concrete particles. Preferably, the old concrete having a particle component having a particle size of 2 mm to 4 mm, 4 mm to 8 mm or 8 mm to 16 mm is fed to the jig.

[0033] The jig is preferably designed such that it separates the material, in particular the ground old concrete, according to the solid density of the particles. Preferably, the particles reaching a certain predetermined density limit value are separated from the particles having a density below this density limit value. The density limit value can preferably be adjusted in the jig. For example, the density limit value is approximately 2000 kg / m3. 3up to 2800 kg / m 3 , in particular approximately 2500 kg / m 3 .

[0034] The apparatus for processing old concrete preferably comprises a first air classifier downstream of the screening device. In particular, the first air classifier is connected to the screening device such that it is fed with the screened old concrete having a particle fraction with a particle size of 2 mm to 16 mm, in particular 4 mm to 16 mm. Preferably, old concrete having a density above a predetermined density limit value is fed to a first product, wherein preferably old concrete having a density below the predetermined density limit value is fed to the grinding device for re-milling.

[0035] Further, the apparatus for processing old concrete comprises a second air classifier, for example downstream of the screening device. In particular, the second air classifier is connected to the screening device such that it is fed with the screened old concrete having a first particle fraction with a particle size of 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm. Preferably, old concrete having a density above a predetermined density limit value is fed to a second product, wherein old concrete having a density below the predetermined density limit value is fed to the grinding device for re-milling. Preferably, exhaust air from the air classifier is fed to a dust removal device and dust is removed.

[0036] Separating the particles of old concrete according to the density of the solids enables to improve the quality of the products. The density of the cement stone is lower than the density of the aggregates, such as sand and gravel, so that particles with a high proportion of cement stone are recycled to the grinding device for re-milling and particles with a high proportion of sand and gravel form the products. In particular, the first product and the second product are used as aggregates in the production of concrete.

[0037] According to a further embodiment, exhaust air from the screening device, the grinding device, the air classifier and / or the screening device is fed to a dust removal device. Dust separated from the air in the dust removal device is preferably fed to a product having a particle size of less than 0.15 mm. This product is preferably mainly ground cement stone. Preferably, this product is fed to a cement production process.

[0038] The present invention also relates to an apparatus for processing old concrete, the apparatus optionally comprising: a comminution device for pre-milling old concrete; a grinding device for grinding old concrete; a classification device for classifying the ground old concrete into at least two products having different particle fractions, wherein the grinding device is designed and configured such that the grinding of the old concrete is carried out at a grinding pressure of less than 50 MPa.

[0039] The above-mentioned embodiments and advantages of the method for processing old concrete also apply to the apparatus for processing old concrete.

[0040] The grinding device comprises a roll mill having two grinding rolls forming a grinding gap between each other, the grinding of the old concrete being carried out with different rotational speeds of the grinding rolls relative to each other. Preferably, the grinding device is designed and configured such that the grinding rolls are rotatable with different rotational speeds from each other. In particular, a control device is provided, which is connected to the grinding device and designed and configured to control the rotational speeds of the grinding rolls such that they have different rotational speeds from each other.

[0041] According to one embodiment, the device comprises a measuring device for determining the particle size distribution of the ground old concrete and an open / closed loop control device connected to the grinding device and the measuring device and designed such that it controls the grinding pressure of the grinding device in an open / closed loop manner depending on the determined particle size distribution.

[0042] According to another embodiment, the sorting device comprises a sieving device for sieving the ground old concrete into at least two particle fractions and a screening device for screening at least a portion of the old concrete sieved in the sieving device.

[0043] According to another embodiment, the sieving device comprises at least two sieves and is designed such that it classifies the ground old concrete into at least three different particle fractions. According to another embodiment, the sieving device is connected to the screening device such that old concrete having a particle size of less than 2 mm, in particular less than 4 mm, is fed to the screening device. Preferably, only old concrete having a particle size of less than 2 mm, in particular less than 4 mm, is fed from the sieving device to the screening device.

[0044] The sieving device is in particular connected to the screening device such that old concrete having a particle size of less than 2 mm, in particular less than 4 mm, is fed to the screening device. The screening device is preferably designed such that it classifies the sieved old concrete into a first particle fraction having a particle size of 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm, and a second particle fraction having a particle size of less than 0.15 mm.

[0045] According to another embodiment, the device comprises at least one air classifier connected to the sieving device and / or the screening device such that old concrete having a particle size of 0.15 mm to 2 mm to 4 mm, or 2 mm to 16 mm, is fed to the air classifier.

[0046] According to another embodiment, the device for processing old concrete comprises a dust removal device connected to the screening device, the grinding device, the air classifier and / or the sieving device such that exhaust air from the screening device, the grinding device, the air classifier and / or the sieving device is fed to the dust removal device. BRIEF DESCRIPTION OF DRAWINGS

[0047] The application is explained in more detail below based on a number of exemplary embodiments with reference to the accompanying drawings.

[0048] Figure 1 A flow chart of a method and apparatus for processing old concrete according to one exemplary embodiment is shown.

[0049] Figure 2 A flow chart of a method and apparatus for processing old concrete according to another exemplary embodiment is shown.

[0050] Figure 1 A schematic view of an apparatus 10 for processing old concrete is shown. Figure 1 The flow chart can also be understood as a method for processing old concrete. The old concrete is for example demolition concrete from a building, wherein the old concrete preferably comprises aggregate, such as sand and / or gravel, and cement stone. The cement stone is to be understood as meaning cement which has been solidified with water, which preferably connects the particles of the aggregate to one another. The processing of the old concrete is to be understood as meaning that the old concrete is processed in such a way that it can be used at least partially as aggregate for producing concrete.

[0051] The apparatus 10 for processing old concrete according to the exemplary embodiments in Figure 1 The apparatus 10 for processing old concrete according to the exemplary embodiments in

[0052] The comminution device 12 adjoins the grinding device 14 in the material flow direction of the old concrete, optionally grinding the pre-comminuted old concrete in the grinding device 14. The grinding device 14 is preferably a roller mill. The grinding device preferably comprises two parallel grinding rollers, which can be rotated in opposite directions and form a grinding gap between them. The old concrete is preferably comminuted in the grinding gap by a grinding pressure. The grinding pressure exerted by the grinding rollers on the old concrete in the grinding gap can preferably be adjusted in the grinding device 14. The old concrete is preferably ground in the grinding device 14 at a grinding pressure of less than 50 MPa. Preferably, the grinding device is connected to an open / closed loop control device 16, which is designed to control the grinding pressure of the grinding device to a value of less than 50 MPa in an open / closed loop manner. For example, the old concrete is analyzed for the properties of the aggregate, consisting of sand and / or gravel, before it is discharged into the grinding device. Preferably, the breaking limit of the aggregate of the old concrete and / or the compressive strength of the old concrete is determined and transmitted to the open / closed loop control device. The open / closed loop control device 16 is preferably designed such that it controls the grinding pressure of the grinding device 14 in an open / closed loop manner depending on the breaking strength of the aggregate and / or the compressive strength of the old concrete.

[0053] The breaking limit of the aggregate is to be understood in particular as meaning the average breaking strength of the aggregate, such as sand and / or gravel, at which the aggregate is comminuted, in particular by pressure. The compressive strength of the old concrete is preferably to be understood as meaning the average compressive strength of the old concrete, at which the old concrete is comminuted, in particular by pressure.

[0054] Preferably, the grinding pressure of the grinding device 14 is adjusted such that it is below the breaking strength of the aggregate and in particular above the compressive strength of the old concrete. Thereby, it is achieved that the cement stone of the old concrete, which connects the particles of the aggregate to one another, is crushed and at the same time the aggregate is not damaged. The aggregate is preferably separated from the cement stone.

[0055] The grinding pressure is preferably adjusted such that it is about 2 MPa to 10 MPa, in particular 5 MPa, below the breaking limit of the aggregate.

[0056] The grinding device 14 is preferably adjoined in the material flow direction of the ground old concrete with a classifying device 18, wherein the ground old concrete is classified into at least two products of different particle size distribution. Preferably, the ground old concrete is classified into three products of different particle size. Preferably, the ground old concrete is classified into a first product having a particle size of, for example, 2 mm to 16 mm, in particular 4 mm to 16 mm, and a second product having a particle size of, for example, 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm. In particular, the old concrete is additionally classified into a third product having a particle size of less than 0.15 mm.

[0057] Preferably, between the grinding device 14 and the classifying device 18 a measuring device 20 for determining the particle size distribution of the ground old concrete is arranged. The measuring device 20 is preferably connected to the open / closed loop control device 16, wherein the grinding pressure is controlled in an open / closed loop manner depending on the determined particle size distribution.

[0058] For example, the determined particle size distribution is compared to a predetermined limit value or limit range and the grinding pressure is increased or decreased in case of a deviation from the limit value or limit range. Preferably, the grinding pressure is increased if the determined particle size distribution exceeds the predetermined limit value or limit range. Preferably, the grinding pressure is decreased if the determined particle size distribution is below the predetermined limit value or limit range.

[0059] The classifying device 18 preferably comprises a sieving device 22 and / or a screening device 24. For example, in the exemplary embodiment of Figure 1 In the exemplary embodiment of the screening device 24 is located downstream of the sieving device 22. The sieving device 22 preferably comprises at least two, preferably three, four or more sieves. In particular, the sieves are arranged one after the other in series and have different aperture sizes. Preferably, the ground old concrete is sieved in the sieving device 22 into a first particle fraction having a particle size of, for example, 2 mm to 16 mm, in particular 4 mm to 16 mm, a second particle fraction having a particle size of more than 16 mm, and a third particle fraction having a particle size of, for example, less than 2 mm, in particular less than 4 mm. Preferably, the second particle fraction is fed to the grinding device 14 and re-ground. In particular, the amount of material of the second particle fraction is determined by the measuring device and is transmitted to the open / closed loop control device. Preferably, the grinding pressure of the grinding device is controlled in an open / closed loop manner depending on the determined amount of the second particle fraction. For example, the determined amount is compared to a predetermined limit value or limit range and the grinding pressure is increased or decreased in case of a deviation from the limit value or limit range. In particular, the grinding pressure is increased if the determined amount exceeds the limit value or limit range. In particular, the grinding pressure is decreased if the determined amount is below the limit value or limit range.

[0060] Preferably, the material of a third particle size fraction, for example less than 2 mm (especially less than 4 mm), sieved in screening device 22, is fed to screening device 24. Screening device 24 is, for example, a dynamic screener with a rotatable rod cage. The dynamic screener additionally includes, for example, a fan for generating screening air and a filter or cyclone separator for separating fine material from the air volume flow. In screening device 24, the sieved old concrete is preferably classified into a first particle size fraction, for example, 0.15 mm to 2 mm (especially 0.15 mm to 4 mm), and a second particle size fraction, less than 0.15 mm.

[0061] Specifically, the material with a particle size of 2 mm to 16 mm (especially 4 mm to 16 mm) sieved in the screening device 22 forms a first product 26. Preferably, the material with a particle size of, for example, 0.15 mm to 2 mm (especially 0.15 mm to 4 mm) sorted in the screening device 24 forms a second product 28. The material with a particle size of less than 0.15 mm sorted in the screening device 24 preferably forms a third product 30.

[0062] The exhaust gas from the screening device 24, the sieving device 22 and / or the grinding device 14 is preferably fed to the dust removal device 32 for dust removal, wherein the dust separated in the dust removal device 32 is preferably fed to the third product 30.

[0063] Figure 2 A schematic diagram of device 10 for processing old concrete is shown, which largely corresponds to Figure 1 The same components in the drawings are represented by the same reference numerals. Figure 2 It can also be understood as a flowchart of a method for treating old concrete. Figure 2 The equipment 10 in the middle also includes, for example, Figure 1 The measuring device 20 and the open-loop / closed-loop control device 16 shown are, for clarity, in Figure 2 They are not shown in the document.

[0064] and Figure 1 compared to, Figure 2 The device also includes two winnowing machines 34 and 36, which are located, for example, downstream of the screening device 22 and the sieving device 24, respectively. Alternatively, the device 10 may include only one winnowing machine 34 or 36, located downstream of the screening device 22 and / or the sieving device 24. The winnowing machines 34 and 36 are preferably designed to classify materials (especially ground old concrete) according to their solid density. Preferably, particles reaching a predetermined density limit are separated from particles with a density lower than that limit. Preferably, this density limit can be adjusted. For example, the density limit is approximately 2000 kg / m³. 3up to 2800 kg / m 3 , in particular approximately 2500 kg / m 3 .

[0065] The plant 10 preferably comprises a first air classifier 34 downstream of the screening device 22. In particular, the first air classifier 34 is connected to the screening device 22 such that it is fed with the screened old concrete having a particle fraction with a particle size of, for example, 2 mm to 16 mm, in particular 4 mm to 16 mm. Preferably, old concrete having a density above a predetermined density limit value is fed to the first product 26, wherein preferably old concrete having a density below the predetermined density limit value is fed to the grinding device 14 for re-milling.

[0066] Furthermore, the plant 10 comprises a second air classifier 36, for example, downstream of the screening device 24. In particular, the second air classifier 36 is connected to the screening device 24 such that it is fed with the screened old concrete having a first particle fraction with a particle size of, for example, 0.15 mm to 2 mm, in particular 0.15 mm to 4 mm. Preferably, old concrete having a density above a predetermined density limit value is fed to the second product 28, wherein old concrete having a density below the predetermined density limit value is fed to the grinding device 14 for re-milling. Preferably, exhaust air from the air classifiers 34, 36 is fed to the dust removal device 32 and dust is removed.

[0067] The classification of the old concrete according to the density of the solids enables the production of products 26, 28 of higher quality. The density of the cement stone is lower than the density of the aggregate, such as sand and gravel, so that particles containing a high proportion of cement stone are recycled to the grinding device 14 for re-milling and particles having a high proportion of sand and gravel form the products 26, 28. In particular, the first product 26 and the second product 28 are used as aggregate in the production of concrete.

[0068] List of reference signs

[0069] 10 plant for processing old concrete

[0070] 12 crushing device

[0071] 14 grinding device

[0072] 16 open / closed loop control device

[0073] 18 classification device

[0074] 20 measuring device

[0075] 22 screening device

[0076] 24 screening device

[0077] 26 first product

[0078] 28 second product

[0079] 30 third product

[0080] 32 dust removal device

[0081] 34 sifter

[0082] 36 sifter

Claims

1. A method for processing old concrete, wherein, The old concrete comprises cement stone and aggregate, wherein the method comprises the steps of: grinding the old concrete in a grinding device (14), classifying the ground old concrete into at least two products (26, 28, 30) having different particle fractions in a classifying device (18), characterized in that: the grinding is performed at a grinding pressure of less than 50 MPa, wherein the grinding device (14) comprises a roller mill having two grinding rollers forming a grinding gap therebetween, and wherein the grinding of the old concrete is performed with different rotational speeds of the grinding rollers relative to each other.

2. The method of claim 1, wherein, the grinding is performed at a grinding pressure below the breaking limit of the aggregate of the old concrete.

3. The method according to any of the preceding claims 1-2, wherein, determining a particle size distribution of the ground old concrete, and controlling the grinding pressure of the grinding device (14) in an open / closed loop manner depending on the determined particle size distribution.

4. The method of claim 3, wherein, the particle size distribution is determined by optical measuring means (20).

5. The method of claim 1, wherein, the ground old concrete is classified in the classifying device (18) into at least two products (26, 28) having different particle fractions, wherein a first product (26) has a particle fraction with a particle size of 2 mm to 16 mm, and a second product (28) has a particle fraction with a particle size of 0.15 mm to 2 mm.

6. The method of claim 1, wherein, the ground old concrete is classified in the classifying device (18) into at least two products (26, 28) having different particle fractions, wherein a first product (26) has a particle fraction with a particle size of 4 mm to 16 mm, and a second product (28) has a particle fraction with a particle size of 0.15 mm to 4 mm.

7. The method of claim 5 or 6, wherein, classifying the ground old concrete comprises sieving the ground old concrete in a sieving device (22).

8. The method according to the preceding claim 7, wherein, classifying the ground old concrete further comprises screening at least a portion of the sieved old concrete in a screening device (24).

9. The method according to the preceding claim 7, wherein, the sieving device (22) comprises at least two sieves, and the ground old concrete is classified into at least three different particle fractions.

10. The method of claim 9, wherein, the classified old concrete having a particle fraction with a particle size of 0.15 mm to 16 mm is fed to a riddle (34, 36) and classified depending on the density of the old concrete.

11. The method of claim 9, wherein, the classified old concrete having a particle fraction with a particle size of 0.15 mm to 4 mm is fed to a riddle (34, 36) and classified depending on the density of the old concrete.

12. The method of claim 9, wherein, the classified old concrete having a particle fraction with a particle size of 2 mm to 16 mm is fed to a riddle (34, 36) and classified depending on the density of the old concrete.

13. The method of claim 9, wherein, the classified old concrete having a particle fraction with a particle size of 4 mm to 16 mm is fed to a riddle (34, 36) and classified depending on the density of the old concrete.

14. The method of claim 8, wherein, the sieved old concrete is classified in the screening device (24) into a first particle fraction having a particle size of 0.15 mm to 2 mm, and a second particle fraction having a particle size of less than 0.15 mm.

15. The method of claim 8, wherein, The sieved old concrete is classified in the screening device (24) into a first particle fraction having a particle size of 0.15 mm to 4 mm and a second particle fraction having a particle size of less than 0.15 mm.

16. The method of the preceding claim 8, wherein, The exhaust air from the screening device (22), the grinding device (14), the sieves (34, 36) and / or the screening device (24) is fed to a dust removal device (32) for dust removal.

17. The method according to any of the preceding claims 1-2, the aggregate being sand and / or gravel.

18. An apparatus (10) for processing old concrete, comprising: a grinding device (14) for grinding the old concrete, a classification device (18) for classifying the ground old concrete into at least two products (26, 28, 30) having no particle fractions, characterized in that: the grinding device (14) is designed and configured such that the grinding of the old concrete is carried out at a grinding pressure of less than 50 MPa, wherein the grinding device (14) comprises a roller mill having two grinding rollers forming a grinding gap therebetween, and wherein the grinding device (14) is designed and configured such that the grinding of the old concrete is carried out with different rotational speeds of the grinding rollers relative to each other.

19. The apparatus (10) of claim 18, wherein, the apparatus (10) comprises a measuring device (20) for determining a particle size distribution of the ground old concrete and an open / closed loop control device (16) connected to the grinding device (14) and the measuring device (20) and designed to control the grinding pressure of the grinding device (14) in an open / closed loop manner depending on the determined particle size distribution.

20. The apparatus of claim 18 or 19, wherein, the classification device (18) comprises a screening device (24) for screening at least a portion of the old concrete screened in the screening device.

21. The apparatus of claim 20, wherein, the classification device (18) further comprises a screening device (24) for screening at least a portion of the old concrete screened in the screening device.

22. The apparatus (10) of claim 20, wherein, the screening device (22) comprises at least two sieves and is designed to classify the ground old concrete into at least three different particle fractions.

23. The apparatus (10) of claim 21, wherein, the apparatus (10) comprises at least one sieve (34, 36) connected to the screening device (22) and / or the screening device (24) such that old concrete having a particle size of 0.15 mm to 2 mm, or old concrete having a particle size of 2 mm to 16 mm is fed to the sieve (34, 36).

24. The apparatus (10) of claim 21, wherein, the apparatus (10) comprises at least one sieve (34, 36) connected to the screening device (22) and / or the screening device (24) such that old concrete having a particle size of 0.15 mm to 4 mm, or old concrete having a particle size of 4 mm to 16 mm is fed to the sieve (34, 36).

25. The apparatus (10) of claim 23 or 24, wherein, The apparatus (10) comprises a dust removal device (32) connected to the classification device (18), to the grinding device (14) and / or to the sieves (34, 36) so that the exhaust air from the classification device (18), from the grinding device (14) and / or from the sieves (34, 36) is fed to the dust removal device (32).

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