Method for recycling aggregates from waste building materials by grinding

Abstract

This invention relates to a method for recovering aggregates from waste building materials by grinding them in a ball mill or compression mill. The method of this invention can be used to recycle waste building materials, particularly concrete or mortar. This invention also relates to the cleaned aggregates obtained from waste building materials by grinding and their use in the production of new building materials.

Description

Technical Field

[0001] This invention relates to a method for recovering aggregates from waste building materials by grinding. The method of this invention can be used to recycle waste building materials, particularly concrete or mortar. This invention also relates to the cleaned aggregates obtained from waste building materials by grinding and their use in the production of new building materials. Existing technology

[0002] To date, a large amount of waste building materials (such as hardened concrete, mortar, plaster, etc.) are disposed of in landfills, and very little of them are partially reused in low-tech applications in the construction industry.

[0003] Current practice involves shredding waste building materials (such as concrete from demolition) and reusing only the coarse portions, discarding the smaller ones due to their detrimental impact on the performance of both fresh and hardened concrete. Therefore, current practice can only be considered incomplete and down-cycling.

[0004] However, waste building materials often contain a significant amount of useful components, such as aggregates or binders, which in principle can be fully recycled and reused in new construction projects. Furthermore, in some regions and countries, waste disposal has become increasingly expensive and difficult due to new regulations. Therefore, the recycling of waste building materials is a crucial issue.

[0005] In the recycling of waste building materials, it is crucial to remove the aggregates contained within them from any binders or other materials adhering to or mixed with them. Thorough cleaning of the aggregates, or in other words, removal of any adhering binders or adhesives, significantly improves their reuse in the manufacture of new building materials (such as new concrete or mortar). In particular, with adequate cleaning, the recycled aggregates from the waste building materials should be able to completely replace fresh aggregates.

[0006] The recycling of waste building materials, especially mixed construction waste, using existing technologies typically requires some sorting steps, such as manual sorting or automated separation by optical detection and blowing. This sorting takes additional time and is generally inefficient.

[0007] JP 3199622 discloses a method in which recycled aggregate from concrete is obtained by crushing and screening to remove any hardened cement adhering to the aggregate.

[0008] WO 2014 / 154741 and WO 2014 / 040852 disclose methods for recycling construction waste. In these methods, the construction waste is carbonated and pulverized to produce clean aggregates and mineral powders, which can be reused, for example, in the formulation of binding materials such as concrete or mortar. WO 2014 / 154741 (page 11, lines 1-23) also describes the importance of pulverizing or disintegrating the construction waste during carbonation for rapidly removing the carbonated material from the aggregate and efficiently obtaining clean aggregates.

[0009] However, aggregates obtained from existing recycling processes of waste building materials are often not clean enough. This means that such aggregates still carry a significant amount of cementitious materials or other binders. Using such insufficiently clean aggregates in the production of, for example, concrete or mortar can impair the performance of the final product. This can be even more problematic when the binder adhering to the aggregates is not cementitious but, for example, gypsum. In particular, when using such incompletely clean aggregates, shrinkage and cracking tendencies, as well as creep properties, are often lower than design values. Recycling mixed construction waste to recover aggregates is particularly problematic. Therefore, it is currently not permitted to replace 100% of the aggregates in a concrete composition with recovered aggregates from waste building materials.

[0010] Therefore, cleaning the aggregates is paramount in the recycling of waste building materials. Further improvements are needed in the recycling processes to obtain clean aggregates and further enhance the overall efficiency of the recycling process. Invention Overview

[0012] One object of the present invention is to provide an improved method for recovering aggregates from waste building materials. In particular, one object of the present invention is to provide a method for recycling waste building materials to produce clean aggregates.

[0013] Surprisingly, the objective of this invention is achieved by the method described in claim 1.

[0014] Therefore, the present invention relates to a method for recycling materials from waste building materials, the method comprising the step of grinding the waste building materials, characterized in that the grinding is performed in a semi-autogeneous mill or on a compression mill.

[0015] The method of the present invention separates waste building materials into clean aggregates and powdered materials. It may be advantageous if the method of the present invention includes grinding in the presence of carbon dioxide.

[0016] The method of the present invention surprisingly results in more efficient aggregate cleaning during the recycling of waste building materials. In particular, the aggregate obtained by the method of the present invention carries less binder, especially cementing material, compared to aggregate obtained by prior art methods. Furthermore, the sieve width and particle shape of the aggregate obtained by the method according to the invention are optimized. This allows for the optimal use of this aggregate in the production of new building materials, particularly concrete or mortar. Moreover, the level of substitution of the recycled aggregate for the original aggregate by the present invention can be very high. Finally, the method of the present invention improves the overall efficiency of the waste building material recycling process, which is evident from the higher specific powder wear per unit time in the grinding step.

[0017] Other aspects of the invention are the subject of the independent claims. Preferred embodiments of the invention are the subject of the dependent claims. Invention Details

[0019] In a first aspect, the present invention relates to a method for recycling materials from waste building materials, the method comprising the step of grinding the waste building materials, characterized in that the grinding is carried out in a semi-automatic mill or on a compression mill.

[0020] In the context of this application, the term "waste building material" refers to any building material that contains aggregate and is not intended for its original purpose. Waste building material includes, in particular, surplus material, non-standard material, recycled material, or demolition waste. In particular, waste building material is demolition waste. In the context of this application, "waste building material" comprises aggregate and at least one binder, but its composition is not limited. In particular, waste building material can be based on different binders, inorganic or organic binders. According to a preferred embodiment, waste building material comprises at least one aggregate and at least one mineral hydraulic binder. Mineral hydraulic binders are, for example, cement, gypsum, lime, clay, latent hydraulic binders, volcanic ash, and geopolymers.

[0021] Cement can specifically be cement, especially Portland cement and slag cement as described in standard EN 197-1, calcium aluminate cement as described in standard EN 14647, and / or calcium sulfoaluminate cement. The term "gypsum" refers to various forms of CaSO4, particularly anhydrous CaSO4 gypsum, CaSO4 α- and β-hemihydrates, and CaSO4 dihydrates. The term "lime" refers to natural hydraulic lime, prepared lime, hydraulic lime, and air-hardening lime, as described in standard EN 459-1:2015. Clay can be any expanding or non-expanding clay. In particular, in the context of this application, "clay" refers to calcined clay materials, preferably bricks. Volcanic ash and potential hydraulic materials are preferably selected from calcined clays, especially metakaolin, slag, kiln ash, silica fume, fly ash, zeolite, rice husk ash, calcined tar shale, and natural volcanic ash such as pumice and volcanic ash. Geopolymers are alumino-siliceous polymers. A specific example of a geopolymer is slag activated with water glass.

[0022] According to the implementation plan, the waste building materials are waste materials selected from the group consisting of: cement-based materials (e.g., concrete and mortar), aerated concrete, gypsum-based materials (e.g., leveling materials, mortar, and stucco), limestone sand, porous filler materials (e.g., foamed glass, vermiculite, pumice, and perlite), or clay-based materials (e.g., bricks). The waste building materials can be mixtures of different materials. For example, the waste building materials can be concrete or mortar, a mixture of concrete and gypsum-based materials, a mixture of concrete and mortar, a mixture of brick and mortar, a mixture of brick, mortar, and mortar, etc. Metal fibers, especially steel fibers, polymer fibers, and / or glass may also be included in the waste building materials. However, it is preferred that the waste building materials do not contain large pieces of metal or wood.

[0023] The method of this invention can also be used to separate steel fibers and / or polymer fibers from waste building materials. Therefore, steel fibers and / or polymer fibers can be considered as aggregates herein.

[0024] According to a particularly preferred embodiment, the waste building material is waste concrete, especially waste concrete from demolition.

[0025] Prior to carrying out the method of the present invention, the waste building materials may be pretreated. Pretreatment particularly involves crushing the waste building materials and / or sorting them according to the material. In the case of crushing, it is preferable that the size of the crushed material is larger than the particle size of the largest aggregate.

[0026] In the context of this application, aggregates are any materials that do not react in the hydration reaction of mineral hydraulic binders. Typical aggregates include, for example, rocks, crushed stone, gravel, slag, sand (especially quartz sand, river sand and / or manufactured sand), foundry sand, glass, expanded glass, hollow glass beads, glass ceramics, volcanic rock, pumice, perlite, vermiculite, quarry waste, raw, fired or molten soil or clay, porcelain, electrofused or sintered abrasives, fired carriers, silica degelatinized gels, thermoplastics, thermosetting plastics, elastomers, rubber, textile fibers, plastic materials reinforced with glass or carbon fiber, fillers from the treatment of excavated sludge, sewage sludge, pulp and paper waste, incinerated paper ash, household waste incineration ash, and / or fine aggregates such as ground limestone, ground dolomite, and / or ground alumina.

[0027] According to a particularly preferred embodiment, the aggregate is selected from gravel and sand.

[0028] Preferably, the aggregate conforms to standard EN 12620:2013.

[0029] The aggregate can have various particle sizes and shapes. Typically, the aggregate of the present invention is characterized by its particle size distribution or sieve width. The particle size distribution can be determined by sieving analysis as described in standard EN 933-1. Preferably, the particle size distribution of the aggregate is according to standard EN 12620:2013. Particle shape can be expressed by platyness, flow coefficient, shape index, sphericity, or roundness. Platyness can be measured according to standard EN 933-3. The shape index can be determined according to standard EN 933-4. The flow coefficient can be determined according to standard EN 933-6. Sphericity or roundness can be determined as described in the paper by Blott et al. (SJBlott, K. Pye, Particleshape: a review and new methods of characterization in Sedimentology (2008) 55, 31-63.). The aggregate obtained in the method of the present invention is also referred to throughout the present invention as "cleaned aggregate".

[0030] The powdered material obtained by the method of the present invention specifically comprises calcite, amorphous silica, amorphous aluminum hydroxide, and aluminates. It can be used, for example, as a filler and / or auxiliary binder (SCM) in binder compositions and / or as a raw material in cement production. Depending on the elemental oxide composition of the powdered material, it can be used for different purposes. For example, in cases where the elemental oxide composition is similar to that of hydraulic mineral binders, the powdered material can be used as a filler or SCM for concrete or mortar. For example, when containing additional calcium sulfate, the powdered material can be used for the sulfation of mineral binders. The particle size of the powdered material ranges from a few nanometers to a few micrometers. Typically, the particle size of the powdered material ranges from 0-0.250 mm or 0-0.125 mm, determined by sieve analysis as described in standard EN 933-1. This facilitates the separation of the powdered material from cleaned aggregates.

[0031] The method of the present invention can be carried out on atrium mills. Particularly suitable atrium mills are semi-automatic mills and compression mills.

[0032] In the context of this application, a compression mill is a type of mill capable of applying compressive force to a bed of material to be ground. Preferably, the compressive force is applied via a rotating cylinder or rotor-stator. A compression mill can be, for example, a crusher or a roller mill. According to embodiments, a compression mill is a vertical roller mill, a horizontal roller mill, or an impact crusher with controllable and adjustable compression.

[0033] According to the implementation plan, the compressive force applied to the bed of waste building materials can be adjusted to a predetermined value. Alternatively, preferably, the residence time can be adjusted by direct adjustment or circulation of the material to be treated.

[0034] Examples of semi-automatic grinding machines are ball mills or stirred mills. According to embodiments, in the method of the present invention, grinding is carried out in a ball mill or stirred mill.

[0035] Preferably, the grinding parameters of the method of the present invention are adjusted according to the type of waste building materials and aggregates to ensure effective cleaning of the aggregates without damaging them.

[0036] According to a particularly preferred embodiment, in the method of the invention, grinding is carried out in a ball mill or a stirred mill (preferably a ball mill), wherein the filling degree of the mill is not higher than 60%, preferably not higher than 50%, more preferably not higher than 40%, even more preferably not higher than 33%, and especially not higher than 25%, in each case based on the volume of the mill.

[0037] It has been found that lower filling levels in ball mills or stirred mills result in more efficient aggregate cleaning. However, if the filling level is too low, the overall process efficiency decreases. Preferably, the filling level is not less than 5%, more preferably not less than 10%, in each case based on the total volume of the mill. Generally, the filling level must increase as the density of the grinding media increases.

[0038] According to a further embodiment, in the method of the present invention, grinding is carried out in a ball mill or a stirred mill, preferably a ball mill, and the mass ratio of waste construction material to grinding media is in the range of 0.2 to 3, preferably 0.2 to 1. It has been found that when the mass ratio of waste construction material to grinding media is higher than 3, preferably higher than 2, and more preferably higher than 1, the cleaning efficiency of the aggregate is lower. Generally, when using higher density grinding media, the mass ratio of waste construction material to grinding media should be higher, and when using lower density grinding media, the mass ratio should be lower.

[0039] According to the implementation plan, grinding is carried out in a ball mill or a stirred mill (preferably a ball mill), and the volume ratio of waste building materials to grinding media is not higher than 1.

[0040] According to a further embodiment, in the method of the present invention, grinding is carried out in a ball mill or a stirred mill, preferably a ball mill, and the grinding media are selected from steel, zirconium oxide, alumina, ceramics, natural stone, concrete or mortar, preferably balls, rods, pebbles or blocks of concrete or mortar.

[0041] According to the implementation scheme, the diameter of the grinding media is slightly larger than the target maximum particle size of the aggregate to be recovered in the method of the present invention. When steel sheets are used as the grinding media, these grinding media can be in the form of chains or chain segments, wherein the inner diameter of each chain segment is slightly larger than the target maximum particle size of the aggregate. This has the advantage that after the steel grinding media is consumed, a minimal amount of such grinding media residue is carried away through the mill outlet, because the outlet typically has a screen that can prevent material larger than the defined maximum particle size of the reclaimed aggregate.

[0042] Particularly preferred is the use of blocks of cured concrete or mortar as the grinding medium. Preferably, the blocks of cured concrete or mortar are the same waste building materials to be processed in the method of the present invention, and are larger blocks obtained from the pre-crushing of waste building materials. The blocks of cured concrete or mortar used as the grinding medium preferably have a diameter of 10-40 cm, more preferably 10-30 cm, and especially 15-30 cm. The blocks can be regular or irregular in shape. The density of the concrete or mortar used as the grinding medium can be 2.2-2.5 g / cm³. 3Higher densities are also possible, such as 2.7 or 3.0. High hardness of the concrete or mortar used as the grinding medium is also preferred. The advantage of using concrete or mortar as the grinding medium in grinding waste building materials is that it does not introduce harmful impurities during the grinding process. When steel is used as the grinding medium, the steel scraps may mix with the aggregate after grinding due to wear, requiring additional separation steps. This is not the case when using concrete or mortar as the grinding medium, as wear only results in the release of additional aggregates and powdery materials.

[0043] According to a further embodiment, in the method of the present invention, grinding is carried out in a ball mill or a stirred mill, preferably a ball mill, and the minimum size of the grinding media is greater than the maximum particle size of the aggregate to be recycled. It has been found that when the grinding media is smaller than the maximum particle size of the aggregate to be recycled, aggregate particles larger than the size of the grinding media are destroyed. For example, in a method for recycling aggregates with particle sizes between 0-32 mm, concrete blocks with an average diameter of 5 cm or larger, particularly 10 cm, 20 cm, or 40 cm, can be used.

[0044] The residence time of waste building materials in the mill is controlled by the grinding time in an intermittent grinding process, by the stirring and circulation in a semi-continuous process, or by the material input flow in a continuous grinding process. The residence time can be controlled, for example, by partially blocking the outlet of the grinding zone in a continuous process or temporarily blocking the outlet of the grinding zone in a semi-continuous or intermittent process. The residence time can be controlled to optimize overall process efficiency and aggregate cleaning efficiency. The residence time can also be controlled to optimize the particle size distribution of the aggregate obtained in the method of the present invention.

[0045] It can also control the rotation speed of semi-automatic mills, especially ball mills, to optimize grinding efficiency.

[0046] According to the implementation scheme, when grinding is carried out in a semi-automatic mill and high-density grinding media are used, the mill filling degree is no higher than 60%, preferably no higher than 50%, more preferably no higher than 30%, and no lower than 10%, preferably no lower than 15%, based on the total volume of the mill in each case. The mass ratio of waste building material to grinding media is 0.2-3, preferably 0.5-2, and the residence time is 15-45 minutes. High density in this document means a density >6 g / ml, preferably >7 g / ml. An example of high-density grinding media is steel balls.

[0047] According to the embodiment, when grinding is carried out in a semi-automatic mill and low-density grinding media are used, the mill filling degree is not higher than 40%, more preferably not higher than 30% and not less than 5%, based on the total volume of the mill in each case, and the mass ratio of waste building material to grinding media is 0.2-3, preferably 0.5-2. In the context of this application, the low density is 2-6 g / ml, preferably 2-5 g / ml, and the residence time is 10-60 minutes. One example of low-density grinding media is concrete or mortar as described above. Another example of low-density grinding media is ceramic balls.

[0048] It is possible, and in some cases preferred, to add a grinding aid in the method of the present invention. Therefore, the present invention also relates to a method as described above, characterized in that a grinding aid is added before and / or during the grinding of waste building materials.

[0049] Grinding aids are known to those skilled in the art. They may be, for example, selected from grinding aids commonly used for grinding cement clinker.

[0050] According to the implementation plan, the grinding aid is selected from polycarboxylic acid ethers, alkanolamines, sugars, sugar acids, hydrogenated sugars, superabsorbent polymers, glycols, glycerols, calcium formate, and mixtures thereof.

[0051] Suitable alkanolamines are preferably selected from monoethanolamine, diethanolamine, triethanolamine (TEA), diethanolisopropanolamine (DEIPA), ethanol diisopropanolamine (EDIPA), isopropanolamine, diisopropanolamine, triisopropanolamine (TIPA), N-methyldiisopropanolamine (MDIPA), N-methyldiethanolamine (MDEA), tetrahydroxyethylethylenediamine (THEED), and tetrahydroxyisopropylethylenediamine (THIPD), as well as mixtures of two or more of these alkanolamines. Salts of these alkanolamines may also be used.

[0052] Suitable examples of glycols are monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and polyethylene glycol, particularly polyethylene glycols having six or more ethylene units, such as PEG 200, neopentyl glycol, hexanediol, propylene glycol, dipropylene glycol, and polypropylene glycol. Mixtures of two or more different glycols, as well as mixtures of at least one glycol and glycerol, can also be used.

[0053] In one implementation, the glycerol is so-called bio-glycerol, which can be produced from renewable raw materials.

[0054] In a particularly preferred embodiment of the invention, at least one polycarboxylate ether (PCE) is used as a grinding aid. Therefore, in these embodiments, the grinding aid comprises at least one PCE or is substantially composed of at least one PCE. The PCE of the present invention comprises:

[0055] (i) Repeating unit A of general structure (I),

[0056]

[0057] and

[0058] (ii) Repeating unit B of general structure (II),

[0059]

[0060] in

[0061] Each Ru independently represents either hydrogen or methyl.

[0062] Each Rv independently represents hydrogen or COOM, where M independently represents H, an alkali metal, or an alkaline earth metal.

[0063] m = 0, 1, 2, or 3

[0064] p = 0 or 1

[0065] Each R 1 Independently -(CH2) z -[YO] n -R4, where Y is a C2 to C4 alkylene and R4 is H, C1 to C20 alkyl, -cyclohexyl, -alkylaryl or -N(-R i ) j -[(CH2) z -PO3M] 3-j ,

[0066] z = 0, 1, 2, 3 or 4, preferably 0.

[0067] n = 2-350, preferably 30-200, especially 35-200, and particularly 40-110.

[0068] j = 0, 1, or 2,

[0069] R i Represents a hydrogen atom or an alkyl group having 1-4 carbon atoms.

[0070] And M represents a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium ion.

[0071] Furthermore, the repeating units A and B in the PCE have a molar ratio of 10:90 to 90:10.

[0072] In a further preferred embodiment, z = 0. In a further preferred embodiment, z = 4.

[0073] In a particularly preferred embodiment, the PCE comprises repeating unit A of general structure (I) and repeating unit B of general structure (II), wherein the molar ratio of A to B is 20:80-80:20, more preferably 30:70-80:20, and particularly 35:65-75:25.

[0074] The PCE preferably has an average molar mass Mw of 1,000-1,000,000, more preferably 1,500-500,000, most preferably 2,000-100,000, and particularly 3,000-75,000 or 3,000-50,000 g / mol. In the case of this invention, the molar mass Mw is determined by gel permeation chromatography (GPC) using polyethylene glycol (PEG) as a standard. This technique is known to those skilled in the art.

[0075] The PCE according to the invention can be a random or non-random copolymer. Non-statistical copolymers are particularly alternating copolymers or block or gradient copolymers or mixtures thereof.

[0076] According to one embodiment, only one type of PCE is used as the grinding additive, optionally mixed with at least one other grinding additive that is not PCE. According to another embodiment, two or more types of PCE are used as the grinding additive, optionally mixed with at least one other grinding additive that is not PCE.

[0077] In this invention, "sugar" refers to a carbohydrate containing an aldehyde group. In a particularly preferred embodiment, the sugar is a monosaccharide or disaccharide. Examples of sugars include, but are not limited to, glyceraldehyde, threose, erythrose, xylose, lythose, ribose, arabinose, allose, azoose, glucose, mannose, gulose, idole, galactose, butter, fructose, sorbitol, lactose, maltose, sucrose, lactulose, trehalose, cellobiose, chitobiose, isomaltose, paragine, mannobiose, raffinose, and xylobiose. Sugars can also be used, for example, in the form of distiller's grains or molasses.

[0078] In the context of this invention, "glycolic acid" is a monosaccharide having a carboxyl group. It can belong to any category of aldonic acid, ursolic acid, uronic acid, or aldonic diacid. Preferably, it is an aldonic acid. Examples of glycolic acids that can be used in this invention include, but are not limited to, glyceric acid, xylanic acid, gluconic acid, ascorbic acid, neuraminic acid, glucuronic acid, galacturonic acid, iduronic acid, tartaric acid, mucoic acid, and glycodiacid. Gluconic acid can be in the form of a free acid or a salt. According to embodiments, the salt of glycolic acid can be a salt of a metal of Group Ia, IIa, Ib, IIb, IVb, or VIIIb of the periodic table. Preferred glycolic acid salts are salts of alkali metals, alkaline earth metals, iron, cobalt, copper, or zinc. Salts of monovalent metals such as lithium, sodium, and potassium are particularly preferred.

[0079] Hydrogenated sugars are particularly hydrogenated starch hydrolysates or hydrogenated glucose syrups. Hydrogenated sugars are produced through the partial hydrolysis of oligosaccharides and polysaccharides, which are then hydrogenated. The result is a mixture of sugar alcohols.

[0080] The term "superabsorbent polymer" refers to a polymer capable of absorbing large amounts of water. When a superabsorbent polymer comes into contact with water, water molecules diffuse into the cavities of the polymer network, hydrating the polymer chains. The polymer can thus swell and form a polymer gel or slowly dissolve. This process is reversible, so superabsorbent polymers can be regenerated to their solid state by removing the water. Water absorption performance is expressed as a swelling ratio, which is the ratio of the weight of the swollen superabsorbent polymer to its weight in its dry state. The swelling ratio is influenced by the degree of branching of the superabsorbent polymer, any cross-linking that may be present, the chemical structure of the monomers forming the superabsorbent polymer network, and external factors such as pH, the ion concentration of the solution, and temperature. Due to their ability to interact with water, superabsorbent polymers are also referred to as hydrogels.

[0081] Examples of superabsorbent polymers that can be used in the context of this invention include, but are not limited to, natural polymers such as starch, cellulose, such as cellulose ethers, chitosan or collagen, alginate, synthetic polymers such as poly(hydroxyethyl methacrylate), poly(ethylene glycol) or poly(ethylene oxide), or ionic synthetic polymers such as polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyacrylamide (PAM), polylactic acid (PLA), polyethyleneimine, polyvinyl alcohol (PVA), or polyvinylpyrrolidone.

[0082] In the context of this invention, particularly suitable superabsorbent polymers are ion-superabsorbent polymers, especially those based on acrylic acid-modified polyacrylamide, which may have a linear or cross-linked structure.

[0083] Abrasive additives can be added in a total amount of 0.01-10w%, preferably 0.05-5w, and especially 0.08-1w%, relative to the total dry weight of waste building materials.

[0084] The method of the present invention may additionally include a carbonation step of waste building materials.

[0085] The term "carbonation" is used herein to refer to the reaction of mineral binders, particularly hardened mineral binders, with CO2. For example, hardened CEM I cement is carbonated by reacting with CO2 from ambient air. Specifically, calcium carbonate is formed. The gradual carbonation of mineral binders, especially hardened mineral binders, can be measured by a decrease in pH value.

[0086] Specifically, as used herein, “carbonation” refers to the incorporation of carbon dioxide into a compound or the chemical reaction of carbon dioxide with a parent material. Therefore, “carbonation” specifically refers to the reaction of the starting material with carbon dioxide. Carbonation of cured mineral binders (e.g., mortar or concrete) occurs to some extent naturally. However, as used herein, the term “carbonation” refers to a process that intentionally enhances or accelerates carbonation compared to the natural process. This can be achieved by providing an excess of carbon dioxide.

[0087] For example, hardened mineral binders in the form of hydraulic cement, which are essentially composed of hydrates of calcium, silicates and aluminum, can react with carbon dioxide to form the corresponding carbonates.

[0088] Essentially, the microstructure of the hardened mineral binder or binder matrix determines the carbonation rate and the process from the exposed surface of the cementing material to its core carbonation front.

[0089] It has been found that cleaning aggregates becomes more effective by carbonizing waste mineral building materials. This is because carbonized mineral binders are easier to remove from the aggregate surface.

[0090] For example, the progress of carbonation can be determined in the method according to the invention by measuring the partial pressure of CO2. If the partial pressure of CO2 decreases, carbonation occurs. If the partial pressure of CO2 does not decrease further, it can be considered that carbonation is substantially complete. Alternatively, the progress of carbonation can be determined, for example, by measuring pH. If the pH decreases, carbonation occurs. If the pH does not decrease further, it can be considered that carbonation is substantially complete. This is typically the case where the pH is 7-10, preferably 7-9.

[0091] Waste building materials can be carbonated before and / or during the grinding step. However, it is preferable to perform carbonation during the grinding step. This is because carbonized material is more easily removed from the aggregate during grinding, releasing a fresh, uncarbonated surface that can then be more easily carbonized and removed. This results in particularly effective cleaning of the aggregate.

[0092] According to the implementation plan, the carbonation of the waste building materials is achieved during the grinding process.

[0093] In particular, carbonation is carried out at a CO2 level equal to or higher than the concentration present in the atmosphere. Specifically, carbon dioxide is introduced along with the process air during grinding. Particularly preferably, the CO2 level in the process air is adjusted to a level higher than the concentration present in standard atmosphere, and this level is sufficient to completely carbonate all carbonatable materials in the waste building materials within the desired residence time of the waste building materials in the semi-automatic mill or compression mill.

[0094] During carbonation, minimal moisture is required in the waste building materials and / or process air to enable carbonation. According to embodiments, the humidity of the process air in the grinding zone is between 0% and 100%, preferably between 30% and 90% relative humidity. It is preferable to limit the relative humidity in the grinding zone to avoid agglomeration of the resulting powdered material. The humidity of the process air can be adjusted to match the humidity of the waste building materials. According to embodiments, the process air has a lower relative humidity when the waste building materials are moist. In this case, the process air can be used to dry the waste building materials to avoid undesirable agglomeration. However, the method of the invention can also be operated at higher humidity, even in a water bath, for example, where the waste building materials are introduced into a semi-automatic mill or compression mill in the form of a slurry or paste. Preferably, the method of the invention is operated at a temperature above 0°C, more preferably above 20°C. Further preferably, the method of the invention is operated at a temperature not exceeding 100°C, preferably not exceeding 80°C.

[0095] It is preferable to remove fine powder and / or powdery materials from the grinding zone during the grinding process. This will improve grinding efficiency. The removal is preferably performed continuously, for example, by blowing air through the grinding zone.

[0096] The method of the present invention may further include the step of separating the cleaned aggregate and the powdered material. According to an embodiment, separation is performed at a predetermined cutoff particle size to recover regenerated cleaned aggregate having a particle size at least the predetermined cutoff particle size and / or to recover powdered material having a particle size below the predetermined cutoff particle size. According to another embodiment, the cleaned aggregate may also be separated into fractions of different particle sizes.

[0097] According to the implementation plan, the particle size fractions are 0.063-4mm, 4-8mm, and 6-16mm. Other particle size fractions are 0.063-4mm, 4-16mm, and 16-32mm. Other particle size fractions are 0-2mm, 2-8mm, 8-16mm, or 8-32mm. Other particle size fractions are 0-4mm, 4-8mm, 8-16mm, and 16-32mm. Other particle size fractions are 0.063-0.125mm, 0.125-0.25mm, and 0.25-0.355mm. Other particle size fractions are 0.08-0.16mm, 0.16-0.50mm, 0.50-1.0mm, 1.0-1.60mm, and 1.60-2.0mm. Other fractions of different particle sizes are 63-300μm, 100-600μm, 500-1200μm, and 900-1500μm.

[0098] Particle size fractions can be abbreviated; for example, a particle size fraction of 4-8 mm can be abbreviated as "4 / 8".

[0099] According to the implementation plan, separation is carried out by filtration, sieving, sedimentation, density separation, air sieving (e.g. in a cyclone separator) and / or centrifugation.

[0100] The method of the present invention can be carried out in an intermittent or continuous manner.

[0101] Secondly, the present invention relates to aggregates obtained by the methods described above. The obtained aggregates have a small amount of adhering material or no adhering material, particularly a small amount of adhesive binder or no adhesive binder. The amount of adhesive binder (especially mineral binder) or the cleanliness of the aggregates can be determined by measuring their water absorption rate according to standard EN 1097-6. ​​Adhering mineral binder will increase the water absorption rate of the aggregates. Therefore, if the water absorption rate is close to or the same as that of the same fresh aggregates, the cleanliness of the aggregates can be considered sufficient. In this document, the term "same fresh aggregates" always refers to aggregates that have never been used in building materials. For example, fresh aggregates are sand from sand pits or rivers that have never been used in concrete or mortar. According to a preferred embodiment, the difference between the water absorption rate of the cleaned aggregates and the water absorption rate of the fresh aggregates is no greater than 300% of the water absorption rate of the same fresh aggregates, preferably no greater than 200%, more preferably no greater than 150%, and especially no greater than 100%.

[0102] In particular, the difference between the water absorption rate of the cleaned aggregate and that of the fresh aggregate shall not exceed 300% of the water absorption rate of the same fresh aggregate, preferably not more than 200%, more preferably not more than 150%, and especially not more than 100%, wherein the aggregate belongs to a particle size range of 4-8 mm, 8-16 mm and / or 16-32 mm.

[0103] A particular advantage of the aggregates obtained by the method of the present invention is that they are exceptionally clean and round. The roundness of the particles can be described, for example, according to sphericity or roundness, as explained in the paper by Blott et al. (SJBlott, K. Pye, Particle shape: a review and new methods of characterization in Sedimentology (2008) 55, 31-63). Roundness measured according to the Cox method described in Blott's paper is particularly suitable. The aggregates recovered by the method of the present invention have a roundness greater than 0.70, preferably greater than 0.73, and more preferably greater than 0.76 as measured by the Cox method.

[0104] In particular, the aggregates of the present invention are more rounded than aggregates recovered from simply crushed raw materials (e.g., rocks or waste building materials). This is due to the friction applied to the edges of the aggregates during the grinding process. The aggregates of the present invention can also be more rounded than naturally occurring aggregates (e.g., sand).

[0105] Another way to measure roundness is to determine the particle shape – shape index, according to standard EN 933-4:2008.

[0106] Another particular advantage of the aggregates obtained by the method of the present invention is that they have a very stable particle size distribution. This means that the particle size distribution curve (which is a graph of the amount of particles of a given size relative to the particle size) steadily increases from very small particle sizes to very large particle sizes. Particularly preferably, there is only one inflection point in the particle size distribution curve.

[0107] This type of aggregate can also be called cleaned aggregate.

[0108] The fineness of the aggregates of the present invention depends on their particle size. Therefore, a given particle size fraction will have a given fineness. The fineness of the aggregates can be measured, for example, by the Blain method as described in standard EN 196-6:2010. According to an embodiment, the Blain fineness of the aggregates according to the present invention is not less than 1000 cm⁻¹. 2 / g. For example, the Brian fineness of the aggregate of the present invention with a particle size fraction of 0 / 4 is not less than 1000 cm. 2 / g.

[0109] It should be understood that this aspect of the invention is also related to any implementation described above and applicable.

[0110] Thirdly, the present invention relates to the use of aggregates obtained by the methods described above in the production of building materials, particularly mortar or concrete.

[0111] The aggregates obtained by the above method, also known as "cleaned aggregates," typically have a lower water absorption rate compared to other aggregates. Lower water absorption is desirable in the production of building materials because using less water generally results in higher strength of the cured material. In building materials, when using the cleaned aggregates of this invention, the amount of binder, especially cement, can also be reduced while still achieving the desired strength because the amount of mixing water required for the desired workability can be reduced. The water absorption rate of the aggregates can be measured according to standard EN 1097-6:2013-09.

[0112] The building materials described in this application context comprise aggregates and at least one binder, but their composition is not limited. In particular, the building materials can be based on various inorganic or organic binders. According to a preferred embodiment, the building materials comprise at least one aggregate and at least one mineral hydraulic binder. Examples of mineral hydraulic binders include cement, gypsum, lime, clay, latent hydraulic binders, volcanic ash, and geopolymers. These binders are described above.

[0113] The building materials described herein optionally also contain fine fillers and / or at least one additive selected from plasticizers, superplasticizers, shrinkage reducers, air-entraining agents, degassing agents, stabilizers, viscosity modifiers, water-reducing agents, accelerators, retarders, waterproofing agents, strength-enhancing additives, fibers, foaming agents, defoamers, redispersible polymer powders, chromate reducing agents, pigments, and steel passivators.

[0114] It should be understood that this aspect of the invention is also related to any implementation described above and applicable.

[0115] Fourthly, the present invention relates to building materials, preferably concrete or mortar, comprising at least a binder and aggregates obtained by the method described above, characterized in that the aggregates obtained by the method described above account for at least 30 wt% of the total weight of the aggregates, preferably at least 50 wt%, more preferably at least 75 wt%, even more preferably at least 90 wt%, and especially at least 99 wt%.

[0116] Typical building materials of the present invention comprise or consist of the following (in each case, relative to the total weight of the building materials):

[0117] a) 10-75 wt%, preferably 15-60 wt%, of a binder, preferably a mineral hydraulic binder, especially a binder selected from cement, gypsum, lime, clay, potential hydraulic binders, volcanic ash, geopolymers, or mixtures thereof.

[0118] b) 15-90 wt%, preferably 25-75 wt% aggregate.

[0119] c) optionally 0.1-10 wt% of at least one additive, and

[0120] d) Optional water

[0121] The characteristic feature is that at least 30 wt%, preferably at least 50 wt%, more preferably at least 75 wt%, even more preferably at least 90 wt%, and especially at least 99 wt% of the total weight of the aggregate is obtained by the method of the present invention.

[0122] It should be understood that this aspect of the invention is also related to any implementation described above and applicable.

[0123] Fifthly, the present invention relates to a method for reducing the water requirement of building materials, particularly mortar or concrete, the method comprising the step of replacing fresh aggregate with aggregate obtained in the method described above.

[0124] The reduction in water demand can be measured as an increase in slump flowability as measured according to standard EN 12350-5:2019-09 and / or a decrease in funnel flow time as measured according to standard EN 12350-9:2010-12.

[0125] Therefore, the methods for reducing the water demand of building materials (especially mortar or concrete) are the same as those for increasing the slump flowability of building materials (especially mortar or concrete) and / or reducing funnel flow time.

[0126] According to the implementation plan, in the method of reducing the water requirement of building materials, especially mortar or concrete, the level of replacement of fresh aggregate with aggregate obtained in the method described above is at least 30 wt% of the total weight of aggregate, preferably at least 50 wt%, more preferably at least 75 wt%, even more preferably at least 90 wt%, and especially at least 99 wt%.

[0127] It should be understood that this aspect of the invention is also related to any implementation described above and applicable.

[0128] In a sixth aspect, the present invention relates to a method for reducing the binder content in building materials, particularly the cement content in mortar or concrete, while maintaining constant strength, the method comprising the step of replacing fresh aggregate with aggregate obtained in the method of the present invention.

[0129] Particularly preferred is that the binder is a cement selected from Portland cement and slag cement (as described in standard EN 197-1), calcium aluminate cement (as described in standard EN 14647) and / or calcium sulfoaluminate cement.

[0130] In particular, in methods for reducing the content of binders in building materials, especially the cement content in mortar or concrete, while maintaining constant strength, this strength refers to the compressive strength measured after the building material has fully hardened, especially the compressive strength after 28 days of hardening.

[0131] According to the implementation plan, in a method for reducing the binder content in building materials, especially the cement content in mortar or concrete, while maintaining constant strength, the level of aggregate substitution for fresh aggregate obtained in the method described above is at least 30% by weight of the total aggregate, preferably at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 90% by weight, and especially at least 99% by weight.

[0132] It should be understood that this aspect of the invention is also related to any implementation described above and applicable.

[0133] The present invention will be further explained and illustrated by way of embodiments. These embodiments are not intended to limit the invention to any particular implementation. Example

[0134] Table 1 below shows an overview of the chemicals used.

[0135] Table 1: Raw Materials Used

[0136]

[0137] Experiment 1 - Aggregate Recovery

[0138] The waste building materials used were pre-crushed concrete from demolition (with 0-32mm main aggregates of sand and gravel).

[0139] A ball mill with a diameter of 60cm and a length of 50cm was used.

[0140] For the grinding operation, introduce the waste building materials into the mill along with the grinding media shown in the table below. Grind at medium speed for 30 minutes. Grinding is carried out at 20°C and 75% relative humidity in the process air.

[0141] Additional grinding aids (if present) are added at a total amount of 0.125% by weight relative to the waste building materials. Carbonation (if used) is carried out by introducing CO2 into the mill along with process air (6% CO2 in the process air).

[0142] The sieve width of the aggregate is determined as described in standard EN 933-1.

[0143] Table 2 below provides an overview of the embodiments performed.

[0144] Table 2: Examples (All embodiments according to the present invention)

[0145]

[0146]

[0147] *1 A fully cured concrete block (irregular shape, approximately 20cm in diameter).

[0148] *2 The mass ratio of waste building materials to grinding media in the mill.

[0149] *3 % of total mill volume

[0150] Table 3 below provides an overview of the results obtained.

[0151] Table 3: Results (based on Examples 1-14 of the present invention)

[0152]

[0153] *4 Cleanliness of aggregate as determined by water absorption rate; water absorption rate of aggregate as determined according to EN 1097-6. ​​The percentage given is relative to untreated waste building material set at 0%.

[0154] *5 :Calculated in w% / hour

[0155] *6 The maximum particle size is 32mm in all cases (100% pass rate).

[0156] When measured according to the Cox method described in Blott's paper above, the roundness of aggregates recovered by the method of this invention is between 0.73 and 0.80. The roundness of aggregates recovered from pre-crushing and not treated by the method of this invention is 0.68. The roundness of aggregates of the same type but never used in the manufacture of building materials is 0.8.

[0157] The comparison of Examples 1-3 shows that using steel balls as the grinding media results in particularly high cleaning efficiency and specific powder abrasion. However, when using steel balls as the grinding media, there is a risk of steel contamination in the obtained aggregate. Additionally, a larger quantity of small particles with a size <0.063 mm is obtained. Using ceramic balls also yields satisfactory results. Compared to grinding with steel balls, the amount of very small particles is significantly lower, and the particle size distribution is more stable, which is beneficial. Surprisingly, using concrete blocks as the grinding media also yields very satisfactory results, comparable to using ceramic balls (see Examples 2 and 3). However, when using concrete blocks as the grinding media, there is no risk of undesirable contamination of the obtained aggregate.

[0158] The comparison of Examples 3-5 shows that increasing the packing density leads to lower cleaning efficiency and lower specific powder wear. Lower cleaning efficiency and lower specific powder wear are undesirable. However, at the same residence time, higher packing density in the mill results in higher material yield, thus leading to improved overall process efficiency. Therefore, the packing density must be selected to allow for a trade-off between cleaning efficiency and material yield. When the packing density is high, the resulting feedstock tends to be coarser.

[0159] A comparison of Examples 4, 7, and 8 shows that increasing the mass ratio of waste construction material to grinding media in the mill reduces cleaning efficiency and specific powder wear. Reduced cleaning efficiency and reduced specific powder wear are undesirable. However, if the mass ratio of waste construction material to grinding media becomes too low, material production and therefore overall process efficiency may be too low. Therefore, this mass ratio must be chosen to strike a trade-off between cleaning efficiency and material production. When this mass ratio increases, the resulting aggregate tends to be coarser.

[0160] Example 9 shows that carbonation leads to increased wear on certain powders (compared to Example 5). Additionally, when grinding is performed with carbonation, the resulting aggregate tends to be finer.

[0161] Finally, Examples 10-14 demonstrate that the method for recovering the material can be further improved by adding a grinding aid. This can be seen, for example, from the higher specific powder abrasion observed in Examples 10-14 compared to Examples 5 or 9.

[0162] Table 4 below shows the results for water absorption. Water absorption was measured according to standard EN 1097-6:2013-09.

[0163] The gravel used as a reference is freshly crushed gravel used as is.

[0164] Table 4: Water absorption rate of cleaned aggregates (according to Examples 1-14 of the present invention)

[0165]

[0166] The same observations can be made as discussed with regard to the results in Table 3. In particular, the results in Table 4 show that the aggregates recovered from the method of the present invention have a much lower water absorption rate compared to untreated waste building materials. The lower water absorption rate of the aggregates is beneficial because it will allow for the formulation of cementitious materials, especially concrete or mortar, with less mixing water and therefore higher strength. It can also be seen that, at least for particle size groups 4 / 8, 8 / 16, and 16 / 32, the cleaned aggregates have water absorption rates similar to those of fresh gravel in the same particle size group. For the 0.063 / 4 particle size group, the observed difference is greater, which is likely due to the presence of finely ground mineral powder generated by the binder in this particle size group.

[0167] Test 2 - Tests in Mortar

[0168] The aggregates recovered by the method of this invention were tested in mortar formulations. The dry mortar consisted of CEM II / B-LL and aggregates, in the amounts shown in Table 5 below. The aggregates used were sand, untreated waste building materials, or aggregates recovered by the method of this invention, as shown in Table 5 below. The dry mortar was mixed with water to a water:binder ratio of 0.4. The mixture was stirred for 3 minutes on a Hobart mixer.

[0169] A commercially available polycarboxylate superplasticizer (SikaViscocrete 3088, available from Sika Schweiz AG) was added to the mixture along with water in an amount of 1 wt% relative to the binder content.

[0170] All aggregates used were water-saturated. The gradation profiles for any aggregates used are as follows:

[0171] Particle size [mm] 0.063 0.125 0.250 0.50 1.0 2.0 4.0 Vol-% through 0％ 6.7％ 15.8 28.2 45.1 68.3 100

[0172] The fineness of this coarse gradation cannot be measured with meaningful results.

[0173] Table 5 below shows an overview of the implemented embodiments and measurement results. Slump flowability was measured according to standard EN 12350-5:2019-09. Funnel flow time was measured according to standard EN 12350-9:2010-12.

[0174] Table 5: Aggregate Tests in Mortar (Examples 2-3 and 2-6 are based on the present invention)

[0175]

[0176]

[0177] *1 CDW: Untreated waste building materials

[0178] *2 Aggregate: Aggregate recovered in the method of the present invention

[0179] As can be seen from Table 5 above, when aggregates recovered by the method of the present invention are used in mortar formulations, the mortar formulations exhibit increased slump flowability and reduced funnel flow time compared to the same mortar using untreated sand or untreated waste building materials. This is the case when the gradation profiles of the individual aggregates are identical. The increased slump flowability and / or reduced funnel flow time indicate lower water requirements. The amount of mixing water in formulations containing aggregates recovered by the method of the present invention can be reduced to adapt the formulation to the same rheological properties as formulations using, for example, standard sand. Reducing the amount of mixing water is desirable because it will result in increased strength of the curing agent. Similarly, in formulations using aggregates recovered by the method of the present invention, the amount of cement and water can be reduced to achieve the same rheological properties and strength as formulations using, for example, standard sand. Cement savings are possible and / or achievable through this high level of replacement of virgin sand.

[0180] Test 3 - Tests in Mortar

[0181] The aggregates obtained by the method of the present invention were tested as follows: 750 g of cement (CEM I 42.5 N), 141 g of limestone filler (Nekafill 15 from Netstal AG), and 2999 g of aggregates (sand, concrete demolition waste, and / or aggregates according to the present invention, respectively) were mixed in a Hobart mixer for 1 minute in a dry state. The aggregates added were of the types shown in Table 6 below. The mass ratios of the aggregates used are also given in Table 6 below. Water was then added to achieve a water-to-cement ratio of 0.46. The mixed water contained 0.6 wt% PCE-1 relative to the cement. Mixing was then continued for 3 minutes. After the time shown in Table 6 below, the slump flowability was measured according to standard EN 12350-5:2019-09. All aggregates used were water-saturated.

[0182] The gradation curves of the aggregates used are as follows:

[0183] Particle size [mm] 0.063 0.125 0.250 0.50 1.0 2.0 4.0 8.0 w% pass 0.1 0.4 1.6 6.9 16.2 27.4 43.9 95.7

[0184] Table 6: Aggregate Tests in Mortar (Examples 3-3 and 3-5 are based on the present invention)

[0185] Example 3-1 3-2 3-3 3-4 3-5 sand 100 70 70 50 50 <![CDATA[CDW *1 ]]> 0 30 0 50 0 <![CDATA[Aggregate *2 > 0 0 30 0 50 Slump flowability @0min [mm] 205 135 204 121 195 Slump flowability @30min [mm] 206 131 202 118 205 Slump flowability @ 60 min [mm] 204 128 200 116 196 Slump flowability @90min [mm] 202 118 195 110 196 Slump flowability @120min [mm] 194 116 191 110 192

[0186] *1 CDW: Untreated waste building materials

[0187] *2 Aggregate: Aggregate recovered in the method of the present invention

[0188] As can be seen from the results in Table 6 above, no significant change in slump flowability was observed at the substitution level of 30 wt% of fresh aggregate obtained by the method of the present invention (see Examples 3-1 and 3-3). Therefore, substitution at this level is possible without any further action. Conversely, when using untreated building materials of the same gradation, a significant loss of slump flowability was observed when 30 wt% of fresh aggregate was replaced by such untreated waste building materials (see Examples 3-1 and 3-2).

[0189] At a replacement level of 50% fresh aggregate obtained using the method of the present invention, the observed change in slump flowability is acceptable for typical applications (see Examples 3-1 and 3-5). When using untreated waste building materials of the same gradation, a significantly reduced slump flowability is obtained (see Examples 3-1 to 3-4).

Claims

1. A method for recycling materials from waste building materials, the method comprising the step of grinding the waste building materials, characterized in that, The grinding is carried out in a ball mill or a stirred mill, and the filling degree of the ball mill or stirred mill is not higher than 25%, based on the volume of the mill in each case, and the mass ratio of waste building materials to grinding media is 0.2 to 1.

2. The method as described in claim 1, characterized in that, The grinding is carried out in a ball mill.

3. The method according to any one of claims 1-2, characterized in that, The grinding media are selected from balls, rods or pebbles made of the following materials: steel, zirconium oxide, alumina, ceramics, natural stone, concrete or mortar.

4. The method as described in claim 3, characterized in that, The grinding media are selected from balls, rods, or pebbles made of materials such as concrete or mortar.

5. The method according to any one of claims 1-2, characterized in that, The minimum size of the grinding media is greater than the maximum particle size of the aggregate to be recycled.

6. The method as described in any one of claims 1-2, characterized in that, Add a grinding aid before and / or during grinding the waste building materials.

7. The method as described in claim 6, characterized in that... The grinding aid is selected from polycarboxylic acid ethers, alkanolamines, sugars, sugar acids, hydrogenated sugars, superabsorbent polymers, glycols, glycerols, calcium formate, and mixtures thereof.

8. The method as described in claim 6, characterized in that, The grinding aid is added in an amount of 0.01-10 w%, in each case relative to the total dry weight of the waste building materials.

9. The method as described in claim 6, characterized in that, The grinding aid is added in an amount of 0.05-5 w%, in each case relative to the total dry weight of the waste building materials.

10. The method as described in claim 6, characterized in that, The grinding aid is added in an amount of 0.08-1 w%, in each case relative to the total dry weight of the waste building materials.

11. The method as described in any one of claims 1-2, characterized in that, The method also includes the step of carbonizing the waste building materials.

12. The method as described in claim 11, characterized in that, The carbonation of the waste building materials is carried out during the grinding of the waste building materials.

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