Mixed cement, method for production thereof, and use of admixture for improving performance of mixed cement

Abstract

The present invention relates to a process for the manufacture of a mixed cement comprising the step of co-grinding Portland clinker and cement-based waste material in the presence of a grinding aid selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof. The invention also relates to a mixed cement obtainable by such a method. Finally, the invention relates to the use of an admixture selected from the group consisting of alkanolamines, glycols and / or glycerol for improving the performance of mixed cement after hardening, said mixed cement comprising Portland clinker and supplemental cementitious materials recovered from cementitious waste materials.

Description

Technical Field

[0001] The present invention relates to the field of blended cement. More specifically, the present invention relates to a method for producing blended cement and a grinding aid that can be used in such a method. The present invention also relates to the field of recycling of cement-based waste materials, in particular the field of waste concrete and mortar after building demolition. Background of the Invention

[0003] For many years, the construction industry has used and continues to use cement, especially ordinary Portland cement (OPC). However, the use of OPC in particular has a high environmental footprint. A major reason is the high CO 2 emissions associated with cement manufacturing. Therefore, many efforts have been made to at least partially replace OPC as a binder in construction materials.

[0004] One possibility is to use so-called supplementary cementitious materials (SCMs) to at least partially replace OPC. Cement containing OPC and SCMs is also referred to as blended cement or composite cement. SCMs known for many years include steelmaking slag, calcined clay, natural pozzolans such as fly ash, silica fume or fly ash.

[0005] For example, WO 2018 / 228839 discloses a composite cement that can be obtained by grinding Portland clinker and potentially hydraulic materials together, optionally in the presence of an alkanolamine grinding aid, and mixing the ground materials with mineral fillers.

[0006] It is also known that hardened concrete, for example in the form of demolition waste, can be processed to recover aggregates and mineral powders suitable as SCMs. For example, a suitable method is disclosed in WO 2021 / 170501 (Sika Technology AG).

[0007] Recycling SCMs from demolition waste and using them to replace Portland cement is an important step towards a circular economy in the field of construction materials.

[0008] An important step in processing waste construction materials to recover mineral powders used as SCMs is the grinding step. In particular, methods and chemicals are needed that can improve the grinding efficiency and at the same time produce SCMs with improved properties. It is particularly desirable that such methods and chemicals can be used for the co-grinding of Portland clinker and cement-based waste materials, especially waste construction materials. Summary of the Invention

[0010] The present invention solves one or more of the following objectives:

[0011] (i) To provide a method for manufacturing blended cement having a Portland cement component and an SCM component derived from cement-based waste materials.

[0012] (ii) Provide a blended cement having a Portland cement component and an SCM component derived from cement-based waste materials.

[0013] (iii) Provide a method for improving the properties of a blended cement having a Portland cement component and an SCM component derived from cement-based waste materials. In particular, improving the compressive strength and / or shrinkage behavior of such a blended cement and construction materials containing such a blended cement.

[0014] (iv) Provide a method for improving the grinding efficiency of cement-based waste materials.

[0015] Surprisingly, it has been found that some of the objectives can be solved by the method claimed in claim 1.

[0016] Also surprisingly, it has been found that some of the objectives can be solved by the targeted use of suitable grinding aids selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof.

[0017] Thus, surprisingly, a favorable blended cement comprising Portland cement and an SCM derived from cement-based waste materials can be obtained by a method comprising the step of co-grinding Portland clinker and cement-based waste materials in the presence of a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof.

[0018] Advantages of the present invention include better activation of SCMs derived from cement-based waste materials, especially construction demolition waste, higher performance of blended cements comprising Portland cement and SCMs derived from cement-based waste materials, reduced waste due to the use of cement-based waste materials, and improved grinding efficiency of blended cements and cement-based waste materials.

[0019] Other aspects of the invention are the subject of the independent claims. Preferred embodiments are the subject of the dependent claims.

[0020] Method for implementing the present invention

[0021] In a first aspect, the present invention relates to a method for manufacturing a blended cement, the method comprising the following steps:

[0022] (1) Provide Portland clinker,

[0023] (2) Provide cement-based waste materials,

[0024] (3) Provide a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof, and

[0025] (4) Co-grind Portland clinker and cement-based waste materials in the presence of said grinding aid.

[0026] In this document, the terms "composite cement" and "blended cement" can be used interchangeably. Both terms refer to a cement that comprises a mixture of at least one hydraulic material and at least one other material, which may be another hydraulic material, a pozzolan, a latent hydraulic material, a non-hydraulic material or a filler.

[0027] A hydraulic material or hydraulic binder is a material that reacts with water in a hydraulic reaction to form a solid hydrate phase. Hydraulic materials are in particular cements, preferably Portland cements. According to EN 206-1, pozzolans and latent hydraulic materials are in particular type II concrete additives having latent hydraulic and / or pozzolanic properties. Typical pozzolans include volcanic ash, pumice, calcined oil shale, clay, calcined clay, rice husk ash, microsilica, silica fume and fly ash. Typical latent hydraulic materials are slags, in particular granulated blast furnace slag and basic oxygen furnace slag.

[0028] In this document, Portland clinker is a sintered product obtained in a cement kiln from limestone and aluminosilicate materials at high temperature. The term "clinker" refers to the unground material, which usually occurs in lumps or nodules. The Portland clinker used in this document can be any type of Portland clinker. The typical phase composition of Portland clinker is 45-80 w% C 3 S, 1-40 w% C 2 S, 0-15 w% C 3 A and 0-20 w% C 4 AF (where "C" represents CaO, "S" represents SiO 2 ,"A" represents Al 2 O 3 ,"F represents Fe 2 O 3 ). The typical chemical composition of Portland clinker is 55-75 w% CaO, 15-25 w% SiO 2 , 2-6 w% Al 2 O 3 , 0-6 w% Fe 2 O 3 , 0-2 w% MgO and 0-2 w% SO 3 .

[0029] The term "cement" in this document refers to the ground material. Thus, for example, Portland cement is a cement obtained by grinding Portland clinker. The Blaine fineness of Portland cement can be in the range of 2500 cm 2 / g to 12000 cm 2 / g, preferably 3000 cm 2 / g to 9000 cm 2 / g, especially 3500 cm 2 / g to 8000 cm 2 / g. The Blaine fineness can be measured according to DIN EN 196-6:2018.

[0030] In this document, the term "cement-based waste material" refers to any cement-based material that cannot be used for its intended purpose or has reached the end of its service life. In this document, a cement-based material is a material that contains at least one hydraulic binder, especially at least one cement. The hydraulic binder can be in an unhardened state, or can be partially or fully hardened. According to certain embodiments, the cement-based waste material contains at least 5 w%, preferably at least 10 w%, more preferably at least 20 w% of at least one hydraulic binder, especially cement, in an unhardened, partially hardened or fully hardened state. In particular, the cement-based waste material is waste construction material. For example, waste construction material is surplus material, defective material, returned material or demolition waste. In particular, the cement-based waste material is demolition waste. According to an embodiment, the cement-based waste material contains aggregate and at least one hydraulic binder, but its composition is not limited. Particularly preferred cement-based waste materials are concrete, especially surplus concrete, defective concrete or demolished concrete.

[0031] The cement-based waste material can be a mixture of different materials. For example, the cement-based waste material can be a mixture of concrete or mortar, concrete and gypsum-based materials, concrete and stucco, bricks and mortar, bricks, mortar and stucco, etc. Metal fibers, especially steel fibers, polymer fibers and / or glass may also be included in the cement-based waste material. In particular, the cement-based waste material contains unhardened, partially hardened or fully hardened cement, aggregate and filler. However, it is preferred that the cement-based waste material does not contain large pieces of metal or wood.

[0032] The cement-based waste material can be pretreated before being used in the method of the present invention. The pretreatment is especially the crushing and / or sorting of the cement-based waste material according to the material. When crushing, the particle size of the crushed material is preferably larger than the particle size of the largest aggregate. Another pretreatment can be the sorting of the cement-based waste material to separate the cement-based material from metal, wood, plastic, paper and / or gypsum. For example, the sorting can be done with a magnet or density separation.

[0033] Advantageously, the cement-based waste material contains some ceramic materials. For example, the cement-based waste material can contain up to 25 w% of ceramic materials, preferably 1-5 w% of ceramic materials.

[0034] Grinding cement-based waste materials generally contain aggregates and supplementary cementitious materials. The supplementary cementitious materials are especially hydraulic, pozzolanic and / or latent hydraulic materials used for manufacturing the original cementitious materials, which can be in a hardened or unhardened state, preferably hardened.

[0035] The grinding aids of the present invention are selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof. The grinding aids of the present invention can be formulated into a solution or dispersion in a liquid, especially in water. Therefore, the grinding aids of the present invention can be in the form of a solution or dispersion of alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof in a liquid, especially in water. Hereinafter, all dosage ranges of the grinding aids refer to alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof, excluding any liquid, especially water.

[0036] The alkanolamines are preferably selected from monoethanolamine, diethanolamine, triethanolamine (TEA), diethanol isopropanolamine (DEIPA), ethanol isopropanolamine (EDIPA), isopropanolamine, diisopropanolamine, triisopropanolamine (TIPA), N-methyl diisopropanolamine (MDIPA), N-methyl diethanolamine (MDEA), tetra-hydroxyethyl ethylene diamine (THEED) and tetra-hydroxyisopropyl ethylene diamine (THIPD), and mixtures of two or more of these alkanolamines. According to a particularly preferred embodiment, the alkanolamines are selected from TEA, TIPA, DEIPA, MDEA or mixtures thereof.

[0037] According to an embodiment, the diols are selected from ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, hexylene glycol. Preferably, the diol is diethylene glycol.

[0038] The carbohydrates of the present invention belong to the group of monosaccharides or disaccharides. Examples of suitable carbohydrates include, but are not limited to, glyceraldehyde, threose, erythrose, xylose, lyxose, ribose, arabinose, allose, altrose, glucose, mannose, gulose, idose, galactose, tagatose, fructose, sorbose, lactose, maltose, sucrose, lactulose, trehalose, cellobiose, chitobiose, isomaltose, palatinose, mannotriose, raffinose and xylobiose. The carbohydrates can also be used in the form of distillers' grains, molasses, etc.

[0039] Herein, the chloride is preferably a chloride of an alkali metal or an alkaline earth metal. In particular, the chloride is sodium chloride or calcium chloride.

[0040] Particularly preferred grinding aids are mixtures of diethylene glycol and glycerol. Another particularly preferred grinding aid is a mixture of triisopropanolamine (TIPA) and diethanol isopropanolamine (DEIPA). Another particularly preferred grinding aid is a mixture of alkanolamines (especially triisopropanolamine (TIPA) or diethanol isopropanolamine (DEIPA)), carbohydrates, and chlorides (especially sodium chloride or calcium chloride).

[0041] The co-grinding in the method of the present invention can be carried out on a grinding machine. Particularly suitable grinding machines are semi-autogenous mills and compressive grinding machines. The compressive grinding machine herein is a grinding machine capable of applying a compressive force to the material bed to be ground. Preferably, the compressive force is applied by a rotating cylinder or a rotor stator. For example, the compressive grinding machine can be a crusher or a roller mill. According to a preferred embodiment, the compressive grinding machine is a vertical roller mill or a horizontal roller mill. Examples of semi-autogenous mills are ball mills or stirred mills. According to an embodiment, in the method of the present invention, the grinding is carried out in a ball mill or a stirred mill.

[0042] The grinding can be carried out batchwise or continuously. Thus, the method of the present invention can be an intermittent process or a continuous process.

[0043] The term "co-grinding" refers to the grinding of Portland clinker and cement-based waste materials in the presence of a grinding aid. In this text, the terms "grinding" and "milling" can be used interchangeably.

[0044] The co-grinding of the present invention is preferably dry. This means that, relative to the total weight of the solid materials to be ground, the amount of water present during the grinding process is less than 10% by weight, preferably less than 5% by weight, especially less than 2% by weight.

[0045] Preferably, the grinding aid is sprayed onto the Portland clinker and cement-based waste materials inside the mill. It is also possible to add the grinding aid to the Portland clinker and / or cement-based waste materials on the conveyor belt feeding the mill. This is particularly preferred when the method of the present invention is a continuous process.

[0046] In the method of the present invention, there may be other materials different from Portland clinker and cement-based waste materials in the co-grinding step. Such other materials are preferably selected from gypsum, pozzolans, and / or latent hydraulic materials. Pozzolans and latent hydraulic materials are as described above. According to an embodiment, in the method of the present invention, gypsum, pozzolans, and / or latent hydraulic materials are also present during the grinding process, where the pozzolans and / or latent hydraulic materials are different from the cement-based waste materials.

[0047] Preferably, in the co-grinding step, the Portland clinker and the cement-based waste are present in a specific weight ratio.

[0048] According to an embodiment, in the method of the present invention, the weight ratio of Portland clinker to cement-based waste materials is between 1:1 and 10:1, preferably between 2:1 and 6:1, and particularly between 2.5:1 and 5:1.

[0049] If the weight ratio falls outside these ranges, the properties of the resulting blended cement after mixing with water and / or hardening, especially workability, shrinkage and / or compressive strength, are not optimal. For example, if the proportion of cement-based waste materials is too large, the compressive strength of the resulting blended cement after hardening may decrease.

[0050] According to an embodiment, in the method of the present invention, the grinding aid is present in an amount of 40 - 2500 ppm, preferably 100 - 1500 ppm, and particularly 800 - 1200 ppm, relative to the total dry weight of Portland clinker, cement-based waste materials, and, if present, gypsum, pozzolan and latent hydraulic materials. Throughout this text, the term "ppm" means "parts per million".

[0051] The method of the present invention may additionally include a step of particle size separation.

[0052] According to an embodiment, the separation is carried out at a predetermined cut-off particle size in order to separate the clean aggregate from the cement-based waste materials from the produced blended cement. The particle size of the aggregate is equal to or greater than the predetermined cut-off particle size. According to an embodiment, the separation is carried out by filtration, screening, sedimentation, density separation, air screening (e.g., in a cyclone) and / or centrifugation.

[0053] This size separation results in the recovery of the aggregate and supplementary cementitious materials (SCM), which then form part of the blended cement.

[0054] However, the SCM obtained by grinding the cement-based waste materials may also contain aggregate.

[0055] The blended cement of the present invention may contain other materials. In particular, such other materials may be other SCM and / or fillers. Suitable other materials are especially gypsum, pozzolan, latent hydraulic materials and / or fine limestone powder. Other materials, especially gypsum, pozzolan and / or latent hydraulic materials, may have been added before or during the co-grinding step of the method of the present invention. This may be particularly useful when the hardness and grindability of the other materials are similar to those of Portland clinker and cement-based waste materials. However, in a separate step of mixing the dry powder, after the co-grinding step, other materials, especially limestone, may also be added. This may be particularly useful when the hardness and grindability of the other materials are different from those of Portland clinker and cement-based waste materials.

[0056] Thus, according to an embodiment, in the method of the present invention, the grinding mixture is mixed with one or more mineral fillers, preferably with limestone.

[0057] Preferably, in the method of the present invention, there is no carbonation in the step of co-grinding Portland clinker and cement-based waste materials. This means that, in the co-grinding step, the Portland clinker and the cement-based waste materials do not react with CO 2 2.

[0058] In another aspect, the present invention relates to a blended cement obtained by the above method.

[0059] Any of the above-mentioned preferences also apply to this aspect.

[0060] Preferably, the blended cement is in the form of dry powder. The Blaine fineness of the blended cement can be in the range of 2500 cm 2 2[ / g] to 12000 cm 2 2[ / g], preferably 3000 cm 2 2[ / g] to 9000 cm 2 2[ / g], especially 3500 cm 2 2[ / g] to 8000 cm 2 2[ / g]. The Blaine fineness can be measured according to DIN EN 196-6:2018.

[0061] According to an embodiment, the blended cement of the present invention comprises or consists of the following components (unless otherwise specified, relative to the total dry weight of the blended cement)

[0062] a) 60 - 90% by weight, preferably 70 - 80% by weight of Portland clinker,

[0063] b) 5 - 35% by weight, preferably 15 - 25% by weight of cement-based waste materials,

[0064] c) Optionally 1 - 10% by weight, preferably 5% by weight of gypsum, and

[0065] d) Relative to the combined total dry weight of the Portland clinker, cement-based waste materials and gypsum (if present), 40 - 2500 ppm, preferably 100 - 1500 ppm, especially 800 - 1200 ppm of a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof.

[0066] In another aspect, the present invention relates to construction materials, especially concrete or mortar, which comprise the blended cement as described above.

[0067] Any of the above-mentioned preferences also apply to this aspect.

[0068] The composition of the construction material is not particularly limited as long as it contains the blended cement of the present invention.

[0069] For example, the construction material of the present invention may additionally contain aggregates such as rock, crushed stone, gravel, sand especially quartz sand, river sand and / or manufactured sand, glass, expanded glass, hollow glass beads, glass ceramics, biogenic materials such as hemp fiber or cork, and synthetic organic materials such as rubber.

[0070] The construction material of the present invention may also contain any other additives common in the mortar and concrete industries. In particular, such other additives are selected from plasticizers, superplasticizers, shrinkage reducing agents, air-entraining agents, air-removing agents, stabilizers, viscosity regulators, thickeners, water reducing agents, retarders, waterproofing agents, fibers, foaming agents, defoaming agents, redispersible polymer powders, dust suppressants, chromate reducing agents, pigments, biocides, corrosion inhibitors and steel passivators. The other additives are chemically different from the above-mentioned grinding aids.

[0071] According to a preferred embodiment, the construction material of the present invention is concrete or mortar.

[0072] The construction material of the present invention can be in dry form or wet form. Here, the dry form means that the construction material is in the form of a free-flowing powder with a water content of not more than 10% by weight, preferably not more than 5% by weight, especially not more than 1% by weight. Here, the wet form means that the construction material is mixed with water. According to the embodiment, the weight mixing ratio of water to the blended cement is between 0.1 - 1.0, preferably 0.2 - 0.6.

[0073] In another aspect, the present invention relates to the use of an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof for reducing the shrinkage of a blended cement or a construction material containing the blended cement during the hardening process, wherein the blended cement contains Portland cement and supplementary cementitious materials recovered from cement-based waste materials.

[0074] Very preferably, the blended cement contains co-grinding of Portland clinker and supplementary cementitious materials recovered from cement-based waste materials in the presence of an admixture. The term "co-grinding in the presence of an admixture" means that the Portland clinker and the supplementary cementitious materials recovered from cement-based waste materials are ground together in the presence of the admixture.

[0075] Any of the above-mentioned preferred features also apply to this aspect.

[0076] In particular, the blended cement is the cement obtained by the above method. However, in this regard, the blended cement can also be obtained by mixing Portland cement and ground cement-based waste materials. The methods for obtaining Portland cement are known to those skilled in the art. In the present context, the ground cement-based waste materials are preferably obtained by the above method and do not contain Portland clinker.

[0077] According to a preferred embodiment, an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof is added to the Portland clinker and / or the cement-based waste materials before or during grinding of the Portland clinker and / or the cement-based waste materials.

[0078] However, an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof can also be added to the Portland cement, the supplementary cementitious materials recovered from the cement-based waste materials or mixtures thereof after grinding.

[0079] Thus, according to a preferred embodiment, the Portland clinker and / or the cement-based waste materials are ground or co-ground in the presence of an admixture.

[0080] The admixture can contain other materials in addition to alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof. For example, the admixture can take the form of a solution or dispersion of alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof in a liquid, especially in water.

[0081] In particular, the building materials are as described above.

[0082] When water is added, the blended cement or the building material of the present invention starts to harden.

[0083] In the present context, shrinkage relates to dimensional stability and can be measured according to standard EN 12617-4.

[0084] Reducing shrinkage is desirable because it results in less cracking, thereby extending the service life of any object obtained by hardening the blended cement or the building material of the present invention.

[0085] In another aspect, the present invention relates to the use of an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof for increasing the compressive strength after hardening of a blended cement or a building material comprising the blended cement, the blended cement comprising Portland cement and supplementary cementitious materials recovered from cement-based waste materials.

[0086] Any of the above preferences also apply to this aspect.

[0087] In particular, the blended cement is the cement obtained by the above method. However, in this regard, the blended cement can also be obtained by mixing Portland cement and ground cement-based waste materials. The methods for obtaining Portland cement are known to those skilled in the art. In this text, the ground cement-based waste materials are preferably obtained by the above method and do not contain Portland clinker.

[0088] According to a preferred embodiment, an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof is added to the Portland clinker and / or the cement-based waste materials before or during the grinding of the Portland clinker and / or the cement-based waste materials.

[0089] However, it is also possible to add an admixture selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof to the Portland cement, the SCM recovered from the cement-based waste materials or mixtures thereof after grinding.

[0090] Therefore, according to a preferred embodiment, the Portland clinker and / or the cement-based waste materials are ground or co-ground in the presence of an admixture.

[0091] The admixture may contain other materials in addition to alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof. For example, the admixture may take the form of a solution or dispersion of alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof in a liquid, especially in water.

[0092] In particular, the building materials are as described above.

[0093] When water is added, the blended cement or the building material of the present invention begins to harden.

[0094] The compressive strength can be measured on 4x4x16 cm prisms according to standard EN 12190.

[0095] An increased compressive strength is desired because this results in an increased load-bearing capacity of any object obtained by hardening the blended cement or the building material of the present invention. In the case of achieving a higher load-bearing capacity of the object, the engineering design of the object can be adjusted to use less hydraulic binder in the building material and / or reduce the thickness of the object.

[0096] In another aspect, the present invention relates to the use of a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof for improving the grinding efficiency of cement-based waste materials, wherein the grinding is carried out without carbonizing the cement-based waste materials.

[0097] Any of the above preferred features also apply to this aspect.

[0098] In this regard, preferred grinding aids are selected from TEA, TIPA, DEIPA, MDEA, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, carbohydrates, sodium chloride, calcium chloride or mixtures thereof. The admixture may take the form of a solution or dispersion of an alkanolamine, a diol, glycerol, a carbohydrate, a chloride or mixtures thereof in a liquid, especially in water.

[0099] According to an embodiment, in this regard, based on the dry weight of the cement-based waste material, the amount of the grinding aid is 100 - 1500 ppm, preferably 250 - 1200 ppm, especially 400 ppm or 1000 ppm.

[0100] Higher grinding efficiency can be increasing the fineness of the ground material within the same grinding time. Higher grinding efficiency can also be reducing the grinding time to achieve the same fineness of the ground material. Higher grinding efficiency can also be reducing the energy consumption of the mill to achieve the same fineness of the ground material. For example, the latter may be due to a more stable grinding bed or less vibration of the mill.

[0101] In this regard, during the grinding of the cement-based waste material, there is no carbonation. This means that in the co-grinding step, Portland clinker and the cement-based waste material do not react with CO 2 react.

[0102] In this regard, the cement-based waste material can be co-ground with other hydraulic materials, pozzolans and / or potentially hydraulic materials.

[0103] Preferably, during or after the grinding of the cement-based waste material, the particles are size-separated. According to an embodiment, the separation is carried out at a predetermined cut-off particle size in order to separate the clean aggregate from the cement-based waste material from the produced blended cement. The particle size of the aggregate is equal to or greater than the predetermined cut-off particle size. By this procedure, the aggregate is separated from the supplementary cementitious material. According to an embodiment, the separation is carried out by filtration, screening, sedimentation, density separation, air screening (e.g., in a cyclone) and / or centrifugation.

[0104] The following examples will provide other embodiments of the present invention to those skilled in the art. Examples

[0105] Example 1

[0106] The cement-based waste material used was pre-crushed concrete after demolition (containing primary aggregate sand and gravel with a size of 0 - 32 mm). A jaw crusher was used to pre-crush the cement-based waste material. Then the pre-crushed material was screened, and the 2 - 4 mm fraction was used for Example 1 (hereinafter referred to as RCD-1). Before grinding, RCD-1 was dried at 105 °C.

[0107] A laboratory ball mill with steel balls was used. For grinding, 300 g of RCD-1 was introduced into the ball mill together with 260 g of steel balls (diameter 45 - 49 mm). The container and the balls were preheated to 105 °C. The grinding aids of the type and amount shown in Table 1 below were added to the mill. Then it was ground for 15 minutes.

[0108] According to Standard EN 196-6:2010, the particle size of the ground RCD-1 was tested by sieving. Table 1 below shows the results.

[0109] Table 1: Examples 1-1 to 1-10 (Example 1-1 is not of the present invention)

[0110] Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 1-10 Grinding aid* none D D D G G G D+G D+G D+G Dosage [ppm] 250 500 1000 250 500 1000 100 200 400 R 32μm [%]** 47 29 25 23 27 26 23 29 25 24 R 45μm [%]** 21 17 14 12 16 15 10 18 16 14 D90 [μm]*** 75.4 64.1 56.2 55.2 63.6 59.1 54 72.8 70.9 63.9

[0111] * D: Diethylene glycol, G: Glycerol, D+G: 1:3 mixture of diethylene glycol and glycerol

[0112] ** w% retained on the sieve

[0113] *** Particle size at which 90 w% of the particles are smaller than it

[0114] As can be seen from Table 1, the addition of the grinding aid led to a decrease in the particle size D90 and a reduction in the retention rate on the 32 μm and 45 μm sieves. Thus, finer particles were obtained within the same grinding time.

[0115] Example 2

[0116] The cement-based waste materials used were the same as those in Example 1.

[0117] Portland clinker CEMI 52.5R was used (according to Standard EN 197-1).

[0118] A laboratory ball mill with steel balls was used. For grinding, a mixture of 10 kg of Portland clinker, gypsum and RCD-1 in the corresponding proportions shown in Table 3 below together with steel balls (diameter 45 - 49 mm) was introduced into the ball mill. The container and the balls were preheated to 100 °C. The corresponding amounts of grinding aids (in all cases a mixture of TIPA and DEIPA in a weight ratio of 2:1) (ppm) relative to the total weight of Portland clinker, gypsum and RCD-1 as shown in Table 3 below were added to the mill. Then it was ground for 2 hours.

[0119] Then the resulting blended cement is mixed with water to obtain a water-cement ratio of 0.5. After the time shown in Table 3 below, the shrinkage rate of the resulting mixture is tested according to Standard EN 12617-4. After the time shown in Table 3 below, the compressive strength is measured on 4x4x16 cm prisms according to Standard EN 12190.

[0120] Table 3: Examples 2-1 to 2-7 (Examples 2-1, 2-2, 2-4 are not of the present invention)

[0121] Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 Portland clinker [%] 95 80 80 70 70 70 70 Gypsum [%] 5 5 5 5 5 5 5 RCD-1 [%] 0 15 15 25 25 25 25 Grinding aid [ppm] none none 800 none 400 600 800 <![CDATA[10h shrinkage rate [μm / m] * > -80 -210 -155 n.m. n.m. n.m. n.m. Compressive strength at 2 days [MPa] 36 31 37 27 29 29 31 Compressive strength at 7 days [MPa] 48 42 47 37 39 40 41 Compressive strength at 28 days [MPa] 55 50 53 42 44 46 48

[0122] * Negative values indicate shrinkage and positive values indicate expansion

[0123] n.m.: Not measured

[0124] From the above results, it can be seen that compared with the cement containing only Portland clinker (see Examples 2-1, 2-2, 2-4), the addition of RCD-1 results in an increase in the shrinkage rate. The addition of the grinding aid of the present invention results in a significant reduction in the shrinkage rate (see Example 2-3 vs. 2-2, and 2-5 vs. 2-4).

[0125] Replacing Portland clinker with RCD-1 powder also results in a decrease in the compressive strength (see Examples 2-1, 2-2, 2-4). The addition of the grinding aid of the present invention results in a significant increase in the compressive strength (see Example 2-3 vs. 2-2, and 2-5 to 2-7 vs. 2-4).

[0126] Example 3

[0127] The cement-based waste materials used are the same as those in Example 1.

[0128] Use Portland clinker of CEMI 52.5R (according to Standard EN 197-1).

[0129] A laboratory ball mill with steel balls was used. For grinding, a mixture of 10 kg of Portland clinker, gypsum, and the corresponding proportions of RCD-1 as shown in Table 4 below was introduced into the ball mill together with steel balls (diameter 45 - 49 mm). The container and the balls were preheated to 100 °C. The corresponding amounts of grinding aids (in all cases a mixture of TIPA and DEIPA with a weight ratio of 2:1) (ppm) relative to the total weight of Portland clinker, gypsum, and RCD-1 as shown in Table 4 below were added to the mill. Then it was ground for 2 hours.

[0130] The resulting blended cement is then mixed with water to obtain a water-cement ratio of 0.5. After the times shown in Table 4 below, the shrinkage of the resulting mixture is tested according to Standard EN 12617-4. After the times shown in Table 4 below, the compressive strength is measured on 4 x 4 x 16 cm prisms according to Standard EN 12190.

[0131] Table 4: Examples 3-1 to 3-6

[0132]

[0133]

[0134] * Negative values indicate shrinkage and positive values indicate expansion

[0135] As can be seen from the results in Table 4, the use of a grinding aid at a weight ratio of Portland clinker to cement-based waste materials of 3.75:1 enables a particularly low 14-day shrinkage (see Examples 3-1 to 3-3). It can further be seen that an increase in the grinding aid dosage does not result in a significant increase in the compressive strength, but may result in a higher shrinkage (see Examples 3-4 to 3-6).

Claims

1. Method for manufacturing blended cement, said method comprises the following steps: (1) Providing Portland clinker, (2) Providing cement-based waste materials, (3) Providing a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof, and (4) Co-grinding Portland clinker and cement-based waste materials in the presence of said grinding aid.

2. The method according to claim 1, characterized in that the weight ratio of Portland clinker to cement-based waste materials is between 1:1 and 10:1, preferably between 2:1 and 6:1, especially between 2.5:1 and 5:

1.

3. The method according to at least one of claims 1-2, characterized in that gypsum, pozzolan and / or latent hydraulic materials are also present during the grinding process, wherein the pozzolan and / or latent hydraulic materials are different from said cement-based waste materials.

4. The method according to at least one of claims 1-3, characterized in that relative to the combined total dry weight of Portland clinker, cement-based waste materials and, if present, gypsum, pozzolan and latent hydraulic materials, the grinding aid is present in an amount of 40-2500 ppm, preferably 100-1500 ppm, especially 800-1200 ppm.

5. The method according to at least one of claims 1-4, characterized in that the grinding aid is selected from triethanolamine, triisopropanolamine, diethanol isopropanolamine, N-methyldiethanolamine, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, carbohydrates, sodium chloride, calcium chloride or mixtures thereof.

6. The method according to at least one of claims 1-5, characterized in that it further comprises a step of particle size separation.

7. Blended cement obtainable by the method according to at least one of claims 1-6.

8. The blended cement according to claim 7, characterized in that it contains (unless otherwise stated, relative to the total dry weight of the blended cement): a) 60-90 wt%, preferably 70-80 wt% of Portland clinker, b) 5-35 wt%, preferably 15-25 wt% of cement-based waste materials, c) Optionally 1-10 wt%, preferably 5 wt% of gypsum, and d) Relative to the combined total dry weight of Portland clinker, cement-based waste materials and, if present, gypsum, 40-2500 ppm, preferably 100-1500 ppm, especially 800-1200 ppm of a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof.

9. Construction materials, especially concrete or mortar, comprising the blended cement according to at least one of claims 7 or 8.

10. Use of an admixture selected from alkanolamines, diols and / or glycerol for reducing the shrinkage of blended cement or construction materials containing blended cement during the hardening process, said blended cement comprising Portland cement and supplementary cementitious materials recovered from cement-based waste materials.

11. Use of an admixture selected from alkanolamines, diols and / or glycerol for increasing the compressive strength after hardening of a blended cement or a construction material comprising a blended cement, said blended cement comprising Portland cement and supplementary cementitious materials recovered from cement-based waste materials.

12. The use according to claim 10 or 11, characterized in that the admixture is added to the Portland clinker and / or the supplementary cementitious materials before or during grinding of the Portland clinker and / or the supplementary cementitious materials.

13. Use of a grinding aid selected from alkanolamines, diols, glycerol, carbohydrates, chlorides or mixtures thereof for improving the grinding efficiency of cement-based waste materials, wherein the grinding is carried out without carbonating the cement-based waste materials.

14. The use according to at least one of claims 10-13, characterized in that the admixture or the grinding aid is selected from triethanolamine, triisopropanolamine, diethanol isopropanolamine, N-methyldiethanolamine, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, hexylene glycol, glycerol, carbohydrates, sodium chloride, calcium chloride or mixtures thereof.

15. The use according to at least one of claims 13 or 14, characterized in that the amount of the grinding aid is 100-1500 ppm, preferably 250-1200 ppm, in particular 400 ppm or 1000 ppm, relative to the dry weight of the cement-based waste materials.

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