Blended cement, its manufacturing method and use of admixtures to enhance the performance of blended cement - Patent Application 20070122997

Abstract

The present invention relates to a method for producing a blended cement, the method comprising the step of co-grinding Portland clinker and cementitious waste in the presence of a grinding aid selected from an alkanolamine, a glycol, glycerol, a carbohydrate, a chloride or mixtures thereof. The invention also relates to a blended cement obtainable by such a method. Finally, the invention relates to the use of an admixture 10 selected from an alkanolamine, a glycol and / or glycerol to enhance the hardened performance of a blended cement comprising Portland clinker and auxiliary cementitious material recovered from cementitious waste.

Description

[Technical Field]

[0001] The present invention relates to the field of blended cements. More particularly, the present invention relates to a method for producing blended cements and to grinding aids useful in such methods. The present invention also relates to the field of recycling cementitious waste, particularly waste concrete and mortar from building demolition. [Background technology]

[0002] For many years, cement, especially ordinary Portland cement (OPC), has been used in the construction industry and continues to be used. However, the use of OPC in particular has a high environmental footprint. One of the main reasons is the high CO2 emissions associated with the production of cement. Therefore, many efforts are being made to at least partially replace OPC as a binder in building materials.

[0003] One possibility is the use of so-called supplementary cementitious materials (SCMs) to at least partially replace OPC. Cements containing OPC and SCMs are also called blended or composite cements. SCMs that have been known for many years include steel slag, calcined clay, natural pozzolans such as volcanic ash, silica fume, or fly ash.

[0004] For example, WO 2018 / 228839 discloses a composite cement that can be obtained by grinding Portland clinker and a latent hydraulic material together, optionally in the presence of an alkanolamine grinding aid, and combining the ground materials with an inorganic filler.

[0005] 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 SCM. One suitable process is disclosed, for example, in WO 2021 / 170501 (Sika Technology AG).

[0006] The recovery of SCM from demolition waste and its use to replace Portland cement represents an important step towards a circular economy in the field of building materials.

[0007] One of the key steps in the processing of waste building materials for the recovery of mineral powders useful as SCMs is the grinding step. Particularly desirable are methods and chemicals that can improve grinding efficiency while simultaneously yielding SCMs with improved properties. Particularly desirable are methods and chemicals that can be used to co-grind Portland clinker with cementitious waste, especially waste building materials. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention solves one or more of the following objectives:

[0009] (i) A method for producing a blended cement, the blended cement having a content of Portland cement and a content of SCM obtained from cementitious waste is provided.

[0010] (ii) Providing a blended cement having a content of Portland cement and a content of SCM obtained from cementitious waste.

[0011] (iii) To provide a method for improving the performance of blended cements having a content of Portland cement and a content of SCM obtained from cementitious waste, in particular improving the compressive strength and / or shrinkage behavior of such blended cements and building materials containing such blended cements.

[0012] (iv) To provide a method for improving the grinding efficiency of cementitious waste. [Means for solving the problem]

[0013] Surprisingly, it has been found that several objects can be solved by a method according to claim 1.

[0014] It has also surprisingly been found that several objectives can be achieved by the targeted use of suitable grinding aids selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof.

[0015] Thus, surprisingly, advantageous blended cements comprising Portland cement and SCM obtained from cementitious waste can be obtained by a process comprising co-grinding Portland clinker and cementitious waste in the presence of a grinding aid selected from an alkanolamine, a glycol, glycerol, a carbohydrate, a chloride, or mixtures thereof.

[0016] Advantages of the present invention include better activation of SCM obtained from cementitious waste, especially construction demolition waste, higher performance of blended cements comprising Portland cement and SCM obtained from cementitious waste, reduction of waste by using cementitious waste, and improved grinding efficiency of blended cement and cementitious waste.

[0017] Further aspects of the invention are the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0018] In a first aspect, the present invention provides a method of making a blended cement, comprising: (1) providing Portland clinker; (2) providing cementitious waste; (3) providing a grinding aid selected from an alkanolamine, a glycol, a glycerol, a carbohydrate, a chloride, or a mixture thereof; (4) co-grinding Portland clinker and cementitious waste in the presence of said grinding aid; The present invention relates to a method comprising:

[0019] In this context, the terms "blended cement" and "composite cement" are used interchangeably: both terms relate to a cement comprising a mixture of at least one hydraulic material with at least one further material, which may be another hydraulic material, a pozzolan, a latent hydraulic material, a non-hydraulic material or a filler.

[0020] Hydraulic materials or hydraulic binders are materials that react with water in a hydraulic reaction to form a solid hydrate phase. Hydraulic materials are, in particular, cement, preferably Portland cement. In particular, pozzolans and latent hydraulic materials are Type II concrete additives with latent hydraulic and / or pozzolanic properties according to standard EN 206-1. Typical pozzolans are volcanic ash, pumice, burnt oil shale, clay, calcined clay, rice husk ash, microsilica, silica fume, and fly ash. Typical latent hydraulic materials are slag, in particular ground granulated blast furnace slag and basic oxygen furnace slag.

[0021] In this context, Portland clinker is a sintered product obtained from limestone and aluminosilicate materials in a cement kiln at high temperatures. The term "clinker" refers to unground material, typically obtained as lumps or nodules. Portland clinker as used in this context can be any type of Portland clinker. The typical phase composition of Portland clinker is 45-80 wt% C3S, 1-40 wt% C2S, 0-15 wt% C3A, and 0-20 wt% C4AF (where "C" represents CaO, "S" represents SiO2, "A" represents Al2O3, and "F" represents Fe2O3). The typical chemical composition of Portland clinker is 55-75 wt% CaO, 15-25 wt% SiO2, 2-6 wt% Al2O3, 0-6 wt% Fe2O3, 0-2 wt% MgO, and 0-2 wt% SO3.

[0022] In this context, the term "cement" means a ground material. Thus, for example, Portland cement is cement obtained by grinding Portland clinker. The Blaine fineness of Portland cement is 2500 cm 2 / g~12000cm 2 / g, preferably 3000 cm 2 / g~9000cm 2 / g, especially 3500cm 2 / g~8000cm 2 / g. Blaine fineness can be measured according to DINEN 196-6:2018.

[0023] In this context, the term "cementitious waste" refers to any cementitious material that cannot be used for its intended purpose or has reached the end of its lifespan. In this context, cementitious material is a material comprising at least one hydraulic binder, in particular at least one cement. This hydraulic binder can be in an unhardened state or can be partially or fully hardened. According to certain embodiments, the cementitious waste comprises at least 5% by weight, preferably at least 10% by weight, more preferably at least 20% by weight, of at least one hydraulic binder, in particular cement, in an unhardened, partially hardened, or fully hardened state. In particular, the cementitious waste is waste building material. The waste building material can be, for example, excess material, off-spec material, returned material, or demolition waste. In particular, the cementitious waste is demolition waste. According to embodiments, the cementitious waste comprises aggregate and at least one hydraulic binder, but its composition is not otherwise limited. A particularly preferred cementitious waste is concrete, in particular excess concrete, off-spec concrete, or concrete obtained from demolition.

[0024] The cementitious waste may be a mixture of different materials. For example, the cementitious waste may be concrete or mortar, a mixture of concrete and gypsum-based materials, a mixture of concrete and plaster, a mixture of brick and mortar, a mixture of brick, mortar and plaster, etc. Metal fibers, especially steel fibers, polymer fibers and / or glass may be contained in the cementitious waste. In particular, the cementitious waste comprises unhardened, partially hardened or fully hardened cement, aggregates and fillers. However, it is preferred that the cementitious waste does not contain large pieces of metal or wood.

[0025] The cementitious waste may be pre-treated before carrying out the method of the present invention. Pre-treatment is in particular crushing and / or sorting of the cementitious waste by material. If crushing is carried out, the size of the crushed material is preferably larger than the particle size of the largest aggregate. Another pre-treatment may be sorting of the cementitious waste to separate the cementitious material from metal, wood, plastic, paper and / or plaster. Sorting may be carried out, for example, using a magnet or by density separation.

[0026] It may be advantageous for the cementitious waste to contain some ceramic material, for example the cementitious waste may contain up to 25% by weight of ceramic material, preferably 1-5% by weight of ceramic material.

[0027] The ground cementitious waste typically comprises aggregates and auxiliary cementitious materials, the latter being hydraulic, pozzolanic and / or latent hydraulic materials that may be hardened or unhardened, preferably hardened, and that are used in the production of the original cementitious material.

[0028] The grinding aid of the present invention is selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof. The grinding aid of the present invention can be formulated as a solution or dispersion in a liquid, particularly in water. Thus, the grinding aid of the present invention can be in the form of a solution or dispersion of alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof in a liquid, particularly in water. Hereinafter, all ranges of the amount of grinding aid used refer to the alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof present without any liquid, particularly water.

[0029] The alkanolamine is preferably selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine (TEA), diethanolisopropanolamine (DEIPA), ethanoldiisopropanolamine (EDIPA), isopropanolamine, diisopropanolamine, triisopropanolamine (TIPA), N-methyldiisopropanolamine (MDIPA), N-methyldiethanolamine (MDEA), tetrahydroxyethylethylenediamine (THEED) and tetrahydroxyisopropylethylenediamine (THIPD), and mixtures of two or more of these alkanolamines. According to a particularly preferred embodiment, the alkanolamine is selected from TEA, TIPA, DEIPA, MDEA, or mixtures thereof.

[0030] According to an embodiment, the glycol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butyl diglycol, neopentyl glycol, hexylene glycol. Preferably, the glycol is diethylene glycol.

[0031] 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, talose, fructose, sorbose, lactose, maltose, sucrose, lactulose, trehalose, cellobiose, chitobiose, isomaltose, palatinose, mannobiose, raffinose, and xylobiose. Carbohydrates can also be used in the form of, for example, distillation residue or molasses.

[0032] The chloride in this context is preferably an alkali metal or alkaline earth metal chloride, in particular sodium chloride or calcium chloride.

[0033] A particularly preferred grinding aid is a mixture of diethylene glycol and glycerol. Another particularly preferred grinding aid is a mixture of triisopropanolamine (TIPA) and diethanolisopropanolamine (DEIPA). Another particularly preferred grinding aid is a mixture of an alkanolamine, particularly triisopropanolamine (TIPA) or diethanolisopropanolamine (DEIPA), a carbohydrate, and a chloride, particularly sodium chloride or calcium chloride.

[0034] The co-grinding in the method of the present invention can be carried out on an attrition mill. Particularly suitable attrition mills are semi-autogenous mills and compression grinders. In this context, compression grinders are a type of grinder that can exert a compressive force on the layer of material to be ground. Preferably, the compressive force is exerted by a rotating cylinder or a rotor stator. The compression grinder can be, for example, a crusher or a roller mill. According to a preferred embodiment, the compression grinder is a vertical roller mill or a horizontal roller mill. Examples of semi-autogenous mills are ball mills or agitator mills. According to an embodiment, in the method of the present invention, grinding is carried out in a ball mill or agitator mill.

[0035] The milling can be carried out batchwise or continuously, and therefore the method of the present invention can be a batch process or a continuous process.

[0036] The term "co-grinding" means that the Portland clinker and cementitious waste are ground in the presence of a grinding aid. The terms "grinding" and "milling" may be used interchangeably in this context.

[0037] The co-grinding of the present invention is preferably a dry process, which means that the amount of water present during grinding is less than 10% by weight, preferably less than 5% by weight, in particular less than 2% by weight, based on the total weight of the solid material.

[0038] The grinding aid is preferably sprayed onto the Portland clinker and cementitious waste in the mill. Similarly, the grinding aid can be added to the Portland clinker and / or cementitious waste on a conveyor belt feeding the mill. This is particularly preferred when the method of the present invention is a continuous process.

[0039] In the method of the present invention, further materials different from the Portland clinker and cementitious waste may be present during the co-grinding step. Such further materials are preferably selected from gypsum, pozzolana and / or latent hydraulic materials. The pozzolana and latent hydraulic materials are as defined above. According to an embodiment, in the method of the present invention, further gypsum, pozzolana and / or latent hydraulic materials are present during grinding, and these pozzolana and / or latent hydraulic materials are different from the cementitious waste.

[0040] Preferably, the Portland clinker and cementitious waste are present in a defined weight ratio in the co-grinding step.

[0041] According to an embodiment, in the method of the invention, the weight ratio of Portland clinker to cementitious waste is between 1:1 and 10:1, preferably between 2:1 and 6:1, in particular between 2.5:1 and 5:1.

[0042] If the weight ratio is outside these ranges, the properties of the resulting blended cement, particularly workability, shrinkage, and / or compressive strength, when mixed with water and / or after hardening may not be optimal. For example, if the proportion of cementitious waste is too high, the compressive strength of the resulting blended cement after hardening may be reduced.

[0043] According to an embodiment, in the method of the invention, the grinding aid is present in an amount of 40 to 2500 ppm, preferably 100 to 1500 ppm, in particular 800 to 1200 ppm, based on the total dry weight of the combined Portland clinker, cementitious waste and, if present, gypsum, pozzolan and latent hydraulic material. Throughout this context, the term "ppm" means "parts per million".

[0044] The method of the present invention may further comprise a step of size separation of the particles.

[0045] According to embodiments, separation is performed at a predefined cut-off size to separate clean aggregate obtained from the cementitious waste from the blended cement to be produced. The aggregate has a size equal to or greater than the predefined cut-off size. According to embodiments, separation is performed by filtration, sieving, sedimentation, density separation, e.g., air sorting in a cyclone and / or centrifugation.

[0046] Such size separation results in the recovery of aggregates and supplementary cementitious materials (SCMs), which then become part of the blended cement.

[0047] However, SCM obtained by grinding cementitious waste may also contain aggregates.

[0048] The blended cement of the present invention may contain additional materials. In particular, such additional materials may be additional SCMs and / or fillers. Suitable additional materials are, in particular, gypsum, pozzolana, latent hydraulic materials, and / or limestone fine powder. The additional materials, in particular gypsum, pozzolana, and / or latent hydraulic materials, may be 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 additional materials are similar to those of the Portland clinker and cementitious waste. However, the additional materials, in particular limestone, may also be added in a separate step of mixing the dry powders after the co-grinding step. This may be particularly useful when the hardness and grindability of the additional materials are different from those of the Portland clinker and cementitious waste.

[0049] Thus, according to an embodiment, in the method of the present invention, the ground mixture is combined with one or more inorganic fillers, preferably limestone.

[0050] In the method of the present invention, it is preferred that no carbonation occurs in the co-grinding step of the Portland clinker and cementitious waste, meaning that the Portland clinker and cementitious waste do not react with CO during the co-grinding step.

[0051] In another aspect, the present invention relates to a blended cement obtainable by the process described above.

[0052] Any features described above as preferred also apply to this aspect.

[0053] Preferably, the blended cement is in the form of a dry powder. The blended cement has a Blaine fineness of 2500 cm 2 / g~12000cm 2 / g, preferably 3000 cm 2 / g~9000cm 2 / g, especially 3500cm 2 / g~8000cm 2 / g. Blaine fineness can be measured in accordance with DIN EN 196-6:2018.

[0054] According to an embodiment, the blended cement of the present invention comprises (based on the total dry weight of the blended cement, unless otherwise specified): a) 60 to 90% by weight, preferably 70 to 80% by weight, of Portland clinker; b) 5 to 35% by weight, preferably 15 to 25% by weight, of cementitious waste; c) optionally 1 to 10% by weight, preferably 5% by weight, of gypsum; d) 40 to 2500 ppm, preferably 100 to 1500 ppm, in particular 800 to 1200 ppm, of a grinding aid selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof, based on the total dry weight of the combined Portland clinker, cementitious waste and, if present, gypsum; It comprises or consists of:

[0055] In another aspect, the present invention relates to a building material, in particular concrete or mortar, comprising the blended cement described above.

[0056] Any features described above as preferred also apply to this aspect.

[0057] The building material is not particularly limited in its composition as long as it contains the blended cement of the present invention.

[0058] For example, the building material of the present invention may further comprise aggregates such as rock, crushed stone, gravel, sand, in particular silica sand, river sand and / or crushed sand, glass, foam glass, hollow glass beads, glass ceramics, biological materials such as hemp fiber or cork, and synthetic organic materials such as rubber.

[0059] The building material of the present invention may also contain any further additives common in the mortar and concrete industry. In particular, such further additives are selected from plasticizers, superplasticizers, shrinkage reducing agents, air entraining agents, degassing agents, stabilizers, viscosity modifiers, thickeners, water reducers, retarders, waterproofing agents, fibers, foaming agents, antifoaming agents, redispersible polymer powders, dust suppressants, chromate reducing agents, pigments, biocides, rust inhibitors and steel passivators. The further additives are chemically different from the grinding aids mentioned above.

[0060] According to a preferred embodiment, the building material of the present invention is concrete or mortar.

[0061] The building material of the present invention can be in dry or wet form. Dry form means that the building material is in the form of a free-flowing powder and has a water content of 10% by weight or less, preferably 5% by weight or less, and in particular 1% by weight or less. Wet form means that the building material is mixed with water. According to an embodiment, the mixing weight ratio of water to mixed cement is 0.1 to 1.0, preferably 0.2 to 0.6.

[0062] In another aspect, the present invention relates to the use of an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof to reduce shrinkage of a blended cement or a building material comprising a blended cement during hardening, wherein the blended cement comprises Portland cement and auxiliary cementitious material recovered from cementitious waste.

[0063] Highly preferably, the blended cement comprises Portland clinker co-ground in the presence of an admixture and supplemental cementitious material recovered from cementitious waste. The term "co-ground in the presence of an admixture" means that Portland clinker and supplemental cementitious material recovered from cementitious waste are ground together in the presence of said admixture.

[0064] Any features described above as preferred also apply to this aspect.

[0065] In particular, the blended cement is a cement obtained by the aforementioned method. However, the blended cement in this embodiment can also be obtained by mixing Portland cement with ground cementitious waste. Methods for obtaining Portland cement are well known to those skilled in the art. In this context, the ground cementitious waste is preferably obtained by the aforementioned method in the absence of Portland clinker.

[0066] According to a preferred embodiment, an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof is added to the Portland clinker and / or cementitious waste before or during its grinding.

[0067] However, it is also possible to add an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof to the Portland cement, SCM recovered from cementitious waste or mixtures thereof after grinding.

[0068] Thus, according to a preferred embodiment, Portland clinker and / or cementitious waste is ground or co-ground in the presence of an admixture.

[0069] The admixture may include other materials in addition to the alkanolamine, glycol, glycerol, carbohydrate, chloride, or mixtures thereof. For example, the admixture may be in the form of a solution or dispersion of the alkanolamine, glycol, glycerol, carbohydrate, chloride, or mixtures thereof in a liquid, particularly water.

[0070] In particular, building materials are as described above.

[0071] Hardening of the blended cement or building material of the present invention begins when water is added.

[0072] In this context, shrinkage relates to dimensional stability and can be measured in accordance with standard EN 12617-4.

[0073] Reduced shrinkage is desirable because it reduces cracking and therefore increases the useful life of any object resulting from the hardening of the blended cement or building material of the present invention.

[0074] In another aspect, the present invention relates to the use of an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof to increase the compressive strength of a blended cement or a building material comprising a blended cement after hardening, wherein the blended cement comprises Portland cement and auxiliary cementitious material recovered from cementitious waste.

[0075] Any features described above as preferred also apply to this aspect.

[0076] In particular, the blended cement is a cement obtained by the aforementioned method. However, the blended cement in this embodiment can also be obtained by mixing Portland cement with ground cementitious waste. Methods for obtaining Portland cement are well known to those skilled in the art. In this context, the ground cementitious waste is preferably obtained by the aforementioned method in the absence of Portland clinker.

[0077] According to a preferred embodiment, an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof is added to the Portland clinker and / or cementitious waste before or during its grinding.

[0078] However, it is also possible to add an admixture selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof to the Portland cement, SCM recovered from cementitious waste or mixtures thereof after grinding.

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

[0080] The admixture may include other materials in addition to the alkanolamine, glycol, glycerol, carbohydrate, chloride, or mixtures thereof. For example, the admixture may be in the form of a solution or dispersion of the alkanolamine, glycol, glycerol, carbohydrate, chloride, or mixtures thereof in a liquid, particularly water.

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

[0082] Hardening of the blended cement or building material of the present invention begins when water is added.

[0083] The compressive strength can be measured according to standard EN 12190 on 4x4x16 cm square pillars.

[0084] Increased compressive strength is desirable because it increases the yield strength of any object resulting from the hardening of the blended cement or building material of the present invention. When a higher yield strength of an object is achieved, 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.

[0085] In another aspect, the present invention relates to the use of a grinding aid selected from an alkanolamine, a glycol, glycerol, a carbohydrate, a chloride or a mixture thereof to improve the efficiency of grinding of cementitious waste, wherein the grinding is carried out without carbonation of the cementitious waste.

[0086] Any features described above as preferred also apply to this aspect.

[0087] Preferred grinding aids in this embodiment are selected from TEA, TIPA, DEIPA, MDEA, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butyl diglycol, 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 the alkanolamine, glycol, glycerol, carbohydrate, chloride, or mixtures thereof in a liquid, particularly water.

[0088] According to an embodiment, in this aspect, the grinding aid is used in an amount of 100 to 1500 ppm, preferably 250 to 1200 ppm, in particular 400 ppm or 1000 ppm, based on the dry weight of the cementitious waste.

[0089] Higher grinding efficiency can result in a higher fineness of the ground material within the same grinding time. Higher grinding efficiency can also reduce the grinding time to achieve the same fineness of the ground material. Higher grinding efficiency can also result in less energy consumption by the mill to achieve the same fineness of the ground material. The latter can result, for example, from a more stable grinding bed or less vibration of the mill.

[0090] In this embodiment, no carbonation occurs during the grinding of the cementitious waste, which means that the Portland clinker and cementitious waste do not react with CO during the co-grinding step.

[0091] In this embodiment, the cementitious waste material can be co-ground with another hydraulic material, a pozzolan and / or a latent hydraulic material.

[0092] Preferably, particle size separation is carried out during or after grinding of the cementitious waste. According to an embodiment, separation is carried out at a predefined cut-off particle size in order to separate clean aggregate obtained from the cementitious waste from the blended cement to be produced. The aggregate has a particle size equal to or greater than the predefined cut-off particle size. This procedure separates the aggregate from the auxiliary cementitious material. According to an embodiment, separation is carried out by filtration, sieving, sedimentation, density separation, e.g., air sorting in a cyclone, and / or centrifugation.

[0093] The following examples provide further embodiments of the present invention to those skilled in the art. [Example]

[0094] Example 1 The cementitious waste used was pre-crushed concrete (with 0-32 mm primary aggregate sand and gravel) obtained from demolition. A jaw crusher was used to pre-crush the cementitious waste. The pre-crushed material was then sieved, and the 2-4 mm fraction was used in Example 1 (hereinafter referred to as RCD-1). RCD-1 was dried at 105°C before grinding.

[0095] A laboratory ball mill with steel balls was used. For grinding, 300 g of RCD-1 was placed in the ball mill along with 260 g of steel balls (diameter 45-49 mm). The container and balls were preheated to 105°C. The type and amount of grinding aids shown in Table 1 below were added to the mill. Then, grinding was carried out for 15 minutes.

[0096] The ground RCD-1 was tested for particle size by sieving according to standard EN 196-6:2010, and the results are shown in Table 1 below.

[0097] [Table 1]

[0098] As can be seen from Table 1, the addition of grinding aid reduced the particle size D90 and resulted in less retention on the 32 μm and 45 μm sieves, thus resulting in finer particles for the same grinding time.

[0099] Example 2 The cementitious waste used was the same as in Example 1.

[0100] Portland clinker for CEM I 52.5 R (according to standard EN 197-1) was used.

[0101] A laboratory ball mill with steel balls was used. For grinding, 10 kg of a mixture of Portland clinker, gypsum, and RCD-1 in the respective ratios shown in Table 3 below was placed in the ball mill together with steel balls (45-49 mm diameter). The container and balls were preheated to 100°C. The respective amounts of grinding aid (a mixture of TIPA and DEIPA in a 2:1 weight ratio in all cases) in ppm relative to the total weight of Portland clinker, gypsum, and RCD-1, as shown in Table 3 below, were added to the mill. Milling was then carried out for 2 hours.

[0102] The resulting blended cement was then mixed with water to obtain a water to cement ratio of 0.5. The shrinkage of the resulting mixtures was tested according to standard EN 12617-4 after the times shown in Table 3 below. The compressive strength was measured on 4x4x16 cm square pillars according to standard EN 12190 after the times shown in Table 3 below.

[0103] [Table 2]

[0104] As can be seen from the above results, the addition of RCD-1 increases shrinkage compared to cement in the presence of Portland clinker alone (see Examples 2-1, 2-2, 2-4). The addition of the grinding aid of the present invention significantly reduces shrinkage (see Examples 2-3 vs. 2-2 and 2-5 vs. 2-4).

[0105] Replacing Portland clinker with RCD-1 powder also results in a decrease in compressive strength (see Examples 2-1, 2-2, 2-4). Addition of the grinding aid of the present invention significantly increases compressive strength (see Examples 2-3 vs. 2-2 and 2-5 to 2-7 vs. 2-4).

[0106] Example 3 The cementitious waste used was the same as in Example 1.

[0107] Portland clinker for CEM I 52.5 R (according to standard EN 197-1) was used.

[0108] A laboratory ball mill with steel balls was used. For grinding, 10 kg of a mixture of Portland clinker, gypsum, and RCD-1 in the respective ratios shown in Table 3 below was placed in the ball mill together with steel balls (diameter 45-49 mm). The container and balls were preheated to 100°C. The respective amounts of grinding aid (a mixture of TIPA and DEIPA in a 2:1 weight ratio in all cases) in ppm relative to the total weight of Portland clinker, gypsum, and RCD-1, as shown in Table 4 below, were added to the mill. Grinding was then carried out for 2 hours.

[0109] The resulting blended cement was then mixed with water to obtain a water to cement ratio of 0.5. The shrinkage of the resulting mixtures was tested according to standard EN 12617-4 after the times shown in Table 4 below. The compressive strength was measured on 4x4x16 cm square pillars according to standard EN 12190 after the times shown in Table 4 below.

[0110] [Table 3]

[0111] As can be seen from the results in Table 4, when the weight ratio of Portland clinker to cementitious waste is 3.75:1 and grinding aid is used, particularly low shrinkage can be achieved after 14 days (see Examples 3-1 to 3-3). It can also be seen that increasing the amount of grinding aid used does not show a significant increase in compressive strength, but can result in greater shrinkage (see Examples 3-4 to 3-6).

Claims

1. 1. A method for producing a blended cement, comprising: (1) providing Portland clinker; (2) providing cementitious waste; (3) providing a grinding aid selected from an alkanolamine, a glycol, a glycerol, a carbohydrate, a chloride, or a mixture thereof; (4) co-grinding the Portland clinker and cementitious waste in the presence of the grinding aid; A method comprising:

2. 2. The method according to claim 1, characterized in that the weight ratio of Portland clinker to cementitious waste is from 1:1 to 10:1, preferably from 2:1 to 6:1, in particular from 2.5:1 to 5:

1.

3. 3. The method according to claim 1 or 2, further characterized in that gypsum, pozzolana and / or latent hydraulic material are present in the grinding, said pozzolana and / or said latent hydraulic material being different from the cementitious waste material.

4. 4. The method according to any one of claims 1 to 3, characterized in that the grinding aid is present in an amount of 40 to 2500 ppm, preferably 100 to 1500 ppm, in particular 800 to 1200 ppm, based on the total dry weight of the combined Portland clinker, cementitious waste and, if present, gypsum, pozzolan and latent hydraulic material.

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

6. The method according to any one of claims 1 to 5, characterized in that it further comprises a step of size separation of the particles.

7. A mixed cement obtainable by the method according to any one of claims 1 to 6.

8. The blended cement, unless otherwise specified, a) 60 to 90% by weight, preferably 70 to 80% by weight, of Portland clinker; b) 5 to 35% by weight, preferably 15 to 25% by weight, of cementitious waste; c) optionally 1 to 10% by weight, preferably 5% by weight, of gypsum; d) 40 to 2500 ppm, preferably 100 to 1500 ppm, in particular 800 to 1200 ppm, of a grinding aid selected from alkanolamines, glycols, glycerol, carbohydrates, chlorides or mixtures thereof, based on the total dry weight of the combined Portland clinker, cementitious waste and, if present, gypsum; The blended cement of claim 7, comprising:

9. 9. A building material, in particular concrete or mortar, comprising the blended cement according to claim 7 or 8.

10. 1. Use of an admixture selected from an alkanolamine, a glycol and / or glycerol to reduce shrinkage of a blended cement or a building material containing the blended cement during hardening, the blended cement comprising Portland cement and auxiliary cementitious material recovered from cementitious waste.

11. 1. Use of an admixture selected from an alkanolamine, a glycol and / or glycerol to increase the compressive strength of a blended cement or a building material containing the blended cement after hardening, the blended cement comprising Portland cement and auxiliary cementitious material recovered from cementitious waste.

12. 12. Use according to claim 10 or 11, characterized in that the admixture is added to the Portland clinker and / or the auxiliary cementitious material before or during its grinding.

13. 1. Use of a grinding aid selected from an alkanolamine, a glycol, a glycerol, a carbohydrate, a chloride or a mixture thereof to improve the efficiency of grinding of cementitious waste, wherein the grinding is carried out without carbonation of the cementitious waste.

14. Use according to any one of claims 10 to 13, characterized in that the admixture or grinding aid is selected from triethanolamine, triisopropanolamine, diethanolisopropanolamine, N-methyldiethanolamine, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butyl diglycol, neopentyl glycol, hexylene glycol, glycerol, carbohydrates, sodium chloride, calcium chloride or mixtures thereof.

15. Use according to claim 13 or 14, characterized in that the grinding aid is used in an amount of 100 to 1500 ppm, preferably 250 to 1200 ppm, in particular 400 ppm or 1000 ppm, based on the dry weight of the cementitious waste.

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