Method for producing mineral binder additive

Abstract

A process for producing a mineral binder additive comprising the steps of: a) providing a source material comprising an uncured mineral binder material, carbonating the source material with carbon dioxide, in particular under grinding conditions such that the mineral binder material is at least partially, in particular completely carbonated to produce a carbonated particulate product, in particular carbonated powder; b) recovering the carbonated particulate product of step a) as a mineral binder additive.

Description

Technical Field

[0001] The present invention relates to a method for producing a mineral binder additive from an uncured mineral binder material. Furthermore, the present invention relates to a mineral binder additive obtainable or obtained by this method, and a method for producing a mineral binder composition using such an additive. Furthermore, the present invention relates to the use of the mineral binder additive as an additive in a mineral binder composition. Background Art

[0002] In the construction industry, a large amount of mineral binder-based materials are used, such as mortar or concrete. However, the production of cement and other mineral binders produces a considerable amount of climate-related carbon dioxide (CO2). In order to reduce carbon dioxide emissions, the cement in the binder composition can be partially replaced by potential hydraulic and / or pozzolanic cement admixtures, such as fly ash, slag or silica fume. This admixture is a by-product of various industrial processes and is therefore advantageous in terms of carbon dioxide balance. However, in the absence of additional measures, the solidification of this cement admixture requires much longer time than the case of hydraulic cement.

[0003] Another method is described in WO 2017 / 041176 A1 (Carboncure Technologies Inc.). Specifically, the wet cement mixture is carbonated to produce carbonated concrete before adding aggregates, admixtures, SCM and / or other components. Thus, carbon dioxide is incorporated into the produced concrete and removed from the environment.

[0004] However, another problem of cement production is that in a large number of cement plants or grinding stations, large amounts of cement that does not meet specifications ("off-spec cements") accumulate and are stored. This is, for example, cement that does not meet certain desired specifications defined in the standards, for example due to temporary processing problems. It is known that the addition of up to 1% by weight of off-spec cement in cement production may not impair the properties of the fresh cement to be produced. However, this rather low proportion sometimes leads to a situation where the stock of off-spec material cannot be consumed within a reasonable time or cannot be used again at some point because exposure to the environment leads to aging-induced decay of this material. In this case, the off-spec cement is essentially lost and must be disposed of, for example, in a landfill. This is a particularly unsatisfactory situation, especially with regard to the carbon dioxide balance.

[0005] Therefore, there remains a need to develop improved solutions which further reduce CO2 emissions in the construction industry. Summary of the invention

[0006] It is an object of the present invention to provide an improved solution which further reduces carbon dioxide emissions in the construction industry. In particular, the solution should allow for the recovery and / or reuse of off-specification mineral binders, in particular off-specification cement.

[0007] Surprisingly, it has been found that these objects can be achieved by a method according to claim 1. In particular, the present invention provides a method for producing a mineral binder additive, the method comprising the following steps:

[0008] a) providing a source material comprising uncured mineral binder material, carbonate the source material with carbon dioxide, in particular under grinding conditions, such that the mineral binder material is at least partially, in particular substantially completely, carbonated to produce a carbonated product;

[0009] b) recovering the carbonated product of step a) as a mineral binder additive in a dry state.

[0010] Mineral binders, such as cement and / or clinker, can be fully carbonated once hydrated. However, these materials can also be directly carbonated in the presence of carbon dioxide, especially under humid conditions. Since cement plants are huge emitters of carbon dioxide produced during the limestone calcination process required for the production of cement clinker, the carbon dioxide can be reused in the method of the present invention to carbonate uncured mineral binder materials, such as substandard cement, contained in the source materials. Thus, the carbon dioxide is sequestered.

[0011] In addition, it has been found that the carbonated product recovered in step b) of the process of the invention can be reused as a mineral binder additive. Specifically, the mineral binder additive can be used, for example, as a cement substitute in a mineral binder composition, as a promoting additive for a mineral binder composition and / or as a rheology modifier.

[0012] In particular, the mineral binder additive obtainable with the process of the invention can be added to the mineral binder composition during and / or after the production of the mineral binder, or it can be used as an admixture which is added later to the mineral binder composition after the production of the mineral binder.

[0013] The method of the invention thus allows a significant reduction in carbon dioxide emissions in cement production while enabling the reuse of waste mineral binder materials.The method of the invention thus has a significant resource saving potential and represents an important step towards a circular economy.

[0014] In the present context, the term "source material" denotes any material comprising or consisting of an uncured mineral binder material. Preferably, the source material is a granular material, in particular a powder.

[0015] If the source material is not a granular material, it can be crushed before step a). This is particularly advantageous if the source material contains a hardened mineral binder. Crushing will increase the surface of the source material, which in turn enhances the carbonation process.

[0016] In particular, the source material may contain a certain proportion of hardened mineral binder material in addition to the uncured mineral binder. This is the case, for example, if waste or off-specification cement is stored and partially hydrated thereby.

[0017] However, in a highly preferred embodiment, the proportion of hardened mineral binder in the source material is less than 50% by weight, in particular less than 5% by weight, especially less than 1% by weight, relative to the total weight of the source material. In particular, the source material does not contain any hardened mineral binder.

[0018] In particular, the proportion of uncured mineral binder in the source material is at least 50% by weight, in particular at least 90% by weight, in particular at least 95% by weight or 99% by weight, relative to the total weight of the source material. In particular, the source material consists entirely of uncured mineral binder.

[0019] "Uncured mineral binder" refers to a mineral binder which has not yet hardened in a chemical hydration reaction. In this case, the mineral binder therefore does not contain hydrates. In particular, the uncured mineral binder comprises or consists of hydraulic, non-hydraulic, latently hydraulic and / or pozzolanic binder materials in the uncured state.

[0020] "Hydraulic binder" means a mineral binder which can be hardened with water or even under water, such as, in particular, cement or hydraulic lime. "Non-hydraulic binder" means a mineral binder which can be hardened even with water (but not under water), such as, in particular, gypsum in the form of anhydrite or gypsum hemihydrate.

[0021] The term "latent hydraulic and / or pozzolanic binder material" particularly denotes a type II concrete additive having latent hydraulic and / or pozzolanic properties according to standard EN 206-1. In particular, the latent hydraulic or pozzolanic binder material comprises or consists of slag, fly ash, silica fume, clay and / or pozzolan.

[0022] In particular, the source material or uncured mineral binder comprises cement clinker or consists of cement clinker. Cement clinker is a solid material produced as an intermediate product in cement manufacturing. Cement clinker occurs particularly in the form of lumps and / or agglomerates. Typically, the diameter size of the clinker particles is several millimeters to 25 millimeters. However, other sizes are also possible. Cement clinker is produced by sintering limestone and aluminosilicate materials, especially in cement kilns. Cement clinker is, for example, Portland cement clinker.

[0023] However, in another embodiment, the uncured mineral binder comprises or consists of a CEM type I, II, III, IV or V cement, in particular a CEM type I or II cement, according to standard EN 197. However, other types of cement may also be used.

[0024] When compared to cement clinker, cement is a finer product. Typically, cement is obtained by grinding cement clinker in a cement mill, optionally together with additional binder components. Typically, cement has a particle size of at least 1000 cm 2 / g, for example 3000-5000cm 2 However, cements with other Blaine surfaces are also known.

[0025] In particular, the uncured mineral binder comprises or consists of an uncured hydraulic binder, such as an uncured cement-based binder. However, the uncured mineral binder may also comprise or consist of an uncured hydraulic binder, an uncured latent hydraulic binder and / or an uncured pozzolanic binder material.

[0026] In particular, the uncured hydraulic binder is uncured cement. Preferably, the uncured latent hydraulic and / or pozzolanic binder material is uncured slag and / or fly ash. A highly preferred uncured latent hydraulic binder material is uncured slag.

[0027] In particular, the uncured mineral binder comprises or consists of 5 to 100% by weight, in particular 50 to 100% by weight, more preferably 65 to 100% by weight, of an uncured hydraulic binder.

[0028] In particular, the uncured mineral binder comprises or consists of 5-95% by weight of an uncured hydraulic binder and 95-5% by weight of an uncured latent hydraulic and / or pozzolanic binder material. More preferably, the uncured mineral binder may comprise or consist of 30-90% by weight of an uncured hydraulic binder and 70-10% by weight of an uncured latent hydraulic and / or pozzolanic binder material.

[0029] In particular, the uncured mineral binder comprises or consists of production waste from cement production. This is, for example, cement clinker and / or cement which, for example due to temporary processing problems, does not meet certain desired specifications.

[0030] The term "hardened mineral binder" refers in particular to a mineral binder that has hardened in a chemical hydration reaction producing hydrates. In particular, the hardened mineral binder has hardened for at least 2 days, preferably at least 7 days, in particular at least 28 or at least 60 days.

[0031] In particular, the hardened mineral binder, if present, comprises or consists of a hardened hydraulic binder, such as a hardened cementitious binder. However, the hardened mineral binder may also comprise or consist of a hardened latent hydraulic and / or pozzolanic binder material.

[0032] In a highly preferred embodiment, the source material has a particle size of 0.5-100 mm, in particular 1-50 mm, in particular 2-30 mm. This is especially true if the source material comprises cement clinker or consists of cement clinker. Therefore, preferably, the particle size is determined by sieve analysis, in particular with a sieve having square openings. In particular, the particle size is represented by the size of the opening of the test sieve, in particular the length of the square opening, which is just passed by the particles in question. Such relatively large particle sizes are particularly suitable for generating abrasive conditions during the carbonation process.

[0033] In another preferred embodiment, the source material, in particular the uncured mineral binder, has a diameter of 0.5 to 8000 cm 2 / g, especially 1-5000cm 2 / g, especially 3000-5000cm 2 / g of Blaine surface. The Blaine surface or fineness is measured in accordance with DIN EN 196-6:2018. However, it is also possible to use source materials with different finenesses. This is particularly true if the source material contains uncured cement or consists of uncured cement.

[0034] The mineral binder additive obtained in step b) is in the form of a granular product, in particular in the form of a powder. In particular, the mineral binder additive is a dry solid granular material. In other words, the mineral binder additive is not in the form of a suspension. In particular, the water content in the mineral binder additive is less than 5% by weight, in particular less than 1% by weight, in particular less than 0.1% by weight, relative to the weight of the mineral binder additive. In particular, the mineral binder additive does not contain any water.

[0035] The water content in the mineral binder additive can be adjusted by drying. Therefore, according to another preferred embodiment, the mineral binder additive is dried before and / or after recovery. This is particularly useful if the treatment is carried out under moist or wet conditions, for example in a liquid.

[0036] In particular, drying is carried out in an oven, in particular at a temperature of 30-150° C., preferably 80-130° C. or 100-120° C. Likewise, drying with the aid of an air stream, in particular a hot air stream, for example at a temperature of 30-150° C. is another option. This results in rapid drying of the mineral binder additive.

[0037] However, the mineral binder additive can be dried, for example, under ambient conditions without further measures. This does not require any additional energy.

[0038] In particular, the mineral binder additive obtained in step b) comprises or consists of calcium carbonate. In particular, it comprises or consists of calcium carbonate, silicon dioxide and aluminum hydroxide.

[0039] Particularly preferably, the mineral binder additive has a Blaine surface area of ​​0.5-8000 cm 2 / g, especially 1-5000cm 2 / g, especially 1-1000cm 2 / g, especially 1-150cm 2 / g, for example 20-100cm 2 / g, where the Blaine surface area is measured according to standard DIN EN 196-6:2018.

[0040] The fineness of the mineral binder additive may be controlled, for example, by the fineness of the source material and / or the carbonation process in step a), as further explained below.

[0041] The progress of the carbonation in step a) can be measured, for example, by measuring the CO2 partial pressure during step a). If the CO2 partial pressure decreases, carbonation occurs. If the CO2 partial pressure does not further decrease during the carbonation process, it can be considered that carbonation is substantially complete. Alternatively, the progress of the carbonation can also be determined, for example, by measuring the pH value of the mixture during the carbonation in step a), especially if step a) is carried out in a liquid. If the pH value decreases, carbonation occurs. If the pH does not further decrease during the carbonation process, it can be considered that carbonation is substantially complete. This is typically a situation where the pH value is 7-10, preferably 7-9.

[0042] In particular, in step a), the carbonation of the source material with carbon dioxide is carried out under grinding conditions. This allows, inter alia, to improve the carbonation process and / or to increase the fineness of the carbonated product when compared to the fineness of the source material.

[0043] In particular, grinding conditions cause friction between particles of source material and / or carbonated material. In turn, this will increase the carbonation rate. In general, grinding conditions improve the output or efficiency of the whole process. Therefore, step a) is composed of a combination of (i) a chemical process, i.e. carbonation, and (ii) the effect of mechanical force. These two processes interact synergistically and significantly promote the whole process.

[0044] In particular, the two methods are run simultaneously and repeatedly until the desired degree of carbonation and / or fineness of the carbonation product or the mineral binder additive, respectively, is achieved.

[0045] Grinding conditions can for example be produced by mechanical grinding and / or abrasion of the source material in the carbonating process, especially by stirring and / or grinding of the source material in the carbonating process.Therefore, in the method for the present invention, the source material is preferably stirred and / or ground in the carbonating process.This can be realized with agitating device, mechanical mixer, rotation and / or vibration drum, crusher, forcing machine, ultrasonic process or its combination.

[0046] In particular, the grinding of the material can be carried out in a cement mill (eg a ball mill).

[0047] In particular, use a mixing process that generates at least 50s -1 , especially at least 100s -1 , especially at least 500s -1 , especially at least 1000s -1 or at least 4000s -1 The average shear rate of the mixer.

[0048] During the carbonation, stirring and / or grinding of the source material is especially carried out for not more than 24 hours, preferably not more than 6 hours, more preferably not more than 2 hours, in particular for 1 to 90 minutes.

[0049] Preferably, the carbonation of the source material in step a) is carried out under a gas atmosphere containing carbon dioxide or consisting of carbon dioxide. Thus, preferably, the source material is in direct contact with the gas atmosphere. In this case, in particular, the source material is not immersed in a liquid, especially water, and / or does not form a suspension with a liquid, especially water, during step a).

[0050] The concentration of carbon dioxide in the gas atmosphere is in particular higher than the carbon dioxide concentration of normal air. The carbon dioxide content in the gas atmosphere is preferably >500 ppm carbon dioxide, in particular >1000 ppm, especially >1500 ppm.

[0051] In particular, a mixture of carbon dioxide and other gaseous substances (e.g. water vapor, nitrogen, oxygen, e.g. air) can be used as the gas atmosphere for the carbonation in step a). Such a mixture contains carbon dioxide in an amount of >1 wt. %, e.g. >8 wt. %, preferably >10 wt. %, particularly preferably >50 wt. %, in particular >95 wt. %, in particular >99 wt. %.

[0052] According to another preferred embodiment, waste gases from industrial processes, in particular flue gases, are used as the gas atmosphere for the carbonation in step a). In particular, waste gases from cement plants are used as the gas atmosphere for the carbonation in step a). Thus, in particular, the carbon dioxide contained in the waste gases is captured before entering the atmosphere and used for the carbonation in step a).

[0053] In these embodiments, the waste gas comprises CO 2. Advantageously, the waste gas comprises about 5-25 wt % CO 2, preferably 8-20 wt % CO 2 or 10-15 wt % CO 2.

[0054] In another preferred embodiment, the gas atmosphere in step a) consists of essentially pure carbon dioxide. The purity of the carbon dioxide is preferably >50% by weight, for example >75% by weight, preferably >90% by weight, in particular >95% by weight, and especially >99% by weight. With regard to the efficiency of the process, essentially pure carbon dioxide is very advantageous.

[0055] If the carbonation of the source material in step a) is carried out under a gas atmosphere, the carbonation in step a) can be carried out under dry conditions or under humid conditions, especially at a relative humidity of 40-100%. Dry conditions are beneficial because the mineral binder additive can be obtained directly in a dry state without further measures. However, humidity in a gas atmosphere is still acceptable because the drying effort is quite low and humidity can even increase the carbonation efficiency.

[0056] Without being bound by theory, it is believed that uncured mineral binders, in particular cement clinker, continue to hydrate to a lesser extent under humid conditions. This appears to significantly increase the carbonation rate, while the carbon dioxide absorption capacity remains at a fairly high level. Therefore, a relative humidity of 40-100% has proven to be very advantageous. When carbonating a cured or hydrated mineral binder material, a different situation is given. In this case, carbonation starts from an already hydrated material with a much lower carbon dioxide absorption capacity. In this case, humidity or water each does not affect the carbonation rate in a similar manner.

[0057] The pressure of the gas atmosphere used for the carbonation of the source material in step a) may range from atmospheric pressure to an overpressure of, for example, 10 bar. For example, an overpressure of 0.1-2 bar is applied.

[0058] The source material may be provided in dry form or in a form moistened with a liquid, especially water. The source material in dry form is beneficial because the carbonated granular product will have a low water content, which in turn makes it easier to obtain the mineral binder additive in a dry state. However, the presence of some water on the source material is still acceptable because the drying effort is relatively low and the liquid, especially water, may even improve the carbonation efficiency.

[0059] However, according to another embodiment, the carbonation of the source material is carried out in a liquid, and preferably, the carbon dioxide is added to the liquid in gaseous form. In this case, the source material is at least partially, in particular completely, immersed in the liquid. Therefore, the liquid is in particular an aqueous liquid, preferably water. This results in the carbon dioxide being dissolved in the aqueous liquid or water. In this case, if a dry mineral binder additive is desired, the carbonated product needs to be dried.

[0060] If the carbonation of the source material is carried out in an aqueous liquid, especially water, the weight ratio of water in the liquid to the source material is in particular 0.1-0.3, in particular 0.1-0.25, for example 0.12-0.2. Further preferred is that in this case the carbonation is carried out under grinding conditions as described above.

[0061] In this embodiment, carbonation and hydration reactions occur simultaneously. Similar to the above-mentioned humid conditions, this seems to significantly increase the carbonation rate, while the carbon dioxide absorption capacity remains at a fairly high level. Due to the low level of water in this embodiment, a granular product can still be obtained. This is especially true if the treatment is carried out under grinding conditions. Therefore, in particular, unlike the method described in WO 2017 / 041176 A1, no processable and hardenable mineral binder composition, such as mortar, mortar or concrete composition is produced. In particular, step a) is carried out at a temperature of -10-100°C, especially -5-75°C or 5-40°C. However, for example, under humid conditions, the treatment can be carried out above 100°C.

[0062] Preferably, the density of the solid material (particularly source material and / or carbonation product) in the processing volume during step a) is about 10-80 volume %, especially 15-75 volume %, particularly 20-70 volume %, more preferably 30-65 volume % or 40-60 volume %.Term " processing volume " represents the volume that effectively carries out carbonation.In other words, processing volume is defined as the space where source material is exposed to carbonation and optional grinding conditions.

[0063] The carbonation of the source material in step a) can be carried out in a batch process or in a continuous process.

[0064] Another aspect of the present invention relates to a mineral binder additive obtainable or obtained by a process as described above.

[0065] In particular, the mineral binder additive contains calcium carbonate or consists of calcium carbonate. In particular, it contains calcium carbonate, silicon dioxide and aluminum hydroxide or consists of calcium carbonate, silicon dioxide and aluminum hydroxide.

[0066] In particular, the mineral binder additive comprises or consists of carbonated cement, for example carbonate cement of type CEM I, II, III, IV or V according to standard EN 197.

[0067] Particularly preferably, the mineral binder additive has a Blaine surface area of ​​0.5-8000 cm 2 / g, especially 1-5000cm 2 / g, especially 1-1000cm 2 / g, especially 1-150cm 2 / g, for example 20-100cm 2 / g.

[0068] In particular, the mineral binder additive is in the form of a granular product, in particular in the form of a powder. In particular, the mineral binder additive is a dry solid granular material. In other words, the mineral binder additive is not in the form of a suspension. In particular, the water content in the mineral binder additive is less than 5% by weight, in particular less than 1% by weight, in particular less than 0.1% by weight, relative to the weight of the mineral binder additive. In particular, the mineral binder additive does not contain any water.

[0069] Another aspect of the present invention relates to a method for producing a mineral binder composition, in particular a mortar and / or concrete composition, comprising the following steps:

[0070] - producing a mineral binder additive as described above or providing a mineral binder additive as described above, and

[0071] - adding further uncured mineral binder material, in particular cement, limestone and / or clay;

[0072] -optionally adding aggregate;

[0073] - optionally adding at least one admixture;

[0074] - Optionally add water.

[0075] The proportion of the mineral binder additive is preferably 0.001 to 40% by weight, in particular 1 to 25% by weight, relative to the total amount of the mineral binder additive and the further uncured mineral binder together.

[0076] The proportion of the mineral binder additive depends on the intended use. For example, if the mineral binder additive is used as an accelerator and / or rheology modifier, the proportion may be in the range of 0.001-10 wt %. However, if the mineral binder additive is used as a cement substitute, the proportion may be selected in the range of 5-40 wt %, in particular 10-25 wt %.

[0077] The further uncured mineral binder material may be selected from the mineral binder materials and / or clays as described above.

[0078] Herein, the clay mineral may be any type of clay-containing material, especially coarse clay, low temperature calcined clay or high temperature calcined clay. According to an embodiment, the clay mineral is selected from coarse clay, low temperature calcined clay and / or high temperature calcined clay.

[0079] Crude clay is a clay mineral extracted, for example, from a quarry, optionally purified and optionally dried. Low-temperature calcined clay is a clay that has been heat-treated at a temperature of 500-1200° C. For example, low-temperature calcined clay minerals can be produced in a rotary kiln or a flash calciner. High-temperature calcined clay is a clay mineral that has been heat-treated at a temperature above 1200° C. and generally between 1300-1400° C. High-temperature calcined clay is generally crystalline or contains a large amount of crystalline phases, in particular crystalline phases of mullite.

[0080] According to an embodiment, the clay mineral of the present invention is a crude clay, in particular a phyllosilicate. In particular, the clay mineral comprises or consists of kaolinite, montmorillonite and / or illite, in particular kaolinite. These are clays that can be calcined and have proven to be suitable as a component of a mineral binder. However, other clay minerals may also be suitable.

[0081] The clay mineral of the present invention may be pure clay or may contain other substances as impurities. According to some embodiments, the clay content of the clay mineral, especially the crude clay, is at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, and especially at least 85% by weight, relative to the dry weight of the crude clay.

[0082] According to another embodiment, the clay mineral in this article is a low-temperature calcined clay, especially a low-temperature calcined kaolinite. Suitable rapid calcination methods are described, for example, in WO 2014 / 085538. According to a particularly preferred embodiment of the present invention, the calcined clay is metakaolin. However, other clay minerals may also be suitable.

[0083] The clay mineral may be added in the form of excavated material from quarries and / or mining, or may be added in pure form.

[0084] Preferably, the weight ratio of clay mineral to carbonated product is 5:1-1:1, in particular 2.5:1-1.5:1, in particular 2:1. The weight of clay mineral is therefore relative to the pure mineral without any possible impurities. This allows, for example, the production of "LC" containing metakaolin, lime, cement and gypsum. 3 "Type cement.

[0085] The aggregate is for example selected from gravel, sand and / or rock aggregate. The corresponding composition can be formulated as a mortar or concrete composition, for example.

[0086] If present, the proportion of aggregate is, for example, 50-85% by weight, in particular 60-75% by weight, relative to the total dry weight of the mineral binder composition, in which case the proportion of mineral binder additive and further mineral binder together is, for example, 15-50% by weight, in particular 20-35% by weight, relative to the total dry weight of the mineral binder composition.

[0087] Furthermore, the mineral binder composition may comprise at least one admixture, such as a concrete admixture and / or a mortar admixture. The at least one admixture comprises, for example, a defoamer, a dye, a preservative, a plasticizer, a retarder, a pore former, a shrinkage reducer and / or a corrosion inhibitor or a combination thereof, usually, if present, such admixture is used in a proportion of 0.0001-10% by weight relative to the total dry weight of the mineral binder composition.

[0088] In particular, if the mineral binder composition contains water, the weight ratio of water to mineral binder may be in the range of 0.25-0.8, such as 0.3-0.6, such as 0.35-0.5. Such a binder composition can be directly processed as a processable mortar or concrete composition.

[0089] When the addition of water is omitted in the above-described method, for example a dry mortar or concrete composition can be prepared.

[0090] Another aspect of the present invention relates to the use of a mineral binder additive as described above as an additive to a mineral binder composition, in particular for accelerating the setting and / or hardening of a mineral binder composition, as a rheology modifier in a mineral binder composition and / or as a cement substitute in a mineral binder composition.

[0091] Further advantageous embodiments of the invention are apparent from the exemplary embodiments.

[0092] Exemplary embodiments

[0093] As an example, uncured off-specification Portland cement clinker was processed in a mixing device (concrete mixer) under continuous mixing, producing grinding conditions at a temperature of 20° C. at atmospheric pressure in a gas atmosphere containing 5000 ppm CO 2 and a relative humidity of 60% by weight.

[0094] The progress of the carbonation process is controlled by measuring the CO2 partial pressure. During the process, the CO2 partial pressure decreases due to the carbonation reaction. Once the CO2 partial pressure does not decrease further, the process is stopped and the carbonated powder product is recovered.

[0095] X-ray analysis shows that the carbonation product is mainly composed of calcium carbonate, silicon dioxide and aluminum hydroxide. Its Blaine surface area is about 100 cm 2 / g.

[0096] The product thus obtained is used as a mineral binder additive as follows:

[0097] - As an accelerating additive in a cementitious mortar composition, the proportion thereof is 1% by weight relative to the total amount of the mineral binder additive and the uncured cement in the mortar composition.

[0098] Thus, the hardening of the mortar composition may be accelerated, as evidenced by a significantly increased 1 d compressive strength, when compared to a similar composition without the additive.

[0099] - as a partial cement replacement in a concrete composition, the proportion of which is in the range of 20% by weight relative to the total amount of mineral binder additive and uncured cement in the concrete composition.

[0100] The concrete compositions thus prepared achieved similar compressive strengths after 28 days when compared to similar compositions without the additive. Thus, the mineral binder additive can be used to reduce the content of cement clinker in the mineral binder composition.

[0101] Those skilled in the art will appreciate that, without departing from the spirit or essential characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, the presently disclosed embodiments are considered in all aspects to be illustrative rather than restrictive.

Claims

1. A method for producing a mineral binder additive, comprising the following steps: a) providing a source material comprising an uncured mineral binder material, carbonate the source material with carbon dioxide, in particular under grinding conditions such that the mineral binder material is at least partially, in particular fully, carbonated to produce a carbonated granulated product, in particular a carbonated powder; b) recovering the carbonated granulated product of step a) as a mineral binder additive.

2. The method according to claim 1, wherein the uncured mineral binder material is cement clinker.

3. The method according to any one of claims 1 to 2, wherein the source material is free of hardened mineral binder material, in particular free of hydrated mineral binder material, especially free of hydrated cement.

4. The method according to any one of claims 1 to 3, wherein step a) is performed so that the fineness of the carbonated product is increased when compared to the fineness of the source material.

5. The method according to any one of claims 1 to 4, wherein the source material, in particular the uncured mineral binder, has a particle size of 0.5-100 mm, in particular 1-50 mm, especially 2-30 mm.

6. The method according to any one of claims 1 to 5, wherein the produced mineral binder additive has a Blaine fineness of 0.5 to 8000 cm 2 / g, especially 1-5000cm 2 / g, especially 1-1000cm 2 / g, especially 1-150cm 2 / g, for example 20-100cm 2 / g.

7. The method according to any one of claims 1 to 6, wherein the source material is stirred and / or ground during carbonation.

8. The method according to any one of claims 1 to 7, wherein the carbonation in step a) is carried out under humid conditions, in particular under a relative humidity of 40-100%.

9. The method according to any one of claims 1 to 8, wherein the carbonation in step a) is carried out under a gas atmosphere containing or consisting of carbon dioxide, wherein the source material is in direct contact with the gas atmosphere.

10. The method according to any one of claims 1 to 9, wherein the carbonation in step a) is carried out in an atmosphere containing air with a carbon dioxide content of >500 ppm, in particular >1000 ppm.

11. Mineral binder additive obtainable or obtained by a process according to any one of claims 1 to 10.

12. The mineral binder additive according to claim 11, wherein the mineral binder additive comprises calcium carbonate, in particular the mineral binder additive comprises calcium carbonate, silicon dioxide and aluminum hydroxide.

13. A method for producing a mineral binder composition, comprising the steps of: - producing a mineral binder additive according to the method of any one of claims 1 to 10 or providing a mineral binder additive according to any one of claims 11 to 12, and - adding further uncured mineral binder material and / or clay; -optionally adding aggregate; - Optionally adding at least one admixture.

14. The method according to claim 13, wherein the proportion of the mineral binder additive is 0.001-40% by weight, in particular 1-25% by weight, relative to the total amount of the mineral binder additive and the further uncured mineral binder together.

15. Use of the mineral binder additive according to any of claims 11 to 12 as an additive to a mineral binder composition, in particular for accelerating the setting and / or hardening of a mineral binder composition, as a rheology modifier in a mineral binder composition, and / or as a cement substitute in a mineral binder composition.