SHRINKAGE REDUCER FOR MINERAL BINDER COMPOSITION AND ITS USE

Abstract

The invention relates to an additive, in particular a shrinkage-reducing agent, for mineral binder compositions comprising at least one superabsorbent polymer SAP and at least one antifoaming agent D. The invention further relates to a mineral binder composition comprising the additive, processes and methods for mixing it, and hardened articles obtainable therefrom.

Description

SHRINKAGE REDUCER FOR MINERAL BINDER COMPOSITION AND ITS USE Technical Field The invention relates to an additive for mineral binder compositions, in particular a shrinkage-reducing agent for mineral binder compositions, and to the use thereof. The invention further relates to a mineral binder composition comprising the additive, hardened articles obtainable therefrom, and a process for preparing the mineral binder composition. Background of the invention Experts in the field have long known that mineral binder compositions, especially cementitious binder compositions, are subject to volume change, most often shrinkage, during the setting and drying process. This volume change, particularly shrinkage, is of great importance for the suitability for use, sustained service life, and strength of the hardened building material, as it is frequently the cause of cracking, slab subsidence, and other defects. In this way, for example, water, dissolved salts, and air can pass through cracks into the concrete, mortar, slab, or grout, thus promoting corrosion in reinforced concrete structures.Furthermore, the cyclical stress caused by freezing and thawing, with the unwanted penetration of water into the building material through cracks, causes mechanical stresses and premature material failures. Therefore, the construction industry is striving to ensure dimensional stability and, in particular, to minimize drying shrinkage and / or drying cracking through a wide variety of measures. Attempts have been made to counteract shrinkage not only through construction methods and the selection of optimized cementitious binder compositions, but more recently, and to a greater extent, also through the addition of admixtures. The first shrinkage reducers were successfully developed and used in Japan in the early 1980s. Since then, the use of various shrinkage reducers in mortar mixes has become widespread. For example, JP6030283 (Nippon Shokubai) describes a shrinkage-reducing agent comprising a polyoxyalkylene glycol with a molecular weight of 400 to 10,000 g / mol and an antifoam selected from the group consisting of mineral oil antifoam, oil / grease antifoam, fatty acid antifoam, fatty acid ester antifoam, oxyalkylene antifoam, alcohol antifoam, amide antifoam, phosphoric acid ester antifoam, metallic soap antifoam, and silicone antifoam. In addition, WO 2012 / 162292 (Premier Magnesia LLC) describes the combination of shrinkage-reducing mixtures, selected from alkylene glycols or poly(oxyalkylene) glycols, with expansive MgO and superabsorbent polymers, which may be selected from cellulose, carboxymethylcellulose, starches, isobutylene maleic anhydride, polyvinyl alcohols, polyacrylonitriles, polyacrylics, and polyacrylamides, for the reduction of shrinkage cracking of Portland cement-based mortars and concretes. Finally, document US 2010 / 0285224 (Fisher) describes the use of a mixture comprising hydrogels, which can also be considered superabsorbent polymers, especially as aqueous suspensions of polyethylene glycol, glycerin, superabsorbent polymers and crushed granulated blast furnace slag for the internal curing of permeable concrete. However, previously known methods and materials for reducing shrinkage in mineral binder compositions are often expensive, complicated to use, or have limited effectiveness. Therefore, there is still a need for new and more effective methods and materials for reducing shrinkage in mineral binder compositions. Brief description of the invention Therefore, the object of the present invention is to overcome the aforementioned disadvantages. In particular, an improved mixture is provided for reducing the shrinkage of mineral binder compositions. The mixture must not reduce the workability, setting behavior, or strength development of the hardening mineral binder compositions. Furthermore, advantageous methods, uses, and mineral binder compositions that allow for effective shrinkage reduction are provided. Surprisingly, it has been found that the object of the invention can be achieved according to claim 1 by means of a mixture for mineral binder compositions, in particular a shrinkage-reducing mixture for mineral binder compositions, comprising at least one superabsorbent polymer SAP and at least one antifoaming agent D. It has been found that mixtures according to the present invention are extremely effective in ensuring dimensional stability, especially by reducing the shrinkage of mineral binder compositions. Tests have shown that mixtures according to the present invention reduce the shrinkage of mineral binder compositions, for example, concrete compositions, and significantly reduce cracking, both during the setting and hardening period and in the cured state. Undesirable drying of mineral binder compositions can be effectively prevented. Therefore, it is not necessary to wet or cover, for example, with wet sheets or plastic coating, the surface of a freshly applied mineral binder composition comprising the mixture of the present invention, which greatly facilitates production processes compared to current standard practices. Furthermore, the mineral binder compositions comprising a mixture of the present invention develop a smoother and more homogeneous surface texture upon hardening compared to the same mineral binder composition without the respective additive. Furthermore, mixtures according to the present invention have been found not to prolong setting time and not to reduce the strength development of mineral binder compositions. A mixture of the present invention can, for example, be added directly to the mixing water. Therefore, prior grinding with cementitious components is unnecessary, which greatly simplifies its use. The mixture of the present invention has also been found to be compatible with other typical additives for mineral binder compositions. Other aspects of the invention are the subject of separate claims. The particularly preferred embodiments of the invention are the subject of dependent claims. Ways to make the invention A first aspect of the present invention relates to an improved blend for shrinkage reduction of mineral binder compositions comprising at least one superabsorbent polymer SAP and at least one antifoaming agent D. A mineral binder composition, as used in the context of the present invention, refers to a mixture comprising at least one mineral binder. It is possible, and in the context of the present invention, also preferred, for the mineral binder composition to further comprise aggregates and / or other additives. A mineral binder composition of the present invention may be essentially water-free and be present in dry form. A mineral binder composition of the present invention may also comprise some or all of the mixing water and be present as a fluid or in rigid form. A mineral binder in the context of the present invention is a binder, particularly an inorganic binder, that reacts in the presence of water in a hydration reaction to form solid hydrates or hydrate phases. This may be, for example, a hydraulic binder (e.g., cement or hydraulic lime), a latent hydraulic binder (e.g., slag or furnace slag), a pozzolanic binder (e.g., fly ash), or a non-hydraulic binder (gypsum or white lime). Mixtures of the various binders are also possible. In particular, the mineral binder comprises a hydraulic binder, preferably cement. A cement with a cement clinker content of >35% by weight is particularly preferred. Preferably, the cement is of type CEM I, CEM II, CEM III, OEM IV, CEM V (according to EN 197-1) or a calcium aluminate cement (according to EN 14647:2006-01) or a calcium sulfoaluminate cement, or a mixture thereof. Of course, cements produced in accordance with relevant alternative standards, for example, relevant ASTM or Chinese standards, are also suitable. In addition, white cement may be used as the mineral binder of the present invention. The proportion of hydraulic binder in the total mineral binder is preferably at least 5% by weight, more preferably at least 20% by weight, even more preferably at least 35% by weight, and in particular at least 65% by weight. According to another advantageous embodiment, the mineral binder consists of at least 95% by weight of hydraulic binder, particularly cement. It may also be advantageous for the mineral binder to contain other binders in addition to or instead of a hydraulic binder. These are, in particular, latent hydraulic binders and / or pozzolanic binders. Suitable latent hydraulic and / or pozzolanic binders include, for example, slag, fly ash, and / or silica powder. The binder composition may also include inert substances such as, for example, limestone powder, quartz powder, and / or pigments. Depending on the embodiment, the mineral binder further comprises up to 40% by weight, preferably up to 35% by weight, and especially up to 20% by weight, each based on the total dry weight of the mineral binder, of calcium sulfate. The calcium sulfate may be present in the form of calcium sulfate hemihydrate, calcium sulfate dihydrate, and / or anhydrite. In a particularly advantageous embodiment, the calcium sulfate is crushed with the hydraulic binder, especially cement. Furthermore, a mineral binder, especially a cement, of the present invention may comprise cement improvers selected from the group consisting of grinding aids, strength enhancers, activators, accelerators, plasticizers, and superplasticizers. The cement improvers may be ground with the mineral binder during grinding. They may also be mixed with the ground mineral binder. The mixture of the present invention comprises at least one superabsorbent polymer (SAP). An SAP, within the context of the present invention, is a polymer that can absorb, retain, and release large quantities of a liquid, especially water, relative to its own mass. Therefore, an SAP can absorb up to 500 times its own weight in water and can swell to a considerable degree. A SAP of the present invention may be characterized by water absorption under a loading of 40 g / cm² of at least 15 g / g of polymer, preferably at least 20 g / g of polymer, more preferably at least 22 g / g of polymer. A SAP of the present invention may also release some or all of the absorbed water. According to embodiments, the SAP of the present invention is a solid, preferably a fine powder. In the preferred case where the SAP is a powder, said powder is characterized by a particle size distribution with SAP particle sizes between 20 and 3000 µm, preferably between 50 and 1000 µm, and more preferably between 90 and 850 µm. The particle size distribution can be obtained by sieving the powder through sieves with different openings. The particle size distribution can be determined by a method as described in ASTM C136 and ASTM C117. The at least one SAP of the present invention is selected from the list consisting of polyacrylamide, polyacrylonitrile, polyvinyl alcohol, isobutylene maleic anhydride copolymers, polyvinylpyrrolidone, homopolymers and copolymers of monoethylenically unsaturated carboxylic acids, such as (meth)acrylic acid, crotonic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, preferably polyacrylic acid, which may be partially or totally neutralized, and copolymers and terpolymers of said monoethylenically unsaturated carboxylic acids with vinylsulfonic acid, (meth)acrylamidoalkylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, vinylphosphonic acid, (meth)acrylamide, N-alkylated (meth)acrylamide, N-methylol (meth)acrylamide, N-vinylamide, N-vinylformamide, N-vinylacetamide, vinylpyrrolidone, hydroxyalkyl (meth)acrylate, ethyl methylacrylate, polyethylene glycol (meth)acrylic acid esters monoalters,vinyl acetate and / or styrene. The homopolymers and copolymers mentioned can be linear or branched; the copolymers can be random, block, or gradient-linked. Furthermore, the preferred homopolymers and copolymers are crosslinked. A method for producing the aforementioned polymers is described in DE19529348, which is incorporated herein by reference. The preferred SAPs in the context of the present invention are polyacrylic acids, which may be partially or totally neutralized and crosslinked. According to the modalities, at least one SAP has a nitrogen content of no more than 4% by weight, preferably no more than 2% by weight, especially no more than 1% by weight, in each case with respect to the total dry weight of the SAP. According to embodiments, the at least one SAP of the present invention consists of at least 70% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, especially at least 98% by weight, each based on the total dry weight of the at least one SAP, of a polymer as described above. Specifically, SAP is chemically different from superplasticizers, as described below. This is especially true for PCE superplasticizers. The appropriate SAP can, for example, be obtained under the Starvis® brand from BASF or under the Sanwet brand from Sanyo Chemical. The mixture of the present invention further comprises at least one antifoaming agent D. The at least one antifoam D is selected from the list consisting of oil-based antifoams, especially mineral oil, vegetable oil or white oil-based antifoams that may comprise a wax and / or hydrophobic silica, silicone-based antifoams, which may be modified by, for example, alkoxylation or fluorination, alkyl esters of phosphoric or phosphonic acid, alkoxylated polyols, especially ethoxylated diols, fatty acid-based antifoams, especially mono- and diglycerides of fatty acids, alkoxylated fatty alcohols or mixtures thereof. The D antifoams can be used as liquids or powders, preferably as liquids. Depending on the embodiment, at least one D antifoam is selected from ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol, a fatty alcohol alkoxylate and polysiloxane combination, or a combination of a mineral oil and a silicone oil comprising hydrophobic silica. Suitable D antifoams can be obtained commercially, for example, under the Ashland Drew brand from Ashland, the Agitan brand from Münzing Chemie, or the Carbowet brand from Air Products. The weight ratio of at least one SAP to at least one antifoaming agent D in a mixture of the present invention is 2:1 - 1:10, preferably 1:1-1:8, more preferably 1:2 - 1:5. Depending on the formulation, the weight ratio of at least one SAP to at least one antifoam D can be 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10. It is also possible for the weight ratio to be between 1:1.1 and 1:10 or between 1.5:1 and 1:10. Another useful weight ratio is within the range of 2:1 to 1:5:1. Other useful weight ratios of at least one SAP to at least one antifoam D are 1:2.5 or 1:7.5. Depending on the embodiment, a mixture of the present invention may be in the form of a dry powder, in the form of a solution or aqueous dispersion, or in the form of two or more separate components that may, independently of each other, be in the form of a powder or liquid. If the mixture of the present invention is provided in the form of an aqueous solution or dispersion, it is preferred that the total content of at least one SAP and at least one antifoaming agent D be up to 85% by weight, preferably up to 66% by weight, especially up to 50% by weight, each based on the total weight of the mixture. Without intending to be limited by any particular theory, it is believed that at least one SAP acts as a small sponge that retains water and counteracts the self-drying of the hardening mineral binder composition, thus effectively reducing shrinkage. It is further believed that the combination of at least one superabsorbent polymer SAP and at least one defoamer D leads to a particularly effective and homogeneous dispersion of the SAP within the mineral binder composition and therefore to a particularly high reduction in shrinkage. In another aspect, the present invention relates to a mineral binding composition as described above and comprising at least one SAP and at least one antifoaming agent D as described above. According to embodiments, the mineral binder composition comprises at least one SAP of the present invention in an amount of 0.01 - 0.5% by weight, preferably 0.02 - 0.25% by weight, more preferably 0.05 - 0.2% by weight, and at least one antifoam D in an amount of 0.05 - 2% by weight, preferably 0.1-1% by weight, more preferably 0.25 - 0.8% by weight, each based on the total dry weight of the mineral binder composition. Preferably, the mineral binder composition of the present invention comprises aggregates. The aggregates may be any material that is non-reactive in the hydration reaction of the mineral binders. The aggregates may be any aggregate typically used for mineral binder compositions, especially cementitious binder compositions. Typical aggregates include, for example, rock, crushed stone, gravel, slag, sand, especially quartz sand, river sand and / or manufactured sand, recycled concrete, glass, expanded glass, pumice, perlite, vermiculite, and / or fine aggregates such as ground limestone, ground dolomite, ground aluminum oxide, silica fume, quartz flour, and / or ground steel slag. The aggregates useful for the present invention may have any shape and size typically found for such aggregates. Preferably, the mineral binder composition of the present invention comprises at least one fine aggregate, especially ground limestone. The aggregates useful for the present invention are as described, for example, in EN 12620:2008-07 and EN 13139:2015-07. The aggregates are typically characterized by their particle size distribution, which can be measured by sieve analysis as set forth in ASTM methods C136 and C117. The particle size of the aggregates depends on the application and ranges from 0.1 µm to 32 mm and larger. Aggregates with different particle sizes are preferably mixed to optimize the properties of the mineral binder composition. It is also possible to use aggregates of different chemical compositions. According to the specifications, the aggregates have particle sizes of no more than 8 mm, more preferably no more than 5 mm, even more preferably no more than 3.5 mm, at most IVIA / a / ZUZI / UIU / ZO preferably not more than 2.2 mm, especially not more than 1.2 mm or not more than 1.0 mm are used in a mineral binder composition of the present invention. The maximum particle size is limited, in particular, by the planned layer thickness during the application of the mineral binder composition mixed with water. For example, the maximum aggregate particle size must be the same as the layer thickness during application. This is especially true when the mineral binder composition is applied using an additive manufacturing method. According to embodiments, the mineral binder composition of the present invention comprises up to 85% by weight, preferably 30-80% by weight, more preferably 40-70% by weight, each based on the total weight of the mineral binder composition, of aggregates, preferably sand, especially quartz sand, and / or a fine carbonate, especially a fine calcium carbonate and / or magnesium carbonate. According to the modality, sand with a particle size of less than 1 mm, preferably less than 0.8 mm, is used for a mineral binder composition of the present invention. According to a particularly preferred embodiment, a mineral binder composition of the present invention comprises a mixture of sand, especially quartz sand, and / or a fine carbonate, especially fine calcium carbonate and / or magnesium carbonate, said carbonates having a particle size of less than 0.125 mm. In this case, the aggregates comprise sand in an amount of 40–98% by weight, preferably 50–95% by weight, especially 60–90% by weight, and fine carbonates in an amount of 2–60% by weight, preferably 5–50% by weight, especially 10–40% by weight, each based on the total dry weight of the aggregate. The fine carbonates improve the processability of the mineral binder composition mixed with water and may increase the strength development of the binder composition. Mineral binder compositions having particle sizes of this type and mixed with water can be easily transported, mix easily with a mixture of the present invention continuously, and give a very homogeneous surface after application. In special applications, aggregates with particle sizes up to 32 mm can also be used, more preferably up to 20 mm, most preferably up to 16 mm. A mineral binder composition advantageously further comprises additives common in the mortar and / or concrete industry, such as, for example, plasticizers and / or superplasticizers, air-entraining agents, stabilizers, viscosity modifiers, water reducers, accelerators, retarders, water-resistant agents, fiber-strengthening admixtures, blowing agents, pigments, corrosion inhibitors, etc. It may be advantageous to combine two or more of the aforementioned additives in a mineral binder composition. An additive for a mineral binder composition within the meaning of the present context is different in chemical composition and structure from any SAP or antifoaming agent D as defined herein. A mineral binder composition of the present invention, therefore, comprises a) 10-65% by weight, preferably 12-55% by weight, especially 15-50% by weight of at least one mineral binder, b) 0.01 - 0.5% by weight, preferably 0.02 - 0.25% by weight, more preferably 0.05 - 0.2% by weight of at least one SAP, c) 0.05 - 2% by weight, preferably 0.1-1% by weight, more preferably 0.25 - 0.8% by weight of at least one antifoaming agent D, d) 0-85% by weight, preferably 30-80% by weight, more preferably 40-70% by weight of aggregates, preferably sand and / or a fine carbonate, especially a fine calcium carbonate and / or magnesium carbonate, e) 0-10% by weight, preferably 0.1-7% by weight, more preferably 0.2-5% by weight of other additives selected from the group consisting of plasticizers, superplasticizers, accelerators, retarders, rheology modifiers, especially thickeners, anti-sedimentation agents, pigments, corrosion inhibitors, fibers, strength enhancers, waterproofing additives, alkali aggregate reaction inhibitors, chromate reducers and / or antimicrobial agents and f) optionally water, each based on the total dry weight of the mineral binder composition. According to embodiments, a mineral binder composition of the present invention comprises a superplasticizer selected from the group consisting of lignosulfonates, sulfonated vinyl copolymers, polynaphthalenesulfonates, sulfonated melamine formaldehyde condensates, polyethylene oxide phosphonates, polycarboxylate ethers (PCE), or mixtures thereof. Preferably, a mineral binder composition of the present invention comprises a PCE. According to the embodiment, the PCE comprises carboxylic acid groups in the form of free, unneutralized carboxylic acid groups and / or in the form of their alkali and / or alkaline earth metal salts. Preference is given to a PCE that, apart from the carboxylic acid groups, contains no other anionic groups. A PCE is further preferred in which the side chains consist of at least 80 mol%, preferably at least 90 mol%, and especially preferably 100 mol%, of ethylene glycol units. Preferably, the side chains have an average molecular weight (Mw) in the range of 500 to 10,000 g / mol, preferably 800 to 8,000 g / mol, and especially preferably 1,000 to 5,000 g / mol. Side chains of different molecular weights may also be present in the PCE. Most preferably, PCE is composed of (meth)acrylic acid and polyalkylene glycol methyl (meth)acrylates.PCE preferably has a mean molecular weight Mw of 8000 to 200,000 g / mol, especially 10,000 to 100,000 g / mol, measured against PEG standards. Such PCE are particularly suitable for enabling good processability of the binder composition even at low water content. Low water content results in high strength of a hardened mineral binder composition. According to certain embodiments, the PCE is incorporated into the mineral binder composition as an aqueous solution, for example, by spraying it onto the aggregates before mixing them with the mineral binder. Preferably, the PCE is present as a polymer powder in the dry mineral binder composition. According to preferred embodiments, the mineral binder composition of the present invention comprises PCE in an amount of 0.02–1.0% by weight, preferably 0.05–0.8% by weight, and especially 0.1–0.5% by weight, each calculated as the dry weight of the PCE and based on the total dry weight of the mineral binder composition.According to embodiments, a mineral binder composition of the present invention comprises an accelerator selected from the group consisting of amino alcohols, alkali or alkaline earth metal nitrates, alkali or alkaline earth metal nitrites, alkali or alkaline earth metal thiocyanates, alkali or alkaline earth metal halides, glycerin, glycerin derivatives, aluminum sulfate, aluminum hydroxide, alkali or alkaline earth metal hydroxides, alkali or alkaline earth metal silicates, alkali or alkaline earth metal oxides, alkali or alkaline earth metal salts of formic acid, or mixtures thereof. According to embodiments, a mineral binding composition of the present invention comprises a thickener selected from the group consisting of starch, pectin, amylopectin, modified starch, cellulose, modified cellulose such as carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, methylhydroxyethylcellulose, casein, xanthan gum, diutane gum, welan gum, galactomannans such as guar gum, tara gum, fenugreek gum, locust bean gum or cassia gum, alginates, tragacanth gum, dextran, polydextrose, stratified silicates such as sepiolite and mixtures thereof. It is preferred that the total amount of thickener be equal to or less than 1% by weight, more preferably equal to or less than 0.75% by weight, and especially equal to or less than 0.6% by weight, each based on the total dry weight of the mineral binder composition. It is especially preferred that the total amount of starch, modified starch, cellulose, and modified cellulose be equal to or less than 1% by weight, and particularly equal to or less than 0.5% by weight, each based on the total dry weight of the mineral binder composition. According to embodiments, a mineral binder composition of the present invention comprises a retarder selected from the group consisting of sugar acids, sugars, sugar alcohols, hydroxycarboxylic acids or their salts, phosphates, phosphonates, borates, and amines. Preferably, the retarder is sodium gluconate. In a particularly preferred embodiment of the present invention, the mineral binder composition comprises a mineral binder selected from CEM I or CEM II as described above and an additional amount of calcium sulfoaluminate cement (CSA). A CSA cement of the present invention is a cement with a main phase consisting of C4(A3.xFx)3$ (4 CaO · 3-x Al2O3 · x Fe2Os · CaSO4) where x is an integer from 0 to 3. CSA cements of the present invention typically comprise additional phases selected from aluminates (CA, C3A, C12A7), belite (C2S), ferrites (C2F, C2AF, C4AF), ternesite (CsS2$) and anhydrite. In the present context, C represents CaO, A represents Al2O3, F represents Fe2O3 and $ represents CaSO4. According to certain embodiments of CSA cements of the present invention, they comprise 20-75 wt%, preferably 25-50 wt% of C4A3, 0-10 wt%, preferably 1-5 wt% of aluminates, 0-70 wt%, preferably 1-50 wt% of belite, 0-35 wt%, preferably 1-10 wt% of ferrites, 0-20 wt%, preferably 1-10 wt% of ternesite, 0-50 wt%, preferably 5-45 wt% of anhydrite, and 0-25 wt% of CaO, preferably 1-20 wt% of CaO, each based on the total dry weight of the CSA cement. The mineral binder composition of the present invention thus preferably comprises 10-65% by weight, preferably 12-55% by weight, especially 15-50% by weight, each based on the dry weight of the mineral binder composition, of a mixture of mineral binders, preferably a mixture comprising a CEM I and / or CEM II, and a CSA cement.Preferably, the mineral binder composition thus comprises 0.1-8 wt., more preferably 0.5-5 wt., especially 1.2-3 wt., each based on the dry weight of the mineral binder composition of a CSA cement and 2-64.9 wt., preferably 4-60 wt., especially 12-48.8 wt., each based on the dry weight of the mineral binder composition of a CEM I and / or a CEM II. According to particularly preferred embodiments, a mineral binder composition of the present invention therefore comprises: 1) 2 - 64.97° by weight, preferably 4 - 607° by weight, especially 12 - 48.87° by weight of a CEM or a CEM II, 2) 0.1 - 8.7° by weight, more preferably 0.5 - 5.7° by weight, especially 1.2-3.7° by weight of a CSA cement, iviA / a / ¿u¿ ι / u 1 u / zo 3) 0.01 - 0.5% by weight, preferably 0.02 - 0.25% by weight, more preferably 0.05 - 0.2% by weight of at least one SAP, 4) 0.05 - 2% by weight, preferably 0.1-1% by weight, more preferably 0.25 - 0.8% by weight of at least one antifoaming agent D, 5) 0-85% by weight, preferably 30-80% by weight, more preferably 40-70% by weight of aggregates, preferably sand and / or a fine carbonate, especially a fine calcium carbonate and / or magnesium carbonate, 6) 0-10% by weight, preferably 0.1-7% by weight, more preferably 0.2-5% by weight of other additives selected from the group consisting of superplasticizers, accelerators, retarders, thickeners and 7) optionally water, each based on the total dry weight of the mineral binder composition. According to certain embodiments, a mixture of the present invention is added to a dry mix of a mineral binder composition. A dry mix in this context refers to a mineral binder composition with a moisture content of no more than 0.5% by weight, based on the total weight of the mineral binder composition. In this case, it is preferred that the mixture not contain water. The storage stability of a dry mix comprising a mixture of the present invention will be enhanced if water is not added. Mixing may be carried out by any process known to the skilled trade for the production of dry mortars. There are no particular limitations as to the order of addition for mixing.Suitable mixers may include single-shaft horizontal mixers, twin-shaft paddle mixers, vertical shaft mixers, ribbon mixers, orbital mixers, interchangeable-can mixers, rotary vessels, vertical stirring chambers, or air-driven mixers. Mixing can be continuous or batch. According to further embodiments, a mixture of the present invention is added to a mineral binder composition along with the mixing water. In such case, it is preferred that the mixture be in the form of an aqueous solution or dispersion, or be readily soluble or dispersible in the mixing water. The mixture of the present invention may be premixed with some or all of the mixing water and then mixed with the mineral binder composition. Alternatively, it may be mixed with the mineral binder composition along with the mixing water without any premixing. The mixing can be continuous or batch-based, preferably continuous. Continuous mixing offers the advantage of high production speed. Furthermore, the already mixed material from a batch process must be discarded in the event of a production stoppage. Continuous mixing of a mineral binder composition with the mixture of the present invention and mixing water is possible using static mixers, dynamic mixers, or combinations of both. According to other embodiments, a mixture of the present invention is added to the mineral binder composition shortly after the mixing water, preferably in a continuous manner as described above. When mixed with water, the mineral binder composition begins to harden. A mixture of the present invention can be used to ensure dimensional stability and, in particular, to reduce shrinkage of a mineral binder composition, especially a cementitious binder composition. Likewise, a mixture of the present invention can be used to improve the surface texture of a hardened mineral binder composition. Therefore, a mineral binder composition of the present invention can have, for example, a smoother surface and / or fewer visual defects compared to the same mineral binder composition without at least one SAP and at least one antifoaming agent D. An improved surface texture can lead to simplified subsequent treatments of said surface, such as tooling, coating, painting, plastering, etc. A mineral binder composition of the present invention can be mixed with water, molded into a desired shape, and cured to produce hardened articles. Therefore, the invention also relates to a method for producing a hardened article comprising the steps of: 1) mixing a mineral binder composition of the present invention with water. 2) Optionally transport the mixture obtained in 1) to the placement location 3) Place the mixture obtained in 1) in any desired shape 4) curing of the mixture obtained in 1). The water may be any available water, such as distilled water, purified water, tap water, mineral water, spring water, and well water. The use of wastewater is only possible when its composition is known and none of the impurities present can affect the functionality of any other component of the composition of the present invention. The use of saltwater is not possible due to its high chloride content and the associated risk of corrosion of the reinforcing steel. The amount of water required to cure a mineral binder composition of the present invention is 10 to 30% by weight, preferably 10 to 20% by weight, each based on the total dry weight of the mineral binder composition. According to certain embodiments, the water comprises part or all of one or more additives selected from the group consisting of plasticizers, superplasticizers, accelerators, retarders, rheology modifiers, especially thickeners, anti-sedimentation agents, pigments, corrosion inhibitors, fibers, strength enhancers, waterproofing additives, alkali aggregate reaction inhibitors, chromate reducers, and / or antimicrobial agents, and which form part of the mineral binder composition as described above. According to preferred embodiments, the water comprises part or all of the mixture of the present invention. It is preferred that if the at least one SAP and the at least one antifoaming agent D of the present invention are added together with the water, the at least one SAP and the at least one antifoaming agent D be water-soluble or readily dispersible in water. According to especially preferred embodiments, the mineral binder composition is therefore present in two or more components. A first component, which is a solid, comprising at least one mineral binder, aggregates, optionally at least one SAP and / or at least one antifoam D, and optionally other additives; a second component, which is a liquid, comprising water and optionally at least one SAP and / or at least one antifoam D, and optionally other additives, wherein the at least one SAP and at least one antifoam D are comprised in the first component or in the second component; and optionally a third component, which is a liquid, comprising a superplasticizer, an accelerator, a thickener and / or a retarder, as described above, and optionally water. The mixing of the components as described above can be carried out by any process known to a person skilled in the art. The mixing can be batch, semi-continuous, or continuous. Suitable mixing equipment includes single-shaft horizontal mixers, twin-shaft paddle mixers, vertical shaft mixers, ribbon mixers, orbital mixers, interchangeable-can mixers, rotary vessels, vertical stirring chambers, air-driven mixers, Hobart mixers, portable concrete mixers, mixer trucks, mixing buckets, paddle mixers, jet mixers, screw mixers, screw extruders, or auger mixers. Furthermore, it is possible to mix a mineral binder composition of the present invention with water, said water optionally comprising additional additives and / or the mixture of the present invention by means of a static mixer or a dynamic mixer. In a preferred embodiment of the present invention, a static mixer is used to mix the components. In a static mixer, the mixing elements are arranged in a jacket that provides a homogeneous mixture of components using the flow energy of the components fed into the static mixer under pressure. Static mixers are easy to use, economical, and particularly suitable for unidirectional use, which is advantageous, especially for the DIY market. iviA / a / zuz ι / u iu / zo According to another preferred embodiment, the components described above are mixed semi-continuously or continuously. The components are usually dosed in a predefined quantity via at least one dosing device, for example, a conveyor belt or screw conveyor, capable of transporting the desired quantity of the components by mass or volume at the desired rate to a mixer. It is particularly preferred to have two separate dosing devices, the first being integrated into a mixer, and the second being integrated into a dosing unit, for example, a nozzle. This allows for particularly stable transport of the mixture, as well as flexible adjustment of the mineral hardening binder composition. In the mixing device, which can be static or dynamic or a combination of both, the components are mixed and the fresh mixture is conveyed through dispensing equipment, for example, a nozzle, and placed in a predefined position. It has been shown that, on the one hand, a mineral binder composition of the present invention can be mixed in this way in the mixing device and at the same time transported in mixed form out of the mixing device. A paste-like consistency of the mineral binder composition after mixing with water is advantageous for easy transport of the material to and through the mixing and dispensing equipment, such as a nozzle. These properties are especially important for use in an automated process, for example, with a robotic system. The mineral binder composition of the present invention can be applied in an automated process, for example, using a robotic system. A robotic system typically applies the mineral binder composition in several layers in a process also known as additive manufacturing. Therefore, a mineral binder composition of the present invention can be used in additive manufacturing. It is advantageous if a mineral binder composition of the present invention, when used for additive manufacturing, comprises the aforementioned components of said mineral binder composition in such proportions as to ensure that the freshly mixed mineral binder composition, as it comes out of the mixer, is still in a plastic state, so that it is moldable by the dispensing equipment, for example a nozzle, does not warp and is self-supporting, and has sufficient yield strength and / or rapid development of compressive strength to support subsequent layers of freshly mixed mineral binder composition, which are applied on top after a short period of time. According to certain embodiments, the surface of the mineral binder composition of the present invention is moistened, for example, by applying water, damp sheets, or a plastic covering, after placement. However, it is not necessary to wet or cover the surface of a freshly applied mineral binder composition of the present invention. According to preferred embodiments, the mineral binder composition is not moistened, for example, by applying water, damp sheets, or a plastic covering, after placement. The mineral binder composition of the present invention can be used for construction, prefabricated elements, repair, and restoration, and is suitable for both professional and personal use. The low shrinkage of a mineral binder composition of the present invention makes it particularly useful in applications where large elements or elements with a long preferred axis are produced. Therefore, the present invention also relates to a molded article, for example, a prefabricated element, a building, or a part of a building, which can be obtained by curing a mineral binder composition comprising a mixture as described above. Brief description of the figures Figure 1 shows the surface of example 8 after 7 days of hardening. The crack on the surface is clearly visible. Figure 2 shows the surface of example 9 after 7 days of hardening. No cracks are visible on the surface. The following practical examples illustrate the invention. The examples are not intended to limit the scope of the invention in any way. Functional examples Examples 1 - 7 1500 g of ordinary Portland cement (CEM I, 52.5 N), 2250 g of quartz sand (particle size 0.06 - 0.3 mm) and 1100 g of calcium carbonate (average particle size 40 pm) were mixed in a Hobart mixer for 1 minute at 23 °C and 50% relative humidity to make dry mix 1. 1500 g of ordinary Portland cement (CEM I, 52.5 N), 100 g of calcium sulfoaluminate cement (Denka CSA#20) and 2250 g of quartz sand (particle size 0.06 0.3 mm), and 1100 g of calcium carbonate (average particle size 40 pm) were mixed in a Hobart mixer for 1 minute at 23 °C and 50% relative humidity to make dry mix 2. Next, 20 g of a polycarboxylate ether (40% in water, polyacrylate main chain with Mn = 7000 g / mol, methyl-terminated PEG side chain with Mn = 2500 g / mol, carboxylate / ester ratio = 3) was added to the respective dry mixture as indicated in Table 1 below, along with the additives in Table 1 below and 800 g of water, and mixing continued for 2 minutes. The total mixing time was approximately 3 minutes. iviA / a / zuzi / uiu / zo Table 1 Example 1 (Ref) 2 (Ref) 3 (Ref) 4 5 6 (Ref) 7 (Ref) Dry mix 1 2 2 2 2 2 2 weight of dry mix [g] 4850 4950 4950 4950 4950 4950 4950 Antifoam D [g] 25* 25* 25** 25** SAP [g] 10 10 10 NPG [g] 25 Thickener [g] 5*** 5*** NPG: neopentyl glycol (Sigma Aldrich, 99% purity) SAP: Starvis S5514F * mixture of mineral oil and silicone oil with hydrophobic silica * * 2,4,7,9-tetramethyl-5-decyn-4,7-diol ethoxylate * ** methylhydroxyethylcellulose Examples 4 and 5 in Table 1 above correspond to the present invention. Examples 1-3 and 6-7 are comparative examples that do not conform to the present invention. Table 2 below provides an overview of the results. Linear shrinkage was measured according to EN 12617-4 on 40 x 40 x 160 mm prisms within 8 h and 16 h of mixing with water. Table 2 Example 1 2 3 4 5 6 7 Linear contraction at 8 h [pm / m] -936 -607 -790 -230 -850 -1880 -950 Linear contraction at 16 h [pm / m] -948 -612 -638 + 100 -700 -1581 -1020 nm: not measured As can be seen from the results above, inventive example 4 shows a reduced linear shrinkage compared to comparative examples 1-3. Inventive example 5 also shows a smaller shrinkage compared to comparative examples 1 and 6. Comparative example 7 shows that the use of neopentyl glycol, an example of an alkylene glycol, cannot reduce shrinkage. Examples 8 - 9 450 g of white Portland cement (CEM I, 52.5 N), 30 g of calcium sulfoaluminate cement (Denka OSA# 20), 195 g of fine quartz sand (particle size 0.075 - 0.3 mm), 435 g of quartz sand (particle size 0.06 - 0.8 mm), 364 g of calcium carbonate (average particle size 50 pm) and 2.25 g of a powdered ether polycarboxylate (polyacrylate main chain with Mn = 5000 g / mol, Me-terminated PEG side chain with Mn = 2700 g / mol, carboxylate / ester ratio = 5.6) were mixed in a Hobart mixer for 1 minute at 23°C and 50% relative humidity to make a dry mix. The additives in Table 3 below were added to the dry mix along with 240 g of water and mixing continued for 2 minutes. The total mixing time was approximately 3 minutes. Table 3 Example 8 (Ref) 9 Antifoam D [g] 7.5* 7.5* SAP [g] 1 Thickener [g] 3** 0.15*** 0.04** 0.15*** SAP: Starvis S5514F * ethoxylated 2,4,7,9-tetramethyl-5-dec¡n-4,7-d¡ol * * methylhydroxyethylcellulose * ** Kelco-crete® D-GF [g] As can be seen in Figures 1 and 2, Example 8, which does not conform to the present invention, shows cracks. Whereas Example 9, which conforms to the present invention, does not show cracks. Examples 10-11 Examples 10 and 11 were prepared in the same manner as Example 4. However, the quantities of SAP and antifoam D were adjusted as shown in Table 4 below. Example 10 is a reference not according to the present invention, while Example 11 is according to the present invention. The linear shrinkage test of Examples 10 and 11 was performed as described above, and the results are included in Table 4. These results show that the inventive Example 11 exhibits low linear shrinkage, while the comparative Example 10, where the weight ratio of SAP to antifoam D is outside the preferred range, exhibits high linear shrinkage. Table 4 Example 10(Ref) 11 Dry mix 2 2 Weight of dry mix [g] 4950 4950 Antifoam D [g] 10* 75* SAP [g] 40 10 Linear shrinkage at 16 h [pm / m] -1654 -736 mixture of mineral oil and silicone oil with hydrophobic silica iviA / a / zuz ι / u iu / zo

Claims

1. A mixture for mineral binder compositions, especially for shrinkage reduction, comprising at least one superabsorbent polymer SAP and at least one defoamer D.

2. A mixture according to claim 1, characterized in that the at least one superabsorbent polymer SAP is selected from the group consisting of polyacrylamide, polyacrylonitrile, polyvinyl alcohol, isobutylene maleic anhydride copolymers, polyvinylpyrrolidone, homopolymers and copolymers of monoethylenically unsaturated carboxylic acids, such as (meth)acrylic acid, crotonic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, preferably polyacrylic acid, which may be partially or totally neutralized, and copolymers and terpolymers of said monoethylenically unsaturated carboxylic acids with vinylsulfonic acid, (meth)acrylamidoalkylsulfonic acid, allylsulfonic acid, etc. vinyltoluenesulfonic acid, vinylphosphonic acid, (meth)acrylamide,N-alkylated (meth)acrylamide, N-methylol (meth)acrylamide, N-vinylamide, N-vinylformamide, N-vinylacetamide, vinylpyrrolidone, hydroxyalkyl (meth)acrylate, ethyl acrylate, methyl acrylate, polyethylene glycol (meth)acrylic acid esters, monoalters, vinyl acetate, and / or styrene.

3. A mixture according to any one of claim 1 or 2, characterized in that at least one SAP superabsorbent polymer is a polyacrylic acid that may be partially or totally neutralized and crosslinked.

4. Mixture according to any of claims 1-3, characterized in that at least one antifoaming agent D is selected from the group consisting of mineral oils, vegetable oils or white oils which may comprise a wax and / or hydrophobic silica, silica, silicones, which may be modified by alkoxylation or fluorination, alkyl esters of phosphoric or phosphonic acid, alkoxylated polyols, especially ethoxylated diols, fatty acid-based antifoaming agents,especially mono- and diglycerides of fatty acids and alkoxylated fatty alcohols.

5. A mixture according to any of claims 1-3, characterized in that the weight ratio of the at least one SAP to the at least one antifoam D is 2:1-1:10, preferably 1:1-1:8, more preferably 1:2-1:

5.

6. A mixture according to any of the preceding claims, characterized in that it is an aqueous solution or dispersion comprising the at least one SAP and the at least one antifoam D in a combined amount of up to 85% by weight, preferably up to 66% by weight, especially up to 50% by weight, each based on the total weight of the mixture.

7. Use of a mixture of any of the preceding claims to improve dimensional stability, especially to reduce shrinkage, of a mineral binder composition.

8. Use of a mixture of any of claims 1 to 6 to improve the surface texture of a hardened mineral binder composition.

9. Use of a mixture of any of claims 1 to 6 in a manual process, a semi-automatic process, or an automated process, preferably a semi-automated or automated process, especially in an additive manufacturing process.

10. A mineral binder composition comprising a) 10-65% by weight, preferably 12-55% by weight, especially 15-50% by weight of at least one mineral binder, b) 0.01-0.5% by weight, preferably 0.02-0.25% by weight, more preferably 0.05-0.2% by weight of at least one SAP, c) 0.05-2% by weight, preferably 0.1-1% by weight, more preferably 0.25-0.8% by weight of at least one antifoaming agent D, d) 0-85% by weight, preferably 30-80% by weight, more preferably 40-70% by weight of aggregates,preferably of sand and / or a fine carbonate, especially a fine calcium carbonate and / or magnesium carbonate, e) 0-10% by weight, preferably 0.1-7% by weight, more preferably 0.2-5% by weight of other additives selected from the group consisting of plasticizers, superplasticizers, accelerators, retarders, rheology modifiers, especially thickeners, anti-sedimentation agents, pigments, corrosion inhibitors, fibers, strength enhancers, waterproofing additives, alkali aggregate reaction inhibitors, chromate reducers and / or antimicrobial agents, and f) optionally water, each based on the total dry weight of the mineral binder composition.

11. A mineral binder composition according to claim 10,characterized in that the at least one mineral binder is a mixture of at least one CEM I or CEM II and at least one calcium sulfoaluminate cement.

12. A mineral binder composition according to any of claims 10 and 11, characterized in that the mineral binder comprises a) 0.1-8% by weight, more preferably 0.5-5% by weight, especially 1.2-3% by weight, each based on the dry weight of the mineral binder composition, of a CSA cement and b) 2-64.9% by weight, preferably 4-60% by weight, especially 12-48.8% by weight, each based on the dry weight of the mineral binder composition, of a CEM I and / or a CEM II.

13. A mineral binder composition according to any of claims 10 to 12, characterized in that it comprises a) 0.02-1.0% by weight, preferably 0.05-0.8% by weight, especially 0.1-0.5% by weight of a polycarboxylate ether composed of (meth)acrylic acid and polyalkylene glycol methyl (meth)acrylates and having a molecular weight Mw of 8000 to 200,000 g / mol, especially 10,000 to 100,000 g / mol and (b) a maximum of 1% by weight, more preferably 0.75% by weight, especially 0.6% by weight of at least one thickener selected from the group consisting of starch, pectin, amylopectin, modified starch, cellulose, modified cellulose, such as carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, methylhydroxyethylcellulose, casein, welan gum, xanthan gum, diutan gum, galactomannans, such as guar gum, tara gum, fenugreek gum, locust bean gum or cassia gum, alginates, tragacanth gum, dextran, polydextrose, stratified silicates such as sepiolite,each based on the total weight of the mineral binder composition.

14. Method of producing a hardened article comprising the steps of: 1) mixing a mineral binder composition according to any of claims 10 to 13 with water, 2) optionally transport the mixture obtained in 1) to the placement site, 3) Place the mixture obtained in 1) in any desired shape, 4) curing the mixture obtained in 1), characterized in that step 1) is carried out in a continuous process by means of a static and / or dynamic mixer.

15. Use of a water-containing mineral binder composition of any of claims 10-13 in an additive manufacturing process.

16. Molded article obtainable by curing a mineral binder composition according to any of claims 10-13.