US20070204544A1

US20070204544A1 - Additive building material mixtures containing solid microparticles

Info

Publication number: US20070204544A1
Application number: US11/388,046
Authority: US
Inventors: Holger Kautz; Jan Hendrik Schattka; Gerd Lohden
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 2006-03-01
Filing date: 2006-03-24
Publication date: 2007-09-06
Also published as: CN101028972A; WO2007099009A1; DE102006009840A1

Abstract

The present invention relates to the use of compact polymeric microparticles in hydraulically setting building material mixtures for the purpose of enhancing their frost resistance and cyclical freeze/thaw durability.

Description

The present invention relates to the use of polymeric microparticles in hydraulically setting building material mixtures for the purpose of enhancing their frost resistance and cyclical freeze/thaw durability.
Concrete is an important building material and is defined by DIN 1045 (07/1988) as artificial stone formed by hardening from a mixture of cement, aggregate and water, together where appropriate with concrete admixtures and concrete additions. One way in which concrete is classified is by its subdivision into strength groups (BI-BII) and strength classes (B5-B55). Adding gas-formers or foam-formers to the mix produces aerated concrete or foamed concrete (Römpp Lexikon, 10th ed., 1996, Georg Thieme Verlag).
Concrete has two time-dependent properties. Firstly, by drying out, it undergoes a reduction in volume that is termed shrinkage. The majority of the water, however, is bound in the form of water of crystallization. Concrete, rather than drying, sets: that is, the initially highly mobile cement paste (cement and water) starts to stiffen, becomes rigid, and, finally, solidifies, depending on the timepoint and progress of the chemical/mineralogical reaction between the cement and the water, known as hydration. As a result of the water-binding capacity of the cement it is possible for concrete, unlike quicklime, to harden and remain solid even under water. Secondly, concrete undergoes deformation under load, known as creep.
The freeze/thaw cycle refers to the climatic alternation of temperatures around the freezing point of water. Particularly in the case of mineral-bound building materials such as concrete, the freeze/thaw cycle is a mechanism of damage. These materials possess a porous, capillary structure and are not watertight. If a structure of this kind that is full of water is exposed to temperatures below 0° C., then the water freezes in the pores. As a result of the density anomaly of water, the ice then expands. This results in damage to the building material. Within the very fine pores, as a result of surface effects, there is a reduction in the freezing point. In micropores water does not freeze until below −17° C. Since, as a result of freeze/thaw cycling, the material itself also expands and contracts, there is additionally a capillary pump effect, which further increases the absorption of water and hence, indirectly, the damage. The number of freeze/thaw cycles is therefore critical with regard to damage.
Decisive factors affecting the resistance of concrete to frost and to cyclical freeze/thaw under simultaneous exposure to thawing agents; are the imperviousness of its microstructure, a certain strength of the matrix, and the presence of a certain pore microstructure. The microstructure of a cement-bound concrete is traversed by capillary pores (radius: 2 μm-2 mm) and gel pores (radius: 2-50 nm). Water present in these pores differs in its state as a function of the pore diameter. Whereas water in the capillary pores retains its usual properties, that in the gel pores is classified as condensed water (mesopores: 50 nm) and adsorptively bound surface water (micropores: 2 nm), the freezing points of which may for example be well below −50° C. [M. J. Setzer, Interaction of water with hardened cement paste, Ceramic Transactions 16 (1991) 415-39]. Consequently, even when the concrete is cooled to low temperatures, some of the water in the pores remains unfrozen (metastable water). For a given temperature, however, the vapor pressure over ice is lower than that over water. Since ice and metastable water are present alongside one another simultaneously, a vapor-pressure gradient develops which leads to diffusion of the still-liquid water to the ice and to the formation of ice from said water, resulting in removal of water from the smaller pores or accumulation of ice in the larger pores. This redistribution of water as a result of cooling takes place in every porous system and is critically dependent on the type of pore distribution.
The artificial introduction of microfine air pores in the concrete hence gives rise primarily to what are called expansion spaces for expanding ice and ice-water. Within these pores, freezing water can expand or internal pressure and stresses of ice and ice-water can be absorbed without formation of microcracks and hence without frost damage to the concrete. The fundamental way in which such air-pore systems act has been described, in connection with the mechanism of frost damage to concrete, in a large number of reviews [Schulson, Erland M. (1998) Ice damage to concrete. CRREL Special Report 98-6; S. Chatterji, Freezing of air-entrained cement-based materials and specific actions of air-entraining agents, Cement & Concrete Composites 25 (2003) 759-65; G. W. Scherer, J. Chen & J. Valenza, Methods for protecting concrete from freeze damage, U.S. Pat. No. 6,485,560 B1 (2002); M. Pigeon, B. Zuber & J. Marchand, Freeze/thaw resistance, Advanced Concrete Technology 2 (2003) 11/1-11/17; B. Erlin & B. Mather, A new process by which cyclic freezing can damage concrete—the Erlin/Mather effect, Cement & Concrete Research 35 (2005) 1407-11].
A precondition for improved resistance of the concrete on exposure to the freezing and thawing cycle is that the distance of each point in the hardened cement from the next artificial air pore does not exceed a defined value. This distance is also referred to as the “Powers spacing factor” [T. C. Powers, The air requirement of frost-resistant concrete, Proceedings of the Highway Research Board 29 (1949) 184-202]. Laboratory tests have shown that exceeding the critical “Power spacing factor” of 500 μm leads to damage to the concrete in the freezing and thawing cycle. In order to achieve this with a limited air-pore content, the diameter of the artificially introduced air pores must therefore be less than 200-300 μm [K. Snyder, K. Natesaiyer & K. Hover, The stereological and statistical properties of entrained air voids in concrete: A mathematical basis for air void systems characterization, Materials Science of Concrete VI (2001) 129-214].
The formation of an artificial air-pore system depends critically on the composition and the conformity of the aggregates, the type and amount of the cement, the consistency of the concrete, the mixer used, the mixing time, and the temperature, but also on the nature and amount of the agent that forms the air pores, the air entrainer. Although these influencing factors can be controlled if account is taken of appropriate production rules, there may nevertheless be a multiplicity of unwanted adverse effects, resulting ultimately in the concrete's air content being above or below the desired level and hence adversely affecting the strength or the frost resistance of the concrete.
Artificial air pores of this kind cannot be metered directly; instead, the air entrained by mixing is stabilized by the addition of the aforementioned air entrainers [L. Du & K. J. Folliard, Mechanism of air entrainment in concrete, Cement & Concrete Research 35 (2005) 1463-71]. Conventional air entrainers are mostly surfactant-like in structure and break up the air introduced by mixing into small air bubbles having a diameter as far as possible of less than 300 μm, and stabilize them in the wet concrete microstructure. A distinction is made here between two types.
One type—for example sodium oleate, the sodium salt of abietic acid or Vinsol resin, an extract from pine roots—reacts with the calcium hydroxide of the pore solution in the cement paste and is precipitated as insoluble calcium salt. These hydrophobic salts reduce the surface tension of the water and collect at the interface between cement particle, air and water. They stabilize the microbubbles and are therefore encountered at the surfaces of these air pores in the concrete as it hardens. The other type—for example sodium lauryl sulfate (SDS) or sodium dodecylphenylsulfonate—reacts with calcium hydroxide to form calcium salts which, in contrast, are soluble, but which exhibit an abnormal solution behavior. Below a certain critical temperature the solubility of these surfactants is very low, while above this temperature their solubility is very good. As a result of preferential accumulation at the air/water boundary they likewise reduce the surface tension, thus stabilize the microbubbles, and are preferably encountered at the surfaces of these air pores in the hardened concrete.
The use of these prior-art air entrainers is accompanied by a host of problems [L. Du & K. J. Folliard, Mechanism of air entrainment in concrete, Cement & Concrete Research 35 (2005) 1463-71]. For example, prolonged mixing times, different mixer speeds and altered metering sequences in the case of ready-mix concretes result in the expulsion of the stabilized air (in the air pores).
The transporting of concretes with extended transport times, poor temperature control and different pumping and conveying equipment, and also the introduction of these concretes in conjunction with altered subsequent processing, jerking and temperature conditions, can produce a significant change in an air-pore content set beforehand. In the worst case this may mean that a concrete no longer complies with the required limiting values of a certain exposure class and has therefore become unusable [EN 206-1 (2000), Concrete—Part 1: Specification, performance, production and conformity].
The amount of fine substances in the concrete (e.g. cement with different alkali content, additions such as flyash, silica dust or color additions) likewise adversely affects air entrainment. There may also be interactions with flow improvers that have a defoaming action, and hence expel air pores, but may also introduce them in an uncontrolled manner.
A relatively new possibility for improving the frost resistance and cyclical freeze/thaw durability is to achieve the air content by the admixing or solid metering of polymeric microparticles (hollow microspheres) [H. Sommer, A new method of making concrete resistant to frost and de-icing salts, Betonwerk & Fertigteiltechnik 9 (1978) 476-84]. Since the microparticles generally have particle sizes of less than 100 μm, they can also be distributed more finely and uniformly in the concrete microstructure than can artificially introduced air pores. Consequently, even small amounts are sufficient for sufficient resistance of the concrete to the freezing and thawing cycle. The use of polymeric microparticles of this kind for improving the frost resistance and cyclical freeze/thaw durability of concrete is already known from the prior art [cf. DE 2229094 A1, U.S. Pat. No. 4,057,526 B1, U.S. Pat. No. 4,082,562 B1, DE 3026719 A1]. The microparticles described therein are notable in particular for the fact that they possess a void smaller than 200 μm (in diameter) and that this hollow core consists of air (or a gaseous substance). This likewise includes porous microparticles from the 100 μm scale, which may possess a multiple of relatively small voids and/or pores.
Compact polymeric microparticles have not been considered to date in practice for the purpose of enhancing the frost resistance and cyclical freeze/thaw durability.
For the hollow microspheres, however, relatively high levels of addition are needed in order to obtain values below the critical “Power spacing factor”, the reason for this lying at least partly in the large particle diameter of >100 μm. This fact, in combination with the high preparation costs, a result of the multistage preparation processes, have been detrimental to the establishment of these technologies on the market.
The object on which the present invention is based, therefore, was to provide a means of improving the frost resistance and cyclical freeze/thaw durability for hydraulically setting building material mixtures that develops its full activity even at relatively low levels of addition, and which, moreover, can be prepared easily and inexpensively. A further object was not, or not substantially, to impair the mechanical strength of the building material mixture as a result of said means.
It has now been found, surprisingly, that compact polymeric microparticles of single-stage or multistage synthesis are also suitable for improvements to the frost resistance and/or cyclical freeze/thaw durability for hydraulically setting building material mixtures. By microparticles of single-stage synthesis are meant a particle (without a shell) which is synthesized homogeneously in the composition. This is all the more surprising since these polymeric microparticles do not entrain any air into the construction mixture.
The mode of action can be explained as follows: the polymeric microparticles of the invention are in homogeneous distribution in the construction mixture. A cavity between microparticle and cured construction mixture, which possibly becomes further enlarged as a result of the contraction of the construction mixture on curing, serves as an expansion site for freezing water. The uniform distribution of these capillary-active pores, with an average spacing from one another which is smaller than the “Power spacing factor”, then provides for the increase in frost resistance and/or cyclical freeze/thaw durability.
Through the use of the polymeric formations of the invention it is possible to keep the introduction of air into the building material mixture at an extraordinarily low level. As a result, markedly improved compressive strengths are achievable in the concrete. Consequently it is possible to achieve strength classes which can be set otherwise only by means of a substantially lower water/cement value (w/c value). Low w/c values, however, in turn considerably restrict the processability of the concrete in certain circumstances. Higher compressive strengths are of interest, in addition and in particular, insofar as it is possible to reduce the cement content of the concrete, which is needed for strength to develop, as a result of which it is possible to achieve a significant lowering in the price per m³of concrete.
The polymeric microparticles comprise at least one monoethylenically unsaturated monomer. The microparticles may be single-stage or multistage, and the comonomer composition of the individual stages may be different. Preferably included are, among others, nitriles of (meth)acrylic acid, and other nitrogen-containing methacrylates, such as methacryloylamidoacetonitrile, 2-methacryloyloxyethylmethylcyanamide, cyanomethyl methacrylate; carbonyl-containing methacrylates, such as oxazolidinylethyl methacrylate, N-(methacryloyloxy)formamide, acetonyl methacrylate, N-methacryloyl-morpholine, N-methacryloyl-2-pyrrolidonone; glycol dimethacrylates, such as 1,4-butanediol methacrylate, 2-butoxyethyl methacrylate, 2-ethoxyethoxymethyl methacrylate, 2-ethoxyethyl methacrylate, methacrylates of ether alcohols, such as tetrahydrofurfuryl methacrylate, vinyloxyethoxyethyl methacrylate, methoxy-ethoxyethyl methacrylate, 1-butoxypropyl methacrylate, 1-methyl-(2-vinyloxy)-ethyl methacrylate, cyclohexyloxymethyl methacrylate, methoxymethoxyethyl methacrylate, benzyloxymethyl methacrylate, furfuryl methacrylate, 2-butoxy-ethyl methacrylate, 2-ethoxyethoxymethyl methacrylate, 2-ethoxyethyl methacrylate, allyloxymethyl methacrylate, 1-ethoxybutyl methacrylate, methoxymethyl methacrylate, 1-ethoxyethyl methacrylate, ethoxymethyl methacrylate; oxiranyl methacrylates, such as 2,3-epoxybutyl methacrylate, 3,4-epoxybutyl methacrylate, glycidyl methacrylate; phosphorus-, boron-and/or silicon-containing methacrylates, such as 2-(dimethylphosphato)propyl methacrylate, 2-(ethylenephosphito)propyl methacrylate, dimethylphosphino-methyl methacrylate, dimethylphosphonoethyl methacrylate, diethyl methacryloylphosphonate, dipropyl methacryloyl phosphate; sulfur-containing methacrylates, such as ethylsulfinylethyl methacrylate, 4-thiocyanatobutyl methacrylate, ethylsulfonylethyl methacrylate, thiocyanatomethyl methacrylate, methylsulfinylmethyl methacrylate, and bis(methacryloyloxyethyl) sulfide; vinyl esters, such as vinyl acetate;
styrene, substituted styrenes with an alkyl substituent in the side chain, such as *methylstyrene and *ethylstyrene, for example, substituted styrenes with an alkyl substituent on the ring, such as vinyl toluene and p-methylstyrene;
heterocyclic vinyl compounds, such as 2-vinylpyridine, 3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinyl-pyrrolidone, 2-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinyl-caprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinylthiophene, vinylthiolane, vinylthiazoles and hydrogenated vinylthiazoles, vinyloxazoles and hydrogenated vinyloxazoles;
vinyl and isoprenyl ethers;
maleic acid derivatives, such as diesters of maleic acid, the alcohol residues having 1 to 9 carbon atoms, maleic anhydride, methylmaleic anhydride, maleimide, and methylmaleimide;
fumaric acid derivatives, such as diesters of fumaric acid, the alcohol residues having 1 to 9 carbon atoms;
α-olefins such as ethene, propene, n-butene, isobutene, n-pentene, isopentene, n-hexene, isohexene; cyclohexene.
In addition it has been found that by means of corresponding monomers it is possible to bring about, in addition to the ionic repulsion, the steric repulsion of the polymeric formations as well. This leads to an additional stabilization of the polymeric formations in the dispersion and the construction mixture.
In accordance with the invention it is therefore also possible to use free-radically polymerizable monomers having a molar mass of greater than 200 g/mol which carry a hydrophilic radical. Particular preference is given to monomers which carry a polyethylene oxide block having two or more units of ethylene oxide. Preference is given to using monomers from the group of (meth)acrylic esters of methoxypoiyethyiene glycol CH₃O(CH₂CH₂O)_nH, (with n=2), (meth)acrylic esters of an ethoxylated C16-C18 fatty alcohol mixture (with 2 or more ethylene oxide units), methacrylic esters of 5-tert-octylphenoxypolyethoxyethanol (with 2 or more ethylene oxide units), nonylphenoxypolyethoxyethanol (with 2 or more ethylene oxide units) or mixtures thereof.
In addition there may be one or more monoethylenically unsaturated monomers containing an acid group present. Preference is given to acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, p-methylacrylic acid (crotonic acid), a-phenylacrylic acid, p-acryloyloxypropionic acid, sorbic acid, a-chlorosorbic acid, 2′-methylisocrotonic acid, cinnamic acid, p-chlorocinnamic acid, p-stearylic acid, itaconic acid, citraconic acid, mesacronic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, and maleic anhydride, hydroxyl-or amino-containing esters of the above acids, preferably of acrylic or methacrylic acid, such as 2-hydroxyethyl acrylate, N,N-dimethylaminoethyl acrylate, and the analogous derivatives of methacrylic acid, particular preference being given to acrylic acid and also methacrylic acid and preference beyond that to acrylic acid.
In addition to the monoethylenically unsaturated monomer containing an acid group, this polymer may also be based on further comonomers other than the monoethylenically unsaturated monomer containing an acid group. Preferred comonomers are ethylenically unsaturated sulfonic acid monomers, ethylenically unsaturated phosphonic acid monomers, and acrylamides, preferably.
Ethylenically unsaturated sulfonic acid monomers are preferably aliphatic or aromatic vinylsulfonic acids or acrylic or methacrylic sulfonic acids. Preferred aliphatic or aromatic vinylsulfonic acids are vinylsulfonic acid, allylsulfonic acid, 4-vinylbenzylsulfonic acid, vinyltoluenesulfonic acid, and styrenesulfonic acid. Preferred acryloyl-and methacryloylsulfonic acids are sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloyloxypropylsulfonic acid, and 2-acrylamido-2-methyl-propanesulfonic acid.
Ethylenically unsaturated phosphonic acid monomers such as vinylphosphonic acid, allylphosphonic acid, vinylbenzylphosphonic acid, acrylamidoalkylphosphonic acids, acrylamidoalkyldiphosphonic acids. Phosphonomethylated vinylamines, (meth)acryloylphosphonic acid derivatives.
Possible acrylamides are alkyl-substituted acrylamides or aminoalkyl-substituted derivatives of acrylamide or of methacrylamide, such as N-vinyl-amides, N-vinylformamides, N-vinylacetamides, N-vinyl-N-methylacetamides, N-vinyl-N-methylformamides, N-methylol(meth)acrylamide, vinylpyrrolidone, N,N-dimethylpropylacrylamide, dimethylacrylamide or diethylacrylamide, and the corresponding methacrylamide derivatives, and also acrylamide and methacrylamide, preference being given to acrylamide.
The chemical crosslinking can be achieved by crosslinkers generally known to the skilled worker. The crosslinkers may be present in any state. Inventively preferred crosslinkers are polyacrylic or polymethacrylic esters, which are obtained, for example, through the reaction of a polyol or ethoxylated polyol such as ethylene glycol, propylene glycol, trimethylolpropane, 1,6-hexanediol-glycerol, pentaerythritol, polyethylene glycol or polypropylene glycol with acrylic acid or methacrylic acid. Use may also be made of polyols, amino alcohols and also their mono(meth)acrylic esters, and monoallyl ethers. Additionally also acrylic esters of monoallyl compounds of the polyols and amino alcohols. Another group of crosslinkers is obtained through the reaction of polyalkylenepolyamines such as diethylenetriamine and triethylenetetra-aminemethacrylic acid or methacrylic acid. Suitable crosslinkers include 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycol dimethacrylate, 1,6-hexanedioi diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dipentaerythritol pentaacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylol trimethacrylate, tris(2-hydroxyethyl)isocyanoratetriacrylate, tris(2-hydroxy)isocyanorate trimethacrylate, divinyl esters of polycarboxylic acids, diallyl esters of polycarboxylic acids, triallyl terephthalate, diallyl maleate, diallyl fumarate, hexamethylenebismaleimide, trivinyl trimellitate, divinyl adipate, diallyl succinate, and ethylene glycol divinyl ether, cyclopentadiene diacrylate, triallylamine, tetraallylammonium halides, divinylbenzene, divinyl ether, N,N′-methylenebisacrylamide, N,N′-methylene-bismethacrylamide, ethylene glycol dimethacrylate, and trimethylolpropane triacrylate. Crosslinkers preferred among these are N,N′-methylene-bisacrylamide, N,N′-methylenebismethacrylamide, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and triallylamine.
The polymeric formations of the invention can be prepared preferably by emulsion polymerization and preferably have an average particle size of 10 to 5000 nm; an average particle size of 150 to 2000 nm is particularly preferred. Most preferable are average particle sizes of 200 to 1000 nm.
The average particle size is determined, for example, by counting a statistically significant amount of particles by means of transmission electron micrographs.
For the preparation of the polymeric formations of the invention it is possible to employ all of the initiators and regulators that are customary for emulsion polymerization. Examples of initiators are inorganic peroxides, organic peroxides or H₂O₂, and also mixtures thereof with, if appropriate, one or more reducing agents.
In accordance with the invention it is possible to employ any ionic or nonionic emulsifier during or after the preparation of the dispersion.
Whereas the water-filled polymeric microparticles are used in accordance with the invention preferably in the form of an aqueous dispersion, it is entirely possible within the context of the present invention to add the water-filled microparticles directly as a solid to the building material mixture. For that purpose the microparticles are for example coagulated—by methods known to the skilled worker—and isolated from the aqueous dispersion by means of standard methods (e.g. filtration, centrifuging, sedimentation and decanting). The material obtained can be washed and is subsequently dried.
The polymeric formations are added to the building material mixture in a preferred amount of 0.01% to 5% by volume, in particular 0.1% to 0.5% by volume. The building material mixture, in the form for example of concrete or mortar, may in this case include the customary hydraulically setting binders, such as cement, lime, gypsum or anhydrite, for example.

Claims

1. A hydraulically setting building material mixture, consisting essentially of:

a hydraulically setting building material: and

polymeric microparticles which are synthesized in one or more stages from at least one ethylenically unsaturated monomer;

wherein said polymeric microparticles are in the form of spray-dried, coagulated or freeze-dried powder: and

wherein said ethylenically unsaturated monomer is selected from the group consisting of nitriles of (meth)acrylic acid, nitrogen-containing methacrylates, carbonyl-containing methacrylates, glycol dimethacrylates, methacrylates of ether alcohols, oxiranyl methacrylates, phosphorus-containing methacrylates, boron-containing methacrylates, silicon-containing methacrylates, sulfur-containing methacrylates, vinyl esters, styrene, substituted styrenes with an alkyl substituent in the side chain, heterocyclic vinyl compounds, vinyl ethers, isoprenyl ethers, maleic acid compounds, fumaric acid compounds, α-olefins and mixtures thereof.

2. The hydraulically setting building material mixture according to claim 1, wherein the ethylenically unsaturated monomer is selected from the group consisting of styrene, butadiene, vinyltoluene, ethylene, propylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, acrylamide, methacrylamide, C₁-C₁₈alkyl esters of acrylic acid, C₁-C₁₈alkyl esters of methacrylic acid, and mixtures thereof.

3. The hydraulically setting building material mixture according to claim 1, wherein said polymeric microparticles further comprise at least one crosslinker.

4. The hydraulically setting building material mixture according to claim 3, wherein said crosslinker is selected from the group consisting ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, allyl (meth)acrylate, divinylbenzene, diallylmaleate, trimethylolpropane trimethacrylate, glycerol dimethacrylate, glycerol trimethacrylate, pentaerythritol tetramethacrylate, and mixtures thereof.

5. The hydraulically setting building material mixture according to claim 1, wherein the said polymeric microparticles are in the form of a dispersion.

6. The hydraulically setting building material mixture according to claim 1 wherein said polymeric microparticles are in the form of spray-dried, coagulated or freeze-dried powder.

7. The hydraulically setting building material mixture according to claim 1, wherein the polymeric microparticles have an average particle size of 10 to 5000 nm.

8. The hydraulically setting building material mixture according to claim 1, wherein the polymeric microparticles are used in an amount of 0.01% to 5% by volume, based on the volume of the building material mixture.

9. The hydraulically setting building material mixture according to claim 1, wherein the polymeric microparticles are used in an amount of 0.1% to 0.5% by volume, based on the volume of the building material mixture.

10. The hydraulically setting building material mixture according to claim 1, further comprising a binder selected from the group consisting of cement, lime, gypsum anhydrite and mixtures thereof.

11. The hydraulically setting building material mixture according to claim 1, which comprises concrete or mortar.

12. A method of producing a hydraulically setting building material mixture, comprising:

adding polymeric microparticles to a setting building material,

wherein said polymeric microparticles are synthesized in one or more stages from at least one ethylenically unsaturated monomer;

wherein said polymeric microparticles are in the form of spray-dried, coagulated or freeze-dried powder,

wherein said hydraulically setting building material mixture consists essentially of said polymeric microparticles and said setting building material; and

13. The method according to claim 1, wherein the ethylenically unsaturated monomer is selected from the group consisting of styrene, butadiene, vinyltoluene, ethylene, propylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, acrylamide, methacrylamide, C₁-C₁₈alkyl esters of acrylic acid, C₁-C₁₈alkyl esters of methacrylic acid, and mixtures thereof.

14. The method according to claim 1, wherein said polymeric microparticles further comprise at least one crosslinker.

15. The method according to claim 14, wherein said crosslinker is selected from the group consisting of ethylene glycol di(meth)acrylate, propylene glycol di (meth)acrylate, allyl (meth)acrylate, divinylbenzene, diallylmaleate, trimethylolpropane trimethacrylate, glycerol dimethacrylate, glycerol trimethacrylate, pentaerythritol tetramethacrylate, and mixtures thereof.

16. The method according to claim 1, wherein said polymeric microparticles are in the form of a dispersion.

17. The method according to claim 1, wherein said polymeric microparticles are in the form of spray-dried, coagulated or freeze-dried powder.

18. The method according to claim 1, wherein the polymeric microparticles have an average particle size of 10 to 5000 nm.

19. The method according to claim 1, wherein the polymeric microparticles are used in an amount of 0.01% to 5% by volume, based on the volume of the building material mixture.

20. The method according to claim 1, wherein the polymeric microparticles are used in an amount of 0.1% to 0.5% by volume, based on the volume of the building material mixture.

21. The method according to claim 1, further comprising a binder selected from the group consisting of cement, lime, gypsum anhydrite and mixtures thereof.

22. The method according to claim 1, which comprises concrete or mortar.

23. A hydraulically setting building material mixture, comprising:

a hydraulically setting building material; and

wherein said polymeric microparticles are homogeneously distributed in said mixture; and

wherein capillary-active pores have an average spacing from one another which is smaller than a power spacing factor.