MX2008009251A - Additive building material mixtures comprising microparticles with apolar shells - Google Patents

Abstract

The invention relates to the use of polymeric microparticles with apolar shells in hydraulically setting building material mixtures, for improving their freeze resistance and/or freeze-thaw resistance.

Description

MIXES OF ADDITIVE CONSTRUCTION MATERIAL WHICH INCLUDES APPARATUS LAYERED MICROPARTICLES The present invention relates to the use of polymeric microparticles in mixtures of hydraulically fixed construction material, for the purpose of improving their resistance to frost and durability against cyclic freezing / thawing. The decisive factors that affect the resistance of concrete to frost and cyclic freezing / thawing under simultaneous exposure to deicing agents are the impermeability of its microstructure, a certain resistance of the matrix, and the presence of a certain pore microstructure. The microstructure of a concrete bound with cement is traversed by capillary pores (radius: 2 μm - 2 mm) and gel pores (radius: 2 - 50 nm). The water present in these pores differs in its state as a function of the pore diameter. While the water in the capillary pores retains its common properties, the water in the gel pores is classified as condensed water (mesopores: 50 nm) and surface water bound by adsorption (micropores: 2 nm), whose freezing points can be example being below -50 ° C [M. J. Setzer, Interaction of water with hardened cement paste, Ceramic Transactions 16 (1991) 415-39]. As a result, even when the concrete cools at low temperatures, some of the water in the pores remains unfrozen (metastable water). However, for a given temperature, the vapor pressure on the ice is less than the pressure on the water. Because the ice and the metastable water are present next to each other simultaneously, a vapor-pressure gradient develops that produces the diffusion of the still liquid water to the ice and the formation of ice from the water mentioned, which results in the elimination of water from smaller pores or the accumulation of ice in larger pores. This new distribution of water as a result of cooling is carried out throughout the porous system and depends critically on the type of distribution of the pores. The artificial introduction of microfine air pores in concrete therefore gives rise above all to the so-called expansion spaces to expand ice and ice-water. Within these pores, the freezing water can expand or the internal pressure and the tensions of ice and ice - water can be absorbed without the formation of micro cracks and therefore without damage caused by the frost to the concrete. The fundamental way in which these air pore systems operate has been described, in connection with the mechanism of damage to frost to concrete, in a large number of reviews [Schulson, Erland M. (1998) Ice damage to concrete . Special Report CRREL 98 - 6; S. Chatterji, Freezing of cement-based materials with occluded air and specific actions of agents with occluded air, Cement and Concrete Compounds 25 (2003) 759-65; G. W. Scherer, J. Chen & J. Valenza, Methods for protecting concrete against freeze damage, U.S. Patent 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 and Concrete Investigation 35 (2005) 1407-11]. A precondition of the improved strength of concrete in exposure to the freeze-thaw cycle is that the distance of each point in the hardened cement from the next artificial air pore does not exceed a value definite. This distance is also known as the "Powers Spacing Factor" [T. C. Powers, The air requirement of frost-resistant concrete, Procedures of the Highway Research Council 29 (1949) 184 - 2002]. Laboratory tests have shown that exceeding the critical "Powers spacing factor" of 500 μm causes concrete damage in the freeze and thaw cycle. In order to achieve this with a limited air pore content, the diameter of the artificially introduced air pores should therefore be less than 200-300 μm [K. Snyder, K. Natesaiyer &; K. Hover, The stereological properties and statistics of air spaces occluded in concrete: A mathematical basis for the classification of air gap systems, Concrete Materials Science VI]. The formation of an artificial air pore system depends mainly on the composition and conformity of the aggregate materials, the type and amount of cement, the consistency of the concrete, the mixer used, the mixing time, and the temperature, but also it depends on the nature and quantity of the agent that forms the pores of air, the air entraining agent. Although these influencing factors can be controlled if the appropriate production standards are taken into account, however, there can be a multiplicity of undesirable adverse effects, which ultimately result in the air content of the concrete being above or below the desired level and thereby adversely affecting the strength or frost resistance of the concrete. Artificial air pores of this type can not be measured directly; instead, the air entrained by the mixture is stabilized by the addition of the aforementioned air entraining agents [L.

Du & K. J. Folliard, Mechanism of Air Occlusion in Concrete, Cement and Concrete Investigation 35 (2005) 1463-71]. Conventional air entraining agents are mainly similar to surfactants in their structure and disintegrate the introduced air by mixing it in small air bubbles with a diameter as small as possible smaller than 300 μm, and stabilize them in the wet concrete microstructure . Below is the difference between the two types. A type - for example sodium oleate, the sodium salt of abietic acid or Vinsol resin, an extract of pine roots - reacts with the calcium hydroxide of the pore solution in the cement paste and precipitates as a salt of insoluble calcium. These hydrophobic salts reduce the surface tension of water and are collected at the interface between the cement particle, air and water. They stabilize the microbubbles and therefore they are on the surfaces of these air pores in the concrete as it hardens. The other type - for example sodium lauryl sulfate (SDS) or sodium dodecyl phenylsulfonate - reacts with calcium hydroxide to form calcium salts which, in contrast, are soluble, but show an abnormal solution behavior. Under 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 the preferential accumulation at the air / water limit, they likewise reduce the surface tension, thereby stabilizing the microbubbles, and are preferably found on the surfaces of these air pores in the hardened concrete. The use of these air entraining agents of the prior art is accompanied by a large number of problems [L. Du & K. J. Folliard, Mechanism of air occlusion in concrete, Cement and Concrete Investigation 35 (2005) 1463-71]. For example, the long mixing times, the different mixer speeds and the altered measurement sequences in the case of prepared mix concrete results in the expulsion of the stabilized air (in the air pores). The transport of concrete with extended transport times, poor temperature control and the different pumping and transport equipment, as well as the introduction of these concretes together with a subsequent altered processing, vibration and temperature conditions, can produce a significant change in the air pore content established previously. In the worst case, this may mean that a concrete no longer meets the required limitation values of a certain exposure class and therefore becomes unusable [EN 206 - 1 (2000), Concrete - Part 1: Specification, compliance, production and compliance]. The amount of fine substances in concrete (for example, cement with different alkali content, additives such as ash dust, silica dust or color additives) likewise adversely affects air entrainment. There may also be interactions with flow improvers that have a defoaming action and therefore expel air pores, but may also introduce them in an uncontrolled manner. All these influences that complicate the production of frost-resistant concrete can be avoided if, instead of the required air pore system being generated by the aforementioned air entraining agents with a structure similar to a surfactant, the Air content is incorporated by mixing or solid measurement of microparticles Polymers (hollow microspheres) [H. Sommer, a new method of manufacturing frost-resistant concrete and antifreeze salts, Betonwerk & Fertigtiltechnik 9 (1978) 476-84]. Because the microparticles usually have particle sizes less than 100 μm, they can also be distributed in a finer and more uniform way in the microstructure of the concrete that can artificially introduce the pores of air. Consequently, even small amounts are sufficient for a sufficient resistance of the concrete to the freeze and thaw cycle. The use of polymeric microparticles of this type to improve frost resistance and durability against cyclic freezing / thawing of concrete is already known in a prior art [see German patent DE 2229094 A1, US patent US 4,057,526 B1, US 4,082,562 B1, and German patent DE 3026719 A1]. The microparticles described therein are notable in particular for the fact that they possess a space that is smaller than 200 μm (diameter) and that this hollow core is composed of air (or a gaseous substance). It likewise includes porous microparticles on a scale of 100 μm which may possess a multiplicity of relatively small spaces and / or pores. With the use of hollow microparticles for the entrainment of artificial air in the concrete, two factors proved to have disadvantages for the implementation of this technology in the market. Relatively high doses are required in order to achieve satisfactory concrete resistance to freeze and thaw cycles. The objective on which the present invention is based was therefore to provide a means to improve the frost resistance and the durability against cyclic freezing / thawing for mixtures of construction that are fixed hydraulically, which develops its full activity even at relatively low doses. The objective has been achieved through the use of polymeric microparticles, which contain a space, in mixtures of building material that are fixed in a hydraulic manner, characterized in that the layer of the microparticles is composed of more than 99% by weight of monomers that have a solubility in water of less than 10"1 mol / l. Unless otherwise indicated, the solubilities referred to in this specification are always those of water at 20 ° C. As a result of the predominant use of monomers with a solubility in water very poor, microparticles having a rather non-polar surface are obtained.Surprisingly, it has been discovered that through the use of these microparticles, it is possible to achieve extremely good activity in the context of improving the resistance against frost and the freeze / thaw cycle The effect is much greater than if particles with a more polar surface are used. The unexpected effect - without any intention of this theory restricting the scope of the invention - it is assumed that microparticles of this type with a non-polar surface show poor adhesion to the mixture of the building material. As a result of this, it is possible for capillary pores to form at the interface between the microparticles and the matrix of the building material, and these pores contribute to an improvement in frost resistance and the freeze / thaw cycle. The layer is composed in accordance with the invention, in more than 99% by weight of monomers with a solubility in water of less than 10 ~ 1 mol / 1. The layer is preferably composed of more than 99.5% by weight of these monomers. With a particular preference, the layer is composed exclusively of these monomers. Because the effect of the invention of the non-polar layer is apparently related to the non-polar surface, it is sufficient if, in the case of a multi-layer structure of the microparticle, the outermost layer fulfills the condition of being composed in more than 99% by weight of monomers with a solubility in water of 10"1 mol / l. In this case, a monomer composition with 99.5% of these monomers is also preferred, and in particular the exclusive use of these monomers is preferred. in the outermost layer The layer, when suitable the outer layer, is preferably composed of styrene In a further preferred embodiment of the invention, the layer, when appropriate the outer layer, is composed of styrene and / on - hexyl (meth) acrylate and / or - butyl (meth) acrylate and / or isobutyl (meth) acrylate and / or propyl (meth) acrylate and / or or ethyl methacrylate and / or ethylhexyl (meth) acrylate. met) acrylate here denotes not only the methacrylate ato, such as methyl methacrylate, ethyl methacrylate, etc., but also acrylate, such as methyl acrylate, ethyl acrylate, etc., and also mixtures of both. The microparticles of the invention can preferably be prepared by emulsion polymerization and preferably have an average particle size of 100 to 5000 nm; an average particle size of 200 to 2000 nm. A maximum preference is given to average particle sizes of 250 to lOOO nm.

The size of the average particle is determined, for example, by counting a statistically significant amount of the particles by means of micrographs of transmitting electrons. In the case of the preparation by emulsion polymerization, the microparticles are obtained in the form of an aqueous dispersion. Accordingly, the addition of the microparticles to the mixture of the building material is carried out in the same way preferably in this form. During the preparation and in the dispersion, the spaces in the microparticles are filled with water. The particles develop their effect of improving the frost resistance and the freeze / thaw cycle in the construction material mixture by at least partially clearing the water during and after curing of the building material mixture, correspondingly producing hollow spheres filled with gas or filled with air. According to a preferred embodiment, the microparticles used are composed of polymer particles having a core (A) and at least one layer (B), the particles of the core polymer / layer have been dilated by means of a base. The core (A) of the particle contains one or more monomers of unsaturated carboxylic acid by means of ethylene (derivative) which allows dilation of the nucleus; these monomers are preferably selected from the group of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and crotonic acid, as well as mixtures thereof. Particular preference is given to acrylic acid and methacrylic acid. The layer - when appropriate, the outermost layer - B includes, of according to the invention, the monomers indicated. When the microparticles are constructed as multilayer particles or as gradient networks, there are no particular restrictions on the monomers used between the core and the outermost layer. The preparation of these polymeric microparticles by emulsion polymerization and their expansion by means of bases such as, for example, alkali metal hydroxides or alkali metal hydroxides and also ammonia or an amine, are described in the same way in the European patents EP 22 633 B1, EP 735 29 B1 and EP 188 325 B1. The polymer content of the microparticles used can be, depending on the diameter and the water content, from 2% to 98% by weight (weight of the polymer in relation to the total weight of the particle filled with water). The polymer contents of 2% to 60% by weight are preferred, and in particular polymer contents of 2% to 40% by weight are preferred. Within the scope of the present invention, it is entirely possible to add the water-filled microparticles directly as a solid to the mixture of the building material. For this purpose, the microparticles - as described above - are coagulated and isolated from the aqueous dispersion by standard methods (eg filtration, centrifugation, sedimentation and decantation) and the particles are subsequently dried. The microparticles filled with water are added to the mixture of the building material in a preferred amount of 0.01% to 5% by volume, in particular from 0.1% to 0.5% by volume. The mixture of the construction material, in the form for example of concrete or mortar, can include in this case the customary hydraulic bonding binders, such as cement, lime, gypsum or anhydrite, for example. A substantial advantage through the use of microparticles filled with water is that only an extremely small amount of air is introduced into the concrete. As a result, significantly improved compression forces can be achieved in the concrete. These are approximately 25% - 50% higher than the compression forces of concrete obtained with conventional air occlusion. In this way, it is possible to achieve strength classifications that can be obtained otherwise only by means of a substantially lower water / cement value (water / cement value). However, low water / cement values, in turn, significantly restrict the processing properties of the concrete in certain circumstances. In addition, higher compression forces can make it possible to reduce the cement content of the concrete that is needed to develop the force and therefore can mean a significant reduction in the price per cubic meter of concrete.

Claims (14)

1. CLAIMS 1. The use of polymeric microparticles, which contain a space, in mixtures of building material that are fixed in a hydraulic manner, characterized in that the layer of the microparticles is composed of more than 99% by weight of monomers having a solubility in water of less than 10 ~ 1 mol / l.
2. 2. The use of polymeric microparticles, which contain a space, in hydraulically fixed construction material mixtures, according to Claim 1, characterized in that the layer of the microparticles is composed exclusively of monomers with a solubility in water of 10"1 mol / l.
3. 3. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the outer layer contains styrene. use of polymeric microparticles, which contain a space, according to Claim 1, characterized in that the outer layer contains styrene and / or on-hexyl (met ) acrylate and / or n-butyl (meth) acrylic acid and / or isobutyl (meth) acrylate and / or propyl (meth) acrylate and / or ethyl methacrylate and / or ethylhexyl (meth) acrylate. 5. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the microparticles are composed of polymer particles that include a polymer core (A), which is dilated by means of an aqueous base and it contains one or more monomers of unsaturated carboxylic acid (derivative), and a polymer shell (B), which is mainly coated with nonionic, unsaturated monomers in the form of ethylene. 6. The use of polymeric microparticles, which contain a space, according to Claim 5, characterized in that the unsaturated carboxylic acid monomers (derivative) are selected from the group of acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, Itaconic acid and crotonic acid. 7. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the microparticles have a polymer content of 2% to 98% by weight. 8. The use of polymeric microparticles, which contain a space, according to Claim 1, characterized in that the microparticles have an average particle size of 100 to 5000 nm. 9. The use of polymeric microparticles, which contain a space, according to Claim 8, characterized in that the microparticles have an average particle size of 200 to 2000 nm. 10. The use of polymeric microparticles, which contain a space, according to claim 9, characterized in that the microparticles have an average particle size of 250 to 1000 nm. 11. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the microparticles are used in an amount of 0.01% to 5% by volume, based on the mixture of the construction material. 12. The use of polymeric microparticles, which contain a space, according to Claim 11, characterized in that the microparticles are used in an amount of 0.1% to 0.5% by volume, based on the mixture of the construction material. 13. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the mixtures of the construction material are composed of a binder selected from the group of cement, lime, gypsum and anhydrite. 14. The use of polymeric microparticles, which contain a space, according to claim 1, characterized in that the mixtures of the construction material are concrete or mortar.