REINFORCEMENT REPAIRING CARBON FIBERS

Description

[0001] The application concerns a textile reinforcement suitable for complete embedding in concrete or a concrete component.

[0002] Concrete has a tensile strength of only about 10% of its compressive strength. To increase the tensile strength of this then-new building material, concrete began to be combined with other, more tensile-strength materials as early as the mid-19th century. The work of the French gardener Joseph Monier, who combined concrete with an iron mesh for planters, is particularly noteworthy. Monier is considered the inventor of steel-reinforced concrete, or simply reinforced concrete. The reinforcing elements cast into reinforced concrete are still colloquially referred to as "Monier iron" in his name. Other materials for producing reinforcements are still the subject of ongoing research and development, especially textile-based reinforcements.

[0003] Various fiber and textile materials are known whose tensile strength significantly exceeds that of steel, while simultaneously being considerably lighter. This allows for substantial weight savings in concrete components or structures, which, for example, has a positive impact on the statics of load-bearing elements such as bridge piers or abutments. At the same time, textiles, for example those based on glass fibers, basalt fibers, carbon fibers, or certain organic polymers, offer the significant advantage of lower susceptibility to corrosion. In contrast, with metal reinforcements, chemical wear of the reinforcing elements is to be expected over time, which can lead to a dangerous reduction in the load-bearing capacity of the affected structural elements, both through failure of the reinforcement itself and through spalling of concrete due to the expansion of the corroding reinforcing elements.In addition to the general oxidation sensitivity of metals, especially structural steel, the fact that the concrete matrix in which the reinforcement elements are embedded is strongly alkaline and therefore chemically very aggressive also plays a role.

[0004] Textile reinforcements are still in the development phase. For example, the world's first bridge made of textile-reinforced concrete was built on the grounds of the state garden show in Oschatz (Saxony) in 2005.

[0005] Carbon fibers have proven to be of interest for the production of textile reinforcements for concrete. Carbon fibers offer high tensile strength and are extremely resistant to environmental influences such as water, oxygen, and the highly alkaline environment within concrete at normal temperatures. While carbon fibers exhibit high tensile strength in the fiber direction, they are very brittle perpendicular to the fiber direction. This disadvantage is overcome by embedding the carbon fibers in a matrix resin, which absorbs the corresponding forces and ensures the cohesion of the carbon fibers among themselves.

[0006] A problem with textile reinforcements is their low heat resistance. Concrete components with textile reinforcements are therefore unsuitable for applications where they are permanently exposed to high temperatures. At the same time, however, temporary resistance to high temperatures must be ensured to guarantee the stability of concrete components with textile reinforcements in the event of a fire. Temporary resistance to high temperatures in the event of a fire is referred to as "fire resistance." It is measured by the duration for which a component retains its function in a fire. A common requirement for fire-prone structures is the fire resistance class "F90-fire-resistant" (functional for at least 90 minutes in the event of a fire). In conventional reinforced concrete construction, protection for more than 90 minutes is primarily achieved through a sufficiently thick concrete cover.

[0007] WO 2018 / 202785 discloses a concrete component with textile reinforcement which has improved resistance in case of fire, which is achieved by modifying the concrete accordingly to prevent spalling, by using inorganically dominated matrix materials for the reinforcement or by surrounding the reinforcement with an oxidation barrier that protects the fibers from the effects of oxygen.

[0008] However, a disadvantage of the state of the art is that the cohesion of the fibers in the textile reinforcement is still achieved by a binder which contains organic components that form gases under the influence of high heat, thus potentially shattering the surrounding concrete and causing the component to collapse.

[0009] The object of the present invention is to provide a textile reinforcement that is highly fire-resistant and at the same time easy to manufacture.

[0010] The problem is solved by a textile reinforcement for embedding in concrete comprising carbon fibers, wherein the reinforcement is coated with a layer protecting against oxidation, wherein the carbon fibers are present as an interwoven, twisted, tangled or cabilized thread-like structure and have a maximum of 5 wt. % of matrix resin, and the layer protecting against oxidation forms a separate layer and can form a chemical bond to a component of concrete.

[0011] The present invention relates to a reinforcement. It should be made clear that the term "reinforcement" always means that a material (namely the reinforcement) is cast or embedded in another material (which is to be reinforced). A textile reinforcement that is to be embedded in concrete (as required in claim 1) means that at least the surface and the underside of the textile reinforcement—which extend as surfaces along the longitudinal extent of the reinforcement and are essentially parallel to each other—are almost completely covered by concrete (see [reference]). Figure 10 The textile reinforcement in question is therefore (with the exception of edge areas) encased in concrete at least on the top and bottom surfaces. A material that is laid on top of concrete and not encased in concrete is not reinforcement.

[0012] A separate oxidation-protective layer is understood to be a layer that essentially completely surrounds the reinforcement as an outer surface or coating. Preferably, the oxidation-protective layer is in the form of an essentially complete coating of the reinforcement. An essentially complete coating of the reinforcement means that less than 30%, less than 20%, less than 10%, or less than 5% of the outer surface of the reinforcement is free of the oxidation-protective layer. The oxidation-protective layer may exhibit isolated cracks. A separate oxidation-protective layer consists essentially entirely, meaning preferably more than 75% by weight, more preferably more than 80% by weight, even more preferably more than 90% by weight, and particularly preferably more than 98% by weight, of the oxidation-protective material.According to the invention, the carbon fibers forming the thread-like structure of the reinforcement consequently contain no more than 5 wt% matrix resin and the reinforcement is surrounded by a separate layer protecting against oxidation.

[0013] No separate protective layer against oxidation within the meaning of the invention is present if the protective material against oxidation is only present in isolated areas and not as a full-surface coating on the reinforcement, on the carbon fibers, or on the thread-like structure. Likewise, no separate protective layer against oxidation is present if the substances protecting against oxidation are merely added as additives in a matrix material for coating the reinforcement or the fibers of the reinforcement.

[0014] The percentage by weight of the separate oxidation-protective layer is less than 15 wt%, preferably less than 10 wt%, more preferably less than 7.5 wt% and most preferably less than 3 wt% based on the total weight of the textile reinforcement.

[0015] Document EP 0 861 862 describes a method for reinforcing structures. For example, a concrete layer is to be reinforced by applying a fiber layer to its surface. The fiber layer is used together with a primer layer and a putty layer and is impregnated with a resin. The fiber layer is not embedded in the concrete. Consequently, the document does not describe any reinforcement. Furthermore, the document does not describe carbon fibers that are in the form of woven, twisted, braided, or calibrated thread-like structures, or carbon fibers that contain a maximum of 5 wt% of a matrix resin. A separate oxidation-protective layer is also not disclosed in the document. Document WO 2015 / 084720 describes an adhesive tape material that can be used for the external repair of structural components (see Figures 1 to 4(of the text). The material is not embedded in concrete, and therefore no reinforcement is described in this document. The material contains reinforcing fibers embedded in a matrix material. There is no indication of carbon fibers present as interwoven, twisted, braided, or wired thread-like structures. A separate oxidation-protective layer is also not disclosed. In theDocument WO 2019 / 091832 describes a fiber product with a coating of aqueous polymer dispersion, the use of which is specified, for example, as reinforcement in concrete. According to the examples, the entire textile formed is impregnated with a polymeric material so that the polymeric coating encapsulates as many individual filaments of the textile as possible, thus enabling internal bonding of the fibers. The document further describes the use of inorganic thickening agents that can be used as additives in the aqueous dispersion. A separate, oxidation-protective layer for the reinforcement is not disclosed in the document.

[0016] The protective layer against oxidation is preferably applied using a water-based system, such as an aqueous dispersion. All common textile coating methods could be used – for example, in the case of a vermiculite-based protective layer, by immersing the reinforcement in an aqueous dispersion of the coating agent. A sol-gel process (where inorganic and hybrid polymer layers can be produced from colloidally dispersed solutions using wet-chemical coating processes and subsequent curing) or an electroplating process could also be employed.

[0017] An advantage of using an aqueous dispersion to form the protective layer against oxidation is that processing can be carried out without solvents (except for water as a solvent), which significantly simplifies processing (also with regard to occupational safety and environmental protection).

[0018] In a general embodiment, the oxidation-protective layer can be further enhanced with agents to increase its stability and / or abrasion resistance. For example, the oxidation-protective layer can contain 80% by weight of oxidation-protective substances and a maximum of 20% by weight of a water-soluble protective polymer, such as that which can also be used for the further protective layer described later. The protective polymer should act as a binder and can, for example, stiffen a vermiculite layer (as one embodiment of the oxidation-protective layer), thus increasing its mechanical strength. Furthermore, the mechanical strength of a vermiculite layer (as one embodiment of the oxidation-protective layer) and its bond to the filamentous structure can be improved by mixing it with binders.This process creates a mixture of oxidation-protective substances and binders, thus eliminating the need for a separate layer. Epoxy resins and phenolic resins, for example, can be used as organic binders for the oxidation-protective layer. The mechanical strength of the oxidation-protective layer, such as a vermiculite layer, can also be increased by mixing the oxidation-protective layer (or its components) with particularly temperature-resistant polymers, such as bismaleimide, phenolic, cyanate ester, or polybenzimidazole resins. Carbon-based materials like graphene and graphene oxide, silicon-based materials such as polysiloxanes or silicone resins, colloidal silica or nanosilica, microsilica, or other inorganic materials such as ZnO nanoparticles (e.g., NANOBYK-3860, [Company Name]) can also be used.BYK (Wesel, Germany), lime, cement, anhydrite, ettringite, silica sol, and water glass can be used as binders in the oxidation-protective layer to improve its properties. The oxidation-protective layer may also contain polyelectrolytes such as polycarboxylate ethers or lignosulfonate, cellulose ethers such as methylcellulose, polyvinyl alcohol, or polyvinylpyrrolidone. However, with all of the aforementioned additives to the oxidation-protective layer, it is important to ensure that the oxidation-protective material remains the primary component of the layer and that the additives do not create an additional layer within the oxidation-protective layer.

[0019] Advantageously, the textile reinforcement has a low organic content, so low that the formation of gaseous decomposition products during heating is negligible, thus preventing the component from bursting in a fire. It is known, for example, that fire resistance tests are not required for concrete components with an organic content of less than 1% by weight. With steel reinforcement, the concrete cover over the reinforcement elements must ensure that the reinforcement does not heat up to more than 550°C, as otherwise the steel would lose its strength. Carbon fibers, on the other hand, are stable at this temperature in the absence of oxygen, allowing for a thinner concrete cover, resulting in a significant weight reduction.

[0020] Textile reinforcement, as defined in this application, is a material based on thread-like structures that is embedded in a surrounding material, such as concrete, for reinforcement purposes. These thread-like structures can be threads in the narrower sense, but they can also be products made from threads. Possible products include yarns, cables, cords, or ropes, which can also be processed into sheet-like products such as woven fabrics, nonwovens, knitted fabrics, braids, crocheted fabrics, trellises, grids, or nets. Textile reinforcements produced in this way are characterized by their flexibility, which allows them to be stored in space-saving roll form, transported to the construction site, and unrolled only immediately before being embedded in the concrete.Furthermore, rigid reinforcement elements such as bars or rigid grids can be produced by using binding agents or by twisting and / or interlacing the thread-like structures. Mechanical stiffening of the thread-like structures, or of the yarns, cables, cords, or ropes produced from them, can also be achieved by wrapping or braiding them with so-called wrapping yarns.

[0021] In one embodiment, the textile reinforcement consists of the aforementioned thread-like structures.

[0022] In one embodiment, the reinforcement has a (further) protective layer in addition to the oxidation-protective layer. This protective layer is preferably located as an outer layer on the finished reinforcement with the separate oxidation-protective layer and preferably does not completely encircle the thread-like structures of the carbon fibers. Preferably, the protective layer covers the surface and / or the underside of the reinforcement. The protective layer can, for example, be a coating that makes the reinforcement easier to coil and thus store as rolled material. The protective layer can also be composed of or contain substances that simplify and / or improve the embedding of the reinforcement in the concrete. For example, the protective layer can contain plasticizers for concrete.Furthermore, the protective layer can also protect the reinforcement from weathering and / or mechanical stresses as long as it has not yet been incorporated into the concrete. The protective layer can be reversibly or permanently bonded to the reinforcement. A reversible protective layer is one that can be peeled off the reinforcement, for example, like a film. In this case, all types of polymer films are conceivable, and the polymer film can also be water-insoluble (for example, a polyethylene film). The protective layer is permanently bonded to the reinforcement when the protective layer and the reinforcement can no longer be separated without damaging the reinforcement. In the case of a protective layer permanently bonded to the reinforcement, the protective layer is preferably water-soluble, so that it dissolves upon contact with water in the concrete.This protective layer protects the reinforcement before it is cast in concrete, but it does not prevent or impair the penetration of the reinforcement by the concrete. The protective layer can, for example, comprise or consist of polyelectrolytes such as polycarboxylate ethers or lignosulfonate, cellulose ethers such as methylcellulose, polyvinyl alcohol, or polyvinylpyrrolidone. Preferably, the reinforcement contains approximately 1 to 10 wt%, preferably 2 to 5 wt%, of the protective layer, based on the total weight of the reinforcement.

[0023] In one embodiment, the textile reinforcement comprises more than one thread-like structure. The individual thread-like structures of the reinforcement can be interwoven, twisted, wound, or wired together. In addition to one or more thread-like structures made of carbon fibers, the textile reinforcement according to the present application can also contain additional thread-like structures made of other fibers. In particular, thread-like structures such as polyamide fibers, aramid fibers, alkali-resistant glass fibers (AR glass fibers), basalt fibers, polypropylene fibers, polyvinyl alcohol fibers, polyester fibers, or fibers made of oxidized, non-melting polyacrylonitrile (e.g., Pyromex®, available from Teijin Carbon Europe, Wuppertal, Germany) are suitable for this purpose.In one embodiment, the additional thread-like structure of the reinforcement consists of a plurality of wrapping threads with which the thread-like structure made of carbon fibers is wound. This wrapping can, for example, increase the mechanical stability of the thread-like structure made of carbon fibers and thus of the reinforcement. The wrapping can be uniform over the entire reinforcement or applied only to certain sections of the reinforcement. For example, only a central area of ​​the reinforcement can be given a particularly strong mechanical reinforcement by means of the wrapping threads.

[0024] In one embodiment, the thread-like structure has a structured surface due to its production by braiding, twisting, plying, or cabling. This structured surface allows the thread-like structure to be brought into a particularly close, form-fitting connection with other materials, for example, coatings, the oxidation-protective layer, the further protective layer, or concrete. In another embodiment of the wrapping threads, the wrapping threads create a structured surface in addition to, or without, mechanical reinforcement, thus enabling a close, form-fitting connection – as described above.

[0025] Interlacing, twisting, twisting, wrapping, or cabling creates a bond between the carbon fibers and / or filaments within the thread-like structures. This allows for a significant reduction in the amount of matrix resin required for fiber cohesion within the thread-like structure, or even the complete elimination of matrix resin. When using only one thread-like structure, the continuous filaments that comprise it are intimately bonded together by interlacing, twisting, twisting, wrapping, or cabling. When using multiple thread-like structures, several of these structures can be intimately bonded together by interlacing, twisting, twisting, wrapping, or cabling, optionally in addition to an intimate bond between the filaments that comprise the thread-like structures.

[0026] A significant disadvantage of the matrix resin is its problematic behavior at high temperatures. At considerably elevated temperatures, the matrix resin begins to soften and can no longer ensure the cohesion of the carbon fibers or compensate for their brittleness perpendicular to the fiber direction. Furthermore, it begins to decompose, even in the absence of air, forming gaseous products that can then fracture the surrounding concrete. At high temperatures and in the presence of oxygen, carbon fibers can also oxidize themselves, whereas they remain stable even at extremely high temperatures when oxygen is excluded.

[0027] In this way, a significant contribution is made to improving the fire resistance of carbon fiber-based textile reinforcements, since the cohesion within the thread-like structure is no longer achieved by a matrix resin that fails rapidly at elevated temperatures, but rather mechanically through the interlocking of the fibers and / or filaments that make up the thread-like structure. Reducing the amount of matrix resin also reduces the amount of thermally decomposable material in the thread-like structures, thus minimizing or even eliminating gas formation under the influence of high temperatures. This, in turn, reduces the risk of structural failure of carbon fiber-reinforced concrete components due to fragmentation in the event of a fire.

[0028] In this application, matrix resin is understood to mean all non-fiber-forming material with which the carbon fibers, the filamentous structures produced therefrom, or the textile reinforcement produced therefrom are coated before the oxidation-protective layer is applied to the reinforcement. In particular, this includes finishing agents applied to improve the processability of the fibers or filamentous structures, for example, agents for breakage protection, for reducing static charge, or for improving the sliding properties of the fibers during the processing. Such fiber finishing agents are known to those skilled in the art as "sizing" or "coating." For this purpose, organic synthetic resins such as epoxy resins or polyurethane-based resins are frequently used. Likewise, a reactive polydimethylsiloxane (e.g., SILRES BS 1042, available from [Company Name]) can be used.Wacker, Munich, Germany) can be used for sizing. If particularly temperature-resistant equipment is required, highly temperature-resistant polymers such as polyphenylene sulfide (PPS), polyetherketones such as polyetheretherketone (PEEK), or polyimides such as polyetherimides can also be used. Furthermore, high-temperature resins such as bismaleimide, phenol, cyanate ester, or polybenzimidazole resins can be used. Carbon-based materials such as graphene and graphene oxide can also be used, as well as silicon-based materials such as colloidal silica or nanosilica (based on sol-gel processes; e.g., LUDOX SM 30 from WR Grace & Co., Columbia, USA), and microsilica (e.g., EMSAC 500 SE from Ha-Be Betonchemie GmbH & Co. KG, Hameln, Germany). In addition, other inorganic materials can be used in combination with water-soluble organic polymers such as... B.Polyvinyl alcohol or polyvinylpyrrolidone can be used as binders. In the examples mentioned, the binders are water-soluble and therefore disperse throughout the concrete. Ferrofluids containing paramagnetic iron can act as radical scavengers and thus as oxidation inhibitors. Furthermore, ZnO nanoparticles (e.g., NANOBYK-3860, BYK, Wesel, Germany), polysiloxanes or silicone resins, or inorganic lubricants based on molybdenum disulfide and / or graphite (e.g., MOLYKOTE 7400 Anti-Friction Coating from DuPont, Wilmington, USA) or so-called ORMOCERE, organically modified ceramics (e.g., InnoSolTEX technology from Fraunhofer ISC, Würzburg, Germany) are also suitable as finishing agents. Other inorganic finishing agents, for example, those based on layered silicates such as vermiculite, can also be used.

[0029] The finishing agent can improve not only the mechanical properties of the fibers but also their bonding to other components of the matrix resin, such as binders. In addition to finishing agents that enhance the processability of carbon fibers or the filamentous structures produced from them, the term "matrix resin" also encompasses binders that serve to hold the carbon fibers or filamentous structures together, compensate for the brittleness of the carbon fibers perpendicular to the fiber direction, or stiffen the filamentous structures or the yarns, cables, cords, or ropes produced from them into rods, or stiffen the fabrics, non-woven fabrics, knitted fabrics, braids, woven fabrics, or twills produced from them into rigid grids.Furthermore, binders prevent uncontrolled penetration of concrete into the textile reinforcement material. This would otherwise lead to telescopic fiber pull-out from the textile reinforcement, with inner fibers or filaments, which are not in contact with the concrete, being more easily pulled out than outer fibers or filaments that are in contact with the concrete. "Uncontrolled penetration" specifically refers to the penetration of concrete between the filaments that make up the thread-like structure. Otherwise, the filaments of the thread-like structure could be destroyed or damaged by the formation of needle-shaped crystallites during the hardening of the concrete. This is achieved through the intimate bonding of the filaments within a thread-like structure to one another, as well as through the intimate bonding of several thread-like structures, e.g.,...Penetrability through concrete can be drastically reduced by interlacing, twisting, braiding, wrapping, or cabling. Binders for thread-like structures made of carbon fibers are known to those skilled in the art as "impregnation" or "impregnation compound." Binders from the group of organic polymers are frequently used, which may be chemically related to the fiber finishing agent. Possible binders include, in particular, thermally or radically curable organic synthetic resins such as epoxy resins or acrylates, and rubbers such as styrene-butadiene rubber or carboxylated styrene-butadiene rubber. To achieve the highest possible temperature resistance of the matrix resin, it is also possible to use inorganic binders based on silicates or cements. The use of silicone resins is also possible.Organopolysiloxanes, especially silicone resins, such as the class of methyl resins and methylphenyl resins, including methylphenyl vinyl and hydrogen-substituted siloxanes, as well as mixtures of these silicone resins and organic resins, have proven suitable. Although alkali resistance is not generally expected from organosilicon compounds, it has surprisingly been demonstrated for some formulations (e.g., Wacker Silres H62C and in combination with Silres MK, both available from Wacker, Munich, Germany) for the specific application of textile reinforcement. Methylphenyl vinyl hydrogen polysiloxanes (e.g., Wacker Silres H62C, available from Wacker, Munich, Germany) and methyl polysiloxanes (e.g., Wacker Silres MK, available from Wacker, Munich, Germany) have also shown this resistance.Surprisingly high alkali resistance has already been demonstrated in textile reinforcement applications using siloxanes (e.g., SILRES BS 1042, available from Wacker, Munich, Germany). Reactive polydimethylsiloxanes (e.g., SILRES BS 1042, available from Wacker, Munich, Germany) have also proven effective. However, inorganic binders with an organic component, especially predominantly inorganic binders that also contain an organic component, tend to develop a porous structure or microcracks in the high-temperature range between 500°C and 1000°C, despite their significantly better high-temperature resistance. Therefore, it is desirable to minimize the amount of binder used in the reinforcement for applications in high-temperature-resistant concrete components.

[0030] A total matrix resin content of no more than 5 wt.% relative to the total reinforcement is therefore preferred in order to achieve the best possible high-temperature resistance of the concrete components containing the textile reinforcement according to the present application. The same material as described above for the matrix resin can be used, but this time the matrix material can be present not only on the carbon fibers but also as a component in other layers of the reinforcement. The matrix resin thus comprises the matrix resin of the carbon fibers and other matrix components of the reinforcement in other layers of the reinforcement. The textile reinforcement can contain a maximum of 4 wt.% matrix resin. The textile reinforcement can contain a maximum of 3 wt.% matrix resin. The textile reinforcement can contain a maximum of 2 wt.% matrix resin. The textile reinforcement can contain a maximum of 1 wt.% matrix resin.In one embodiment, the textile reinforcement is free of matrix resin. The binder content of the textile reinforcement can be 5 wt.%, 4 wt.%, 3 wt.%, 2 wt.%, or 1 wt.%, or the textile reinforcement can be binder-free. A reduction in the proportion of finishing agents on the carbon fibers is also possible. Here, proportions of less than 1.5 wt.%, less than 1 wt.%, or even less than 0.5 wt.% are possible. In one embodiment, both the carbon fibers and the textile reinforcement are free of finishing agents.

[0031] Unlike the matrix resin, which is particularly susceptible to thermal decomposition in the event of a fire due to its organic components, the carbon fibers are largely stable at high temperatures as long as they are kept away from oxygen. For this reason, the reinforcement according to the present application is coated with a separate oxidation-protective layer. In principle, all materials that do not react with oxygen, even under the influence of high temperatures, are suitable for this layer. This is particularly true for inorganic compounds.

[0032] In one embodiment, the oxidation-protective layer therefore has a proportion of inorganic material of at least 80% by weight. In another embodiment, the oxidation-protective layer therefore has a proportion of inorganic material of at least 70% by weight. In another embodiment, the oxidation-protective layer therefore has a proportion of inorganic material of at least 60% by weight. In another embodiment, the oxidation-protective layer therefore has a proportion of inorganic material of at least 50% by weight. In another embodiment, the oxidation-protective layer therefore has a proportion of inorganic material of at least 40% by weight. Oxide materials or materials whose components are highly oxidized are particularly suitable, provided they do not themselves have an oxidizing effect.Materials based on stable metal and metalloid oxides, such as the oxides of calcium, magnesium, aluminum, and silicon, are of particular importance. The oxides of these elements are characterized by high oxidation stability, low oxidation activity, and readily available resources. Materials derived from these oxides include quartz, clay, cement, and the large group of silicates, in which the aforementioned elements can be associated with other elements in their oxidized forms, such as iron or alkali metals.

[0033] What makes this selection special is that all these materials exhibit a high degree of chemical similarity to certain components of concrete, such as cement. This chemical similarity allows a chemical bond to form between the material of the oxidation-protective layer and certain components of concrete, resulting in particularly strong adhesion between the oxidation-protective layer of the textile reinforcement and the surrounding concrete of a concrete component.

[0034] In one embodiment, the layer protecting against oxidation comprises ORMOCERE, i.e., an organically modified ceramic (e.g., InnoSolTEX technology from Fraunhofer ISC, Würzburg, Germany), or polysilazanes.

[0035] In one embodiment, the oxidation-protective layer therefore contains at least 5 wt.% silicon. This can include silicon-oxygen compounds such as silicates or silicones. Silicon-oxygen compounds are characterized by particularly high chemical stability. In particular, due to the high chemical affinity of silicon for oxygen, silicon-oxygen compounds are extremely stable against reduction, do not release oxygen even under fire conditions, and therefore do not undergo chemical changes. It is known to those skilled in the art, for example, that various silicon-oxygen compounds are used as fire extinguishing agents. An important example of this is sand (chemically mostly silicon dioxide, SiO₂), which can be used to cover fires. Layered silicates such as vermiculite can also be used as fire extinguishing agents.

[0036] The protective layer against oxidation lies on and around the reinforcement and can be present on and around the textile reinforcement in a variety of ways. For example, the protective layer can be produced by plasma treatment. In plasma treatment, the object to be treated is exposed to a plasma to which a gaseous precursor for the desired surface coating is added. For example, plasma treatment in the presence of hexamethyldisiloxane as a precursor leads to the formation of a layer containing silicon-oxygen compounds on the treated surface, in this case, the surface of the textile reinforcement. The silicon-oxygen compounds can be, for example, silicon dioxide. Layers of amorphous silicates or polymer layers containing silanol groups are also possible. In one embodiment, the layer containing silicon-oxygen compounds consists of at least 30 wt.% of silicon dioxide. In one embodiment, the layer containing silicon-oxygen compounds has silanol groups on its surface.

[0037] In one embodiment, the silicon-oxygen compound layer has a thickness of less than 500 nanometers and is therefore significantly thinner than conventional oxidation-protective layers. In another embodiment, the silicon-oxygen compound layer has a thickness of less than 300 nanometers. In another embodiment, the silicon-oxygen compound layer has a thickness of less than 100 nanometers. In yet another embodiment, the silicon-oxygen compound layer has a thickness of less than 50 nanometers, and in yet another, less than 30 nanometers.

[0038] This also results in a high degree of flexibility in the reinforcement compared to other oxidation-protective layers. In this embodiment, the textile reinforcement retains its drapability even when coated with the oxidation-protective layer. It is therefore possible to shape it immediately before casting it in concrete and to produce, for example, curved or contoured concrete components with minimal effort. The silicon-oxygen compound-containing layer can be chemically bonded to the carbon fibers themselves or to the finishing agent applied to the carbon fibers and, in turn, allows for chemical bonding to components of concrete, such as cement.

[0039] Silicates are also suitable materials for the oxidation-protective layer, which can be applied to the reinforcement using wet chemical processes, for example. Layered silicates, which are capable of forming flexible, inorganic films, are one such example. Inorganic films made of vermiculite have excellent mechanical properties (for example, tensile strength and tensile modulus) and are superior to some organic films.

[0040] In one embodiment, a flexible, oxidation-protective layer is formed by the layered silicate vermiculite. This is particularly the case when vermiculite is applied to a surface in the form of an aqueous suspension and subsequently dried. Such dispersions are available, for example, under the name AVD (Aqueous Vermiculite Dispersion), among other things as fire extinguishing agents. The oxidation-protective layer of layered silicates can be positively anchored in the structured surface of the reinforcement. For this purpose, for example, the layered silicate applied in the form of an aqueous suspension can form a structure that engages with the structure on the surface of the filamentous structure or the carbon fibers, thus ensuring an intimate bond between the filamentous structure or the carbon fibers and the oxidation-protective layer.For example, after its production from the thread-like structure of carbon fibers, the reinforcement can be soaked in an immersion bath of aqueous suspension with layered silicate, so that a separate layer protecting against oxidation is created on and around the reinforcement (i.e. the outer surfaces of the reinforcement).

[0041] Optionally, an adhesive layer can also be used to create a chemical bond between the thread-like structure and the oxidation-protective layer, such as the layered silicate. This can involve both direct chemical bonds between the carbon fibers of the oxidation-protective layer, such as the layered silicate, and chemical bonds between the finishing agent on the carbon fibers and the oxidation-protective layer. If epoxy resins are used as finishing agents, organically functionalized silanes with amino or epoxy groups can be used for the adhesive layer. These silanes can form a chemical bond with the epoxy resin via their organic ends, while the silane groups can form a chemical bond with the oxidation-protective layer, such as the layered silicate.Examples of such products are Dynasylan SIVO 110 and Dynasylan HYDROSIL 2776, both available from Evonik AG, Essen. Organically functionalized silanes mediate a chemical bond between the finishing agent (especially epoxy resin) on the carbon fiber on one side and the layered silicate on the other.

[0042] The adhesive layer is preferably applied to the reinforcement; that is, the thread-like structure made of interwoven, twisted, braided, or wired carbon fibers has the adhesive layer. However, in another embodiment, it is also conceivable that the carbon fibers have the adhesive layer before the thread-like structure is produced.

[0043] If an adhesive layer is used, the adhesive layer constitutes less than 3 wt%, preferably less than 2 wt%, and more preferably less than 1.5 wt%, and even more preferably less than 1 wt%, in relation to the total weight of the reinforcement in all embodiments.

[0044] In one embodiment, the layered silicate layer has a maximum thickness of 200 µm. In one embodiment, the layered silicate layer has a maximum thickness of 150 µm. In one embodiment, the layered silicate layer has a maximum thickness of 100 µm. In one embodiment, the layered silicate layer has a maximum thickness of 75 µm. In one embodiment, the layered silicate layer has a maximum thickness of 50 µm. In one embodiment, the layered silicate layer has a maximum thickness of 40 µm. In one embodiment, the layered silicate layer has a maximum thickness of 30 µm. In one embodiment, the layered silicate layer has a maximum thickness of 20 µm. In one embodiment, the layered silicate layer has a maximum thickness of 10 µm.

[0045] The layered silicate layer can have a uniform or uneven thickness on and around the reinforcement.

[0046] Preferably, in all embodiments of the textile reinforcement, the proportion of organic substances in all layers that are irreversibly and directly or indirectly (via a layer) connected to the reinforcement is less than 5% by weight based on the total weight of the textile reinforcement, whereby the thread-like structure of carbon fibers is not counted as a layer. This means that even if the reinforcement has fibers with a sizing (matrix), a separate oxidation-protective layer, an adhesive layer, and a further protective layer irreversibly connected to the reinforcement, the reinforcement as a whole contains less than 5% by weight of organic substances, based on the total weight of the textile reinforcement.

[0047] The present application further relates to a concrete component comprising reinforcement according to the present application. In one embodiment, the textile reinforcement is embedded in the concrete component such that it has a concrete cover of at most 10 millimeters. Concrete cover is understood to mean the thickness of the concrete layer that lies between the concrete surface and the surface of the textile reinforcement. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 15 millimeters. In another embodiment, the reinforcement in the concrete component has a concrete cover of at most 20 millimeters. In In one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 25 millimeters. In In one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 30 millimeters. InIn one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 35 millimeters. In In one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 40 millimeters. In In one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 45 millimeters. In In one embodiment, the reinforcement in the concrete component has a concrete cover of no more than 50 millimeters. In In one embodiment, the concrete cover of the textile reinforcement is lower than the concrete cover of a comparable steel reinforcement with the same mechanical properties, which means a significant weight advantage.

[0048] The concrete covering of the textile reinforcement makes a crucial contribution to the fire resistance of the textile reinforcement through its heat-insulating and oxygen-protective effect.

[0049] The concrete cover over the textile reinforcement can be designed in conjunction with the properties and thickness of the oxidation-protective layer to achieve a desired fire resistance class.

[0050] The invention is described in more detail with reference to experiments and figures, without this constituting any limitation of the general inventive concept. Figure 1 shows a comparison of the tensile strength of carbon fiber yarns with a solid matrix resin content as a function of their twist (t / m). Figure 2 shows the influence of a vermiculite coating on the temperature resistance of carbon fibers. Figure 3 shows the basic structure of a single-filament coating system. Figure 4 shows a schematic diagram of a coating loop (cross-section on the right). Figure 5 shows a schematic diagram of a winding board. Figure 6 shows a heating curve of a muffle furnace for the yarn samples. Figure 7 shows a target arrangement of yarn strands for Example 3. Figure 8 shows the installed yarn strands for Example 3. Figure 9 shows a test setup (rotated) for Example 3. Figure 10 schematically shows a textile reinforcement embedded in concrete.

[0051] The Figures 7 to 9 These are taken from the reports of TU Dortmund / WdB. Example 1

[0052] In the present example 1, it is intended to show how the tensile strength of thread-like structures changes depending on their consolidation.

[0053] The thread-like structures to be tested are carbon fiber yarn type STS40 F13 24K from Teijin Carbon Europe with a density of 1600 tex and a 1% polyurethane coating as the matrix resin content. A STS40 E23 24K yarn from Teijin Carbon Europe, impregnated with 39% wt. epoxy-based matrix resin, is used as a comparison yarn.

[0054] The comparison yarn was impregnated with the following resin mixture: Epikote 828: 100 parts Epicure 113: 30 parts Acetone: 15 parts Sample preparation:

[0055] For the tensile test and data determination, yarn samples are provided with 50 mm long cardboard strips, which serve to introduce force to the test device.

[0056] For this purpose, a two-component adhesive is used which, after curing, completely encloses the samples in the area of ​​a cardboard strip and no air inclusions are present. Adhesive approach: AW 106 100% by weight HV 953 80 parts by weight

[0057] A potting time of 45 minutes is recommended.

[0058] To produce yarn tensile test specimens, two cardboard strips, aligned parallel to each other using a 200 mm wide template, are adhered to a glass plate covered with PTFE-coated glass using polyester adhesive tape. To ensure a uniform adhesive film between the cardboard strips and the test specimens, the yarn is first applied using a drawing tool (which must be selected according to the yarn fineness).

[0059] The samples are now to be laid out along the marked lines and fixed in place with polyester adhesive tape. Ensure that the individual test specimens are parallel. The upper cardboard strips (clearly labeled), which are also coated with adhesive film, are then placed on top and secured. A layer of PTFE-coated fiberglass fabric is placed over this and weighted down with a second glass plate.

[0060] This setup is placed in a preheated convection oven at 70 °C for one hour. After the yarn tensile test specimens have cooled, they are cut with a band saw along the outer edges and the designated cutting lines. Measurement:

[0061] The test specimens are stored for at least 24 hours in the test room climate at 23 °C / 50% relative humidity before measurement.

[0062] A tensile test is performed on the impregnated carbon fiber strand, which is provided on both sides with force introduction elements (cardboard strips), using a length change sensor. Device:

[0063] Tensile / compression testing machine with a constant testing speed adjustable to < 1% in the range of 0 < v ≤ 20 mm / min. Calibrated force transducer with suitable force measuring range according to DIN EN ISO 7500-1. Calibrated displacement measuring system with suitable displacement measuring range according to DIN EN ISO 9531. Extensometer (211 mm). Test condition:

[0064] Standard atmosphere for testing impregnated yarn tensile samples, i.e. 23°C ± 2 and 50% ± 5 relative humidity. Test parameters:

[0065] Test speed: 5 mm / min Free clamping length: 200 mm Pre-force: 2 cN / tex Sensor measuring length: 100 mm Start of E-module: 40 cN / tex End of E-module: 80 cN / tex Conducting the test:

[0066] The test is performed as follows: The tensile clamps are installed in the material testing machine (MPM), aligned centrally, and the required clamping length between the clamps is set as specified in the applicable standard or specification. The specimen stops are then adjusted so that the specimens are loaded centrally in the MPM. When clamping, care must be taken to ensure that the specimens are held perpendicular to the clamping jaws.

[0067] Before the test begins, the zero point of the force channel is approached. During the test, the testing machine moves the specimen, recording the measured values, until fracture occurs or until the specified force or length change value is reached. After the test is complete, the fracture pattern is entered and the measurement data is saved. The specimen is removed from the testing chamber, and the fixture and clamps are cleaned. To ensure unambiguous traceability of the specimens even after testing, the specimen numbering is checked and, if necessary, renewed on both sides. The MPM traverse is returned to its starting position, and the next specimen can be tested. Six tests are performed per specimen using this procedure.

[0068] Determination of the tensile strength σ B : σ B = F max A F N / mm 2 σ B = tensile strength in N / mm² < F max = maximum tensile force in NAF = yarn cross-sectional area in mm² <

[0069] The yarn cross-sectional area is calculated as follows: A F = T t ρ * 100 3 mm 2 AF = Yarn cross-sectional area in mm² < Tt = Yarn fineness in tex ρ = Yarn density in g / cm³ <

[0070] Yarn fineness and yarn density were taken from the yarn data sheets and not additionally determined by measurement.

[0071] Elongation at maximum force: ϵ B = Δ L Fmax x 100 L 0 % ε B = relative Change in length in % Δ L 0 = absolute change in length at maximum force in mm l 0 = Measuring length of the strain gauge in mm Modulus of elasticity:

[0072] E = ρ × Δ F × 10 3 T t × l 0 Δ l N / mm E = Modulus of elasticity in N / mm² < ρ Yarn density in g / cm² < Δ F =predefined force difference in N T t Yarn count in tex l 0 = measuring length of the strain gauge in mm Δ l = Length difference of the specified force difference in mm Results:

[0073] The results are in Figure 1 graphically represented.

[0074] In Figure 1The tensile strength in MPa is shown as a function of yarn twist in t / m. The first four samples, as described above, contain 1 wt% matrix resin. The last comparison sample is a 1600 tex STS40 E23 24K carbon fiber yarn from Teijin Carbon Europa, impregnated with an epoxy-based resin. The resin content in the yarn was 39 wt%. The first sample, with 0Z, exhibits no twist and achieves a tensile strength of 1955 MPa. With increasing twist, it is evident that the tensile strength increases despite the same proportion of matrix resin in the fibers. At a twist of 15Z, i.e., 15 t / m, right-hand twist, a tensile strength of 2309 MPa is achieved. This represents an increase of approximately 18%, attributable to the twist of the yarn.It is assumed that twisting, interlacing, or twisting the carbon fibers into a thread-like structure creates a similar bond between the filaments as would occur through fiber impregnation. This bonding gives the thread-like structure good tensile strength. Due to the very low matrix content of the thread-like structure, the material is particularly well-suited for use as fire-resistant reinforcement. As previously mentioned, high temperatures, such as those generated in a fire, can decompose the matrix resin, releasing gas. This results in the loss of filament cohesion and can lead to the concrete component bursting. Consequently, the component fails. With a matrix content of 5% by weight or less, it can be assumed that gas production is insufficient to damage the component.This advantageously achieves good tensile strength of the textile reinforcement while simultaneously providing good fire resistance. Example 2

[0075] Example 2 investigates the temperature resistance of carbon fibers as a function of a vermiculite coating. The vermiculite coating represents one embodiment of the separate, oxidation-protective layer. Coating the carbon fiber is comparable to coating reinforcement, as the coating generally improves the heat resistance of the fibers from which the reinforcement is constructed. Material:

[0076] STS40 E23 24K 1600tex, 5Z Vermiculite Dispersion (AVD, Manufacturer: Dupré Minerals Ltd., GB) Single-filament coating system (unwind stand with unwind spindle and brake for adjusting filament tension, cup bath for resin impregnation with adjustable cup holder and base plate for mounting the rollers ( Fig. 3 ) and coating eyelets ( Fig. 4 )) Changing board ( Fig. 5 Drying oven with a temperature range up to at least 150 °C; yarn scissors; steel blade; plastic cutting board; plastic hammer; Alsint trays (H x L x W: 15 mm x 200 mm x 15 mm); muffle furnace with a temperature range up to at least 1000 °C; scale with an accuracy of ± 0.001 g Implementation:

[0077] The spool of twisted yarn is mounted on the unwinding stand. The yarn is guided through a cup bath containing coating dispersion to the eyelet via easily removable and cleanable rollers ( Fig. 3 ). The eyelet ( Fig. 4) removes the excess dispersion from the yarn. The drive is manual, achieved by winding the yarn after the eyelet onto a winding board ( Fig. 5 A thread brake keeps the yarn under slight tension during manual unwinding. This ensures continuous coating of the yarn. The resulting vermiculite coating is shown in Table 1. Table 1 Vermiculite bath concentration [%] Eyelet diameter [mm] Achieved vermiculite content [%] 0 no 0 5 2,6 3,7 12 3,0 13

[0078] For each sample, four 16 cm lengths of yarn are placed in an Alsint dish (pure carbon fiber weight approx. 1 g) and placed in a muffle furnace at room temperature. The furnace is heated to 900 °C. Upon reaching this temperature, the dishes are immediately removed and placed on a sand bed to cool. Once the samples have cooled back to room temperature, the total mass loss is determined by backweighing. This is then converted to the mass loss of the carbon fiber. At least one duplicate determination is performed.

[0079] Figure 2 represents the result of example 2.

[0080] For a yarn without a vermiculite coating as an oxidation protection layer, the average mass loss is approximately 68 wt%. For a yarn with a 3.7 wt% vermiculite coating as an oxidation protection layer, the average mass loss was reduced by approximately 11 wt%, amounting to about 56 wt%. With a 13 wt% vermiculite coating on the carbon fibers, the average mass loss was approximately 30 wt%, resulting in a reduction of more than 50 wt% compared to the uncoated carbon fiber yarn. Example 2 thus demonstrates that a separate coating with an oxidation protection layer can protect the carbon fibers even at high temperatures, ensuring that the carbon fibers remain temperature-resistant even in the presence of oxygen.Reinforcement that has such a separate layer protecting against oxidation retains its reinforcing properties even in the event of a fire, so that the component with the reinforcement does not fail in the event of a fire or fails at a later time. Example 3

[0081] In example 3, a tensile test was performed. Fiber samples P11 and P12 (sample details can be found in Table 2) were embedded in concrete and the maximum load was determined using a tensile test. Sample preparation:

[0082] After delivery, the yarn strands were stored dry at room temperature until the concrete was poured. The tensile specimens, measuring 800 x 60 x 15 mm, were produced in plastic molds. Four specimens of each yarn type were produced standing upright (60 mm height). Each specimen contained eight yarn strands. The intended position of the yarn strands can be Figure 7 can be taken.

[0083] Sample production took place over three consecutive days, with two sample sets produced each day. Four individual samples were produced from each sample set. First, the yarn strands were fixed in the formwork using springs with slight pre-tension. To secure them, the yarn strands were bent at their ends and fastened with cable ties and superglue. Figure 8 shows the built-in yarn strands.

[0084] A fine-grained ready-mix concrete with a maximum aggregate size of 1 mm (compressive strength > 60 N / mm²) was used. The dry mix was homogenized for all pours and then portioned for each individual pour. The dry mix was blended in a bucket mixer with an automatic timer according to the manufacturer's instructions. Following mixing, two formworks were poured for each pour under continuous vibration within less than 30 minutes. The specimens were then covered and stored at room temperature for 20-24 hours until demolding. After demolding, the specimens were stored in a climate chamber at 20 °C and > 95% relative humidity for a maximum of six days. Finally, they were stored at 22 °C and 65% relative humidity until testing. Examination of the extensible specimen samples:

[0085] The tensile test specimens were tested 13 or 14 days after production. The tests were performed using a universal testing machine equipped with a Class 1 load cell with a maximum load of 50 kN (calibrated in December 2020). For testing, the specimens were clamped in bolted steel clamps over a length of 250 mm. The steel clamps are coated with compensating layers to compensate for surface irregularities and ensure secure adhesion of the specimen in the clamping area. The clamping jaws were connected to the testing machine via ball joints. Figure 9 The test setup is shown (rotated).

[0086] Prior to testing, the specimens were measured for their geometric properties. The specimen width (target dimension 60 mm) and thickness (target dimension 15 mm) were determined at the top, middle, and bottom of the free extension length. The measured values ​​were within normal tolerances. After installing the specimens, the force was zeroed with the specimen suspended. The weight of the specimen and the lower clamping structure was approximately 65 N. The specimen was then manually preloaded to < 150 N, and the test was started. The approach speed of the testing machine was 0.5 mm / min, followed by a test speed of 1 mm / min. The test was automatically stopped if the force dropped by more than 90%. During the test, the machine travel (crosshead travel) and the force were recorded at a sampling rate of 50 Hz. Results:

[0087] Table 2: Fiber type Yarn type Rotations Vermiculite Sample name Date of manufacture Test date Old Maximum load Fmax Mean Fmax First crack load Number of cracks mean crack spacing average mean crack spacing Type of failure [Weight %] [d] [N] [mm] P11 STS40 F13 24K 1600tex 5 0 P11-A 21.02.2021 03.02.2021 13 3496 3543 3920 1 300 300 Withdrawal failure P11-B 3244 3519 1 300 Withdrawal failure P11-C 3588 3783 1 300 Withdrawal failure P11-D 3844 3482 1 300 Withdrawal failure P12 STS40 F13 24K 1600tex 30 0 P12-1 4820 4980 2712 2 150 138 Withdrawal failure P12-2 5212 3690 3 100 Withdrawal failure P12-3 4762 3924 2 150 Withdrawal failure P12-4 5127 3433 2 150 Withdrawal failure

[0088] The number of cracks was determined and recorded during the inspection of the completed crack pattern. Cracks near the jaw exits were counted, even if they were slightly inside the jaws. The reported mean values ​​(arithmetic mean) refer to four individual results. The maximum force was determined after the first crack appeared. The mean crack spacing (e) was calculated as follows: e = L0 / number of cracks, where L0 = free extension length = 300 mm.

[0089] Unlike in Example 1, this example demonstrates that the twisted fibers exhibit good tensile strength even when embedded in concrete without matrix impregnation. Furthermore, this example shows that the twisting of the fiber samples, even when embedded in concrete, surprisingly influences the tensile strength. The maximum load of the fiber sample with only 5 twists per meter is, on average, slightly less than 30% lower than the average maximum load of the same fiber sample with only 30 twists per meter. Thus, the twisting of the fibers is surprisingly effective in increasing the close bond between the fibers, even without matrix material, and thereby improving the tensile strength of the entire composite. The results are shown in Table 2.

Claims

1. Textile reinforcement for embedding in concrete, comprising carbon fibres, wherein the reinforcement is coated with an oxidation-protective layer which can establish a chemical bond to a component of concrete, characterised in that ∘ the carbon fibres are in the form of an interlaced, twisted, plied or cabled filamentary structure and comprise a maximum of 5 wt.% of a matrix resin, and ∘ the oxidation-protective layer forms a separate layer.

2. Textile reinforcement according to claim 1, wherein the textile reinforcement comprises at least one further filamentary structure, preferably in the form of winding threads.

3. Textile reinforcement according to claim 2, wherein the further filamentary structure may contain carbon fibres, aramid fibres, polyamide fibres, AR-glass fibres, polypropylene fibres, polyvinyl alcohol fibres, oxidised, non-fusible polyacrylonitrile fibres, polyester fibres and / or a mixture of the aforementioned fibre types.

4. Textile reinforcement according to any one of the preceding claims, wherein the filamentary structure has a structured surface.

5. Textile reinforcement according to any one of the preceding claims, wherein the oxidation-protective layer consists of at least 80 wt.% of inorganic material.

6. Textile reinforcement according to any one of the preceding claims, wherein the oxidation-protective layer contains at least 5 wt.% of silicon.

7. Textile reinforcement according to claim 6, wherein the oxidation-protective layer contains silanol groups on its surface.

8. Reinforcement according to claim 6 or 7, wherein the oxidation-protective layer consists of at least 30% of silicon dioxide.

9. Textile reinforcement according to claim 1, wherein the oxidation-protective layer contains a sheet silicate.

10. Textile reinforcement according to claim 9, wherein the sheet silicate is vermiculite.

11. Textile reinforcement according to claim 1, wherein an adhesion layer is located between the carbon fibres and the oxidation-protective layer.

12. Textile reinforcement according to claim 11, wherein the adhesion layer contains organically functionalised silanes.

13. Textile reinforcement according to at least one of the preceding claims, wherein the textile reinforcement comprises a protective layer.

14. Concrete component comprising a textile reinforcement according to claim 1.

15. Concrete component according to claim 14, wherein the textile reinforcement has a maximum concrete cover of 50 mm and a fire resistance class of at least R 60.