EP4107343A1 - Reinforcement containing carbon fibers - Google Patents

Abstract

The invention relates to a textile reinforcement for integrating into concrete, having carbon fibers. The reinforcement is coated with a layer which protects against oxidation, wherein the carbon fibers are provided in the form of an interlaced, twisted, or cabled thread structure and have 5 wt.% of matrix resin, and the layer which protects against oxidation is a separate layer and can produce a chemical bond to a component of the concrete. The invention additionally relates to a concrete part which has a textile reinforcement.

Description

Reinforcement comprising carbon fibers

Description:

The application relates to a textile reinforcement that is suitable for being completely poured into concrete or a concrete component.

Compared to the compressive strength, concrete only has a tensile strength of about 10%. In order to increase the tensile strength of the then new building material concrete, concrete began to be combined with other, more tensile materials as early as the middle of the 19th century. Particularly noteworthy here are the work of the French gardener Joseph Monier, who combined concrete with an iron mesh for planters. Today Monier is considered to be the inventor of reinforced or reinforced concrete, or reinforced concrete for short. After him, the reinforcing elements cast in reinforced concrete are still colloquially called "reinforcement iron". Other materials for making reinforcement are still the subject of current research and development, particularly textile-based reinforcement.

Various fiber and textile materials are known whose tensile strength significantly exceeds that of steel, but which at the same time are significantly lighter than steel. Massive weight savings in concrete components or concrete structures are therefore possible, which, for example, has a positive effect on the statics of load-bearing components such as bridge piers or abutments. At the same time, textiles, for example based on glass fibers, basalt fibers, carbon fibers (“carbon”, “carbon fibers”) or certain organic polymers offer the big ones The advantage of a lower susceptibility to corrosion, while in the case of metal reinforcement, chemical wear of the reinforcement elements is to be expected in the long run, which can lead to a dangerous reduction in the load-bearing capacity of the structural elements concerned, both due to the failure of the reinforcement itself and due to the spalling of the concrete due to the expansion of the corrosive reinforcement elements. In addition to the general sensitivity of metals, in particular structural steel, to oxidation, the fact that the concrete matrix in which the reinforcement elements are embedded has a strong alkaline reaction and is therefore chemically very aggressive.

Textile reinforcements are still in the development phase. In 2005, for example, the world's first bridge made of textile-reinforced concrete was built on the grounds of the State Horticultural Show in Oschatz (Saxony).

Carbon fibers have proven to be of interest for the production of textile reinforcements for concrete. Carbon fibers offer high tear strength and are extremely resistant to environmental influences such as water, oxygen or the strongly alkaline environment in concrete at normal temperatures. Carbon fibers show a high tensile strength in the direction of the fibers, but are very brittle transversely to the direction of the fibers. This disadvantage is remedied by embedding carbon fibers in a matrix resin that absorbs the corresponding forces and ensures that the carbon fibers are held together.

The problem with textile reinforcements is their poor heat resistance. Concrete components with textile reinforcement are therefore unsuitable for applications in which they are permanently exposed to high temperatures. At the same time, however, a temporary resistance to high temperatures must be guaranteed in order to ensure the stability of concrete components with textile reinforcement in the event of fire. A temporary resistance to high temperatures in the event of fire is called "fire resistance". He will based on the duration for which a component retains its function in the event of a fire. A common practical requirement for fire-endangered structures is the fire resistance class "F90 fire-resistant" (in the event of fire, functional for at least 90 minutes). With conventional reinforced concrete construction, protection over 90 minutes is achieved primarily through a sufficiently large concrete cover.

WO 2018/202785 discloses a concrete component with textile reinforcement, which has improved resistance in the event of fire, which is brought about by the concrete being modified accordingly to prevent flaking, inorganically dominated matrix materials are used for the reinforcement or the reinforcement of a Oxidation barrier is surrounded, which protects the fibers from the action of oxygen.

However, the disadvantage of the prior art is that the cohesion of the fibers in the textile reinforcement is still achieved by a binding agent that has organic components that form gases under the action of large flecks, thus bursting the surrounding concrete and causing the component to collapse can.

The object of the present invention is to provide a textile reinforcement that is outstandingly fire-resistant and at the same time easy to use.

The object is achieved by a textile reinforcement for embedding in concrete comprising carbon fibers, the reinforcement being coated with a layer protecting against oxidation, the carbon fibers being in the form of braided, twisted, twisted or cabled thread-like structures and having a maximum of 5% by weight of matrix resin and the layer protecting against oxidation forms a separate layer and can produce a chemical bond to a component of concrete. The present invention relates to 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 here that at least the surface and the lower surface of the textile reinforcement - which each extend as surfaces in the longitudinal extension of the reinforcement and run essentially parallel to each other - from Concrete are almost completely covered (see Figure 10). The present textile reinforcement is therefore (with the exception of edge areas) at least on the upper and lower surface of concrete. A material that is placed on concrete and not enclosed by concrete is not reinforcement.

A separate layer protecting against oxidation should be understood to mean a layer which essentially lies completely around the reinforcement as an outer surface or coating. The layer protecting against oxidation is preferably in the form of an essentially complete coating of the reinforcement. A substantially complete coating of the reinforcement means that less than 30% of the outer surface, less than 20% of the outer surface, less than 10% of the outer surface or less than 5% of the outer surface of the reinforcement is free of the protective layer against oxidation. The layer protecting against oxidation can occasionally have cracks. A separate layer protecting against oxidation consists essentially completely, that is to say 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 material protecting against oxidation . According to the invention, the carbon fibers that form the thread-like structure of the reinforcement consequently have no more than 5% by weight of matrix resin and the reinforcement is surrounded by a separate layer protecting against oxidation.

There is no separate layer protecting against oxidation within the meaning of the invention if the material protecting against oxidation is only isolated and not as full-surface coating is present on the reinforcement or on the carbon fibers or on the thread-like structure. There is also no separate layer protecting against oxidation if the substances protecting against oxidation are only added as additives in a matrix material for coating the reinforcement or the fibers of the reinforcement.

The percentage by weight of the separate layer protecting against oxidation is less than 15% by weight, preferably less than 10% by weight, even more preferably less than 7.5% by weight and very particularly preferably less than 3% by weight based on the total weight of the textile reinforcement.

The document EP 0861 862 describes a method for reinforcing structures. For example, a concrete layer should be reinforced by applying a fiber layer to the surface of the concrete layer. 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 set in concrete. Consequently, the document does not describe any reinforcement either. In addition, the document does not describe any carbon fibers which are in the form of a braided, twisted, twisted or cabled thread-like structure or carbon fibers which have at most 5% by weight of a matrix resin. A separate layer protecting against oxidation 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 components (see FIGS. 1 to 4 of the document). The material is not embedded in concrete and therefore no reinforcement is described in this document. The material has reinforcing fibers which are embedded in a matrix material. There are no references to carbon fibers that are in the form of intertwined, twisted, twisted or cabled filamentary structures. A separate layer protecting against oxidation is also not disclosed. In the document WO 2019/091832 a fiber product with a coating is made from aqueous polymer dispersion described, 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 for this purpose, so that the coating made of polymeric material encloses as much as possible all of the individual filaments of the textile and thus enables an internal bond between the fibers. The document also describes the use of inorganic thickeners which can be used as additives in the aqueous dispersion. A separate layer of the reinforcement protecting against oxidation is not disclosed in the document.

The layer protecting against oxidation is preferably applied via a water-based system, for example an aqueous dispersion. All common textile coating processes - in the case of a layer of vermiculite protecting against oxidation, for example by dipping the reinforcement in an aqueous dispersion of the coating agent - could be used. A sol-gel process (in this case, inorganic and hybrid polymer layers can be produced from colloid-disperse solutions by wet-chemical coating processes and subsequent hardening) or a galvanic process could also be used.

The advantage of an aqueous dispersion to form the layer protecting against oxidation is that processing can be carried out without solvents (with the exception of water as the solvent), which makes processing considerably easier (also with regard to occupational health and safety and environmental protection).

In a general embodiment, means for increasing the stability and / or the abrasion resistance can also be added to the layer protecting against oxidation. For example, the layer protecting against oxidation can have 80% by weight of substances protecting against oxidation and a water-soluble protective polymer, such as can also be used, for example, for the further protective layer described later, added to a maximum of 20% by weight be. The protective polymer should act as a binder and can, for example, stiffen a vermiculite layer (as an embodiment of the layer protecting against oxidation), so that the mechanical load-bearing capacity is increased. Furthermore, the mechanical load-bearing capacity of a vermiculite layer (as an embodiment of the layer protecting against oxidation) and its connection to the thread-like structure can be improved by mixing it with binders. This creates a mixture of substances that protect against oxidation and binders and therefore no additional layer. Epoxy resins and phenolic resins, for example, can be used as organic binders for the layer protecting against oxidation. The increase in the mechanical strength of the layer protecting against oxidation, for example a vermiculite layer, can also be achieved by mixing the layer protecting against oxidation (or its components) with particularly temperature-resistant polymers, such as bismaleimide, phenol, cyanate ester or polybenzimidazole -Resins can be achieved. Carbon-based materials such as graphene and graphene oxide, silicon-based materials such as polysiloxanes or silicone resins, colloidal silica or nanosilica, microsilica or other inorganic materials such as. B. ZnO nanoparticles (e.g. NANOBYK-3860, BYK, Wesel, Germany), lime, cement, anhydrite, ettringite, silica sol and water glass can be used as binders in the layer protecting against oxidation to improve the properties of the layer will. The layer protecting against oxidation can furthermore contain polyelectrolytes such as polycarboxylate ethers or lignin sulfonate, cellulose ethers such as methyl cellulose, polyvinyl alcohol or polyvinylpyrrolidone. With all the mentioned admixtures to the layer protecting against oxidation, however, it should be noted that the material protecting against oxidation always remains the main component of the layer and that the admixtures also do not result in an additional layer of these admixtures in the layer protecting against oxidation.

The textile reinforcement advantageously has a proportion of organic substance which is so low that gaseous substances are formed Decomposition products are no longer significant when heated and so the component cannot be exploded in the event of a fire. The person skilled in the art knows, for example, that no fire resistance tests are required for concrete components with an organic content of less than 1% by weight. In the case of steel reinforcement, the concrete covering of the reinforcement elements must ensure that the reinforcement does not heat up to over 550 ° C, as otherwise the steel would lose its strength. Carbon fibers, on the other hand, are stable in the absence of oxygen at this temperature and thus allow less concrete cover, which results in significant weight savings.

A textile reinforcement in the sense of the present application is a material based on thread-like structures that is embedded in a surrounding material, for example concrete, for reinforcement. The thread-like structures can be present as threads in the narrower sense, but they can also be products made from threads. Possible products are, for example, yarns, cables, cords or ropes, which can also be processed into flat products such as woven fabrics, non-woven fabrics, knitted fabrics, braids, warp knitted fabrics, grids or nets. The textile reinforcements produced in this way are characterized by their flexibility, which makes it possible to store the textile reinforcement in a space-saving manner, for example in rolls, and to transport it to the construction site and only unroll it immediately before setting it in concrete. By using binding agents or by twisting and / or interlacing the thread-like structures accordingly, rigid reinforcement elements such as rods or rigid grids can also be produced. So-called wrapping yarns, with which the thread-like structures or the yarns, cables, cords or ropes made from them are wrapped or braided, can mechanically stiffen the thread-like structures, the yarns, cables, cords, ropes, fabrics, scrims, knitted fabrics , Braids, knitted fabrics, Drebe, grids or nets can be realized. In one embodiment, the textile reinforcement consists of the thread-like structures mentioned.

In one embodiment, the reinforcement has a (further) protective layer in addition to the layer that protects against oxidation. The protective layer is preferably located as an outer layer on the finished reinforcement with the separate layer protecting against oxidation and preferably not over the entire area around the thread-like structure of the carbon fibers. The protective layer preferably covers the surface and / or the lower surface of the reinforcement. The protective layer can, for example, be a coating through which the reinforcement can (better) be wound up and can thus be stored as rolled goods. The protective layer can also be composed of substances or contain substances that simplify and / or improve the embedding of the reinforcement in the concrete. For example, the protective layer can contain superplasticizers for concrete. Furthermore, the protective layer can also protect the reinforcement from weathering and / or mechanical loads as long as it has not yet been installed in the concrete. The protective layer can be provided reversibly or permanently with the reinforcement. A reversible protective layer is present when the protective layer can be removed from the reinforcement, for example as a kind of foil. In this case, all types of polymer films are conceivable as films, it also being possible for the polymer film to be insoluble in water (for example a polyethylene film). The protective layer is firmly connected to the reinforcement when the protective layer and the reinforcement can no longer be detached from one another without destroying the reinforcement. In the case of a protective layer firmly connected to the reinforcement, the protective layer is preferably designed to be water-soluble, so that it dissolves in the concrete on contact with the water. As a result, the protective layer can protect the reinforcement from being set in concrete, but does not prevent or worsen the penetration of the reinforcement with the concrete. The protective layer can, for example, have or consist of polyelectrolytes such as polycarboxylate ethers or ligninsulphonate, cellulose ethers such as methyl cellulose, polyvinyl alcohol or polyvinylpyrrolidone. The reinforcement preferably has about 1 to 10% by weight, preferably 2 to 5% by weight, of the protective layer, based on the total weight of the reinforcement.

In one embodiment, the textile reinforcement has more than one thread-like structure. In one embodiment, the textile reinforcement consists of more than one thread-like structure. The individual thread-like structures of the reinforcement can be intertwined, twisted, twisted or wired with one another. 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. For this purpose, 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, infusible polyacrylonitrile (e.g. Pyromex®, available from Teijin Carbon Europe, Wuppertal, Germany) come into consideration. In one embodiment, the additional thread-like structure of the reinforcement is a plurality of winding threads with which the thread-like structure made of carbon fibers is wound around. The winding can, for example, increase the mechanical stability of the thread-like structure made of carbon fibers and thus the reinforcement. The wrapping can be carried out uniformly over the entire reinforcement or there is only a wrapping in partial areas of the reinforcement. For example, only a central area of the reinforcement can be reinforced particularly mechanically by means of the wrapping threads.

In one embodiment, the thread-like structure has a structured surface due to its manufacture by braiding, twisting, twisting or cabling. This structured surface makes it possible to bring the thread-like structure into a particularly intimate, form-fitting connection with other materials, for example coatings, the layer protecting against oxidation, the additional protective layer or concrete. In one embodiment of the wrapping threads, the wrapping threads produce in addition to mechanical reinforcement or a structured surface without mechanical reinforcement and thus enable an intimate, form-fitting connection - as described above.

By intertwining, twisting, twisting, wrapping or cabling, the carbon fibers and / or filaments are held together in the thread-like structures, which makes it possible to significantly reduce or even completely reduce the amount of matrix resin necessary for the fibers to be held together within the thread-like structure to forego a matrix resin. If only one thread-like structure is used, the endless filaments that make up this thread-like structure are intimately connected to one another by braiding, twisting, twisting, winding or cabling. When using several thread-like structures, several thread-like structures can be intimately connected to one another by braiding, twisting, twisting, wrapping or cabling, optionally also in addition to an intimate connection of the filaments making up the thread-like structures.

A major disadvantage of the matrix resin is its problematic behavior at high temperatures. In the case of significantly increased temperatures, the matrix resin begins to soften and can no longer ensure the cohesion of the carbon fibers with one another and can no longer compensate for the brittleness of the carbon fibers transverse to the fiber direction. In addition, it begins to decompose, even in the absence of air, with the formation of gaseous products, which can then burst the surrounding concrete. At high temperatures and in the presence of oxygen, carbon fibers can also oxidize themselves, while in the absence of oxygen they are stable even at extremely high temperatures.

In this way, a significant contribution is made to the better fire resistance of the textile reinforcements based on carbon fibers, since the cohesion within the thread-like structure is no longer due to a Temperature increases quickly failing matrix resin is realized, but by mechanical means by the entanglement of the fibers and / or filaments making up the thread-like structure. By reducing the amount of matrix resin, the amount of thermally decomposable material in the thread-like structures can also be reduced, so that gas formation under the action of high temperatures is minimized or excluded. This goes hand in hand with a reduction in the risk of structural failure of concrete parts provided with carbon fiber-based reinforcement due to bursting in the event of fire.

In the present application, matrix resin is understood to mean the entirety of all non-fiber-forming material with which the carbon fibers, the thread-like structures made therefrom or the textile reinforcement made therefrom are provided before the layer protecting against oxidation is applied to the reinforcement. In particular, they are to be understood as finishing agents that are applied with the aim of improving the processability of the fibers or the thread-like structures, for example agents for breaking protection, for reducing static charging or for improving the sliding properties of the fibers in the processing process. Such finishes of fibers are known to the person skilled in the art under the designation “sizing” or “sizing”. Organic synthetic resins such as epoxy resins or polyurethane-based resins are often used for this purpose. A reactive polydimethylsiloxane (for example SILRES BS 1042, available from Wacker, Munich, Germany) can also be used as the sizing. In the event that particularly temperature-resistant equipment is necessary, particularly temperature-resistant polymers such as polyphenylene sulfide (PPS), polyether ketones such as polyether ether ketone (PEEK) or polyimides such as polyether imides can also be used. In addition, flotation 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 can silicon-based materials such as colloidal silica or nanosilica (based on sol-gel processes; e.g. LUDOX SM 30 from WR Grace & Co.-Conn., Columbia, USA), microsilica (e.g. EMSAC 500 SE from Fla-Be Betonchemie GmbH & Co. KG, Flameln, Germany). In addition, other inorganic materials in connection with water-soluble organic polymers such as. B. polyvinyl alcohol or polyvinylpyrrolidone can be used as a binder. In the examples given, the binders are water-soluble and accordingly distribute themselves in the concrete. Ferrofluids containing paramagnetic iron can act as free radical scavengers and thus as oxidation inhibitors. In addition, ZnO nanoparticles (e.g. NANOBYK-3860, BYK,

Wesel, Germany), polysiloxanes or silicone resins or inorganic lubricants based on molybdenum sulfide 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). Other inorganic finishes, for example based on sheet silicates such as vermiculite, can also be used.

In addition to the mechanical properties of the fibers, the finishing agent can also provide a better connection to other parts of the matrix resin, for example to binding agents. In addition to finishing agents that improve the processability of the carbon fibers or the thread-like structures made from them, the term "matrix resin" also includes binders that serve to hold the carbon fibers or the thread-like structures together, but also reduce the brittleness of the carbon fibers across the fiber direction compensate or, if necessary, for stiffening the thread-like structures or the yarns, cables, cords or ropes made from the thread-like structures into rods or rigid grids for the stiffening of the woven fabrics, scrims, knitted fabrics, braids, knitted fabrics or twines produced from the thread-like structures can worry. In addition, binders prevent uncontrolled penetration of concrete into the material of the textile reinforcement. This would mean that there would be a telescopic extraction of fibers from the textile Reinforcement could come, with inner fibers or filaments that have no contact with concrete, are easier to pull out than fibers or filaments lying further outside that are in contact with concrete. The term “uncontrolled penetration” specifically refers to the penetration of the concrete between the filaments that build up the thread-like structure. Otherwise, the filaments of the thread-like structure can be destroyed or damaged due to the formation of needle-shaped crystallites when the concrete hardens. By intimate connection of the filaments of a thread-like structure with each other as well as by intimate connection of several thread-like structures z. B. by intertwining, twisting, twisting, winding or cabling, the penetrability through concrete can be drastically reduced. Binders for thread-like structures made of carbon fibers are known to those skilled in the art under the names “impregnation” or “impregnation compound”. Binders from the group of organic polymers, which can be chemically related to the finishing agent of the fibers, are often used. 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. In order 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, in particular silicone resins, such as, in particular, the substance group of methyl resins and methylphenyl resins, such as, for example, methyl-phenyl-vinyl and drug-substituted siloxanes, and mixtures of the silicone resins in question and organic resins have proven to be suitable. Although no basic resistance to alkali is to be expected with organosilicon compounds, this could surprisingly be demonstrated in some formulations (e.g. Wacker Silres H62C and in combination with Silres MK, both available from Wacker, Munich, Germany) for the special application of textile reinforcement. In the case of methyl phenyl vinyl hydrogen polysiloxanes (e.g. Wacker Silres H62C, available from Wacker, Munich, Germany), methyl polysiloxanes (for example Wacker Silres MK, available from Wacker, Munich, Germany) and in particular suitable mixtures of these two siloxanes already had surprisingly high alkali resistance in the field of textile reinforcement be detected. Reactive polydimethylsiloxanes (for example SILRES BS 1042, available from Wacker, Munich, Germany) have also proven useful. Inorganic binders with an organic component, in particular predominantly inorganic binders that also have an organic component, still tend to develop a porous structure or microcracks in the high temperature range between 500 ° C and 1000 ° C despite significantly better high temperature resistance. For this reason, it is desirable to minimize the amount of binding agent used in the reinforcement for use in high-temperature-resistant concrete parts.

A total proportion of not more than 5% by weight of matrix resin based on the entire reinforcement is preferred for this reason in order to achieve the best possible high temperature resistance of the concrete parts containing a textile reinforcement corresponding to the present application. The same material as described above for the matrix resin can be used as the amount of matrix resin, but this time the matrix material can not only be present on the carbon fibers, but can also occur as a component in other layers of the reinforcement. The amount of 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 have a maximum of 4% by weight of matrix resin. The textile reinforcement can have a maximum of 3% by weight of matrix resin. The textile reinforcement can have a maximum of 2% by weight of matrix resin. The textile reinforcement can have a maximum of 1% by weight of matrix resin. In one embodiment, the textile reinforcement is free of matrix resin. The binder content of the textile reinforcement can be 5% by weight, 4% by weight, 3% by weight, 2% by weight, 1% by weight, or the textile reinforcement can be free of binders. A reduction in the proportion of finishing agent on the carbon fibers is also possible. Here proportions of less than 1.5% by weight, less than 1% by weight or even less than 0.5% by weight are possible. In one embodiment, the carbon fibers and also the textile reinforcement are free of finishing agents.

In contrast to the matrix resin, the organic components of which are particularly affected by thermal decomposition in the event of fire, the carbon fibers are largely stable to high temperatures as long as they are kept away from oxygen. For this reason, according to the present application, the reinforcement is coated with a separate layer that protects against oxidation. In principle, all materials that do not react with oxygen even when exposed to high temperatures are suitable for this layer. This is particularly the case with inorganic compounds.

In one embodiment, the layer protecting against oxidation therefore has a proportion of inorganic material of at least 80% by weight. In one embodiment, the layer protecting against oxidation therefore has a proportion of inorganic material of at least 70% by weight. In one embodiment, the layer protecting against oxidation therefore has a proportion of inorganic material of at least 60% by weight. In one embodiment, the layer protecting against oxidation therefore has a proportion of inorganic material of at least 50% by weight. In one embodiment, the layer protecting against oxidation therefore has a proportion of inorganic material of at least 40% by weight. Oxidic materials or materials whose constituents are oxidized to a large extent as long as they do not themselves have an oxidizing effect are particularly suitable. Materials based on stable metal and semi-metal oxides, such as the oxides of calcium, magnesium, aluminum and silicon, are of particular importance.

The oxides of these elements are characterized by a high oxidation stability and a low oxidation effect as well as easy availability. from Materials derived from these oxides are, for example, quartz, clay, cement or the large group of substances called silicates, in which the elements mentioned can be associated with other elements in their oxidized forms, for example with iron or alkali metals.

The special thing about this selection is that all of these materials have a great chemical similarity to certain components of concrete, for example cement. This chemical similarity makes it possible for a chemical bond to occur between the material of the layer protecting against oxidation and certain constituents of concrete, which enables particularly strong adhesion between the layer of protection against oxidation of the textile reinforcement and the surrounding concrete of a concrete component.

In one embodiment, the layer protecting against oxidation has ORMOCERE, that is to say an organically modified ceramic (for example InnoSolTEX technology from Fraunhofer ISO, Würzburg, Germany), or polysilazanes.

In one embodiment, the layer protecting against oxidation therefore contains at least 5% by weight silicon. This can include silicon-oxygen compounds such as silicates or silicones. Silicon-oxygen compounds are characterized by a 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 give off oxygen even under the conditions of a fire and accordingly do not change chemically. For example, the person skilled in the art knows that various silicon-oxygen compounds are used as fire extinguishing agents. An important example of this is sand (chemically mostly silicon dioxide, S1O2), which can be used to cover fires. Layered silicates such as vermiculite can also be used as fire extinguishing agents. The layer protecting against oxidation lies on and around the reinforcement and can be present in very different ways on and around the textile reinforcement. For example, it is conceivable to produce the layer protecting against oxidation by means of a plasma treatment. In a plasma treatment, the object to be treated is exposed to a plasma to which a gaseous precursor is added for the desired surface coating. For example, a 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, here on the surface of the textile reinforcement. The silicon-oxygen compounds can be silicon dioxide, for example. 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% by weight of silicon dioxide. In one embodiment, the layer containing silicon-oxygen compounds has silanol groups on its surface.

In one embodiment, the layer containing silicon-oxygen compounds has a thickness of less than 500 nanometers and is therefore significantly thinner than conventional layers protecting against oxidation. In one embodiment, the layer containing silicon-oxygen compounds has a thickness of less than 300 nanometers. In one embodiment, the layer containing silicon-oxygen compounds has a thickness of less than 100 nanometers. In one embodiment, the layer containing silicon-oxygen compounds has a thickness of less than 50 nanometers, of less than 30 nanometers.

This also requires a great flexibility of the reinforcement in comparison with other layers protecting against oxidation. In this embodiment, the textile reinforcement retains its drapability even when coated with the layer protecting against oxidation. It is therefore possible to shape them into a desired shape immediately before pouring them into concrete and, for example, to shape curved or curved concrete components with little effort to manufacture. The layer containing silicon-oxygen compounds can be chemically bonded to the carbon fibers themselves or to the finishing agent applied to the carbon fibers and in turn allows a chemical bond to constituents of concrete, for example to cement.

Silicates, which can be applied to the reinforcement using a wet chemical method, for example, can also be used as the material for the layer protecting against oxidation. Layered silicates, for example, which are able to form flexible, inorganic films, should be mentioned in this context. Inorganic films made from vermiculite have excellent mechanical properties (for example in relation to tensile strength and tensile modulus) and are superior to some organic films.

In one embodiment, a flexible layer protecting against oxidation 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 then dried. Such dispersions are available, for example, under the name AVD (Aqueous Vermiculite Dispersion), inter alia, as fire extinguishing agents. The layer of layered silicates that protects against oxidation can be anchored in a form-fitting manner 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 in the structure on the surface of the thread-like structure or the carbon fibers and thus ensures an intimate connection between the thread-like structure or the carbon fibers and the layer protecting against oxidation . For example, after the reinforcement has been produced from the thread-like structure of the carbon fibers in an immersion bath of aqueous suspension, it can be soaked with sheet silicate, so that a separate layer protecting against oxidation is created on and around the reinforcement (i.e. the outer surfaces of the reinforcement). In addition, an adhesive layer can optionally be used, which ensures a chemical bond between the thread-like structure and the layer that protects against oxidation, such as the layered silicate. Both direct chemical bonds between the carbon fibers of the layer protecting against oxidation, such as the layered silicate, for example, and chemical bonds between the finishing agent on the carbon fibers and the layer protecting against oxidation are conceivable here. If epoxy resins are used as finishing agents, organically functionalized silanes with amino or epoxy groups can be used for the adhesive layer for example, can produce layered silicate. Possible products are, for example (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 the one hand and the layered silicate on the other.

The adhesive layer is preferably applied to the reinforcement, that is to say, the thread-like structure of interwoven, twisted, twisted or cabled carbon fibers has the adhesive layer. In another embodiment, however, it is also conceivable that the carbon fibers have the adhesive layer before the production of the thread-like structure.

If an adhesive layer is used, the adhesive layer makes up less than 3% by weight, preferably less than 2% by weight and even more preferably less than 1.5% by weight, even more preferably less than 1% by weight, based on the total weight of the reinforcement .

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.

The layered silicate layer can have a uniform or non-uniform thickness on and around the reinforcement.

In all embodiments of the textile reinforcement, the proportion of organic substances in the entire layers that are not reversibly 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, with the thread-like structure made of carbon fibers is not counted as a layer. This means that even if the reinforcement has fibers with a sizing (matrix), a separate layer protecting against oxidation, an adhesive layer and a further protective layer that is not reversibly connected to the reinforcement, the reinforcement has less than 5% by weight of organic substances in total, based on the total weight of the textile reinforcement.

The present application also relates to a concrete component that has reinforcement according to the present application. In one embodiment, the textile reinforcement is embedded in the concrete component in such a way that it has a concrete cover of at most 10 millimeters. The concrete cover is understood to mean the thickness of the concrete layer that is at least 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 a Embodiment, the reinforcement in the concrete component has a concrete cover of at most 20 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 25 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 30 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 35 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 40 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 45 millimeters. In one embodiment, the reinforcement in the concrete component has a concrete cover of at most 50 millimeters. 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 clear weight advantage.

The concrete covering of the textile reinforcement makes a decisive contribution to the fire resistance of the textile reinforcement due to its heat-insulating and oxygen-protecting effect.

The concrete covering of the textile reinforcement can be designed in interaction with the nature and the layer thickness of the layer protecting against oxidation in such a way that a desired fire resistance class is achieved.

The invention is described in more detail with the aid of experiments and figures, this not to be understood as a 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).

FIG. 2 shows the influence of a vermiculite coating on the temperature resistance of carbon fibers. Figure 3 shows the basic structure of a single-thread coating system Figure 4 shows the basic sketch of a coating eyelet (right in cross section)

Figure 5 shows the schematic diagram of a changing board

FIG. 6 shows a heating curve of a muffle furnace for the yarn samples

FIG. 7 shows a desired position of yarn strands for example 3

FIG. 8 shows the built-in yarn strands for example 3

FIG. 9 shows a test setup (rotated) for example 3

Figure 10 shows schematically a textile reinforcement that is embedded in concrete.

Figures 7 to 9 come from the reports of the TU Dortmund / WdB.

example 1

In the present example 1 it should be shown how the tensile strength of thread-like structures changes depending on their consolidation.

The thread-like structures to be tested are carbon fiber yarn of the type STS40 F1324K from Teijin Carbon Europe with 1600 tex and 1% polyurethane coating as the matrix resin content. An STS40 E2324K yarn from Teijin Carbon Europe, which has been thoroughly impregnated with 39% by weight of matrix resin based on epoxy, is selected as a comparison yarn.

The comparison yarn was impregnated with the following flarz mixture: Epikote 828: 100 parts Epikure 113: 30 parts acetone: 15 parts

Sample preparation:

For the tensile test and determination of the data, yarn samples are provided with 50 mm long cardboard strips, which are used to apply force to the test device. For this purpose, a two-component adhesive is used which, after hardening, completely encloses the samples in the area of a cardboard strip and there are no air pockets.

Adhesive approach: AW 106 100 part by weight

HV 953 80 parts by weight

Reference is made to a pot life of 45 minutes.

To produce yarn tensile test pieces, two cardboard strips, which are aligned parallel to one another with a 200 mm wide template, are firmly glued with polyester adhesive tape on a glass plate covered with PTFE glass. In order to ensure an even adhesive film between the cardboard strips and the test specimens, these are applied beforehand using a pulling element (which must be selected depending on the yarn count).

The samples must now be placed along the marking lines and fixed with polyester adhesive tape. Attention must be paid to the parallelism between the individual test specimens. The upper cardboard strips (provided with clear lettering), which are also provided with an adhesive film, are placed and fixed on this. On top of this is a layer of PTFE glass fabric, which is weighted down with a second glass plate.

This structure is left in a preheated convection oven at 70 ° C for one hour. After the yarn tensile test specimens have cooled down, cut them with a band saw on the outer edges and on the intended dividing lines.

Measurement:

The test specimens are kept for at least 24 hours in the test room climate at 23 ° C / 50% rel. Humidity stored before the measurement. A tensile test is carried out on the impregnated carbon fiber strand, which is provided with force introduction elements on both sides (cardboard glue), using an extensometer.

Device:

• Tensile / compression testing machine with a constant test speed adjustable to <1% in the range of 0 <v <20 mm / min

• Calibrated force transducer with a suitable force measuring range according to DIN EN ISO 7500-1

• Calibrated position measuring system with suitable position measuring range DIN EN ISO 9531 • Extensometer (211 mm)

Test condition:

Standard atmosphere for testing impregnated yarn tensile samples, i.e. 23 ° C ± 2 and 50% ± 5 relative humidity.

Test parameters:

Test speed: 5 mm / min free clamping length: 200 mm

Initial force: 2 cN / tex

Measuring length of probe: 100 mm

Start of modulus of elasticity: 40 cN / tex

End of modulus of elasticity: 80 cN / tex

Execution of the test:

The test is carried out as follows:

The tension clamps are installed in the material testing machine (MPM), aligned centrally and the required clamping length between the tension clamps is, as in the required standard or specification set, set. The test specimen stops are then adjusted in such a way that the test specimens are loaded centrally in the MPM. When clamping, make sure that the specimens are clamped perpendicular to the clamping jaws.

Before starting the test, the zero point of the force channel is approached. During the test, the testing machine moves, recording the measured values, until the breakage or until the specified force or elongation value is reached. After the test process is finished, the fracture pattern is entered and the measurement data is saved. The test specimen is removed from the test room and the device and the clamps are cleaned. In order to ensure that the test specimens can be clearly traced even after the test, the specimen numbering is checked and, if necessary, renewed on both sides. The traverse of the MPM is moved back to the starting position and the next specimen can be tested. According to this procedure, six tests are carried out per sample.

Determination of the tensile strength OB: r rmm

OB = ^Afr [N / mm ² ]

OB = tensile strength in N / mm ²

Fmax = maximum tensile force in N

AF = yarn cross-sectional area in mm ²

The cross-sectional area of the yarn is calculated as follows:

AF yarn cross-sectional area in mm Tt yarn count in tex

P yarn density in g / cm ³ Yarn count and yarn density were taken from the data sheets for the yarns and not additionally determined by measurement.

Elongation at maximum force: e _B = relative change in length in%

AL ₀ = absolute change in length at maximum force in mm i ₀ = measuring length of the extensometer in mm

Modulus of elasticity:

E modulus of elasticity in N / mm ²

P yarn density in g / cm ²

AF specified force difference in N

T _t yarn count in tex lo measuring length of the extensometer in mm

Al difference in length of the specified force difference in mm

Results:

The results are shown graphically in FIG.

FIG. 1 shows the tensile strength in MPa as a function of the twist of the yarn in t / m. As also described above, the first four samples contain 1% by weight of matrix resin. The last comparison sample is an STS40 E2324K carbon fiber yarn from Teijin Carbon Europa with 1600 tex, which has been impregnated with an epoxy-based resin material. The resin content in the yarn was 39% by weight. The first sample shows no twist with 0Z or Torsion and reaches a tensile strength of 1955 MPa. With increasing twisting or twisting, it can be seen that the tensile strength increases despite the same proportion of matrix resin in the fibers. With a twist of 15Z, i.e. 15 t / m, turned to the right, a tensile strength of 2309 MPa is achieved. This means that there is an increase of around 18%, which can be attributed to the twisting or twisting of the yarn. It is assumed that the twisting, interlacing or twisting of the carbon fibers to form the thread-like structure can bring about the cohesion of the filaments to one another in a similar way to what would be the case with the impregnation of the fibers. Because the filaments are held together, the thread-like structure then achieves good tensile strengths. Due to the very low matrix content of the thread-like structure, the material can be used particularly well as fire-resistant reinforcement. As already stated, high temperatures, such as those that arise in a fire, can decompose the matrix resin with the formation of gas. The cohesion of the filaments with one another is lost and the concrete component can explode. As a result, the component fails. With a matrix content of at most or below 5% by weight, it can be assumed that the gas formation is insufficient to damage the component. In this way, a good tensile strength of the textile reinforcement with good fire resistance is achieved in an advantageous manner.

Example 2

In example 2, the temperature resistance of carbon fibers is investigated as a function of a vermiculite coating. The vermiculite coating represents an embodiment for the separate layer protecting against oxidation. The coating of the carbon fiber is comparable to a coating of an armouring, since the coating can generally show the improvement in the litz resistance of the fibers from which the armouring is built up. Material:

STS40 E2324K 1600tex, 5Z

Vermiculite dispersion (AVD, manufacturer: Dupre Minerals Ltd., GB) Single thread coating system (unwinding stand with run-off spindle and brake for adjusting the thread tension, cup bath for resin impregnation with adjustable cup holder and base plate for fastening the rollers (Fig. 3) and coating eyelets (Fig. 4 ))

Changing board (Fig. 5)

Drying cabinet with a temperature range of at least 150 ° C

Yarn scissors

Steel blade

Plastic cutting board

Plastic hammer

Alsint bowls (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, balance with an accuracy of ± 0.001 g

Execution:

The bobbin with the twisted thread is mounted on the unwind stand. The yarn is fed through a bath of tubs with coating dispersion to the eyelet via rollers that are easy to dismantle and clean (Fig. 3). The eyelet (Fig. 4) removes the excess dispersion from the yarn. The drive is done manually by winding the yarn after the eyelet on a winding board (Fig. 5). A thread brake keeps the thread under slight tension when it is pulled off manually. In this way the yarn is continuously coated. The vermiculite coating achieved is given in Table 1. Table 1

For each sample, four pieces of yarn, each 16 cm in length, are placed in an Alsint dish (pure CF weight approx. 1 g) and placed in a muffle furnace at room temperature. The oven is heated to 900 ° C, the dishes are removed immediately when this temperature is reached and placed on a bed of sand to cool down. When the samples have cooled down to room temperature again, the total loss of mass is determined by reweighing. This is converted to the loss of mass of the carbon fiber. At least one double determination is carried out.

FIG. 2 shows the result of Example 2.

In the case of a yarn without a vermiculite coating as a protective layer against oxidation, the averaged mass loss is about 68% by weight. In the case of a yarn with a 3.7% by weight vermiculite coating as a protective layer against oxidation, the averaged mass loss could be reduced by about 11% by weight and was still about 56% by weight. In the case of a vermiculite coating of the carbon fibers with 13% by weight, the averaged mass loss was around 30% by weight, so that a reduction in mass loss of more than 50% by weight could be achieved compared to the uncoated carbon fiber yarn. Example 2 thus shows that a separate coating with a layer protecting against oxidation can protect the carbon fibers even at high temperatures, so that the carbon fibers remain temperature-resistant even when oxygen is present. A reinforcement that has such a separate layer protecting against oxidation therefore retains its own in the event of a fire reinforcing properties, so that the component with the reinforcement does not fail or fails at a later point in time, even in the event of a fire.

Example 3

In example 3, a tensile test was carried out. The fiber samples P11 and P12 (sample details can be found in Table 2) were embedded in concrete and the maximum load was determined by means of a tensile test.

Sample preparation:

After delivery, the strands of yarn were stored in a dry place in a room climate until they were concreted. The tensile specimens with the dimensions 800x60x15 mm ^{3 were produced} in plastic formwork. Four test specimens standing (standing height 60 mm) were produced for each yarn type. Each sample contained eight strands of yarn. The desired position of the yarn strands can be seen in FIG.

The samples were prepared on three consecutive days with two sets of samples each time. Four individual samples were produced with one set of samples. First, the strands of twine were fixed in the formwork using springs with a slight pre-tension. To fix it, the ends of the yarn strands were bent over and fastened with cable ties and superglue. Figure 8 shows the built-in yarn strands.

The concrete used was a ready-mixed fine concrete with a maximum grain size of 1 mm (compressive strength> 60 N / mm ² ). The dry mix was homogenized for all concreting and then bottled for the individual concreting. The dry mix was mixed in a bucket mixer with an automatic timer according to the manufacturer's instructions. After the mixing process, two formworks were concreted in less than 30 minutes per concreting with constant vibration. The test specimens were then covered and stored in a room climate until they were removed from the formwork after 20-24 hours. After stripping the formwork, the test specimens were placed in a climatic cabinet at 20 ° C and> 95% rel. Humidity stored for a maximum of six days. Finally, it was stored at 22 ° C. and 65% rel. Humidity up to the test.

Testing of tensile specimens:

The tensile specimens were tested 13 and 14 days after manufacture. The tests were carried out with a universal testing machine equipped with a class 1 load cell with a maximum load of 50 kN (calibrated in December 2020). For the test, the samples were clamped in screwed steel straps over a length of 250 mm each. The steel straps are provided with leveling layers to compensate for surface inaccuracies and to ensure that the sample adheres securely in the clamping area. The connection of the clamping jaws to the testing machine was realized via ball joint heads. In Figure 9, the test setup is shown (rotated).

Before the test, the specimens were measured with regard to their geometric properties. For this purpose, the specimen width (nominal dimension 60 mm) and the specimen thickness (nominal dimension 15 mm) in the area of the free stretching length were determined at the top, in the middle and at the bottom. The measured values were within the usual tolerances. After the test specimen had been installed, the force with the specimen suspended was tared to zero. The weight of the test specimen and the lower clamping structure was approx. 65 N. The test was then manually approached to a preload of <150 N and the test started. The approach speed of the testing machine was 0.5 mm / min and the subsequent testing speed 1 mm / min. If the force dropped by> 90%, the experiment was stopped automatically. During the test, the machine path (traverse path) and the force were recorded at a measuring rate of 50 Hz. Results: Table 2:

The number of cracks was determined 5 and recorded in the completed crack pattern during the test. Cracks near the jaw exits were counted, even if they were slightly inside the jaws. The specified mean values (arithmetic mean) relate to 4 individual results. The determination of the maximum force took place after the first tear. The mean crack spacing (e) was determined as follows: e = L0 / number of cracks with L0 = free expansion length = 300 mm.

In contrast to example 1, it can be demonstrated that the twisted fibers have good tensile strength even when embedded in concrete without matrix impregnation. Furthermore, this example could prove that

15 that the twisting of the fiber samples, even when embedded in concrete, surprisingly has an influence on the tensile strength. The maximum load of the fiber sample with only 5 revolutions per meter is on average a little less than 30% lower than the average maximum load of the same fiber sample with only 30 revolutions per meter. The twisting of the fibers is therefore surprisingly suitable for increasing the intimate connection of the fibers to one another even without matrix material and thus improving the tensile strength of the entire composite. The results are shown in Table 2.

Claims

Expectations:

1. Textile reinforcement for embedding in concrete comprising carbon fibers, the reinforcement being coated with a layer protecting against oxidation, wherein

- the carbon fibers are in the form of intertwined, twisted, twisted or cabled thread-like structures and have a maximum of 5% by weight of a matrix resin,

- the layer protecting against oxidation forms a separate layer and can create a chemical bond to a component of concrete.

2. Textile reinforcement according to claim 1, wherein the textile reinforcement has at least one further thread-like structure, preferably in the form of wrapping threads.

3. Textile reinforcement according to claim 2, wherein the further thread-like structure can contain carbon fibers, aramid fibers, polyamide fibers, AR glass fibers, polypropylene fibers, polyvinyl alcohol fibers, oxidized, infusible polyacrylonitrile fibers, polyester fibers and / or a mixture of the said types of fibers.

4. Textile reinforcement according to one of the preceding claims, wherein the thread-like structure has a structured surface.

5. Textile reinforcement according to one of the preceding claims, wherein the layer protecting against oxidation consists of at least 80% by weight of inorganic material.

6. Textile reinforcement according to one of the preceding claims, wherein the layer protecting against oxidation contains at least 5% by weight of silicon.

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

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

9. Textile reinforcement according to claim 1, wherein the layer protecting against oxidation contains a layered silicate.

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

11. Textile reinforcement according to claim 1, wherein there is an adhesive layer between the carbon fibers and the layer protecting against oxidation.

12. Textile reinforcement according to claim 11, wherein the adhesive layer contains organically functionalized silanes.

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

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

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