Method for producing composite material

Abstract

The invention relates to a method for producing a composite material from set cement, aggregate and reinforcing material. In this case, the set cement is produced by providing a starting product, which contains at least 20 mass% of one or more of the following components: superaumasitic rock, weathered products of superaumasitic rock, olivine, industrial waste; homogenizing the initial product; and subjecting the homogenized starting product to hydro-thermal treatment in a thermal treatment apparatus at a temperature above 100 DEG C for at least 12 hours. Furthermore, it is provided that the converted starting product is dehydrated by heat treatment and / or reaction milling in order to remove bound water. Subsequently, the converted and dehydrated starting product is used as a binder, where solidification water is added for hardening, where the water / binder ratio is 1: 2 or less. Before, after and / or simultaneously with the addition of the solidification water, an aggregate is added to the converted and dehydrated starting product, and a reinforcing material is added to increase the load bearing capacity wherein the reinforcing material is resistant to and / or protected from a pH below 11. Additionally or alternatively, an agent for increasing the pH of the pore solution of the set cement may be added to the starting product of the set cement.

Description

[0001] The present invention relates to a method for producing a composite material from a cement stone, aggregates and reinforcing material.

[0002] In today's form of the construction industry, the use of reinforced concrete is indispensable. In reinforced concrete, the concrete absorbs compressive stresses, while the steel reinforcement is responsible for reducing tensile stresses. At the same time, the concrete also protects the steel from corrosion. This corrosion protection is based on the very high pH value in the pore solution of the concrete. Above a pH value of approximately 11, ordinary reinforcement steel no longer rusts, because a very thin passivation layer forms on its surface, which leads to a sealed steel surface to prevent the penetration of oxygen and water, thus preventing corrosion. In the pore solution of the concrete produced using cements according to DIN EN 197, the pH value is above 12, which means that using these cements enables an effective corrosion protection for the steel reinforcement. Composite reinforced concrete has high performance and durability as well as low costs and is therefore widely used. However, the production of conventional cements has a large impact on the environment. New binders have been proposed to replace cement, especially with the aim of reducing the carbon dioxide emissions of concrete. However, after hardening, some of the binders have a pH value below 11.5 and are therefore not suitable for the production of reinforced concrete, because the concrete reinforcement is no longer protected from corrosion.

[0003] In order to replace the steel reinforcement, various alternative materials have also been proposed. In particular, carbon fibers and glass fibers are included. Both materials have a very high tensile strength and can also be used to reduce tensile stresses in reinforced concrete. Another advantage is that both fiber types have good corrosion resistance. Carbon fibers and glass fibers generally do not react with water and / or oxygen. However, a high pH value can have a negative effect on the composite effect and durability of carbon fibers and / or glass fibers. Therefore, difficulties can arise when used in cements according to DIN EN 197, because the pH value in the pore solution of these cements is high. For glass fibers, such a high pH value can dissolve the fibers and thus weaken their strength. Therefore, the glass species used as reinforcing material in concrete structures must have a higher chemical resistance to alkalis or the glass must be protected from direct contact with the pore solution of the cement stone by a protective layer. For carbon fibers, the plastic used to bond the individual carbon fibers to each other can be adversely affected. Therefore, a high pH value can impair both types of reinforcement.

[0004] The use of mineral fibers and inorganic binders such as cement is known from DE 2409231 A1. In order to prevent the above-mentioned problems, it is suggested to reduce the pH value by additional treatment with CO2.

[0005] Furthermore, a binder based on magnesium oxide and aluminum phosphate is known from US 5,002,610, which hardens very quickly. However, the manufacturing method is extremely complex and requires multiple drying and grinding as well as repeated mixing of the various components.

[0006] It is therefore an object of the present application to provide a method for producing a composite material from cement stone, aggregate and reinforcing material, which can contain carbon fibers, glass fibers and steel reinforcement as reinforcing material.

[0007] According to the application, this object is achieved by a method having the features of claim 1.

[0008] Further advantageous embodiments are given in the dependent claims, the further explanations and the examples.

[0009] According to claim 1, for producing the composite material of the present application, at least cement stone, aggregate and reinforcing material are used, similar to conventional concrete.

[0010] For the purposes of the present application, the term "cement stone" is also used for hardened binders, which differ from conventional cement stones containing a high proportion of hardened Portland cement according to the present application. The present application primarily relates to the use of binders based on magnesium silicates, which do not necessarily contain Portland cement clinker. Although these binders do not comply with DIN EN 197, the terms "cement stone" and "concrete" are used for the products made therefrom within the scope of the present application.

[0011] According to the present application, for producing the cement stone, a starting product is provided, which contains at least 20 mass%, preferably at least 40 mass%, more preferably at least 60 mass%, even more preferably at least 80 mass% of one or more of the following ingredients. These ingredients can be ultramafic rocks, such as dunite, weathering products of ultramafic rocks, in particular serpentinite, olivine, or industrial waste. It is important here that all these raw materials each have a Mg concentration or Mg content of at least 5 mass%, preferably 10 mass%, more preferably more than 20 mass%, ideally more than 30 mass%. The stated values refer to the content of the element magnesium in the entire sample, wherein the element magnesium can be contained in various phases, such as olivine, enstatite, serpentine or other compounds. The concentrations mentioned therefore do not refer to the content of the MgO phase (periclase) in the starting product. Preferably, the starting product does not contain free MgO (periclase), but contains the mentioned concentrations of the element magnesium. The starting product provided has a fineness corresponding to a BET surface area of 0.1 m 2 / g or finer. It is advantageous here for the BET surface area to be 0.5 m 2 / g, and more preferably for the BET surface area to be 1.0 m 2 / g, and in particular for the BET surface area to be 3.0 m 2 / g or finer.

[0012] An important mineral in ultramafic rocks is olivine. It is a solid solution series between fayalite (Fe2Si04), forsterite (Mg2Si04), and Mn2Si04) and other A2[Si04] type minerals, where A can be a variety of divalent ions and combinations of various cations. The natural origin of olivine is documented in the literature, and olivine is generally a magnesium-rich mineral that contains iron.

[0013] Serpentine is a metamorphic rock that is formed from the weathering of ultramafic rocks and can contain mineral phases such as lizardite, antigorite, talc and other crystalline and amorphous compounds.

[0014] Examples of industrial waste materials that can be used in the present invention include foundry sand or refractory materials.

[0015] After providing the starting product, the starting product is homogenized, if necessary. The above-mentioned possible components of the starting product are generally materials in natural rocks or natural deposits. Experience shows that these components are neither in pure form nor homogenized. Homogenization can be carried out, for example, using a mixer, or simultaneously when grinding to the desired fineness.

[0016] After homogenization, the starting product thus prepared is subjected to a hydrothermal treatment. This is carried out in a heat treatment device at temperatures above 100°C for at least 12 hours, preferably at least 24 hours. The heat treatment device can be, for example, a heating tunnel, but also an autoclave. An autoclave is generally understood to be a pressure vessel that can be hermetically sealed and which can be used to heat treat substances in the overpressure range. The heat treatment device is preferably understood to be a combination of a container, a device, for example an oven and a sealing mold, or a device for enclosing a volume. The treatment is preferably carried out at temperatures above 100°C, in particular above 150°C, more preferably above 200°C, and even more preferably above 250°C. It is advantageous for good conversion that the treatment is carried out for more than 36 hours, and even more preferably for more than 48 hours. However, particularly good results can be obtained if the treatment is carried out for longer, for more than a few days, for example 4 days, more preferably 7 days or more.

[0017] It is furthermore provided that water is added to the homogenized starting product by directly adding water and mixing the water with the starting product before, after and / or simultaneously with the homogenization in the previous step. Alternatively or additionally, water vapor can also be introduced into the heat treatment device.

[0018] During the hydrothermal treatment of the homogenized starting product, it is at least partially converted in the presence of H2O into magnesium hydroxide Mg(OH)2and / or magnesium silicate hydrate (Mg3Si2O5(OH)4, Mg3Si4O 10(OH)2). The basic reactions are as follows, where these reactions are shown in simplified form starting from forsterite (Mg2SiO4): (1) 2 Mg2SiO4+ 3 H2O → Mg3Si2O5(OH)4+ Mg(OH)2 (2) 3 Mg2SiO4+ 5 SiO2+ 2 H2O → 2 Mg3Si4O 10 (OH)2 Here, reaction (1) occurs predominantly. This is also preferred in the present application, since Mg3Si2O5(OH)4is more suitable for subsequent hardening than Mg3Si4O 10 (OH)2. It should also be noted that the amounts of the respective products and their ratios depend, inter alia, on the exact composition of the starting products.

[0019] Magnesium hydroxide (Mg(OH)2) can be present here as brucite. Magnesium silicate hydrate (Mg3Si2O5(OH)4, Mg3Si4O 10 (OH)2) can be present in the form of serpentine, antigorite, talc and other forms. It should be noted here that the stoichiometric water content is sometimes (13 mass% in antigorite) lower than that which can be determined by testing (16 mass% to 20 mass%). This can be explained by the fact that some materials are very fine, so that water can also adhere to their surface.

[0020] Similarly, this deviation from stoichiometry also applies to the ratio between Mg and Si. In addition, foreign ions such as Fe can also be incorporated into the reaction products. However, other reaction products can also be formed, such as hydromagnesite, hematite, magnetite or gibbsite. This depends on the exact composition of the starting products, respectively. All or part of the reaction products can contain iron, carbonate and alkali ions or other foreign ions.

[0021] During the treatment, the magnesium silicates contained in the starting material (e.g. olivine or enstatite) do not decompose into oxides; in particular, no unbound SiO2, either in crystalline or amorphous form, is formed. In the subsequent treatment steps, either, no SiO2is formed from the magnesium silicates.

[0022] The converted starting products are then at least partially dehydrated by means of a thermal treatment and / or reaction grinding in order to remove the bound water. The bound water is sometimes also referred to as crystal water. It must be distinguished from unbound water (which can be regarded as free H2O). Complete dehydration can be achieved by high outlay. According to the present application, the water content of the bound water should be reduced by at least 60%, preferably by at least 80%.

[0023] For the heat treatment, the converted starting product can be heated to temperatures of from 180 °C to 1000 °C. Here, depending on the fineness present, heating for a few minutes is sufficient. The heat treatment should not last longer than one hour. Temperatures of from 300 °C to 800 °C are preferred, and temperatures of from 500 °C to 700 °C are even more advantageous. Alternatively or additionally, the converted starting product can also be subjected to reactive grinding in order to bring about a rearrangement of the crystal structure. In the so-called reactive grinding, it is also possible to remove crystallization water from the converted starting product by rearrangement of the crystal structure. For this purpose, an auxiliary agent such as quartz can be added for the grinding.

[0024] By the dehydration, the magnesium hydroxide (Mg(OH)2) present in the starting product converted in this step is at least partially converted into magnesium oxide (MgO, periclase) and the magnesium silicate hydrate (Mg3Si2O5(OH)4, Mg3Si4O 10 (OH)2) is at least partially converted into dehydrated magnesium silicate hydrate, which can be represented in simplified form as xMgO-SiO2-yH2O. Dehydration here means the reduction of the crystallization water or crystallization water in the converted starting product.

[0025] The underlying chemical processes here are again simplified as follows: (3) Mg(OH)2→ MgO + H2O (4) Mg3Si2O5(OH)4→ 2 xMgO-SiO2-yH2O + z H2O (5) Mg3Si4O 10 (OH)2→ 4 aMgO-SiO2-bH2O + c H2O Where (4) produces a reaction product which is essentially amorphous, has a Mg to Si ratio of from 1.5 to 2 and a residual water content of about 3%. The reaction product formed in equation (5) has a lower Mg to Si ratio. Accordingly, the variables a, b, c, x, y and z are also so. These depend on the exact composition of the starting product and the treatment parameters, respectively.

[0026] After the dehydration, the water content of the bound water in the converted and dehydrated starting product is preferably less than 10 mass%, advantageously less than 5 mass%, more preferably less than 3.5 mass% and even more preferably less than 2.5 mass%.

[0027] The converted and dehydrated starting product thus exists as a multiphase product. Other possible secondary phases include hematite, magnetite, enstatite, feldspar, pyroxene, quartz and amorphous phases.

[0028] The at least partially transformed and dehydrated starting product is used as a binder. For hardening, aggregate and setting water are added to the transformed and dehydrated starting product, wherein the ratio of water to binder is in particular 1 :2 or less. In other words, the transformed and dehydrated starting product is used as a total or partial cement replacement for the production of cement stone. The ratio of water to binder is preferably 1 :2 or less. This means that the ratio is 1 :2.22, preferably 1 :2.5, ideally 1 :2.86, even better 1 :3.33 or less. It has been found that a higher ratio, i.e. a higher water content, prolongs the hardening and reduces the strength. The concrete produced in this way has bound CO2from the ambient air even at ambient air and ambient temperature. The CO2partial pressure should not exceed 1000 ppm, because otherwise an increased shrinkage can result. During the hardening process, no heat treatment for increasing the reaction temperature should be carried out, in particular no heating treatment.

[0029] After mixing with water, a chemical reaction between the transformed and dehydrated starting material and the mixing water takes place. The phases formed in the previous combustion process, such as MgO, xMgO SiO2 yH2O, aMgO SiO2 bH2O, react again with water to form hydrates, such as Mg(OH)2, Mg3Si2O5(OH)4, Mg3Si4O 10 (OH)2and other compounds. This corresponds to equations (3) to (5), only with the reaction arrows reversed. The time course of the hydration reaction can be monitored calorimetrically (see Figure 1 ). The speed of the exothermic reaction depends on various factors.

[0030] If the starting product provided already contains at least 20 mass%, preferably at least 40 mass%, more preferably at least 60 mass%, even more preferably at least 80 mass% of magnesium silicate hydrate, as is the case for example with serpentine, the addition of water and the hydrothermal treatment step can be omitted. In other words, the starting product can be processed only by the grinding and dehydration steps, without a transformation step. Serpentine is a metamorphic rock, which is formed from ultramafic rocks by natural transformation, in particular weathering.

[0031] For the production of the composite material according to the application, aggregate, such as sand or gravel, is added to the transformed and dehydrated starting product before, after and / or simultaneously with the addition of the setting water. Within the scope of the present application, for the sake of simplicity, transformed starting product is referred to, which also includes serpentine as a starting product, which does not need to be transformed in the strict sense.

[0032] In the construction industry, natural and artificial rock particles are generally referred to as aggregate. They can be derived for example from natural deposits, or produced in the recycling of construction materials or as industrial by-products. Alternatively, names which are no longer used in the construction industry at present but have essentially the same meaning include concrete additives, mineral mixtures, mineral mixtures or minerals.

[0033] Furthermore, a reinforcing material is added to the optionally transformed and dehydrated starting product before, after and / or simultaneously with the addition of the setting water, in order to increase the load-bearing capacity. For this purpose, a reinforcing material is selected which is resistant to a pH value below 11, is configured to be protected from a pH value of 11 and / or an agent is added to the starting product, in particular to the transformed and dehydrated starting product, for increasing the pH value of the pore solution of the cement stone to a pH value above 11.0.

[0034] According to the present application, it has been recognized, on the one hand, that by the combination of a hydrothermal treatment with the expulsion of crystal water from natural materials such as ultramafic rocks, an intermediate can be produced which is suitable for binding with water and setting.

[0035] Olivine-rich rocks which can be used according to the present application include, for example, dunite, harzburgite and lherzolite. These rocks usually have a low degree of weathering. However, weathered rocks which are similar in chemical composition but have a higher water content can also be used. Weathered rocks are, for example, serpentinite.

[0036] A further basic idea of the present application can be that, by using the intermediate, cement is produced which differs from known Portland cement-based cements, which have a relatively high pH value. According to the present application, it has been recognized that the pore solution of the cement stone produced from the transformed and dehydrated starting product as understood by the present application usually has a pH value below 11. As a result, reinforcing materials made of glass fibers or carbon fibers or a combination of both can be used, which are not stable in a medium with a pH value above 11 without further treatment.

[0037] If other reinforcing materials, for example steel reinforcing elements, are to be used, according to the present application, they should be configured to be protected from the pH value below 11 present in the pore solution of the cement stone according to the present application.

[0038] Alternatively or additionally, depending on the reinforcing material used, further agents for increasing the pH value of the pore solution to a pH value above 11.0 can also be added to the serpentine and / or olivine-based binder. For this purpose, for example, slaked lime, quicklime, alkalis such as sodium hydroxide or potassium hydroxide, CKD (cement kiln dust, furnace dust produced in cement production) can be added.

[0039] At least when tempered serpentine is used in the starting product, but preferably also when natural or artificial olivine sources are used, the starting product should be free of tricalcium silicate and dicalcium silicate, since these cause hardening disorders.

[0040] Advantageously, the pore solution of the cement stone has a pH value of 11 or less. This is particularly true when the cement stone according to the application consists essentially of the transformed and dehydrated starting product. In this way, the starting material of the cement stone does not have to be further adjusted in order to be used with reinforcing materials made of glass fibers and / or carbon fibers.

[0041] In principle, any reinforcing material can be used according to the application. However, it is particularly advantageous to select a reinforcing material that comprises carbon fibers or carbon fibers, mineral fibers, in particular basalt fibers, and / or glass fibers. These fibers have the advantage over conventional steel reinforcements in that they are lighter on the one hand and produce significantly less CO2 during their production on the other hand.

[0042] According to one embodiment, reinforcing materials can be selected that are designed to withstand a pH value of less than 11 without a protective layer. This is particularly possible for reinforcing materials made of carbon fibers and / or glass fibers. However, in principle, a protective layer can also be applied to withstand such low pH values. This is particularly true for steel reinforcements.

[0043] It is also advantageous to select reinforcing materials that comprise carbon fibers, mineral fibers, in particular basalt fibers, and / or glass fibers in the form of fiber reinforcement, mat reinforcement, rod-like reinforcement and / or other reinforcement forms. The use of carbon fibers, mineral fibers, in particular basalt fibers, and / or glass fibers has the advantage that they can be processed into any desired shape and can then be used to produce composite materials. Thereby, the best reinforcement form can be selected depending on the expected load.

[0044] In another embodiment, alternatively or additionally, steel reinforcements can also be used in the composite material according to the application. If steel reinforcements are used, it is preferred that, in addition to the transformed and dehydrated starting product, in particular Portland cement clinker is added to the cement stone. This is particularly suitable for increasing the pH value in order to prevent corrosion of the steel reinforcement due to the low pH value. In addition, Portland cement clinker has the advantage over other substances that influence the pH value that it itself also contributes to the strength alone.

[0045] It can also be provided that the reinforcing material is equipped with at least one protective layer for protection from an alkaline environment with a pH value of less than 11. The protective layer can be formed, for example, by applying an ink and / or a lacquer. The protective layer can be based on plastic. Another possibility is to apply hot-dip galvanizing on the steel reinforcement.

[0046] The hydrothermal treatment of the homogenized starting product to convert it at least partially into magnesium hydroxide and / or magnesium silicate hydrate is one of the most time-consuming process steps according to the application. Therefore, preferably, one or more pre-treatments are carried out to accelerate the reactions that take place during the hydrothermal treatment. For this purpose, various pre-treatment methods are available, which can be carried out individually or in combination with one another. This will be explained in more detail below. Here, all or only some of the pre-treatment methods listed can be combined with one another.

[0047] One possibility is to comminute or crush the homogenized starting product, in particular to grind it to the finest, continuously or discontinuously during the hydrothermal treatment in the heat treatment device or between multiple hydrothermal treatments, in order to accelerate the conversion.

[0048] By continuous or discontinuous comminution, it is possible to prevent or reduce the caking or agglomeration of the substances present during the hydrothermal treatment. This ensures that there is also a sufficiently large surface area available for carrying out the process described above. Various possibilities exist for precise implementation.

[0049] On the one hand, it is possible to interrupt the hydrothermal treatment, to remove the material from the heat treatment device and to comminute or crush it, for example to grind it, and to supply it to the heat treatment device again.

[0050] On the other hand, it is also possible to provide a corresponding comminution device in the heat treatment device, which comminates continuously or discontinuously during the hydrothermal treatment.

[0051] Another possibility is to operate the heat treatment device, in particular continuously, and to remove a portion of the material from the heat treatment device during the hydrothermal treatment, to comminute it and to feed it back into the device again. This is particularly suitable if the starting product is present in the heat treatment device in the form of a suspension or at least in a pumpable form. At this point, for example, a line from the autoclave can be provided, which is connected to a comminution device, for example a grinder, and is returned to the autoclave, which is an example of a heat treatment device within the scope of the application. This can be referred to as an uninterrupted circulation method.

[0052] Another possibility to accelerate the reaction is to provide the homogenized starting product in the form of a suspension during the hydrothermal treatment in the heat treatment device, which is continuously or discontinuously stirred during the hydrothermal treatment. At this point, for example, a stirrer can be provided which ensures the movement of the suspension.

[0053] In this context, it is also alternatively or additionally possible to provide grinding, as described above. Wet grinding is particularly suitable here, so that a portion of the suspension can be output from the heat treatment device, wet ground and added back into the device. However, wet grinding can also be carried out directly in the heat treatment device.

[0054] It can be advantageous to dry the homogenized and converted starting product to remove unbound water before the dehydration step, i.e. the separation of the bound water. This is particularly desirable and expedient if the hydrothermal treatment of the starting product is carried out in an aqueous suspension.

[0055] The dried starting product can now be supplied to the dehydration step. The heat treatment proposed for this can also be referred to as tempering or calcination. This can be carried out in a heat treatment device such as a rotary kiln, or by means of a hot gas circulating fluidized bed. When using a fluidized bed, the dehydration is completed within a few seconds. Alternatively, the required energy can also be applied electrically, for example in a muffle furnace. This requires a time of about 5 to 10 minutes. It is preferable in principle for the system to be such that the material is not in direct contact with the flame, since in this case it is easier to maintain the combustion temperature precisely. Furthermore, in order to expel the water vapor produced and thus to make the reaction proceed more quickly, it is preferable to use an open system.

[0056] It is advantageous for the heat treatment device to have a substantially uniform temperature distribution. This makes it possible to achieve good dehydration without the production of unwanted by-products. It is therefore advantageous for the furnace to be heated indirectly in order to be able to maintain the required dehydration temperature in the furnace as precisely as possible over the residence time of the material. In this case, the material is briefly exposed to extremely high temperatures, which can lead to the formation of olivine. For example, the temperature distribution in a directly heated rotary kiln is too inhomogeneous. It is therefore advantageous to use a rotary kiln, in particular an indirectly heated rotary kiln in which there is no open flame in the reaction chamber, as a heat treatment device. In an electrically heated furnace, the temperature during the heat treatment, also referred to as the combustion temperature, can be controlled particularly precisely. In particular, an electric heating should be used to maintain the target temperature in the furnace precisely. It is advantageous to use electrical energy generated from renewable sources to heat the furnace, since this neither produces CO2 emissions and exhaust gases nor consumes fuel. Instead, it is also possible to use other heat sources for preheating, in particular to use a heat exchanger which extracts a portion of the heat from the dehydrated starting product, for example from the combusted serpentine, in order to cool it down, wherein at the same time heat is supplied to the uncombusted serpentine. Furthermore, the use of flue gases produced by a combustion process should be avoided as far as possible, since this can lead to uncontrolled binding of CO2, for example.

[0057] In order to achieve a sufficient residence time at the target temperature, a rotary kiln is preferred, since it has a large volume and thus a high throughput can be achieved. Furthermore, a rotary kiln is also characterized by a good thermal efficiency.

[0058] Another alternative is to subject the homogenized starting product to ultrasonic treatment. As with the comminution process, it is ensured here that the substance formed on the starting product, for example magnesium hydroxide and / or magnesium silicate hydrate, is separated from the remaining substance of the starting product, so that there is again a sufficiently large surface area for the reaction to be able to proceed quickly. This can be achieved, for example, using an ultrasonic horn or the like.

[0059] Another possibility is to add nucleating agents, agents for increasing the pH value, foreign ions and / or other auxiliaries for accelerating the reaction process to the starting product already at the beginning, before or during the homogenization or after the homogenization or even in the heat treatment device.

[0060] As nucleating agents, for example brucite, cumengeite, antigorite, pre-hydrated olivine-containing rocks or mixtures of these substances can be added. Preferably at least 2 mass% of nucleating agents are added.

[0061] As agents for modifying the solution in which the reaction takes place for increasing the pH value, substances can be added which release NaOH, KOH, NaCI, KCI, Na2SO4, MgSO4, K2SO4, Na2CO3, Ca(OH)2and / or K2CO2after their addition, thereby increasing the pH value in the solution, so that the reaction proceeds more rapidly.

[0062] Other additives which also accelerate the reaction include, for example, dolomite, feldspar, pyroxene and mixtures thereof, wherein the addition of these substances can lead to the formation of new reaction products. Examples of foreign ions include aluminium ions, sulphate ions or alkali metal ions. Likewise, it is also possible that new reaction products are formed. Preferably, auxiliaries containing magnesite, brucite and / or hydromagnesite should be avoided, since in some cases these substances slow down the reaction.

[0063] In principle, the reaction progress can already be achieved in the autoclave by increasing the temperature. In particular, temperatures above 150°C, preferably above 200°C, more preferably above 250°C can be employed here.

[0064] In order to achieve a fineness of the starting product provided which corresponds to a BET surface area of 0.1 m 2 / g or finer, preferably the starting product is ground, in particular wet ground. Even if the starting product is already very fine due to natural weathering, it usually cannot achieve a higher fineness. By grinding, its fineness can easily be increased. Here too, wet grinding is preferred, since it is usually more energy-efficient than dry grinding. Since the starting product is subsequently subjected to a hydrothermal treatment, in which it is brought into contact with water, the advantages of wet grinding can already be utilized in this step, in particular since the ground material does not have to be dried.

[0065] The starting products according to the application are generally not pure substances, so that impurities are present in high amounts. However, it is advantageous if the molar ratio of Mg to Ca is at least 10:1 or higher and / or the molar ratio of Si to Al is also at least 10:1 or higher. It has been shown that the presence of calcium and aluminium, respectively, relative to magnesium or silicon, slows down the reaction or sometimes leads to a complete stop. It is therefore crucial to move the respective molar ratio significantly in the direction of magnesium or silicon. Preferably, the molar ratio of Mg to Ca is at least 20:1 and / or the molar ratio of Si to Al is at least 20:1.

[0066] The application will be explained in more detail below by way of examples with reference to the single drawing. The drawing shows: Figure 1 Hydration curve of the product produced according to the method of the application.

[0067] In order to verify the application, in particular the studies described in more detail below were carried out. Therein, on the one hand, pure forsterite was used in a first study and natural forsterite in a second study. In addition, in a fourth study, serpentine was used.

[0068] Pure Forsterite The first study employed forsterite (Mg2SiO4), which was produced by burning a mixture of basic magnesium carbonate and amorphous SiO2 in a laboratory furnace. After the burn, the starting material was ground in a disc-type vibration mill. The specific surface area according to the BET method was 1 m 2 / g.

[0069] A mixture of forsterite and a 1 molar NaOH solution in a ratio of 1 :2.2 was prepared and treated in an autoclave at a temperature of 200°C. The reaction was interrupted during the period and the material was dried and ground. After a treatment time of 4 weeks, no forsterite was detected any more in the treated and washed material by X-ray phase analysis. After the completion of the autoclave treatment, the loss on ignition was 19.3 mass%.

[0070] The dried and ground material was burned in a muffle furnace at 450°C, 600°C and 750°C, respectively, for 1 hour in the form of 3.0 g, respectively, in a platinum crucible. The loss on ignition of the burned samples was 13.5% (450°C), 2.8% (600°C) and 0.52% (750°C), respectively.

[0071] The reactivity of the material as a binder was investigated by determining the water-binding behaviour after 7 days of hydration. For this purpose, the material burned at different temperatures was ground in a mortar and mixed with water in a ratio of water to binder of 0.40 (1 :2.5) and stored in a sealed container at 22°C for 7 days. Thereafter, the hydration of the samples was stopped by drying at 60°C and the loss on ignition was determined by thermal analysis.

[0072] This resulted in burn-off losses of 20.5% (450°C), 25.3% (600°C) and 7.1% (750°C), respectively. Thus, all three binders underwent hydration and bound water.

[0073] The hydration curve of the sample combusted at 600°C was investigated at 25°C using calorimetry (DCA). The results show that the reaction is very rapid, with the main hydration phase peaking after about 2 hours, where the reaction is completed after less than 24 hours. As shown in Figure 2, a total of about 450 J / g of heat is released. Figure 1

[0074] Thus, the reaction of this binder is faster than most conventional cements. The hydrated and dried sample was analysed according to DCA and the results are shown in Figure 3. 29 Si MAS NMR spectroscopy showed that all silicon was present as magnesium silicate hydrate.

[0075] Natural olivine A second study used natural olivine from a Norwegian occurrence. The chemical analysis showed the following composition: 41.9% Si02, 49.9% MgO, 6.9% Fe203, 0.6% AI2O3, 0.1% CaO, 0.5% burn-off.

[0076] The material was ground in a ball mill to a fineness of 7300 cm 2 / g Blaine and mixed with a 1 molar NaOH solution in a ratio of 1 :2. Subsequently, autoclave treatment was performed at 200°C for 22 days, where the material was ground once in between.

[0077] After autoclave treatment, the intermediate product was dried, ground and analysed for burn-off (16.3%).

[0078] Individual batches of the intermediate product were combusted at different temperatures and the water binding properties were investigated by hydration at 22°C for 7 days. Before hydration, the burn-off (6.8% after 550°C, 3.1% after 600°C, 2.2% after 650°C and 1.7% after 700°C) was lower than the burn-off of the material reacted with water and subsequently dried at 60°C (20.1% after 550°C, 23.7% after 600°C, 24.7% after 650°C and 22.8% after 700°C).

[0079] Thus, natural materials such as olivine can also be used for binder production, where the hydration can be verified after the above-mentioned pre-treatment.

[0080] pH value ​Furthermore, the pH value of the cement stone according to the application was analyzed. For this purpose, a binder was analyzed which was made from pure synthetic forsterite without foreign ions.

[0081] After half a year of hydration, the pH value of the sample was 9.5.

[0082] In further investigations, the pH value in the pore solution of the binder according to the application was measured. For this purpose, serpentine was ground to a specific surface area of 0.55 m 2 / g and 1 kg of the ground material was burned at 700°C for 1 hour. Subsequently, depolymerization was carried out by grinding in a ball mill for 5 minutes. The resulting binder was mixed with water in a ratio of water to binder of the value 0.40. The binder paste could be hardened at room temperature for 2 days and then pressed out of the pore solution using a high-pressure press (testing machine) and a press mold. The pH value was determined in the solution and was 10.3.

[0083] Furthermore, a comparative sample was produced in which 1.6% NaOH was added (based on the binder). After hardening, the pH value was measured when the alkali-containing pore solution was pressed out and was 12.4. Thus, by adding an alkali-containing compound, the pH value can be increased, avoiding corrosion of the steel reinforcement.

[0084] Thus, by using forsterite which belongs to the olivine group, a binder for composites can be produced which has a pH value which is far lower than a cement stone made from conventional Portland cement clinker. By this low pH value, for the first time, it is possible to use glass fibers and / or carbon fiber reinforcement without further pretreatment.

Claims

1. A method for producing composite materials from cement paste, aggregates and reinforcing materials. In order to produce cement stone a) Provide a starting product comprising at least 20% by mass of one or more of the following components: Ultramafic rocks, especially pure peridotite, Weathering products of ultramafic rocks, especially serpentinite. Peridot, Industrial waste They each have a Mg concentration of at least 5% by mass and a corresponding BET surface area of ​​0.1 m². 2 / g or finer, b) Homogenize the starting product. c) The homogenized starting product is subjected to hydrothermal treatment in a heat treatment apparatus at a temperature above 100°C for at least 12 hours. d) Add water to the homogenized starting product in the following manner: Water is added directly before, after, and / or simultaneously with homogenization in step b), and the starting product is mixed with water, and / or Water vapor is introduced into the heat treatment device. In step c), the starting product is at least partially converted to magnesium hydroxide Mg(OH)2 and / or magnesium silicate hydrate in the presence of H2O. e) The converted starting products are at least partially dehydrated by heat treatment and / or reactive milling to remove bound water. During the heat treatment process, the starting products of the conversion are processed at temperatures ranging from 180°C to 1000°C. During the reactive grinding process, the crystal structure of the converted starting product undergoes rearrangement. Following step e), the magnesium hydroxide present in the transformed and dehydrated starting product is at least partially dehydrated to magnesium oxide, and the present magnesium silicate hydrate is at least partially dehydrated and can thereby be transformed into dehydrated magnesium silicate hydrate. f) Using the converted and dehydrated starting product as a binder, and adding coagulation water to the converted and dehydrated starting product for hardening, wherein the water to binder ratio is particularly 1:2 or less. When providing a starting product containing at least 20% by mass magnesium silicate hydrate, such as serpentine, steps c) and d) can be omitted. This involves adding aggregate, such as sand or gravel, to the converted and dehydrated starting product before, after, and / or simultaneously with the addition of coagulation water. In this process, reinforcing materials are added to the converted and dehydrated starting products before, after, and / or simultaneously with the addition of coagulation water to improve load-bearing capacity. - Choose reinforcing materials that can tolerate pH values ​​below 11. - The reinforcing material is configured to be protected against pH 11 and / or - Add a reagent to the starting product to raise the pH of the pore solution of the cement stone to 11 or higher.

2. The method according to claim 1, Its features The pH of the pore solution in cement stone is 11 or lower.

3. The method according to claim 1 or 2, Its features The selected material is a reinforcing material designed to resist pH values ​​less than 11 without a protective layer.

4. The method according to any one of claims 1 to 3, Its features Select reinforcing materials containing carbon fiber, mineral fiber, especially basalt fiber and / or glass fiber as reinforcing materials.

5. The method according to claim 3 or 4, Its features Carbon fibers, mineral fibers, especially basalt fibers and / or glass fibers are selected and designed as reinforcing materials in the form of fiber reinforcement, felt reinforcement, rod reinforcement and / or other reinforcement forms.

6. The method according to any one of claims 1 to 5, Its features Select a reinforcing material that includes steel reinforcements as the reinforcing material.

7. The method according to any one of claims 1 to 6, Its features The reinforcing material is equipped with a protective layer to protect it from alkaline environments with a pH value less than 11.

8. The method according to any one of claims 1 to 7, Its features The reinforcing material is hot-dip galvanized and / or equipped with an ink layer or paint layer, particularly an ink layer or paint layer made of plastic, to be protected from alkaline environments with a pH value less than 11.

9. The method according to any one of claims 1 to 8, Its features In order to at least partially convert the starting product in step c), one or more treatments are performed to accelerate the reaction that occurs during the hydrothermal treatment.

10. The method according to any one of claims 1 to 9, Its features Before, during, or between multiple hydrothermal treatments in the heat treatment apparatus of step c), the homogenized starting product is continuously or discontinuously pulverized, especially finely ground, to accelerate the conversion.

11. The method according to any one of claims 1 to 10, Its features In order to perform hydrothermal treatment on the homogenized starting product in a heat treatment apparatus, the homogenized starting product exists in the form of a suspension, which is continuously and / or discontinuously stirred during the hydrothermal treatment process.

12. The method according to any one of claims 1 to 11, Its features In step c), the homogenized starting product is subjected to ultrasonic treatment.

13. The method according to any one of claims 1 to 12, Its features To provide a surface area corresponding to BET of 0.1 m² 2 The starting product is ground, especially by wet grinding, with a fineness of / g or finer.

14. The method according to any one of claims 1 to 13, Its features The starting product has a Mg to Ca molar ratio of 10:1 or greater, and / or a Si to Al molar ratio of 10:1 or greater.

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