Composite Materials

Abstract

The present invention relates to a composite material comprising a hardened cementitious body of MgO and / or olivine binder and reinforcing elements for increasing the load-bearing capacity, the reinforcing elements being resistant and / or having protection against pH values ​​below 11. Additionally or alternatively, an agent for increasing the pH value of the pore solution of the hardened cementitious body is added to the MgO and / or olivine binder of the hardened cementitious body.

Description

[Technical field]

[0001] The present invention relates to a composite material composed of a hardened cement body and a reinforcing element.

[0002] The use of reinforced concrete is essential for the current construction industry. In reinforced concrete, the concrete absorbs compressive stresses, while the steel reinforcing inserts are responsible for transmitting tensile forces. At the same time, the concrete protects the steel from corrosion. This corrosion protection is based on very high pH values ​​in the pore solution of the concrete. At pH values ​​of about 11 and above, normal reinforcing steel does not rust, because a very thin passivation layer is formed on its surface, which seals the steel surface against the ingress of oxygen and water and thus prevents corrosion. In the pore solution of concrete produced with cements according to DIN EN 197, pH values ​​above 12.5 are present, and the use of these cements therefore means an effective corrosion protection for the steel reinforcement. Reinforced concrete, a composite building material, offers high performance and durability at low cost and is often used for these reasons. However, the production of reinforcing steel entails a high environmental load, including high CO2 emissions during the production of pig iron and steel.

[0003] In order to reduce the carbon dioxide emissions during the manufacture of reinforcement, various alternative materials have been proposed. These include, among others, carbon and glass fibers. Both materials have very high tensile strength and can also be used to transmit tensile forces in reinforced concrete. Another advantage is the corrosion resistance of both types of fibers. Both carbon and glass fibers do not normally react with water and / or oxygen.

[0004] However, high pH values ​​can have a detrimental effect on the binding effect and durability of carbon and / or glass fibres. For this reason, use in standard cements according to DIN EN 197 can pose difficulties, since these cements have high pH values ​​in the pore solution. With glass fibres, such high pH values ​​dissolve the fibres and therefore weaken their strength. For this reason, either types of glass with high chemical resistance to alkalis are used as reinforcement in concrete construction, or the glass must be protected from direct contact with the pore solution of the hardened cement body with a protective layer. In the case of carbon fibres, the plastics that bind the individual carbon fibres together can be affected. High pH values ​​can therefore damage both types of reinforcement.

[0005] From DE 2409231 A1 the use of mineral fibres with inorganic binders, such as cement, is known. In order to avoid the above problems, it is proposed to lower the pH value by additional treatment with CO2.

[0006] Furthermore, binders based on magnesium oxide and aluminum phosphate are known from US 5,002,610, which harden very quickly, but the manufacturing process is quite complicated, requiring multiple drying, grinding and remixing of the various components. Summary of the Invention [Problem to be solved by the invention]

[0007] An object underlying the present invention is therefore to provide a composite material which may contain, as reinforcing elements, carbon fibre, glass fibre and steel reinforcements. [Means for solving the problem]

[0008] According to the invention, this object is achieved by a composite material having the features of claim 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Further advantageous embodiments are specified in the dependent claims, the further description and the exemplary embodiments.

[0010] According to claim 1 it is provided that the composite material according to the invention comprises a cementitious body composed of MgO and / or an olivine binder. The olivine binder uses as starting material a forsterite source in the form of a natural or artificial olivine source and / or in the form of reinforced serpentine. In the context of the present invention, reinforced serpentine is understood in particular as a serpentine that has been heated to a temperature of at least 500° C. Instead of the term "reinforced", the term "calcined" is often used.

[0011] Furthermore, the composite material according to the invention contains reinforcing elements for increasing the load-bearing capacity. According to the invention, these reinforcing elements are resistant to pH values ​​below 11, have a protection against pH values ​​below 11, and / or an agent is added to the MgO and / or olivine binder of the hardened cement body to increase the pH value of the pore solution of the hardened cement body to a pH value above 11. In other words, according to the invention, at least one of the above three conditions is provided.

[0012] The basic idea of ​​the present invention can be seen in departing from the known Portland cement-based cements, which have relatively high pH values. According to the present invention, it is recognized that the pore solution of hardened cement bodies made with MgO- or olivine-based binders, as understood according to the present invention, usually has a pH value of less than 11. This makes it possible to use reinforcing elements made of glass or carbon fibers or a combination of both, which are not stable to media with pH values ​​above 11 without further treatment.

[0013] If other reinforcing elements are used, then according to the invention they are provided with protection against pH values ​​below 11 present in the pore solution of the hardened cementitious bodies according to the invention.

[0014] Alternatively or additionally, depending on the reinforcing material used, other agents can be added to the MgO and / or olivine binders to raise the pH value of the pore solution to pH values ​​higher than 11. For example, hydrated lime, quicklime, alkalis such as sodium hydroxide or potassium hydroxide, CKD (cement kiln dust, kiln dust from cement production) can be added for this purpose.

[0015] At least when reinforced serpentine is used in the starting product, and preferably also when natural or artificial olivine sources are used, the starting product should not contain alite and belite, as these may cause hardening problems. A method for producing hardened cement bodies from MgO and / or olivine-based binders is described, for example, in PCT / EP2021 / 061726.

[0016] It is advantageous if the pH value of the pore solution of the hardened cement body is less than or equal to 11. This is particularly true if the hardened cement body according to the invention consists of MgO and / or olivine-based binders. In this way, no further adjustments of the base material of the hardened cement body are necessary for use with reinforcing elements made of glass and / or carbon fibers.

[0017] It is advantageous if the MgO or olivine based binder comprises MgO and SiO2, MgO and MgCO3, MgO and glass powder, olivine and SiO2, olivine and glass powder, olivine and truss, olivine and pozzolan, reinforced serpentine and SiO2, reinforced serpentine and glass powder, and / or any combination thereof. By using these starting materials, it is possible to produce a hardened cement body having good strength compared to Portland cement based mixtures and a pH of 11 or less.

[0018] Truss is a natural pozzolan consisting mainly of silicon and aluminum compounds. Pozzolans are man-made or natural rocks made from silicon dioxide, alumina, limestone, iron oxide and alkaline substances, usually formed under the influence of heat. When combined with calcium hydroxide and water, they are able to bind.

[0019] In principle, any reinforcing element can be used according to the invention. However, it is particularly advantageous if the reinforcing element comprises carbon and / or glass fibres. These fibres offer the advantage over conventional steel reinforcements that they are lighter whilst producing significantly less CO2 during manufacture.

[0020] Advantageously, the reinforcing element is configured to withstand, without a protective layer, pH values ​​below 11. This is possible in particular with reinforcing elements made of carbon and / or glass fibres. In principle, however, a protective layer can also be applied for such low pH values.

[0021] It is further advantageous if the carbon and / or glass fibers are in the form of fiber reinforcements, mesh reinforcements, bar reinforcements, and other reinforcements. The advantage of using carbon and / or glass fibers is that they can be formed into any shape and then used to manufacture composite materials. This means that depending on the expected loads, the optimum form of reinforcement can be provided.

[0022] In a further embodiment, steel reinforcement may alternatively or additionally be present in the composite material according to the invention. When using steel reinforcement, it is preferred to add, in addition to MgO and / or olivine binder, especially Portland cement clinker to the cementitious hardened body. This is particularly suitable for increasing the pH value so that corrosion of the steel reinforcement due to low pH value is prevented. Moreover, Portland cement clinker has an advantage over other substances that affect the pH value, namely that it contributes separately to the strength by itself.

[0023] The reinforcing elements may also have at least one protective layer to protect against alkaline environments with a pH value below 11. This protective layer can be applied, for example, by applying a paint and / or a varnish. The protective layer can be plastic-based. Another option is to apply hot-dip galvanizing to the steel reinforcement.

[0024] To verify the invention, the pore solutions of two binders according to the invention were examined in more detail after six months of hydration.

[0025] First, a binder consisting of pure synthetic forsterite without any foreign ions was analyzed. In the second sample, a mixture of forsterite and silica glass in a 2:1 ratio was used instead of pure forsterite to produce a composite cementitious body.

[0026] After six months of hydration, the pH value of the first sample was 9.5, while the pH value of the second sample was around 8.2.

[0027] The use of forsterite, which belongs to the olivine group, therefore makes it possible to produce binders for composites with a very low pH value compared to cementitious bodies produced from classical Portland cement clinker. Due to this low pH value, glass and / or carbon fiber reinforcements can be used right from the start without additional pretreatment.

[0028] By using the composite material according to the invention, it is possible to avoid the use of steel reinforcements, the production of which has a very high CO2 footprint.

Claims

1. A hardened cement body composed of MgO and / or an olivine-based binder, said hardened cement body containing as starting material a forsterite source in the form of a natural or artificial olivine source and / or in the form of a reinforced serpentine source; and a reinforcing element for increasing load bearing capacity; The reinforcing element comprises: Tolerant to pH values ​​below 11; and / or has protection against pH values ​​below 11; A composite material, characterized in that an agent for increasing the pH value of the pore solution of the hardened cement body to a pH value of 11 or more is added to the MgO and / or the olivine-based binder of the hardened cement body.

2. 2. The composite material of claim 1, wherein the pore solution of the hardened cement has a pH value of 11 or less.

3. The MgO and / or the olivine-based binder is MgO and SiO ２ , MgO and MgCO ３ , MgO and glass powder, olivine and SiO ２ , Olivine and glass powder, Olivine and trass, Olivine and pozzolan, Reinforced serpentine and SiO ２ 3. The composite material of claim 1 or 2, comprising: a reinforced serpentine and glass powder; or a combination thereof.

4. A composite material according to any one of claims 1 to 3, wherein the reinforcing elements comprise carbon fibres and / or glass fibres.

5. 5. The composite material according to claim 1, wherein the reinforcing elements are configured to withstand pH values ​​below 11 without a protective layer.

6. 6. A composite material according to claim 4 or 5, wherein the carbon fibres and / or the glass fibres are in the form of fibre reinforcement, mesh reinforcement, bar reinforcement and / or other reinforcement.

7. 7. The composite material according to claim 1, wherein Portland cement clinker is included in the hardened cement body in addition to the MgO and / or the olivine-based binder.

8. A composite material according to any one of claims 1 to 7, wherein the reinforcing elements comprise steel reinforcements.

9. 9. The composite material according to claim 1, wherein the reinforcing element comprises a protective layer for protection against alkaline environments having a pH value below 11.

10. 10. The composite material according to claim 1, wherein the reinforcing elements are hot-dip galvanized and / or comprise a layer of paint or varnish, in particular a layer made of plastic, for protection against alkaline environments with a pH value below 11.

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