Reinforced composite material of magnesium silicate hydrate

Abstract

The invention relates to a composite material comprising a cementitious stone formed from a binder based on MgO and / or olivine, and reinforcing elements to increase its load-bearing capacity. These reinforcing elements are resistant to pH values ​​below 11 and / or are protected against pH values ​​below 11. Furthermore, or alternatively, elements to raise the pH of the porous solution can be added to the MgO and / or olivine-based binder of the cementitious stone.

Description

[0001] The invention relates to a composite material made of cement stone and reinforcing materials.

[0002] The use of reinforced concrete is indispensable for construction in its current form. In reinforced concrete, the concrete absorbs compressive stresses, while the steel reinforcement is responsible for transferring tensile forces. At the same time, the concrete protects the steel from corrosion. This corrosion protection is based on a very high pH value in the concrete's pore solution. Above a pH value of approximately 11, normal reinforcing steel no longer rusts because very thin passivation layers form on the surface, sealing the steel surface against the ingress of oxygen and water and thus preventing corrosion. In the pore solution of concretes produced with cements conforming to DIN EN 197, pH values ​​above 12.5 are present, and accordingly, the use of these cements provides effective corrosion protection for steel reinforcement.Reinforced concrete, a composite building material, offers high performance and durability at low cost, and is therefore frequently used. However, the production of reinforcing steel is associated with significant environmental impacts, including high CO2 emissions during pig iron and steel production.

[0003] To reduce carbon dioxide emissions during reinforcement production, various alternative materials have been proposed. These include, in particular, carbon and glass fibers. Both materials exhibit very high tensile strength and can also be used to transfer tensile forces in reinforced concrete. A further advantage is the corrosion resistance of both fiber types. Neither carbon nor glass fibers typically react with water and / or oxygen.

[0004] However, high pH values ​​can negatively impact the bond strength and durability of carbon and / or glass fibers. Therefore, their use in standard cements according to DIN EN 197 can be problematic, as these cements contain high pH values ​​in the pore solution. In the case of glass fibers, such high pH values ​​can dissolve and thus weaken the fibers. For this reason, glass types with higher chemical resistance to alkalis must be used for reinforcement in concrete construction, or the glass must be protected with a protective layer to prevent direct contact with the pore solution of the cement paste. In the case of carbon fibers, the polymers used to bond the individual carbon fibers to each other can be affected. Thus, high pH values ​​can lead to damage in both types of reinforcement.

[0005] German patent DE 2409231 A1 discloses the use of mineral fibers with an inorganic binder such as cement. To prevent the problems described above, it is proposed to lower the pH value through additional CO2 treatment.

[0006] Furthermore, US patent 5,002,610 discloses a binder based on magnesium oxide and aluminum phosphate that hardens very quickly. However, the manufacturing process is extremely complex and requires multiple drying and grinding steps, as well as remixing of various components.

[0007] EP 2 508 496 A1 describes a binder composition comprising magnesium oxide, reactive silica (SiO₂), and hydrated magnesium carbonate. Through reaction with water, magnesium silicate hydrate can be formed, making the composition suitable for applications in the construction industry with potentially favorable strength properties and CO₂ balance.

[0008] The invention therefore lies in the Task The basis is to specify a composite material that can contain carbon, glass fibers, or steel reinforcement as reinforcement.

[0009] This problem is solved according to the invention by a composite material having the features of claim 1.

[0010] Further advantageous embodiments are specified in the dependent claims, the further description and the exemplary embodiments.

[0011] According to claim 1, the composite material according to the invention comprises cement stone made of MgO-based binders and / or olivine-based binders. The olivine-based binders use as a starting material a forsterite source in the form of a natural or artificial olivine source and / or in the form of tempered serpentinite. For the purposes of the invention, tempered serpentinite can be understood to mean, in particular, serpentinite that has been heated to a temperature of at least 500°C. The term "calcined" is often used instead of "tempered".

[0012] Furthermore, the composite material according to the invention comprises reinforcing elements according to claim 1.

[0013] A key aspect of the invention is the departure from known Portland cement-based cements, which have a relatively high pH value. According to the invention, it has been recognized that the pore solution of a cement paste made from an MgO- or olivine-based binder, as understood according to the invention, typically has pH values ​​below 11. This allows the use of reinforcing materials made of glass fibers or carbon fibers, or combinations of both, which are not stable against media at pH values ​​above 11 without further treatment.

[0014] If other reinforcing agents are to be used, it is in accordance with the invention to equip them with protection against the pH values ​​of less than 11 present in the pore solution of the cement stone according to the invention.

[0015] As an alternative or additional measure, depending on the reinforcing agent used, other agents can be added to the MgO and / or olivine-based binder to raise the pH of the pore solution to a pH of 11 or higher. Examples of such agents include slaked lime, quicklime, alkalis such as sodium hydroxide or potassium hydroxide, and CKD (cement kiln dust).

[0016] At least when using tempered serpentinite in the starting material, but preferably also when using a natural or artificial olivine source, the starting material should be free of alite and belite, as these can cause hardening defects. A manufacturing process for cement stone from an MgO and / or olivine-based binder is described, for example, in PCT / EP2021 / 061726.

[0017] It is advantageous if the pore solution of the cement paste has a pH value of 11 or lower. This is particularly the case if the cement paste according to the invention consists of an MgO and / or olivine-based binder. In this way, no further adjustments to the starting material of the cement paste are necessary for use with reinforcing materials made of glass fibers and / or carbon fibers.

[0018] It is advantageous if the MgO-based or olivine-based binder contains MgO and SiO₂, MgO and MgCO₃, MgO and glass flour, olivine and SiO₂, olivine and glass flour, olivine and trass, olivine and pozzolan, tempered serpentinite and SiO₂, tempered serpentinite and glass flour, and / or individual components or combinations thereof. By using these aggregates, a cement stone can be produced that exhibits good strength compared to Portland cement-based mixtures, yet has a pH of 11 or lower.

[0019] Trass is a natural pozzolan consisting mainly of silicon and aluminum compounds. Pozzolans are artificial or natural rocks made of silicon dioxide, alumina, limestone, iron oxide, and alkaline substances, mostly formed under the influence of heat. They are capable of binding substances when combined with calcium hydroxide and water.

[0020] In principle, any reinforcement material can be used according to the invention. However, it is in accordance with the invention if the reinforcement material comprises carbon or carbon and / or glass fibers. These fibers have the advantage over conventional steel reinforcements that they are lighter and their production generates significantly less CO2.

[0021] It is advantageous if the reinforcement is designed without a protective coating to withstand pH values ​​below 11. This is particularly possible with carbon and / or glass fiber reinforcement. However, a protective coating against such low pH values ​​can also be applied.

[0022] It is further advantageous if the carbon and / or glass fibers are formed as fiber reinforcement, mesh reinforcement, bar reinforcement, or other reinforcement forms. The advantage of using carbon and / or glass fibers is that they can be formed into any desired shape and then used to manufacture the composite material. This allows for the optimal reinforcement configuration depending on the expected load.

[0023] In a further embodiment of the invention, steel reinforcement can also be present in the composite material according to the invention, either alternatively or additionally. If this is used, it is preferred to add Portland cement clinker to the cement paste in addition to the MgO- and / or olivine-based binder. This is particularly suitable for raising the pH value, thus preventing corrosion of the steel reinforcement due to the low pH value. Furthermore, Portland cement clinker offers the advantage, compared to other substances that influence the pH value, of making its own separate contribution to the strength.

[0024] Furthermore, it is provided that the reinforcement elements have at least one protective layer to protect against an alkaline environment with a pH value below 11. This protective layer is applied, for example, by applying paint and / or varnish. The protective layer can be polymer-based. Another possibility according to the invention is to apply hot-dip galvanizing to steel reinforcements.

[0025] To verify the invention, the pore solution of two binders according to the invention was examined in more detail after six months of hydration.

[0026] Firstly, a binder made of pure synthetic forsterite without foreign ions was analyzed. In a second sample, a mixture of forsterite and silica glass in a 2:1 ratio was used instead of pure forsterite to produce the cement paste of the composite material.

[0027] After half a year of hydration, the pH value in the first sample was 9.5 and in the second sample the pH value was even in the range of 8.2.

[0028] According to this, the use of forsterite, which belongs to the olivine group, can produce a binder for a composite material that has a very low pH value compared to cement paste made from conventional Portland cement clinker. This low pH value allows, for the first time, the use of glass and / or carbon fiber reinforcements without further pretreatment.

[0029] With the composite material according to the invention, it is thus possible to do without the use of steel reinforcements, which have a very high CO2 emission during their production.

Claims

1. Composite material, comprising: cement stone composed of an MgO-based binder and / or olivine-based binder, which comprises, as a starting material, a forsterite source in the form of a natural or artificial olivine source and / or in the form of tempered serpentinite, as well as reinforcing elements for increasing the load-bearing capacity, wherein the reinforcing elements - comprise carbon fibers and / or glass fibers which are resistant to pH values below 11, and / or - steel reinforcements, which are hot-dipped and / or comprise a layer of paint or varnish, whereby they have protection against pH values of less than 11.

2. Composite material according to claim 1, characterized in that the pore solution of the cement stone has a pH value of 11 or lower.

3. Composite material according to claim 1 or 2, characterized in that the MgO-based binder and / or olivine-based binder comprises MgO and SiO2, MgO and MgCO3, MgO and glass powder, olivine and SiO2, olivine and glass powder, olivine and trass, olivine and pozzolan, tempered serpentinite and SiO2, tempered serpentinite and glass powder, or combinations thereof.

4. Composite material according to any one of claims 1 to 3, characterized in that the carbon fiber and / or glass fibers are in the form of fiber reinforcement, mat reinforcement, bar reinforcements and / or other forms of reinforcement.

5. Composite material according to any one of claims 1 to 4, characterized in that a binder that comprises Portland cement clinker is added to the cement stone for producing, in addition to the MgO-based binder and / or olivine-based binder.

6. Composite material according to any one of claims 1 to 5, characterized in that the reinforcing elements as paint or varnish layer comprise a layer of paint or varnish made of plastic, for protection against an alkaline environment with a pH value of less than 11.