Ultra-high performance fiber reinforced grouting

Abstract

The present application relates to a dry cement-based composition comprising, relative to the total dry weight of the cement-based composition, a) from 4 to 80% by weight of a cement-based binder, preferably ordinary Portland cement, b) from 5 to 95% by weight of an aggregate wherein the aggregate has a particle size of 0.001 mm to 8 mm, c) from 0.005 to 5% by weight of carbon fibers having a sizing agent, preferably a polymeric sizing agent, and / or in the form of a carbon fiber reinforced polymer sheet. A preferred application of the cementitious composition is grouting of offshore or onshore wind turbine towers. The invention further relates to application of the carbon fibers in preparation of ultra-high performance fiber reinforced grouting (UHPFRG) or ultra-high performance fiber reinforced concrete (UHPFRC).

Description

Technical Field

[0001] The present invention relates to a dry cementitious composition comprising a cementitious binder, an aggregate, and specific carbon fibers, which is suitable for preparing ultra-high performance fiber-reinforced grout (UHPFRG) or ultra-high performance fiber-reinforced concrete (UHPFRC). The present invention also relates to the use of the specific carbon fibers as a reinforcing material for UHPFRG or UHPFRC. Background of the Invention

[0003] Cement-based materials are commonly used in concrete or grouting, and they typically also contain aggregates and additives. For use, cement-based compositions are mixed with water, allowing a reaction between the cement and water to occur, commonly known as hydration. After hydration, the cement hardens and forms a solid building material.

[0004] In recent years, specialty concretes such as high performance concrete (HPC) and ultra-high performance concrete (UHPC), as well as high performance and ultra-high performance grouts (UHPG) have been introduced to the market.

[0005] These special concretes and mortars usually contain a high proportion of mineral binders and a high proportion of fine-grained aggregates. The high proportion of fine particles leads to good homogeneity of the material, and the high proportion of mineral binders leads to high strength.

[0006] High-strength concrete and grouts also contain little to no water, as any water not needed for cement hydration evaporates, leaving behind pores that reduce strength. For conventional concrete, the w / c ratio, or the ratio of water to cement by mass, is typically between 0.45 and 0.60. For HPC and UHPC, the w / c ratio is much lower, less than 0.40 and often less than 0.30 or 0.25.

[0007] However, UHPG and UHPC also exhibit certain disadvantages, such as low tensile strength and low resistance to cracking and crack propagation. To meet these challenges, fiber-reinforced systems have been developed, which are known as ultra-high performance fiber-reinforced concrete (UHPFRC) and ultra-high performance fiber-reinforced grout (UHPFRG), respectively.

[0008] Steel fibers are commonly used in these systems, offering high peak load and ductility under compressive loads. However, the incorporation of steel fibers has disadvantages such as high corrosion potential and high density. Furthermore, UHPFRG and UHPFRC with steel fibers exhibit poor flowability and weak self-consolidation.

[0009] Other types of fibers have also been used for fiber reinforcement, but the properties obtained are generally unsatisfactory. SUMMARY OF THE INVENTION

[0011] The object of the present invention is to provide a dry cementitious composition suitable for UHPFRC and UHPFRG which overcomes the disadvantages of the prior art. In particular, the object of the present invention is to provide a dry cementitious composition suitable for UHPFRC and UHPFRG which exhibits high ultimate flexural and compressive strengths and improved fatigue behavior and elastic modulus, while reducing the weight of the fibers used therein.

[0012] Surprisingly, this object could be achieved by a dry cementitious composition comprising specific aggregates in combination with specific carbon fibers.

[0013] The present invention therefore relates to a dry cementitious composition comprising, relative to the total dry weight of the cementitious composition:

[0014] a) 4 to 80% by weight, preferably 10 to 60% by weight, particularly preferably 15 to 50% by weight, of a cement-based binder, preferably ordinary Portland cement,

[0015] b) 5 to 95% by weight, preferably 20 to 80% by weight, particularly preferably 30 to 70% by weight, of aggregates, wherein the aggregates have a particle size of 0.001 mm to 8 mm, determined by sieve analysis in accordance with EN 12192-1:2002 or EN 933-1:2012,

[0016] c) 0.005 to 5% by weight, preferably 0.01 to 4% by weight, particularly preferably 0.1 to 3% by weight, of carbon fibers provided with a sizing, preferably a polymer sizing, and / or in the form of carbon fiber-reinforced polymer sheets.

[0017] Surprisingly, it has been found that the dry cementitious composition of the present invention can provide cements or grouts with increased flexural / compressive strength, compressive E-modulus and fatigue behavior.

[0018] Thus, the use of specific carbon fibers, particularly micro carbon fibers, in the composition of the present invention enhances the ultimate strength, E-modulus and fatigue resistance of ultra-high performance fiber reinforced grout (UHP-FRG) or ultra-high performance fiber reinforced concrete (UHP-FRC).

[0019] Further advantages of the present invention are the low tendency to autogenous shrinkage, the good flowability and the self-consolidating properties of the compositions according to the invention during processing.

[0020] At the same time, the low density of carbon fibers compared to steel fibers allows for lower static loads on components and limited corrosion. This improves resistance to harsh conditions such as seawater or high-chloride environments.

[0021] Further embodiments of the invention are described in the other independent claims. Preferred embodiments of the invention are described in the dependent claims. Detailed Description of the Invention

[0023] In a first aspect, the present invention relates to a dry cementitious composition comprising, relative to the total dry weight of the cementitious composition:

[0024] a) 4 to 80% by weight of a cement-based binder, in particular ordinary Portland cement,

[0025] b) 5 to 95 wt. % of aggregates, wherein the aggregates have a particle size in the range of 0.001 mm to 8 mm, determined by sieve analysis according to EN 12192-1:2002 or EN 933-1:2012,

[0026] c) 0.005 to 5% by weight of carbon fibers provided with a sizing, preferably a polymer sizing, and / or in the form of carbon fiber-reinforced polymer sheets.

[0027] According to an embodiment, the dry cementitious composition comprises, relative to the total dry weight of the cementitious composition:

[0028] a) 4 to 80% by weight, preferably 10 to 60% by weight, more preferably 15 to 50% by weight of a cement-based binder, preferably ordinary Portland cement,

[0029] b) 5 to 95 wt. %, preferably 20 to 80 wt. %, more preferably 30 to 70 wt. % of aggregates, wherein the aggregates have a particle size in the range of 0.001 mm to 8 mm, determined by sieve analysis according to EN 12192-1:20 02 or EN 933-1:20 12,

[0030] c) 0.005% to 5% by weight, preferably 0.01% to 4% by weight, more preferably 0.1% to 3% by weight of carbon fibers provided with a sizing, preferably a polymer sizing, and / or in the form of carbon fiber-reinforced polymer sheets, and / or

[0031] The average length of the carbon fibers is from 0.001 to 35 mm, preferably from 0.001 to 25 mm, more preferably from 0.1 to 20 mm, even more preferably from 4 to 15 mm, most preferably from 6 to 12 mm.

[0032] In a preferred embodiment, the dry cementitious composition comprises, relative to the total dry weight of the cementitious composition:

[0033] a) 10 to 60% by weight, preferably 15 to 50% by weight, of a cement-based binder,

[0034] b) 20 to 80% by weight, preferably 30 to 70% by weight, of aggregate, and

[0035] c) 0.01 to 4% by weight, preferably 0.1 to 3% by weight, of carbon fibers.

[0036] The dry cementitious composition of the present invention comprises a cementitious binder, which can also be a combination of different cementitious binders. Cementitious binders are, in particular, materials that react in a hydration reaction in the presence of water to form a solid hydrate or hydrate phase. This can be, in particular, hydraulic binders that harden with water even underwater, such as, in particular, cement, or latent hydraulic binders that set with water, such as, in particular, granulated blast furnace slag and calcined clay, or pozzolanic binders, such as, in particular, fly ash, silica fume, microsilica, or mixtures thereof.

[0037] In this context, the cementitious composition of the present invention preferably does not contain any reactive polymer or polymer resin. In particular, the cementitious composition preferably does not contain epoxy resin.

[0038] The dry cementitious composition generally has a water content of not more than 10% by weight, preferably not more than 3% by weight, in particular not more than 1% by weight, relative in each case to the total weight of the dry cementitious composition.The dry cementitious composition is generally a powdered cementitious composition.

[0039] The cement binder of the dry cement-based composition of the present invention preferably comprises or is Ordinary Portland Cement (OPC).

[0040] In a preferred embodiment, the content of OPC in the cementitious composition of the invention is 4 to 80% by weight, preferably 26 to 75% by weight, in particular 30 to 66% by weight, in each case relative to the total dry weight of the cementitious composition.

[0041] Suitable OPCs are classified, for example, under standard DIN 197-1 as CEM I. However, other OPCs, for example classified under the relevant ASTM, JIS or Chinese standards, are also suitable.

[0042] Instead of OPC, it is also possible to use mixed cements as cement-based binders according to DIN 197-1, such as Portland composite cement (CEM I), blast furnace cement (CEM III), pozzolanic cement (CEM V) and composite cement (CEM V).

[0043] In addition to OPC, special cements such as calcium sulfoaluminate cement, calcium aluminate cement or mixtures thereof can also be used as cement-based binders.

[0044] In a preferred embodiment, the OPC is CEMI. According to a further embodiment, the OPC is white cement. White cements may be preferred herein because they have a lower water demand. According to a preferred embodiment, the cement-based binder, in particular the OPC, has a low content of tricalcium aluminate (CA). Low content means that the content of CA in the cement-based binder of the present invention is preferably <10 wt%, more preferably <5 wt%, each based on the total dry weight of the cement-based binder.

[0045] The cementitious binder of the dry cementitious composition of the invention may also contain a latent hydraulic binder and / or a pozzolanic binder. Suitable latent hydraulic binders and / or pozzolanic binders are in particular granulated blast furnace slag, calcined clay, fly ash, silica fume and / or microsilica.

[0046] According to an embodiment, the cementitious binder comprises 1 to 65% by weight, preferably 5 to 35% by weight, more preferably 10 to 20% by weight, in each case relative to the total dry weight of the cementitious binder, of latent hydraulic and / or pozzolanic binder. Advantageous latent hydraulic and / or pozzolanic binders are granulated blast furnace slag, calcined clay, fly ash, silica fume and / or microsilica.

[0047] In a preferred embodiment, the cement-based binder consists of 100% by weight of ordinary Portland cement.

[0048] Suitable cementitious binders may also comprise or consist of the following, in each case relative to the total dry weight of the cementitious binder:

[0049] a) at least 35% by weight, preferably at least 65% by weight, most preferably at least 80% by weight, of ordinary Portland cement,

[0050] b) 1 to 65% by weight, preferably 5 to 35% by weight, more preferably 10 to 20% by weight, of at least one latent hydraulic and / or pozzolanic binder.

[0051] The at least one latent hydraulic and / or pozzolanic binder is preferably selected from granulated blast furnace slag, calcined clay, fly ash, silica fume and / or microsilica.

[0052] The dry cementitious composition according to the invention comprises 4 to 80 wt.-%, preferably 10 to 60 wt.-%, more preferably 15 to 50 wt.-% of cementitious binder, relative to the total dry weight of the cementitious composition.

[0053] The dry cementitious composition according to the present invention further comprises aggregate, wherein the aggregate has a particle size of 0.001 mm to 8 mm, determined by sieve analysis according to EN 12192-1:2002 and / or EN 933-1:2012.

[0054] The aggregate is preferably selected from at least one of limestone, granite, basalt, olivine, aluminum oxide, sand or a combination thereof, preferably sand and / or aluminum oxide.

[0055] The dry cementitious composition contains 5 to 95 wt. %, preferably 20 to 80 wt. %, preferably 30 to 70 wt. % of aggregate relative to the total dry weight of the cementitious composition, wherein the aggregate is preferably selected from at least one of limestone, granite, basalt, olivine, aluminum oxide and sand, preferably aluminum oxide and / or sand.

[0056] According to the present invention, the aggregate is used as a powder. Therefore, the aggregate can be characterized by its particle size distribution. Particle size can be analyzed by sieve analysis, for example, as described in EN 12192-1:2002 or EN 933-1:2012. This method separates fine particles from coarser particles by passing the material through a number of sieves of varying mesh sizes. The material to be analyzed is vibrated through a series of successively smaller sieves using either horizontal, vertical, or rotational motions, alone or in combination. For particles with a particle size of less than 75 μm, the wet method of EN 933-1:2012 is used.

[0057] The lower limit of the particle size distribution can then be given by the mesh size of the sieve that retains 100% of the particles, and the upper limit can be given by the smallest mesh size of the sieve through which 100% of the particles still pass. In the following, the mesh sizes of the particle size distribution and therefore the lower and upper limits are given in mm.

[0058] The aggregate, preferably an aggregate selected from at least one of limestone, granite, basalt, olivine, aluminum oxide and sand, preferably has a particle size of 0.036 mm to 7 mm, preferably 0.125 mm to 6 mm, more preferably 0.25 mm to 3 mm, as determined by sieve analysis according to EN 12192-1:2002 or EN 933-1:2012.

[0059] Common aggregates are described in, for example, EN 12620:2008-07 and EN 13139:2015-07.

[0060] Sand is a naturally occurring granular material consisting of finely divided rock or mineral particles. Examples of sand are river sand and / or manufactured sand, for example from granite or limestone, or mixtures thereof. Sand is preferably silica sand or quartz sand. Suitable sands are described in standards ASTM C778 or EN 196-1.

[0061] In this context, aluminum oxide refers to materials having an Al2O3 content of at least 5% by weight, preferably at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 85% by weight, and in particular at least 90% by weight, in each case relative to the total dry weight of the material. The aluminum oxides according to the invention generally also contain SiO2, Fe2O3, TiO2, and / or oxides of alkali metals and alkaline earth metals. Preferred aluminum oxides are aluminum oxides, especially α-aluminum oxide, which may be calcined. A further preferred material is calcined bauxite.

[0062] In this context, aluminum oxide does not refer to aluminates or aluminosilicates. Thus, aluminum oxide is not aluminate cement or any aluminosilicate. In this context, aluminum oxide does not refer to fibrous aluminum oxide. In this context, aluminum oxide preferably also does not refer to nanomaterials based on aluminum oxide.

[0063] When aluminum oxide is used as an aggregate, it is particularly preferred that the aluminum oxide is characterized by a bimodal particle size distribution. This bimodal particle size distribution can be produced by mixing two aluminum oxides with different particle size distributions. Therefore, it is preferred that the aluminum oxide used in the cementitious composition of the present invention is a mixture of two aluminum oxides with different particle size distributions.

[0064] Without wishing to be bound by theory, it is believed that the aluminum oxide has a porous structure that allows water to be absorbed from the cement paste onto the aluminum oxide. The absorbed water is retained within the aluminum oxide during cement hydration, thereby significantly reducing autogenous shrinkage during hydration. The free water retained within the aluminum oxide eventually diffuses into the cement matrix and reacts with unreacted cement after final setting, resulting in a stronger bond between the aluminum oxide and the cement matrix.

[0065] The dry cement-based composition also contains carbon fibers. The carbon fibers have a sizing agent, preferably a polymer sizing agent, and / or are in the form of carbon fiber reinforced polymer flakes. The sizing agent is also beneficial because it improves the flowability of the wet mix.

[0066] The amount of carbon fibers in the form of a sizing agent, preferably a polymer sizing agent, and / or carbon fiber-reinforced polymer flakes in the dry cementitious composition according to the invention is from 0.005 to 5% by weight, preferably from 0.1 to 4% by weight, more preferably from 0.1 to 3% by weight, in each case relative to the total dry weight of the dry cementitious composition. The amounts indicated refer to carbon fibers in the form of a sizing agent, preferably a polymer sizing agent, and / or carbon fiber-reinforced polymer flakes, i.e. including the included polymer material.

[0067] Carbon fibers provided with a sizing agent, preferably a polymer sizing agent, carbon fibers in the form of carbon fiber reinforced polymer sheets, or combinations thereof may be used.

[0068] Such carbon fibers are known to those skilled in the art and are commercially available. For example, carbon fibers with polymer sizing are available in various sizes and variations under the trade name Available from Teijin, or under the trade name Available from Toray. Carbon fibers in the form of carbon fiber reinforced polymer sheets are available in various sizes and variations under the trade name Obtained from Sika.

[0069] In one embodiment, carbon fiber is a carbon fiber with a sizing agent, preferably a polymer sizing agent. Sizing agent or polymer sizing agent is typically a thin coating applied to the fiber surface. In one embodiment, carbon fiber is a carbon fiber in the form of a carbon fiber reinforced polymer sheet. In these sheets, carbon fiber bundles are embedded or incorporated in a polymer matrix. Sheet generally refers to a plate-like structure. Sheet is typically obtained by pultrusion (pultruded carbon fiber reinforced polymer sheet).

[0070] The following indications regarding suitable morphologies of carbon fibres apply both to carbon fibres provided with a sizing, preferably a polymeric sizing, and to carbon fibres in the form of carbon fibre-reinforced polymer sheets.

[0071] In a particularly preferred embodiment, the carbon fibers are microcarbon fibers, the term microcarbon fibers generally being used for carbon fibers having a diameter of less than 0.3 mm. Particularly preferred carbon fibers have a diameter of 1 to 100 μm.

[0072] Preferably, the carbon fibers, in particular the microfibers, have an average length of 0.001 to 35 mm, preferably 0.001 to 25 mm, more preferably 0.1 to 20 mm, more preferably 4 to 15 mm, and most preferably 6 to 12 mm. For chopped carbon fibers, the average length generally corresponds to the cut length. In the context of this application, average length refers to the number-average length.

[0073] Preferably, the carbon fibers, in particular the microcarbon fibers, have an aspect ratio of 1 to 15000, preferably 20 to 15000, more preferably 1000 to 5000. The aspect ratio is defined as the fiber length divided by its diameter.

[0074] An aspect ratio of carbon fibers within the above preferred ranges results in improved properties, particularly improved crack resistance. Without wishing to be bound by any theory, it is believed that the preferred aspect ratios result in a higher amount of carbon fibers in the crack plane, thereby improving crack propagation behavior.

[0075] Preferably, the carbon fiber is chopped carbon fiber. Chopped and ground carbon fiber can also be used. Chopped carbon fiber of desired length can be obtained, for example, by cutting carbon fiber filaments provided with a sizing agent (preferably a polymer sizing agent), or by cutting carbon fiber reinforced polymer sheets typically supplied with a roll. The advantage of chopped carbon fiber is that the carbon fiber length is very uniform. In another embodiment, chopped and ground carbon fiber is used.

[0076] The sizing agent is preferably a polymer sizing agent or an organic polymer sizing agent, respectively. In the carbon fibers with sizing agent, the amount of sizing agent, preferably polymer sizing agent, is preferably 0.1-10 wt%, preferably 0.5-5 wt%, based on the weight of the fiber.

[0077] The amount of polymer in the carbon fiber reinforced polymer sheet is preferably in the range of 0.1 to 10 wt. %, preferably 0.1 to 5 wt. %, based on the weight of the fibers.

[0078] Suitable materials for sizing, preferably polymer sizing and / or reinforcing polymers, in particular examples of polymers are polyvinyl alcohol, polyvinyl pyrrolidone (PVP), polyamide (PA), polyacrylate, polydopamine (PDA), 4,4'-diaminodiphenylmethane (MDA), carbon nanotubes, poly(thioarylidene phosphine oxide) (PTPO), N-(4,4-diaminodiphenylmethane)-2-hydroxypropyl methacrylate (DMHM), (3-glycidoxypropyl) trimethoxysilane (GPTMS), phenoxy polyhydroxy ethers, polypropylene, polyethylene, epoxy resins, in particular epoxy vinyl esters, carboxymethyl cellulose, polyurethane, vinyl ester resins or combinations thereof. Preferred polymers are polypropylene alcohol, polypropylene, polyethylene, epoxy resins, in particular epoxy vinyl esters, carboxymethyl cellulose, polyurethane, vinyl ester resins or combinations thereof. Particularly useful sizing agents can be obtained from non-ionic aqueous dispersions of solid bisphenol A epoxy resins having a molecular weight per epoxide of 100-10,000.

[0079] The chopped carbon fiber may have a bulk density of 200 to 800 g / L, preferably 300 to 500 g / L.

[0080] One advantage of the present invention is that the weight of carbon fiber is significantly lower than the weight of steel fiber commonly used in UHPFRG and UHPFRC. This also makes handling easier. In addition, carbon fiber is more suitable in terms of safety.

[0081] UHPFRG and UHPFRC with steel fibers show poor flowability and weak self-consolidation. In contrast, UHPFRG and UHPFRC prepared with dry cement-based compositions containing defined carbon fibers have been shown to have appropriate flowability and self-consolidation properties.

[0082] The combination of carbon fibers provided with a sizing agent, preferably a polymer sizing agent, or in the form of carbon fiber-reinforced polymer flakes, with aggregate also ensures that the concrete or mortar has a particularly high compressive strength.

[0083] The dry cement-based composition of the present invention preferably further contains a fine filler. The fine filler does not react in the hydration reaction of the cement binder and has a particle size that mainly passes through a 0.125 mm sieve, preferably a 0.063 mm sieve. Typical fillers include finely ground stone powder.

[0084] Preferably, fillers of different particle sizes are mixed in order to optimally adjust the properties of the cementitious composition. Such mixtures are known to those skilled in the art.

[0085] The cementitious composition of the present invention advantageously further comprises additives commonly used in the mortar and / or concrete industry, such as plasticizers and / or superplasticizers, redispersible polymers, accelerators, retarders, air entraining agents, stabilizers, viscosity modifiers, thickeners, water reducers, accelerators, retarders, water repellents, strength enhancing additives, foaming agents, pigments, corrosion inhibitors, etc. It may be advantageous to combine two or more of the above-mentioned additives in one cementitious composition.

[0086] According to a suitable embodiment, the dry cementitious composition of the invention comprises, relative to the total dry weight of the cementitious composition:

[0087] a) 4 to 80% by weight, preferably 10 to 60% by weight, particularly preferably 15 to 50% by weight, of a cement-based binder, preferably ordinary Portland cement,

[0088] b) 5 to 95% by weight, preferably 20 to 80% by weight, particularly preferably 30 to 70% by weight, of aggregates, wherein the aggregates have a particle size of 0.001 to 8 mm, preferably 0.036 to 7 mm, more preferably 0.125 to 6 mm, even more preferably 0.25 to 3 mm, as determined by sieve analysis in accordance with EN 12192-1:2002 or EN 933-1:2012,

[0089] c) 0.005 to 5% by weight, preferably 0.01 to 4% by weight, particularly preferably 0.1 to 3% by weight, of carbon fibers, preferably microcarbon fibers, provided with a sizing, preferably a polymer sizing, or in the form of carbon fiber-reinforced polymer flakes.

[0090] d) optionally additional fine aggregate or filler,

[0091] e) Optional other additives.

[0092] The dry cement-based composition according to the present invention is preferably a grouting composition or a concrete composition, in particular a grouting composition. In a preferred embodiment, the dry cement-based composition according to the present invention is a cement-based composition suitable for ultra-high performance fiber-reinforced grouting (UHPFRG) or ultra-high performance fiber-reinforced concrete (UHPFRC), in particular UHPFRG.

[0093] Another aspect of the present invention is the use of carbon fibers, in particular micro carbon fibers, provided with a sizing, preferably a polymer sizing, or in the form of carbon fiber reinforced polymer sheets, as fiber reinforcement for grout or concrete, in particular for ultra-high performance fiber reinforced grout (UHPFRG) or ultra-high performance fiber reinforced concrete (UHPFRC).

[0094] Another aspect of the present invention is the use of the dry cementitious composition of the present invention as described above for the preparation of ultra-high performance fiber-reinforced grout (UHPFRG) or ultra-high performance fiber-reinforced concrete (UHPFRC), in particular for grouting of offshore or onshore wind turbine towers or as a repair mortar. The dry cementitious composition of the present invention is particularly suitable for grouting of offshore or onshore wind turbine towers.

[0095] Another aspect of the invention is the use of the dry cementitious composition of the invention as described above in a system according to principles 3, 4 and 7 of EN 1504-3:2006 or in a system according to EN 1504-6:2006 or as a high-strength grout according to DAfStb guideline VEBMR:2019 or as a non-shrinkage grout of classes A, B, C according to ASTM C1107:2020.

[0096] All aspects, proportions and embodiments described above with respect to the dry cementitious composition of the invention, eg with respect to the carbon fibres, aggregates and cementitious binder, also apply to these inventive uses, so that reference is made thereto.

[0097] DIN EN 1504-3:2006 describes products and systems for the protection and repair of concrete structures. Principle 3 covers concrete repair, Principle 4 covers structural reinforcement, and Principle 7 covers the maintenance of passive restoration.

[0098] The dry cement-based composition according to the invention is therefore particularly suitable for use as a mortar for concrete repair, as well as for mortar, concrete or crack filler for structural reinforcement, and for increasing the cover on steel reinforcement or replacing carbonated concrete.

[0099] EN 1504-6:2006 relates to products and systems for anchoring steel reinforcement. Therefore, the cement-based composition of the present invention is suitable for anchoring steel reinforcement.

[0100] The DAfStb's VEBMR:2019 guideline addresses grouting materials with high early strength and compressive strength class C50 / 60 or higher. Therefore, the cementitious compositions of the present invention are suitable for use as supplementary concrete materials and cement mortars in thin layers, for example, for grouting joints or concreting columns in sleeve foundations.

[0101] Another aspect of the present invention is a method for preparing a hardened cementitious body comprising the following steps:

[0102] - mixing a dry cementitious composition according to the invention as described above with water to obtain a wet cementitious composition,

[0103] - shaping or moulding the wet cement composition, and

[0104] - Hardening the formed or moulded wet cementitious composition.

[0105] All aspects, proportions and embodiments described above with respect to the dry cementitious composition of the invention, eg with respect to the carbon fibres, aggregates and cement binder, also apply to the method of the invention, so that reference is made thereto.

[0106] The present invention also relates to a cementitious composition comprising a dry cementitious composition according to the invention and water, wherein the amount of water is from 5 to 50% by weight, preferably from 5 to 40% by weight, more preferably from 6 to 30% by weight, still more preferably from 6 to 20% by weight, most preferably from 7 to 10% by weight, in each case relative to the total weight of the dry cementitious composition.

[0107] In a preferred embodiment, the cementitious composition is an ultra-high performance fiber reinforced grout (UHPFRG) or an ultra-high performance fiber reinforced concrete (UHPFRC).

[0108] The water may be any available water, such as distilled water, purified water, tap water, mineral water, spring water, and well water. Wastewater may be used only if its composition is known and if the impurities it contains are unlikely to impart a function to any of the other components of the composition of the invention. Salt water may not be used due to its high chloride content and the associated risk of corrosion of the steel bars.

[0109] The method and apparatus that are used to mix dry cement-based composition and water are well known to those skilled in the art.Dry cement-based composition and the mixing of water can for example be finished with hand-held mixer, Hobart mixer, portable concrete mixer, mixing car, mixing bucket, paddle mixer, jet mixer, screw mixer, spiral mixer, horizontal single shaft mixer, twin shaft paddle mixer, vertical shaft mixer, ribbon mixer, orbital mixer, can change mixer, tumble container, vertical mixing chamber or air agitation operation.Mixing can be continuous, semi-continuous or carry out in batches.Continuous mixing provides the advantage of high production speed.

[0110] The water used for mixing the dry cementitious composition may contain at least one additive customary in the concrete and / or grouting industry, particularly preferably a plasticizer or superplasticizer.

[0111] The shaping or moulding of the wet cementitious composition is then carried out according to conventional methods known to those skilled in the art.The hardening of the dry cementitious composition begins upon mixing with water, resulting in a hardened cementitious body.

[0112] Another aspect of the present invention is a hardened cementitious body obtainable by the process of the invention as described above.

[0113] In a preferred embodiment, the hardened cement body obtained has a compressive strength after 28 days of at least 120 MPa, preferably at least 140 MPa, determined according to EN 12190:1998.

[0114] The hardened cementitious body is preferably a mortar or concrete composition, in particular a self-compacting concrete, a high-strength or ultra-high-strength concrete or a high-strength or ultra-high-strength mortar.

[0115] The hardened cementitious body is particularly preferably an ultra-high performance fiber reinforced grout (UHPFRG) or ultra-high performance fiber reinforced concrete (UHPFRC), in particular UHPFRC. UHPFRG and UHPFRC can be considered as grouts or concretes having a compressive strength after 28 days of at least 120 MPa, preferably at least 140 MPa or even at least 150 MPa, as determined in accordance with EN 12190:1998.

[0116] Despite the absence of steel fibers typically used in UHPFRG or UHPFRC, the hardened cement body obtainable by the dry cementitious composition according to the invention ensures relatively good compressive strength, has increased corrosion protection and is relatively low in weight, which makes the use of the dry cementitious composition according to the invention particularly easy to handle and versatile. Example

[0117] Table 1 below gives an overview of the materials used.

[0118] Table 1

[0119]

[0120]

[0121] tex: nominal linear density (without sizing agent)

[0122] A powder grouting composition was prepared with the composition according to Table 2 below.

[0123] Table 2

[0124]

[0125] *1 A mixture of quartz sand and bauxite (0-3 mm; 2.5:1 by weight)

[0126] *2 Defoaming agent, plasticizer, stabilizer

[0127] The examples were prepared by mixing a powdered grouting composition and fibers in a bag and then mixing with water according to EN 13395-1:2002 (Hobart 3' slow + 2' fast) to obtain a fiber-containing grouting composition. The fibers used are given in Tables 3 and 4 below, where the weight proportions and properties of the fibers are also given (see below). The lengths given are cut lengths.

[0128] The examples presented in Table 3 compare the grout compositions of Table 2 with various types of fibers (material, length, sizing) from Table 1. Example 1 was performed without the addition of fibers as a reference example. Examples 11 and 12, which contain carbon fibers, are examples of the present invention. The other examples are comparative examples.

[0129] The examples given in Table 4 compare the grouting compositions of Table 2 with carbon fibers having two types of sizing agents (PU and epoxy vinyl ester) and different fiber lengths (12, 24 and 34 mm). Example 14 was performed without the addition of fibers as a reference sample.

[0130] Quality refers to the quality of the fiber used.

[0131] Parts refer to the weight proportion of the fibers relative to the total weight of the grouting composition containing the fibers.

[0132] Density Fiber refers to the density of the fiber.

[0133] Volume fiber refers to the volume of fiber used.

[0134] Water is added to the fiber-containing grouting composition in an amount sufficient to produce 7.5% by weight relative to the total weight of the dry fiber-containing grouting composition.

[0135] The wet composition thus obtained was measured according to the following procedure.

[0136] Tested according to EN 12190:1998.

[0137] Slump flow: tested according to EN 13391:2004

[0138] FS28: Flexural strength tested according to EN 12190:1998

[0139] CS28: Compressive strength of prisms 40 x 40 x 160 mm measured according to EN 12190:1998 after 28 days of underwater hardening

[0140] EMC28: E-modulus tested under compression according to EN 13412:2006

[0141] N cycles to failure: fatigue resistance

[0142]

[0143]

Claims

1. A dry cement-based composition comprising, relative to the total dry weight of the cement composition: a) 4 to 80% by weight, preferably 10 to 60% by weight, more preferably 15 to 50% by weight of a cement-based binder, preferably ordinary Portland cement, b) 5 to 95 wt. %, preferably 20 to 80 wt. %, more preferably 30 to 70 wt. % of aggregates, wherein the aggregates have a particle size in the range of 0.001 mm to 8 mm, determined by sieve analysis according to EN 12192-1:2002 or EN 933-1:2012, c) 0.005 to 5% by weight, preferably 0.01 to 4% by weight, more preferably 0.1 to 3% by weight of carbon fibers provided with a sizing, preferably a polymer sizing, and / or in the form of carbon fiber-reinforced polymer sheets.

2. The dry cement-based composition according to claim 1, wherein the carbon fibers have an aspect ratio of 1 to 15,000, preferably 20 to 15,000, more preferably 1,000 to 5,000, and / or wherein the carbon fibers are micro carbon fibers having a diameter less than 0.3 mm, and / or The carbon fibers are chopped carbon fibers or chopped and ground carbon fibers.

3. The dry cement-based composition according to claim 1 or 2, wherein the aggregate is selected from at least one of limestone, granite, basalt, olivine, aluminum oxide, sand or a combination thereof, preferably sand and / or aluminum oxide.

4. The dry cementitious composition according to any one of the preceding claims, wherein the carbon fibers have an average length of 0.001 to 35 mm, preferably 0.001 to 25 mm, more preferably 0.1 to 20 mm, even more preferably 4 to 15 mm, most preferably 6 to 12 mm, and / or The diameter of the carbon fibers is in the range of 1 to 100 μm.

5. Dry cementitious composition according to any one of the preceding claims, wherein the amount of sizing agent, preferably polymeric sizing agent, in the carbon fibers provided with a sizing agent is in the range of 0.1 to 10 wt.-%, preferably 0.5 to 5 wt.-%, based on the weight of the carbon fibers, and / or The amount of the polymer in the carbon fiber reinforced polymer sheet is in the range of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, based on the weight of the carbon fibers.

6. The dry cementitious composition according to claim 1 , wherein the polymer of the sizing agent, preferably the polymeric sizing agent, and / or the reinforcing polymer is selected from polyvinyl alcohol, polyvinyl pyrrolidone (PVP), polyamide (PA), polyacrylate, polydopamine (PDA), 4,4′-diaminodiphenylmethane (MDA), carbon nanotubes, poly(thioarylenephosphine oxide) (PTPO), N-(4,4-diaminodiphenylmethane)-2-hydroxypropyl methacrylate (DMHM), (3-glycidoxypropyl)trimethoxysilane (GPTMS), phenoxypolyhydroxy ether, polypropylene, polyethylene, epoxy resins, in particular epoxy vinyl esters, carboxymethyl cellulose, polyurethanes, vinyl ester resins, or combinations thereof.

7. A dry cementitious composition according to any one of the preceding claims, wherein the aggregate has a particle size of 0.036 mm to 7 mm, preferably 0.125 mm to 6 mm, more preferably 0.25 mm to 3 mm.

8. The dry cementitious composition according to claim 1, and water, wherein the amount of water is from 5 to 50% by weight, preferably from 5 to 40% by weight, more preferably from 6 to 30% by weight, still more preferably from 6 to 20% by weight, in particular from 7 to 10% by weight, in each case relative to the total weight of the dry cementitious composition.

9. Use of carbon fibers, in particular micro carbon fibers, wherein the carbon fibers have a sizing, preferably a polymer sizing, or are in the form of carbon fiber reinforced polymer sheets, as fiber reinforcement for grouting or concrete, in particular for ultra-high performance fiber reinforced grouting (UHPFRG) or ultra-high performance fiber reinforced concrete (UHPFRC).

10. Use of the dry cementitious composition according to any one of claims 1 to 8 for the preparation of ultra-high performance fiber reinforced grout (UHPFRG) or ultra-high performance fiber reinforced concrete (UHPFRC), in particular for grouting of offshore or onshore wind turbine towers or as a repair mortar.

11. Use of the dry cementitious composition according to any one of claims 1 to 8 in a system according to principles 3, 4 and 7 of EN 1504-3:2006 or in a system according to EN 1504-6:2006 or as a high-strength grout according to DAfStb guideline VEBMR:2019 or as a non-shrinkage grout of classes A, B, C according to ASTM C1107:2020.

12. A method for preparing a hardened cement body, the method comprising the steps of: - mixing a dry cementitious composition according to any one of claims 1 to 7 with water to obtain a wet cementitious composition, - shaping or molding the wet cementitious composition, and - Hardening the formed or moulded wet cementitious composition.

13. The process according to claim 12, wherein the amount of water is 5 to 50% by weight, preferably 5 to 40% by weight, more preferably 6 to 30% by weight, still more preferably 6 to 20% by weight, in particular 7 to 10% by weight, in each case relative to the total weight of the dry cementitious composition.

14. A hardened cement body obtainable by the method according to claim 12 or claim 13.

15. The hardened cementitious body according to claim 14, which has a compressive strength after 28 days of at least 120 MPa, preferably at least 140 MPa according to EN 12190:1998.

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