Carbon fiber-containing concrete or mortar composition, carbon fiber-reinforced concrete or mortar structure, and method for producing the same

Abstract

Purposes of the present invention are to provide a carbon-fiber-containing concrete or mortar composition which has excellent handleability due to a reinforcement produced from precut raw-material carbon fibers, such as short fibers, scrap fibers resulting from processes, or carbon fibers reclaimed from CFRPs, etc., and to provide a carbon-fiber-reinforced concrete or mortar structure which is a cured object formed from the carbon-fiber-containing concrete or mortar composition and in which the fibers have a high reinforcing effect. This carbon-fiber-containing concrete or mortar composition includes carbon-fiber masses each configured at least from carbon fibers and a binder, and is characterized in that the carbon-fiber masses each have the shape of a spindle.

Description

[Technical Field]

[0001] The present disclosure relates to a concrete or mortar composition containing spindle-shaped carbon fiber aggregates, a concrete or mortar structure reinforced therewith, and a manufacturing method thereof. In particular, the present disclosure relates to a concrete or mortar composition containing spindle-shaped carbon fiber aggregates manufactured from recycled carbon fibers (recycled carbon fibers), a concrete or mortar structure reinforced therewith, and a manufacturing method thereof. [Background technology]

[0002] Concrete or mortar structures, which contain cement as the main component, are used in large quantities in the fields of construction and civil engineering due to their excellent properties such as compressive strength, durability, non-combustibility, etc., as well as their low cost. However, even when these structures use aggregates such as sand or gravel, they are fundamentally brittle, and have drawbacks such as being easily cracked or broken when subjected to stresses such as tension, bending, and flexure.

[0003] To overcome these drawbacks, in addition to the various conventional aggregates, fiber-reinforced plastic wire (FRP wire) made from steel fiber, synthetic fiber, aramid fiber, glass fiber, etc. is sometimes used as a reinforcing material, which greatly improves the mechanical properties such as bending strength and bending toughness of the cement composite material (reinforced concrete or mortar structure).

[0004] Carbon fiber has excellent specific strength and specific modulus, and is lightweight, so it is used as a reinforcing fiber for various materials. Furthermore, as a reinforcing fiber used in cement composite materials, it is also used in the construction and civil engineering fields because it is relatively resistant to degradation in alkali. In particular, many methods have been investigated for using composite wires manufactured from carbon fiber reinforced plastics (CFRP) using continuous carbon fiber in cement composite materials.

[0005] For example, Patent Documents 1 to 3 describe cement composite materials made using composite wires obtained by adhering a resin matrix, or alternatively an inorganic matrix, to continuous carbon fibers, followed by curing and cutting the resulting fibers. However, because these methods involve cutting the continuous fibers after curing, they cannot be applied to pre-cut short fibers, process waste fibers, recycled carbon fibers recovered from CFRP, etc. Furthermore, the manufacturing energy or cost involved in the curing process can be problematic.

[0006] On the other hand, when pre-cut carbon fibers are used as reinforcing materials without undergoing a hardening treatment, they tend to disperse into single fibers when mixed with concrete compositions, etc. Dispersion into single fibers poses problems, such as breakage of the dispersed single fibers upon contact with aggregate and an increase in the viscosity of the material during mixing, making it difficult to handle. Furthermore, there is a problem of a decrease in reinforcing effects such as flexural toughness.

[0007] Patent Document 4 describes a cement composite material reinforced with carbon fibers having an average fiber length of 3 mm or less. Because the average fiber length is short, the probability of breakage of dispersed single fibers is low, but the reinforcing effect of the resulting cement composite material, such as flexural strength and flexural toughness, is expected to be small. In addition, due to an increase in material viscosity, the slump and fluidity, which are characteristic values ​​of the mortar composition before curing, decrease. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5046276 [Patent Document 2] Patent No. 5054906 [Patent Document 3] Patent No. 5182779 [Patent Document 4] Patent No. 5809019 Summary of the Invention [Problem to be solved by the invention]

[0009] The present disclosure aims to provide a carbon fiber-containing concrete or mortar composition that is easy to handle, using a reinforcing material made from pre-cut carbon fibers such as short fibers, process waste fibers, and recycled carbon fibers recovered from CFRP, and to provide a carbon fiber-reinforced concrete or mortar structure that is the hardened product thereof and has a high fiber reinforcing effect. Another object of the present disclosure is to provide a method for producing a carbon fiber reinforced concrete or mortar structure. [Means for solving the problem]

[0010] The above-mentioned problems can be solved by the following aspects of the present invention: <Aspect 1> A carbon fiber-containing concrete or mortar composition containing a carbon fiber aggregate composed at least of carbon fibers and a binder, The carbon fiber aggregate has a spindle shape; A carbon fiber-containing concrete or mortar composition comprising: <Aspect 2> 2. The carbon fiber-containing concrete or mortar composition according to aspect 1, wherein the spindle-shaped carbon fiber aggregates have an average length of 1.5 mm to 60 mm. <Aspect 3> 3. The carbon fiber-containing concrete or mortar composition according to aspect 1 or 2, wherein the average maximum width of the spindle-shaped carbon fiber aggregates is 0.1 mm to 3.0 mm. <Aspect 4> 4. The carbon fiber-containing concrete or mortar composition according to any one of aspects 1 to 3, wherein the carbon fibers have an average length of 1 mm or more and less than 30 mm. <Aspect 5> A carbon fiber-containing concrete or mortar composition according to aspect 4, wherein the average length of the carbon fiber aggregates is 1.2 to 5.0 times the average length of the carbon fibers contained in the carbon fiber aggregates. <Aspect 6> 6. The carbon fiber-containing concrete or mortar composition according to any one of aspects 1 to 5, wherein the content of the binder is 0.1 to 10% by weight based on the weight of the spindle-shaped carbon fiber aggregates. <Aspect 7> 7. The carbon fiber-containing concrete or mortar composition according to any one of aspects 1 to 6, wherein the carbon fibers comprise recycled carbon fibers. <Aspect 8> Aspect 8. The carbon fiber-containing concrete or mortar composition according to any one of Aspects 1 to 7, wherein the carbon fibers are recycled carbon fibers. <Aspect 9> 9. The carbon fiber-containing concrete or mortar composition according to claim 7 or 8, wherein the recycled carbon fibers contain residual carbon components, and the residual carbon components are greater than 0% and not more than 5.0% by weight based on the weight of the recycled carbon fibers. <Aspect 10> A carbon fiber reinforced concrete or mortar structure in which the composition according to any one of aspects 1 to 9 has been cured. <Aspect 11> Producing a spindle-shaped carbon fiber aggregate composed of at least carbon fibers and a binder; A method for producing a carbon fiber reinforced concrete or mortar structure, comprising: <Aspect 12> 12. The method of claim 11, wherein the carbon fibers comprise recycled carbon fibers. <Aspect 13> 13. The method of claim 11 or 12, wherein the carbon fibers are recycled carbon fibers. <Aspect 14> 14. The method according to claim 12 or 13, comprising decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce the recycled carbon fiber. [Effects of the Invention]

[0011] According to the present invention, a carbon fiber-containing concrete or mortar composition that is easy to handle can be provided by using a reinforcing material made from pre-cut carbon fibers, such as short fibers, process waste fibers, or recycled carbon fibers recovered from CFRP, etc., and the hardened product, a carbon fiber-reinforced concrete or mortar structure with a high fiber reinforcing effect, and a method for producing the same can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of one embodiment of an agitator granulator that can be used in the present disclosure. [Figure 2] FIG. 2 is a photograph of a plurality of carbon fiber aggregates according to Example 1. As shown in FIG. [Figure 3] FIG. 3 is a photograph of one carbon fiber aggregate according to Example 1. [Figure 4] FIG. 4 is a photograph of a plurality of carbon fiber aggregates according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The concrete or mortar composition according to the present disclosure comprises: The carbon fiber aggregate includes at least a carbon fiber aggregate including at least a carbon fiber and a binder. Contains spindle-shaped carbon fiber aggregates It is characterized by:

[0014] The concrete or mortar composition according to the present disclosure contains spindle-shaped carbon fiber aggregates. While not intending to be limited by theory, it is believed that the spindle-shaped carbon fiber aggregates are produced by a rolling granulation method, an agitation granulation method, or the like, and therefore the carbon fibers are subjected to a stress in a certain direction, such as centrifugal force, causing the carbon fibers to be bundled together while oriented in a certain direction and firmly fixed by the binder. Therefore, it is believed that the bundles are less likely to come undone when mixed with a concrete composition or the like, and dispersion into individual fibers can be suppressed.

[0015] Furthermore, the concrete or mortar structure according to the present disclosure is preferably reinforced with spindle-shaped carbon fiber aggregates having an average length of 1.5 mm to 60 mm. A feature of spindle-shaped carbon fiber aggregates is that they can be extended as the average length of the carbon fiber aggregates even when the length of the pre-cut carbon fibers used as raw materials is less than 1.5 mm. This increases the anchoring strength of the carbon fiber aggregates as a reinforcing material to concrete structures, etc., making them less likely to be pulled out of the concrete structure, etc., in the presence of tensile stress, resulting in good reinforcing efficiency.

[0016] That is, the present disclosure has discovered that spindle-shaped carbon fiber aggregates have excellent properties as a reinforcing material for concrete structures and the like made from pre-cut carbon fibers, and has thereby provided a cement composite material with a high fiber reinforcing effect.

[0017] The invention according to the present disclosure will be described in further detail below.

[0018] <Carbon fiber aggregate> The carbon fiber aggregate according to the present disclosure is an aggregate composed of at least carbon fibers and a binder. In the carbon fiber aggregate, the individual fibers are bound to each other by the binder.

[0019] The amount of binder in the carbon fiber aggregate is preferably 0.1 to 10% by weight, and particularly may be 0.5 to 8% by weight, or 1 to 6% by weight, relative to the carbon fiber aggregate. If the amount of binder is less than 0.1% by weight, the fibers tend to be unbundled and dispersed into single fibers when mixed with a concrete composition or the like, which can lead to breakage of the single fibers and an increase in the viscosity of the material during mixing, resulting in poor handleability, which is undesirable.

[0020] Furthermore, if the amount of binder exceeds 10% by weight, the weight ratio of the carbon fibers that make up the carbon fiber aggregates will be small, and when compared with the same amount of aggregate added, good reinforcing efficiency will tend not to be obtained.

[0021] The carbon fiber aggregate according to the present disclosure has a spindle shape, which means a shape that is thick in the center and gradually tapers toward both ends.

[0022] As a particularly preferred embodiment of the method according to the present disclosure, a method for obtaining a spindle-shaped carbon fiber aggregate using an agitation granulation method will be described later. As a similar method, a method for obtaining a spindle-shaped carbon fiber aggregate using a tumbling granulation method can be found in, for example, Japanese Patent No. 3452363.

[0023] (average length of aggregates) The average length of the carbon fiber aggregates may be 1.5 mm to 60 mm. Preferably, the average length of the aggregates is 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, or 25 mm or more, and / or preferably 55 mm or less, 50 mm or less, 45 mm or less, or 40 mm or less. If the average length of the carbon fiber aggregates is less than 1.5 mm, the anchoring strength to a concrete structure or the like is small, and the aggregates are likely to be pulled out of the concrete structure or the like as a base material by tensile stress, making it impossible to obtain good reinforcing efficiency, which is not preferable.

[0024] Furthermore, if the average length of the carbon fiber aggregates is greater than 60 mm, it may be difficult to mix the aggregates uniformly into a concrete composition, etc. Furthermore, if the aggregates become entangled during mixing, it may become even more difficult to disperse them uniformly into a concrete composition, etc.

[0025] The average length of the carbon fiber aggregates can be calculated by measuring the lengths of 50 carbon fiber aggregates in the major axis direction visually using a vernier caliper or in an image obtained using a digital camera or an optical microscope, and averaging the measured values.

[0026] Preferably, the average length of the carbon fiber aggregates is 1.2 to 5.0 times the average length of the carbon fibers contained in the carbon fiber aggregates. When the average length of the carbon fiber aggregates is within the above range, good reinforcing efficiency may be obtained.

[0027] Particularly preferably, the average length of the carbon fiber aggregates is 1.4 times or more, 1.5 times or more, or 1.6 times or more, and / or 4.5 times or less, 4.0 times or less, 3.5 times or less, 3.0 times or less, or 2.5 times or less, the average length of the carbon fibers. When the average length of the carbon fiber aggregates is within the above ranges, particularly good reinforcing efficiency may be obtained.

[0028] (average maximum width of the cluster) The average maximum width of the carbon fiber aggregates may be 0.1 mm to 3.0 mm. Preferably, the average length of the aggregates is 0.2 mm or more, 0.3 mm or more, 0.4 mm or more, or 0.5 mm or more, and / or preferably 2.8 mm or less, 2.6 mm or less, 2.4 mm or less, 2.2 mm or less, or 2.0 mm or less. The average maximum width of the carbon fiber aggregates is the largest average length (width) in a direction perpendicular to the longitudinal direction. If the average maximum width of the carbon fiber aggregates is less than 0.1 mm, the aggregates may break, resulting in a large number of short aggregates with low anchoring power to concrete structures, etc., and thus failing to achieve good reinforcing efficiency, which is not preferred.

[0029] Furthermore, when the average maximum width of the carbon fiber aggregates is greater than 3.0 mm, the number of aggregates dispersed in the concrete structure, etc., decreases when compared with the same amount of aggregate added. As a result, the total surface area in contact with the concrete structure, etc., decreases, and good reinforcing efficiency tends to be difficult to achieve.

[0030] The average maximum width of the carbon fiber aggregates can be calculated by measuring the lengths of 50 carbon fiber aggregates in the minor axis direction visually using a vernier caliper or in an image obtained using a digital camera or an optical microscope, and averaging the measured values.

[0031] (aspect ratio) The aspect ratio of the aggregate may be 5 to 150. Preferably, the aspect ratio of the aggregate is 10 or more, 15 or more, 20 or more, 25 or more, or 30 or more, and / or 120 or less, 100 or less, 80 or less, or 60 or less. The aspect ratio of the carbon fiber aggregate is the value obtained by dividing the major axis of the spindle-shaped aggregate by the minor axis, and can be expressed as the average length / average maximum width. The aspect ratio increases as the degree of elongation increases. An aspect ratio of less than 5 is not preferable because the total contact surface area with the concrete structure or the like decreases, resulting in a reduced anchorage, making it impossible to obtain good reinforcing efficiency.

[0032] If the aspect ratio is greater than 150, it becomes difficult to mix uniformly into concrete compositions, etc., and the aggregates may break, so good reinforcing efficiency tends not to be achieved.

[0033] (carbon fiber) Carbon fibers are raw materials for aggregates, and examples thereof include ordinary carbon fibers (carbon fibers that are not recycled, so-called virgin carbon fibers), recycled carbon fibers, and mixtures thereof. The carbon fibers may be, for example, PAN-based carbon fibers or pitch-based carbon fibers.

[0034] The form of the carbon fiber is not particularly limited, but may be a carbon fiber bundle composed of a plurality of single threads (filaments). The number of filaments constituting the carbon fiber bundle may be in the range of 1,000 to 80,000, or 3,000 to 50,000. The diameter of the filaments constituting the carbon fiber may be 0.1 μm to 30 μm, 1 μm to 10 μm, or 3 μm to 8 μm.

[0035] (recycled carbon fiber) Recycled carbon fibers (recycled carbon fibers) contain carbon fiber components and carbon components other than the carbon fiber components (particularly residual carbon components). In recycled carbon fibers, the carbon components other than the carbon fiber components are usually attached to the surface of the carbon fiber components.

[0036] The recycled carbon fiber is not particularly limited, but may be, for example, recycled carbon fiber obtained by heat treating a carbon fiber-containing plastic product such as carbon fiber reinforced plastic (CFRP).

[0037] Particularly preferably, the recycled carbon fibers are recycled carbon fibers obtained by a semiconductor thermal activation method. A particularly preferred embodiment of the following method according to the present disclosure includes decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce recycled carbon fibers.

[0038] The "thermal activation of semiconductors" (TASC method) is a method for decomposing compounds such as polymers using the thermal activation of semiconductors (TASC). For information on methods for producing recycled carbon fiber by decomposing plastic components contained in carbon fiber-containing plastic products using the thermal activation of semiconductors, see, for example, Japanese Patent No. 4517146 and Japanese Patent Laid-Open No. 2019-189674.

[0039] The carbon fiber component in the recycled carbon fiber may be modified by heat treatment or the like during the manufacturing process of the recycled carbon fiber. For details of the carbon fiber component in the recycled carbon fiber, please refer to the above description of the carbon fiber.

[0040] The residual carbon component in recycled carbon fiber is usually derived from the resin contained in the carbon fiber-containing plastic product used as a raw material in producing the recycled carbon fiber. Generally, during the heat treatment process of the carbon fiber-containing plastic product, the plastic component is thermally decomposed, leaving residual carbon on the surface of the carbon fiber component.

[0041] In the present disclosure, the residual carbon component is preferably more than 0% by weight and not more than 5.0% by weight of the recycled carbon fibers, which may result in an assembly with improved reinforcing efficiency.

[0042] Without intending to be limited by theory, it is believed that when the residual carbon component is more than 0 wt % and not more than 5.0 wt %, there is a relatively small amount of carbon components (especially charcoal) that can become foreign matter that can prevent the single fibers from being bundled while aligning them in a certain direction when producing a spindle-shaped carbon fiber aggregate. Therefore, it is believed that since an aggregate that is firmly fixed by the binder can be obtained, the bundle is less likely to come undone when mixed with a concrete composition or the like, and dispersion into the single fibers can be suppressed.

[0043] Preferably, the residual carbon component is 4.0% by weight or less, 3.0% by weight or less, or 2.0% by weight or less relative to the recycled carbon fiber. It is preferable that the residual carbon component is as low as possible, but it may be 0.1% by weight or more, 0.2% by weight or more, 0.4% by weight or more, 0.6% by weight or more, 0.8% by weight or more, 1.0% by weight or more, or 1.2% by weight or more relative to the carbon fiber.

[0044] The content of residual carbon components in recycled carbon fibers can be measured by thermogravimetric analysis (TGA).

[0045] The residual carbon content by thermogravimetry can be measured by the following procedure: (i) A sample piece of 1 to 4 mg obtained by pulverizing the recycled carbon fiber was subjected to a thermogravimetric analysis at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording speed of 1 / 6 s. Temperature rise from room temperature to 100°C, Hold at 100°C for 30 minutes, Temperature increase from 100°C to 400°C, and 480 minutes at 400°C The thermogravimetric analysis was carried out over a total of approximately 600 minutes. (ii) In a graph plotting the weight loss rate against time, the inflection point of the slope is identified, and the amount of residual carbon is calculated by subtracting the weight loss rate during the holding period at 100°C from the weight loss rate value at that inflection point.

[0046] If the inflection point of the slope cannot be identified under the above conditions, instead of holding at 400°C for 480 minutes, the sample may be held at a specific temperature in the range of more than 400°C and not more than 500°C for 480 minutes.

[0047] Furthermore, if the recycled carbon fiber contains a resin derived from a sizing agent or the like, the above measurement can be carried out after removing the resin.

[0048] (average length of carbon fibers) The carbon fibers can have an average length of 1 mm or more and less than 30 mm. Fibers having lengths in this range can be obtained, for example, by cutting fibers having a relatively long dimension. The average length of the carbon fibers can be 2 mm or more, 3 mm or more, or 4 mm or more, and / or 29 mm or less, 28 mm or less, 27 mm or less, 26 mm or less, 25 mm or less, 24 mm or less, 23 mm or less, 22 mm or less, 21 mm or less, or 20 mm or less. In particular, the average length of the carbon fibers can be 8 mm to 25 mm, or 9 mm to 20 mm.

[0049] When the average length of the carbon fibers is 1 mm or more but less than 30 mm, it is believed that the fibers are promoted to be bundled while oriented in a certain direction, making the bundle less likely to unravel when mixed with a concrete composition or the like, and preventing dispersion into individual fibers. While not intending to be limited by theory, it is believed that a sufficiently long average length of the raw material fibers makes it easier for the fibers to be oriented in one direction, resulting in the formation of a spindle-shaped aggregate. Furthermore, a sufficiently short average length of the fibers is believed to prevent the fibers from becoming entangled with each other, thereby promoting uniform fiber orientation.

[0050] The average length of the carbon fibers can be calculated by measuring the lengths of 50 carbon fibers visually using a caliper or in an image obtained using a digital camera or optical microscope, and averaging the measured values.

[0051] <Method for manufacturing spindle-shaped carbon fiber aggregate> The method for producing a spindle-shaped carbon fiber aggregate according to the present disclosure includes the following steps: Providing a mixture at least comprising carbon fibers and a binder-containing liquid (providing step); The mixture is rolled in a container to produce a spindle-shaped precursor (granulation step); Drying the precursor (drying step).

[0052] For each component involved in the above manufacturing method, reference can be made to the above description of the assembly according to the present disclosure.

[0053] <Providing process> The method according to the present disclosure includes providing a mixture at least comprising carbon fibers and a binder-containing liquid. The mixture particularly comprises carbon fibers and a binder-containing liquid.

[0054] The amount of binder-containing liquid in the mixture is preferably 10% by weight to 70% by weight, and particularly preferably 15% by weight to 60% by weight, or 20% by weight to 50% by weight. In this case, the liquid contained in the binder allows the fibers to be bundled particularly well. Also, in this case, the load of the drying process can be reduced because the amount of liquid contained in the binder is not excessive.

[0055] (binder-containing liquid) The binder-containing liquid is a binder dispersion or binder solution, and contains a binder and a solvent or dispersion medium.

[0056] (binder) The binder serves to bundle the carbon fibers in the aggregate and maintain the shape of the aggregate. The binder is not particularly limited, but is preferably a thermoplastic resin or a thermosetting resin. More specifically, examples of binders include epoxy resins, urethane-modified epoxy resins, vinyl ester resins, acrylic resins, polyester resins, phenolic resins, polyamide resins, polyurethane resins, polycarbonate resins, polyetherimide resins, polyamideimide resins, polyimide resins, bismaleimide resins, polysulfone resins, polyethersulfone resins, epoxy-modified urethane resins, polyvinyl alcohol resins, and polyvinylpyrrolidone resins. These resins may be used alone or in combination of two or more.

[0057] Examples of binders include bentonite, lignin sulfonate, molasses, carboxymethyl cellulose, konjac flour, sodium alginate, polyacrylamide, polyvinyl acetate, polyvinyl alcohol, and starch. These can be used alone or in combination of two or more, and can also be used in combination with the above-mentioned resins.

[0058] (solvent, dispersion medium) The solvent or dispersion medium is not particularly limited as long as it is a liquid that can dissolve or disperse the binder. Examples of the solvent or dispersion medium include water, alcohol (e.g., methanol or ethanol), ketone (e.g., methyl ethyl ketone or acetone), hydrocarbon (e.g., cyclohexane, toluene, or xylene), halogenated hydrocarbon (e.g., dichloromethane), amide (e.g., N-methylpyrrolidone or dimethylformamide), and ether (e.g., tetrahydrofuran). The solvent or dispersion medium is particularly preferably water.

[0059] The binder-containing liquid used in the present disclosure can be prepared, for example, by further adding a solvent or dispersion medium to a commercially available sizing agent having a relatively high concentration, which is composed of a binder and a solvent or dispersion medium. In particular, the binder-containing liquid can be prepared by adding a dispersion medium (particularly water) to a sizing agent having a binder and a dispersion medium (particularly water).

[0060] The sizing agent (and the binder-containing liquid obtained by adding a solvent or dispersion medium to the sizing agent) may be, for example, in the form of a water emulsion in which the binder is dispersed in water, and may in particular be a water-based polyurethane.

[0061] The concentration of the binder in the sizing agent is not particularly limited, but may be, for example, 10 to 80% by weight, 20 to 60% by weight, or 30 to 50% by weight.

[0062] The amount of the binder may be 0.5% by weight or more, 1% by weight or more, 1.5% by weight or more, 2.0% by weight or more, or 3.0% by weight or more, and / or 20% by weight or less, 18% by weight or less, 16% by weight or less, 14% by weight or less, or 12% by weight or less, based on the binder-containing liquid. The amount of the binder is particularly preferably 1% by weight to 16% by weight, or 2% by weight to 12% by weight, based on the binder-containing liquid.

[0063] The amount of the binder is preferably 0.1% by weight to 10% by weight, and particularly preferably 0.5% by weight to 8% by weight, or 1% by weight to 6% by weight, based on the carbon fiber aggregate.

[0064] (Open fiber) The fiber components, particularly the carbon fibers, may be subjected to a fiber-opening treatment in advance, which may eliminate entanglement between the fibers and promote the fibers to be oriented in one direction during the granulation step. Carbon fibers that can be used to produce a spindle-shaped carbon fiber aggregate can be subjected to a fiber-opening treatment in advance. By performing the fiber-opening treatment, it may be possible to promote bundling of single fibers while arranging them in a certain direction in the granulation step.

[0065] The method of opening the fibers is not particularly limited, but can be performed by using, for example, a rotary blade. The rotary blade for opening the fibers may be an auxiliary blade provided in the granulator.

[0066] The opening process can also be carried out by high speed stirring.

[0067] (mixture) In the method for producing a spindle-shaped carbon fiber aggregate, the method for obtaining a mixture from carbon fibers and a binder-containing liquid is not particularly limited. The carbon fibers and the binder-containing liquid can be charged in the form of a mixture into a container used in the granulation step. For example, the binder-containing liquid may be poured into a mass of carbon fibers and optionally stirred to obtain a mixture, and this mixture may be charged into a container. Alternatively, the carbon fibers and the binder-containing liquid may be charged separately into a container and mixed in the container to obtain a mixture. Mixing and granulation may be performed simultaneously.

[0068] The carbon fibers and binder-containing liquid in the mixture do not necessarily need to be uniformly distributed within the mixture, and the mixture can be agitated during the granulation process to improve uniformity.

[0069] <Granulation process> In the method for producing a spindle-shaped carbon fiber aggregate according to the present disclosure, a mixture is rolled in a container (hereinafter, this process may be referred to as a "granulation process") to produce a spindle-shaped precursor.

[0070] The method for rolling the mixture in the container is not particularly limited, and any known method (particularly a known granulation method) can be used.

[0071] In particular, a spindle-shaped precursor is produced by rolling the mixture in a container in the clearance between the inner wall of the container and a rotating body in the container. Without intending to be limited by theory, it is believed that by rolling the mixture containing carbon fibers and a binder-containing liquid in the clearance between the inner wall of the container and a rotating body in the container, the fibers are bound to each other via the binder while being oriented in a specific direction, and as a result, a precursor having a spindle shape can be particularly efficiently obtained.

[0072] The method for rolling the mixture in the clearance between the inner wall of the container and the rotating body inside the container is not particularly limited, and an exemplary method for doing so will be described below with reference to FIG.

[0073] FIG. 1 is a schematic diagram of one embodiment of an agitation granulator that can be used in the present disclosure. The agitation granulator 10 in FIG. 1 has a cylindrical container portion 12 as a container and an agitation blade 14 as a rotating body. The agitation granulator 10 in FIG. 1 is horizontal, and in normal use, the opening of the container portion 12 opens to the side. FIG. 1 is a view seen from a perspective looking into the inside of the container portion. A shaft portion 16 is attached to the inner wall of the container portion 12 facing the opening (the wall on the far side from the above perspective). The shaft portion 16 extends horizontally. The agitation blade 14 can rotate around this shaft portion 16 (counterclockwise (“A”) in the example in FIG. 1, but clockwise rotation is also possible). In other words, the agitation blade 14 in FIG. 1 is configured to rotate in a plane parallel to the direction of gravity. Although not shown in FIG. 1, an auxiliary blade for opening fibers can also be installed in the container portion 12.

[0074] In the granulation process, the mixture containing the carbon fiber and the binder-containing liquid is mixed and stirred as desired by the stirring blade 14 rotating in the container portion 12, and is rolled in the clearance (indicated by the symbol "C" in Figure 1) between the inner wall of the container portion 12 and the stirring blade 14 inside the container portion 12.

[0075] The granulation process can be carried out at ambient temperature or with heating, for example, for 1 minute to 1 hour, 5 minutes to 20 minutes, or 8 minutes to 15 minutes.

[0076] (container) The container of the present disclosure is not particularly limited as long as it is suitable for holding the mixture therein and for subjecting the mixture to the above-described granulation treatment. The container is preferably made of a material that is excellent in rigidity and durability. In particular, it is preferable that the inner wall of the container be made of a material that does not undergo wear during the rolling of the mixture, or that the surface of the material be treated to prevent wear.

[0077] In one embodiment according to the present disclosure, the container is not inclined and is substantially parallel to the horizontal direction. For example, a portion of the inner wall of the container that is located lower in the direction of gravity may be not inclined and is substantially parallel to the horizontal direction.

[0078] (rotating body) The rotating body is configured to rotate within the container, thereby allowing the mixture containing the carbon fibers and the binder-containing liquid to roll between the rotating body itself and the inner wall of the container. The rotating body is attached to a shaft portion installed within the container, for example, and is configured to rotate around the shaft portion.

[0079] The rotating body preferably has the form of a blade (impeller). The rotating body is particularly preferably an agitating blade (agitating impeller). The agitating blade is preferably made of a material having excellent rigidity and durability, and in particular, is preferably made of a material that does not wear out while the mixture is rolling, or is preferably surface-treated for this purpose.

[0080] (clearance) The size of the clearance between the inner wall of the container and the rotating body, i.e., the distance between the inner wall of the container and the rotating body, may be constant or may vary continuously or discontinuously.

[0081] The size of the clearance between the inner wall of the container and the rotating body inside the container, i.e., the distance between the inner wall of the container and the rotating body, can be appropriately set depending on the desired size of the carbon fiber aggregate, and may be, for example, 1 to 10 mm.

[0082] (Agitating granulator) As the device having the above-mentioned container and rotor, a known agitation granulator can be used. The agitation granulator is not particularly limited, but for example, a Henschel-type granulator (Henschel mixer), a bag mill-type granulator, or an Eirich-type agitation granulator can be used. The agitation granulator can be either a vertical or horizontal type.

[0083] (fusiform precursor) The spindle-shaped precursor contains carbon fibers and a binder, and also contains a liquid (particularly water) derived from the binder-containing liquid. The liquid (particularly water) in the precursor can be removed by the drying step described below.

[0084] <Drying process> In the method for producing a spindle-shaped carbon fiber aggregate according to the present disclosure, the obtained spindle-shaped precursor is dried.

[0085] The method for drying the precursor is not particularly limited, and the temperature conditions, time conditions, etc. can be determined appropriately depending on the moisture content of the obtained precursor, etc.

[0086] <Carbon fiber-containing concrete or mortar composition> The mortar composition according to the present disclosure can be obtained by adding water to spindle-shaped carbon fiber aggregates, cement, fine aggregate such as sand, and admixtures, and then kneading the mixture. A concrete composition can be obtained by kneading these raw materials with coarse aggregate such as gravel. Such concrete or mortar compositions may contain various additives and other raw materials to improve the properties depending on the application.

[0087] <Carbon fiber addition rate> The carbon fiber content (content) of the spindle-shaped carbon fiber aggregate according to the present disclosure can be selected depending on the application, but is preferably 0.01 to 10% by volume, particularly 0.05 to 5% by volume, 0.1 to 3% by volume, or 0.2 to 1.5% by volume, based on the total volume of the concrete or mortar composition. Furthermore, the spindle-shaped carbon fiber aggregate according to the present disclosure can be used in combination with existing reinforcing fiber materials. A carbon fiber content of less than 0.01% by volume is not preferred because it is difficult to achieve good reinforcing efficiency.

[0088] Furthermore, if the carbon fiber content exceeds 10% by volume, it may be difficult to uniformly mix the aggregates into a concrete composition, etc. Furthermore, the aggregates may become entangled during mixing, making it even more difficult to uniformly disperse them in a concrete composition, etc. Furthermore, this is undesirable because it may increase the viscosity of the concrete composition, etc., making it difficult to handle.

[0089] <Method of adding carbon fiber aggregates> Examples of methods for adding the spindle-shaped carbon fiber aggregate according to the present disclosure to a concrete composition or the like include a method in which cement, fine aggregate, coarse aggregate, etc., and the aggregate are first dry premixed, and then water is added and mixed; or a method in which cement, fine aggregate, coarse aggregate, etc., and water are thoroughly stirred, and then the aggregate is added and mixed.

[0090] As the mixer for kneading, a pan mixer, a tilting mixer, an omni mixer, a Hobart mixer, a truck mixer, or the like can be used.

[0091] <Carbon fiber reinforced concrete or mortar structure> The concrete or mortar structure according to the present disclosure can be produced by curing the concrete or mortar composition obtained as described above. In these structures, the carbon fibers may be present in the form of spindle-shaped carbon fiber aggregates according to the present disclosure, or some or all of the aggregates may be debundled and dispersed into single fibers or fiber bundles. In the methods for producing these structures, by mixing the carbon fiber aggregates with the concrete composition or the like, it is possible to obtain structures in which the carbon fibers are uniformly dispersed with relatively little breakage, even if the carbon fibers are dispersed into single fibers or fiber bundles during production.

[0092] The method for hardening the concrete or mortar composition is not particularly limited, and the curing method and conditions can be determined appropriately depending on the type of structure, construction conditions, location conditions, environmental conditions, etc. For example, the composition may be used in construction and repair methods such as 3D printing, coating, injection, filling, plastering, and spraying. [Example]

[0093] The present invention will be described in more detail below using examples. Note that the examples are merely illustrative and the present application is not limited thereto.

[0094] Example 1 <Material Preparation> (carbon fiber) The carbon fibers used were recycled carbon fibers obtained by semiconductor thermal activation, with an average single fiber diameter of 6.7 μm, a single fiber tensile strength of 5.3 GPa, a Weibull shape factor of 7.6, and a residual carbon content of 1.4 wt%.

[0095] (single fiber tensile strength) The single fiber tensile strength was measured in accordance with JIS R7606 as follows: At least 30 single fibers were collected from the fiber bundle. The diameter of the single fiber is measured in a side image of the single fiber taken by a digital microscope, and the cross-sectional area is calculated. The sampled single fiber was fixed to a perforated mount using adhesive. The mount on which the single fiber was fixed was attached to a tensile tester, and a tensile test was performed with a test length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress. The tensile strength is calculated from the cross-sectional area and tensile breaking stress of the single fiber. The single fiber tensile strength was determined as the average of the tensile strengths of at least 30 single fibers.

[0096] (Weibull shape factor) The Weibull shape factor was calculated according to the following formula: lnln{1 / (1-F)}=m×lnσ+C (In the formula, F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape coefficient, and C is a constant.) A Weibull plot was made using lnln{1 / (1-F)} and lnσ, and the Weibull shape factor m was calculated from the linearly approximated slope.

[0097] (carbon residue amount) The amount of residual carbon in the recycled carbon fiber was determined by thermogravimetric analysis (TGA method) as follows: (i) A 4 mg sample piece obtained by pulverizing the recycled carbon fiber was subjected to a thermogravimetric analysis for a total of approximately 600 minutes, the analysis comprising steps of heating from room temperature to 100°C, holding at 100°C for 30 minutes, heating from 100°C to 400°C, and holding at 400°C for 480 minutes, with an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording speed of 1 / 6 s, in a thermogravimetric analyzer; (ii) In a graph plotting the weight loss rate against time, the inflection point of the slope was identified, and the amount of residual carbon was calculated by subtracting the weight loss rate during the holding period at 100°C from the weight loss rate value at that inflection point.

[0098] (average length of carbon fibers) Recycled carbon fibers cut to an average length of 15 mm were used.

[0099] (binder-containing liquid) A binder-containing liquid (water emulsion sizing agent) containing 10.2 g of urethane resin as a binder and 255 g of water as a dispersion medium was prepared.

[0100] (Granulation processing) For the granulation process, a vertical stirring granulator (30 L MTI mixer, manufactured by Tsukishima Kikai Co., Ltd.) was used.

[0101] The agitator granulator had an agitator blade and also had an auxiliary blade to promote opening of the fibers.

[0102] At the same time as the stirring blade started to rotate, 500 g of the recycled carbon fiber and 265 g of the binder-containing liquid were added to the container of the stirring granulator, and mixing and granulation processing was carried out at ambient temperature for 10 minutes to obtain a spindle-shaped precursor.

[0103] The moisture content of the mixture was 33.3% by weight. The rotation speed of the stirring blade was 290 rpm, and the rotation speed of the auxiliary blade was 5,000 rpm.

[0104] (Drying process) The obtained precursor was dried in a dryer to obtain the carbon fiber aggregate according to Example 1.

[0105] (aggregate) 2 and 3 are photographs of the carbon fiber aggregate according to Example 1. As can be seen from these figures, the carbon fiber aggregate according to Example 1 had a spindle-like shape.

[0106] (binder content) The binder content in the assembly of Example 1 was 2.0 wt %.

[0107] (average length and average maximum width) Measurements were taken using a vernier caliper on 50 specimens (N=50), and the average length of the carbon fiber aggregates according to Example 1 was 32.8 mm and the average maximum width was 0.9 mm. Since the average length of the recycled carbon fibers was 15 mm, the average length of the carbon fiber aggregates was 2.2 times the average length of the recycled carbon fibers.

[0108] (aspect ratio) The aspect ratio (major axis / minor axis) of the aggregates in Example 1 was calculated. The major axis is the length of the aggregate, and the minor axis is the maximum width of the aggregate. From the above measured values, the average value was calculated for 50 specimens (N=50), and the aspect ratio was found to be 36.

[0109] <Production of carbon fiber-containing mortar composition> (Preparation of fresh mortar composition) 9.0 g of the carbon fiber aggregate according to Example 1 was mixed with 1265 g of low-heat Portland cement (manufactured by Taiheiyo Cement Corporation), 569 g of fine aggregate (No. 6 silica sand, manufactured by San-ei Silica Co., Ltd.), 4.5 g of an admixture (water-reducing agent Masterglanium SP8HU, manufactured by BASF), and 380 g of water, using a mortar mixer (5 L MIC-362 model, manufactured by Marui Co., Ltd.) at a stirring speed of 140 rpm for approximately 3 minutes.

[0110] The carbon fiber content in the resulting raw mortar composition was 0.5% by volume, the water / cement ratio was 30.0% by weight, and the fine aggregate / cement ratio was 45.0% by weight.

[0111] (Bundling of carbon fibers after kneading) A small amount of the raw mortar composition was scooped out, washed with water, and the extracted carbon fiber aggregates were visually observed. When the spindle-shaped carbon fiber aggregates were maintained and no cement penetration between the individual fibers was observed, the bundling quality was judged to be good. On the other hand, when the aggregates in which the bundling had come undone and cement penetration between the individual fibers was observed accounted for 10% by weight or more of the total, the bundling quality was judged to be poor. The results are shown in Table 1 below.

[0112] (Fluidity of fresh mortar composition) A flow cone (a hollowed-out cone with a height of 6 cm, a bottom inner diameter of 10 cm, and a top inner diameter of 7 cm) was placed on a horizontally placed 50 cm square aluminum plate, and the ready-mixed mortar composition was poured in at a level level, after which the flow cone was slowly pulled up vertically. The diameter of the ready-mixed mortar composition that spread in a circle on the aluminum plate was measured as the flow value, or, if the circle was distorted, the arithmetic mean of the shortest and longest diameters. The flow value reflects the fluidity of the ready-mixed mortar composition, and ready-mixed mortar compositions with a high flow value tend to have good formability and workability. The results are shown in Table 1 below.

[0113] <Manufacturing carbon fiber reinforced mortar structures> The raw mortar composition of Example 1 was poured into a formwork measuring 40 mm wide x 40 mm high x 160 mm long, cured in air at 20°C for 2 days, and then cured in water at 20°C for 4 days to produce a mortar structure specimen (hardened product) for measuring bending fracture energy.

[0114] The obtained specimens were subjected to three-point bending measurements in accordance with JIS R 5201. More specifically, a universal testing machine (Tensilon universal testing machine RTF2410, manufactured by A&D Co., Ltd.) was used to compress the center of a 10 cm distance between supports at a rate of 2 mm / min. The bending strength was calculated from the maximum bending stress obtained. In addition, the area under the bending stress-loading point displacement curve obtained up to a loading point displacement of 4 mm was calculated and used as the bending fracture energy. The results are shown in Table 1 below.

[0115] Example 2 <Material Preparation> (carbon fiber) The carbon fibers used were the same recycled carbon fibers as in Example 1, except that they were cut to an average length of 10 mm.

[0116] (binder-containing liquid) A binder-containing liquid (water emulsion sizing agent) containing 10.2 g of urethane resin as a binder and 291 g of water as a dispersion medium was prepared.

[0117] <Granulation process> For the granulation treatment, a horizontal stirring granulator (20 L Lödige Mixer, manufactured by Matsubo Co., Ltd.) was used.

[0118] The agitator granulator had an agitator blade and also had an auxiliary blade to promote opening of the fibers.

[0119] At the same time as the stirring blade started to rotate, 500 g of the recycled carbon fiber and 301 g of the binder-containing liquid were added to the container of the stirring granulator, and mixing and granulation processing was carried out at ambient temperature for 10 minutes to obtain a spindle-shaped precursor.

[0120] The moisture content of the mixture was 36.3% by weight. The rotation speed of the stirring blade was 320 rpm, and the rotation speed of the auxiliary blade was 3,000 rpm.

[0121] (Drying process) The obtained precursor was dried in a dryer to obtain a carbon fiber aggregate according to Example 2.

[0122] (aggregate) Fig. 4 is a photograph of the carbon fiber aggregate according to Example 2. The obtained carbon fiber aggregate had a spindle shape.

[0123] (binder content) The binder content in the assembly of Example 2 was 2.0 wt %.

[0124] (average length and average maximum width) The carbon fiber aggregates evaluated in the same manner as in Example 1 had an average length of 18.9 mm and an average maximum width of 1.6 mm. Since the average length of the recycled carbon fibers was 10 mm, the average length of the carbon fiber aggregates was 1.9 times the average length of the recycled carbon fibers.

[0125] (aspect ratio) From the above measured values, the aspect ratio evaluated in the same manner as in Example 1 was 12.

[0126] <Production of carbon fiber-containing mortar composition and carbon fiber reinforced mortar structure> A ready-mixed mortar composition and a mortar structure were prepared and evaluated in the same manner as in Example 1, except that the carbon fiber aggregate of Example 2 was used instead of the carbon fiber aggregate of Example 1. The results are shown in Table 1 below.

[0127] Comparative Example 1 In Comparative Example 1, a raw mortar composition and a mortar structure were produced and evaluated in the same manner as in Example 1, except that virgin carbon fiber bundles cut to an average length of 10 mm (24,000 single fibers per bundle, average single fiber diameter 6.8 μm, single fiber tensile strength 5.4 GPa, Weibull shape coefficient 4.9) were used instead of the aggregate of recycled carbon fibers. The results are shown in Table 1 below.

[0128] ≪Reference example 1≫ Except for not adding carbon fiber and not using fiber reinforcement, a ready-mix mortar composition and a mortar structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[0129] The ready-mixed mortar compositions according to Examples 1 and 2 exhibited fluidity equivalent to that of the ready-mixed mortar composition without fiber reinforcement according to Reference Example 1, and showed better fluidity than the ready-mixed mortar composition according to Comparative Example 1. The reason for this is that the carbon fiber aggregates according to Examples 1 and 2 had a higher bundling power than the cut virgin carbon fiber bundles of Comparative Example 1, and dispersion into single fibers was suppressed, so the viscosity of the ready-mixed mortar compositions did not increase. Furthermore, the mortar structures according to Examples 1 and 2 had higher bending strengths and bending fracture energies than the mortar structure without fiber reinforcement according to Reference Example 1. Therefore, by using the ready-mixed mortar compositions according to Examples 1 and 2, excellent molding workability and reinforcing efficiency can be obtained simultaneously.

[0130] Furthermore, the mortar structure according to Example 1 had even greater bending strength and bending fracture energy than the mortar structure according to Example 2, and despite containing recycled carbon fibers, it exhibited higher bending strength and bending fracture energy than the mortar structure according to Comparative Example 1. Without intending to be limited by theory, the reason for this may be that the carbon fiber aggregates of Example 1 had a longer average length than the aggregates of Example 2, which further increased the anchoring force with the mortar, making the aggregates even more difficult to pull out of the mortar under tensile stress, resulting in particularly good reinforcing efficiency.

[0131] [Table 1] [Explanation of symbols]

[0132] 10 Stirring granulator 12 Container section 14 stirring blades 16 Shaft A Rotation direction C Clearance

Claims

1. A carbon fiber-containing concrete or mortar composition containing a carbon fiber aggregate composed at least of carbon fibers and a binder, The carbon fiber aggregate has a spindle shape; the carbon fiber single fibers are fixed with a binder in a bundled state while being aligned in a certain direction; The average length of the carbon fibers is 1 mm or more and less than 30 mm; the average maximum width of the carbon fiber aggregate is 0.1 mm to 3.0 mm; The average length of the carbon fiber aggregates is 1.2 to 5.0 times the average length of the carbon fibers contained in the carbon fiber aggregates; and The content of the binder is 0.1% by weight to 10% by weight with respect to the carbon fiber aggregate; A carbon fiber-containing concrete or mortar composition comprising:

2. 2. The carbon fiber-containing concrete or mortar composition according to claim 1, wherein the carbon fiber aggregates have an average length of 1.5 mm to 60 mm.

3. 3. The carbon fiber-containing concrete or mortar composition according to claim 1, wherein the carbon fiber comprises recycled carbon fiber and the recycled carbon fiber comprises a residual carbon component, and the residual carbon component is more than 0% by weight and not more than 5.0% by weight relative to the recycled carbon fiber.

4. 4. The carbon fiber-containing concrete or mortar composition of claim 3, wherein the carbon fibers are recycled carbon fibers.

5. A carbon fiber reinforced concrete or mortar structure in which the composition of claim 1 or 2 has been cured.

6. Producing a spindle-shaped carbon fiber aggregate composed of at least carbon fibers and a binder; Including, the carbon fiber single fibers are fixed by a binder in a bundled state while being aligned in a certain direction, The average length of the carbon fibers is 1 mm or more and less than 30 mm, The average maximum width of the carbon fiber aggregate is 0.1 mm to 3.0 mm, The average length of the carbon fiber aggregate is 1.2 to 5.0 times the average length of the carbon fibers contained in the carbon fiber aggregate, and The content of the binder is 0.1% by weight to 10% by weight with respect to the carbon fiber aggregate. A method for manufacturing carbon fiber reinforced concrete or mortar structures.

7. The method according to claim 6, wherein the carbon fiber comprises recycled carbon fiber and the recycled carbon fiber comprises a residual carbon component, and the residual carbon component is greater than 0% by weight and not more than 5.0% by weight relative to the recycled carbon fiber.

8. The method of claim 7 , wherein the carbon fibers are recycled carbon fibers.

9. 9. The method according to claim 7 or 8, comprising producing the recycled carbon fiber by decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method.

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