Concrete reinforcement building materials and concrete components or structures

Abstract

To provide a building material for concrete reinforcement that has high tensile elastic modulus and is excellent in alkali resistance, creep resistance, and productivity, as well as a concrete member or structure reinforced by using the building material.SOLUTION: A building material for concrete reinforcement is composed of polyparaphenylene terephthalamide fibers and a matrix resin. A crystallinity of the polyparaphenylene terephthalamide fibers measured by wide-angle X-ray diffraction is 70% or more. A concrete member or structure is reinforced by the building material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a building material for reinforcing concrete and to a concrete element or structure reinforced thereby. [Background technology]

[0002] Reinforced concrete is widely used in buildings and other structures. In reinforced concrete, the compressive strength is ensured by the concrete itself, and reinforcing bars are embedded in the concrete to reinforce the tensile and shear strength that are insufficient with the concrete alone.

[0003] The service life of reinforced concrete varies depending on the use and environment, but is generally said to be around 50 years, and it is known that the main cause of deterioration of reinforced concrete is rust from the buried reinforcing bars.

[0004] The interior of concrete is a highly alkaline environment (pH = 12.0 or higher), and buried rebars form a stable, thin passive film on their surface to prevent rust. However, over time, carbon dioxide in the air and acid rain cause neutralization (pH drops below 10.0), destroying the passive film and exposing the rebar to a rust-prone environment. For this reason, methods such as coating the rebar surface with epoxy resin, increasing the cover thickness, and applying finishing materials have been used to reduce the risk of rebar rust, but the problem has not yet been completely eliminated.

[0005] Cement, one of the raw materials used in concrete, is known to emit large amounts of carbon dioxide during its production. In fact, the domestic cement industry emits carbon dioxide equivalent to approximately 4% of Japan's total greenhouse gas emissions, making measures to reduce these emissions a crucial issue for realizing a sustainable society.

[0006] In this context, blended cement, which includes blast furnace cement, silica cement, and fly ash cement, is known to have 40% lower CO2 emissions per unit cost than the commonly used ordinary Portland cement, making it an advantageous cement type in terms of "environmental impact," and its use is already being widely promoted.

[0007] On the other hand, concrete made with the above-mentioned blended cement is known to have a faster rate of carbonation than ordinary Portland cement, and the risk of rusting of buried reinforcing bars is higher than with ordinary Portland cement.

[0008] In recent years, aramid fibers braided into a braid and hardened with epoxy resin (hereinafter referred to as "aramid reinforcing bars") have been developed as a reinforcing material for concrete structures instead of steel bars. Aramid reinforcing bars are known to be lightweight, have high tensile strength, and do not rust compared to steel bars of the same diameter.

[0009] On the other hand, aramid fibers are susceptible to hydrolysis in alkaline environments. Therefore, in Patent Document 1, polyparaphenylene terephthalamide fibers are impregnated with a thermosetting resin to form a fiber-reinforced plastic with improved alkali resistance. However, if the polyparaphenylene terephthalamide fibers are exposed due to manufacturing defects or handling during construction, there is a risk of a decrease in strength. Furthermore, because the condition cannot be confirmed after burial, the problem cannot be detected until the concrete collapses.

[0010] Patent Document 2 proposes a fiber composite in which the surface of an aramid fiber is coated with a polyethylene-based resin having excellent alkali resistance. Although the composite certainly has excellent alkali resistance, it requires a step of coating with a thermoplastic resin in advance, and the coated polyethylene-based resin has problems such as poor adhesion to concrete and aramid fibers.

[0011] Patent Document 3 describes that polyparaphenylene terephthalamide fibers with controlled crystal size have excellent alkali resistance and are therefore effective for reinforcing concrete. However, the degree of crystallinity of polyparaphenylene terephthalamide fibers is at most about 65%, which is not sufficient. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-074146 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-186131 [Patent Document 3] Japanese Patent Application Publication No. 58-004812 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made in consideration of the above circumstances, and aims to provide a building material for concrete reinforcement that has a high tensile modulus of elasticity, excellent alkali resistance and creep resistance, and excellent productivity, as well as a concrete member or structure reinforced with the material. [Means for solving the problem]

[0014] In order to achieve the above object, the present inventors have found that the properties of aramid fibers and aramid fibers differ depending on the crystallinity of the polyparaphenylene terephthalamide fibers, 、 Although the details are unclear, this was made based on the finding that polyparaphenylene terephthalamide fibers that meet the objectives of the present invention have a crystallinity of 70% or more as measured by wide-angle X-ray diffraction. That is, the present invention provides polyparaphenylene terephthalamide fibers To the product matrix resin Impregnated withA building material for concrete reinforcement, wherein the polyparaphenylene terephthalamide fiber has a crystallinity measured by wide-angle X-ray diffraction of 75 % or more and The tensile modulus determined in accordance with ASTM D7269 is 100 GPa or more. Tensile strength retention rate after alkali treatment (pH=12.8, 70℃, 48 hours) is 90% or more The present invention provides a building material for reinforcing concrete, characterized by: The present invention also provides a concrete member or structure reinforced with the above-mentioned building material for reinforcing concrete. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a building material for concrete reinforcement that has a high tensile modulus, excellent alkali resistance and creep resistance, and excellent productivity, as well as a concrete member or structure reinforced with the material. DETAILED DESCRIPTION OF THE INVENTION

[0016] The building material for concrete reinforcement of the present invention is composed of polyparaphenylene terephthalamide fibers and a matrix resin, and is characterized in that the polyparaphenylene terephthalamide fibers have a crystallinity of 70% or more as measured by wide-angle X-ray diffraction. This allows for sufficient tensile modulus, alkali resistance, and creep resistance to be obtained when the building material for concrete reinforcement is prepared. The crystallinity is preferably 75% or more, more preferably 78% or more. If the crystallinity is less than 70%, the tensile modulus of the polyparaphenylene terephthalamide fibers becomes insufficient, and sufficient alkali resistance and creep resistance cannot be obtained. On the other hand, if the crystallinity exceeds 85%, the breaking elongation of the polyparaphenylene terephthalamide fibers decreases significantly, and the resulting building material for concrete reinforcement also tends to have a reduced breaking elongation.

[0017] The polyparaphenylene terephthalamide fiber of the present invention preferably has a tensile strength retention of 90% or more after alkali treatment (pH = 12.8, 70°C, 48 hours). If the tensile strength retention is 90% or more, even if the building material for concrete reinforcement of the present invention is defective or the polyparaphenylene terephthalamide fiber is exposed due to handling during construction, deterioration of the performance of the building material is suppressed, thereby preventing a shortened lifespan of the concrete structure. On the other hand, if the tensile strength retention is less than 90%, there is the disadvantage of a shortened lifespan of the concrete structure. The tensile strength retention is preferably 95% or more, and more preferably 98% or more.

[0018] The polyparaphenylene terephthalamide fiber of the present invention desirably has a tensile modulus of 100 GPa or more. Since the building material for concrete reinforcement of the present invention is composed of polyparaphenylene terephthalamide fiber and a matrix resin, the polyparaphenylene terephthalamide fiber is responsible for most of the mechanical properties of the building material for concrete reinforcement of the present invention. If the polyparaphenylene terephthalamide fiber has a tensile modulus of 100 GPa or more, it can exhibit a sufficient reinforcing effect as a building material for concrete reinforcement. On the other hand, if the tensile modulus of the polyparaphenylene terephthalamide fiber is less than 100 GPa, there is the disadvantage that a sufficient reinforcing effect cannot be obtained. The tensile modulus is preferably 105 GPa or more, and more preferably 110 GPa or more.

[0019] The polyparaphenylene terephthalamide fiber of the present invention desirably has a creep of 3.0% or less after being left for 1,000 hours at a temperature of 20°C and a humidity of 65% RH under a stress of 50% of the tensile breaking load determined in accordance with ASTM D7269. If the creep is 3.0% or less, the building material for concrete reinforcement of the present invention will be able to withstand long-term use. If the creep of the polyparaphenylene terephthalamide fiber exceeds 3.0%, there is the disadvantage that the concrete reinforcing effect tends to decrease over time. The creep is preferably 2.9% or less, and more preferably 2.8% or less.

[0020] <Polyparaphenylene terephthalamide fiber> As described above, it is essential for the concrete reinforcing building material of the present invention to use polyparaphenylene terephthalamide fibers having a high tensile modulus and excellent alkali resistance and creep resistance.

[0021] In the present invention, polyparaphenylene terephthalamide (PPTA) is a polymer obtained by polycondensation of terephthalic acid and paraphenylenediamine, but a copolymer of small amounts of dicarboxylic acid and diamine can also be used. The molecular weight (weight average molecular weight) of the polymer or copolymer is usually 20,000 to 25,000.

[0022] Ordinary polyparaphenylene terephthalamide fibers are produced by dissolving polyparaphenylene terephthalamide in concentrated sulfuric acid, extruding the resulting viscous solution through a spinneret, and spinning it into air or water to form filaments, which are then neutralized with an aqueous sodium hydroxide solution and finally dried and heat-treated at 120 to 500°C. An oil is then applied and allowed to penetrate the fibers (see U.S. Patent No. 3,767,756).

[0023] The polyparaphenylene terephthalamide fiber of the present invention is prepared by, in addition to the usual drying and heat treatment, further adjusting the heat treatment conditions at 200°C or higher under a constant tension while adjusting the crystallinity of the polyparaphenylene terephthalamide fiber to 70% or higher as measured by wide-angle X-ray structural diffraction. The additional heat treatment may be carried out in a separate step after the production of ordinary polyparaphenylene terephthalamide fibers, or may be carried out immediately after the ordinary drying and heat treatment step.

[0024] The oil may be any of the common oils that can be used with polyparaphenylene terephthalamide fibers, such as fatty acid esters, polyoxyethylene polyoxypropylene copolymers or their derivatives, and mineral oils. Among these, an oil containing at least one polyether compound selected from polyoxyethylene polyoxypropylene copolymers and their derivatives in an amount of at least 50% by mass based on the total amount of the oil is preferred. The polyether compounds are easy to handle (easily refined) because they can be easily washed away with aqueous solvents, and are also preferred because they often have excellent affinity with matrix resins. The amount of oil applied to the polyparaphenylene terephthalamide fibers is preferably 0.3 to 5% by mass, more preferably 0.4 to 3% by mass, and even more preferably 0.5 to 2% by mass.

[0025] It is more preferable that the oil contains a component having a reactive functional group, such as a curable epoxy compound (aliphatic epoxy compound or aromatic epoxy compound).The use of such an oil can improve the adhesion between the polyparaphenylene terephthalamide fiber and the matrix resin. Examples of the curable epoxy compound include polyglycidyl ethers of polyhydric alcohols. Specific examples include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether. The curable epoxy compound may be used alone or in combination of two or more.

[0026] The curable epoxy compound is preferably blended in an amount of 20 to 50 mass % relative to the total amount of the oil solution, more preferably 30 to 50 mass %, and even more preferably 35 to 50 mass %. By using such blended oil solutions, polyparaphenylene terephthalamide fibers can be obtained that have good adhesion to the matrix resin and are excellent in productivity and sizing. Furthermore, increased adhesive strength between the polyparaphenylene terephthalamide fibers and the matrix resin leads to improved interfacial adhesion between the polyparaphenylene terephthalamide fibers and the matrix resin, thereby preventing external alkaline solutions from penetrating into the polyparaphenylene terephthalamide fiber bundle.

[0027] The polyparaphenylene terephthalamide fibers of the present invention may be continuous fibers, and there are no limitations on the thickness of the fibers as long as they are capable of functioning as a building material for reinforcing concrete.

[0028] <Matrix resin> In the present invention, the matrix resin is an essential component of the building material for reinforcing concrete of the present invention, and is used by impregnating polyparaphenylene terephthalamide fibers. The type of matrix resin is not particularly limited, and at least one selected from thermoplastic resins and thermosetting resins can be used depending on the purpose. Thermoplastic resins exhibit plasticity when heated, so using a thermoplastic resin can provide a building material for concrete reinforcement that can be bent on-site. Thermosetting resins do not exhibit plasticity when heated, so using a thermosetting resin can provide a building material for concrete reinforcement that has excellent heat resistance and fire resistance.

[0029] Examples of thermoplastic resins include polypropylene resin, polyethylene resin, ABS resin, polyvinyl chloride resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene sulfide resin, polyamide resin, modified polyphenylene ether resin, liquid crystal polyester resin, polyimide resin, syndiotactic polystyrene resin, polycyclohexanedimethylene terephthalate resin, thermoplastic epoxy resin, etc. Examples of thermosetting resins include unsaturated polyester resin, phenol resin, vinyl ester resin, thermosetting epoxy resin, urea resin, etc.

[0030] Among the above resins, resins that have excellent alkali resistance and excellent adhesion to polyparaphenylene terephthalamide fibers are preferred, and specific examples include thermoplastic epoxy resins, urea resins, unsaturated polyester resins, thermosetting epoxy resins, etc. The use of these matrix resins has the advantage of extending the life of the building material for concrete reinforcement of the present invention and the concrete reinforced with said building material.

[0031] The matrix resin used in the present invention can be blended with various additives as needed, as long as the effects of the present invention are not impaired. Examples of additives include heat stabilizers, light stabilizers, UV absorbers, hydrolysis inhibitors, antioxidants, lubricants, nucleating agents, plasticizers, color inhibitors, matting agents, flame retardants, antistatic agents, mold release agents, fillers (fillers such as glass fiber, carbon fiber, glass beads, hollow glass, and talc), pigments, and dyes. One or more additives selected from these additives can be blended. The amounts of these additives to be blended may be those typically used.

[0032] <Construction material for concrete reinforcement> The building material for reinforcing concrete of the present invention can be produced by impregnating the above-mentioned polyparaphenylene terephthalamide fiber with a matrix resin. As a specific example, the building material for concrete reinforcement of the present invention is produced through a) a step of producing a textile product such as a braided cord or cloth from polyparaphenylene terephthalamide fibers, b) a step of impregnating the obtained textile product such as the braided cord or cloth with a matrix resin, c) a step of curing the impregnated matrix resin, and, if necessary, d) a step of cutting the obtained polyparaphenylene terephthalamide fiber-matrix resin composite. Before or after the above step a), a step of washing away the oil agent adhering to the surface of the polyparaphenylene terephthalamide fiber (refining step) may be included. Furthermore, in the above step b), the impregnation rate, as represented by the following formula (I), is preferably 95% or more, and more preferably 97% or more. If the impregnation rate is less than 95%, stress transmission is likely to be insufficient, and not only will the function (reinforcing effect) of a building material for reinforcing concrete not be fully exhibited, but there is also the risk that alkaline liquids will easily penetrate into the unimpregnated portions. Impregnation rate (%)=A / (A+B)×100 (I) A: The total area of ​​the fiber and resin in any cross section of the building material B: The total area of ​​voids in any cut surface of the building material

[0033] Furthermore, curved building materials are manufactured through the steps of: a) producing a braid or the like from polyparaphenylene terephthalamide fiber yarn; b) impregnating the obtained braid or the like with a matrix resin; c) setting the braid or the like in a molding frame having a desired curved shape; d) curing the impregnated matrix resin; and e) cutting the obtained resin-impregnated braid or the like.

[0034] The above manufacturing process may include, as desired, a step of attaching powdery material such as sand or silica to a fiber product such as a braided cord or fabric impregnated with a matrix resin in order to improve adhesive strength with concrete. The particle size of the powdery material is not limited as long as it does not impair the object of the present invention, but a particle size of approximately 0.1 to 5.0 mm is preferred.

[0035] As for the form of the above-mentioned fiber product, braided cord, twisted cord, or fabric is desirable, with braided cord and twisted cord being more preferable, because they have a moderate surface unevenness and excellent adhesive strength to concrete. Known methods can be used for the braiding method. Braided cords are usually produced using a braiding machine (braiding machine), and any braided cord shape, such as round braid, square braid, or flat braid, can be produced. Examples of knitting methods include a method in which four filaments are prepared and the right and left filaments are alternately placed in the middle and braided. The number of filaments used for braiding is not limited to four, but can be eight, twelve, sixteen, or the like. The number of braided cords or twisted cords used in building materials for concrete reinforcement is not particularly limited, and any desired number can be used.

[0036] The shape of the building material for concrete reinforcement may be linear or curved, and an appropriate shape can be selected as desired. Examples of the curved shapes include U-shapes, L-shapes, and spiral shapes, as well as polygonal shapes such as triangles, squares, pentagons, and hexagons. The curved shapes are not limited to these, and materials bent into various shapes can be used depending on the case.

[0037] One of the reasons for using polyparaphenylene terephthalamide fiber in the present invention, which has a crystallinity of 70% or more as measured by wide-angle X-ray diffraction, is that it has a higher tensile modulus than copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fiber. Therefore, if the polyparaphenylene terephthalamide fiber of the present invention is not used, aramid fiber satisfying the tensile strength retention, tensile modulus, and creep defined in the present invention cannot be obtained. In other words, the key point is to be able to maintain a high tensile strength retention in an alkaline environment, which is important for building materials used in concrete reinforcement.

[0038] <Concrete members or structures> Another aspect of the present invention is a concrete member or a concrete structure using the above-mentioned building material for reinforcing concrete as a reinforcing material.

[0039] Concrete components include components used in existing concrete structures that are subject to external impacts, such as PC sleepers and utility poles.

[0040] When the building material for concrete reinforcement of the present invention is applied to a concrete member, the building material is preferably formed into at least one of the following forms using polyparaphenylene terephthalamide fibers: strand, woven or knitted fabric, braided cord, or twisted cord. For example, the concrete member is reinforced on-site by using a woven or knitted fabric made of polyparaphenylene terephthalamide fibers and a matrix resin, and adhering the polyparaphenylene terephthalamide fibers impregnated with the matrix resin to the surface of the concrete member.

[0041] In another embodiment, a concrete member is reinforced by using a braided or twisted cord made of polyparaphenylene terephthalamide fiber and a matrix resin, and the polyparaphenylene terephthalamide fiber is impregnated with the matrix resin, which is inserted into or penetrates holes in the concrete member and adhered thereto.

[0042] In another embodiment, a concrete member is reinforced by a method in which a strand, woven or knitted fabric, or braided cord made of polyparaphenylene terephthalamide fiber and a matrix resin are used, and the polyparaphenylene terephthalamide fiber is impregnated with the matrix resin and spirally wound around the concrete member.

[0043] Concrete structures for civil engineering applications include, for example, railway facilities, road facilities, energy facilities (thermal power plants, wind power plants, nuclear power plants, hydroelectric power plants, gas storage facilities, etc.), dam and river facilities, water supply and sewerage facilities, airport facilities, etc., and for architectural applications include, for example, buildings, hospitals, schools, houses, factories, etc.

[0044] When the building material for concrete reinforcement of the present invention is applied to a concrete structure, the building material is formed into a braided cord using polyparaphenylene terephthalamide fibers, and the braided cord and a matrix resin are used to impregnate the polyparaphenylene terephthalamide fibers with the matrix resin, and the resulting material is molded into a braided rod, a round rod, an irregularly shaped rod, a flat rod, a two-dimensional lattice, or the like.

[0045] The concrete reinforcement building material of the present invention has excellent alkali resistance, and therefore is particularly effective in the embodiment relating to the concrete members and concrete structures described above, in which it is embedded inside concrete to reinforce it. Furthermore, the building material for concrete reinforcement of the present invention is suitable for civil engineering applications. This is because civil engineering work is mainly carried out outdoors, and there are many environmental factors that cause conventional reinforcing bars to rust (rain, acid rain, seawater, corrosive gases such as SOx and NOx, lightning, snow-melting agents, etc.). Use of the building material for concrete reinforcement of the present invention is expected to reduce management costs and extend the lifespan of structures. Therefore, it can be said that the building material for concrete reinforcement of the present invention can provide great benefits.

[0046] In recent years, in connection with various efforts to reduce the environmental impact, efforts have been made to reduce the amount of cement used, which has a large environmental impact among the materials that make up concrete, and to utilize industrial by-products instead. For example, as representative examples of cement that incorporates a large amount of industrial by-products with low CO2 emissions per unit cost, blast furnace cement that uses blast furnace slag as an admixture, silica cement that uses a silica-based admixture, and fly ash cement that uses fly ash as an admixture have been proposed. Concrete using blended cement in which such admixtures are mixed with conventional Portland cement is expected to contribute to decarbonization (see, for example, JP 2018-145033 A and JP 2015-202978 A).

[0047] However, concrete containing a high proportion of blast furnace slag has the problem of a faster rate of carbonation than conventional concrete. To solve these problems, methods have been proposed, such as using water-reducing agents to suppress carbonation and removing causative substances from siliceous by-products, but the use of the building material for concrete reinforcement of the present invention may make a significant contribution to decarbonization. Here, neutralization refers to the process in which, when originally alkaline concrete is left in the air for a long period of time, the surface reacts with carbon dioxide (CO2) in the air, producing calcium carbonate as shown in equation (II), and the pH decreases to around 8.5 to 10. Ca(OH)2+CO2→CaCO3+H2O (II)

[0048] Carbonation of concrete containing reinforcing bars, unlike when the soil is alkaline, reduces the anti-corrosion function of the reinforcing bars, causing deterioration of concrete structures. When reinforcing bars rust, the volume of the rust increases to 2 to 4 times the original volume of the reinforcing bars, which causes more cracks to form on the concrete surface, allowing water and air to penetrate through the cracks and accelerating corrosion of the reinforcing bars in the concrete. In other words, carbonation has a significant impact on the durability of reinforced concrete structures. The prediction formula for this carbonation rate is known to follow the √t law of elapsed time, and is based on the relationship x = A√t between the carbonation period t and the carbonation depth x.

[0049] Because the building material for concrete reinforcement of the present invention has excellent alkali resistance, it can be preferably used for concrete with a carbonation rate coefficient of 2.5 mm / √week or more in an accelerated test, as determined by JIS A1153:2012, Accelerated Carbonation Test Method for Concrete, 6.1, Carbonation Acceleration Method (conventional concrete carbonation rate coefficient: 2.1 mm / √week). Carbonation causes the reinforcing steel bars in concrete members to rust and expand, causing cracks in the concrete and shortening the concrete's lifespan. Concrete with a carbonation rate coefficient of 2.5 mm / √week or more has a significant impact on the reinforcing steel bars. However, by applying the building material for concrete reinforcement of the present invention, it is possible to eliminate deterioration due to rusting of the reinforcing steel bars.

[0050] On the other hand, concrete with a carbonation rate coefficient of less than 2.5 mm / √week has the disadvantage that it is difficult to obtain the sufficient effect of the building material for concrete reinforcement of the present invention.In order to expect the sufficient effect of the building material for concrete reinforcement of the present invention, the carbonation rate coefficient of the concrete structure is preferably 3.0 mm / √week or more, and more preferably 4.0 mm / √week or more.

[0051] As described above, the building material for concrete reinforcement of the present invention is composed of polyparaphenylene terephthalamide fibers with a high degree of crystallinity and a matrix resin, and has excellent alkali resistance and low creep, making it suitable for a wide range of uses. Furthermore, unlike reinforcing bars, it is lightweight and easy to handle. Unlike reinforcing bars, it can be used to construct concrete members and structures without the risk of corrosion. [Example]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In the following examples, "% by mass" will be abbreviated to "%" unless otherwise specified. The evaluation methods described in the examples are as follows.

[0053] (1) Crystallinity A 20 mg piece of polyparaphenylene terephthalamide fiber bundle was cut into 4 cm pieces and weighed. Both ends of the fiber bundle were tied with enameled wire to prepare a sample. The prepared sample was placed in a fiber sample holder and subjected to wide-angle X-ray diffraction measurement. The obtained wide-angle X-ray diffraction pattern was subjected to peak separation, and the degree of crystallinity was calculated from the obtained crystalline peak area and amorphous peak area. <Measurement conditions> Equipment: Rigaku SmartLab for polymers X-ray source: CuKα (using Ni filter) Output: 40kV 50mA Detector: D / teX (one-dimensional detector) Measurement direction: Equatorial scan <Calculation of crystallinity> Crystallinity (%) = crystalline peak area / (crystalline + amorphous peak area) × 100

[0054] (2) Tensile properties The polyparaphenylene terephthalamide fibers obtained in the Production Examples were evaluated in accordance with ASTM D7269 to measure the tensile strength (Section 11; Breaking Strength) and tensile modulus (Section 15; Modulus).

[0055] (3) Alkali resistance evaluation The polyparaphenylene terephthalamide fibers obtained in the Production Example were placed in a pressure vessel so that they were completely immersed in a sodium hydroxide solution adjusted to pH 12.8. After closing the lid of the pressure vessel, the fibers were treated in an oven at 70°C for 48 hours. After treatment, the fibers were washed with ion-exchanged water (until the pH of the aqueous solution reached 8.6 or less), dried at 50°C for at least 4 hours until the moisture content of the fibers reached 10% or less, and then left to stand in a room at 20°C and 65% RH for 24 hours. The tensile strength was determined by the method (2) above, and the retention rate before and after the treatment was calculated.

[0056] (4) Creep resistance evaluation The polyparaphenylene terephthalamide fibers obtained in the Production Examples were measured for breaking load (Section 12: Breaking Tenacity) at room temperature of 20°C and humidity of 65%RH using a constant-rate extension tensile tester according to ASTM D7269. After applying a load of 50% of the breaking load for 1000 hours, the fiber length was measured and the creep rate was calculated using the following formula. Creep rate (%) = [(Lc-Lo) / Lo] x 100 (Lo: original yarn length (mm), Lc: yarn length after 1000 hours (mm))

[0057] [Manufacturing Example 1] 1 kg of paraphenylene terephthalamide (molecular weight approximately 20,000) obtained by a conventional method was dissolved in 4 kg of concentrated sulfuric acid, and the solution was passed through a die with 1,000 holes of 0.1 mm diameter at a shear rate of 30,000 sec -1 The mixture was extruded so that the melting point was 100°C, spun into water at 4°C, neutralized with a 10% aqueous sodium hydroxide solution at 10°C for 15 seconds, and then heated and dried at 200°C for 15 seconds. The mixture was then further heated and dried at 220°C for 10 seconds at half the tension used in the above-mentioned heating and drying process, yielding polyparaphenylene terephthalamide fiber (total fineness 3,300 dtex) with a moisture content of 3.0%. A polyoxyethylene polyoxypropylene copolymer was applied as an oil to the polyparaphenylene terephthalamide fiber in an amount of 1.0% based on the fiber mass when converted to a moisture content of 0%, and then the fiber was wound up and packaged.

[0058] [Manufacturing Example 2] The same procedure as in Production Example 1 was carried out except that the additional drying heating conditions were 240°C x 10 seconds, to obtain polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 2.8%.

[0059] [Manufacturing Example 3] The same procedure as in Production Example 1 was carried out, except that the oil applied was a mixture of glycerol polyglycidyl ether and polyethylene glycol fatty acid ester in a mass ratio of 60:40, to obtain polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 3.2%.

[0060] [Manufacturing Example 4] The same procedure as in Production Example 1 was carried out except that the additional drying heating conditions were 260°C x 10 seconds, to obtain polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 2.8%.

[0061] [Manufacturing Example 5] The same procedure as in Production Example 1 was carried out except that no additional drying and heating was carried out, to obtain polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 6.8%.

[0062] [Manufacturing Example 6] The fiber used was "Technora" (registered trademark) manufactured by Teijin Ltd. (copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fiber; 3,300 dtex).

[0063] [Examples 1 to 4, Comparative Examples 1 and 2] The evaluation results of the crystallinity, tensile modulus, tensile strength retention (alkali resistance), and creep resistance of the polyparaphenylene terephthalamide fibers obtained in Production Examples 1 to 5 and the copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fiber obtained in Production Example 6 are shown in Table 1.

[0064] [Table 1]

[0065] As shown in Table 1, polyparaphenylene terephthalamide fibers with a crystallinity of less than 70% were poor in tensile modulus, alkali resistance, and creep resistance (Comparative Example 1). Aramid fibers containing copolymer components were excellent in alkali resistance but poor in tensile modulus and creep resistance (Comparative Example 2). This shows that these fibers are insufficient as building materials for concrete reinforcement.

[0066] On the other hand, the polyparaphenylene terephthalamide fibers of Examples 1 to 4 are excellent in tensile modulus, alkali resistance and creep resistance, and are therefore capable of exhibiting excellent functionality as building materials for reinforcing concrete. [Industrial Applicability]

[0067] The construction material for concrete reinforcement of the present invention is useful as a substitute for reinforcing bars and can contribute to the realization of a carbon-free society.

Claims

1. A building material for concrete reinforcement, in which a polyparaphenylene terephthalamide fiber product is impregnated with a matrix resin, The polyparaphenylene terephthalamide fiber is The crystallinity as measured by wide-angle X-ray diffraction is 75% or more, and The tensile modulus determined in accordance with ASTM D7269 is 100 GPa or more, A building material for reinforcing concrete, characterized in that it has a tensile strength retention rate of 90% or more after alkali treatment (pH = 12.8, 70°C, 48 hours).

2. 2. The building material for concrete reinforcement according to claim 1, wherein the polyparaphenylene terephthalamide fiber has a creep of 3.0% or less after being left for 1,000 hours at a stress of 50% of the tensile breaking load determined in accordance with ASTM D7269.

3. A building material for reinforcement of coke as described in claim 1, wherein the polyparaphenylene terephthalamide fiber has an oil applied to its surface.

4. A concrete member or structure reinforced with the building material according to any one of claims 1 to 3.

5. 5. The concrete member or structure according to claim 4, wherein the carbonation rate coefficient in an accelerated test determined in accordance with JIS A1153 is 2.5 mm / √week or more.

6. 6. The concrete member or structure according to claim 4 or 5, which is used for civil engineering purposes.

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