JP2023023903A - Building material for concrete reinforcement, and concrete member or structure - Google Patents

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

The present invention relates to a building material for concrete reinforcement and a concrete member or structure reinforced thereby.

Reinforced concrete is widely used for structures such as buildings. Reinforced concrete secures compressive strength with concrete, and reinforcing bars are embedded in the concrete to reinforce tensile strength and shear strength that are insufficient in concrete alone.

The service life of reinforced concrete depends on the application and environment, but it is generally said to be around 50 years, and it is known that the main cause of deterioration of reinforced concrete is deterioration due to rusting of embedded reinforcing bars. .

The inside of concrete is in a highly alkaline environment (pH = 12.0 or higher), and the embedded reinforcing bars form a stable thin passive film on their surfaces to prevent the generation of rust. However, as time passes, carbon dioxide in the air, acid rain, etc. progresses neutralization (pH becomes 10.0 or less), destroying the passive film and exposing it to a rusting environment. For this reason, methods such as coating the surface of reinforcing bars with epoxy resin, increasing the thickness of the cover, and applying finishing materials have been used to reduce the risk of rusting on reinforcing bars, but the risk has not been completely eliminated. .

By the way, it is known that cement, which is one of raw materials for concrete, emits a large amount of carbon dioxide during its production. In fact, the domestic cement industry emits carbon dioxide equivalent to about 4% of Japan's total greenhouse gas emissions. It has become a challenge.

Under these circumstances, mixed cement containing blast-furnace cement, silica cement, and fly ash cement has a 40% lower _CO2 emissions per unit price than ordinary Portland cement, which is widely used in general. It is known to be a cement type with strengths, and its utilization has already been widely promoted.

On the other hand, concrete using the mixed cement is known to have a faster neutralization rate than ordinary Portland cement, and the risk of rusting of embedded reinforcing bars is higher than that of ordinary Portland cement.

In recent years, aramid fibers are braided into braids and hardened with epoxy resin (hereinafter referred to as "aramid bars") as reinforcing members for concrete structures in place of reinforcing bars. Aramid steel is lighter than steel bars of the same diameter, has higher tensile strength, and is known as a material that does not rust.

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 improve alkali resistance as a fiber-reinforced plastic. However, if the polyparaphenylene terephthalamide fiber is exposed due to defects during manufacturing or handling during construction, there is a risk that the strength will decrease. can't notice

Patent Document 2 proposes a fiber composite in which the surfaces of aramid fibers are 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 resin has poor adhesion to concrete and aramid fibers. be.

Patent Document 3 describes that polyparaphenylene terephthalamide fibers whose crystal size is controlled are excellent in alkali resistance and are effective for reinforcing concrete. However, the crystallinity of polyparaphenylene terephthalamide fibers is at most about 65%, which is not sufficient.

JP 2003-074146 A JP 2016-186131 A JP-A-58-004812

The present invention has been made in view of the above circumstances, and has a high tensile modulus, excellent alkali resistance and creep resistance, and excellent productivity. The object is to provide a concrete member or structure.

In order to achieve the above object, the present inventors have obtained the knowledge obtained from the results of examination of aramid fibers and aramid muscles, that is, that the properties of polyparaphenylene terephthalamide fibers differ depending on the degree of crystallinity, and that the details are unknown. However, it was made based on the finding that the polyparaphenylene terephthalamide fiber that meets the object of the present invention has a degree of crystallinity of 70% or more as measured by wide-angle X-ray diffraction.
That is, the present invention provides a building material for concrete reinforcement comprising a polyparaphenylene terephthalamide fiber and a matrix resin, wherein the polyparaphenylene terephthalamide fiber has a degree of crystallinity measured by wide-angle X-ray diffraction. To provide a building material for reinforcing concrete, characterized in that the is 70% or more.
The present invention also provides a concrete member or structure reinforced by the building material for concrete reinforcement.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a building material for concrete reinforcement which has a high tensile modulus, excellent alkali resistance and creep resistance, and excellent productivity, and a concrete member or structure reinforced thereby. can be done.

The building material for concrete reinforcement of the present invention is composed of polyparaphenylene terephthalamide fibers and a matrix resin, and the polyparaphenylene terephthalamide fibers have a crystallinity measured by wide-angle X-ray diffraction. is 70% or more. This makes it possible to obtain sufficient tensile modulus, alkali resistance, and creep resistance when preparing a building material for reinforcing concrete. The crystallinity is preferably 75% or more, more preferably 78% or more. If the degree of crystallinity is less than 70%, the tensile elastic modulus of the polyparaphenylene terephthalamide fiber is insufficient, and sufficient alkali resistance and creep resistance cannot be obtained. On the other hand, when the degree of crystallinity exceeds 85%, the elongation at break of the polyparaphenylene terephthalamide fiber is extremely lowered, and the elongation at break of the resulting building material for reinforcing concrete tends to be lowered.

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 rate is 90% or more, even if the building material for concrete reinforcement of the present invention has a product defect, or even if the polyparaphenylene terephthalamide fiber is exposed due to handling during construction. Since deterioration of the performance of building materials is suppressed, it is possible to prevent shortening of the service life of concrete structures. On the other hand, when the tensile strength retention rate is less than 90%, there is a problem that the service life of the concrete structure is shortened. The tensile strength retention rate is preferably 95% or more, more preferably 98% or more.

The polyparaphenylene terephthalamide fiber of the present invention preferably 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 matrix resin, the polyparaphenylene terephthalamide fiber is the mechanical property of the building material for concrete reinforcement of the present invention. responsible for most of the If the tensile elastic modulus of the polyparaphenylene terephthalamide fiber is 100 GPa or more, it can exhibit a sufficient reinforcing effect as a building material for reinforcing concrete. On the other hand, if the tensile elastic modulus of the poly-paraphenylene terephthalamide fiber is less than 100 GPa, there is an inconvenience that a sufficient reinforcing effect cannot be obtained. The tensile elastic modulus is preferably 105 GPa or more, more preferably 110 GPa or more.

The poly-p-phenylene terephthalamide fiber of the present invention has a stress of 50% of the tensile breaking load determined according to ASTM D7269, a temperature of 20 ° C. and a humidity of 65% RH for 1,000 hours. It is desirable to be 3.0% or less. If the above creep is 3.0% or less, the building material for reinforcing concrete of the present invention can withstand long-term use. If the creep of the polyparaphenylene terephthalamide fiber exceeds 3.0%, there is a problem that the reinforcing effect of concrete tends to decrease with time. The creep is preferably 2.9% or less, more preferably 2.8% or less.

<Polyparaphenylene terephthalamide fiber>
As described above, it is essential for the building material for concrete reinforcement of the present invention to use polyparaphenylene terephthalamide fibers that have a high tensile modulus and are excellent in alkali resistance and creep resistance.

In the present invention, poly-p-phenylene terephthalamide (PPTA) is a polymer obtained by polycondensation of terephthalic acid and p-phenylenediamine, but copolymers 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 desirably 20,000 to 25,000.

Ordinary poly-p-phenylene terephthalamide fibers are made by dissolving poly-p-phenylene terephthalamide in concentrated sulfuric acid, extruding the viscous solution from a spinneret, and spinning in air or water to form filaments. It is neutralized with an aqueous sodium oxide solution, and finally dried and heat-treated at 120 to 500°C. After that, an oil solution is applied and the fibers are permeated to manufacture (see US Pat. No. 3,767,756).

The polyparaphenylene terephthalamide fiber of the present invention is measured by wide-angle X-ray structure diffraction while changing the heat treatment conditions at 200 ° C. or higher under constant tension in addition to ordinary drying and heat treatment. The crystallinity of the amide fiber is adjusted to 70% or more.
The above additional heat treatment may be carried out in a separate step after the normal polyparaphenylene terephthalamide fiber is produced, or may be carried out continuously immediately after the normal drying and heat treatment steps.

As the oil agent, general oil agents that can be used for polyparaphenylene terephthalamide fibers can be used, and examples thereof include fatty acid esters, polyoxyethylene polyoxypropylene copolymers or derivatives thereof, and mineral oils. be done. Among them, an oil containing at least 50% by mass of at least one polyether compound selected from polyoxyethylene polyoxypropylene copolymers and derivatives thereof is preferred. The above polyether compounds are preferable because they are easy to handle (easy to refine) because they can be easily washed away with an aqueous solvent, and they often have excellent affinity with the matrix resin. The amount of the oil agent attached to the polyparaphenylene terephthalamide fiber is preferably 0.3 to 5% by mass, more preferably 0.4 to 3% by mass, and still more preferably 0.5 to 2% by mass.

Further, it is more preferable that the oil contains a component having a reactive functional group, such as a curable epoxy compound (aliphatic epoxy compound, aromatic epoxy compound). By using such an oil agent, it is possible to improve the adhesiveness between the polyparaphenylene terephthalamide fiber and the matrix resin.
Examples of the curable epoxy compounds include polyglycidyl etherified polyhydric alcohols. Specific examples include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether and the like. The curable epoxy compounds may be used singly or as a mixture of two or more.

The curable epoxy compound is preferably blended in an amount of 20 to 50% by mass, with the total amount of the oil agent being 100%. More preferably 30 to 50 mass %, still more preferably 35 to 50 mass %. By using such a blended oil agent, it is possible to obtain polyparaphenylene terephthalamide fibers that have good adhesiveness to the matrix resin and are excellent in productivity and bundling properties. Further, when the adhesive strength between the polyparaphenylene terephthalamide fiber and the matrix resin increases, it leads to the improvement of the interfacial adhesiveness between the polyparaphenylene terephthalamide fiber and the matrix resin. It is possible to suppress the intrusion of the alkaline solution from the

Since the polyparaphenylene terephthalamide fiber of the present invention may be a continuous fiber, the thickness of the fiber is not limited as long as it can exhibit its function as a building material for reinforcing concrete.

<Matrix resin>
In the present invention, the matrix resin is an essential component of the building material for concrete reinforcement of the present invention, and is used by impregnating the polyparaphenylene terephthalamide fiber.
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. Since thermoplastic resins exhibit plasticity when heated, building materials for reinforcing concrete that can be bent on site can be provided by using thermoplastic resins. Since thermosetting resins do not have plasticity due to heat, the use of thermosetting resins makes it possible to provide building materials for concrete reinforcement that are excellent in heat resistance and fire resistance.

Examples of thermoplastic resins include polypropylene resins, polyethylene resins, ABS resins, polyvinyl chloride resins, polycarbonate resins, polyacetal resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polyphenylene sulfide resins, polyamide resins, modified polyphenylene ether resins, and liquid crystals. polyester resins, polyimide resins, syndiotactic polystyrene resins, polycyclohexanedimethylene terephthalate resins, thermoplastic epoxy resins, and the like. Examples of thermosetting resins include unsaturated polyester resins, phenol resins, vinyl ester resins, thermosetting epoxy resins, urea resins, and the like.

Among the above resins, resins having excellent alkali resistance and excellent adhesiveness with polyparaphenylene terephthalamide fibers are preferred. Specific examples include thermoplastic epoxy resins, urea resins, unsaturated polyester resins, and thermosetting resins. An epoxy resin etc. can be illustrated. By using these matrix resins, there is an advantage that the life of the building material for reinforcing concrete of the present invention and the concrete reinforced with the building material is extended.

Various additives can be added to the matrix resin used in the present invention as necessary within a range that does not impair the effects of the present invention. Examples of additives include heat stabilizers, light stabilizers, ultraviolet absorbers, hydrolysis inhibitors, antioxidants, lubricants, nucleating agents, plasticizers, coloring inhibitors, matting agents, flame retardants, antistatic agents, Release agents, fillers (fillers such as glass fiber, carbon fiber, glass beads, hollow glass, talc, etc.), pigments, dyes, etc., and one or more selected from these additives are blended. be able to. The blending amount of these may be the amount normally used.

<Building materials for concrete reinforcement>
The building material for concrete reinforcement of the present invention can be produced by impregnating the polyparaphenylene terephthalamide fiber with a matrix resin.
Specifically, as an example thereof, a) a step of producing a textile product such as a braid or a fabric from a polyparaphenylene terephthalamide fiber, b) a step of impregnating the obtained braid or a textile product such as a fabric with a matrix resin, Through the step of c) curing the impregnated matrix resin and optionally d) cutting the obtained polyparaphenylene terephthalamide fiber-matrix resin composite, the building material for concrete reinforcement of the present invention is obtained. manufactured.
Before and after the above step a), a step (refining step) of washing off the oil agent adhering to the surface of the polyparaphenylene terephthalamide fiber may be included.
In step b) above, the impregnation rate represented by the following formula (I) is desirably 95% or more, more desirably 97% or more. If the impregnation rate is less than 95%, the stress transmission tends to be insufficient, and the function (reinforcing effect) as a building material for reinforcing concrete cannot be sufficiently exhibited. there is a risk of becoming
Impregnation rate (%)=A/(A+B)×100 (I)
A: Total area occupied by fiber and resin on any cross section of the building material B: Total area of voids on any cross section of the building material

In addition, bending-shaped building materials are produced by a) a step of producing a braid or the like from polyparaphenylene terephthalamide fiber threads, b) a step of impregnating the obtained braid or the like with a matrix resin, and c) forming a desired bending shape. It is manufactured through the steps of setting in a frame, d) curing the impregnated matrix resin, and e) cutting the resulting resin-impregnated cord yarn.

In the above-mentioned manufacturing process, in order to improve the adhesive strength with concrete, if desired, a step of adhering powdery substances such as sand and silica to fiber products such as braids and fabrics impregnated with matrix resin. be able to. The particle size of the powder is not limited as long as it does not impair the purpose of the present invention, but it is preferably about 0.1 to 5.0 mm.

As the form of the textile product, braided cord, twisted cord, or fabric is desirable because the surface has moderate unevenness and excellent adhesion to concrete, and braided cord or twisted cord is more preferable. new. A known means can be used as the method of making the string. Usually, a braid is produced by a braiding machine (a braiding machine), for example, a braid of any braid shape such as round, square, or flat braid is produced. As a knitting method, for example, a method of preparing four filaments, arranging the yarn on the right side or the left side alternately in the middle, and braiding them, or the like can be mentioned. The number of filaments used for string making is not limited to 4, but may be 8, 12, 16, or the like. The number of braided cords or twisted cords used in building materials for reinforcing concrete is not particularly limited, and a desired number may be used.

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 bent shape include U-shaped, L-shaped, U-shaped, spiral, triangular, quadrangular, pentagonal, hexagonal and other polygonal shapes. The bent shape is not limited to this, and various bent shapes can be used depending on the case.

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

<Concrete member or structure>
Another form of the present invention is a concrete member or concrete structure using the building material for reinforcing concrete as a reinforcing material.

Concrete members include members used in existing concrete structures that receive impacts from the outside. Examples include PC sleepers, utility poles, and the like.

When the building material for concrete reinforcement of the present invention is applied to a concrete member, the building material is formed into at least one form of strand, woven or knitted fabric, braid, and twisted cord using polyparaphenylene terephthalamide fiber. is good. For example, a woven or knitted fabric made of polyparaphenylene terephthalamide fiber and a matrix resin are used on site, and the polyparaphenylene terephthalamide fiber impregnated with the matrix resin is adhered to the surface of the concrete member to reinforce the concrete member. do.

In another embodiment, a braided or twisted cord made of polyparaphenylene terephthalamide fibers and a matrix resin are used, and the polyparaphenylene terephthalamide fibers impregnated with the matrix resin are inserted or inserted into the holes of the concrete member. By penetrating and bonding, the concrete member is reinforced.

In another embodiment, strands, woven or knitted fabrics, or braids made of polyparaphenylene terephthalamide fibers and a matrix resin are used, and the polyparaphenylene terephthalamide fibers impregnated with the matrix resin are spirally attached to the concrete member. Reinforcing concrete members by wrapping them around.

As concrete structures, in civil engineering applications, for example, railroad facilities, road facilities, energy facilities (thermal power generation, wind power generation, nuclear power generation, hydraulic power generation, gas storage facilities, etc.), dam/river facilities, water supply and sewage facilities, airport facilities etc., and examples of architectural uses include buildings, hospitals, schools, residences, factories, and the like.

When the building material for concrete reinforcement of the present invention is applied to a concrete structure, the building material is formed into a braid using polyparaphenylene terephthalamide fiber, and the braid and a matrix resin are used to form the braid. , Polyparaphenylene terephthalamide fibers impregnated with a matrix resin are formed into a braided rod, a round rod, a deformed rod, a flat plate rod, a two-dimensional lattice, or the like.

Since the building material for concrete reinforcement of the present invention is excellent in alkali resistance, it exhibits its effect particularly in the mode of embedding and reinforcing concrete, among the embodiments relating to the above-mentioned concrete members and concrete structures.
Moreover, the building material for concrete reinforcement of the present invention is suitable for civil engineering applications. The reason is that civil engineering is mainly done outdoors, and there are many environmental factors (rain, acid rain, seawater, corrosive gases such as SOx and NOx, lightning, snow melting agents, etc.) that rust conventional reinforcing bars. mentioned. By using the building material for concrete reinforcement of the present invention, effects such as reduction of management costs and extension of the life of structures are expected. Therefore, it can be said that the building material for reinforcing concrete of the present invention is in a state of being able to receive great benefits.

In recent years, in connection with various efforts to reduce the environmental load, efforts have been made to reduce the amount of cement used, which has a large environmental load among the materials constituting concrete, and to utilize industrial by-products. For example, representative examples of cement containing a large amount of industrial by-products with low _CO2 emission unit costs are blast furnace cement using blast furnace slag as an admixture, silica cement using a siliceous admixture, and fly ash as an admixture. The fly ash cement etc. which used it are proposed. Concrete using mixed cement in which such an admixture is mixed with conventional Portland cement is expected to contribute to decarbonization (for example, JP-A-2018-145033, JP-A-2015-202978. Gazette).

However, concrete containing a high proportion of blast-furnace slag has the problem of a faster neutralization rate than conventional concrete. In order to solve these problems, a method of suppressing neutralization with a water reducing agent, a method of removing the causative substance from the siliceous by-product, etc. have been proposed, but the building material for concrete reinforcement of the present invention is used. This has the potential to contribute significantly to decarbonization.
Here, neutralization means that when concrete, which is originally alkaline, is left in the air for a long time, the surface reacts with carbon dioxide gas (CO ₂ ) in the air to form calcium carbonate as shown in formula (II). It means that the pH is reduced to about 8.5 to 10.
Ca(OH) ₂ + _CO2 → _CaCO3 + _H2O (II)

Neutralization of concrete in which reinforcing bars are located causes deterioration of concrete structures because the anti-corrosion function of the reinforcing bars is lowered unlike in the case of alkalinity. If the reinforcing steel rusts, the volume of the rust increases to 2 to 4 times that of the original reinforcing steel. Corrosion of the reinforcing steel inside progresses. In other words, neutralization has a significant effect on the durability of reinforced concrete structures. It is known that the prediction formula for predicting the neutralization speed follows the √t law regarding elapsed time, and the relationship x=A√t is established between the neutralization period t and the neutralization depth x. It is based on doing

Since the building material for concrete reinforcement of the present invention has excellent alkali resistance, it is neutralized in the accelerated test determined by JIS A1153:2012 Concrete Accelerated Neutralization Test Method 6.1 Accelerated Neutralization Method It can be preferably used in concrete having a rate coefficient of 2.5 mm/√week or more (conventional concrete neutralization rate coefficient: 2.1 mm/√week). Neutralization causes the reinforcing bars in the concrete members to rust and expand, causing cracks in the concrete and shortening the life of the concrete. Concrete with a neutralization rate coefficient of 2.5 mm/√week or more has a large effect on reinforcing bars. However, by applying the building material for concrete reinforcement of the present invention, it becomes possible to eliminate deterioration due to rust of reinforcing bars.

On the other hand, concrete having a neutralization rate coefficient of less than 2.5 mm/√week has the disadvantage that it is difficult to obtain a sufficient effect from the building material for reinforcing concrete of the present invention. The neutralization rate coefficient of concrete structures is preferably 3.0 mm/√week or more, more preferably 4.0 mm/√week or more, in that sufficient effects can be expected from the building material for concrete reinforcement of the present invention. .

As described above, the building material for reinforcing concrete 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. Available. Also, unlike reinforcing bars, it is lightweight and therefore easy to handle. Concrete members and structures can be constructed without worrying about corrosion, unlike reinforcing bars.

EXAMPLES The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to them. In addition, in the following examples and the like, "% by mass" is abbreviated as "%" unless otherwise specified. The evaluation methods described in the examples are as follows.

(1) Crystallinity 20 mg of a polyparaphenylene terephthalamide fiber bundle cut into 4 cm was weighed. A sample was prepared by binding both ends of this fiber bundle with an enameled wire. Wide-angle X-ray diffraction was measured by placing the prepared sample in a fiber sample holder. The obtained wide-angle X-ray diffraction pattern was peak-separated, and the degree of crystallinity was calculated from the obtained crystal peak area and amorphous peak area.
<Measurement conditions>
Apparatus: SmartLab for polymers manufactured by Rigaku
X-ray source: CuKα ray (using Ni filter)
Output: 40kV 50mA
Detector: D/teX (one-dimensional detector)
Measurement direction: Equatorial direction scan <calculation of crystallinity>
Crystallinity (%) = crystalline peak area / (crystalline + amorphous peak area) x 100

(2) Tensile Properties The polyparaphenylene terephthalamide fibers obtained in Production Examples were evaluated according to ASTM D7269 to measure tensile strength (Section 11; Breaking Strength) and tensile modulus (Section 15; Modulus).

(3) Alkali Resistance Evaluation The polyparaphenylene terephthalamide fiber obtained in Production Example was set in a pressure vessel so as to be completely immersed in an aqueous sodium hydroxide solution adjusted to pH=12.8. After closing the lid of the pressure-resistant container, it was treated in an oven at 70° C. for 48 hours. After treatment, wash with ion-exchanged water (until the pH of the aqueous solution is 8.6 or less), dry at 50°C for 4 hours or more until the moisture content of the yarn is 10% or less, temperature 20°C, humidity 65%. It was left in a RH room for 24 hours.
The tensile strength was determined by the method (2) above, and the retention before and after the treatment was calculated.

(4) Evaluation of Creep Resistance The polyparaphenylene terephthalamide fiber obtained in Production Example was tested in accordance with ASTM D7269 using a constant-speed extension tensile tester in a room at a temperature of 20° C. and a humidity of 65% RH. Breaking load (Section 12; Breaking Tenacity) when cutting was measured. After applying a load of 50% of the breaking load for 1000 hours, the yarn length was measured and the creep rate was calculated by the following formula.
Creep rate (%) = [(Lc - Lo) / Lo] x 100
(Lo: original yarn length (mm), Lc: yarn length after 1000 hours (mm))

[Production Example 1]
1 kg of paraphenylene terephthalamide (molecular weight: about 20,000) obtained by a conventional method was dissolved in 4 kg of concentrated sulfuric acid, and was passed through a die having 1,000 holes with a diameter of 0.1 mm at a shear rate of 30,000 sec ⁻¹ . After being discharged and spun in water at 4°C, it was neutralized with a 10% sodium hydroxide aqueous solution under the conditions of 10°C for 15 seconds, and then dried by heating under the conditions of 200°C for 15 seconds. The fibers were additionally heated and dried at 220° C. for 10 seconds at half the tension used for drying by heating to obtain polyparaphenylene terephthalamide fibers (total fineness of 3,300 dtex) with a moisture content of 3.0%.
A polyoxyethylene polyoxypropylene copolymer as an oil agent is applied to the polyparaphenylene terephthalamide fiber so that it becomes 1.0% with respect to the fiber mass when converted to a moisture content of 0%, and then wound up and packaged. bottom.

[Production Example 2]
Polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 2.8% were obtained in the same manner as in Production Example 1 except that the conditions for additional drying and heating were 240° C.×10 seconds.

[Production Example 3]
The procedure was carried out in the same manner as in Production Example 1, except that the oil to be applied was a mixture of glycerol polyglycidyl ether and polyethylene glycol fatty acid ester at a ratio of 60:40 (mass ratio). A phenylene terephthalamide fiber (total fineness 3,300 dtex) was obtained.

[Production Example 4]
Polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 2.8% were obtained in the same manner as in Production Example 1 except that the additional drying and heating conditions were 260° C.×10 seconds.

[Production Example 5]
Polyparaphenylene terephthalamide fibers (total fineness 3,300 dtex) with a moisture content of 6.8% were obtained in the same manner as in Production Example 1 except that additional drying and heating were not performed.

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

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

As shown in Table 1, the polyparaphenylene terephthalamide fiber with a crystallinity of less than 70% was inferior in tensile modulus, alkali resistance and creep resistance (Comparative Example 1). Aramid fibers containing a copolymer component had excellent alkali resistance, but were inferior in tensile modulus and creep resistance (Comparative Example 2). From this, it can be seen that these fibers are insufficient as building materials for concrete reinforcement.

On the other hand, the poly-p-phenylene terephthalamide fibers of Examples 1 to 4 are excellent in tensile modulus, alkali resistance and creep resistance, and can exhibit excellent functions as building materials for reinforcing concrete.

The building material for concrete reinforcement of the present invention is useful as a substitute for reinforcing bars and can contribute to the realization of a decarbonized society.

Claims (7)

A building material for reinforcing concrete comprising a polyparaphenylene terephthalamide fiber and a matrix resin, wherein the polyparaphenylene terephthalamide fiber has a crystallinity of 70% or more as measured by wide-angle X-ray diffraction. A building material for reinforcing concrete, characterized by: The polyparaphenylene terephthalamide fiber has a tensile strength retention rate of 90% or more after alkali treatment (pH = 12.8, 70 ° C., 48 hours).
A building material for reinforcing concrete according to claim 1. The polyparaphenylene terephthalamide fiber has a tensile modulus of 100 GPa or more, as determined according to ASTM D7269.
A building material for reinforcing concrete according to claim 1 or 2. The creep after standing for 1,000 hours at a stress of 50% of the tensile breaking load determined according to ASTM D7269 of the polyparaphenylene terephthalamide fiber is 3.0% or less.
A building material for reinforcing concrete according to any one of claims 1 to 3. A concrete member or structure reinforced with the building material according to any one of claims 1 to 4. 6. The concrete member or structure according to claim 5, having a neutralization rate coefficient of 2.5 mm/√week or more in an accelerated test determined according to JIS A1153. The concrete member or structure according to claim 5 or 6, which is used for civil engineering applications.