Concrete reinforcement method

Abstract

To provide a concrete reinforcement method capable of reinforcing concrete by forming one reinforcing layer.SOLUTION: In a concrete reinforcing method in which a fiber sheet is attached to a surface of a concrete structure to form a reinforcing layer, the reinforcing layer is composed of only one layer of a bidirectional carbon fiber sheet attached to the surface to make it into a carbon fiber reinforced plastic. The bidirectional carbon fiber sheet is a carbon fiber fabric containing carbon fiber in both the warp and weft threads, and has a fabric weight of 300 g / m2 to 800 g / m2 and a crimp angle θ of 1.0° to 3.3°.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a concrete reinforcement method for reinforcing concrete using a carbon fiber sheet. In particular, it relates to a concrete reinforcement method for reinforcing the lining concrete of an existing tunnel using a carbon fiber sheet.

Background Art

[0002] The repair and reinforcement work of the lining concrete of an existing tunnel is roughly classified into measures against chipping and internal surface reinforcement. For the internal surface reinforcement of tunnel lining, generally, the "continuous fiber bonding method" using a "carbon fiber sheet" is adopted. In the "continuous fiber bonding method", the "carbon fiber sheet" is made into carbon fiber reinforced plastic (CFRP) using a matrix resin. CFRP is excellent in light weight and mechanical properties and is suitable for the internal surface reinforcement of tunnel lining.

[0003] The "carbon fiber sheet" used in the "continuous fiber bonding method" is a general-purpose product for seismic reinforcement work, and the "high-strength type" of the "unidirectional carbon fiber sheet" in which the fibers are continuous in the reinforcement direction is used. The basis weight (the weight of carbon fiber per 1 m 2 ; g / m 2 ) is set according to the expected reinforcement effect, and 200 g / m 2 of the standard design is often applied.

[0004] The construction of the "continuous fiber bonding method" is carried out as shown in FIG. 6. First, surface treatment (step S101), primer application (step S102), and unevenness correction (step S103) are carried out as pre-treatment steps. Next, as the main reinforcement material, first, a "unidirectional carbon fiber sheet" is attached in the circumferential direction of the tunnel to make it CFRP in the first layer (step S104), and in order to connect and prevent the first layer from falling, a "unidirectional carbon fiber sheet" is attached in the axial direction of the tunnel to make it CFRP in the second layer (step S105). Finally, the undercoat (step S106) and topcoat (step S107) of the finish coating are carried out as post-treatment steps.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The process of CFRP conversion of the "unidirectional carbon fiber sheet" is, as shown in Fig. 6, carried out layer by layer in the following steps: (1) primer coating of the adhesive impregnating resin, (2) sheet attachment, (3) defoaming and impregnation, (4) top coating of the adhesive impregnating resin, and (5) curing and aging. Therefore, the number of construction days increases as the number of layers increases. In particular, after the top coating of the adhesive impregnating resin, curing and aging are required to wait for the resin to cure. Therefore, the construction of the second layer is carried out the next day, resulting in an increase in the number of construction days.

[0007] Note that a method for reinforcing a concrete structure using a bidirectional composite fiber sheet has been proposed (see, for example, Patent Document 1). However, the bidirectional composite fiber sheet used in Patent Document 1 bundles a plurality of warp yarns and weft yarns arranged in parallel without crossing with each other using a plurality of knitting yarns. When the sheet that bundles the warp yarns and weft yarns using the knitting yarns has a high basis weight in order to obtain the allowable stress defined in the design, it becomes difficult to impregnate the resin into the carbon fiber sheet during CFRP conversion. Therefore, an unimpregnated portion may remain in the carbon fiber sheet, or the carbon fiber may meander or be damaged due to squeezing the carbon fiber sheet strongly to impregnate it, resulting in a decrease in the excellent mechanical properties of the carbon fiber sheet.

[0008] The present invention has been made in view of such a situation, and an object thereof is to provide a concrete reinforcement method that solves the above problems and can reinforce concrete by forming a single reinforcing layer.

Means for Solving the Problems

[0009] The concrete reinforcement method of the present invention is a concrete reinforcement method in which a fiber sheet is attached to the surface of a concrete structure to form a reinforcement layer. The reinforcement layer is composed of only one layer in which a two-way carbon fiber sheet is attached to be carbon fiber reinforced plastic. The two-way carbon fiber sheet is a carbon fiber fabric containing carbon fibers in each of the warp yarns and weft yarns that are woven yarns, and the fabric basis weight is 300 g / m 2 or more and 800 g / m 2 or less, and the crimp angle is 1.0° or more and 3.3° or less. Furthermore, in the concrete reinforcement method of the present invention, the weave density of the carbon fiber may be 1,000 g / m (1,000 tex) or more and 4,000 g / m (4,000 tex) or less. Furthermore, in the concrete reinforcement method of the present invention, the sizing adhesion rate of the carbon fiber may be 0.5% by mass or more and 10% by mass or less. Furthermore, in the concrete reinforcement method of the present invention, the shear rigidity of the two-way carbon fiber sheet may be 0.40 N / ° or more and 10 N / ° or less. Furthermore, in the concrete reinforcement method of the present invention, the stiffness-flexibility of the two-way carbon fiber sheet may be 170 mm or more and 400 mm or less. Furthermore, in the concrete reinforcement method of the present invention, the aperture ratio of the two-way carbon fiber sheet may be 0.1% or more and 10% or less. Furthermore, in the concrete reinforcement method of the present invention, the tensile strength of the carbon fiber may be 3,000 MPa or more and 7,000 MPa or less, and the tensile elastic modulus may be 200 GPa or more and 600 GPa or less. Furthermore, in the concrete reinforcement method of the present invention, the two-way carbon fiber sheet may contain heat-sealing fibers in at least one of the warp yarns or the weft yarns, and the heat-sealing fibers may be heated and welded to seal the carbon fibers. Furthermore, in the concrete reinforcement method of the present invention, a marking yarn may be arranged at the position of the lap length from the end of the two-way carbon fiber sheet, and the two-way carbon fiber sheet may be attached by lapping the lap length.

Advantages of the Invention

[0010] According to the present invention, by using a biaxial carbon fiber sheet that allows easy resin impregnation even with a high basis weight, it is possible to reinforce concrete by forming a single layer of reinforcing layer, and the effect of shortening the construction period can be achieved.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0012] Next, modes for carrying out the present invention (hereinafter simply referred to as "embodiments") will be specifically described with reference to the drawings. The concrete reinforcement method of the present embodiment is a method for reinforcing the lining concrete of an existing tunnel. The concrete reinforcement method of the present embodiment can also be applied to concrete structures such as bridge decks, beams, and bridge piers.

[0013]

[0014] ​Next, a "biaxial carbon fiber sheet" is attached as a reinforcing layer to make it carbon fiber reinforced plastic (CFRP) (step S201). In the concrete reinforcement method of the present embodiment, the reinforcing layer is composed of only one layer of CFRP formed in step S201.

[0015] To make the "biaxial carbon fiber sheet" into CFRP, first, (1) a primer of an adhesive impregnating resin is applied. The adhesive impregnating resin is a matrix resin of CFRP (for example, epoxy resin, unsaturated polyester resin, vinyl ester resin, urethane resin, acrylic resin, etc.).

[0016] Next, (2) the "biaxial carbon fiber sheet" is attached. The "biaxial carbon fiber sheet" is a carbon fiber fabric containing carbon fibers in each of the warp yarns and weft yarns which are woven yarns. The "biaxial carbon fiber sheet" is attached with one of the warp yarns and weft yarns in the tunnel circumferential direction and the other in the tunnel axial direction respectively. The "biaxial carbon fiber sheet" is attached by wrapping a predetermined length (the wrap length is, for example, 50 mm). As a guideline during construction, it is advisable to arrange a marking yarn at the position of the wrap length from the end.

[0017] Next, (3) the "biaxial carbon fiber sheet" is squeezed with a roller or the like to discharge (degas) the air bubbles in the carbon fibers and impregnate the carbon fibers with the adhesive impregnating resin.

[0018] Next, (4) a top coat of the adhesive impregnating resin is applied, and (5) curing and curing are performed, whereby CFRP composed of the "biaxial carbon fiber sheet" and the adhesive impregnating resin is formed.

[0019] Finally, the primer of the finish coating (step S106) and the top coat of the finish coating (step S107) are performed as post-treatment steps.

[0020] The configuration of the "biaxial carbon fiber sheet" will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a partial plan view of a carbon fiber fabric 3 composed of a fabric with carbon fibers (warp yarn 1, weft yarn 2) as woven yarns, and FIG. 3 is a cross-sectional view of the carbon fiber fabric 3 taken along line A-A in FIG. 1.

[0021] The "two-direction carbon fiber sheet" is a carbon fiber fabric with a fabric basis weight of 300 g / m 2 or more and 800 g / m 2 or less, and a crimp angle θ of 1.0° or more and 3.3° or less. The carbon fiber used for the "two-direction carbon fiber sheet" can be, for example, polyacrylonitrile (PAN-based), pitch-based, cellulose-based, vapor-phase growth fibers by hydrocarbons, graphite fibers, etc., and two or more of these may be used in combination. Preferably, PAN-based carbon fibers with excellent balance between mechanical properties and price are good.

[0022] In FIG. 3, two adjacent warp yarns 1a are arranged at a weaving density d [yarns / 25 mm]. The straight line 6 connecting the intersection points 5a, 5b of two perpendicular lines 4a, 4b passing through the warp yarn 1a and the center line 2c of one weft yarn 2a intersecting with the warp yarn 1a, and the straight line 7 parallel to the arrangement direction of the warp yarn 1a, the angle formed therebetween is the crimp angle θ referred to in the present invention.

[0023] In FIG. 2, the crimp angle parallel to the warp yarn arrangement direction is shown, but for the crimp angle θ regarding the weft yarn arrangement direction, it can be similarly defined for the B-B cross section of FIG. 2. Therefore, in the embodiment shown in FIG. 3, when the center distance between two warp yarns 1a is 25 / d [mm] and the thickness of the fabric is t [mm], the above crimp angle θ is obtained by the following formula 1. θ = arctan(td / 50) [°] ··· Formula 1

[0024] The thickness t of the fabric is measured in accordance with JIS-R7602. That is, it is the thickness when a load of 50 kPa is applied for 20 seconds using a dial gauge. The weaving density d is measured in accordance with JIS-R7602. That is, it is the number of weaving yarns arranged per 25 mm.

[0025] If the fabric basis weight is 300 g / m 2 or more and the crimp angle θ is less than 1.0°, since the weaving density is small, the reinforcing fibers are likely to meander during molding, and the mechanical properties that are the characteristics of the reinforcing fibers are not fully exhibited. If the fabric basis weight is 800 g / m2 When it exceeds this value, it becomes difficult for the resin to impregnate into the carbon fiber bundle during CFRP formation, and unimpregnated portions may remain in the reinforcing fibers, or the reinforcing fibers may meander or be damaged, such as by strongly squeezing the reinforcing fibers to allow impregnation, resulting in a decrease in the excellent mechanical properties of the reinforcing fibers. When the fabric basis weight is less than 300 g / m 2 If it is less, for the reinforcement of the lining concrete of an existing tunnel, since a large amount of reinforcing fibers is required, even when using a "biaxial carbon fiber sheet", it is necessary to laminate multiple layers, and there is a concern about cost increase due to an increase in working time.

[0026] The fabric basis weight of the "biaxial carbon fiber sheet" is preferably 350 g / m 2 or more and 700 g / m 2 or less, more preferably 380 g / m 2 or more and 600 g / m 2 or less. The crimp angle θ is preferably 1.0° or more and 2.5° or less, more preferably 1.0° or more and 2.0° or less.

[0027] The strand count of the carbon fibers of the "biaxial carbon fiber sheet" is preferably 1.000 g / m (1,000 tex) or more and 4.000 g / m (4,000 tex) or less. If it is less than 1.000 g / m (1,000 tex), it is necessary to increase the weaving density to increase the fabric basis weight, which may increase the crimp angle θ and result in a decrease in mechanical properties. If it exceeds 4.000 g / m (4,000 tex), it becomes a soft fabric with a small weaving density, and the reinforcing fibers are likely to meander during molding, and the high mechanical properties characteristic of the reinforcing fibers may not be fully exhibited. More preferably, it is 1.500 g / m (1,500 tex) or more and 2.000 g / m (2,000 tex) or less, and even more preferably 1.600 g / m (1,600 tex) or more and 1.800 g / m (1,800 tex) or less.

[0028] The aperture ratio of the "biaxial carbon fiber sheet" is preferably 0.1% or more and 10% or less. The closer the aperture ratio is to 0%, the more evenly the woven yarns are arranged, making it less likely for the carbon fibers to meander during construction. However, on the other hand, when impregnating with the matrix resin, air bubbles in the carbon fibers and excess resin tend to be less likely to be discharged. Therefore, the aperture ratio is preferably within the above range. If it exceeds 10%, the carbon fibers are likely to move through the gaps, and meandering of the carbon fibers may easily occur during construction. The aperture ratio of the "biaxial carbon fiber sheet" is more preferably 0.1% or more and 4% or less, and even more preferably 0.1% or more and 1% or less.

[0029] Here, the aperture ratio of the carbon fiber is determined by setting an area S 1 on the fabric, and the area of the voids formed in the woven yarns within the area S 1 is denoted as S 2 , and refers to the value defined by the following formula (2). Aperture ratio [%] = S 2 / S 1 × 100 ··· Formula (2) For measuring the aperture ratio, the entire width of the fabric may be captured as an image with a scanner, and the aperture ratio may be derived using image processing software. When the fabric width is wide, a plurality of rectangles with at least one side of 20 cm or more may be evenly sampled in the width direction, and the average value may be used as the aperture ratio.

[0030] The carbon fibers of the "biaxial carbon fiber sheet" preferably have a tensile strength of 3,000 MPa or more and 7,000 MPa or less, and a tensile elastic modulus of 200 GPa or more and 600 GPa or less. More preferably, the tensile strength is 4,000 MPa or more and 6,000 MPa or less, and the tensile elastic strength is 210 GPa or more and 260 GPa or less. Even more preferably, the tensile strength is 4,500 MPa or more and 6,000 MPa or less, and the tensile elastic strength is 220 GPa or more and 250 GPa or less.

[0031] The carbon fibers of the "two-directional carbon fiber sheet" are preferably flat. For the woven yarns composed of such flat carbon fibers, it is preferable that the fibers are parallel with substantially no twist. Here, "substantially no twist" means a state where there is no twist of one turn or more per 1 m of yarn length. That is, it refers to a practically untwisted state, and it is preferable that there is substantially no twist in the state of the fabric. As a method for obtaining such a fabric, there is a method in which a bobbin of untwisted flat reinforcing fibers is unwound laterally, and the warp and weft yarns are supplied so that no unwinding twist is introduced to form a fabric.

[0032] The sizing adhesion rate of the carbon fibers of the "two-directional carbon fiber sheet" is preferably 0.5% by mass or more and 10% by mass or less. If it is less than 0.5% by mass, the shrinkage of the carbon fibers is low, the reinforcing fibers are likely to meander during molding, the convergence of the reinforcing fibers becomes too strong, and the shapeability of the fabric and the impregnability of the matrix resin into the carbon fibers may deteriorate. Preferably, it is 0.6% by mass or more and 3.0% by mass or less, and more preferably 0.8% by mass or more and 1.6% by mass or less.

[0033] The shear rigidity of the "two-directional carbon fiber sheet" is preferably 0.40 N / ° or more and 10 N / ° or less as measured by the picture frame method. If it is less than 0.40 N / °, the shape of the fabric may easily collapse during shaping or resin impregnation. If it exceeds 10 N / °, the fabric is too stiff and the shapeability may deteriorate. More preferably, it is 0.45 N / ° or more and 5 N / °, and even more preferably 0.50 N / ° or more and 1.0 N / ° or less.

[0034] The measurement of the shear rigidity of the "two-directional carbon fiber sheet" by the picture frame method is performed using the picture frame jig 30 shown in FIG. 4. The evaluation method of the shear deformation performance using the picture frame jig 30 is the picture frame method by the two-side gripping method. The picture frame jig 30 includes four frames 31a, 31b, 31c, and 31d. Both ends of each of the four frames 31a, 31b, 31c, and 31d are rotatably connected to the adjacent frames so as to form each side of the rectangle.

[0035] The picture frame jig 30 is attached to a universal material testing machine (omitted in Fig. 5) with the diagonal connection parts placed vertically so that the inner angles at the four enclosed corners are 90 degrees. The opposing frames 31a and 31b have gripping parts that can grip the test piece X. The test piece X is cut out into five rectangular pieces with a long side of 220 mm and a short side of 150 mm from a "biaxial carbon fiber sheet" that has been left standing at 25°C for 1 hour.

[0036] One end of the short side of the test piece X is fixed to the gripping part of the frame 31a. At this time, the distance between the frame 31a and the frame 31b is 200 mm. The other end of the short side of the test piece X is attached to the gripping part of the frame 31b so that the long side is parallel to the frames 31c and 31d.

[0037] When the attachment of the test piece X to the frames 31a and 31b is completed, the inner angle between the frames 31d and 31b is taken as the measurement angle α [°], and it is confirmed that the measurement angle α [°] is 90°. Next, the picture frame jig 30 is pulled vertically at a speed of 50 mm / min by a universal material testing machine, and the changes in the tensile force F [N] and the measurement angle α [°] are measured. Then, ΔF / Δβ when the shear angle β [°]=90° - measurement angle α [°] is between 0.1 and 1.0 is calculated, and the average of the five pieces is taken as the shear rigidity of the "biaxial carbon fiber sheet".

[0038] When the carbon fiber types and configurations are different in the warp direction and the weft direction of the "biaxial carbon fiber sheet", two types of test pieces X are prepared, one with the long side in the warp direction and the short side in the weft direction, and the other with the long side in the weft direction and the short side in the warp direction, and the tests are carried out in the same way. In this case, it is preferable that the shear rigidity is within the above range in both directions.

[0039] The "biaxial carbon fiber sheet" preferably has a flexural rigidity of 170 mm or more and 400 mm or less as measured by the cantilever method in both the longitudinal and transverse directions. If it is less than 170 mm in both directions, the fabric will be too soft and may easily fray during shaping. If it exceeds 400 mm in both directions, the fabric will become too hard and the formability may deteriorate. Preferably, it is 180 mm or more and 250 mm or less, and more preferably, 185 mm or more and 210 mm or less.

[0040] The concrete reinforcement method of this embodiment was verified using the beam bending testing machine 10 shown in Fig. 5. The beam bending testing machine 10 includes a support portion 11 that supports both ends of an arc-shaped concrete segment (hereinafter referred to as segment 20) with roller fulcrums, and a load portion 12 that applies a load from above to the segment 20 supported by the support portion 11 with the concave surface corresponding to the inner peripheral surface of the overlay concrete facing downward.

[0041] The segment 20 with its concave surface reinforced by the concrete reinforcement method of this embodiment was taken as the [Example]. The "biaxial carbon fiber sheet" used in the [Example] was woven from carbon fiber fabric with a plain weave structure having a weaving density of 3.17 threads / 25 mm, using "TORAYCA (registered trademark)" T700SC - 24K - 50C aligned parallel in one direction as the warp threads and inserting "TORAYCA (registered trademark)" T700SC - 24K - 50C and "ELDER (registered trademark)" in the orthogonal direction as the weft threads. Next, the woven carbon fiber fabric was heated so that the surface temperature became 13°C to melt the heat - welded fibers and seal the warp and weft threads. · "TORAYCA (registered trademark)" T700SC - 24K - 50C (manufactured by Toray Industries, Inc., tensile strength: 4,900 MPa, tensile modulus of elasticity: 230 GPa, sizing adhesion rate: 1.0 mass%, linear density: 1.650 g / m (1,650 tex), density: 1.80 g / cm 3 ) · "ELDER (registered trademark)" (manufactured by Toray Industries, Inc., low - melting - point nylon thread, linear density: 54.8 decitex, melting point: 110°C)

[0042] The fabric areal weight of the "biaxial carbon fiber sheet" used in the [Example] was 418 g / m2 The fabric thickness measured based on JIS-R7602 was 0.46 mm, the opening ratio was 0.5%, and the crimp angle θ calculated from the weave density and fabric thickness was 1.7°. Also, the shear rigidity was 0.58 N / ° in the warp direction and 0.60 N / ° in the weft direction, the stiffness flexibility was 167 mm in the warp direction and 192 mm in the weft direction, the tensile strength was 4,724 MPa, and the tensile elastic modulus was 246 GPa.

[0043] Taking the segment 20 without implementing the concrete reinforcement method as [Comparative Example 1], and the segment 20 with two layers of reinforcement layers formed by the "unidirectional carbon fiber sheet" as [Comparative Example 2], a comparative verification was conducted with [Example]. As a result, the load at which the segment 20 is destroyed became approximately equally large for [Comparative Example 2] and [Example] compared to [Comparative Example 1], indicating that the effect of the concrete reinforcement method can be obtained. And it can be seen that [Example] obtains the same effect as [Comparative Example 2] despite having only one layer of reinforcement layer.

[0044] As described above, the present embodiment is a concrete reinforcement method for forming a reinforcement layer by attaching a fiber sheet to the surface of a concrete structure. The reinforcement layer is composed of only one layer obtained by attaching a bidirectional carbon fiber sheet to make it carbon fiber reinforced plastic. The bidirectional carbon fiber sheet is a carbon fiber fabric containing carbon fibers in each of the warp yarns and weft yarns that are the weaving yarns, and the fabric areal density is 300 g / m 2 above 800 g / m 2 below, and the crimp angle θ is 1.0° or more and 3.3° or less. With this configuration, by using a bidirectional carbon fiber sheet that allows easy resin impregnation even with a high areal density, the concrete can be reinforced by forming one layer of reinforcement layer, and the construction period can be shortened. By making the reinforcement layer one layer, it is possible to prevent quality degradation due to poor resin curing between layers or human error, resulting in high quality. The fabric areal density of the bidirectional carbon fiber sheet is 300 g / m 2 above 800 g / m 2Hereinafter, by setting the crimp angle θ to 1.0° or more and 3.3° or less, a predetermined strength can be satisfied, and the adhesive impregnated resin can easily infiltrate the surface of the unidirectional carbon fiber sheet, preventing the sheet from peeling off due to its own weight.

[0045] As described above, the present invention has been described based on the embodiments. These embodiments are illustrative, and it is understood by those skilled in the art that various modifications are possible for the combinations of their respective components and the like, and such modifications are also within the scope of the present invention.

Explanation of Signs

[0046] 1, 1a warp 2, 2a weft 2c center line 3 carbon fiber fabric 4a, 4b perpendicular 5a, 5b intersection point 6, 7 straight line 10 beam bending tester 11 support part 12 load part 20 segment 30 picture frame jig 31a, 31b, 31c, 31d frame F tensile force X test piece α measurement angle θ crimp angle

Claims

1. A concrete reinforcement method in which a fiber sheet is attached to the surface of a concrete structure to form a reinforcing layer, The reinforcing layer is composed of only one layer of a bidirectional carbon fiber sheet bonded to a carbon fiber reinforced plastic, The bidirectional carbon fiber sheet is a carbon fiber woven fabric containing carbon fibers in both the warp and weft yarns, and has a fabric weight of 300 g / m ２ 800g / m or more ２ and the crimp angle is 1.0° or more and 3.3° or less.

2. 2. The method for reinforcing concrete according to claim 1, wherein the carbon fiber has a weave density of 1.000 g / m (1,000 tex) to 4.000 g / m (4,000 tex).

3. The method for reinforcing concrete according to claim 1 or 2, wherein a sizing adhesion rate of the carbon fiber is 0.5% by mass or more and 10% by mass or less.

4. 3. The method for reinforcing concrete according to claim 1, wherein the bidirectional carbon fiber sheet has a shear stiffness of 0.40 N / ° or more and 10 N / ° or less.

5. 3. The method for reinforcing concrete according to claim 1, wherein the bending resistance of the bidirectional carbon fiber sheet is 170 mm or more and 400 mm or less.

6. 3. The method for reinforcing concrete according to claim 1, wherein the bidirectional carbon fiber sheet has an opening ratio of 0.1% or more and 10% or less.

7. 3. The concrete reinforcing method according to claim 1, wherein the carbon fiber has a tensile strength of 3,000 MPa or more and 7,000 MPa or less and a tensile modulus of elasticity of 200 GPa or more and 600 GPa or less.

8. The concrete reinforcement method according to claim 1 or 2, wherein the bidirectional carbon fiber sheet contains heat-sealed fibers in at least one of the warp threads or the weft threads, and the heat-sealed fibers are heated and fused to seal the carbon fibers.

9. The bidirectional carbon fiber sheet has a marker thread disposed at a position a wrap length from an end thereof, The concrete reinforcing method according to claim 1 or 2, wherein the bidirectional carbon fiber sheet is attached by wrapping the lap length.

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