JPH10253561A - Carbon fiber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber sheet for detecting distortion, fatigue, and deterioration of a concrete structure. SOLUTION: This carbon fiber sheet is formed by disposing a sub carbon fiber yarn line whose breaking ductility is smaller than that of a main carbon fiber yarn line and is electrically insulated against the main carbon fiber yarn line between the insides or rows of a plurality of main carbon fiber yarn lines arranged in parallel to each other. A carbon fiber-reinforced plastic layer including the carbon fiber sheet is formed on the surface of the concrete structure so as to be integral with the structure to reinforce the structure. By measuring a change in the electric resistance of the sub carbon fiber yarn line, it is possible to detect the distortion, fatigue, and deterioration of the structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon fiber sheet used for forming carbon fiber reinforced plastic (CFRP), and a method for monitoring the state of fatigue or deterioration of a structure using the same.

[0002]

2. Description of the Related Art Concrete bridges, tunnels, chimneys, buildings and other structures are subject to deterioration due to neutralization of concrete, generation of rust, salt damage and the like when used for many years. In addition, repairs and reinforcements are required because there are increases in the load due to the reduction in the weight of passing vehicles, damages due to earthquakes, and revisions to seismic standards that assume a larger earthquake.

As a method of repairing and reinforcing a concrete structure, a steel plate reinforcing method of bonding a steel plate to a concrete structure is known. However, this method has a problem in terms of ease of construction and the like because the weight of the steel sheet is large.
Therefore, in recent years, a hand lay-up method of attaching a carbon fiber sheet to a structure while impregnating it with a resin and curing the resin has resulted in construction that is easy to perform, has a large reinforcing effect, and is compatible with the complex surface of the structure. Attention has come to the point that it can be done.

[0004] However, even if repair and reinforcement are performed, the fatigue and deterioration of the concrete structure due to neutralization and rust progresses, and it is necessary to constantly observe the state. For this reason, methods of monitoring the state of fatigue and deterioration of a structure based on a change in its electrical resistance by utilizing the conductivity of carbon fibers have been studied.

[0005] For example, Japanese Patent Application Laid-Open No. 8-193939 discloses that a CFRP plate containing carbon fiber threads arranged at intervals and having different elastic moduli is attached to a concrete structure.
A method for detecting a crack in concrete by detecting a change in electrical resistance due to breakage of a single yarn constituting a carbon fiber thread is described. Since a carbon fiber yarn having a high elastic modulus has a larger load load than a carbon fiber yarn having a low elasticity and generally has a small elongation at break, a crack in the plate can be detected as a change in electric resistance due to the breakage of the carbon fiber yarn. However, this method has good workability because the CFRP plate is attached, but has the trouble of making the flat plate follow the surface of a structure having a complicated shape,
It takes time to process the flat plate according to the surface to be pasted. Further, when the plate is formed, a phenomenon that the single yarn constituting the carbon fiber yarn is easily bent, that is, easily meanders occurs. Such a phenomenon is often seen especially in the hand lay-up method. If the single yarn meanders, stress will be concentrated on the bent part, so the distortion level of the target structure will not be reflected, and the single yarn will break with less strain, and the electrical resistance of the carbon fiber yarn Becomes large. Therefore, although it is known that it is a low-reliability and effective monitoring method in principle, it has not been put to practical use. It is easy to monitor the change in the electrical resistance of the carbon fiber yarn itself used for repair / reinforcement, but the elongation at break of such a carbon fiber yarn is generally as large as 1.5 to 2.0%. Since almost no fracture occurs in the low strain region, it is difficult to grasp the state of fatigue and deterioration of the structure.

On the other hand, JP-A-5-332965 discloses that
Glass fiber reinforced plastic (GF) using glass fiber as the reinforcing fiber and using carbon fiber for the measurement of electrical resistance
RP). According to this, since the glass fiber does not have conductivity, it is possible to predict the destruction without interposing an insulator between the glass fiber and the carbon fiber. However, the strength of glass fiber is deteriorated by alkali, and therefore, the durability is low.
In addition, since the specific strength is lower than that of carbon fiber, the amount of glass fiber increases when trying to have the same reinforcing effect as carbon fiber, the weight of the base material increases, and the lower surface is reinforced as in the reinforcement of a high-bridge floor slab. It becomes easy to fall when pasted on.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a carbon fiber sheet suitable for detecting fatigue or deterioration of a structure. Another object of the present invention is to provide a method for monitoring fatigue and deterioration of a structure using such a carbon fiber sheet.

[0008]

According to the present invention for achieving the above object, the breaking elongation is smaller than that of the main carbon fiber yarn so as to be parallel to the main carbon fiber yarn, and
The present invention is characterized in that a carbon fiber sheet on which a secondary carbon fiber yarn electrically insulated from the main carbon fiber yarn is arranged.

Further, in order to achieve the above object, the present invention provides a method for breaking and elongating a plurality of main carbon fiber yarns arranged in parallel with each other inside or between the main carbon fiber yarns. Provided is a carbon fiber sheet characterized in that a secondary carbon fiber yarn, which has a small degree and is electrically insulated from the main carbon fiber yarn, is disposed.

In the above, the breaking elongation of the secondary carbon fiber yarn is preferably in the range of 0.3 to 0.6%. Preferably, the electrical insulation is provided by an electrically insulating fiber yarn covered by the secondary carbon fiber yarn. Further, it is preferable that the single yarn constituting the secondary carbon fiber yarn is in a bundled state. Furthermore, the secondary carbon fiber yarn preferably has a twist of 35 to 150 turns / m.

In order to monitor the fatigue and deterioration of the structure, a carbon fiber reinforced plastic layer including the above-mentioned carbon fiber sheet is formed on the surface of the structure so as to be integral with the structure, and the structure is reinforced. At the same time, the measurement is performed by measuring a change in electric resistance of the secondary carbon fiber yarn.
The structure is generally a concrete structure.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon fiber yarn used in the present invention is:
Polyacrylonitrile-based (PAN-based) or pitch-based may be used, but in order to sufficiently exhibit the reinforcing effect of the structure, the tensile strength must be 2,000M.
Those having Pa or more are preferable. 4,700MP in the sense that a large reinforcing effect can be obtained with less usage
It is preferably at least a. Similarly, when the purpose is to reinforce the structure, the tensile modulus is preferably 200 GPa or more, and more preferably 400 GPa or more.

The thickness of the carbon fiber yarn used in the present invention is such that if the carbon fiber yarn is thick, a gap is present between the threads, and the gap prevents the air from being trapped during lamination and resin impregnation. Since it becomes possible, it is good that it is 1,500 denier or more, preferably 6,000 denier or more. On the other hand, if the thickness is too large, the surface smoothness is impaired when CFRP is used, and the appearance of the reinforced structure is deteriorated. Therefore, the denier is preferably 100,000 denier or less.

On the other hand, the secondary carbon fiber yarn may be made of any one of a PAN type and a pitch type like the main carbon fiber yarn. However, the elongation at break of the secondary carbon fiber yarn is smaller than that of the main carbon fiber yarn. Especially,
Concrete structures have elastic deformation strain of 0.1 to
When the strain is higher than 0.2%, the rebar yields and the tensile elongation at break of concrete is less than 0.2%.
Since it is as small as 1%, the breaking elongation of the secondary carbon fiber yarn is preferably in the range of 0.3 to 0.6% in order to detect the yield or fracture state in these low strain regions.
If it is less than 0.3%, the carbon fiber yarns that are subjected to the fatigue due to the repeated load of the structure are also fatigued, and are likely to be finally broken, and the change in the electrical resistance of the carbon fiber yarns over a long term, that is, the structure It becomes difficult to monitor fatigue and deterioration. On the other hand, if it exceeds 0.6%, the number of fractures of the secondary carbon fiber yarns in the low strain region decreases, so that the change in electric resistance also decreases, and the fatigue of the structure increases.
It becomes difficult to detect the deterioration state. As a result, if the elongation at break of the secondary carbon fiber thread is in the range of 0.3 to 0.6%, it becomes possible to detect the fatigue and the deterioration state of the structure with high sensitivity. In addition, the breaking elongation of the main carbon fiber yarn,
A larger value of 1.5 to 2.0% is preferable because fracture in a low strain region hardly occurs and a large reinforcing effect can be expected.

The single yarns constituting the carbon fiber yarns are not uniform in strength even if manufactured under the same conditions because foreign matter is mixed in the manufacturing process or foreign matter adheres to the surface. There are also weak single yarns, and the strength varies considerably.
Therefore, when such a carbon fiber yarn is pulled, the weak single yarn is first broken, and the conductivity at that portion is lost or deteriorated. When the tensile strain level of the carbon fiber yarn increases, the number of broken single yarns increases, and the electric resistance also increases. Such a phenomenon is not related to the impregnation of the resin into the carbon fiber yarns and the curing, but the impregnation with the resin is more effective against the change in the electric resistance since the single yarns are electrically insulated by the resin. Sensitivity increases. The elongation at break of the carbon fiber yarn is measured according to JIS R7601.

In order to increase the number of breaks in the low strain region and increase the change in electric resistance, it is preferable to twist the secondary carbon fiber yarn in the range of 35 to 150 turns / m. preferable. Then, the long single yarn in the yarn swells outward, and the short single yarn is pulled and a large stress acts on the short single yarn, so that the single yarn is easily broken one after another, and the change in electric resistance can be increased. When the number of twists is less than 35 turns / m, the sequential breaking of the single yarn does not occur so much. On the other hand, if the number of twists exceeds 150 turns / m, the impregnation of the resin is hindered, and the contact between the single yarns increases, so that even if the single yarns are sequentially broken, the change in electric resistance does not become so large.

The electrical insulation of the carbon fiber yarn can be performed by winding an electrically insulating material such as a fiber yarn or a film. Examples of the fiber yarn used for winding include glass fiber, polyaramid fiber, vinylon fiber, polyester fiber, nylon fiber, polyamide fiber, polyethyl fiber, and polypropylene fiber. By being fibrous, when the resin is impregnated, the adhesion to the resin is improved, and the coverage ratio for the sub carbon fiber yarn can be freely set by changing the pitch of the winding and the thickness of the yarn. Can be. In addition, by winding a fiber thread or a film around such a carbon fiber thread, it is possible to easily impart a bunching property to the secondary carbon fiber thread. With convergence,
The meandering of the single yarn constituting the carbon fiber yarn during molding can be suppressed. Therefore, it is possible to accurately detect and monitor the state of distortion or deterioration received by the structure from the change in the electrical resistance of the secondary carbon fiber yarn. If the coating ratio is high, insulation of the surrounding main carbon fiber yarns is sufficiently ensured, so that a change in electric resistance can be detected more accurately. Since there is a tendency to be inhibited, the content is preferably in the range of 20 to 50%. Within this range, sufficient convergence of the carbon fiber yarn can be obtained, and there is little possibility that impregnation with the resin is hindered.

The form of the carbon fiber sheet may be a unidirectional woven fabric in which both main and slave carbon fiber yarns are arranged in the warp direction, and weaving and weaving fine auxiliary yarns as weft yarns, and through both the main and slave carbon fiber yarns.
It can be a two-way woven fabric arranged in both weft directions. However, in the case of a bidirectional woven fabric, it is preferable to arrange the secondary carbon fiber yarns in either one of the warp and weft directions so that the change in electrical resistance can be more clearly determined. In addition to the woven fabric, a unidirectional sheet in which both carbon fiber yarns of the master and slave are arranged in a sheet in parallel in one direction, and this is supported by a support material such as silicon paper or sheet mesh via an adhesive. It may be. Note that the carbon fiber sheet may be impregnated with a resin to form a prepreg.

It is sufficient that at least one secondary carbon fiber thread exists in the carbon fiber sheet, and the position may be on the surface of the sheet or inside the sheet. When many are arranged, they can be arranged at intervals of about 5 to 50 cm. When a large number of carbon fiber sheets are laminated on the surface of the structure, at least one carbon fiber sheet of the present invention is included.

In the case where the carbon fiber sheet is a woven fabric, it is preferable that the warp and the weft intersect with each other with an adhesive to seal the portion. When the sealing is performed in this way, even when pressure is applied by a roller or a spatula during resin impregnation, it is difficult for the yarn to meander, and even when cut according to the shape of the structure, the woven yarn is not easily frayed. . As an adhesive for filling,
Preferably, a thermoplastic polymer is used. In particular, when the resin impregnating the carbon fiber sheet is an epoxy resin, a copolymer nylon having good adhesion to the epoxy resin is preferable.

Further, the auxiliary yarn is preferably made of glass fiber which does not shrink even when the woven fabric is stored at room temperature or heat-treated. When the auxiliary yarn as the weft shrinks, the weaving density of the main carbon fiber yarn as the warp increases and the reinforcing effect differs, and the reinforcing area also changes as the width of the fabric decreases.

If the basis weight of the carbon fiber sheet is too small, the number of layers increases in order to secure the amount of fibers for reinforcement,
Conversely, if it is too large, the impregnating property of the resin is reduced.
It is preferably in the range of about 700 g / m ² .

The carbon fiber sheet is applied to the surface of a concrete structure or the like to be repaired or reinforced while impregnating the resin with the resin, and after the resin is cured, the change in the electric resistance value of the secondary carbon fiber yarn is changed. , It is possible to monitor the state of strain, fatigue and deterioration occurring in the structure.

That is, first, dirt such as oil adhering to the surface of the concrete structure is washed, cracks are filled with a putty or the like, and irregularities on the surface are corrected smoothly with a mortar or a putty. Next, a primer for improving the adhesion between the concrete and the CFRP is applied, and is left to dry overnight. Thereafter, a cold-setting epoxy resin serving as a matrix of CFRP is applied, a carbon fiber sheet is attached, and the distribution of the resin is made uniform with a roller or a spatula, and the resin is impregnated into the carbon fiber sheet. Further, a resin is applied thereon, and pressure is applied with a roller or a rubber spatula. After repeating such a step as necessary, the resin is cured to form CFRP.

In order to observe the state of the distortion of the structure from the change in the electric resistance of the carbon fiber yarn, a conductive paint is applied to both ends of the carbon fiber yarn, and the lead wire is further adhered. After the terminal is connected, an electric resistance meter is connected to this terminal, and the electric resistance measured by this is detected as a strain applied to the structure by a conversion table of electric resistance value and strain prepared in advance. . Further, if the change in the electric resistance is monitored continuously or periodically, it is possible to detect the state of fatigue and deterioration of the structure. In this way, structures such as concrete bridge decks, bridge girders, piers, building columns, walls, floor decks, girders,
It is possible to know the state of distortion, fatigue and deterioration of the walls, columns and girders of the tunnel.

The resin impregnated in the carbon fiber sheet is as follows:
In repairing and reinforcing concrete structures, epoxy resin, vinyl ester resin, unsaturated polyester resin,
Thermosetting resins such as phenolic resins are preferred. Among them, epoxy resin is preferable because it has a large adhesive strength to concrete, is resistant to alkali, and has excellent adhesiveness to carbon fiber. Since the epoxy resin can be cured by leaving it at the construction site, a two-pack type epoxy resin comprising a main agent and a curing agent is preferable. The main component is mainly composed of an epoxy resin composition that is liquid at an ambient temperature of 5 to 30 ° C, and the curing agent is mainly composed of an amine compound that is liquid at 5 to 30 ° C. In addition, epoxy resin
It is preferable that the glass transition temperature when cured and cured at room temperature for 10 days is 45 ° C. or higher so that CFRP can exhibit sufficiently high strength after curing.

[0027]

EXAMPLE A carbon fiber yarn having a breaking elongation of 0.
After using 5% PAN-based high-modulus type carbon fiber and coating it with polyester fiber, it is arranged between the main carbon fiber yarns so as to be parallel to the main carbon fiber yarns of the unidirectional carbon fiber fabric. Thus, a carbon fiber sheet was obtained. The coverage of the secondary carbon fiber yarn was 45%. This carbon fiber sheet is impregnated with a room temperature curing type epoxy resin, molded and CF
An RP plate was obtained. The molding was performed by hand lay-up using a roller, and the curing was performed at room temperature of 23 ° C.

The tensile fatigue test was performed according to JIS K7073. 12.5mm width, 2 length from CFRP board
Cut out a test piece of 50 mm, and 0 to 0.2% in the fiber direction
Was given repeatedly. The strain was read by a strain gauge attached to the test piece, and the strain applied to the test piece was controlled. The test was performed in an atmosphere at 23 ° C. at a speed of 1 mm / min.

The electrical resistance was measured by polishing both ends of the test piece, applying a conductive paint to the ends to form terminals, and connecting a Wheatstone bridge to the terminals. The electrical resistance of the secondary carbon fiber yarn after 50 times of the fatigue test increased by 0.48% as compared to before the test. Another similar test
When the test was performed on each of the test pieces, the electrical resistance increased by 0.50% and 0.54%, respectively.

[0030]

The carbon fiber sheet of the present invention has an elongation at break smaller than that of the main carbon fiber yarn so as to be in parallel with the main carbon fiber yarn, and has an electric resistance with respect to the main carbon fiber yarn. Insulated secondary carbon fiber yarns are placed on the surface and used to repair or reinforce structures such as concrete structures. You can easily know the status.

Claims (8)

[Claims] Claims: 1. A breaking elongation smaller than that of a main carbon fiber yarn so as to be parallel to the main carbon fiber yarn, and
A carbon fiber sheet, wherein a secondary carbon fiber yarn electrically insulated from the main carbon fiber yarn is arranged. 2. The main carbon fiber yarn, wherein the main carbon fiber yarn has a smaller breaking elongation than the main carbon fiber yarn inside or between a plurality of main carbon fiber yarns arranged in parallel with each other. A carbon fiber sheet comprising a secondary carbon fiber thread electrically insulated from the carbon fiber sheet. 3. A carbon fiber yarn having a breaking elongation of 0.3 to less.
The carbon fiber sheet according to claim 1, wherein the carbon fiber sheet is in a range of 0.6%. 4. The carbon fiber sheet according to claim 1, wherein the electrical insulation is provided by an electrically insulating fiber yarn covered by the secondary carbon fiber yarn. 5. The carbon fiber sheet according to claim 1, wherein the single yarns constituting the secondary carbon fiber yarns are in a bundle state. 6. The secondary carbon fiber yarn has a length of 35 to 150 times / m.
The carbon fiber sheet according to any one of claims 1 to 5, which has a twist of: 7. A structure in which a carbon fiber reinforced plastic layer containing the carbon fiber sheet according to any one of claims 1 to 6 is formed on the surface of the structure so as to be integral with the structure, and the structure is reinforced. And a method for monitoring fatigue of the structure by measuring a change in electrical resistance of the carbon fiber yarn. 8. The method for monitoring a structure according to claim 7, wherein the structure is a concrete structure.