Concrete reinforcement method and concrete structure

Abstract

To provide a technique for reinforcing a concrete structure by attaching a fiber-reinforced resin sheet to the surface opposite to the surface receiving an impact, and for making it easier to grasp the extent of damage when the structure is damaged.SOLUTION: There is provided a concrete reinforcement method for preventing back surface damage, in which the other surface (rear surface 12) opposite to one surface (front surface 11) of concrete 1 is damaged due to the collision of a flying object 2 with the one surface (front surface 11), by attaching a fiber-reinforced resin sheet 3 having translucency and reinforcing fibers to the other surface (rear surface 12). When the fiber-reinforced resin sheet 3 is attached to the other surface (rear surface 12) of the concrete 1, back surface damage that occurs on the other surface (rear surface 12) of the concrete 1 can be visually observed from the outside through the fiber-reinforced resin sheet 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a concrete reinforcement method for reinforcing by attaching a fiber-reinforced resin sheet to one surface of concrete, and a concrete structure (also referred to as a "concrete structure") having a fiber-reinforced resin sheet on one surface of concrete.

Background Art

[0002] When a relatively large-mass object such as a falling rock, debris flow, or avalanche collides with a concrete structure at a low speed, overall failure accompanied by large deformations such as flexural failure or shear failure occurs in the concrete. On the other hand, when a relatively small-mass object collides at high speed, such as a bullet or explosive collision, or a flying object collision caused by a typhoon or tornado, local failure progresses in the process of concrete surface destruction, penetration, back surface peeling, and penetration. Thus, in a concrete member that undergoes a high-speed collision of a flying object at a speed of several tens of m / s to several hundreds of m / s, the aspect is completely different from overall failure due to flexural failure or shear failure.

[0003] Conventionally, as a concrete member that undergoes a collision of a high-speed flying object, non-porous concrete having a relatively high strength of about 400 N / mm 2 has been studied (Non-Patent Document 1). This concrete has a compressive strength more than 14 times that of general concrete of about 28 N / mm 2 , but the member thickness can only be reduced by about 30%. In addition, it is difficult to industrially mass-produce non-porosity that allows not even one defect, and in order to ensure non-porosity, it is also necessary to perform a full inspection, which is lacking in practicality.

[0004] Another study also reports that although surface local penetration due to an increase in the compressive strength of concrete is slightly suppressed, no suppression effect on back surface peeling is recognized (Non-Patent Document 2). From the above, although concrete is an indispensable material for mass production, it is clear that increasing the strength of concrete is not a solution for suppressing back surface failure against the collision of a high-speed flying object.

[0005] On the other hand, an impact-resistant member for a high-speed flying object using ceramics has also been proposed (Patent Document 1). However, ceramics are expensive materials for mass production, resulting in an excessive economic burden and limited application scope.

[0006] In addition, as a method for preventing the back surface failure of concrete due to the collision of a high-speed flying object, a reinforcement method of attaching a sheet of aramid fiber or carbon fiber to the back surface of the concrete has also been proposed (Non-Patent Document 3). Non-Patent Document 3 shows the generation process of back surface peeling as shown in FIG. 12. FIG. 13 shows an image of an example of back surface peeling. FIG. 13(a) is an example described in Non-Patent Document 3, and FIGS. 13(b) and 13(c) are examples described in Non-Patent Document 4. These are examples where no particular reinforcement is provided by the sheet.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] In recent years, there have been many reports of damage to shelters caused by volcanic projectiles and damage to buildings caused by tornado projectiles, and there is a need to establish a method for reinforcing concrete structures such as shelters, protective walls, and buildings. Even if such a concrete structure is damaged by a projectile, it cannot be repaired immediately, and in some cases, it is necessary to continue using it as it is for a certain period. Therefore, it is necessary to determine which concrete structures can continue to be used as they are or which require urgent repair.

[0010] An object of the present invention is to provide a technique for sufficiently increasing the strength after reinforcement and making it easy to grasp the degree of damage when a concrete structure is damaged.

Means for Solving the Problems

[0011] According to the present invention, the following techniques are provided. [1] A concrete reinforcement method for preventing back surface failure in which the other surface opposite to one surface of the concrete is damaged by the impact of a projectile on one surface of the concrete, by attaching a fiber-reinforced resin sheet having translucency and reinforcing fibers to the other surface, A concrete reinforcement method in which, in a state where the fiber-reinforced resin sheet is attached to the other surface of the concrete, the back surface failure occurring on the other surface of the concrete can be visually recognized from the outside through the fiber-reinforced resin sheet. [2] The fiber-reinforced resin sheet has a transparent base material, and the concrete reinforcement method according to [1]. [3] The fiber-reinforced resin sheet is obtained by impregnating and curing a resin in a glass fiber sheet, and is a concrete reinforcement method described in [2]. [4] The fiber-reinforced resin sheet is attached to the concrete using an adhesive, The adhesive contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin, and is a concrete reinforcement method described in any one of [1] to [3]. [5] The application amount of the adhesive is 200 g / m 2 or more and 2000 g / m 2 or less, and is a concrete reinforcement method described in [4]. [6] When the back surface peeling limit energy calculated by the modified NDRC formula applied to the standardized concrete having a shape of 500 mm in length × 500 mm in width × 80 mm in thickness and a compressive strength of 53 N / mm 2 is defined as U1, and when the fiber-reinforced resin sheet is attached to the back surface of the standardized concrete and the impact energy when back surface failure occurs due to one impact of the flying object is defined as U2, U2 / U1 ≧ 1.2, and is a concrete reinforcement method described in any one of [1] to [5]. [7] The step of attaching the fiber-reinforced resin sheet to the other surface of the concrete is to adhere the fiber-reinforced resin sheet to the concrete using an adhesive after prepregulating the fiber-reinforced resin sheet, and is a concrete reinforcement method described in any one of [1] to [6]. [8] The impregnation amount of the resin impregnated into the fiber-reinforced resin sheet for prepregulating is 50 g / m 2 or more and 1400 g / m 2 or less, and is a concrete reinforcement method described in [7]. [9] The basis weight of the fiber-reinforced resin sheet is 200 g / m 2 or more and 1400 g / m 2The concrete reinforcement method according to any one of [1] to [8] below.

[10] A concrete reinforcement method used for a concrete structure, in which a fiber-reinforced resin sheet having reinforcing fibers with translucency on the opposite surface of one surface facing outward is attached to the concrete. A concrete back surface reinforcement method in which, in a state where the fiber-reinforced resin sheet is attached to the opposite surface of the concrete, the damage state occurring on the opposite surface of the concrete due to an object colliding with the surface facing outward can be visually recognized from the outside through the fiber-reinforced resin sheet.

[11] Concrete, A fiber-reinforced resin sheet having reinforcing fibers and having translucency, attached to the first surface of the concrete, and comprising, A concrete structure in which the back surface damage occurring on the first surface due to a flying object colliding with the second surface opposite to the first surface can be visually recognized from the outside through the fiber-reinforced resin sheet.

[12] The concrete structure according to

[11] , wherein the fiber-reinforced resin sheet has a transparent base material.

[13] The concrete structure according to

[12] , wherein the fiber-reinforced resin sheet is obtained by impregnating and curing a resin in a glass fiber sheet.

[14] The fiber-reinforced resin sheet is attached to the concrete by an adhesive, The concrete structure according to any one of

[11] to

[13] , wherein the adhesive contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin.

[15] The coating amount of the adhesive is 200 g / m 2 or more and 2000 g / m 2 or less. The concrete structure according to

[14] .

[16] Let U1 be the back surface peeling limit energy calculated by the modified NDRC formula applied to the concrete. With the first surface of the concrete as the back surface and the second surface as the front surface, when the fiber reinforced resin sheet is attached to the first surface and back surface failure occurs due to a single impact on the second surface of the flying object, let the impact energy at this time be U2. U2 / U1≥1.2 The concrete structure according to any one of

[11] to

[15] .

[17] The fiber reinforced resin sheet is a prepreg sheet impregnated with resin and is adhered to the first surface of the concrete using an adhesive. The concrete structure according to any one of

[11] to

[16] .

[18] In the prepreg sheet, the impregnation amount of the impregnated resin is 50 g / m 2 or more and 1400 g / m 2 or less. The concrete structure according to

[17] .

[19] The basis weight of the fiber reinforced resin sheet is 200 g / m 2 or more and 1400 g / m 2 or less. The concrete structure according to any one of

[11] to

[18] .

Advantages of the Invention

[0012] According to the present invention, in a concrete structure, it is possible to provide a technique for sufficiently increasing the strength after reinforcement and making it easy to grasp the degree of damage when damaged.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

[0014] <Summary of This Embodiment> In this embodiment, a concrete back surface reinforcement technique will be described. FIG. 1 is a view showing concrete 1 with a fiber-reinforced resin sheet 3 attached to the back surface 12, FIG. 1(a) is a front view, FIG. 1(b) is a side view, and FIG. 1(c) is a rear view. FIG. 2 is an enlarged view of region A in FIG. 1(b). In FIG. 2, the concrete 1 is represented by hatching. FIG. 3 is an example of the concrete 1, FIG. 3(a) is an image of the concrete 1 before the fiber-reinforced resin sheet 3 is attached (blank), and FIG. 3(b) is an image of the concrete 1 with the fiber-reinforced resin sheet 3 attached.

[0015] Examples of concrete structures (structures of concrete 1) that can adopt the concrete 1 include (1) facilities related to public facilities, (2) living infrastructure, communication, and transportation facilities, and (3) facilities important for national defense and disaster prevention facilities. More specifically, they are as follows. (1) Examples of facilities related to public facilities include, for example, schools, research facilities, hospitals, police stations, fire stations, gymnasiums, community centers, government offices, libraries, museums, art galleries, stadiums, etc. (2) Examples of living infrastructure, communication, and transportation facilities include, for example, power plants, substations, gas facilities, waterworks, communication bases, broadcasting stations, stations, subways, port facilities, airports, etc. (3) Examples of facilities important for national defense and disaster prevention facilities include, for example, Self-Defense Force garrisons, bases, airports, nuclear facilities (nuclear reactors, nuclear power plants, nuclear fuel processing facilities, reprocessing facilities, spent fuel storage facilities), shelters, mountain huts, etc. Note that the above concrete structures are examples and are also applicable to concrete structures other than the above.

[0016] The concrete back surface reinforcement method of this embodiment is to attach a fiber-reinforced resin sheet 3 having translucency and reinforcing fibers to the back surface 12 in order to prevent back surface failure, which is a phenomenon in which the other surface (hereinafter referred to as "back surface 12") on the side opposite to the surface 11 is damaged when a flying object 2 (also referred to as a high-speed flying object) collides with one surface of the concrete 1 (i.e., the structure of the concrete 1). Note that the surface 11 and the back surface 12 of the concrete 1 are not particularly distinguished by the structure or the like, but are based on the difference in whether the fiber-reinforced resin sheet 3 is attached or not. In other words, the back surface 12 of the concrete 1 refers to the back surface, not the surface (surface 11) where the flying object 2 collides. With the fiber-reinforced resin sheet 3 attached to the back surface 12 of the concrete 1, the back surface failure occurring on the back surface 12 of the concrete 1 can be visually recognized from the outside through the fiber-reinforced resin sheet 3.

[0017] In other words, in the concrete 1, one surface faces outward (i.e., the side where the flying object 2 is likely to fly in, generally the outside), and a fiber-reinforced resin sheet 3 having translucency and reinforcing fibers is attached to the surface opposite to the one surface (the inner surface). In the state where the fiber-reinforced resin sheet 3 is attached to the opposite surface of the concrete 1, the damage state occurring on the opposite surface (back surface 12) of the concrete 1 due to the collision of an object (flying object 2) with the surface facing outward (here, the surface 11) can be visually recognized from the outside through the fiber-reinforced resin sheet 3.

[0018] In this embodiment, back surface failure (also referred to as "back surface peeling") refers to a state in which peeling occurs on the back surface 12 due to the collision of the flying object 2 with the surface 11. For an example of back surface failure, refer to FIG. 13 above. Also, as another example of back surface peeling in FIG. 10, two examples are shown regarding the state before and after the collision of the flying object 2, one with the fiber-reinforced resin sheet 3 attached and the other without the fiber-reinforced resin sheet 3 attached. The fiber-reinforced resin sheet 3 is obtained by impregnating and curing a resin in a glass fiber sheet. FIG. 11 shows the states of the surface 11 and the back surface 12 of the concrete 1 before and after the collision of the flying object 2 (for experiment) with the surface 11 of the concrete 1 to which the fiber-reinforced resin sheet 3 is attached.

[0019] <Concrete>

[0020] First, the concrete 1 to be back-reinforced will be described. Subsequently, the test concrete 101 and the back-reinforced concrete 102 will be described.

[0021] In this embodiment, the concrete 1 generically refers to concrete, mortar, and cement paste. Also, the concrete 1 may be plain concrete or reinforced concrete.

[0022] The concrete 1 may be fiber-reinforced concrete in which short fibers are mixed into the concrete. The short fibers to be mixed may be of one type or multiple types. As the short fibers, for example, polypropylene, polyethylene terephthalate, or vinylon can be used. As the size of the short fibers, for example, the fiber diameter can be 0.01 mm to 0.1 mm, and the fiber length can be 10 mm to 30 mm.

[0023] The fiber-reinforced concrete can be expected to have the effect of dispersing the impact when the flying object 2 collides and the effect of suppressing the scattering of concrete pieces. The usage amount of the short fibers can be, for example, 1 to 5 Vol.% in terms of volume ratio. If it is 1 Vol.% or more, the impact resistance and the prevention of the scattering of broken concrete pieces will be sufficient, and if it is 5 Vol.% or less, sufficient performance can be expected.

[0024] From the viewpoint of preventing back surface failure caused by the collision of the flying object 2, the strength level of the concrete 1 is preferably such that the compressive strength is 18 N / mm 2 or more and 200 N / mm 2 or less. The lower limit of the compressive strength is preferably 50 N / mm 2 or more, and more preferably 75 N / mm 2 or more. The upper limit is preferably 175 N / mm 2 or less, and more preferably 150 N / mm 2 or less. If it is 18 N / mm 2 or more, the impact resistance will be sufficient, and if it is 200 N / mm2 In the following cases, the production of concrete slabs becomes easier, productivity improves, and costs tend to be reduced.

[0025] The required compressive strength varies depending on the mass and velocity of the flying object 2 that collides, that is, the collision energy per impact. For example, whether to obtain the compressive strength that can withstand one impact under the condition of a large collision energy per impact, or whether to obtain the compressive strength that can withstand multiple impacts although the collision energy per impact is not so large, the required compressive strength varies.

[0026] <Fiber Reinforced Resin Sheet> The fiber reinforced resin sheet 3 is attached to the back surface of the concrete 1 using adhesives 50 (the first adhesive 51 and the second adhesive 52 described later). Although details will be described later, the first adhesive 51 is applied as a primer to the back surface 12 of the concrete 1, the fiber reinforced resin sheet 3 is attached, and then the second adhesive 52 is applied as a topcoat if necessary. Hereinafter, when the first adhesive 51 and the second adhesive 52 are not distinguished, they will be described as the adhesive 50. Note that the fiber reinforced resin sheet 3 may be a single sheet or may be composed of a plurality of sheets.

[0027] The fiber reinforced resin sheet 3 has a transparent base material. Specifically, examples of the transparent base material include resin sheets reinforced with fibers such as glass fiber, polyester fiber, vinylon fiber, polyamide fiber, polyethylene fiber, polyparaphenylene fiber, and polyarylate fiber. From the viewpoints of transparency, strength, and affinity with the adhesive, a glass fiber sheet can be preferably used.

[0028] The glass filaments constituting the glass fiber sheet may be, for example, E glass, AR glass, S glass, C glass, D glass, ECR glass, or the like. Among these, from the viewpoints of strength, durability, and the balance between these and cost, the glass fiber sheet preferably contains one or more selected from the group consisting of E glass, AR glass, and ECR glass.

[0029] The lower limit of the air permeability of the glass fiber sheet is, for example, 30 cm 3 / (cm 2 ·s) or more, preferably 50 cm 3 / (cm 2 ·s) or more, more preferably 60 cm 3 / (cm 2 ·s) or more. Thereby, the impregnation property of the adhesive 50 can be improved. Further, when the glass fiber sheet is attached and impregnated with a roller after applying the adhesive 50, air bubbles can easily escape, so that the appearance of the base can be improved and the glass fiber sheet can be prevented from floating. The upper limit of the air permeability of the glass fiber sheet is, for example, 800 cm 3 / (cm 2 ·s) or less, preferably 600 cm 3 / (cm 2 ·s) or less, more preferably 500 cm 3 / (cm 2 ·s) or less. Thereby, the yarn can be prevented from being entangled and the workability can be improved.

[0030] The lower limit of the fineness of the fiber bundle constituting the glass fiber sheet is, for example, 50 tex or more, preferably 60 tex or more, more preferably 70 tex or more. Thereby, the opening of the fiber sheet can be appropriately formed. When the glass fiber sheet is attached and impregnated with a roller after applying the adhesive 50, air bubbles can easily escape, so that the appearance of the base can be improved and the fiber sheet can be prevented from floating. The upper limit of the fineness of the fiber bundle is, for example, 4000 tex or less, preferably 3000 tex or less, more preferably 2000 tex or less. Thereby, the density of the glass fiber sheet can be configured to be a certain level or more, and the yarn entanglement prevention property can be improved.

[0031] The upper limit of the loss on ignition of the fiber bundle constituting the glass fiber sheet is, for example, 5% or less, preferably 3% or less, more preferably 1% or less. Thereby, the impregnation property of the fiber adhesive can be improved. The lower limit of the loss on ignition of the fiber bundle is not particularly limited, but may be 0.01% or more.

[0032] The fiber-reinforced resin sheet 3 may be a unidirectional sheet (UD material) formed by arranging fiber bundles in one direction, or a biaxial sheet (cross sheet) formed by weaving fiber bundles as warp and weft in two axes. As the weaving method, there are many patterns in which the warp and weft intersect, such as plain weave, twill weave, and satin weave, but the pattern is not limited. Also, in the case of a biaxial sheet, it may be a sheet (laminated sheet) in which two unidirectional sheets are laminated so that the directions of the fiber bundles are different. Also, in the case of a biaxial sheet, the directions of the fiber bundles may be slightly inclined without being orthogonal. Also, it may be a multi-axial sheet in which a unidirectional sheet and a biaxial sheet are combined and laminated in three or more layers. In the case of a multi-axial sheet, different types of fiber-reinforced resin sheets 3 (for example, an aramid fiber sheet and a carbon fiber sheet) may be laminated. From the viewpoint of impregnating the fiber-reinforced resin sheet 3 with an adhesive, a biaxial sheet woven in plain weave is preferable. That is, the adhesive easily impregnates the unevenness on the front and back surfaces of the fiber-reinforced resin sheet 3 formed by plain weave.

[0033] <Areal weight of fiber-reinforced resin sheet> The areal weight (also referred to as "areal density") of the fiber-reinforced resin sheet 3 is appropriately set. For example, it can be 200 g / m 2 or more and 1400 g / m 2 or less. The lower limit of the areal weight is preferably 250 g / m 2 or more, and more preferably 300 g / m 2 or more. The upper limit of the areal weight is preferably 1200 g / m 2 or less, and more preferably 1000 g / m 2 or less. Note that this areal weight may be achieved by one sheet, or may be a total of two or more sheets.

[0034] When the areal weight is 200 g / m 2If it is more than the above, the amount of fibers increases, and the desired strength (i.e., the strength capable of preventing back surface fracture) can be obtained as the fiber-reinforced resin sheet 3. Also, since the gaps between the fibers do not become too wide, the amount of adhesive required to attach the fiber-reinforced resin sheet 3 to the concrete 1 does not increase too much, and the curing time does not become longer as the amount of the adhesive increases, improving the workability.

[0035] The basis weight is 1400 g / m 2 If it is less than the above, the adhesive easily impregnates between the fibers, making it easy to obtain the desired adhesive strength.

[0036] <Light transmittance of the fiber-reinforced resin sheet> The fiber-reinforced resin sheet 3 has light transmittance. In the present embodiment, "having light transmittance" means that the visible light transmittance (wavelength 380 to 780 nm) of the fiber-reinforced resin sheet 3 is 60% or more. The visible light transmittance is measured in accordance with JIS A 5759. The visible light transmittance is preferably 65% or more, and more preferably 70% or more. When the visible light transmittance is in such a range, the back surface fracture can be clearly visually recognized through the fiber-reinforced resin sheet 3. Specifically, when a back surface fracture occurs on the back surface 12 of the concrete 1, the refractive index changes due to deformation of the interface between the concrete 1 and the first adhesive 51, the internal structure of the first adhesive 51, the internal structure of the fiber-reinforced resin sheet 3, etc., and it is presumed that the portion with the back surface fracture appears discolored (see FIGS. 10 and 11). For example, when a back surface fracture occurs in the concrete 1, a part of the first adhesive 51 fixed to the back surface 12 deforms or the first adhesive 51 and the back surface 12 are separated due to cracks or peeling accompanying the back surface fracture. As a result, the refractive index changes at the deformed portion and appears discolored when visually recognized.

[0037] <Adhesive (first adhesive, second adhesive)> As the adhesive 50, the first adhesive 51 is used as the primer and the second adhesive 52 is used as the topcoat. The first adhesive 51 and the second adhesive 52 may be of the same type or different types of adhesives. The presence of the first adhesive 51 and the second adhesive 52 causes the first adhesive 51 and the second adhesive 52 to come into contact through the fiber-reinforced resin sheet 3, resulting in increased adhesion strength. When the basis weight of the fiber-reinforced resin sheet 3 is small, the application of the second adhesive 52 can be omitted. When the basis weight is small, for example, when the basis weight is 400 g / m 2 The following cases are meant. When the basis weight of the fiber-reinforced resin sheet 3 is small, as described above, the interval between the fibers becomes wide, so the amount of the first adhesive 51 used increases, and the first adhesive 51 may ooze out to the front side of the fiber-reinforced resin sheet 3. Therefore, in some cases, the same effect as when using the second adhesive 52 as the topcoat can be obtained only by using the first adhesive 51 as the primer. In such cases, the second adhesive 52 can be omitted.

[0038] As the type of the adhesive 50, an adhesive containing a (meth)acrylic resin ((meth)acrylic resin-based adhesive), an adhesive containing an epoxy resin (epoxy resin-based adhesive), etc. can be used. The (meth)acrylic resin-based adhesive contains (meth)acrylic acid or its derivatives (such as methyl methacrylate) as the main component. In this embodiment, it includes an adhesive containing a methacrylic (MMA) resin-based adhesive (MMA resin-based adhesive). The first adhesive 51 and the second adhesive 52 being of the same type includes, for example, the case where both are acrylic resin-based adhesives of the same type (component), and the case where the components are different but they are different types of (meth)acrylic resin-based adhesives. The first adhesive 51 and the second adhesive 52 may be of any type as long as the desired adhesiveness and workability are achieved.

[0039] [(Meth)acrylic monomers and their oligomers] This embodiment contains, as a (meth)acrylic adhesive component, a monofunctional, bifunctional or trifunctional or higher (meth)acrylic monomer, or a (meth)acrylic oligomer in which a plurality of these (meth)acrylic monomers are bonded. The (meth)acrylic adhesive component is a radically polymerizable component.

[0040] Examples of the (meth)acrylic monomer include (meth)acrylic acid or its derivative, (meth)acrylamide or its derivative, etc., and one kind or a mixture of two or more kinds may be used.

[0041] Examples of the above (meth)acrylic acid derivative include the following.

[0042] (i) A monomer represented by the following formula (1). Z-O-R1(1) (In the formula, Z represents a (meth)acryloyl group, a CH2=CHCOOCH2-CH(OH)CH2O- group or a CH2=C(CH3)COOCH2-CH(OH)CH2O- group, and R1 represents hydrogen, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, a benzyl group, a phenyl group, a tetrahydrofurfuryl group, a glycidyl group, a dicyclopentyl group, a dicyclopentenyl group, a (meth)acryloyl group and an isobornyl group)

[0043] Examples of such a monomer include methyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenyl (meth)acrylate, glycerol (meth)acrylate, glycerol di(meth)acrylate, isobornyl (meth)acrylate and (meth)acrylic acid, etc.

[0044] (ii) A monomer represented by the following formula (2). Z-O-(R2O) p -R1(2) (wherein Z and R1 are as described above. R2 is -C2H4-, -C3H6-, -CH2CH(CH3)-, -C4H8- or -C6H 12 -, and p represents an integer from 1 to 25)

[0045] Examples of such monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethoxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, tripropylene glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate, etc.

[0046] (iii) A monomer represented by the following formula (3).

[0047] [Chemical formula] (wherein Z and R2 are as described above. Z' represents a (meth)acryloyl group, a CH2=CHCOOCH2-CH(OH)CH2O- group or a CH2=C(CH3)COOCH2-CH(OH)CH2O- group, R'2 is -C2H4-, -C3H6-, -CH2CH(CH3)-, -C4H8- or -C6H 12 (-, R3 and R'3 represent hydrogen or an alkyl group having 1 to 4 carbon atoms, q + q' represents an integer from 0 to 20, preferably an integer from 0 to 8. Z and Z' may be the same or different. R2 and R2' may be the same or different. R3 and R'3 may be the same or different.)

[0048] Examples of such monomers include 2,2-bis(4-(meth)acryloxyphenyl)propane, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypropoxyphenyl)propane, 2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane, and 2,2-bis(4-(meth)acryloxypolyethoxyphenyl)propane, bisphenol A ethylene oxide modified di(meth)acrylate, and the like.

[0049] (iv) (Meth)acrylic acid esters of polyhydric alcohols not contained in the monomers described in (i), (ii), or (iii) above.

[0050] Examples of such monomers include trimethylolpropane tri(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, and the like.

[0051] (v) Urethane prepolymers having a (meth)acryloyloxy group. Such monomers can be obtained, for example, by reacting (meth)acrylic acid esters having a hydroxyl group, organic polyisocyanates, and polyhydric alcohols.

[0052] Examples of (meth)acrylic acid esters having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, and the like.

[0053] Examples of the above organic polyisocyanates include toluene diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate, and the like.

[0054] Examples of the above polyhydric alcohol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyester polyol, and the like.

[0055] One or more of the above monomers (i) to (v) can be used. Among these, one or more of the group consisting of (i) and (iii) are preferable, and it is more preferable to use (i) and (iii) in combination, in terms of large adhesiveness and small adhesion strain of the adherend after adhesion. When (i) and (iii) are used in combination, the composition ratio is preferably (i):(iii) = 50 to 95:5 to 50 by mass ratio, and more preferably 60 to 80:20 to 40.

[0056] [Epoxy monomer and its oligomer] This embodiment may contain an epoxy monomer or an epoxy oligomer in which a plurality of these epoxy monomers are bonded as an epoxy adhesive component.

[0057] Examples of the epoxy monomer include bisphenol type such as bisphenol A type, bisphenol F type, bisphenol AD type, bromine-containing bisphenol A type; phenol novolak type, cresol novolak type, polyphenol type, linear aliphatic type, butadiene type, glycidyl ester type epoxy monomers such as urethane; aliphatic glycidyl ester type epoxy monomers such as hexahydrophthalic acid glycidyl ester, dimer type glycidyl ester, aromatic type, cycloaliphatic type; methyl-substituted type epoxy monomers such as ester type, high molecular weight ether ester type, ether ester type, bromine-based novolak type; heterocyclic type epoxy monomers; glycidyl amine type epoxy monomers such as triglycidyl isocyanurate, tetraglycidyl diaminodiphenylmethane; linear aliphatic type epoxy monomers such as epoxidized polybutadiene, epoxy soybean oil; cycloaliphatic type epoxy monomers, naphthalene-based novolak type epoxy monomers; diglycidyl oxy naphthalene type epoxy monomers, and the like. These epoxy monomers may be used as a mixture of one or more.

[0058] <Elastomer (B)> In this embodiment, by using the elastomer (B), the toughness of the adhesive composition can be enhanced, and the adhesion and adhesiveness can be improved. Further, it is preferable that the elastomer (B) is soluble in the reactive component (A).

[0059] Examples of the elastomer (B) include one or more selected from the group consisting of methyl (meth) acrylate-butadiene-styrene copolymer (such as MBS resin), butadiene rubber, butadiene-(meth)acrylonitrile copolymer (such as NBR (nitrile rubber)), methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer (such as MABS resin), etc. (meth)acrylonitrile copolymers, and modified polyvinyl alcohol. Among them, from the viewpoint of compatibility, one or more selected from the group consisting of butadiene-(meth)acrylonitrile copolymer, methyl (meth) acrylate-butadiene-styrene copolymer, and methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer are preferable, one or more selected from the group consisting of butadiene-(meth)acrylonitrile copolymer and methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer are more preferable, and it is even more preferable to use a combination of butadiene-(meth)acrylonitrile copolymer and methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer. When using a combination of butadiene-(meth)acrylonitrile copolymer and methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer, the combined ratio is preferably butadiene-(meth)acrylonitrile copolymer:methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer = 10 - 90:10 - 90, more preferably 25 - 75:25 - 75, and even more preferably 40 - 60:40 - 60 in a total of 100 parts by mass of butadiene-(meth)acrylonitrile copolymer and methyl (meth) acrylate-(meth)acrylonitrile-butadiene-styrene copolymer.

[0060] The content of the elastomer (B) based on 100 parts by mass of the total content of the reaction component (A) and the elastomer (B) is preferably 15 to 35 parts by mass, more preferably 15 to 30 parts by mass, and still more preferably 15 to 28 parts by mass. By setting the content of the elastomer (B) to be equal to or higher than the above lower limit value, the stress relaxation property becomes good. On the other hand, by setting the content of the elastomer (B) to be equal to or lower than the above upper limit value, the coating property becomes good.

[0061] The adhesive composition of the present embodiment may further contain the following components.

[0062] <Polymerization initiator (C)> The adhesive composition of the present embodiment preferably contains a polymerization initiator (C) for reacting the reaction component (A). Among them, as the polymerization initiator (C), a radical polymerization initiator is preferable. As the radical polymerization initiator, an organic peroxide is preferable. The organic peroxide decomposes by heating to generate free radicals, and can promote the curing of the adhesive by causing an addition reaction to the (meth)acrylic monomer and its oligomer. As the organic peroxide, from the viewpoint of improving the storage stability of the adhesive composition of the present embodiment, it is preferable to use one having a decomposition temperature (1-hour half-life temperature) for obtaining a half-life of 1 hour of 100 °C or higher. Examples of the organic peroxide include peroxy esters such as t-butyl peroxybenzoate (half-life temperature for 1 hour: 125°C), t-butyl peroxyacetate (half-life temperature for 1 hour: 121°C), and t-butyl peroxylaurate (half-life temperature for 1 hour: 118°C); peroxy ketals such as 1,1-di(t-butylperoxy)cyclohexane (half-life temperature for 1 hour: 111°C) and 1,1-di(t-hexylperoxy)cyclohexane (half-life temperature for 1 hour: 107°C); and hydroperoxides such as p-menthane hydroperoxide (half-life temperature for 1 hour: 151°C), cumene hydroperoxide (half-life temperature for 1 hour: 188°C), and diisopropylbenzene hydroperoxide (half-life temperature for 1 hour: 173°C). Among these, cumene hydroperoxide is preferred in terms of stability.

[0063] The content of the polymerization initiator (C) is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1.2 to 8 parts by mass with respect to 100 parts by mass of the reaction component (A). By setting the content of the polymerization initiator (C) to be not less than the above lower limit value, it becomes easier to improve the curing rate. On the other hand, by setting the content of the polymerization initiator (C) to be not more than the above upper limit value, good storage stability can be maintained.

[0064] [Reducing agent (D)] The reducing agent (D) may be any one that reacts with the polymerization initiator (C) to generate radicals, and known reducing agents can be used. Examples of the reducing agent (D) include tertiary amines, thiourea derivatives, and transition metal salts.

[0065] Examples of the above tertiary amines include triethylamine, tripropylamine, tributylamine, and N,N-dimethyl-p-toluidine. Examples of the above thiourea derivatives include 2-mercaptobenzimidazole, methylthiourea, dibutylthiourea, tetramethylthiourea, and ethylene thiourea. Examples of the above transition metal salts include cobalt octylate, cobalt naphthenate, copper naphthenate, vanadyl acetylacetonate, etc. Among these, from the viewpoint of reactivity, transition metal salts are preferred. Among the transition metal salts, cobalt octylate is more preferred.

[0066] The content of the reducing agent (D) is preferably 0.05 to 15 parts by mass, more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the reaction component (A). By setting the content of the reducing agent (D) to be not less than the above lower limit value, the curing rate can be increased. On the other hand, by setting the content of the reducing agent (D) to be not more than the above upper limit value, it is possible to suppress the progress of curing during storage and maintain good storage stability.

[0067] <Hardener or curing accelerator> When the adhesive composition of the present embodiment contains an epoxy monomer and its oligomer, a hardener or a curing accelerator for curing or promoting the effect thereof can be used. As the hardener or curing accelerator, those generally used for curing epoxy resins can be widely used. For example, acid anhydrides, phenol - hydroxyl group - containing resins, phosphorus compounds, imidazole compounds, polyamine compounds, amide compounds, imidazoline compounds, urea - based compounds, organic acid metal salts, polyamide amines, Lewis acids, amine complex salts, etc. can be mentioned. Examples of the above acid anhydrides include octenyl succinic anhydride, dodecenyl succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, tetrabromophthalic anhydride, hymic anhydride, methylnadic anhydride, trialkyltetrahydrophthalic anhydride, etc.

[0068] The above phenolic hydroxyl group-containing resins include, for example, phenol novolak resins, cresol novolak resins, aromatic hydrocarbon formaldehyde resin-modified phenol resins, dicyclopentadiene phenol addition type resins, phenol aralkyl resins (zylok resins), naphthol aralkyl resins, trimethylolmethane resins, tetraphenylol ethane resins, naphthol novolak resins, naphthol-phenol co-condensed novolak resins, naphthol-cresol co-condensed novolak resins, biphenyl-modified phenol resins (polyhydric phenol compounds in which phenol nuclei are linked by bismethylene groups), biphenyl-modified naphthol resins (polyhydric naphthol compounds in which phenol nuclei are linked by bismethylene groups), aminotriazine-modified phenol resins (polyhydric phenol compounds in which phenol nuclei are linked by melamine, benzoguanamine, etc.), alkoxy group-containing aromatic ring-modified novolak resins (polyhydric phenol compounds in which phenol nuclei and alkoxy group-containing aromatic rings are linked by formaldehyde), and other polyhydric phenol compounds.

[0069] The above phosphorus compounds include, for example, alkylphosphines such as ethylphosphine and butylphosphine, primary phosphines such as phenylphosphine; dialkylphosphines such as dimethylphosphine and dipropylphosphine; secondary phosphines such as diphenylphosphine and methylethylphosphine; tertiary phosphines such as trimethylphosphine, triethylphosphine, and triphenylphosphine, phosphate esters, and the like.

[0070] The above-mentioned imidazole compounds include, for example, imidazole, 1-methylimidazole, 2-methylimidazole, 3-methylimidazole, 4-methylimidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 3-ethylimidazole, 4-ethylimidazole, 5-ethylimidazole, 1-n-propylimidazole, 2-n-propylimidazole, 1-isopropylimidazole, 2-isopropylimidazole, 1-n-butylimidazole, 2-n-butylimidazole, 1-isobutylimidazole, 2-isobutylimidazole, 2-undecyl-1H-imidazole, 2-heptadecyl-1H-imidazole, 1,2-dimethylimidazole, 1,3-dimethylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-phenylimidazole, 2-phenyl-1H-imidazole, 4-methyl-2-phenyl-1H-imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole isocyanurate adduct, 2-methylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 1-benzyl-2-phenylimidazole hydrochloride, and the like. The curing agent or curing accelerator may be used alone or in combination of two or more.

[0071] The content of the curing agent is calculated based on the functional group equivalent of the curing agent and the reactive group equivalent of the selected reactive component (A) (for example, the epoxy equivalent in the case of epoxy monomers and their oligomers). Generally, the content of the curing agent or the curing accelerator is preferably 0.1 to 45 parts by mass, more preferably 0.1 to 20 parts by mass, still more preferably 1 to 10 parts by mass, and even more preferably 2 to 8 parts by mass, based on 100 parts by mass of the epoxy monomer and its oligomer. By setting the content of the curing agent or the curing accelerator to be not less than the above lower limit value, good curing can be obtained. On the other hand, by setting the content of the curing agent or the curing accelerator to be not more than the above upper limit value, the storage stability of the adhesive layer obtained by the adhesive composition can be improved.

[0072] <Others> In addition to the above components, the adhesive composition of the present embodiment may contain paraffins, antioxidants, polymerization inhibitors, inorganic fine particles, inorganic fillers, ultraviolet absorbers, silicon-based additives, fluorine-based additives, flame retardants, plasticizers, silane coupling agents, organic beads, defoaming agents, anti-fogging agents, colorants, and organic solvents, etc. These various components may be added in any amount according to the desired performance.

[0073] The polymerization inhibitor is used to improve the storage stability. Examples of the polymerization inhibitor include hydroquinone, methyl hydroquinone, t-butyl hydroquinone, hydroquinone monomethyl ether, quinone hydrazone, p-benzoquinone, toluquinone, 6-t-butyl-2,4-xylenol, 2,6-di-t-butyl-4-methylphenol, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis[6-(1-methylcyclohexyl)-p-cresol], 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, etc.

[0074] The content of the polymerization inhibitor is preferably 0.01 to 2 parts by mass, more preferably 0.02 to 1 part by mass, and still more preferably 0.05 to 1 part by mass, based on 100 parts by mass of the reactive component (A).

[0075] [Method for manufacturing adhesive] The adhesive composition of the present embodiment can be prepared by uniformly mixing the above various components using a pot mill, ball mill, bead mill, roll mill, homogenizer, super mill, homodisper, planetary mixer, universal mixer, Banbury mixer, kneader, or the like. The mixing method is appropriately set according to the raw material components, and various methods can be adopted, such as a method of mixing all the components at once, a method of mixing any component first and then mixing the remaining components at once or sequentially. Also, the settings of the stirring speed, stirring time, temperature, etc. during mixing are appropriately adjusted according to the raw materials.

[0076] [Usage mode] As an embodiment of the present invention of this embodiment, preferably, it can be used as a two-component adhesive composition. For the two-component type, all the essential components of the adhesive composition of this embodiment are not mixed during storage, and the adhesive composition is divided into a first agent and a second agent. A polymerization initiator is stored separately in the first agent, and a reducing agent is stored separately in the second agent. The two-component type is preferable in terms of excellent storage stability. In this case, both agents can be applied simultaneously or separately, brought into contact, and cured to be used as a two-component adhesive composition.

[0077] [Light transmittance of adhesive] The adhesive 50 preferably has a certain light transmittance. The visibility of the back surface fracture through the fiber reinforced resin sheet 3 tends to depend on the light transmittance of the fiber reinforced resin sheet 3. The glass fiber sheet itself of the fiber reinforced resin sheet 3 is generally not transparent and appears white due to scattering in the air layer in the fiber bundle. Transparency is exhibited only when the transparent base material is sufficiently impregnated with a resin (adhesive 50) having a refractive index comparable to that of glass. Therefore, when the resin is transparent, the basis weight of the glass fiber sheet is small, and the adhesive 50 is easily impregnated, the transparency tends to be high. Here, if the transparency of the adhesive 50 is low, the visibility of the back surface fracture may be reduced due to the influence of the adhesive 50 that penetrates between the fibers in the fiber reinforced resin sheet 3. Therefore, it is preferable that the adhesive 50 has a certain light transmittance. Specifically, the visible light transmittance of the cured product of the material of the adhesive 50 can be 40% or more, preferably 50% or more, more preferably 60% or more at a wavelength of 380 to 780 nm. There is no particular limitation on the upper limit, but it can be 90% or less, preferably 85% or less, more preferably 80% or less as a realistic range. The visible light transmittance of the adhesive 50 may be set according to the visible light transmittance and basis weight of the fiber reinforced resin sheet 3.

[0078] The method for measuring the visible light transmittance is as follows. First, the adhesive 50 is applied onto a PET sheet so that the thickness of the cured body is about 1 mm, cured at 23 °C and 50% relative humidity for 7 days to prepare a cured body with a thickness of 1 mm. The PET sheet is peeled off from this cured body to obtain a measurement sample. For the obtained measurement sample, using a spectrophotometer, in accordance with the visible light transmittance test of JIS A 5759, the spectral transmittance in the range of wavelengths 380 to 780 nm is measured from the normal (90°) direction, and using the "weighting coefficient for calculating the visible light transmittance" defined in JIS A 5759, the weighting coefficient is multiplied for each wavelength and weighted-averaged to calculate the visible light transmittance (%). In the case of a two-component adhesive, a mixture of the main agent and the curing agent is used as the above-mentioned adhesive 50. Also, the method for measuring the visible light transmittance may be applicable to the cured body of the anti-peeling sheet.

[0079] <Coating amount of the adhesive> The coating amount of the adhesive 50 is 200 g / m 2 or more and 2000 g / m 2 or less. The lower limit is preferably 250 g / m 2 or more, and more preferably 300 g / m 2 or more. The upper limit is preferably 1800 g / m 2 or less, and more preferably 1600 g / m 2 or less.

[0080] The coating amount of the adhesive 50 can be the sum of the coating amounts of the first adhesive 51 and the second adhesive 52. That is, the sum of the coating amounts of the first adhesive 51 and the second adhesive 52 is within the range of the coating amount of the above-mentioned adhesive 50. Specifically, the coating amount of the first adhesive 51 is 200 g / m 2 or more and 2000 g / m 2 or less. The coating amount B of the second adhesive 52 is 0 g / m 2 or more and 500 g / m 2 or less.

[0081] The coating amount A of the first adhesive 51 and the coating amount B of the second adhesive 52 are appropriately adjusted according to the basis weight of the fiber-reinforced resin sheet 3. For example, they can be set as follows.

[0082] When the basis weight of the fiber-reinforced resin sheet 3 is small (for example, 200 to 400 g / m 2 ), the coating amount A of the first adhesive 51 is 1000 g / m 2 or more and 2000 g / m 2 or less, and the coating amount B of the second adhesive 52 is 0 g / m 2 or more and 200 g / m 2 or less, and the sum of the coating amount A of the first adhesive 51 and the coating amount B of the second adhesive 52 (that is, the coating amount of the adhesive 50) is within the range of 200 g / m 2 or more and 2000 g / m 2 or less described above.

[0083] When the basis weight is small, the fiber spacing is wide and the first adhesive 51 may ooze out to the surface of the fiber reinforced resin sheet 3. In such a case, the coating amount of the second adhesive 52, which is the topcoat, is omitted or reduced. On the other hand, even when the basis weight of the fiber reinforced resin sheet 3 is small, if the fiber reinforced resin sheet 3 is thin and has a uniform surface structure, the first adhesive 51 does not necessarily ooze out to the surface of the fiber reinforced resin sheet 3. In such a case, a certain amount of the second adhesive 52 is applied. When the surface of the fiber reinforced resin sheet 3 is uniform, since the need to level the surface is low, the coating amount of the second adhesive 52 may be small.

[0084] When the basis weight of the fiber reinforced resin sheet 3 is medium (for example, 400 to 1000 g / m 2 ), the coating amount A of the first adhesive 51 is 400 g / m 2 or more and 1000 g / m 2 or less, and the coating amount B of the second adhesive 52 is 0 g / m 2 or more and 300 g / m 2 or less. The total of the coating amount A of the first adhesive 51 and the coating amount B of the second adhesive 52 (that is, the coating amount of the adhesive 50) can be in the range of 200 g / m 2 or more and 2000 g / m 2 or less as described above.

[0085] When the basis weight of the fiber reinforced resin sheet 3 is large (for example, 1000 to 1400 g / m 2 ), the coating amount A of the first adhesive 51 is 200 g / m 2 or more and 400 g / m 2 or less, and the coating amount B of the second adhesive 52 is 0 g / m 2 or more and 400 g / m 2 or less. The total of the coating amount A of the first adhesive 51 and the coating amount B of the second adhesive 52 (that is, the coating amount of the adhesive 50) can be in the range of 200 g / m 2 or more and 2000 g / m 2It can be within the following ranges. For example, when the basis weight of the fiber-reinforced resin sheet 3 is large, the fiber spacing tends to be narrow and the amount of the first adhesive 51 impregnating the fiber-reinforced resin sheet 3 tends to be small. On the other hand, since the unevenness (specifically, the unevenness of plain weave) of the fiber-reinforced resin sheet 3 becomes large, a large amount of resin may be required to level it. Therefore, by increasing the amount of the second adhesive 52 which is a topcoat agent and leveling the unevenness of the fiber-reinforced resin sheet 3, the visibility of the back surface breakage can be ensured well.

[0086] In the above example, the basis weight of the fiber-reinforced resin sheet 3 is divided into three levels, but it is not limited to this meaning, and it may be divided into two levels or four levels or more. Further, the application amount of the adhesive 50 (the first adhesive 51, the second adhesive 52) may be adjusted according to the unevenness and thickness of the surface of the fiber-reinforced resin sheet 3. Furthermore, the application amount may be adjusted according to the light transmittance of the adhesive 50 (the first adhesive 51, the second adhesive 52).

[0087] <Pregforming of the fiber-reinforced resin sheet> The step of attaching the fiber-reinforced resin sheet 3 to the other surface of the concrete 1 (that is, the back surface 12) may be to bond the fiber-reinforced resin sheet 3 to the concrete 1 using the adhesive 50 after pregforming the fiber-reinforced resin sheet 3.

[0088] The impregnation amount of the resin impregnated into the fiber-reinforced resin sheet 3 for pregforming is 50 g / m 2 to 1400 g / m 2 or less. The lower limit is preferably 100 g / m 2 or more, and more preferably 150 g / m 2 or more. The upper limit is preferably 1200 g / m 2 or less, and more preferably 1000 g / m 2 or less. By setting the resin impregnated into the fiber-reinforced resin sheet 3 for pregforming within the above range, the desired visibility can be ensured. The visible light transmittance of the fiber-reinforced resin sheet 3 in the pregformed state is 60% or more, preferably 70% or more, and more preferably 80% or more.

[0089] As the resin to be impregnated into the fiber reinforced resin sheet 3 for prepreg formation, it can be selected and used from those exemplified as the adhesive 50 (the first adhesive 51 and the second adhesive 52), and the same one as the adhesive 50 (the first adhesive 51 and the second adhesive 52) may be selected, or different ones may be selected.

[0090] Note that the mass of the fiber reinforced resin sheet 3 in the prepreg state can be grasped as the sum of the mass of the resin sheet (for example, glass fiber sheet) constituting the fiber reinforced resin sheet 3 and the mass of the impregnated resin.

[0091] <Concrete Reinforcement Method> Referring to FIGS. 4 and 5, the concrete reinforcement method of the present embodiment will be described. FIG. 4 is a flowchart showing the concrete reinforcement method. FIG. 5 is an image showing the attachment process (particularly the attachment state) of the fiber reinforced resin sheet 3 to the concrete 1 in each step of the concrete reinforcement method. Note that in FIG. 5, an example is shown in which the fiber reinforced resin sheet 3 is attached not only to the back surface 12 but also to the side surface and the like.

[0092] The concrete back surface reinforcement method of the present embodiment includes a member preparation step S10 and a resin sheet attachment step S20.

[0093] Member preparation step S10: The member preparation step S10 includes a concrete preparation step S11 and a fiber sheet preparation step S12. The order of the concrete preparation step S11 and the fiber sheet preparation step S12 is not particularly limited.

[0094] The concrete preparation step S11 is a step of preparing the concrete 1 to which the fiber-reinforced resin sheet 3 is to be attached. The concrete 1 may be a newly constructed concrete structure or an existing concrete structure. At this time, the back surface 12 of the concrete 1 may be coated with a primer or a putty material as a base treatment, or may be roughened with a disk sander or the like. By using the same material as the first adhesive 51 as the primer or the putty material, the construction period can be shortened. Note that the base treatment may be performed in the resin sheet attachment step S20 described later.

[0095] The fiber sheet preparation step S12 is a step of preparing the fiber-reinforced resin sheet 3 to be attached to the concrete 1. It is preferable that the fiber-reinforced resin sheet 3 is previously impregnated with a resin (that is, the adhesive 50). The impregnation of the resin may be performed on-site before attachment, or may be previously impregnated at a factory or the like. The impregnated resin may be uncured, semi-cured, or completely cured.

[0096] Resin sheet attachment step S20: The resin sheet attachment step S20 is a step of attaching the fiber-reinforced resin sheet 3 to the back surface 12 of the concrete 1, and specifically includes a primer coating step S21, a fiber sheet pasting step S22, and a topcoat coating step S23.

[0097] The primer coating step S21 is a step of applying the first adhesive 51 as a primer to the back surface 12 of the concrete 1 prepared in the member preparation step S10. At this time, on the back surface 12, a coating film of the first adhesive 51 is formed so as to cover at least the region where the fiber-reinforced resin sheet 3 is to be attached. The application amount A of the first adhesive 51 is preferably 100 g / m 2 or more and 1000 g / m 2 or less, and is adjusted according to the basis weight of the fiber-reinforced resin sheet 3.

[0098] The fiber sheet attachment step S22 is a step of attaching the fiber reinforced resin sheet 3 from above the first adhesive 51. It is preferable to attach the fiber reinforced resin sheet 3 before the drying and curing of the first adhesive 51, which is a primer, are completed. Thereby, the fiber reinforced resin sheet 3 can be appropriately attached onto the coating film of the first adhesive 51.

[0099] The topcoat application step S23 is a step of applying the second adhesive 52 as a topcoat onto the fiber reinforced resin sheet 3 attached to the concrete 1 by the first adhesive 51. Specifically, application is performed with the second adhesive 52, which is a topcoat, so as to cover the first adhesive 51 and the fiber reinforced resin sheet 3, and a coating film of the second adhesive 52 is formed. From the viewpoint of shortening the construction period, it is preferable to complete the attachment of the fiber reinforced resin sheet 3 and the application of the second adhesive 52 before the drying and curing of the first adhesive 51 are completed.

[0100] The application amount B of the second adhesive 52 is 0 g / m 2 or more and 500 g / m 2 or less, and is adjusted according to the basis weight of the fiber reinforced resin sheet 3, the prepreg state, and the application amount A of the first adhesive 51. The ratio B / A of the application amount A of the first adhesive 51 to the application amount B of the second adhesive 52 is adjusted to be 0 or more and 1.0 or less.

[0101] <Relationship between the back surface peeling limit energy and the impact energy of a high-speed flying object> The characteristics of the concrete 1 with the fiber reinforced resin sheet 3 attached can be defined as follows based on the relationship between the back surface peeling limit energy U1 in the concrete 1 and the impact energy U2 (kinetic energy) of the flying object 2 colliding with the concrete 1.

[0102] It has a shape of 500 mm in length × 500 mm in width × 80 mm in thickness and a compressive strength of 53 N / mm 2Let U1 be the back surface peeling limit energy calculated by the modified NDRC formula applied to the normalized concrete 1, and when a fiber-reinforced resin sheet 3 is attached to the back surface 12 of the normalized concrete 1 and the impact energy U2 at the time of back surface fracture due to a single impact of the flying object 2 is considered, U2 / U1 ≧ 1.2.

[0103] U2 / U1 can be said to be the effect of reinforcement when the fiber-reinforced resin sheet 3 is attached to the back surface 12 of the concrete 1. That is, it defines the degree of reinforcement effect achieved by the fiber-reinforced resin sheet 3.

[0104] The lower limit value of U2 / U1 is preferably 1.4 or more, more preferably 1.6 or more. By setting U2 / U1 to be equal to or higher than the lower limit value, the fiber-reinforced resin sheet 3 can be provided to exhibit the desired reinforcement effect, and the visibility of the back surface fracture can be realized.

[0105] The upper limit value of U2 / U1 is not particularly limited, but as a practical value, it is 5 or less, preferably 3 or less, more preferably 2 or less. When strengthening the reinforcement effect by the fiber-reinforced resin sheet 3, it is necessary to sufficiently increase the amount of fibers, that is, the basis weight, contained in the fiber-reinforced resin sheet 3 as described above. On the other hand, when the basis weight of the fiber-reinforced resin sheet 3 is small, the adhesive 50 easily impregnates between the fibers and it becomes easy to obtain the desired adhesive strength. Therefore, an upper limit may be set for the strength (that is, the basis weight) of the fiber-reinforced resin sheet 3 so that U2 / U1 is equal to or lower than the above upper limit value.

[0106] The back surface peeling limit energy U1 is represented by the following formula (1) and is derived from the modified NDRC formula (Yoshiomi Ota et al., Experimental study on local damage evaluation of reinforced concrete slabs due to impact of soft projectiles, Japan Society of Civil Engineers, Journal of Structural Engineering, Vol. 65A, p890-900, March 2019). The impact energy U2 is calculated as the kinetic energy of the flying object 2.

Equation

[0107] The symbols in the formula represent the following. Es: Rear surface peeling limit energy fc’: Compressive strength of concrete (N / m 2 ) d: Diameter of the flying object (m) H: Thickness of the concrete slab (m) V: Mass of the flying object (kg) N: Tip shape coefficient (flat type…0.72, hemispherical type…0.84, blunt head type…1.0, sharp type…1.14)

[0108] Figure 6 is a diagram showing a high-pressure air type flying object generator 90 used in an experiment to measure the conditions under which back surface failure occurs when the flying object 2 collides with the standardized concrete 1. Figure 7 is a diagram showing an installation device 80 for installing the test concrete 101 (the back surface reinforced concrete 102) in the experiment using the high-pressure air type flying object generator 90. Figure 7(a) is a side view, and Figure 7(b) is a front view. Figure 8 is a diagram showing the state in which the test concrete 101 is attached to the installation device 80 of Figure 7. Figure 8(a) is a side view, and Figure 8(b) is a front view. Figure 9 is a diagram of the test flying object 21 (corresponding to the flying object 2) to be launched from the high-pressure air type flying object generator 90 toward the concrete 1. The high-pressure air type flying object generator 90 is a device for accelerating the test flying object 21 to a predetermined speed with air pressure and colliding it against the back surface reinforced concrete 102.

[0109] As shown in Figure 6, the high-pressure air type flying object generator 90 includes, in order from the upstream side, a compressor 91, an air chamber 93, a launch tube 94, and a bounce prevention jig. Further, a speed sensor 95 is attached to the bounce prevention jig.

[0110] The air compressed by the compressor 91 is sent into the air chamber 93 and pressurized to a pressure corresponding to the set speed of the test flying object 21. Before pressurization, the test flying object 21 is hydraulically installed in the air chamber 93. A launch tube 94 is attached to the tip of the air chamber 93, and the compressed air compressed to the set pressure is supplied to the launch tube 94 at the timing by the operation and setting of the experimenter.

[0111] The launch tube 94 has an inner diameter slightly larger than the outer diameter of the test flying object 21 and a length of 12,000 mm. The compressed air introduced from the air chamber 93 accelerates the test flying object 21 to a desired speed inside and launches it from the launch port 96. The speed of the launched test flying object 21 is measured by the speed sensor 95.

[0112] As shown in FIGS. 7 and 8, the installation device 80 for installing the test concrete 101 is formed in a frame shape by H-shaped steel, and has two front and rear base beams 82a, 82b bolt-fixed to the ground and a reaction wall 81 fixed on them. Two beams 83a, 83b at predetermined intervals are attached to the two columns 81a, 81b on the front surface of the reaction wall 81 for attaching the test concrete 101. The interval between the two columns 81a, 81b is 400 mm, and the two beams 83a, 83b are also 400 mm. In the front view, the installation device 80 forms a 400 mm × 400 mm space surrounded by the two columns 81a, 81b and the two beams 83a, 83b.

[0113] As shown in FIG. 8, in the front view, the test concrete 101 is attached to the beams 83a, 83b so as to block this 400 mm × 400 mm space. At this time, in the regions of the upper and lower widths of 50 mm each of the upper and lower edges of the test concrete 101, it is attached to the beams 83a, 83b by the fastening member 85 with the reinforcing plate 86 attached. In addition, a support base 89 (shown by a broken line in the figure) is attached to the lower side of the test concrete 101, and the lower side of the test concrete 101 is supported assistively.

[0114] The dimensions of the test concrete 101 are 500 mm in length × 500 mm in width × 80 mm in thickness. The compressive strength of the test concrete 101 is 53 N / mm 2 is as follows.

[0115] On the back surface of the test concrete 101, a fiber-reinforced resin sheet 3 is attached by an adhesive 50 (first adhesive 51, second adhesive 52).

[0116] As shown in Fig. 9, the test flying object 21 has a rigid body with a dome-shaped tip and a cylindrical fixing member for fixing the rigid body. The rigid body has a radius of 90 mm and a length of 55 mm. The fixing member has a length of 225 mm. The mass of the test flying object 21 is 4.5 kg.

[0117] Using a high-pressure air type flying object generator 90, the test flying object 21 is made to collide with the concrete 102 with the back surface reinforced, and the speed at which back surface failure occurs is measured. If the relationship between the collision energy U2 calculated based on the measurement results and the back surface peeling limit energy U1 of the concrete 1 is, for example, U2 / U1 ≥ 1.2, it can be determined that the concrete 1 with the fiber-reinforced resin sheet 3 attached has a certain strength against back surface failure and the state of back surface failure can be grasped through the fiber-reinforced resin sheet 3.

[0118] <Summary of this embodiment> [1] A concrete reinforcement method for preventing back surface failure in which the other surface (back surface 12) opposite to the one surface (front surface 11) of the concrete 1 is damaged due to the collision of the flying object 2 on the one surface (front surface 11) of the concrete 1, and a fiber-reinforced resin sheet 3 having translucency and reinforcing fibers is attached to the other surface (back surface 12), A concrete reinforcement method in which the back surface failure occurring on the other surface (back surface 12) of the concrete 1 can be visually recognized from the outside through the fiber-reinforced resin sheet 3 in a state where the fiber-reinforced resin sheet 3 is attached to the other surface (back surface 12) of the concrete 1. [2] The fiber reinforced resin sheet 3 has a transparent base material, and the concrete reinforcement method according to [1]. [3] The fiber reinforced resin sheet 3 is obtained by impregnating and curing a resin in a glass fiber sheet, and the concrete reinforcement method according to [2]. [4] The fiber reinforced resin sheet 3 is attached to the concrete 1 using an adhesive 50. The adhesive 50 contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin-based adhesive, and the concrete reinforcement method according to any one of [1] to [3]. [5] The application amount of the adhesive 50 is 200 g / m 2 or more and 2000 g / m 2 or less, and the concrete reinforcement method according to [4]. [6] For the standardized concrete 1 having a shape of 500 mm in length × 500 mm in width × 80 mm in thickness and a compressive strength of 53 N / mm 2 the back surface peeling limit energy calculated by the modified NDRC formula applied to it is defined as U1. When the fiber reinforced resin sheet 3 is attached to the back surface 12 of the standardized concrete 1 and the impact energy when back surface failure occurs due to a single impact of the flying object 2 is defined as U2. U2 / U1 ≥ 1.2 and the concrete reinforcement method according to any one of [1] to [5]. [7] The step of attaching the fiber reinforced resin sheet 3 to the other surface (back surface 12) of the concrete 1 is to bond the fiber reinforced resin sheet 3 to the concrete 1 using an adhesive 50 after prepregging it, and the concrete reinforcement method according to any one of [1] to [6]. [8] The impregnation amount of the resin impregnated into the fiber reinforced resin sheet 3 for prepregging is 50 g / m 2 or more and 1400 g / m 2 or less, and the concrete reinforcement method according to [7]. [9] The basis weight of the fiber-reinforced resin sheet 3 is 200 g / m 2 or more and 1400 g / m 2 or less, and the concrete reinforcement method according to any one of [1] to [8].

[10] A concrete reinforcement method used for the structure of concrete 1, in which one surface (surface 11) faces outward in the concrete 1, and a fiber-reinforced resin sheet 3 having reinforcing fibers with translucency is attached to the opposite surface (back surface 12) of the one surface, A concrete back surface reinforcement method in which, in a state where the fiber-reinforced resin sheet 3 is attached to the opposite surface (back surface 12) of the concrete 1, the damage state developed on the opposite surface (back surface 12) of the concrete 1 due to an object (projectile 2) colliding with the surface (surface 11) facing outward can be visually recognized from the outside through the fiber-reinforced resin sheet 3.

[11] Concrete 1, A fiber-reinforced resin sheet 3 having reinforcing fibers and having translucency, attached to the first surface (back surface 12) of the concrete 1, and, A concrete structure (concrete 102 with back surface reinforced) in which the back surface damage developed on the first surface (back surface 12) due to the projectile 2 colliding with the second surface (surface 11) opposite to the first surface (back surface 12) can be visually recognized from the outside through the fiber-reinforced resin sheet 3.

[12] The fiber-reinforced resin sheet 3 has a transparent base material, and the concrete structure (concrete 102 with back surface reinforced) according to

[10] .

[13] The fiber-reinforced resin sheet 3 is obtained by impregnating and curing a resin in a glass fiber sheet, and the concrete structure (concrete 102 with back surface reinforced) according to

[11] .

[14] The fiber-reinforced resin sheet 3 is attached to the concrete 1 by an adhesive 50, The adhesive 50 contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin-based resin, and is the concrete structure (back surface-reinforced concrete 102) according to any one of

[11] to

[13] .

[15] The application amount of the adhesive 50 is 200 g / m 2 or more and 2000 g / m 2 or less, and is the concrete structure (back surface-reinforced concrete 102) according to

[14] .

[16] It has a shape of 500 mm in length × 500 mm in width × 80 mm in thickness, and the back surface peeling limit energy calculated by the modified NDRC formula applied to the standardized concrete 1 (test concrete 101) with a compressive strength of 53 N / mm 2 is defined as U1. Using the first surface of the standardized concrete 1 as the back surface 12 and the second surface as the front surface 11, when the fiber-reinforced resin sheet 3 is attached to the first surface and the back surface is damaged due to a single collision of the flying object 2 against the second surface, the collision energy is defined as U2. U2 / U1 ≥ 1.2, and is the concrete structure (back surface-reinforced concrete 102) according to any one of

[11] to

[15] .

[17] The fiber-reinforced resin sheet 3 is a prepreg sheet impregnated with resin and is adhered to the first surface (back surface 12) of the concrete 1 using an adhesive, and is the concrete structure (back surface-reinforced concrete 102) according to any one of

[11] to

[16] .

[18] In the prepreg sheet, the impregnation amount of the impregnated resin is 50 g / m 2 or more and 1400 g / m 2 or less, and is the concrete structure (back surface-reinforced concrete 102) according to

[17] .

[19] The basis weight of the fiber-reinforced resin sheet 3 is 200 g / m 2 or more and 1400 g / m 2The concrete structure (concrete 102 with back surface reinforcement) according to any one of

[11] to

[18] below.

Example

[0119] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0120] [Verification Experiment 1: Difference in visibility of back surface destruction depending on the type of fiber sheet] In Verification Experiment 1, a test was conducted to see how the visibility of back surface destruction would be affected by the type of fiber sheet. A steel sphere with a diameter of 30 mm and a mass of 300 g was collided with a concrete slab (500 mm in length × 500 mm in width × 80 mm in thickness) having a compressive strength of 53 N / mm 2 at a speed of 100 m / s. At this time, various fiber sheets shown in Table 1 were pasted with an adhesive A application amount of 300 g / m 2 to perform back surface reinforcement, and the occurrence or non-occurrence of scattering of concrete fragments to the back surface (back surface destruction) and whether the situation of back surface destruction could be visually observed were observed. The results are shown in Table 1 and Figure 14.

[0121] Fiber sheet Comparative Example 1: Without fiber sheet Comparative Example 2: Carbon fiber sheet Name: High-strength carbon fiber Structure: Two-way Areal density: 200 g / m 2 Tensile strength: 2900 N / mm 2 Comparative Example 3: Aramid fiber sheet Name: Aramid 1 Structure: Plain weave Areal density: 330 g / m 2 Tensile strength: 2060 N / mm 2 Example 1: Glass fiber sheet Name: E-glass Structure: Plain weave Areal density: 570 g / m 2 Tensile strength: 1500 N / mm 2 Adhesive A (acrylic resin adhesive) 70 parts by mass of bisphenol A ethylene oxide modified (4 mol addition) dimethacrylate ((meth)acrylic compound, manufactured by MIWON Co., Ltd., trade name "Miramer M241"), 30 parts by mass of bisphenol A ethylene oxide modified (10 mol addition) dimethacrylate ((meth)acrylic compound, manufactured by MIWON Co., Ltd., trade name "Miramer M2101"), 3 parts by mass of cumene hydroxyperoxide (organic peroxide, manufactured by KAYAKU Nouryon Co., Ltd., trade name "Trigonox K-80"), and 0.05 parts by mass of hydroquinone (polymerization inhibitor, manufactured by Seiko Chemical Co., Ltd., trade name "Hydroquinone") were mixed in a container to obtain a mixture, and then this mixture was stirred to prepare the first agent of Adhesive A. 70 parts by mass of bisphenol A ethylene oxide modified (4 mol addition) dimethacrylate ((meth)acrylic compound, manufactured by MIWON Co., Ltd., trade name "Miramer M241"), 30 parts by mass of bisphenol A ethylene oxide modified (10 mol addition) dimethacrylate ((meth)acrylic compound, manufactured by MIWON Co., Ltd., trade name "Miramer M2101"), 3 parts by mass of cobalt 2-ethylhexanoate (reducing agent, manufactured by Tokyo Fine Chemical Co., Ltd., trade name "Co-12E"), and 0.05 parts by mass of hydroquinone (polymerization inhibitor, manufactured by Seiko Chemical Co., Ltd., trade name "Hydroquinone") were mixed in a container to obtain a mixture, and then this mixture was stirred to prepare the second agent of Adhesive A. During application, a mixture obtained by stirring and mixing equal amounts of the first agent and the second agent was used as Adhesive A.

[0122]

Table 1

[0123] [Verification Experiment 2: Difference in Adhesives] In Verification Experiment 2, a confirmation experiment on the visibility of back surface failure was conducted when the type and application amount of the adhesive were changed. Here, except that glass fiber was used with a basis weight of 570 g / m 2 and the type and application amount of the adhesive were changed as shown in Table 2, it was carried out in the same manner as Verification Experiment 1. The results are shown in Table 2.

[0124] Fiber sheet Examples 2 - 5: Glass fiber sheet with a basis weight of 570 g / m 2 Adhesive B (Epoxy resin-based adhesive) 72.2 parts by mass of bisphenol A type epoxy resin (epoxy compound, manufactured by ADEKA CORPORATION, trade name "Adekarezine EP-4100"), 12.8 parts by mass of propylene oxide-added bisphenol A type epoxy resin (epoxy compound, manufactured by ADEKA CORPORATION, trade name "Adekarezine EP-4005"), and 15 parts by mass of orthocresyl glycidyl ether (manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., trade name "SY-OCG") were mixed in a container to obtain a mixture, and then this mixture was stirred to prepare the main agent. Also, 38.9 parts by mass of polyamide amine (manufactured by T&K TOKA CORPORATION, trade name "Tolimid 245-S") was used as the curing agent. By mixing these main agent and curing agent, an adhesive composition was obtained.

[0125]

Table 2

Explanation of Signs

[0126] 1 Concrete 2 Projectile (sometimes referred to as a high-speed projectile) 3 Fiber Reinforced Resin Sheet 11 Front Surface 12 Back Surface 51 First Adhesive 52 Second Adhesive 80 Installation Device 90 High-Pressure Air Type Projectile Generator 91 Compressor 92 Booster 93 Air Chamber 94 Launch Tube 95 Speed Sensor 96 Launch Port 101 Test Concrete 102 Concrete with Reinforced Back Surface

Claims

1. A concrete reinforcement method for preventing back surface breakage in which the other surface opposite to one surface of concrete is broken by the collision of a flying object on one surface of the concrete, comprising attaching a fiber-reinforced resin sheet having translucency and reinforcing fibers to the other surface, A concrete reinforcement method in which, with the fiber-reinforced resin sheet attached to the other surface of the concrete, the back surface breakage occurring on the other surface of the concrete can be visually recognized from the outside through the fiber-reinforced resin sheet.

2. The concrete reinforcement method according to claim 1, wherein the fiber-reinforced resin sheet has a transparent base material.

3. The concrete reinforcement method according to claim 2, wherein the fiber-reinforced resin sheet is obtained by impregnating and curing a resin in a glass fiber sheet.

4. The fiber-reinforced resin sheet is attached to the concrete using an adhesive, The concrete reinforcement method according to claim 1 or 2, wherein the adhesive contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin.

5. The coating amount of the adhesive is 200 g / m ２ or more and 2000 g / m ２ or less. The concrete reinforcement method according to claim 4.

6. It has a shape of 500 mm in length × 500 mm in width × 80 mm in thickness, and the back surface peeling limit energy calculated by the modified NDRC formula applied to the standardized concrete with a compressive strength of 53 N / mm ２ is defined as U1, and When the fiber-reinforced resin sheet is attached to the back surface of the standardized concrete and the collision energy when back surface breakage occurs due to a single collision of the flying object is U2, U2 / U1 ≥ 1.2, The concrete reinforcement method according to any one of claims 1 to 3.

7. The concrete reinforcement method according to any one of claims 1 to 3, wherein the step of attaching the fiber-reinforced resin sheet to the other surface of the concrete is to bond the fiber-reinforced resin sheet to the concrete using an adhesive after prepregulating the fiber-reinforced resin sheet.

8. The impregnation amount of the resin impregnated into the fiber reinforced resin sheet for prepreg is 50 g / m ２ or more and 1400 g / m ２ or less. The concrete reinforcement method according to claim 7.

9. The basis weight of the fiber reinforced resin sheet is 200 g / m ２ or more and 1400 g / m ２ or less. The concrete reinforcement method according to any one of claims 1 to 3.

10. A concrete reinforcement method used for a concrete structure, in which one surface of the concrete faces outward, and a fiber-reinforced resin sheet having translucency and reinforcing fibers is attached to the surface opposite to the one surface, A concrete reinforcement method in which, with the fiber-reinforced resin sheet attached to the opposite surface of the concrete, the state of breakage occurring on the opposite surface of the concrete due to an object colliding with the outward-facing surface can be visually recognized from the outside through the fiber-reinforced resin sheet.

11. Concrete, and A fiber-reinforced resin sheet having reinforcing fibers and having translucency, attached to the first surface of the concrete, Comprising. A concrete structure in which when a flying object collides with a second surface opposite to the first surface, the back surface failure occurring on the first surface can be visually recognized from the outside through the fiber reinforced resin sheet.

12. The concrete structure according to claim 11, wherein the fiber reinforced resin sheet has a transparent base material.

13. The concrete structure according to claim 12, wherein the fiber reinforced resin sheet is obtained by impregnating and curing a resin in a glass fiber sheet.

14. The fiber reinforced resin sheet is attached to the concrete by an adhesive, The concrete structure according to any one of claims 11 to 13, wherein the adhesive contains at least one of a (meth)acrylic resin-based adhesive and an epoxy resin.

15. The coating amount of the adhesive is 200 g / m ２ or more and 2000 g / m ２ or less. The concrete structure according to claim 14.

16. Let the back surface peeling limit energy calculated by the modified NDRC formula applied to the concrete be U1, When the first surface of the concrete is used as the back surface and the second surface is used as the front surface, the fiber reinforced resin sheet is attached to the first surface, and when back surface failure occurs due to a single collision of the flying object against the second surface, the collision energy is U2, U2 / U1 ≥ 1.2, The concrete structure according to any one of claims 11 to 13.

17. The concrete structure according to any one of claims 11 to 13, wherein the fiber reinforced resin sheet is a prepreg sheet impregnated with a resin and is adhered to the first surface of the concrete using an adhesive.

18. In the prepreg sheet, the impregnation amount of the impregnated resin is 50 g / m ２ or more and 1400 g / m ２ or less. The concrete structure according to claim 17.

19. The basis weight of the fiber reinforced resin sheet is 200 g / m ２ or more and 1400 g / m ２ or less. The concrete structure according to any one of claims 11 to 13.

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