JP7788533B2 - Concrete back reinforcement method - Google Patents

Description

The present invention relates to a method for reinforcing the back surface of concrete.

When a concrete structure is hit by a relatively large object, such as a falling rock, debris flow, or avalanche, at low speed, the concrete will experience total failure accompanied by large deformations such as bending failure and shear failure. On the other hand, when a relatively small object, such as a cannonball or explosive, or a flying object hit by a typhoon or tornado, hits at high speed, localized failure progresses through a process of destruction, penetration, backside peeling, and penetration of the concrete surface. In this way, concrete members that are hit at high speeds by flying objects at speeds of tens to hundreds of meters per second will experience a completely different pattern from total failure due to bending failure or shear failure.

Conventionally, non-porous concrete with a high compressive strength of approximately 400 N/ ^mm2 has been studied as a concrete component to be impacted by a high-speed projectile (Non-Patent Document 1). This concrete has a compressive strength 14 times or more greater than that of ordinary concrete, which has a compressive strength of approximately 28 N/ ^mm2 , but the thickness of the component can only be reduced by approximately 30%. Furthermore, it is difficult to industrially mass-produce a non-porous concrete that does not allow even a single defect, and in order to guarantee non-porousness, it is necessary to conduct 100% inspection, which makes it impractical.

Another study also reported that while increasing the compressive strength of concrete somewhat reduces localized surface penetration, it does not have any effect in reducing backside spalling (Non-Patent Document 2). From the above, it is clear that while concrete is an indispensable material for mass production, increasing the strength of concrete is not a solution for preventing backside damage in the event of a high-speed projectile impact.

On the other hand, ceramic impact-resistant components for high-speed projectiles have also been proposed (Patent Document 1). However, ceramics are too expensive a material to be applied to mass production, which would impose too great an economic burden and limit the scope of application.

In addition, a reinforcement method has been proposed to prevent damage to the backside of concrete due to the impact of a high-speed projectile by attaching a sheet of aramid fiber or carbon fiber to the backside of the concrete (Non-Patent Document 3). Non-Patent Document 3 shows the process by which backside peeling occurs, as shown in Figure 8. Figure 9 shows an image of an example of backside peeling. Figure 9(a) is the example described in Non-Patent Document 3, and Figures 9(b) and 9(c) are examples described in Non-Patent Document 4. These are examples in which no particular sheet reinforcement is used.

Patent No. 05405844

Kono et al., "Protective Performance of Fiber-Reinforced PFC Panels Against High-Speed Projectile Impact," Pacific Cement Research Report, No. 180 (2021) Minami et al., "Evaluation of Impact Resistance of Various Concrete Types to Impact of High-Speed Projectiles," Proceedings of the Japan Concrete Institute, Vol. 35, No. 1, pp. 1255-1260 (2013) Beppu et al., "Mechanism of Backside Peeling of Concrete Plates Subjected to High-Speed Impact and the Effect of Continuous Fiber Sheet Reinforcement," Journal of the Japan Society of Civil Engineers, A1 (Structural and Earthquake Engineering), Vol. 68, No. 2, pp. 398-412 (2012) Beppu et al., "Experimental Study on Localized Damage of Concrete Plates Subjected to High-Speed Impact of Steel Projectiles," Journal of the Japan Society of Civil Engineers, Vol. 63, No. 1, pp. 178-191 (2007)

In recent years, there have been many reports of damage to evacuation shelters caused by volcanic cinder impacts and damage to buildings caused by tornado-related debris, creating a need for methods to reinforce concrete structures such as shelters, protective walls, and buildings. In such disasters, there is a possibility that flying debris (projectiles) may repeatedly collide with structures. While the effectiveness of backside reinforcement against a single impact has been evaluated, no studies have been conducted on the situation when projectiles repeatedly impact.

The present invention aims to provide technology that prevents damage to the underside of concrete when projectiles repeatedly collide with it.

The present invention provides the following techniques.
[1]
A concrete back surface reinforcement method for preventing back surface damage in which a surface opposite to one surface of concrete is damaged by a collision of a flying object with the other surface, comprising attaching a fiber sheet to the other surface,
The resin sheet attaching step of attaching the fiber sheet to the other surface of the concrete includes a step of applying a first adhesive to the other surface of the concrete and attaching the fiber sheet on top of the first adhesive,
A test concrete is prepared as the concrete, and after the fiber sheet is attached to the other surface of the test concrete, a cumulative fracture value, which is a cumulative value of collision energy from when the flying object collides with the one surface until the back surface is fractured, is 7.0 kJ or more, and the collision energy of the flying object per collision is 0.1 kJ or more but less than 7.0 kJ,
The test concrete has a size of 1100 mm long x 1100 mm wide x 150 mm thick and a compressive strength of 24 N / mm ² or more.
Concrete back reinforcement method.
[2]
The concrete back surface reinforcement method described in [1], wherein the resin sheet attachment process further includes a process of applying a second adhesive onto the fiber sheet attached to the back surface of the concrete with the first adhesive.
[3]
The concrete back surface reinforcement method according to [2], wherein the first adhesive and the second adhesive contain at least one of a (meth)acrylic resin-based adhesive and an epoxy resin-based adhesive.
[4]
the application amount A of the first adhesive is 100 g/m ² or more and 1000 g/m ² or less,
The concrete back surface reinforcement method according to [2] or [3], wherein the application amount B of the second adhesive is 0 g/m ² or more and 1500 g/m ² or less.
[5]
The ratio B/A of the application amount of the first adhesive (A kg/m ²⁾ to the application amount of the second adhesive (B kg/m ²⁾ is 0 or more and 4.0 or less, [2] to [4]. The concrete back surface reinforcement method according to any one of [2] to [4].
[6]
The concrete back surface reinforcement method according to any one of [1] to [5], wherein the fiber sheet has a basis weight of 50 g / m ² or more and 1000 g / m ² or less.
[7]
The concrete back surface reinforcement method according to any one of [1] to [6], wherein the fiber sheet includes a bidirectional sheet in which fibers are arranged along two different axial directions, or a laminated sheet in which two unidirectional sheets in which fibers are arranged along one axial direction are stacked so that the axial directions intersect with each other.
[8]
The concrete back surface reinforcement method according to any one of [1] to [7], wherein the fiber sheet is an aramid fiber sheet.
[9]
The concrete back surface reinforcement method according to any one of [1] to [8], wherein the cumulative fracture value is 10 kJ or more.
[10]
A concrete back surface reinforcement method according to any one of [1] to [9], in which, after attaching the fiber sheet to the other side of the test concrete using a high-pressure air projectile generating device under the following experimental conditions, no damage occurs to the back surface when projectiles are collided with the test concrete three times.
Experimental conditions:
・Device: High-pressure air projectile generator ・Projectile mass: 4.5 kg (Φ 90 mm)
- Flying object setting speed: 20m/s, 40m/s
[11]
The collision energy of the projectile per collision is 0.5 kJ or more and less than 1.5 kJ,
The concrete back surface reinforcement method according to any one of [1] to [10], wherein the cumulative fracture value is 15.0 kJ or more.
[12]
The collision energy of the projectile per collision is 3.0 kJ or more and less than 4.0 kJ,
The concrete back surface reinforcement method according to any one of [1] to [10], wherein the cumulative fracture value is 25.0 kJ or more.
[13]
A concrete structure reinforced using the concrete back surface reinforcement method according to any one of [1] to [12].

The present invention provides technology that prevents damage to the underside of concrete when projectiles repeatedly collide.

FIG. 10 is a diagram showing concrete having a fiber sheet attached to the back surface according to an embodiment. FIG. 2 is an enlarged view of region A in FIG. 1( b ) according to the embodiment. 1 is a flowchart showing a concrete rear surface reinforcing method according to an embodiment. 10 is an image showing the process of attaching a fiber sheet to concrete in each step of the concrete back surface reinforcing method according to the embodiment. FIG. 1 is a diagram showing a high-pressure air projectile generating device used in an experiment according to an embodiment. FIG. 1 is a diagram showing a back-reinforced concrete according to an embodiment. 1 is a diagram showing a test projectile launched toward concrete from a high-pressure air projectile generating device according to an embodiment. FIG. 1A and 1B are diagrams illustrating the process by which back surface damage occurs. 10A and 10B are diagrams illustrating an example of back surface damage. 10 is an image illustrating the state of rear surface destruction in Examples 1 to 3. 10 is an image illustrating the state of rear surface destruction in Examples 4 to 6.

<Outline of this embodiment>
In this embodiment, a concrete back surface reinforcing technique will be described.
FIG. 1 shows concrete 1 with a fiber sheet 3 attached to its back surface 12, with FIG. 1(a) being a front view, FIG. 1(b) being a side view, and FIG. 1(c) being a back view. FIG. 2 is an enlarged view of area A in FIG. 1(b). In FIG. 2, the concrete 1 is indicated by hatching. Examples of concrete buildings (structures) that can use the concrete 1 include: (1) public facility-related equipment; (2) infrastructure for daily life, communications, and transportation-related equipment; and (3) facilities important for national defense and disaster prevention facilities. More specifically, they are as follows:
(1) Examples of public facility-related equipment include schools, research facilities, hospitals, police stations, fire stations, gymnasiums, community centers, government offices, libraries, museums, art galleries, and stadiums.
(2) Examples of infrastructure for daily life, communications, and transportation-related facilities include power plants, substations, gas facilities, waterworks, communications bases, broadcasting stations, train stations, subways, port facilities, and airports.
(3) Examples of facilities important for national defense and disaster prevention facilities include Self-Defense Force garrisons, bases, and airfields, nuclear facilities (nuclear reactors, nuclear power plants, nuclear fuel processing facilities, reprocessing facilities, and spent fuel storage facilities), shelters, and mountain huts.
The above concrete structure is merely an example, and the present invention can also be applied to other concrete structures.

The concrete back surface reinforcement technology of this embodiment attaches a fiber sheet 3 to the back surface 12 of concrete 1 (hereinafter referred to as "front surface 11") to prevent back surface damage, a phenomenon in which the other surface (hereinafter referred to as "back surface 12") opposite the front surface 11 is destroyed when a flying object 2 collides with the front surface 11. Note that the front surface 11 and back surface 12 of concrete 1 are not distinguished by their structure or other factors, but rather by whether or not a fiber sheet 3 is attached. In other words, the back surface 12 of concrete 1 refers not to the surface (front surface 11) that the flying object 2 collides with, but to the back surface thereof.

Concrete 1 standardized for testing (hereinafter referred to as "test concrete 101") is prepared, and a fiber sheet 3 is attached to the back surface 12 of the test concrete 101 using the process described below (see Figures 3 and 4). Hereinafter, the test concrete 101 with the fiber sheet 3 attached to the back surface 12 is referred to as "back surface reinforced concrete 102."

The cumulative fracture value ES is the cumulative value of the collision energy EA from when the flying object 2 collides with the surface 11 of the back-reinforced concrete 102 until the back surface is fractured. In other words, if the cumulative fracture value ES is equal to or greater than a predetermined value, it is evaluated that the concrete 1 having the fiber sheet 3 on the back surface 12 has a certain strength that takes back surface fracture into consideration.
The evaluation is carried out under three different evaluation conditions 1 to 3 according to the magnitude of the impact energy EA of the projectile 2 per collision.
Evaluation condition 1:
The collision energy EA of the projectile 2 per collision is 0.1 kJ or more and less than 7.0 kJ, and the cumulative destruction value ES is 7.0 kJ or more.
Evaluation condition 2:
The collision energy EA of the projectile 2 per collision is 0.5 kJ or more and less than 1.5 kJ, and the cumulative destruction value ES is 15.0 kJ or more.
Evaluation condition 3:
The collision energy EA of the projectile 2 per collision is 3.0 kJ or more and less than 4.0 kJ, and the cumulative destruction value ES is 25.0 kJ or more.
The specific details will be explained below.

In this embodiment, back surface damage (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 projectile 2 with the front surface 11. For examples of back surface damage, please refer to Figures 8 and 9 above.

<Concrete (test concrete)>
The back-reinforced concrete 102 includes a test concrete 101, which is concrete 1 standardized for testing, and a fiber sheet 3 attached to a back surface 12 of the test concrete 101. The fiber sheet 3 is attached to the back surface 12 of the test concrete 101 with adhesives 50 (a first adhesive 51 and a second adhesive 52) by a process described below.

First, we will explain concrete 1, which is reinforced on the back side. Next, we will explain test concrete 101 and concrete with reinforced back side 102.

In this embodiment, concrete 1 is a general term for concrete, mortar, and cement paste. Furthermore, concrete 1 may be unreinforced concrete or reinforced concrete.

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 one type or multiple types.
The short fibers may be made of, for example, polypropylene, polyethylene terephthalate, or vinylon, and may have a diameter of 0.01 mm to 0.1 mm and a length of 10 mm to 30 mm.

Fiber-reinforced concrete is expected to have the effect of dispersing the impact of a projectile 2 when it hits, and preventing concrete fragments from scattering. The amount of short fibers used can be, for example, 1 to 5 vol. % by volume. At 1 vol. % or more, impact resistance and prevention of broken concrete fragments from scattering are sufficient, while at 5 vol. % or less, sufficient performance can be expected.

The strength level of the concrete 1 is preferably a compressive strength of about 18 N/mm ² to 200 N/mm ² from the viewpoint of preventing damage to the rear surface due to the impact of the flying object 2. If it is 18 N/mm ² or more, impact resistance is sufficient, and if it is 200 N/mm ² or less, the concrete slab becomes easier to manufacture, productivity improves, and costs tend to be lower.

The required compressive strength varies depending on the mass and speed of the colliding projectile 2, i.e., the impact energy per impact. For example, the required compressive strength will differ depending on whether the required compressive strength is one that can withstand a single impact under conditions where the impact energy per impact is large, or one that can withstand multiple impacts where the impact energy per impact is not as large.

In this embodiment, assuming conditions where the impact energy EA of the flying object 2 per impact against the back-reinforced concrete 102 having a fiber sheet 3 attached to the back surface 12 of the test concrete 101 is 0.1 kJ or more and less than 7.0 kJ, and the cumulative fracture value ES is 7.0 kJ or more, the compressive strength of the test concrete 101 can be made 24 N/ ^mm2 or more.

The lower limit of the compressive strength is preferably 30 N/ ^mm2 or more, more preferably 40 N/ ^mm2 or more. The upper limit of the compressive strength is not particularly limited, but is, for example, 60 N/ ^mm2 or less, preferably 55 N/ ^mm2 or less, more preferably 50 N/ ^mm2 or less. The compressive strength is set according to the expected kinetic energy (impact energy) of the flying object 2. In other words, it is set according to the level of strength required for the test concrete 101.

The test concrete 101 has a rectangular parallelepiped shape measuring 1100 mm in length, 1100 mm in width, and 150 mm in thickness. One side defined by the length and width is the front side 11, and the other side is the back side 12.

<Fiber sheet>
The fiber sheet 3 is attached to the back surface 12 of the concrete 1 using an adhesive 50 (a first adhesive 51 and a second adhesive 52, which will be described later). As will be described in detail later, the first adhesive 51 is applied as a primer to the back surface 12 of the concrete 1, the fiber sheet 3 is attached, and then the second adhesive 52 is applied as a top coat, if necessary.

Examples of the fiber sheet 3 include sheets made of fibers such as aramid fiber and carbon fiber. From the standpoint of strength and compatibility with the adhesive 50, aramid fiber sheets are preferably used.

Aramid fiber sheets are preferably woven sheets in which fibers are arranged in two directions as warp and weft threads, and of these, isotropic sheets in which the type, thickness, and number of filaments of aramid fibers making up the warp and weft threads are the same are particularly preferred.

The tensile strength of the fibers constituting the aramid fiber sheet can be, for example, 1 cN/dtex or more and 40 cN/dtex or less. The lower limit is preferably 5 cN/dtex or more, more preferably 10 cN/dtex or more. The upper limit is preferably 35 cN/dtex or less, more preferably 25 cN/dtex or less. By setting the tensile strength of the fibers constituting the aramid fiber sheet within the above range, even if the concrete 1 breaks, protrusion of the broken concrete 1 (or components contained in the concrete 1, such as rebar) can be prevented. A tensile strength of 1 cN/dtex or more can sufficiently prevent protrusion of the rebar when it breaks, although this depends on the length of the rebar (steel material) arranged in the concrete 1. On the other hand, a tensile strength of 40 cN/dtex or less requires a reduction in the number and thickness of filaments to achieve such a high tensile strength, allowing sufficient impregnation of the adhesive 50 to proceed.

The fiber amount of the aramid fiber sheet can be, for example, 50 g/ ^m2 or more and 1000 g/ ^m2 or less. The lower limit is preferably 100 g/ ^m2 or more, more preferably 180 g/ ^m2 or more. The upper limit is preferably 800 g/ ^m2 or less, more preferably 650 g/ ^m2 or less. When the fiber amount is 50 g/ ^m2 or more, the tensile strength of the aramid fiber sheet is sufficient. When the fiber amount is 1000 g/ ^m2 or less, impregnation of the adhesive 50 proceeds sufficiently, and sufficient adhesive strength is obtained.

The fiber sheet 3 may be a uniaxial sheet (UD material) formed by arranging fiber bundles in one direction, or a biaxial sheet (cross sheet) formed by weaving fiber bundles biaxially as warp and weft threads. There are many weaving patterns in which the warp and weft threads of a woven fabric are crossed, such as plain weave, twill weave, and satin weave, but these patterns are not limited to these. In the case of a biaxial sheet, two uniaxial sheets may be stacked together so that the fiber bundles run in different directions (laminated sheet). In the case of a biaxial sheet, the fiber bundles may run in a slightly tilted direction rather than perpendicularly. A multiaxial sheet may also be formed by stacking three or more layers of uniaxial and biaxial sheets. In the case of a multiaxial sheet, different types of fiber sheets 3 (e.g., aramid fiber sheets and carbon fiber sheets) may be stacked together. From the perspective of impregnating the fiber sheet 3 with adhesive 50, a biaxial sheet woven in a plain weave is preferred. In other words, the plain weave allows the adhesive to more easily penetrate the unevenness on the front and back surfaces of the fiber sheet 3.

<Weight of fiber sheet>
The basis weight (also referred to as "basis weight") of the fiber sheet 3 is set appropriately, but can be, for example, 50 g/ ^m2 or more and 1000 g/ ^m2 or less. The lower limit of the basis weight is preferably 100 g/ ^m2 or more, more preferably 180 g/ ^m2 or more. The upper limit of the basis weight is preferably 800 g/ ^m2 or less, more preferably 650 g/ ^m2 or less.

When the basis weight is 50 g/ ^m2 or more, the fiber content is increased, and the desired strength (i.e., strength that can prevent back surface damage) of the fiber sheet 3 can be obtained. Furthermore, since the gaps between the fibers are not too wide, the amount of adhesive 50 required to attach the fiber sheet 3 to the concrete 1 is not too large, and the curing time does not increase as the amount of adhesive 50 increases, improving workability.

When the basis weight is 1000 g/m ² or less, the adhesive 50 easily penetrates between the fibers, making it easier to obtain the desired adhesiveness.

<Adhesives (First Adhesive, Second Adhesive)>
The adhesive 50 includes a first adhesive 51 as an undercoat and a second adhesive 52 as a topcoat. The first adhesive 51 and the second adhesive 52 may be the same or different. The presence of the first adhesive 51 and the second adhesive 52 allows the first adhesive 51 and the second adhesive 52 to come into contact with each other through the fiber sheet 3, increasing adhesive strength. Note that if the fiber sheet 3 has a small basis weight, the application of the second adhesive 52 can be omitted. A small basis weight refers to a basis weight of 200 g/ ^m² or less, for example. When the fiber sheet 3 has a small basis weight, the spacing between fibers becomes wider as described above, resulting in a larger amount of first adhesive 51 being used and the first adhesive 51 possibly seeping to the front side of the fiber sheet 3. Therefore, the use of the first adhesive 51 as an undercoat alone may achieve the same effect as using the second adhesive 52 as a topcoat. In such cases, the second adhesive 52 can be omitted.

Types of adhesive 50 that can be used include adhesives containing (meth)acrylic resins ((meth)acrylic resin adhesives) and adhesives containing epoxy resins (epoxy resin adhesives). (Meth)acrylic resin adhesives have (meth)acrylic acid or its derivatives (such as methyl methacrylate) as their main component, and in this embodiment, they include an adhesive containing methacrylic (MMA) resin (MMA resin adhesive). The first adhesive 51 and the second adhesive 52 being of the same type include, for example, cases where both are acrylic resin adhesives of the same type (components) and cases where they are different types of (meth)acrylic resin adhesives but with different components. Regardless of the type of adhesive selected for first adhesive 51 and second adhesive 52, it is sufficient that the desired adhesion and workability are achieved.

[(Meth)acrylic Monomers and Oligomers Thereof]
In this embodiment, the (meth)acrylic adhesive component contains a monofunctional, difunctional, trifunctional or higher functional (meth)acrylic monomer or a (meth)acrylic oligomer in which a plurality of such (meth)acrylic monomers are bonded. The (meth)acrylic adhesive component is a radically polymerizable component.

(Meth)acrylic monomers include, for example, (meth)acrylic acid or its derivatives, (meth)acrylamide or its derivatives, etc., and these may be used alone or in combination of two or more.

Examples of the above-mentioned (meth)acrylic acid derivatives include the following:

(i) A monomer represented by the following formula (1):
Z-O-R ₁ (1)
(wherein Z represents a (meth)acryloyl group, a CH ₂ ═CHCOOCH ₂ —CH(OH)CH ₂ O— group, or a CH ₂ ═C(CH ₃ )COOCH ₂ —CH(OH)CH ₂ O— group, and R ₁ represents a hydrogen atom, 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, or an isobornyl group.)

Examples of such monomers 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.

(ii) A monomer represented by the following formula (2):
Z-O-(R ₂ O) _p -R ₁ (2)
(wherein Z and R ₁ are as defined above; R ₂ represents —C ₂ H ₄ —, —C ₃ H ₆ —, —CH ₂ CH(CH ₃ )—, —C ₄ H ₈ — or —C ₆ H ₁₂ —; and p represents an integer of 1 to 25.)

Examples of such monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethoxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, tripropylene glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate.

(iii) A monomer represented by the following formula (3):

(In the formula, Z and _R2 are as defined 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 represents _-C2H4- , _-C3H6- , _-CH2CH ( _CH3 )-, _-C4H8- , or _-C6H12- ; _R3 and _R'3 represent hydrogen or an _alkyl group having ₁ to ₄ carbon atoms; and q+q' represents an integer of 0 to 20, preferably an integer of 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.)

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.

(iv) A (meth)acrylic acid ester of a polyhydric alcohol not included in the monomers described in (i), (ii), or (iii) above.

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

(v) A urethane prepolymer having a (meth)acryloyloxy group.
Such a monomer can be obtained, for example, by reacting a (meth)acrylic acid ester having a hydroxyl group, an organic polyisocyanate, and a polyhydric alcohol.

Here, examples of (meth)acrylic acid esters having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

Examples of the organic polyisocyanates include toluene diisocyanate, 4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

Examples of the polyhydric alcohols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyester polyols.

The above monomers (i) to (v) can be used singly or in combination. Of these, one or more of the group consisting of (i) and (iii) are preferred, as they provide high adhesiveness and little adhesive distortion on the adherend after bonding, and it is even more preferable to use (i) and (iii) in combination. When (i) and (iii) are used in combination, the composition ratio by mass of (i):(iii) is preferably 50-95:5-50, and more preferably 60-80:20-40.

[Epoxy Monomers and Their Oligomers]
In this embodiment, the epoxy adhesive component may contain an epoxy monomer or an epoxy oligomer in which a plurality of such epoxy monomers are bonded together.

Epoxy monomers include, for example, glycidyl ester-type epoxy monomers such as bisphenols (e.g., bisphenol A, bisphenol F, bisphenol AD, and bromine-containing bisphenol A), phenol novolacs, cresol novolacs, polyphenols, linear aliphatic, butadiene, and urethane; aliphatic glycidyl ester-type epoxy monomers (e.g., hexahydrophthalic acid glycidyl ester, dimer glycidyl ester, aromatic, and cyclic aliphatic); methyl-substituted epoxy monomers (e.g., esters, high-molecular-weight ether esters, ether esters, and bromine novolacs); heterocyclic epoxy monomers; glycidyl amine-type epoxy monomers (e.g., triglycidyl isocyanurate and tetraglycidyldiaminodiphenylmethane); linear aliphatic epoxy monomers (e.g., epoxidized polybutadiene and epoxy soybean oil); cyclic aliphatic epoxy monomers, naphthalene novolac-type epoxy monomers; and diglycidyloxynaphthalene-type epoxy monomers. These epoxy-based monomers may be used alone or in combination of two or more.

<Elastomer (B)>
In this embodiment, the use of the elastomer (B) can increase the toughness of the adhesive composition and improve its adhesion and bonding properties. In addition, it is preferable that the elastomer (B) is soluble in the reactive component (A).

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

The content of the elastomer (B) relative to 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 even more preferably 15 to 28 parts by mass.
By setting the content of the elastomer (B) to the above lower limit or more, the stress relaxation property becomes good, while by setting the content of the elastomer (B) to the above upper limit or less, the coatability becomes good.

The adhesive composition of this embodiment may further contain the following components:

<Polymerization initiator (C)>
The adhesive composition of this embodiment preferably contains a polymerization initiator (C) for reacting the reactive component (A).
Among these, a radical polymerization initiator is preferred as the polymerization initiator (C). An organic peroxide is preferred as the radical polymerization initiator. The organic peroxide decomposes upon heating to generate free radicals, which cause an addition reaction with the (meth)acrylic monomer and its oligomer, thereby accelerating the curing of the adhesive.
In order to improve the storage stability of the adhesive composition of the present embodiment, it is preferable to use an organic peroxide whose decomposition temperature for obtaining a half-life of one hour (one-hour half-life temperature) is 100°C or higher.
Examples of organic peroxides include peroxyesters such as t-butyl peroxybenzoate (1-hour half-life temperature: 125°C), t-butyl peroxyacetate (1-hour half-life temperature: 121°C), and t-butyl peroxylaurate (1-hour half-life temperature: 118°C); peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane (1-hour half-life temperature: 111°C) and 1,1-di(t-hexylperoxy)cyclohexane (1-hour half-life temperature: 107°C); and hydroperoxides such as p-menthane hydroperoxide (1-hour half-life temperature: 151°C), cumene hydroperoxide (1-hour half-life temperature: 188°C), and diisopropylbenzene hydroperoxide (1-hour half-life temperature: 173°C). Among these, cumene hydroperoxide is preferred from the viewpoint of stability.

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, per 100 parts by mass of the reaction component (A).
By setting the content of the polymerization initiator (C) to the above lower limit or more, the curing rate can be easily improved, while by setting the content of the polymerization initiator (C) to the above upper limit or less, good storage stability can be maintained.

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

Examples of the tertiary amine include triethylamine, tripropylamine, tributylamine, and N,N-dimethyl-p-toluidine.
Examples of the thiourea derivatives include 2-mercaptobenzimidazole, methylthiourea, dibutylthiourea, tetramethylthiourea, and ethylenethiourea.
Examples of the transition metal salt include cobalt octoate, cobalt naphthenate, copper naphthenate, and vanadyl acetylacetonate. Among these, transition metal salts are preferred in terms of reactivity. Among the transition metal salts, cobalt octoate is more preferred.

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, per 100 parts by mass of the reaction component (A).
By setting the content of the reducing agent (D) to the above lower limit or more, the curing rate can be increased, while by setting the content of the reducing agent (D) to the above upper limit or less, the progress of curing during storage can be suppressed, and good storage stability can be maintained.

<Curing agent or curing accelerator>
When the adhesive composition of the present embodiment contains an epoxy-based monomer and an oligomer thereof, a curing agent or curing accelerator can be used to accelerate the curing or curing effect of these.
The curing agent or curing accelerator can be a wide variety of those generally used for curing epoxy resins, and examples thereof include acid anhydrides, phenolic hydroxyl group-containing resins, phosphorus compounds, imidazole compounds, polyamine compounds, amide compounds, imidazoline compounds, urea compounds, organic acid metal salts, Lewis acids, and amine complex salts.
Examples of the acid anhydride include octenyl succinic anhydride, dodecenyl succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, tetrabromophthalic anhydride, himic anhydride, methylnadic anhydride, and trialkyltetrahydrophthalic anhydride.

Examples of the phenolic hydroxyl group-containing resins include polyphenol compounds such as phenol novolac resin, cresol novolac resin, aromatic hydrocarbon formaldehyde resin-modified phenolic resin, dicyclopentadiene phenol adduct resin, phenol aralkyl resin (Xyloc resin), naphthol aralkyl resin, trimethylolmethane resin, tetraphenylolethane resin, naphthol novolac resin, naphthol-phenol co-condensed novolac resin, naphthol-cresol co-condensed novolac resin, biphenyl-modified phenolic resin (a polyphenol compound in which phenol nuclei are linked by bismethylene groups), biphenyl-modified naphthol resin (a polyphenol compound in which phenol nuclei are linked by bismethylene groups), aminotriazine-modified phenolic resin (a polyphenol compound in which phenol nuclei are linked by melamine, benzoguanamine, etc.), and alkoxy group-containing aromatic ring-modified novolac resin (a polyphenol compound in which phenol nuclei and alkoxy group-containing aromatic rings are linked by formaldehyde).

Examples of the phosphorus compounds include alkyl phosphines such as ethylphosphine and butylphosphine, primary phosphines such as phenylphosphine, dialkyl phosphines such as dimethylphosphine and dipropylphosphine, secondary phosphines such as diphenylphosphine and methylethylphosphine, tertiary phosphines such as trimethylphosphine, triethylphosphine and triphenylphosphine, and phosphate esters.

Examples of the imidazole compound include 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 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 socyanuric acid adduct, 2-methylimidazole isocyanuric acid 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 kinds.

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 reaction component (A) (for example, the epoxy equivalent in the case of an epoxy-based monomer and its oligomer). Generally, the content of the curing agent or curing accelerator is, for example, preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 2 to 8 parts by mass, per 100 parts by mass of the epoxy-based monomer and its oligomer.
By setting the content of the curing agent or curing accelerator to the above lower limit or more, good curing can be achieved, whereas by setting the content of the curing agent or curing accelerator to the above upper limit or less, the storage stability of the adhesive layer obtained from the adhesive composition can be improved.

<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, defoamers, anti-fogging agents, colorants, organic solvents, etc. These various components may be added in any amount depending on the desired performance.

[Method of manufacturing adhesive]
The adhesive composition of the present embodiment can be prepared by uniformly mixing the various components described above 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 determined depending on the raw material components, and various methods can be used, such as a method of mixing all the components at once, a method of mixing any components and then mixing the remaining components at once or sequentially, etc. In addition, the stirring speed, stirring time, temperature, etc. during mixing are also appropriately adjusted depending on the raw materials.

[Usage]
A preferred embodiment of the present invention is the use of a two-component adhesive composition. In the two-component type, all of the essential components of the adhesive composition of this embodiment are not mixed during storage, but the adhesive composition is separated into a first component and a second component, with the polymerization initiator stored in the first component and the reducing agent stored in the second component separately. The two-component type is preferred because of its excellent storage stability. In this case, the two components can be applied simultaneously or separately, brought into contact with each other, and cured to form a two-component adhesive composition.

<Amount of adhesive (first adhesive, second adhesive) applied>
The amount of adhesive 50 applied is 100 g/ ^m2 or more and 1500 g/ ^m2 or less. The lower limit of the amount of adhesive 50 applied is preferably 150 g/ ^m2 or more, and more preferably 200 g/ ^m2 or more. The upper limit is preferably 1300 g/ ^m2 or less, and more preferably 1000 g/ ^m2 or less.

The application amount of the adhesive 50 can be the sum of the application amounts of the first adhesive 51 and the second adhesive 52. In other words, the sum of the application amounts of the first adhesive 51 and the second adhesive 52 is within the above-mentioned range of the application amount of the adhesive 50. Specifically, the application amount A of the first adhesive 51 is 100 g/ ^m² or more and 1000 g/ ^m² or less. The lower limit of the application amount A of the first adhesive 51 is preferably 150 g/ ^m² or more, and more preferably 200 g/ ^m² or more. The upper limit is preferably 900 g/ ^m² or less, and more preferably 800 g/ ^m² or less.

The application amount B of the second adhesive 52 is 0 g/m ² or more and 1500 g/m ² or less.
The lower limit of the application amount B of the second adhesive 52 is preferably 50 g/ ^m2 or more, and more preferably 100 g/ ^m2 or more. The upper limit is preferably 1300 g/ ^m2 or less, and more preferably 1000 g/ ^m2 or less.

The ratio B/A of the application amount A kg/ ^m2 of the first adhesive 51 to the application amount B kg/ ^m2 of the second adhesive 52 is 0 or more and 4.0 or less. The lower limit of the ratio B/A is preferably 0.1 or more, and more preferably 0.2 or more. The upper limit of the ratio B/A is preferably 3.0 or less, and more preferably 2.5 or less.

The application amount A of the first adhesive 51 and the application amount B of the second adhesive 52 are appropriately adjusted depending on the basis weight of the fiber sheet 3, and can be set, for example, as follows.
When the basis weight of the fiber sheet 3 is small (for example, 50 to 200 g/ ^m2 ), the application amount A of the first adhesive 51 is set to 100 g/ ^m2 or more and 600 g/ ^m2 or less, and the application amount B of the second adhesive 52 is set to 0 g/ ^m2 or more and 600 g/ ^m2 or less. Furthermore, the sum of the application amount A of the first adhesive 51 and the application amount B of the second adhesive 52 (i.e., the application amount of the adhesive 50) is set to the above-mentioned 100 g/ ^m2 or more and 1500 g/ ^m2 or less, and the ratio B/A is set to 0 or more and 4.0 or less.

When the fiber sheet 3 has a small basis weight, the spacing between fibers is large and the first adhesive 51 may seep onto the surface of the fiber sheet 3. In such cases, the amount of second adhesive 52 applied as a topcoat is omitted or reduced. On the other hand, even when the fiber sheet 3 has a small basis weight, if the fiber sheet 3 is thin and has a uniform surface structure, the first adhesive 51 may not necessarily seep onto the surface of the fiber sheet 3. In such cases, a certain amount of second adhesive 52 is applied. If the surface of the fiber sheet 3 is uniform, there is less need to smooth the surface, so the amount of second adhesive 52 applied may be reduced.

When the basis weight of the fiber sheet 3 is medium (for example, 200 to 500 g/ ^m2 ), the application amount A of the first adhesive 51 is set to 300 g/ ^m2 or more and 800 g/ ^m2 or less, and the application amount B of the second adhesive 52 is set to 0 g/ ^m2 or more and 1300 g/ ^m2 or less. Furthermore, the sum of the application amount A of the first adhesive 51 and the application amount B of the second adhesive 52 (i.e., the application amount of the adhesive 50) is set to the above-mentioned 100 g/ ^m2 or more and 1500 g/ ^m2 or less, and the ratio B/A is set to 0 or more and 4.0 or less.

When the basis weight of the fiber sheet 3 is high (for example, 500 to 1000 g/m ² ), the application amount A of the first adhesive 51 is set to 400 g/m ² or more and 1000 g/m ² or less, and the application amount B of the second adhesive 52 is set to 0 g/m ² or more and 1500 g/m ² or less. Furthermore, the sum of the application amount A of the first adhesive 51 and the application amount B of the second adhesive 52 (i.e., the application amount of the adhesive 50) is set to the above-mentioned 100 g/m ² or more and 1500 g/m ² or less, and the ratio B/A is set to 0 or more and 4.0 or less. For example, when the basis weight of the fiber sheet 3 is high, the fiber spacing tends to become narrower, and the amount of the first adhesive 51 impregnated into the fiber sheet 3 tends to decrease. On the other hand, since the unevenness of the fiber sheet 3 (specifically, the unevenness of the plain weave) becomes large, a large amount of resin may be required to smooth it out. Therefore, by increasing the amount of the second adhesive 52, which is a topcoat, and smoothing out the irregularities of the fiber sheet 3, it is possible to ensure good visibility of damage to the back surface.

In the above example, the basis weight of the fiber sheet 3 is divided into three levels, but this is not intended to be limiting and it may be divided into two levels or four or more levels. Furthermore, the amount of adhesive 50 (first adhesive 51, second adhesive 52) applied may be adjusted depending on the surface irregularities and thickness of the fiber sheet 3.

<Collision energy and cumulative damage value>
In this embodiment, a projectile 2 collides with the surface 11 of the test concrete 101, the back surface 12 of which has been reinforced by the fiber sheet 3, and the cumulative fracture value ES is evaluated, which is the cumulative value of the collision energy EA until the back surface is fractured. Assuming that the collision energy (i.e., kinetic energy) of the projectile 2 is not so large, the following three evaluation conditions 1 to 3 are assumed.
Evaluation condition 1:
The collision energy EA of the projectile 2 per collision is 0.1 kJ or more and less than 7.0 kJ, and the cumulative destruction value ES is 7.0 kJ or more.
Evaluation condition 2:
The collision energy EA of the projectile 2 per collision is 0.5 kJ or more and less than 1.5 kJ, and the cumulative destruction value ES is 15.0 kJ or more.
Evaluation condition 3:
The collision energy EA of the projectile 2 per collision is 3.0 kJ or more and less than 4.0 kJ, and the cumulative destruction value ES is 25.0 kJ or more.

For evaluation condition 1:
The cumulative value of the collision energy from the collision of the flying object 2 until the back surface is broken (i.e., the cumulative fracture value ES) is 7.0 kJ or more. In other words, when the flying object 2 collides multiple times, if the cumulative fracture value ES is less than 7.0 kJ, the back surface will not be broken. If the cumulative fracture value ES is a predetermined value or more, the concrete 1 having the fiber sheet 3 on the back surface 12 is evaluated to have been constructed so as to have a certain strength that takes back surface breakage into consideration.
The lower limit of the cumulative destruction value ES is preferably 10 kJ or more, and more preferably 15 kJ or more. There is no particular limitation on the upper limit of the cumulative destruction value ES, but a realistic value is 50 kJ or less, or it may be 40 kJ or less, or it may be 30 kJ or less. For example, when the kinetic energy (impact energy) of the expected flying object 2 is small, the cumulative destruction value ES is set to "7.0 kJ or more." Furthermore, when the kinetic energy (impact energy) of the flying object 2 is large near a volcano or the like or when repeated collisions are expected, the cumulative destruction value ES is set to "15 kJ or more." By assigning multiple levels of evaluation ranking depending on the set cumulative destruction value ES, it becomes easier to determine whether the concrete structure being constructed has the required strength.

For evaluation condition 2:
The cumulative value of the collision energy from the collision of the flying object 2 until the back surface is broken (i.e., the cumulative fracture value ES) is 15 kJ or more. In other words, when the flying object 2 collides multiple times, if the cumulative fracture value ES is less than 15 kJ, the back surface will not be broken. If the cumulative fracture value ES is a predetermined value or more, the concrete 1 having the fiber sheet 3 on the back surface 12 is evaluated to have been constructed so as to have a certain strength that takes back surface breakage into consideration.
The lower limit of the cumulative destruction value ES is preferably 20 kJ or more, and more preferably 25 kJ or more. There is no particular limitation on the upper limit of the cumulative destruction value ES, but a realistic value is 50 kJ or less, and it may be 45 kJ or less, or it may be 40 kJ or less. For example, when the kinetic energy (impact energy) of the expected flying object 2 is small, the cumulative destruction value ES is set to "15 kJ or more." Furthermore, when the flying object 2 is close to a volcano or the like and the kinetic energy (impact energy) of the flying object 2 is large or repeated collisions are expected, the cumulative destruction value ES is set to "25 kJ or more." By assigning multiple levels of evaluation ranking depending on the set cumulative destruction value ES, it becomes easier to determine whether the concrete structure being constructed has the required strength.

For evaluation condition 3:
The cumulative value of the collision energy from the collision of the flying object 2 until the back surface is broken (i.e., the cumulative fracture value ES) is 25 kJ or more. In other words, when the flying object 2 collides multiple times, if the cumulative fracture value ES is less than 25 kJ, the back surface will not be broken. If the cumulative fracture value ES is a predetermined value or more, the concrete 1 having the fiber sheet 3 on the back surface 12 is evaluated to have been constructed so as to have a certain strength that takes back surface breakage into consideration.
The lower limit of the cumulative destruction value ES is preferably 30 kJ or more, and more preferably 35 kJ or more. There is no particular limitation on the upper limit of the cumulative destruction value ES, but a realistic value is 50 kJ or less, and it may be 45 kJ or less, or it may be 40 kJ or less. For example, when the kinetic energy (impact energy) of the expected flying object 2 is small, the cumulative destruction value ES is set to "25 kJ or more." Furthermore, when the flying object 2 is close to a volcano or the like and the kinetic energy (impact energy) of the flying object 2 is large or repeated collisions are expected, the cumulative destruction value ES is set to "30 kJ or more." By assigning multiple levels of evaluation ranking depending on the set cumulative destruction value ES, it becomes easier to determine whether the concrete structure being constructed has the required strength.

Of the above evaluation conditions, evaluation condition 3 is the strictest, followed by evaluation condition 2. Evaluation condition 1 is the least strict of the three evaluation conditions. In this way, by providing multiple indicators with different levels of evaluation condition strictness, it is possible to propose more detailed construction conditions depending on the facility to which they are applied. In other words, it is possible to determine the optimal construction conditions that are neither too high nor too low in the required level of construction depending on the type of facility, construction location, and required durability.

<Concrete backside reinforcement method>
The concrete back surface reinforcement method will be described with reference to Figures 3 and 4. Figure 3 is a flowchart showing the concrete back surface reinforcement method. Figure 4 is an image showing the process of attaching a fiber sheet 3 to concrete 1 (particularly the attached state) in each step of the concrete back surface reinforcement method. Note that Figure 4 shows an example in which the fiber sheet 3 is attached not only to the back surface 12 but also to the side surfaces, etc.

The concrete back surface reinforcement method of this embodiment includes a component preparation process S10 and a resin sheet attachment process S20.

Component preparation step S10:
The component 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.

The concrete preparation step S11 is a step of preparing the concrete 1 to which the fiber sheet 3 is to be attached. The concrete 1 may be a new or existing concrete structure. At this time, the back surface 12 of the concrete 1 may be painted with a primer or putty material as a surface preparation. Using a material similar to the first adhesive 51 as the primer or putty material can shorten the construction period. Note that this surface preparation may also be performed in the resin sheet attachment step S20, which will be described later.

The fiber sheet preparation step S12 is a step of preparing the fiber sheet 3 to be attached to the concrete 1. As described above, the fiber sheet 3 is preferably impregnated with resin (i.e., adhesive 50) to form a prepreg.

Resin sheet mounting step S20:
The resin sheet attachment process S20 is a process of attaching a fiber sheet 3 to the back surface 12 of the concrete 1, and specifically includes a primer application process S21, a fiber sheet attachment process S22, and a topcoat application process S23.

The primer application step S21 is a step of applying a first adhesive 51 as a primer to the back surface 12 of the concrete 1 prepared in the component preparation step S10. At this time, a coating of the first adhesive 51 is formed on the back surface 12 so as to cover at least the area where the fiber sheet 3 is to be attached. The application amount A of the first adhesive 51 is preferably 100 g/ ^m² or more and 1000 g/ ^m² or less, as described above, and is adjusted depending on the basis weight of the fiber sheet 3.

The fiber sheet attachment process S22 is a process of attaching the fiber sheet 3 onto the first adhesive 51. It is preferable to attach the fiber sheet 3 before the first adhesive 51, which serves as an undercoat, has completely dried and hardened. This allows the fiber sheet 3 to be properly attached onto the coating of the first adhesive 51.

The topcoat application process S23 is a process of applying a second adhesive 52 as a topcoat material onto the fiber sheet 3 attached to the concrete 1 with the first adhesive 51. Specifically, the second adhesive 52, which is a topcoat material, is applied to cover the first adhesive 51 and the fiber sheet 3, forming a coating of the second adhesive 52. From the perspective of shortening the construction period, it is preferable to complete the attachment of the fiber sheet 3 and the application of the second adhesive 52 before the first adhesive 51 has completely dried and hardened.

As described above, the application amount B of the second adhesive 52 is 0 g/ ^m2 or more and 1500 g/ ^m2 or less, and is adjusted depending on the basis weight of the fiber sheet 3, the state of prepregging, 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 4.0 or less.

<Characteristics of back-reinforced concrete>
The back-reinforced concrete 102 manufactured under the above conditions does not suffer backside failure when tested under the following experimental conditions. In other words, a preliminary experiment is conducted to design the concrete 1 to be reinforced so that backside failure does not occur, and the fiber sheet 3 is applied to the concrete 1 to be reinforced using the above process.

Figure 5 shows the high-pressure air projectile generator 90 and back-reinforced concrete 102 used in the experiment. Figure 6 shows the back-reinforced concrete 102. Figure 7 shows the test projectile 21 (corresponding to projectile 2) launched from the high-pressure air projectile generator 90 toward concrete 1. The high-pressure air projectile generator 90 is a device that uses air pressure to accelerate the test projectile 21 to a predetermined speed and cause it to collide with the back-reinforced concrete 102.

As shown in Figure 5, the high-pressure air projectile generating device 90 comprises, from upstream to downstream, an air compressor 91, an air chamber 93, a launch tube 94, and a rebound prevention jig 97. A speed sensor 95 is attached to the rebound prevention jig 97. In front of the rebound prevention jig 97, a back-reinforced concrete 102 is fixed to the reaction wall 80, and the projectile 2 (high-speed projectile) is designed to collide perpendicularly with the center of the surface 11 of the back-reinforced concrete 102. The maximum capacity of the air compressor 91 is, for example, 4 MPa.

Air compressed by air compressor 91 is sent into air chamber 93, where it is increased in pressure to a level corresponding to the set speed of the test projectile 21. Before the pressure is increased, the test projectile 21 is hydraulically placed in the projectile fixing portion 98 of the air chamber 93. A launch tube 94 is attached to the tip of the air chamber 93, and compressed air compressed to the set pressure is supplied to the launch tube 94 at a predetermined timing (set or operated by the experimenter).

The launch tube 94 has an inner diameter (100 mm) slightly larger than the outer diameter of the test projectile 21 and is 2200 mm long. Compressed air introduced from the air chamber 93 accelerates the test projectile 21 inside to the desired speed, and the test projectile 21 is then launched from the launch port 96. The speed of the launched test projectile 21 is measured by a speed sensor 95. A load cell 81 is installed on the reaction wall 80, which can measure the load when the projectile 2 impacts.

Figure 6 shows the back-reinforced concrete 102 used in the experiment, with Figure 6(a) being a rear view and Figure 6(b) being a cross-sectional view taken along the line A-A in Figure 6(a). The back-reinforced concrete 102 has test concrete 101 and a fiber sheet 3 attached to the back surface 12.

The dimensions of the test concrete 101 are 1100 mm x 1100 mm x 150 mm. The compressive strength of the test concrete 101 is 30 N/ ^mm2 . To prevent concrete fragmentation after impact with the flying object 2, 12 D13 rebars 15 (one piece) are arranged with a rebar ratio of 0.57% (0.49% within the back indicator). As shown in the figure, a plurality of through-holes 16 are provided in the peripheral region of the test concrete 101 (the region where the fiber sheet 3 is not provided) that penetrate from the front surface 11 to the back surface 12. The through-holes 16 are used to screw the back-reinforced concrete 102 to the reaction wall 80.

A fiber sheet 3 is attached to the back surface 12 of the test concrete 101 with adhesive 50 (first adhesive 51, second adhesive 52). The area of the attached fiber sheet 3 is 830 mm x 830 mm. The materials described above can be used for the fiber sheet 3 and adhesive 50 (first adhesive 51, second adhesive 52).

As shown in Figure 7, the test projectile 21 has a dome-shaped tip and a cylindrical body to which the tip is fixed. The tip is made of alloy tool steel with a radius of 90 mm and a length of 55 mm. The body is made of duralumin with a length of 225 mm. The mass of the test projectile 21 is 4.5 kg.

The launch speed of the test projectile 21, i.e., the projectile's set speed when impacting the concrete 1, is 20 m/s and 40 m/s.

When a test projectile 21 is collided three times with backside reinforced concrete 102 using a high-pressure air projectile generator 90, if no backside damage occurs at any of the projectile's set speeds, it can be determined that the required strength against the collision of the projectile 2 is achieved.

<Summary of this embodiment>
[1]
A concrete back surface reinforcement method for preventing back surface damage, in which a surface (back surface 12) opposite to one surface (front surface 11) of concrete 1 is damaged due to a collision of a flying object 2 with the surface, comprises attaching a fiber sheet 3 to the other surface (back surface 12),
The resin sheet attaching step S20 for attaching the fiber sheet 3 to the other surface (back surface 12) of the concrete 1 includes a step of applying a first adhesive 51 (primer) to the other surface (back surface 12) of the concrete 1 (primer application step S21), and a step of attaching the fiber sheet 3 from above the first adhesive 51 (fiber sheet attaching step S22).
After the fiber sheet 3 is attached to the other surface (back surface 12) of the test concrete 101, the cumulative fracture value ES, which is the cumulative value of the collision energy EA from the time the flying object 2 collides with the one surface (front surface 11) until the back surface is destroyed, is 7.0 kJ or more, and the collision energy EA per collision of the flying object 2 is 0.1 kJ or more and less than 7.0 kJ,
The test concrete 101 has a shape of 1100 mm long x 1100 mm wide x 150 mm thick, and its compressive strength is 24 N / mm ² or more.
Concrete back reinforcement method.
[2]
The resin sheet attachment process S20 further includes a process of applying a second adhesive (top coat material) onto the fiber sheet 2 attached to the back surface 12 of the concrete 1 with the first adhesive (top coat material application process S23). [1] The concrete back surface reinforcement method described.
[3]
The concrete back surface reinforcement method according to [2], wherein the first adhesive and the second adhesive contain at least one of a (meth)acrylic resin adhesive and an epoxy resin.
[4]
the application amount A of the first adhesive is 100 g/m ² or more and 1000 g/m ² or less,
The concrete back surface reinforcement method according to [2] or [3], wherein the application amount B of the second adhesive is 0 g/m ² or more and 1500 g/m ² or less.
[5]
The ratio B/A of the application amount of the first adhesive (A kg/m ²⁾ to the application amount of the second adhesive (B kg/m ²⁾ is 0 or more and 4.0 or less, [2] to [4]. The concrete back surface reinforcement method according to any one of [2] to [4].
[6]
The concrete back surface reinforcing method according to any one of [1] to [5], wherein the fiber sheet 3 has a basis weight of 50 g / m ² or more and 1000 g / m ² or less.
[7]
The concrete back surface reinforcement method according to any one of [1] to [6], wherein the fiber sheet 3 includes a bidirectional sheet in which fibers are arranged along two different axial directions, or a laminated sheet in which two unidirectional sheets in which fibers are arranged along one axial direction are stacked so that the axial directions intersect with each other.
[8]
The concrete back surface reinforcing method according to any one of [1] to [7], wherein the fiber sheet 3 is an aramid fiber sheet.
[9]
The concrete back surface reinforcement method according to any one of [1] to [8], wherein the cumulative fracture value is 10 kJ or more.
[10]
A concrete back surface reinforcement method according to any one of [1] to [9], in which no back surface damage occurs when a projectile 2 is collided three times against the standardized concrete 1 using a high-pressure air projectile generator under the following experimental conditions.
Experimental conditions:
・Device: High-pressure air projectile generator (National Defense Academy)
・Concrete specimen (standardized concrete): 1100mm x 1100mm x 150mm
- Flying object mass: 4.5kg (Φ90mm)
- Flying object setting speed: 20m/s, 40m/s
[11]
The collision energy of the flying object 2 per collision is 0.5 kJ or more and less than 1.5 kJ,
The concrete back surface reinforcement method according to any one of [1] to [10], wherein the cumulative fracture value is 15.0 kJ or more.
[12]
The collision energy of the flying object 2 per collision is 3.0 kJ or more and less than 4.0 kJ,
The concrete back surface reinforcement method according to any one of [1] to [10], wherein the cumulative fracture value is 25.0 kJ or more.
[1] - [12] A concrete structure (rear-reinforced concrete 102) reinforced using the concrete rear surface reinforcement method described in any one of [1] to [12].

The present invention will be explained in detail below using examples, but the present invention is not limited to these examples.

As explained above in Figures 5 to 7, a high-pressure air projectile generator and concrete with backside reinforcement (Examples 1 to 6) and concrete without backside reinforcement (Comparative Examples 1 to 3) were prepared as concrete specimens, and experiments were conducted in which projectile 2 was struck multiple times, observing the number of collisions until the backside was destroyed and the condition of the backside at that time.

The experimental conditions are summarized as follows. In the embodiment, two types of projectile set speeds, 20 m/s and 40 m/s, were described. In this example, an experiment was conducted in Comparative Example 3 as a reference example, with a projectile set speed of 60 m/s.
・Device: High-pressure air projectile generator (National Defense Academy)
- Concrete specimen: 1100mm x 1100mm x 150mm, 28-day compressive strength 30N/ ^mm2 (measured in accordance with JIS A 1108:2018)
Fiber sheet area: 830mm x 830mm
・Project mass: 4.5kg
Projectile set speed: 20 m/s (Examples 1 to 3, Comparative Example 1)
40 m/s (Examples 4 to 6, Comparative Example 2)
60m/s (Comparative Example 3)

In Examples 1 to 6, a reinforcing fiber sheet was attached to the concrete specimen. In Comparative Examples 1 to 3, the concrete specimen was used as is. The specifications of the fiber sheet used in Examples 1 to 6 (test level (fiber sheet reinforcement)) are as shown in Table 1.
As the fiber sheets, three types of bidirectional aramid fiber sheets with different basis weights (180 g/m ² , 330 g/m ² , 650 g/m ² ) were used. Table 2 shows the basis weight, primer, coating amount, and adhesive coating amount (undercoat/topcoat) for each type of bidirectional aramid fiber sheet.
As a primer, a two-component acrylic resin adhesive (product name: Denka DK550-003, manufactured by Denka Co., Ltd.) was used.
As the adhesive, a two-component acrylic resin adhesive (product name: Denka Acrisave K, manufactured by Denka Co.) was used.

The concrete specimens of the backside reinforced concrete in Examples 1 to 6 were prepared by the concrete backside reinforcement method described with reference to FIGS.
Specifically, the concrete specimen was first subjected to a surface preparation process, namely, scraping, to prepare the surface of the concrete specimen, and then a primer was applied to the area of the concrete specimen where the fiber sheet was to be attached.
Thereafter, each fiber sheet corresponding to Examples 1 to 6 was attached to the area where the primer had been applied, and then cured for a predetermined time.

The resulting concrete with backside reinforcement (Examples 1-6) and concrete without backside reinforcement (Comparative Examples 1-3) were used as test specimens, and projectiles were collided with the test specimens using the above-mentioned high-pressure air projectile generator to calculate the number of collisions and cumulative kinetic energy required to cause backside peeling.

The results are shown in Table 3. Figure 10 shows images of the condition of the backside after the final number of collisions for Examples 1 to 3. Figure 11 shows images of the condition of the backside after the final number of collisions for Examples 4 to 6.

For the test specimens of Examples 1 to 6, it was confirmed that fiber sheet reinforcement prevented backside peeling. In Comparative Examples 1 to 3, there was no fiber sheet reinforcement, and backside peeling was confirmed.

In all of the test specimens in Examples 1 to 6, the fiber sheet did not break or peel off even when the number of collisions was increased, and the center of the sheet swelled. This was because the test was discontinued when it was determined that the projectiles would not be able to be removed from the test specimens after multiple collisions, making it impossible to continue the test.
For this reason, the backside peeling limit energy could not be calculated directly, but it was determined that there was a high probability that the fiber sheet would break or peel in the next collision, and so it was adopted as a value to evaluate the cumulative kinetic energy up to the time of interruption.
Furthermore, the cumulative kinetic energy in Comparative Examples 1 to 3 was 6.3 kJ in Comparative Example 1, 7.2 kJ in Comparative Example 2, and 8.1 kJ in Comparative Example 3. However, the collision energy per collision in Comparative Examples 2 and 3 was 3.6 kJ and 8.1 kJ, respectively. Considering the increase in cumulative kinetic energy when the number of collisions increases by one, the cumulative kinetic energy when backside peeling occurred was estimated to be less than 7 kJ.

1. Concrete 2. Projectile (sometimes called high-speed projectile)
3 Fiber sheet 11 Surface 12 Back surface 21 Test projectile 51 First adhesive 52 Second adhesive 80 Reaction wall 81 Load cell 90 High-pressure air projectile generator 91 Air compressor 93 Air chamber 94 Launch tube 95 Speed sensor 97 Rebound prevention jig 101 Test concrete 102 Back-reinforced concrete

Claims (18)

A concrete back surface reinforcement method for preventing back surface damage, in which a surface opposite to one surface of concrete that is a part of a structure is damaged due to a collision of a flying object against the one surface, by attaching a fiber sheet to the other surface,
A testing process in which evaluation tests are conducted in advance;
and a resin sheet attaching step of attaching the fiber sheet to the other surface of the concrete,
The resin sheet attaching step includes applying a first adhesive to the other surface of the concrete;
a step of attaching the fiber sheet onto the first adhesive,
The evaluation test is
A test concrete is prepared, and the fiber sheet is attached to the other surface of the test concrete using the same method as in the resin sheet attaching step. Then, a cumulative fracture value, which is a cumulative value of collision energy from when the projectile collides with the one surface until the back surface is destroyed, is 7.0 kJ or more, and the collision energy of the projectile per collision is 0.1 kJ or more but less than 7.0 kJ,
The test concrete has a size of 1100 mm long x 1100 mm wide x 150 mm thick, and its compressive strength is 30 N/mm ² ,
the application amount A of the first adhesive is 100 g/m ² or more and 1000 g/m ² or less ,
The resin sheet attaching step uses the concrete, the fiber sheet, and the first adhesive prepared in accordance with the regulations of the evaluation test, and attaches the fiber sheet to the concrete using the first adhesive by a construction method in accordance with the regulations of the evaluation test.
Concrete back reinforcement method. The concrete back surface reinforcement method described in claim 1, wherein the resin sheet attachment process further includes a process of applying a second adhesive onto the fiber sheet attached to the back surface of the concrete with the first adhesive. The concrete back surface reinforcement method described in claim 2, wherein the first adhesive and the second adhesive include at least one of a (meth)acrylic resin-based adhesive and an epoxy resin-based adhesive. The concrete back surface reinforcing method according to claim 2 or 3, wherein the amount B of the second adhesive to be applied is 1500 g/m ² or less. The concrete back surface reinforcement method according to claim 2 or 3, wherein the ratio B/A of the application amount of the first adhesive (Ag/m2 ⁾ to the application amount of the second adhesive (Bg/m2 ⁾ is 4.0 or less. The concrete back surface reinforcing method according to any one of claims 1 to 3, wherein the fiber sheet has a basis weight of 50 g / m ² or more and 1000 g / m ² or less. The concrete underside reinforcement method according to any one of claims 1 to 3, wherein the fiber sheet includes a bidirectional sheet in which fibers are arranged along two different axial directions, or a laminated sheet in which two unidirectional sheets in which fibers are arranged along one axial direction are stacked so that the axial directions intersect. The concrete back surface reinforcement method described in any one of claims 1 to 3, wherein the fiber sheet is an aramid fiber sheet. The concrete back surface reinforcement method according to any one of claims 1 to 3, wherein the cumulative fracture value is 10 kJ or more. 4. The concrete back surface reinforcement method according to claim 1, wherein no back surface damage occurs when a projectile is collided three times with the test concrete to which the fiber sheet is attached using a high-pressure air projectile generator under the following experimental conditions:
Experimental conditions:
・Device: High-pressure air projectile generator ・Projectile mass: 4.5 kg (Φ90 mm)
- Flying object setting speed: 20m/s, 40m/s The collision energy of the projectile per collision is 0.5 kJ or more and less than 1.5 kJ,
The concrete back surface reinforcement method according to any one of claims 1 to 3, wherein the cumulative fracture value is 15.0 kJ or more. The collision energy of the projectile per collision is 3.0 kJ or more and less than 4.0 kJ,
The concrete back surface reinforcement method according to any one of claims 1 to 3, wherein the cumulative fracture value is 25.0 kJ or more. The concrete back surface reinforcement method according to claim 1, wherein when the basis weight of the fiber sheet is 50 g/m ² or more and less than 200 g/m ² , the application amount A of the first adhesive is 100 g/m ² or more and 600 g/m ² or less. The resin sheet attaching step further includes a step of applying a second adhesive onto the fiber sheet attached to the back surface of the concrete with the first adhesive,
The concrete back surface reinforcing method according to claim 13, wherein the application amount B of the second adhesive is 600 g/m ² or less. The concrete back surface reinforcing method according to claim 1, wherein when the basis weight of the fiber sheet is 200 g/m ² or more and less than 500 g/m ² , the application amount A is 300 g/m ² or more and 800 g/m ² or less. The resin sheet attaching step further includes a step of applying a second adhesive onto the fiber sheet attached to the back surface of the concrete with the first adhesive,
The concrete back surface reinforcing method according to claim 15, wherein the application amount B of the second adhesive is 1300 g/m ² or less. The concrete back surface reinforcing method according to claim 1, wherein when the basis weight of the fiber sheet is 500 g/m ² or more and 1000 g/m ² or less, the application amount A is 400 g/m ² or more and 1000 g/m ² or less. The resin sheet attaching step further includes a step of applying a second adhesive onto the fiber sheet attached to the back surface of the concrete with the first adhesive,
The concrete back surface reinforcing method according to claim 17, wherein the application amount B of the second adhesive is 1500 g/m ² or less.