JP7541219B2 - Concrete spalling prevention method - Google Patents

Description

The present invention relates to a method for preventing concrete spalling from concrete structures (hereinafter also referred to as a concrete spalling prevention method), and in particular to a concrete spalling prevention method that can be applied in a short time using a simple method even to concrete structures installed in various environments, and that can achieve a stable, high level of spalling prevention function.

Concrete structures are widely used for viaducts, tunnels, bridges, and other structures due to the need to improve their strength and durability.However, in recent years, concrete has deteriorated due to corrosion of reinforcing bars caused by salt damage to concrete, neutralization due to exhaust gases, alkali-aggregate reactions, freezing of water that has penetrated into cracks, etc., and as deterioration progresses, pieces of concrete peel off from the surface of the concrete structure, causing problems such as a decrease in the strength and aesthetics of the concrete structure itself, and the risk of accidents due to spalling.
Under these circumstances, and taking into consideration these issues, methods for preventing concrete spalling are being developed from various perspectives.

JP 2018-3444 A describes a method for preventing concrete from spalling from a concrete structure by forming a laminate comprising an undercoat coating film, a fiber sheet, and a topcoat coating film on the surface of the concrete structure, the method being characterized in that the undercoat paint and the topcoat paint contain a polyol having a number average molecular weight of 300 to 10,000 and a number of hydroxyl groups per molecule of 2.0 to 9.0, and a polyisocyanate having an isocyanate group ratio of 10.0 to 20.0 mass%, the polyisocyanate having an isocyanate group equivalent of 0.5 to 1.5 relative to the hydroxyl groups of the polyol, and the polyisocyanate is a two-component curing paint that is at least one type selected from the group consisting of aliphatic polyisocyanates and alicyclic polyisocyanates, and the method describes that a concrete spalling prevention method can be provided that allows the construction of a spalling prevention system to be implemented in a short period of time.

JP 2004-27718 A describes a sheet for repairing, reinforcing, and preventing deterioration of concrete structures, which is characterized by bonding a protective layer and an adhesive-coated layer and forming an adhesive layer on the adhesive surface of the adhesive-coated layer to the concrete structure, and a method for repairing, reinforcing, and preventing deterioration of concrete structures, which is characterized by attaching the sheet for repairing, reinforcing, and preventing deterioration of concrete structures to the concrete structure using the adhesive layer on the adhesive surface of the sheet to be adhered to the concrete structure, which is said to reduce and shorten the repair and reinforcement work to prevent concrete spalling.

JP 2015-78600 A describes a method for repairing or reinforcing concrete, which comprises providing concrete with an adhesive layer that contains an acrylic resin with a glass transition temperature of 15°C or less and further contains a liquid epoxy resin, a solid epoxy resin, and a hardener, and a sheet for repairing or reinforcing concrete that covers the adhesive layer, and the method describes how the sheet can be temporarily fixed to the adherend when it is attached to the adherend, such as concrete, making it easy to repair or reinforce the adherend.

JP 2017-119995 A describes a method for applying an adhesive article to prevent spalling of a concrete structure, the method comprising a step of directly applying the adhesive article, which includes an adhesive layer containing an adhesive acrylic polymer and inorganic fine particles and a fiber sheet disposed in the adhesive layer, the adhesive layer being present on both main surfaces of the article, to the concrete structure, and claims that this allows application in a shorter time than conventional application methods and further improves the ability to prevent concrete pieces from spalling.

JP 2018-3444 A JP 2004-27718 A JP 2015-78600 A JP 2017-119995 A

The concrete spalling prevention method described in Patent Document 1 is a concrete spalling prevention method that allows the installation of a spalling prevention system to be carried out in a short period of time, and can perform in one day, whereas conventional methods required two or more days, and can achieve a high level of spalling prevention performance. However, there is still a demand for further process reduction and simplification of the work.

On the other hand, the methods described in Patent Documents 2 to 4 aim to simplify the work by using a composite sheet having an adhesive layer or a pressure-sensitive adhesive layer, but in the methods described in Patent Documents 2 to 4, such a composite sheet is attached directly to the concrete substrate or attached onto a dried coating film formed on the concrete substrate. However, it cannot be said that the methods described in Patent Documents 2 to 4 can provide a stable, high level of peeling prevention function to the surface of concrete structures, which have various sizes and density of voids.

The object of the present invention is to provide a method for preventing concrete spalling that solves the problems of the conventional technology, can be applied to concrete structures installed in various environments in a simple manner in a short time, and can achieve a stable, high level of spalling prevention function.

As a result of extensive research into achieving the above object, the inventors discovered that a stable and high level of anti-peeling function can be achieved for a variety of concrete structures by painting the surface of a concrete structure with a primer paint, and then, while the primer paint applied to the concrete structure is still wet, placing a composite sheet comprising an adhesive layer and a fiber sheet layer on the primer layer formed from the primer paint, and thus completed the present invention.

That is, the concrete spalling prevention method of the present invention is a method for preventing concrete from spalling from a concrete structure by forming a laminate having a primer layer, an adhesive layer, and a sheet layer on the surface of the concrete structure,
A first step of painting a surface of a concrete structure with a primer paint;
and a second step of placing a composite sheet having an adhesive layer and a fiber sheet layer on a primer layer formed from the primer paint applied to the concrete structure while the primer paint is still wet.

In a preferred embodiment of the concrete spalling prevention method of the present invention, the composite sheet is placed on the primer layer within one hour after the primer coating is completed.

In another preferred embodiment of the concrete spalling prevention method of the present invention, the primer coating contains at least an epoxy resin with a weight average molecular weight of 1,000 to 200,000.

In another preferred embodiment of the concrete spalling prevention method of the present invention, the primer coating contains at least one organic solvent selected from the group consisting of methyl ethyl ketone and ethyl acetate, and the volatile content of the primer coating is within the range of 40 to 90 mass %.

In another preferred embodiment of the concrete spalling prevention method of the present invention, the primer coating is applied by aerosol spray coating.

In another preferred embodiment of the concrete spalling prevention method of the present invention, the laminate has a primer layer thickness in the range of 0.01 to 0.1 mm, an adhesive layer thickness in the range of 0.1 to 2.0 mm, and a sheet layer thickness in the range of 0.001 to 0.5 mm.

The present invention provides a method for preventing concrete spalling that can be applied in a short time and with a simple method, even to concrete structures installed in a variety of environments, and that can achieve a stable, high level of spalling prevention functionality.

1 is a schematic cross-sectional view of a laminate formed on the surface of a concrete structure by one embodiment of the concrete spalling prevention method of the present invention. FIG.

The concrete spalling prevention method of the present invention is described in detail below. The concrete spalling prevention method of the present invention is a method for preventing concrete from spalling from a concrete structure by forming a laminate comprising a primer layer, an adhesive layer, and a sheet layer on the surface of the concrete structure, and is characterized by including a first step of painting the surface of the concrete structure with a primer paint, and a second step of placing a composite sheet comprising an adhesive layer and a fiber sheet layer on the primer layer formed from the primer paint while the primer paint applied to the concrete structure is still wet.

In the concrete spalling prevention method of the present invention, first, the surface of the concrete structure is painted with a primer paint (first step). A primer layer can be formed by the first step. As described below, in the concrete spalling prevention method of the present invention, a composite sheet having an adhesive layer and a fiber sheet layer is placed while the primer paint applied to the concrete structure is still wet.

In this specification, "concrete structure" refers to a structure that uses concrete alone, a structure that uses reinforced concrete, or components thereof. Specific examples include various concrete structures and components thereof, such as viaducts, bridges, piers, abutments, girders, decks, parapets, dolphins, tunnels, roads, water channels, storage tanks, and walls.

In this specification, the term "primer paint" refers to a paint that is applied in advance to a substrate for the purpose of achieving some kind of improvement effect. The primer paint that is applied before applying a sheet to a concrete structure, such as in the concrete spalling prevention method of the present invention, is intended to improve the adhesion of the sheet, etc.

The primer coating preferably contains an epoxy resin. Since the epoxy resin has excellent adhesion to concrete structures, it can provide high-level concrete spalling prevention performance. Here, the epoxy resin is preferably a resin having at least two epoxy groups in one molecule, for example, one obtained by reacting a polyhydric alcohol or a polyhydric phenol with a halohydrin. Specific examples include bisphenol A type epoxy resin, halogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyglycol type epoxy resin, bisphenol F type epoxy resin, epoxidized oil, 1,6-hexanediol diglycidyl ether, and neopentyl glycol diglycidyl ether, as well as modified epoxy resins such as amine-modified epoxy resin, isocyanate-modified epoxy resin, acrylic-modified epoxy resin, urethane-modified epoxy resin, and polyester-modified epoxy resin, which are modified products of such epoxy resins. Among these, bisphenol A type epoxy resin and bisphenol F type epoxy resin are preferred from the viewpoint of durability of the coating film and adhesion to concrete structures. These epoxy resins may be used alone or in combination of two or more.
In the above primer coating, the content of the epoxy resin is preferably 10 to 50% by mass.

The epoxy resin preferably has a weight average molecular weight of 1,000 to 200,000, more preferably 5,000 to 100,000, and particularly preferably 8,000 to 70,000. If the primer coating contains a high molecular weight epoxy resin with a weight average molecular weight in the above specified range, for example, high adhesion can be imparted to the primer layer after drying when the solvent has evaporated. If the weight average molecular weight of the epoxy resin is 200,000 or less, coating workability can be easily ensured.
In this specification, the weight average molecular weight is a value measured by gel permeation chromatography (GPC), using polystyrene as the standard substance and tetrahydrofuran as the mobile phase.

The softening point of the epoxy resin is preferably within the range of 20 to 80° C. When the primer coating contains an epoxy resin having a softening point within the above specified range, a coating film having excellent moisture resistance can be obtained.
In this specification, the softening point is a value measured by the softening point test method (ring and ball method) specified in JIS K 7234.

The above primer coating can use water, an organic solvent, or a mixture of these as the solvent. The organic solvent is not particularly limited, and various organic solvents such as hydrocarbons (aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, etc.), ketones, esters, ethers, alcohols, etc. can be used. The organic solvents can be used alone or in combination of two or more.

The primer coating preferably contains at least one organic solvent (a) selected from the group consisting of methyl ethyl ketone and ethyl acetate. From the viewpoint of providing a stable and high level of anti-peeling function, it is preferable to blend the preferred organic solvent (a) in the primer coating.
In the above primer coating, the content of the organic solvent (a) is preferably 30 to 60% by mass or more.

The above primer paint may contain other components, such as other resins, hardeners, pigments, thickeners, rust inhibitors, dispersants, defoamers, leveling agents, anti-settling agents, anti-sagging agents, hardening accelerators, anti-algae agents, anti-mold agents, preservatives, ultraviolet absorbers, and light stabilizers, as needed.

From the viewpoint of providing a stable and high level of anti-flaking function, the volatile content of the primer coating is preferably within the range of 40 to 90 mass%, more preferably within the range of 50 to 90 mass%, and particularly preferably within the range of 65 to 85 mass%. In this specification, "volatile content" refers to components that volatilize during the concrete spalling prevention method of the present invention and do not remain in the final laminate, and examples of such components include solvents.

The above primer coating can be prepared by mixing various components selected as needed.

The means for applying the primer coating is not particularly limited, and known coating means such as brush coating, roller coating, trowel coating, spatula coating, flow coater coating, and spray coating (e.g., aerosol spray coating, air spray coating, airless spray coating, etc.) can be used. From the viewpoint of simplifying the application work, however, aerosol spray coating is preferred.
In the aerosol spray coating, a propellant is used as a solvent for spraying the primer paint from a spray can. The propellant is enclosed in the spray can together with the primer paint. Examples of the propellant include dimethyl ether (DME), liquefied petroleum gas (LPG), and HFO-1234zE, with dimethyl ether (DME) being preferred. Commercially available propellants can be used.

In the concrete spalling prevention method of the present invention, next, while the primer paint applied to the concrete structure is still wet, a composite sheet having an adhesive layer and a fiber sheet layer is placed on the primer layer formed from the primer paint (second step). A laminate can be formed on the concrete structure by the second step, in which the adhesive layer of the laminate is constituted by the adhesive layer of the placed composite sheet, and the sheet layer of the laminate is constituted by the sheet of the placed composite sheet.

In the concrete spalling prevention method of the present invention, a composite sheet having an adhesive layer and a fiber sheet layer is attached while the primer paint applied to the concrete structure is still wet (i.e., without waiting for the primer layer to dry), so that a high level of spalling prevention function can be stably imparted to concrete structures installed in various environments. In addition, since the work can be completed by the above-mentioned first and second steps, construction can be completed in a short time by a simple method. Therefore, the concrete spalling prevention method of the present invention can be applied to concrete structures that require work using a high-altitude work vehicle.
Furthermore, in the second step of the concrete spalling prevention method of the present invention, it is believed that the solvent contained in the primer paint penetrates into part of the adhesive layer, forming a mixed layer at the interface between the primer layer and the adhesive layer where the components of each layer are mixed, and/or that some of the components of each layer react, improving the adhesion of the composite sheet to the concrete structure via the primer layer. This is believed to achieve a high level of spalling prevention function.

In this specification, "wet state" means a state in which volatile matter remains in the applied paint or the coating film (also referred to as "layer" in this specification) formed from the paint, and "dry state" means a state in which volatile matter is not present in the applied paint or the coating film formed from the paint.

In the second step, a composite sheet comprising an adhesive layer and a fiber sheet layer is placed on a primer layer formed from the primer paint applied on the concrete structure while the primer paint is still wet. From the viewpoint of providing a more reliable, stable and high level of anti-peeling function, the composite sheet is preferably placed on the primer layer within one hour after the completion of painting with the primer paint, and more preferably within 30 minutes after the completion of painting with the primer paint.
In this specification, "completion of painting with primer paint" means the point at which painting work using a primer paint application means is finished, and in the concrete spalling prevention method of the present invention, at least the surface area of the concrete structure where the composite sheet is to be placed is usually painted with primer paint.

The composite sheet used in the concrete spalling prevention method of the present invention comprises an adhesive layer and a sheet, but in the second step, the adhesive layer is placed on the primer layer, so that the adhesive layer is present on at least one surface of the composite sheet.

The adhesive layer contains an adhesive, and as the adhesive, known adhesives such as acrylic adhesives, urethane adhesives, and butyl rubber adhesives can be used, with acrylic adhesives being preferred. The adhesive is also called a pressure-sensitive adhesive.

The acrylic adhesive is, for example, a polymer obtained by polymerizing a first monomer consisting of at least one (meth)acrylic acid ester of a non-tertiary alcohol in which the alkyl group has 4 to 20 carbon atoms, and a second monomer that copolymerizes with the first monomer as necessary. However, the second monomer is a monomer different from the first monomer.

The first monomer may be a monomer that, when homopolymerized, gives a polymer with a glass transition temperature of 0°C or less. Here, the glass transition temperature refers to the temperature at the peak position of tan δ in dynamic viscoelasticity measurement (the frequency can be 1.0 Hz, and the heating rate can be 5°C/min). Examples of the first monomer include monofunctional (meth)acrylic acid esters of non-tertiary alkyl alcohols in which the alkyl group has 4 to 20 or 4 to 18 carbon atoms, and specific examples include n-butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, n-decyl acrylate, n-dodecyl acrylate, and octadecyl acrylate. The first monomer may be used alone or in combination of two or more types.

The second monomer may be a monomer that has at least one ethylenically unsaturated group and that, when homopolymerized, gives a polymer with a glass transition temperature exceeding 0°C. From the viewpoint of improving the peeling prevention function, it is preferable that the acrylic adhesive contains the second monomer as a repeating unit. Specific examples of the second monomer include (meth)acrylic acid, N-vinylpyrrolidone, N-vinylcaprolactam, substituted (meth)acrylamides such as N,N-dimethylacrylamide, acrylonitrile, isobornyl acrylate, acrylates of alcohols having an alkyl group with 1 to 3 carbon atoms, and carboxyethyl acrylate, and (meth)acrylic acid is preferable. The second monomer may be used alone or in combination of two or more kinds. When a basic monomer such as a substituted (meth)acrylamide is used as the second monomer, a weakly basic tertiary amine compound or the like may be used.

Regarding the mass ratio of the first monomer to the second monomer, it is preferable that the proportion of the first monomer is 50% by mass or more, 60% by mass or more, or 70% by mass or more, and 100% by mass or less, 98% by mass or less, or 95% by mass or less, and the proportion of the second monomer is 0% by mass or more, 2% by mass or more, or 5% by mass or more, and 50% by mass or less, 40% by mass or less, or 30% by mass or less.

In the adhesive layer, the adhesive content can be, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more, and 99% by mass or less, 97% by mass or less, or 95% by mass or less.

The pressure-sensitive adhesive layer preferably contains inorganic fine particles. As the inorganic fine particles, known inorganic fine particles such as silica fine particles and mineral fine particles can be used. The inorganic fine particles may be solid or hollow. The shape of the inorganic fine particles is not limited to spherical, and irregular shapes such as flat shapes can also be used.

The inorganic fine particles preferably include first inorganic fine particles having a particle diameter (median diameter) of 1 μm or more, 5 μm or more, or 10 μm or more, and 500 μm or less, 300 μm or less, or 100 μm or less. In this specification, the particle diameter (median diameter) refers to the 50% particle diameter (D ₅₀ ) of the volume-based particle size distribution, and can be obtained from the particle size distribution measured using a laser diffraction/scattering type particle size distribution measuring device. And, the particle diameter in this specification is represented by the sphere equivalent diameter by the laser diffraction/scattering method.

In the above adhesive layer, the content of the first inorganic microparticles is preferably 0.1 parts by mass or more, 1 part by mass or more, or 3 parts by mass or more, and 20 parts by mass or less, 18 parts by mass or less, or 15 parts by mass or less, per 100 parts by mass of the adhesive.

In addition to the first inorganic fine particles having the above-mentioned specific particle diameter (median diameter), the inorganic fine particles preferably further include second inorganic fine particles having a particle diameter (median diameter) of 0.0001 μm or more, 0.001 μm or more, or 0.005 μm or more, 1 μm or less, 0.1 μm or less, or 0.05 μm or less. In this case, with regard to the mass ratio of the first inorganic fine particles to the second inorganic fine particles, for example, the proportion of the first inorganic fine particles may be 1 mass% or more, 3 mass% or more, or 5 mass% or more, 100 mass% or less, 20 mass% or less, or 10 mass% or less, and the proportion of the second inorganic fine particles may be 0 mass% or more, 80 mass% or more, or 90 mass% or more, 99 mass% or less, 97 mass% or less, or 95 mass% or less.

As the first inorganic microparticles, for example, K15 manufactured by 3M and Microsphere M-600 manufactured by Matsumoto Yushi Co., Ltd. can be used. As the second inorganic microparticles, for example, A-200 and R-972 manufactured by Nippon Aerosil Co., Ltd. can be used.

The adhesive layer may further contain a tackifier. Examples of tackifiers include hydrocarbon resins, terpene phenol resins, rosin resins, rosin ester resins, and hydrogenated versions of these. Examples of available tackifiers include RegalrezTM1085, RegalrezTM1094, RegalrezTM6108, and GegalrezTM3102 manufactured by Eastman Chemical Japan Co., Ltd., and Arkon P-140 manufactured by Arakawa Chemical Industries, Ltd.

In the above adhesive layer, the content of the tackifier is preferably 10 parts by mass or less, or 5 parts by mass or less, per 100 parts by mass of the adhesive. The content of the tackifier may be, for example, 0.5 parts by mass or more per 100 parts by mass of the adhesive.

In addition to the above-mentioned components, the adhesive layer may further contain known additives used in adhesive layers, such as a polymerization initiator, a crosslinking agent, a plasticizer, a filler, an anti-aging agent, an ultraviolet absorber, and a dye.

The pressure-sensitive adhesive layer preferably has a gel fraction in the range of 50 to 70% by mass.
The gel fraction can be calculated from the following formula (1).
Gel fraction (mass%)=(B/A)×100 Formula (1)
A: Weight of the adhesive layer (test piece) B: Dry weight of the insoluble portion of the adhesive layer after immersing the adhesive layer (test piece) in tetrahydrofuran at 23° C. for 12 hours

A fiber sheet can be used as a sheet constituting the composite sheet used in the concrete spalling prevention method of the present invention. The shape of the fiber sheet is not particularly limited, and may be, for example, a nonwoven fabric, but is preferably a lattice-shaped sheet. Examples of the fiber sheet include sheets made of fibers such as glass fiber, polyester fiber, vinylon fiber, polyamide fiber, polyethylene fiber, polyparaphenylene fiber, polyarylate fiber, aramid fiber, and carbon fiber.
Although the fiber sheet may be used alone, a composite fiber sheet having a fiber sheet, an intermediate layer and another fiber sheet in this order may also be used.

The intermediate layer constituting the composite fiber sheet is preferably a resin film. Specific examples of resin films include ethylene-vinyl alcohol copolymer resin (EVOH resin) film, polyvinylidene chloride (PVDC) resin film, polyvinyl alcohol (PVA) resin film, resin film formed by vapor deposition of a metal or its oxide, PVDC-coated film, PVA-coated film, and nylon film containing metaxylenediamine as the amine component. The resin film may be a laminate of different resin films, an example of which is a laminate film formed by laminating nylon films on both sides of an EVOH resin layer. The metal or its oxide is preferably, for example, aluminum, silicon, or an oxide thereof.

In the composite fiber sheet, the fiber sheet and the resin film may be laminated, for example, via an adhesive. Any known adhesive can be used as the adhesive, and specific examples include urethane adhesives, ester adhesives, silicone adhesives, acrylic adhesives, epoxy adhesives, and rubber adhesives.

The structure of the composite sheet used in the concrete spalling prevention method of the present invention is not particularly limited as long as an adhesive layer is present on at least one surface, and the adhesive layer and the sheet may each be one layer or multiple layers. In addition, the composite sheet may have an additional layer for the purpose of weather resistance, antifouling properties, waterproof properties, gas barrier properties, salt insulation properties, sound absorption properties, etc. Various sheets and films can be applied as the additional layer depending on the performance to be imparted.
Specific examples of the structure of the composite sheet include a structure having an adhesive layer and a sheet in this order, a structure having an adhesive layer, an additional layer and a sheet in this order, a structure having an adhesive layer, a sheet and an additional layer in this order, and a structure having an adhesive layer, an additional layer, a sheet and an additional layer in this order.

Examples of additional layers that may constitute the composite sheet used in the concrete spalling prevention method of the present invention include polyethylene film, polypropylene film, polyester film, polycarbonate film, polyvinyl chloride film, polystyrene film, polyamide film, ethylene-vinyl alcohol copolymer resin (EVOH resin) film, polyvinylidene chloride (PVDC) resin film, polyvinyl alcohol (PVA) resin film, resin film formed by vapor deposition of metal or its oxide, PVDC coated film, PVA coated film, nylon film containing metaxylenediamine as the amine component, acrylic foam sheet, polyethylene foam sheet, chloroprene foam sheet, urethane foam sheet, and structures formed of materials containing inorganic compounds or metals.

In the composite sheet, the adhesive layer, the sheet, and the additional layer may be laminated, for example, via an adhesive. Any known adhesive may be used as the adhesive, and specific examples include urethane adhesives, ester adhesives, silicone adhesives, acrylic adhesives, epoxy adhesives, and rubber adhesives.

The composite sheet can be manufactured according to conventional methods, but commercially available products can also be used.

The laminate obtained by the concrete spalling prevention method of the present invention comprises a primer layer, an adhesive layer, and a sheet layer. Here, the primer layer is a coating film formed by a primer paint, and the thickness thereof is preferably within the range of 0.01 to 0.1 mm. The adhesive layer is constituted by the adhesive layer of the composite sheet, and the thickness thereof is preferably within the range of 0.1 to 2.0 mm, and more preferably within the range of 0.1 to 1.0 mm. The sheet layer is constituted by a sheet of the composite sheet, and the thickness thereof is preferably within the range of 0.001 to 0.5 mm, and more preferably within the range of 1 to 500 μm, and particularly preferably within the range of 5 to 200 μm. The thickness of the laminate formed on the concrete structure is preferably within the range of 0.2 to 2.5 mm.

The above laminate can have an additional layer on the sheet layer, for example by painting the sheet layer with a topcoat paint. However, from the viewpoint of simplifying the work, it is preferable that the layer derived from the composite sheet arranged in the second step, such as the sheet layer, is the outermost layer (the outermost layer furthest from the surface of the concrete structure).
The surface of the outermost layer constituting the laminate is preferably a concrete color of about N7.5, which reduces the color difference with the surface of the concrete structure and makes the laminated portion less noticeable to the general public.

Next, a laminate formed on the surface of a concrete structure by one embodiment of the concrete spalling prevention method of the present invention will be described with reference to the drawings. The laminate 1 in Fig. 1 comprises a primer layer 3 arranged on a concrete structure 2, an adhesive layer 4 arranged on the primer layer 3, and a sheet layer 5 arranged on the adhesive layer 4. Although not shown, a mixed layer is formed at the interface between the primer layer 3 and the adhesive layer 4.
Further, in order to obtain the laminate 1 of FIG. 1, a composite sheet including a sheet and a pressure-sensitive adhesive layer disposed on the sheet is used.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Example of primer paint preparation)
A primer coating was prepared according to the formulation shown in "Primer" in Tables 1 and 2.

(Example of composite sheet production)
According to the formulation shown in "Adhesive" in Tables 1 and 2, adhesive compositions were prepared. Specifically, acrylic monomers were partially polymerized to obtain a prepolymer with a viscosity adjusted to 5000 cps, and other additives were added thereto to prepare the adhesive composition. The polymerization method may be thermal polymerization or photopolymerization.
The obtained pressure-sensitive adhesive composition was applied to a PET separator to a specified thickness, and the applied pressure-sensitive adhesive composition was covered with another PET separator. Next, the adhesive sheet was irradiated with ultraviolet light so that the gel fraction was 50 to 70% by mass, thereby producing a pressure-sensitive adhesive sheet.
The obtained pressure-sensitive adhesive sheet was attached to a fiber sheet shown in the "Sheet" column in Tables 1 and 2 to prepare a composite sheet comprising a pressure-sensitive adhesive layer and a fiber sheet layer.

(Examples 1 to 20 and Comparative Examples 1 to 4)
The primer paint prepared according to the above Preparation Example and the composite sheet prepared according to the above Production Example were used to carry out a load resistance test and a moisture resistance test. The results are shown in Tables 1 and 2.

<Load resistance test>
The primer paint was packed in an aerosol can together with a propellant (dimethyl ether (DME)), and the paint was aerosol spray-applied onto a concrete substrate.
After the concrete substrate was completely coated with the primer paint, a laminate was produced by placing a composite sheet on the primer layer formed from the primer paint according to the "time until placing the composite sheet" shown in Tables 1 and 2. The resulting laminate was then dried for 168 hours at a temperature of 23°C and a relative humidity of 50%.
The concrete substrates used were those shown in Tables 1 and 2. Specifically, substrate 1 and substrate 2 are both U-shaped covers, named type 1 (400 x 600 x 60 mm), as specified in JIS A 5372:2004 (precast reinforced concrete products), but substrate 1 is a concrete substrate with a surface unevenness difference of 1 mm or less, and substrate 2 is a concrete substrate with a surface unevenness difference of 2 to 3 mm.
After drying the laminate, a spalling prevention performance test was conducted on the concrete substrate provided with the laminate in accordance with the Metropolitan Expressway Company Limited's Bridge Structure Design Guidelines, Concrete Piece Spalling Prevention Edition, August 2006 Edition, and the load resistance was evaluated according to the following criteria.
In Comparative Example 3, a laminate having an adhesive layer and a fiber sheet layer without a primer layer was used, so the composite sheet was placed directly on the concrete substrate. In Comparative Example 4, a fiber sheet was used instead of the composite sheet, and a laminate having a primer layer and a fiber sheet layer without an adhesive layer was used.
◎: Punching load of 0.3 kN or more per φ10 cm.
◯: Punching load per φ10 cm is 0.1 kN or more and less than 0.3 kN.
×: Punching load per φ10 cm is less than 0.1 kN.

<Moisture resistance test>
A laminate was prepared in the same manner as in the load resistance test, except that the concrete substrate was changed to mortar (70 x 70 x 20 mm) specified in JSCE-K511-2007. The dew receiving plate of the JIS K 5600-7-2 (5. Rotary type) humidity box was removed, a wire mesh was placed horizontally in its place, and the concrete substrate with the laminate on the wire mesh was left to stand for 10 days, and the appearance was evaluated.
○: No swelling, peeling or cracking was observed.
×: Any of swelling, peeling, and cracking is observed.

(Note 1) Bisphenol A type epoxy resin with a weight average molecular weight of 35,000 (Note 2) Bisphenol A type epoxy resin with a weight average molecular weight of 4,700 (Note 3) Bisphenol A type epoxy resin with a weight average molecular weight of 150,000 (Note 4) Bisphenol A type epoxy resin with a weight average molecular weight of 900 (Note 5) Bisphenol A type epoxy resin with a weight average molecular weight of 200,000 (Note 6) "Desmodur E14" manufactured by Covestro
(Note 7) Inorganic fine particles manufactured by 3M Limited (Note 8) Tackifier manufactured by Arakawa Chemical Industries Co., Ltd. (Note 9) "ShieM-CS Sheet" manufactured by K.F.C. Co., Ltd.
(Note 10) "KSM Sheet" manufactured by Kyowa Co., Ltd.

REFERENCE SIGNS LIST 1 Laminate 2 Concrete structure 3 Primer layer 4 Adhesive layer 5 Sheet layer

Claims (6)

A method for preventing concrete from peeling off from a concrete structure by forming a laminate having a primer layer, an adhesive layer, and a sheet layer on a surface of the concrete structure, comprising:
A first step of painting a surface of a concrete structure with a primer paint;
and a second step of placing a composite sheet comprising an adhesive layer and a composite fiber sheet layer on a primer layer formed from the primer paint applied to the concrete structure while the primer paint is still wet, wherein the adhesive layer contains 50% by mass or more of an acrylic adhesive . The method according to claim 1, characterized in that the composite sheet is placed on the primer layer within one hour immediately after the completion of painting with the primer paint. The method according to any one of claims 1 to 2, characterized in that the primer coating contains at least an epoxy resin having a weight average molecular weight of 1,000 to 200,000. The method according to any one of claims 1 to 3, characterized in that the primer coating contains at least one organic solvent selected from the group consisting of methyl ethyl ketone and ethyl acetate, and the volatile content of the primer coating is within the range of 40 to 90 mass %. The method according to any one of claims 1 to 4, characterized in that the means for applying the primer paint is aerosol spray painting. The method according to any one of claims 1 to 5, characterized in that the laminate has a primer layer thickness in the range of 0.01 to 0.1 mm, a pressure-sensitive adhesive layer thickness in the range of 0.1 to 2.0 mm, and a sheet layer thickness in the range of 0.001 to 0.5 mm.

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