JP3069799B2 - Electrocorrosion protection method for reinforced concrete structures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for preventing a reinforced concrete structure from being electrically protected.

[0002]

2. Description of the Related Art Since concrete exhibits a strong alkali, cement has a γ-Fe ₂ O ₃ .multidot.
It is said that a hydrate consisting of nH ₂ O is formed, which protects the internal steel material and suppresses the progress of rust, so that it is maintenance-free and has a service life of 100 years or more.

[0003] However, in an environment such as a highly corrosive shore or ocean, salt spray adheres due to waves and sea breeze, and components such as chlorine ions invade into the concrete over time and destroy the passive film. As a result, the steel material may corrode and expand in volume, causing cracking or peeling of the concrete, and this phenomenon is generally called salt damage.

[0004] In order to suppress this phenomenon, it is important to block corrosion factors such as water, chlorides and oxygen from the outside, and the Japan Road Association is currently used as a means for corrosion protection of concrete. In general, as indicated in the “Guidelines for Salt Damage Countermeasures for Road Bridges (Draft)” and the “Guidelines for Corrosion Protection of Marine Concrete Structures (Draft)” issued by the Japan Concrete Institute, etc. No way has been done.

(1) Method of blocking corrosive substances on concrete surface (lining etc.) (2) Method of suppressing permeation of corrosive substances by concrete itself (polymer cement concrete, polymer impregnated concrete, permeable waterproofing agent, etc.) (3) Method to block corrosive substances on steel surface (metal plating, resin coating, etc.) (4) Method to suppress corrosive environment of steel in concrete (rust preventive, etc.)

However, all of these methods have problems such as a limited range of application, and in fact, other better methods are being studied.

For example, a method of electrically suppressing the corrosion of steel has been studied. As one of the methods, a mesh such as a mesh protected with a conductive oxide is inserted into the surface of titanium metal, and the mesh is inserted into concrete. In this method, an electric circuit is formed between a net and a reinforcing bar to prevent corrosion.

This method can be applied irrespective of the size of the concrete cover and the presence or absence of cracks, and can be expected to have a sufficient effect in the sea or in a wet state.
In addition, it is attracting attention as a new technology because it can be applied regardless of whether the object is new or existing.

[0009] However, a mesh is laid between concrete and a few cm is further fixed on the mesh.
It is necessary to form a mortar protective layer, and the work is complicated at present.

As another means, "Technical Survey Report on Deterioration Prevention and Repair of Port Harbor Concrete Structures-Manual for Prevention and Repair of Deterioration-Repair (published)-" issued by Coastal Development Technology Research Center, Public Works Research Institute, Ministry of Construction As described in the Joint Research Report on Cathodic Protection of Concrete Structures published by the Chemistry Laboratory of the Faculty of Geochemistry and the Civil Engineering Research Center, etc., a conductive coating is applied to the concrete surface and the coating is applied. There is known a method of preventing corrosion by using a small DC current as an anode and passing a weak DC current through a reinforcing bar in concrete.

[0011] However, the conductive paint used to obtain the conductive coating film serving as the coating anode contains carbon powder, but is used in the cathodic protection method for reinforced concrete structures. The conductivity required as a coating anode cannot be said to be sufficiently provided.

[0012] This is considered to be due to the fact that there is a point of poor contact between the carbon powders, which are conductive materials, and the flow of DC current is interrupted at that point. For this reason, it was not possible to achieve a uniform distribution of the direct current over the entire surface of the concrete, and thus it was not possible to achieve a satisfactory anticorrosion effect on the reinforcing steel in the concrete.

The purpose of making the distribution of DC current uniform over the entire surface of the concrete using the coating film anode is to increase the thickness of the coating film, for example, to 400 μm, or to apply a wire to the coating film anode. It is possible to some extent by increasing the number of anodes and making the installation interval as narrow as possible. However, it has the drawbacks that the amount of the conductive paint applied and the number of the linear anodes are increased to be uneconomical, and that the construction efficiency is deteriorated.

[0014]

Therefore, as a result of diligent research, the present inventors have been able to develop a conductive paint having extremely good conductivity as compared with the conventional paint, thereby forming and installing a coating anode. This has led to the invention of the cathodic protection method of the present invention.

[0015]

According to the present invention, there is provided a method for preventing corrosion of a reinforced concrete structure, comprising the steps of: providing 0.1 to 20% by weight of carbon fiber in a solid content of a coating;
A water-based conductive coating containing 0% by weight is applied to the surface of concrete to a thickness of 10 to 300 μm to form a conductive coating film serving as a coating anode, and furthermore, a good interlayer adhesion is obtained on the coating film. A film having a thickness of 50 to 1000 μm and / or
Alternatively, a multi-layer structure is formed by laminating coating films having a good weather resistance and having a thickness of 10 to 300 μm, and a plurality of wires arranged at a distance of 2 to 1000 cm on the conductive coating film serving as the coating anode. DC current supplied through the strip anode is passed from the coating anode to a reinforcing bar in concrete.

Preferred metal powders are Ni, Zn, Zr, P
d, Sn, Al, Cu, Mg, Ta, Nb, Mn, C
It is a simple substance or an alloy containing at least one metal selected from r, W, Fe, Co, Si, Ag, Ti and Pb, and a preferable carbon fiber is a pitch-based carbon fiber.

The vehicle of the coating material is preferably a polyester-based water-soluble or emulsion resin, an epoxy-based water-soluble or emulsion resin, or a polymerizable vinyl monomer containing acrylate, methacrylate or styrene as a main component. It is a water-soluble or emulsion resin obtained by copolymerization in the presence.

As the film and / or coating film which forms a multilayer structure on the conductive coating film, preferably a polyethylene resin, polyester resin, acrylic resin, urethane resin, polyvinyl chloride resin, polyvinylidene chloride resin, Alternatively, one or more kinds of polyvinylidene fluoride resins are used.

Hereinafter, the present invention will be described in more detail. First, the present invention essentially requires the conductive coating to contain carbon fiber, and a fiber chain forms a path between the conductive powder and the metal powder used in combination, so that a constant current is always ensured. .

It is known that conductive carbon black called Ketjen black is used as a pigment as one of means for imparting conductivity to a coating film. However, in order for carbon black, which usually has a diameter of several μm to several tens of μm, to have electrical conductivity in a coating film, it is essential that the arrangement of the particles is in a chain like a bead, and a stable conductive property is obtained. In order to secure the property, a large amount must be used, and the dispersion of the pigment is difficult, and the viscosity of the coating material increases, so that the improvement of the conductivity is naturally limited. Therefore, in the present invention, carbon fibers are used in place of the above carbon black, whereby fiber chains are always present, so that a stable conductive property is always obtained without being affected by changes in manufacturing conditions or coating conditions. An effect can be obtained.

As another means for imparting conductivity to the coating film, there is a method using metal powder. However, by using this in combination with carbon fiber rather than using it alone, the carbon fiber has a lower weight. Further, the content of the metal powder in the paint can be reduced, and as a secondary effect thereof, there is little change in the paint over time due to precipitation of the metal powder and the like, and a composition having excellent storage stability can be provided.

The carbon fibers used are pitch-based and polyacrylonitrile (hereinafter referred to as "PAN").
Long fibers, short fibers, high-strength products, high-modulus products, and general-purpose products may be used. Pitch-based short fiber carbon fibers are more suitable for ball milling than PAN-based carbon fibers.
It is particularly preferable because it can be easily dispersed by a general paint dispersing machine such as a sand mill and can be uniformly dispersed in a coating film. The amount of the additive is 0.1% in the solid content of the coating material, that is, in the coating film forming component.
It is necessary to contain 1 to 20% by weight, particularly preferably 3 to 15% by weight. If it is less than 0.1% by weight, the conductivity tends to be unstable, and if it is more than 20% by weight, it is difficult to uniformly disperse it in the paint, and long fibers remain in the paint.
JIS A 6910 multi-layer finish coating material finish (thickness several mm)
Therefore, it is not suitable for anticorrosion of concrete structures, which is the object of the present invention, because the conductivity cannot be obtained stably and the drying property is slow.

Specific examples of carbon fibers include pitch-based carbon fibers such as Creca (manufactured by Kureha Chemical Co., Ltd.), Carbonic (manufactured by Kashima Oil Co., Ltd.), Donna Carbo (manufactured by Donac Co., Ltd.), and Vesfight (Toho Rayon). Co., Ltd.), Trading Card (Toray Co., Ltd.),
PA such as Pyrofile (Mitsubishi Rayon Co., Ltd.) and High Carbon (Asahi Nippon Carbon Fiber Co., Ltd.)
N-based carbon fibers can be mentioned. Also,
When preparing a paint, chopped or milled fibers are preferred.

Next, as the metal powder used in the present invention,
Ni, Zn, Zr, Pd, Sn, Al, Cu, Mg, T
a, Nb, Mn, Cr, W, Fe, Co, Si, Ag,
Metal powder consisting of a simple substance selected from Ti and Pb or alloy powder consisting of two or more of these metals can be used. In addition to these metal powders, only one of them can be used alone.
Two or more kinds can be used as a mixture. As preferred of these metal powders, it is particularly easy to obtain,
And Ni, Zn, Sn, Al having excellent conductivity.
One or more of simple metal powders and alloy powders containing metals of Cu and Mn can be mentioned. That is, specifically, for example, Ni powder, Zn powder, Al powder, Mn powder, Zn-
Mn powder, Ni-Mn powder, Sn-Ni powder, Mg-Cu powder,
Al-Zr-Ni powder and the like.

Such a metal powder contains 20%
The content is required to be 70 to 70% by weight, preferably 30 to 50% by weight. If it is less than 20% by weight, it is difficult to stably obtain conductivity, and if it exceeds 70% by weight, it exceeds the critical pigment volume concentration (CPVC). In addition, the washing resistance (JIS K 5663, etc.) for testing the property of the coating film to be hardly worn or damaged is deteriorated, and it is difficult to obtain the durability.

Next, the vehicle of the conductive coating used in the present invention is preferably a water-soluble resin or an emulsion resin. The type of resin is one obtained by copolymerizing a polyester-based resin, an epoxy-based resin, or a polymerizable vinyl monomer containing acrylate, methacrylate or styrene as a main component in the presence of a polymerization initiator. Emulsions obtained by copolymerizing a polymerizable vinyl monomer in the presence of a polymerization initiator are particularly preferable in view of the alkalinity or workability of concrete among these.

This vehicle has good adhesion to concrete and at the same time has excellent alkali resistance. In particular, it is considered that the emulsion resin partially has a space in the film even after forming a continuous film. When moisture or vapor passes therethrough, blisters and the like are less likely to occur than when a film is formed with a solvent-type resin, which is suitable in terms of durability. In particular, the concrete structure that is the subject of the present invention contains water inevitably from its composition, and is covered with an emulsion resin film having moisture permeability rather than covering the water that escapes from the inside with a continuous film. It is clear that the method is more effective in preventing the occurrence of blisters and in the resistance to peeling.

The water-based conductive paint may include, if necessary, a coloring pigment such as titanium dioxide, carbon black, iron oxide and the like, and other pigments for the purpose of giving a reinforcing effect to the coating film.
For example, hydrous magnesium silicate, aluminum silicate, calcium carbonate, etc. may be used alone or in combination of two or more. Also, if necessary, a pigment dispersant, a wetting agent,
Anti-settling agent, thickening agent, anti-freezing agent, coalescent, defoamer,
Preservatives, fungicides and the like can also be added.

As means for applying the aqueous conductive paint to the concrete surface, a brush, a roller, a spray, or the like can be used. The film thickness is preferably from 10 to 300 μm, and particularly preferably from 50 to 100 μm from the viewpoint of conductivity and durability.

Further, in the present invention, the coating film anode, that is, the surface of the coating film formed by applying the conductive paint, has a good interlayer adhesion and weather resistance of 50 to 1000 to protect it.
μm thick film and / or 10-300 μm
As a result, it is possible to stably supply a current to the coating film anode. That is, with the conductive coating film alone, good conductivity may not be maintained for a long period of time in the initial stage.

As these films or coatings, one or two or more of polyethylene resins, polyester resins, acrylic resins, urethane resins, polyvinyl chloride resins, polyvinylidene chloride resins, or polyvinylidene fluoride resins having good weather resistance are used. Among them, acrylic resin and urethane resin are preferable.

[0032]

The coating film anode used in the present invention basically ensures the required conductivity by directly contacting the carbon fibers mixed in the conductive paint.
Since the metal powder makes up for the contact between the carbon fibers, even if the direct contact between the carbon fibers is insufficient, the indirect contact via the metal powder
The DC current always flows in a good state.

Therefore, according to the method of the present invention, the coating anode is made to have a relatively small film thickness and a small number of wire anodes, that is, the interval between the wire anodes is widened, so that the whole concrete can be coated. Achieves the desired anti-corrosion effect by realizing a uniform distribution of DC current, and saves the amount of conductive paint and wire anode that form the coating anode, and also facilitates construction. .

[0034]

EXAMPLES Examples and comparative examples of the present invention will be described below in detail.

Preparation of Paint The paints of Examples 1 to 6 and Comparative Examples 1 to 6 were prepared as follows.

Carbon fiber and metal powder were blended in the proportions shown in Table 1, and 34.7% by weight of water was added thereto, and a pigment dispersant [polycarboxylic acid sodium salt (trade name, manufactured by Rohm and Haas Co., Ltd., trade name: Tamol 731SD)] 0.2
% By weight and 0.2% by weight of a wetting agent [alkyl lauryl polyether (trade name: Triton CF-10, HLB: 14.0, manufactured by Rohm and Haas Co., Ltd.)] and sufficiently mixed with a known stirrer. And then dispersed using a desktop sand mill (manufactured by Campe Hapio Co., Ltd.).

The emulsion resin shown in Table 1 was mixed with the emulsion resin in the ratio shown in Table 1 as a vehicle resin.
Thickener [hydroxyethylcellulose (UCC.
0.3% by weight, defoaming agent [special nonionic surfactant (manufactured by San Nopco Co., Ltd., trade name: SN Deformer 154)] 0.5% by weight, film forming aid [2,2,4-trimethylpentanediol monoisobutyrate (trade name: Texanol, manufactured by Eastman Chemical Co., Ltd.)] 4.0% by weight and a preservative [1,2-benzoisothiazolone (Dainippon Ink Chemical Industry Co., Ltd.) Company name, product name: Best Side FX)]
1% by weight was added to prepare a paint.

The carbon fibers used were pitch-based graphite-based short fibers having an average fiber length of 0.13 mm and an average fiber diameter of 14.5 μm (manufactured by Kureha Chemical Co., Ltd., trade name: Crecachop M-201S). As the metal powder or alloy powder, Ni powder (I) having an average particle size of 2.2 to 2.8 μm is used.
NCO, trade name: TYPE 255), average particle size 7.
5 μm Zn powder (Honjo Chemical Co., Ltd., trade name: F
-500) or Sn-Ni powder (trade name: NP-205, manufactured by Nisso Metals Chemical Co., Ltd.) having an average particle size of 25 µm. Further, the emulsion resin used as the vehicle resin is an acrylic styrene emulsion resin (AS,
Dainippon Ink & Chemicals, Inc., trade name: Boncoat 5410) and vinyl acetate-acryl emulsion resin (VAA, Dainippon Ink & Chemicals, Inc., trade name:
Bon coat 9180).

Preparation of test pieces The following tests and tests were performed according to JIS K 5400-1990.
In addition to the flexible board specified in 3.6,
Was applied so that the paint and the 1.0 ± 0.1cm ³ / 1dm ² created above using each brush cement mortar plate specified in JIS K 5400-1990 3.7 as use, at room temperature After drying for 2 hours, it was similarly applied once more and dried for 5 days. Thereafter, coated campesterol GP paint (Kansai Paint Co., Ltd. The (JIS K 5660 gloss organic synthetic resin emulsion paints standard product) so that 1.0 ± 0.1cm ³ / 1dm ² dried further 5 days.

Test Method Surface Resistance Value The surface resistance value of the test piece at the time when the conductive paint prepared above was applied was measured using a resistance measuring instrument (K70 manufactured by Kyowa Riken Co., Ltd.).
5RD). Further, the surface resistance value after the repeated heating / cooling test was also measured.

Alkali Resistance Based on JIS K 5063 5.10, it was immersed in a calcium hydroxide saturated solution. However, the immersion time was set to 720 hours, and those without abnormality were judged as ○, and those with abnormality were judged as ×.

Water resistance Based on JIS K 5663 5.9, it was immersed in water. However, the immersion time was set to 720 hours, and those without abnormality were judged as ○, and those with abnormality were judged as ×.

Washing resistance Based on JIS K 5663 5.11, the surface was rubbed 500 times with a washing tester, and the presence or absence of exposure of the substrate due to peeling and abrasion was visually observed. Those were evaluated as x.

Adhesion Strength Adhesion strength under standard conditions and after immersion was measured based on JIS A 6909 5.8.

Resistance to repeated warming / cooling action A test was conducted in accordance with JIS A 6909 5.9. After repeating 10 times, the surface was visually inspected for peeling, cracking, and swelling. Those with were judged as x. Table 1 shows the test results.

[0046]

[Table 1]

Example 7 On the concrete surface of the reinforced concrete structure, linear electrodes were installed at required intervals of 30 cm using plastic pins. Next, the wire electrode is fixed with a conductive putty in order to improve the current supply from the wire electrode, and then the above-prepared paint is applied to a concrete surface containing the conductive putty to a thickness of 100 μm to form a coating film. An anode was formed. Alternatively, after applying the above-prepared paint to a thickness of 100 μm on the concrete surface of the reinforced concrete structure,
A linear electrode was installed at a required interval of 30 cm using a plastic pin. Thereafter, the linear electrode was integrated with the conductive coating using a conductive putty to form a coating anode.

A glossy synthetic resin emulsion paint Kampe GP paint (manufactured by Kansai Paint Co., Ltd.) having weather resistance was applied to the entire surface of the coating film anode formed by the above method to form a protective film. Then, the anode of the DC power supply was connected to the above-mentioned wire anode, and the cathode of the DC power supply was connected to the reinforcing steel buried in the concrete, and a required DC was passed.

[0049] As a result, it is possible to flow a concrete surface area m 10～30MA about ² per always corrosion of rebar, or 100mV was uniformly obtained throughout construct as its polarization.

[0050]

As is clear from the above description,
According to the cathodic protection method for a reinforced concrete structure of the present invention, the anode of the coating film can secure required conductivity by direct contact between carbon fibers mixed in the conductive paint. Even in an inadequate portion, direct current can always flow in a good state by indirect contact via metal powder. For this reason, a uniform distribution of DC current can be realized over the entire surface of the concrete with a small number of linear anodes having a relatively thin coating anode and a large interval between the installations, thereby achieving the desired anticorrosion. The effect can be obtained.

Further, since the amount of the conductive paint and the linear anode used can be reduced as compared with the related art, the construction can be made easier and the construction cost can be reduced.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shimohiko Morita 2nd Sanbancho, Chiyoda-ku, Tokyo Tobishima Construction Co., Ltd. (72) Inventor Kazuhiro Ono 2nd Sanbancho, Chiyoda-ku, Tokyo Tobishima Construction Co., Ltd. (72) Inventor Hatsuo Inagaki 30-301 Ari, Kisarazu-shi, Chiba (72) Inventor Toshio Matsushima 44-7, Imaiue-cho, Nakahara-ku, Kawasaki-shi, Kanagawa (72) Inventor Hironobu Kawasaki Aisato, Kisarazu-shi, Chiba 30-2-402 (58) Field surveyed (Int. Cl. ⁷ , DB name) C23F 13/00-13/02

Claims (5)

(57) [Claims] 1. The method according to claim 1, wherein the carbon fiber content is 0.1% in the solid content of the paint.
A water-based conductive paint containing 1 to 20% by weight and one or more metal powders 30 to 70% by weight is applied to the concrete surface.
It is applied to a thickness of 0 to 300 μm to form a conductive coating film serving as a coating anode, and a film of 50 to 1000 μm with good interlayer adhesion and / or a good thickness of weather resistance is formed on the coating film. DC current supplied through a plurality of linear anodes placed at a distance of 2 to 1000 cm on the conductive coating film as an anode of the coating film by forming a multilayer structure by stacking coating films of 10 to 300 μm in thickness. A corrosion protection method for a reinforced concrete structure, characterized in that the steel is flowed from the coating film anode to a reinforcing bar in the concrete. 2. The aqueous conductive paint according to claim 1, wherein the metal powder is Ni, Zn,
Zr, Pd, Sn, Al, Cu, Mg, Ta, Nb, M
n, Cr, W, Fe, Co, Si, Ag, Ti and P
3. The method according to claim 1, wherein the method is a simple substance or an alloy containing at least one metal selected from b. 3. The carbon fiber of the water-based conductive paint is a pitch-based carbon fiber.
The method for anticorrosion of a reinforced concrete structure as described. 4. The vehicle of the water-based conductive paint is formed by polymerizing a polyester-based water-soluble or emulsion resin, an epoxy-based water-soluble or emulsion resin, or a polymerizable vinyl monomer containing acrylate, methacrylate or styrene as a main component. 5. The method according to claim 1, wherein the water-soluble or emulsion resin is obtained by copolymerizing in the presence of an initiator. 5. A film and / or a coating film to be overlaid on the aqueous conductive coating film is one of a polyethylene resin, a polyester resin, an acrylic resin, a urethane resin, a polyvinyl chloride resin, a polyvinylidene chloride resin or a polyvinylidene fluoride resin. The method according to claim 2, 3, 4, or 5, wherein the method is an anticorrosion method for a reinforced concrete structure.