Method for re-alkalizing concrete structure, electrochemical corrosion prevention method for concrete structure, and concrete structure

Abstract

To provide a method for re-alkalizing a concrete structure, in which a surface layer portion of concrete is densified and the concrete structure exhibits good anti-corrosion effect, an electrochemical anticorrosion method for the concrete structure, and the concrete structure.SOLUTION: A method of re-alkalizing a concrete structure includes: a neutralization step of neutralizing or spontaneously neutralizing a surface layer portion of a concrete structure in which a steel material is embedded inside concrete to form a neutralized region; and a re-alkalization step of making the neutralized area into a re-alkalized area by using an alkali electrolyte, using an electrode installed on a surface side of the neutralized area as an external electrode and using the steel material as an internal electrode, by passing a direct current between the external electrode and the internal electrode.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for re-alkalization treatment of a concrete structure, an electrochemical corrosion prevention method for a concrete structure, and a concrete structure.

Background Art

[0002] Conventionally, for civil engineering structures such as roads and railways, specifically, for the substructure of bridges, bridge girders of bridges, underground structures or semi-underground structures such as tunnels, and the construction of culverts, etc., concrete structures in which steel bars or steel materials such as PC steel materials are arranged in concrete such as reinforced concrete (RC) and prestressed concrete (PC) are generally used. Reinforced concrete (RC) is a building material that combines concrete with high compressive strength performance and steel bars with high tensile strength performance to have both compressive strength and tensile strength. Prestressed concrete (PC) is a building material that can suppress the cracking of concrete by arranging PC steel materials (PC steel wires, PC steel bars, PC steel stranded wires, etc.) in concrete so that a reverse force is applied before a load acts on the concrete member, so that a tensile force is not generated in the concrete.

[0003] In a concrete structure, the steel materials arranged in the concrete may corrode due to salt damage or the like. When the steel materials corrode, the deterioration of the concrete structure progresses, and the durability is greatly reduced. Therefore, as a method for repairing a corroded concrete structure, a method of performing repair by an electrochemical method without accompanying destruction has been proposed and implemented (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] In Patent Documents 1 and 2, it is expected that the durability can be restored by repairing the corroded concrete structure. On the other hand, the repair work of the corroded concrete structure requires personnel and time for identifying the corroded part and restoring the corroded part. Therefore, it is required that the steel material does not corrode.

[0006] From the above, an object of the present invention is to provide a re-alkalization treatment method for a concrete structure that densifies the surface layer of concrete and enables the concrete structure to exhibit a good rust prevention effect, an electrochemical corrosion prevention method for a concrete structure, and a concrete structure. [Means for Solving the Problems]

[0007] As a result of intensive studies to solve the above problems, the present inventor has conceived the following present invention and found that the problems can be solved. That is, the present invention is as follows. [1] A neutralization step of neutralizing or naturally neutralizing the surface layer of a concrete structure in which a steel material is embedded inside the concrete to form a neutralization region, and using an electrolytic solution of an alkali, with an electrode installed on the surface side of the neutralization region as an external electrode, the steel material as an internal electrode, and passing a direct current between the external electrode and the internal electrode to make the neutralization region a re-alkalization region, and a re-alkalization treatment method for a concrete structure including a re-alkalization step. [2] In the re-alkalization step, the current density of the direct current on the surface of the concrete flowing between the external electrode and the internal electrode is 0.1 to 5 A / m 2 The re-alkalization treatment method for a concrete structure according to [1].[[]END]] [3] In the re-alkalization step, the pH of the re-alkalization region is set to 10 or higher. The re-alkalization treatment of the electrochemical corrosion prevention method for a concrete structure according to [1] or [2]. [4] A neutralization step of neutralizing or naturally neutralizing the surface layer portion of a concrete structure in which steel is embedded inside the concrete to form a neutralization region, and using an electrode installed on the surface side of the neutralization region as an external electrode, and the steel as an internal electrode, and passing a direct current between the external electrode and the internal electrode to make the neutralization region a re-alkalization region, thereby preventing corrosion of the concrete structure. An electrochemical corrosion prevention method for a concrete structure including a corrosion prevention step. [5] In the corrosion prevention step, the designed corrosion prevention current density flowing between the external electrode and the internal electrode is 1 to 30 mA / m per unit surface area of the steel. 2 The electrochemical corrosion prevention method for a concrete structure according to [4]. [6] A neutralization step of neutralizing or naturally neutralizing the surface layer portion of a concrete structure in which steel is embedded inside the concrete to form a neutralization region, and impregnating or applying an alkaline-imparting material from the surface side of the neutralization region to impart alkalinity to the surface layer portion, and making the neutralization region a re-alkalization region. A method for re-alkalizing a concrete structure including an alkaline-imparting step. [7] A concrete structure in which a re-alkalization region is provided in the surface layer portion of the concrete, and the pH of the re-alkalization region is 10 or higher, in a concrete structure in which steel is embedded inside the concrete. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a method for re-alkalizing a concrete structure, an electrochemical corrosion prevention method for a concrete structure, and a concrete structure in which the surface layer portion of the concrete is densified and the concrete structure exhibits a good rust prevention effect. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in more detail with reference to embodiments.

[0011] [Method for Re-alkalization Treatment of Concrete Structures] (First Embodiment) The method for re-alkalization treatment of a concrete structure according to the first embodiment of the present invention includes a neutralization step and a re-alkalization step.

[0012] <Neutralization Step> The neutralization step is a step of neutralizing or naturally neutralizing the surface layer of a concrete structure in which steel materials are embedded inside the concrete to form a neutralized region. Neutralization in the neutralization step is to supply carbon dioxide gas such as carbon dioxide to the surface layer of the concrete structure, and calcium hydroxide in the surface layer reacts with the carbon dioxide gas to become calcium carbonate, forming a neutralized region. On the other hand, natural neutralization in the neutralization step is that carbon dioxide gas such as carbon dioxide in the air penetrates into the surface layer of the concrete structure, and calcium hydroxide in the surface layer reacts with the carbon dioxide gas to become calcium carbonate, forming a neutralized region. The neutralized region obtained through the neutralization process is dense, preventing salts and other corrosion-causing substances from reaching the steel materials disposed inside the concrete structure, and is a region capable of improving the rust prevention effect. Here, "densification" refers to a state where the amount of pores in the surface layer of the concrete decreases and the pore diameter becomes minute. Specifically, it means that the total pore volume of the surface layer of the concrete is 0.08 mg / L or less, and the average pore diameter of the surface layer of the concrete is 0.04 μm or less.

[0013] The pH of the surface of the neutralized region is preferably 7 or more and 9.5 or less, more preferably 7 or more and 9.0 or less, and even more preferably 7 or more and 8.5 or less.

[0014] <Re-alkalization process> The re-alkalization process is a process in which an electrolytic solution of an alkali is used, the electrode installed on the surface side of the neutralized region is used as an external electrode, the steel material is used as an internal electrode, a direct current is passed between the external electrode and the internal electrode, and the neutralized region is made into a re-alkalized region.

[0015] The re-alkalization treatment system used in the re-alkalization process will be described. An example of the re-alkalization treatment system will be described with reference to FIG. 1. The re-alkalization treatment system shown in FIG. 1 includes an anode material 21 and an electrolytic solution holding material 22 that holds an electrolytic solution of an alkali. The electrode installed on the surface side of the neutralized region 10 is used as an external electrode 20, and the steel material embedded inside the neutralized region 10 is used as an internal electrode 30. A direct current is passed between the external electrode 20 and the internal electrode 30 to make the neutralized region 10 into a re-alkalized region. Note that the anode material 21 constituting the external electrode 20 and the steel material (internal electrode 30) embedded inside the neutralized region 10 are each connected to a wiring material 23 such as an electric wire cable, and a direct current is supplied from a direct current power supply device 24 to the wiring material 23, so that a direct current can be passed between the external electrode 20 and the internal electrode 30.

[0016] <<Anode material>> As the anode material 21 constituting the external electrode 20, a material excellent in corrosion resistance and a conductive material excellent in conductivity may be selected. For example, titanium, a titanium alloy, platinum, or a metal plated with these metals can be mentioned. Further, examples of the anode material 21 include carbon materials such as carbon fibers and carbon rods, and conductive polymers. The anode material 21 is preferably the above-mentioned conductive material in a net shape, a mesh shape, or a sheet shape. For example, a titanium mesh, a carbon fiber sheet, etc. can be mentioned.

[0017] <<Electrolyte holding material>> As the electrolyte holding material 22 constituting the external electrode 20, a non-woven fabric made of a hydrophilic material, a hydrophilized non-woven fabric, or felt can be used. The non-woven fabric made of a hydrophilic material is a non-woven fabric manufactured from raw materials having hydrophilicity in the material itself, such as regenerated fibers such as rayon and cupra, and natural fibers such as cotton, and having been subjected to a predetermined hydrophilic treatment. The hydrophilized non-woven fabric is a non-woven fabric manufactured from synthetic fibers such as olefin-based, polyester-based, and polyamide-based synthetic fibers such as polyethylene or polypropylene. In the manufacturing process of the synthetic fibers, a method of polymerizing in the coexistence of a compound having a hydrophilic group, such as an oxidation product of polyethylene glycol, or a method of treating with a metal salt such as stannous chloride to partially dissolve the surface to make it porous and deposit a metal hydroxide can be used to swell or make the synthetic fibers porous, and a method of applying the capillary phenomenon to impart hydrophilicity can be used. Felt is obtained by felting wool or other animal hair fibers into a sheet shape.

[0018] The manufacturing method of the non-woven fabric is not particularly limited, and various non-woven fabrics obtained by appropriate processing methods such as the spunlace method, the spunbond method, the thermal bond method, the meltblown method, and the needle punch method can be used.

[0019] The thickness of the electrolyte holding material 22 is preferably 2 to 15 mm, more preferably 2 to 10 mm, and even more preferably 2 to 5 mm. When the thickness of the electrolyte holding material 22 is at least the above lower limit value, the retention of the electrolyte solution is ensured, and the mechanical strength is excellent. On the other hand, when the thickness of the electrolyte holding material 22 is at most the above upper limit value, it is easy to adhere to the surface of the neutralization region 10.

[0020] The density of the electrolyte holding material 22 is preferably 200 to 500 g / m 2 and more preferably 300 to 400 g / m 2 When the density of the electrolyte holding material 22 is at least the above lower limit value, the retention of the electrolyte solution can be ensured. On the other hand, when the density of the electrolyte holding material 22 is at most the above upper limit value, weight reduction can be achieved and the handleability is excellent.

[0021] From the viewpoint of keeping the neutralization region 10 in a wet state, the water retention amount of the electrolyte holding material 22 is preferably 0.1 to 1.5 ml / cm 3 and more preferably 0.4 to 0.8 ml / cm 3 The water retention amount of the electrolyte holding material 22 can be obtained as follows. Water retention amount (ml / cm 3 ) = (wet mass (g) - absolutely dry mass (g)) / volume of electrolyte holding material (cm 3 ) Note that the specific gravity of water is not considered, and it is calculated assuming 1 g = 1 ml.

[0022] <<Electrolyte solution>> The electrolyte constituting the electrolyte solution reduces the electrical resistance of the neutralization region 10 by penetrating into the neutralization region 10, making it easier for electricity to flow. Any solution in which positive ions and negative ions are present in the solution may be used. Specifically, as the electrolyte solution, an aqueous solution in which various alkali metal salts and alkaline earth metal salts are dissolved in water as a solvent is preferably used. Examples of the alkali metal salts and alkaline earth metal salts include carbonates, nitrates, nitrites, sulfates, borates such as lithium, sodium, potassium, magnesium, and calcium, as well as hydroxides and chlorides.

[0023] After the electrolyte solution is supplied from an electrolyte solution storage tank (not shown) that stores the electrolyte solution to the electrolyte holding member 22, it is preferably returned to the electrolyte solution storage tank and circulated so as to be supplied from the electrolyte solution storage tank to the electrolyte holding member 22 again. During such electrolyte solution circulation treatment, it is preferable to measure and monitor the pH of the electrolyte solution. This is because the liquidity of the electrolyte may change over time, and it is preferable to manage the liquidity at regular intervals.

[0024] In the re-alkalization process using the above re-alkalization treatment system, by passing a direct current between the external electrode 20 and the internal electrode 30, chloride ions (CL - ) inside the neutralization region 10 can be migrated to the external electrode 20 side and removed. By this action, the alkalinity of the neutralization region 10, which has been neutralized by electroosmotically infiltrating an alkaline electrolyte solution into the neutralization region 10 toward the steel material side, can be restored, and the neutralization region can be made into a re-alkalization region.

[0025] In the re-alkalization process, the current density of the direct current on the surface of the concrete flowing between the external electrode 20 and the internal electrode 30 is preferably 0.1~5A / m 2 and more preferably 0.5~4.5A / m 2 and even more preferably 1~4A / m 2It is more preferable that it is so. By the current density of the direct current on the surface of the concrete being within the above range, the re-alkalization treatment can be efficiently performed.

[0026] In the re-alkalization step, the pH of the re-alkalized region in the surface layer portion of the concrete is preferably 10.7 or more, more preferably 11.5 or more, and even more preferably more than 12.0. By the pH of the re-alkalized region being not less than the above lower limit value, the concrete structure exhibits a good rust prevention effect.

[0027] In the re-alkalization step, the pH of the steel material is preferably 11.5 or more, more preferably 12 or more, and even more preferably 13.0 or more. By the pH of the steel material being not less than the above lower limit value, the steel material in the concrete structure exhibits a good rust prevention effect.

[0028] (Second Embodiment) The method for re-alkalizing a concrete structure according to the second embodiment of the present invention includes a neutralization step and an alkalinity imparting step.

[0029] <Neutralization Step> The neutralization step is the same as the neutralization step in the method for re-alkalizing a concrete structure according to the first embodiment described above, and thus is omitted.

[0030] <Alkalinity Imparting Step> The alkalinity imparting step is a step of imparting alkalinity to the surface layer portion by impregnating or applying an alkaline imparting material from the surface side of the neutralized region to make the neutralized region a re-alkalized region.

[0031] The alkalinity imparting step improves the corrosion environment of the steel material by impregnating or applying a permeable alkaline imparting material such as a lithium silicate-based, sodium silicate-based, or potassium silicate-based material from the surface side of the neutralized region to impart alkalinity to the surface layer portion and making the neutralized region a re-alkalized region. As the permeable alkali-imparting material, commercially available products can be appropriately selected. Specifically, "RF-100" (manufactured by Pacific Materials Co., Ltd.) and the like can be mentioned.

[0032] In the alkali-imparting step, the pH of the re-alkalized region in the surface portion of the concrete is preferably 10.7 or more, more preferably 11.5 or more, and even more preferably more than 12.5. When the pH of the re-alkalized region is at least the above lower limit value, the concrete structure exhibits a good rust prevention effect.

[0033] In the alkali-imparting step, the pH of the steel material is preferably 11.5 or more, more preferably 12 or more, and even more preferably 13.2 or more. When the pH of the steel material is at least the above lower limit value, the steel material in the concrete structure exhibits a good rust prevention effect.

[0034] [Electrochemical corrosion prevention method for concrete structures] The electrochemical corrosion prevention method for the concrete structure of the present invention includes a neutralization step and a corrosion prevention step.

[0035] <Neutralization step> The neutralization step is the same as the neutralization step in the re-alkalization treatment method for the concrete structure according to the above-described first embodiment, and thus is omitted.

[0036] <Corrosion prevention step> The corrosion prevention step is a step of preventing corrosion of the concrete structure by using an electrode installed on the surface side of the neutralized region as an external electrode, the steel material as an internal electrode, passing a direct current between the external electrode and the internal electrode, and making the neutralized region a re-alkalized region.

[0037] An anticorrosion treatment system used in an anticorrosion project will be described. An example of the anticorrosion treatment system will be described with reference to FIG. 2. The anticorrosion treatment system shown in FIG. 2 has an external electrode 20 installed on the surface side of the neutralization region 10, with the steel material embedded inside the neutralization region 10 serving as the internal electrode 30. A direct current is passed between the external electrode 20 and the internal electrode 30 to make the neutralization region 10 a re-alkalized region. Note that the external electrode 20 and the steel material (internal electrode 30) embedded inside the neutralization region 10 are each connected to a wiring material 23 such as an electric wire cable. By supplying a direct current from a direct current power supply device 24 to the wiring material 23, a direct current can be passed between the external electrode 20 and the internal electrode 30.

[0038] In the anticorrosion process using the anticorrosion treatment system, by passing a direct current between the external electrode 20 and the internal electrode 30, chloride ions (Cl - ) inside the neutralization region 10 can be migrated to the external electrode 20 side and removed. By this action, an alkaline electrolyte solution can be electro-osmotically permeated to the steel material side inside the neutralization region 10 to make the neutralization region 10 alkaline, and the neutralization region can be made into a re-alkalized region.

[0039] In the anticorrosion process, the designed anticorrosion current density flowing between the external electrode 20 and the internal electrode 30 is preferably 1 to 30 mA / m per unit steel material surface area 2 , more preferably 3 to 25 A / m 2 , and even more preferably 5 to 20 A / m 2 . By having the designed anticorrosion current density within the above range, the re-alkalization treatment can be efficiently carried out, and the anticorrosion treatment of the steel material can be well performed.

[0040] In the anticorrosion process, the pH of the re-alkalized region in the surface layer of the concrete is preferably 10.7 or higher, more preferably 11.5 or higher, and even more preferably 12.5 or higher. When the pH of the re-alkalized region is not less than the above lower limit value, the concrete structure can exhibit a good rust prevention effect.

[0041] In the anti-corrosion project, the pH of the steel material is preferably 11.5 or more, preferably 12 or more, and more preferably 13.2 or more. When the pH of the steel material is equal to or higher than the above lower limit value, the steel material in the concrete structure exhibits a good rust prevention effect.

[0042] [Concrete structure] The concrete structure of the present invention is a concrete structure in which a steel material is embedded inside the concrete, and has a re-alkalization region in the surface layer portion of the concrete, and the pH of the re-alkalization is 10 or more.

[0043] The re-alkalization region is a densified region, which can prevent salts and the like that cause corrosion from reaching the steel material disposed inside the concrete structure, and is a region that can improve the rust prevention effect. Here, "densification" refers to a state in which the amount of pores in the surface layer portion of the concrete decreases and the pore diameter becomes minute. Specifically, it means that the total pore volume of the surface layer portion of the concrete is 0.080 mg / L or less. Incidentally, the average pore diameter of the surface layer portion of the concrete, which is a densified region, is 0.040 μm or less.

[0044] If the pH of the re-alkalization region in the surface layer portion of the concrete is less than 10, the concrete structure cannot exhibit a good rust prevention effect. Therefore, the pH of the re-alkalization region in the surface layer portion of the concrete is preferably 10.7 or more, preferably 11.5 or more, and more preferably 12.5 or more. When the pH of the re-alkalization region in the surface layer portion of the concrete is equal to or higher than the above lower limit value, the concrete structure exhibits a good rust prevention effect.

[0045] The pH of the steel material in the concrete structure is preferably 11.5 or more, preferably 12 or more, and more preferably 13.2 or more. When the pH of the steel material in the concrete structure is equal to or higher than the above lower limit value, the steel material in the concrete structure exhibits a good rust prevention effect.

[0046] The cement used in the concrete constituting the concrete structure is not particularly limited, and various cements such as ordinary, early-strength, ultra-early-strength, low-heat, and medium-heat cements, various blended cements obtained by mixing blast furnace slag, fly ash, silica fume, etc. with these cements, environmentally friendly cements (eco-cements) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials, commercially available fine particle cements, etc. may be mentioned, and it is also possible to use various cements and various blended cements after pulverizing them into fine powder. In addition, those adjusted by increasing or decreasing the amount of components (for example, gypsum, etc.) usually used in cement can also be used. In the present invention, from the viewpoints of heat of hydration, drying shrinkage, and filling property, it is preferable to select ordinary Portland cement or early-strength Portland cement.

[0047] From the viewpoints of manufacturing cost and strength development property, the Blaine specific surface area value of the cement used in the present invention is preferably 2,500 cm 2 / g or more and 7,000 cm 2 / g or less, more preferably 2,750 cm 2 / g or more and 6,000 cm 2 / g or less, and even more preferably 3,000 cm 2 / g or more and 4,500 cm 2 / g or less. The Blaine specific surface area value is determined in accordance with JIS R 5201:2015 (Physical testing methods for cement).

[0048] In the concrete constituting the concrete structure, from the viewpoint of improving the chloride ion penetration resistance and obtaining a good rust prevention effect, for example, it is preferable to contain latent hydraulic substances such as blast furnace slag (blast furnace slowly cooled slag, blast furnace granulated slag), steelmaking slag (converter slag, electric furnace slag), fly ash, silica fume, metakaolin, pulp sludge incineration ash, sewage sludge incineration ash, volcanic glass fine powder, waste glass powder, etc. The latent hydraulic substances may be used alone or in combination of two or more.

[0049] The content ratio ((P / P+C)×100) of the latent hydraulic substance (P) to cement (C) is preferably 20 to 88%, more preferably 30 to 80%, and even more preferably 40 to 70% in terms of improving the chloride ion penetration resistance of the concrete contained in the concrete constituting the concrete structure and obtaining a good rust prevention effect. By having the content of the latent hydraulic substance within the above range, concrete with high chloride ion penetration resistance can be obtained, and a better rust prevention effect can be obtained in a concrete structure containing steel materials such as reinforcing bars.

[0050] The concrete structure of the present invention can be adopted when newly constructing civil engineering structures such as roads and railways, specifically, the substructure of a bridge, the bridge girder of a bridge, underground structures or semi-underground structures such as tunnels, and structures such as culverts. Further, the concrete structure of the present invention may be a structure obtained by treating the surface layer portion of the concrete of the concrete structure constituting an existing building so as to have a re-alkalized region.

Examples

[0051] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples and comparative examples as long as the gist thereof is not deviated from.

[0052] 〔Preparation of Specimens〕 As specimens of the concrete structure used in the examples and comparative examples, using concrete 11 with the composition shown in Table 1 below and steel materials (reinforcing bars) 31 with a diameter of 13 mm, prismatic specimens 14 with dimensions of 100 mm × 100 mm × 400 mm and a cover of 30 mm as shown in FIGS. 2(A) and (B) were prepared. The concrete was used in the test after being sealed and cured for 28 days. In addition, in Mixes 2 and 3, blast furnace slag (Blaine value 4,000 cm 2 / g) was incorporated.

[0053]

Table 1

[0054] (Examples 1-1 to 1-7) As a neutralization process, carbon dioxide gas was supplied to the surface layer of the prism test specimen 14 made of the concrete of Mix 1 to form a neutralized region. Then, as a re-alkalization process, as shown in FIGS. 3(A) and (B), a 5-mm-thick electrolyte holding material (nonwoven fabric) 22 immersed in an electrolyte solution was placed on the lower surface of the prism test specimen 14, and the electrolyte holding material 22 (density 350 g / m 2 , water retention 0.7 ml / cm 3 ) and the anode material (titanium mesh) 21 were arranged in this order. Epoxy resin (Bond Quick Mender, manufactured by Konishi Co., Ltd.) was applied to the side surface on the lower surface side of the steel material (reinforcing bar) 31 of the prism test specimen 14 and heated to provide an epoxy resin coating 36. Using the steel material 31 as the internal electrode and the anode material 21 as the external electrode, a direct current could be passed between them. For energization, the direct current power supply method used the constant current method (passing a constant current value), measured the voltage required to pass a predetermined current, and recorded and stored the change in voltage over time using a data logger. The energization of the concrete was carried out by changing the current density (A / m 2 ) of the direct current on the concrete surface and the time (min) for which the direct current was passed as shown in Table 2-1. As the electrolyte, 0.3 mol / L potassium carbonate (K2CO3) or 0.18 mol / L lithium carbonate (Li2CO3) was used, and a nonwoven fabric which is a polypropylene-made Hazmat Pig absorbent (MSD-015 manufactured by New Pig Corporation) was impregnated to produce an electrolyte holding material that holds the electrolyte. In the concrete structure that has undergone the re-alkalization process, the results regarding the evaluation of the densification and rust prevention effects described later are shown in Table 2-1.

[0055] (Comparative Example 1-1) In Example 1-3, the same procedure was carried out except that the neutralization process was omitted.

[0056] (Examples 1-8 to 1-14) As the neutralization step, the same procedure as in Examples 1-1 to 1-7 was carried out except that the square column test specimen 14 made of the concrete of Mix 2 was used, and the evaluation results are shown in Table 2-2.

[0057] (Comparative Example 1-2) In Example 1-10, the same procedure was carried out except that the neutralization step was omitted.

[0058] (Examples 1-15 to 1-21) As the neutralization step, the same procedure as in Examples 1-1 to 1-7 was carried out except that the square column test specimen 14 made of the concrete of Mix 3 was used, and the evaluation results are shown in Table 2-3.

[0059] (Comparative Example 1-3) In Example 1-17, the same procedure was carried out except that the neutralization step was omitted.

[0060] 〔Evaluation〕 <Densification> To evaluate the degree of densification of the surface layer of the concrete, the measurement of the pore size distribution by the mercury intrusion method was carried out in accordance with JIS R 1655:2003 Test method for pore size distribution of shaped bodies by mercury intrusion method for fine ceramics, and the measurement of the total pore volume of the surface layer of the concrete was carried out.

[0061] <Rust prevention effect> To evaluate the rust prevention effect of the concrete structure, the pH measurement of the re-alkalized region in the concrete structure after the re-alkalization step was carried out. In addition, to evaluate the rust prevention effect of the concrete structure, the reinforcing bars after the re-alkalization step were taken out from the concrete structure, and the pH measurement of the surface of the reinforcing bars was carried out. For the pH measurement, pH test papers (AZY (Alizarin Yellow): pH 10 to 12, ALB (Alkaline Blue): pH 11 to 13.6) of Advantec Toyo Filter Paper Co., Ltd. were used.

[0062]

Table 2

[0063] As shown in Tables 2-1 to 2-3, in the concrete structures of the examples where the re-alkalization process was carried out after the neutralization process, it was found that the surface layer of the concrete was densified and a good rust prevention effect was exerted. On the other hand, in the concrete structures of the comparative examples where the neutralization process was omitted, the densification of the surface layer of the concrete was insufficient.

[0064] (Example 2-1) As the neutralization process, carbon dioxide gas was supplied to the surface layer of the prismatic test specimen 14 made of the concrete of Mix 1 to form a neutralized region. And as the alkalinity imparting process, the neutralized region was impregnated with a permeable alkalinity imparting material ("RF-100", manufactured by Pacific Materials Co., Ltd.) from the surface side of the neutralized region to make the neutralized region a re-alkalized region. In the concrete structure that has undergone the alkalinity imparting process, the results regarding the evaluation of the densification and rust prevention effect described later are shown in Table 3-1.

[0065] (Comparative Example 2-1) In Example 2-1, it was the same except that the neutralization process was omitted.

[0066] (Example 2-2) As the neutralization process, it was the same as Example 2-1 except that the prismatic test specimen 14 made of the concrete of Mix 2 was used, and the evaluation results are shown in Table 3-2.

[0067] (Comparative Example 2-2) In Example 2-2, it was the same except that the neutralization process was omitted.

[0068] (Example 2-3) As the neutralization process, it was the same as Example 2-1 except that the prismatic test specimen 14 made of the concrete of Mix 3 was used, and the evaluation results are shown in Table 3-3.

[0069] (Comparative Example 2-3) In Example 2-3, it was the same except that the neutralization process was omitted.

[0070] 〔Evaluation〕 <Densification> In order to evaluate the degree of densification of the surface layer of concrete, measurement of the pore size distribution by mercury intrusion porosimetry was carried out on the surface layer of concrete in accordance with JIS R 1655:2003 Test Method for Pore Size Distribution of Formed Bodies by Mercury Intrusion Porosimetry of Fine Ceramics Measurement of the total pore volume was performed.

[0071] <Rust prevention effect> In order to evaluate the rust prevention effect of concrete structures, pH measurement of the re-alkalized region in the concrete structure after the alkalization step was carried out. In addition, in order to evaluate the rust prevention effect of concrete structures, the reinforcing bars after the alkalization step were taken out from the concrete structures, and pH measurement of the reinforcing bar surfaces was carried out. For pH measurement, pH test papers (AZY (Alizarin Yellow): pH 10 - 12, ALB (Alkaline Blue): pH 11 - 13.6) of Advantec Toyo Filter Paper Co., Ltd. were used.

[0072]

Table 3

[0073] As shown in Tables 3-1 to 3-3, in the concrete structures of the examples where the alkalization step was carried out after the carbonation step, it was found that the surface layer of the concrete was densified and a good rust prevention effect was exhibited. On the other hand, in the concrete structures of the comparative examples where the carbonation step was omitted, the densification of the surface layer of the concrete was insufficient and the rust prevention effect was also insufficient.

[0074] (Examples 3-1 to 3-7) As the carbonation step, carbon dioxide gas was supplied to the surface layer of the fabricated prism test specimen 14 to form a carbonated region. And as the anticorrosion step, with the steel material 31 as the internal electrode and the anode material 21 as the external electrode, a direct current was made to be passed between them. For the energization, the DC power supply method used a constant current method (energizing with a constant current value), measured the voltage required to pass a predetermined current, and recorded and stored the change in voltage over time using a data logger. The energization of the concrete was carried out by changing the current density (A / m 2 ) of the direct current and the time (min) during which the direct current was passed as shown in Table 4-1. Regarding the concrete structure that has undergone the anticorrosion process, the results regarding the evaluation of the densification and rust prevention effects described later are shown in Table 4-1.

[0075] (Comparative Example 3-1) In Example 3-3, it was the same except that the neutralization process was omitted.

[0076] (Examples 3-8 to 3-14) As the neutralization process, it was the same as in Examples 3-1 to 3-7 except that the prism test specimen 14 made of the concrete of formulation 2 was used, and the evaluation results are shown in Table 4-2.

[0077] (Comparative Example 3-2) In Example 1-10, it was the same except that the neutralization process was omitted.

[0078] (Examples 3-15 to 3-21) As the neutralization process, it was the same as in Examples 3-1 to 3-7 except that the prism test specimen 14 made of the concrete of formulation 3 was used, and the evaluation results are shown in Table 3-3.

[0079] (Comparative Example 3-3) In Example 3-17, it was the same except that the neutralization process was omitted.

[0080] 〔Evaluation〕 <Densification> To evaluate the degree of densification of the surface layer of the concrete, the measurement of the pore size distribution by mercury intrusion method was carried out in accordance with JIS R 1655:2003 Method for Testing Pore Size Distribution of Formed Bodies by Mercury Intrusion Method for Fine Ceramics, and the measurement of the total pore volume of the surface layer of the concrete was performed.

[0081] <Rust prevention effect> To evaluate the rust prevention effect of a concrete structure, pH measurement of the re-alkalized region in the concrete structure after the corrosion protection process was performed. Also, to evaluate the rust prevention effect of a concrete structure, the reinforcing bars after the corrosion protection process were taken out from the concrete structure, and pH measurement of the surface of the reinforcing bars was performed. For pH measurement, pH test papers (AZY (Alizarin Yellow): pH 10 - 12, ALB (Alkaline Blue): pH 11 - 13.6) of Advantec Toyo Filter Paper Co., Ltd. were used.

[0082]

Table 4

[0083] As shown in Tables 4-1 to 4-3, it was found that in the concrete structures of the examples where the corrosion protection process was carried out after the carbonation process, the surface layer of the concrete was densified and a good rust prevention effect was exhibited. On the other hand, in the concrete structures of the comparative examples where the carbonation process was omitted, the densification of the surface layer of the concrete was insufficient.

Explanation of symbols

[0084] 10 Concrete 14 Prismatic test specimen 20 External electrode 21 Anode material 22 Electrolyte holding material 23 Wiring material 24 DC power supply device 30 Internal electrode 31 Steel material

Claims

1. A neutralization step of neutralizing or naturally neutralizing the surface layer of a concrete structure in which steel materials are embedded inside the concrete to form a neutralization region; A re-alkalization step of using an electrolytic solution of alkali, using an electrode installed on the surface side of the neutralization region as an external electrode, using the steel material as an internal electrode, passing a direct current between the external electrode and the internal electrode, and making the neutralization region a re-alkalization region; A method for re-alkalizing a concrete structure including the above.

2. In the re-alkalization step, the current density of the direct current flowing on the surface of the concrete between the external electrode and the internal electrode is 0.1 to 5 A / m ２ The method for re-alkalizing a concrete structure according to claim 1, wherein the current density is as described above.

3. The re-alkalization treatment of the electrochemical corrosion prevention method for a concrete structure according to Claim 1, wherein in the re-alkalization step, the pH of the re-alkalization region is 10 or more.

4. A neutralization step of neutralizing or naturally neutralizing the surface layer of a concrete structure in which steel materials are embedded inside the concrete to form a neutralization region; An anticorrosion step of using an electrode installed on the surface side of the neutralization region as an external electrode, using the steel material as an internal electrode, passing a direct current between the external electrode and the internal electrode, and making the neutralization region a re-alkalization region to prevent corrosion of the concrete structure; An electrochemical corrosion prevention method for a concrete structure including the above.

5. In the anticorrosion process, the designed anticorrosion current density flowing between the external electrode and the internal electrode is 1 to 30 mA / m per unit surface area of the steel material. ２ The electrochemical anticorrosion method for a concrete structure according to claim 4, wherein the designed anticorrosion current density flowing between the external electrode and the internal electrode is 1 to 30 mA / m per unit surface area of the steel material.

6. A neutralization step of neutralizing or naturally neutralizing the surface layer of a concrete structure in which steel materials are embedded inside the concrete to form a neutralization region; An alkalinity-imparting step of imparting alkalinity to the surface layer by impregnating or applying an alkalinity-imparting material from the surface side of the neutralization region to make the neutralization region a re-alkalization region; A method for re-alkalizing a concrete structure including the above.

7. In a concrete structure in which steel materials are embedded inside the concrete, The surface layer of the concrete has a re-alkalization region, A concrete structure in which the pH of the re-alkalization region is 10 or more.

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