JP2021059927A - Method for removing salt from concrete structure - Google Patents

Abstract

To provide a method for removing salt from a concrete structure, which can be easily constructed, saves labor, saves energy, and can be carried out at a low cost, and can be expected to have a sufficient salt removing effect.SOLUTION: The inside of the target concrete is moistened with a humidity of 98% or higher, and a water-retaining material impregnated with a hygroscopic aqueous solution having an equilibrium relative humidity of 95% or lower is attached to the surface of the concrete and brought into contact with the aqueous solution, and further chloride ions inside the concrete is moved to the outside of the concrete. As the aqueous solution to be brought into contact with the surface of concrete, an aqueous solution of lithium nitrite having a concentration of 16% or higher is used. In addition, a film or cover (drying prevention means) is attached so as to cover the outside of the attached water-retaining material. Further, the attached water-retaining material is regularly replaced with a water-retaining material newly impregnated with the aqueous solution.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method (salt removal method) for reducing the chloride ion concentration in the skeleton before damage due to salt damage (corrosion of steel materials, etc.) becomes apparent in a concrete structure damaged by salt damage. It relates to a method for removing salt from a concrete structure, which can be carried out with labor and energy saving.

Skeleton body to the chloride ions of the concrete structure by salt damage, etc. (Cl ^-) may had penetrated a predetermined amount or more, the steel (rebar is embedded therein, PC steel material) dense formed on the surface of There is a high risk that the passive film will be destroyed and the steel material will corrode. When the steel material corrodes in the skeleton, the volume of the steel material expands several times at the corroded part, which may cause cracks in the concrete along the steel material. When cracks occur, the supply of oxygen and water becomes easy, and corrosion progresses at an accelerating rate, and as a result, concrete may peel off or the member strength may decrease due to a decrease in the cross-sectional area of the steel material.

As one of the countermeasures when chloride ions invade the skeleton of the concrete structure due to salt damage, etc., a method of reducing the chloride ion concentration in the skeleton (salt removal method of the concrete structure) is implemented. Has been done. Various methods have been proposed as a method for removing salt from a concrete structure. For example, an electrolyte solution is held on the outer surface of the concrete structure, an electrode (anode) is installed, and a steel material in the skeleton is used as a cathode. A method of energizing a DC current and moving chloride ions that have entered the concrete by the principle of electrophoresis to the outside of the concrete (electrolyte solution side) (electrochemical desalting method using electrophoresis) is known. Has been done.

JP-A-2018-199596 JP-A-2018-124286 Japanese Unexamined Patent Publication No. 2009-126728 Japanese Unexamined Patent Publication No. 2000-303700 Japanese Unexamined Patent Publication No. 7-89773

However, the electrochemical desalting method using electrophoresis requires a large amount of equipment, requires considerable labor and time in preparation work and withdrawal work, and consumes a large amount of electrical energy, resulting in construction cost. There is a problem that it becomes expensive. In addition, drilling work or the like is required to access the internal steel material used as the cathode, which may impose a burden on the concrete structure.

The present invention is intended to solve the above-mentioned problems in the prior art, and can be easily constructed, labor-saving, energy-saving, and low-cost, and is expected to have a sufficient salt removal effect. It is an object of the present invention to provide a method for removing salt from a concrete structure that can be used.

In the method for removing salt from a concrete structure according to the present invention, the inside of the target concrete is in a wet state with a humidity of 98% or more, and a hygroscopic aqueous solution having an equilibrium relative humidity of 95% or less is brought into contact with the surface of the concrete. It is characterized in that it is allowed to stand and allowed to move chloride ions inside the concrete to the outside of the concrete.

As the aqueous solution having hygroscopicity, it is preferable to use an aqueous solution of lithium nitrite having a concentration of 16% or more. Further, in order to bring the aqueous solution into contact with the surface of concrete, it is preferable to attach the water-retaining material containing the aqueous solution to the surface of concrete, or to include the aqueous solution in the water-retaining material attached to the surface of concrete. As the water-retaining material, it is preferable to use a ^{material capable of retaining 1000 g / m 2 or more of an aqueous solution.}

Further, as the water-retaining material, a fibrous material having water retention (for example, pulp, cloth, non-woven fabric, etc.) is molded into a sheet, or a porous material having water retention (for example, zeolite, silas, etc.). A board-shaped (plate-shaped) molded balloon, foamed beads, etc., or an organic polymer material having water retention (for example, a polyacrylic acid-based water-absorbing polymer material) having water permeability. It is preferable to use a sheet-shaped product that is housed in a bag.

Further, as the water-retaining material, a porous material having water retention (for example, zeolite, shirasu balloon, or foamed beads, etc.) or an organic polymer material having water retention (for example, polyacrylic acid-based high water absorption) Molecular materials, etc.) may be used and sprayed onto the surface of the concrete to adhere them to form a water-retaining layer. Further, as the water-retaining material, it is preferable to use a material that does not deteriorate the water-retaining performance when an aqueous solution of lithium nitrite is used.

Further, in order to bring the aqueous solution into contact with the surface of concrete, a water storage tank may be installed so as to cover the surface of the concrete, and the aqueous solution may be stored in the water storage tank to bring the aqueous solution into contact with the surface of concrete. It is preferable that the water-retaining material adhered to the concrete surface or the aqueous solution stored in the water storage tank be replaced regularly. Further, it is preferable to attach a film or a cover (drying prevention means) so as to cover the outside of the water-retaining material or the water storage tank.

Further, when the surface of concrete is painted after the salt removing method as described above is carried out, the risk of deterioration due to re-invasion of salt can be suitably avoided.

Although the method for removing salt from a concrete structure according to the present invention can be carried out extremely easily, labor saving, energy saving, and low cost, a sufficient salt removing effect can be expected. ..

FIG. 1 is an explanatory diagram of a container 1, a test body 2, and the like used in the experiment of Example 1. FIG. 2 is an explanatory diagram of the container 1, the test body 2'and the like used in the experiment of Example 1. FIG. 3 is an explanatory diagram of a method of collecting a sample from the test body 2 used in the experiment of Example 1. FIG. 4 is a graph showing the measurement results of the chloride ion concentration in the sample obtained in the experiment of Example 1. FIG. 5 is a graph showing the correlation between the chloride ion concentrations of the outer portion 2d and the inner portion 2e of the test body IC16 (test body immersed in a 16% lithium nitrite aqueous solution) of Example 1. FIG. 6 is an explanatory diagram of an embodiment of the present invention, and is an explanatory diagram of a method of bringing the aqueous solution 3 into contact with the surface of the concrete structure 11 using the water storage tank 12.

The "method for removing salt from a concrete structure" according to the present invention is a method for reducing the chloride ion concentration in the skeleton of a concrete structure, and water is applied from the surface of the concrete to moisten the inside of the concrete (humidity 98). % Or more), and an aqueous solution having a hygroscopic property having an equilibrium relative humidity of 95% or less is brought into contact with the surface of concrete and allowed to stand, and chloride ions inside the concrete are moved to the outside of the concrete. It is a thing.

As a specific method for bringing the aqueous solution into contact with the surface of concrete, a method using a water-retaining material, a method using a water tank, or the like can be adopted. When a water-retaining material is used, for example, a fibrous substance having water retention (pulp, cloth, non-woven fabric, etc.) molded into a sheet (water-retaining sheet), or an organic polymer material having water retention. (Polyacrylic acid-based water-absorbing polymer material) is housed in a water-permeable bag and molded into a sheet (water-retaining sheet) impregnated with an aqueous solution, and this is attached to the surface of concrete. Alternatively, a porous material having water retention (zeolite, silas balloon, foamed beads, etc.) molded into a board shape (plate shape) (water retention board) is impregnated with an aqueous solution, and this is impregnated on the surface of concrete. It may be brought into close contact with. Further, a porous material having water retention or an organic polymer material having water retention is sprayed onto the surface of concrete to be adhered to form a water retention layer made of the water retention material so that the water retention layer contains an aqueous solution. It may be.

As the water-retaining material, it is preferable to use a material having as high a water-retaining property as possible (a material ^{capable of retaining 1000 g / m 2 or more of an aqueous solution).} For example, when two sheets having a thickness of 6 mm and a water absorption of ^{about 5000 g / m 2} are used in a stacked state, sufficient water retention can be obtained.

On the other hand, when a water storage tank is used, for example, as shown in FIG. 6, the water storage tank 12 is installed so as to cover the surface of the concrete structure 11, and the aqueous solution 3 is stored in the water storage tank 12 to store the surface of the concrete. To contact.

In addition, it is preferable to take measures against drying of the water-retaining material and the water storage tank. For example, it is highly airtight (airtight) so as to cover the outside of a water-retaining sheet attached to the surface of concrete, a water-retaining board, a water-retaining layer formed by spraying on the surface of concrete, or a water storage tank. Attach a plastic film (low degree) or a metal or synthetic resin cover (drying prevention means). The drying prevention means needs to be configured so as to be in close contact with the surface of the surrounding concrete such as the attached water-retaining sheet.

Further, as the aqueous solution to be contained in the water-retaining material or stored in the water storage tank, a lithium nitrite aqueous solution having a concentration of 16% (or 16% or more) (concentration 16%: equilibrium relative humidity 90%) may be used. it can. When the lithium nitrite aqueous solution is contained in the water-retaining material, as a matter of course, a water-retaining material that does not deteriorate due to contact with the lithium nitrite aqueous solution and does not deteriorate in water-retaining performance is used.

The period during which the aqueous solution is brought into contact with the surface of the concrete can be appropriately determined according to the degree of salt damage (the amount of invaded chloride ions) in the target concrete structure. Furthermore, it is preferable that the water-retaining material and the aqueous solution are replaced with new ones on a regular basis (for example, every 4 weeks).

Specifically, when a water-retaining sheet or a water-retaining board is used (attached to the concrete surface) as a water-retaining material that brings the aqueous solution into contact with the concrete surface, they are peeled off from the concrete surface and removed. Then, replace it with a new water-retaining sheet or a water-retaining board newly impregnated with the aqueous solution. When a water-retaining layer is formed on the concrete surface by spraying a water-retaining material such as a porous material, the water-retaining layer is peeled off and removed, and the water-retaining material is sprayed again to renew the water-retaining layer. And add a new aqueous solution. When a water tank is used, the aqueous solution 3 (see FIG. 6) stored inside is replaced with a new one.

Further, it is preferable to apply a coating to the surface of the concrete after the above-mentioned salt removal treatment is completed, and in this case, deterioration due to re-invasion of the salt can be preferably avoided.

Hereinafter, the results of various experiments conducted by the inventors regarding the effects of the method according to the present invention will be described as Examples 1 to 4.

An experiment was conducted to confirm the salt removal effect of an aqueous solution of lithium nitrite. In this experiment, test specimens (mortar mass) containing a certain amount of chloride ions were prepared, and these specimens were immersed in an aqueous solution of lithium nitrite and other aqueous solutions for a certain period of time, and then each test was performed. Chloride ion concentration inside the body was measured and analyzed. In addition, the test specimens produced under the same conditions were subjected to electrochemical desalting treatment, and the effects were compared.

The test piece was produced by kneading sodium chloride into a 1: 2 mortar having a water-cement ratio (w / c) of 40% and molding it into a cylinder having a diameter of 50 mm and a height of 100 mm. Then, water is applied from the outer surface to bring each test piece into a wet state (humidity 98% or more), and as shown in FIG. 1, the test piece 2 is housed and immersed in a container 1 filled with an aqueous solution 3. The upper part of the container 1 was sealed and allowed to stand for 26 weeks in a room not exposed to direct sunlight.

As the aqueous solution 3 for immersing the test body 2, an aqueous solution of lithium nitrite having a concentration of 16% (solvent: lime water (saturated aqueous solution of calcium hydroxide, pH 12 or higher)) was used. In addition, as a comparative example, lime water and an anion exchange resin (strong basic OH ^- type) in a sufficient amount (amount capable of adsorbing the entire amount of chloride ions contained in the test body) were added to the lime water. The aqueous solution was prepared and the test piece was immersed under the same conditions.

Further, in parallel with the above dipping treatment, an electrochemical desalting treatment was performed. Specifically, a cylindrical test body 2'(conditions such as compounding and chloride ion concentration are the same as those of the test body 2 of FIG. 1) having a cavity having a diameter of 5 mm at the center position was produced, and FIG. 2 shows. As shown, a carbon rod 4 having a diameter of 5 mm is inserted into the cavity and housed in the container 1, and a titanium mesh material 5 is arranged so as to surround the test piece 2'inside the container 1. The electrolyte solution 3'was added to the test piece 2'and the mesh material 5 was immersed in the test piece 2'. Then, the carbon rod 4 and the mesh material 5 are connected to the power supply unit 6, respectively, the carbon rod 4 is used as a cathode and the mesh material 5 is used as an anode, and a direct current of 1 A / m ² is applied from the power supply unit 6 to continue for 8 weeks. It was energized and desalted using the principle of electrophoresis. As the electrolyte solution 3', lime water (pH 12 or higher) was used.

Next, the test body 2 (see FIG. 1) in which the immersion experiment was performed was taken out from the container 1, and as shown in FIG. 3, a position 25 mm below the upper end and a position 25 mm above the lower end (in the dashed line in FIG. 3). Cut in the horizontal direction at the indicated position), remove the upper part 2a and the lower part 2c to extract the middle part 2b, and further, the middle part 2b is the outer part 2d (the part from the outer peripheral surface to the depth of 7 mm toward the center). And the inner part 2e (the part shown by the diagonal line in FIG. 3) were separated, and a sample was taken. Further, the test piece 2'(see FIG. 2) subjected to the electrochemical desalting treatment was also separated into an outer part and an inner part by the same method, and a sample was collected. Then, those samples were individually pulverized, and the chloride ion concentration of each sample was measured in accordance with JIS A 1154 “Test method for chloride ions contained in hardened concrete”. The results are shown in FIG.

In the graph of FIG. 4, "IA" is a test body immersed in lime water, "IB" is a test body immersed in an aqueous solution to which an anion exchange resin is added, and "IC16" is a 16% lithium nitrite aqueous solution. The immersed test piece, "ID", is a test piece that has been subjected to an electrochemical desalting treatment, and "R" is a test piece that has been stored as it is after being manufactured without being immersed. _{The broken line (Clim} ) shown in FIG. 4 is the value (2.86 kg / m) obtained by converting the chloride ion concentration at which corrosion of the steel material occurs in terms of mortar ( ^{assuming a volume of 0.6 m 3} / m ^{3 excluding the aggregate). 3} ).

As shown in FIG. 4, in the test piece ID subjected to the electrochemical desalting treatment, the chloride ion concentration was significantly reduced in both the outer portion and the inner portion. On the other hand, in the test bodies IA, IB, and IC16 that had undergone the immersion treatment, a decrease in the chloride ion concentration was confirmed in the outer portion 2d, but no significant decrease in the concentration was observed in the inner portion 2e.

In addition, from the results of this experiment, the salt removal effect (effect of reducing chloride ion concentration) that can be expected by performing the immersion treatment with an aqueous solution of lithium nitrite or the like is effective up to a depth of at least about 7 mm from the outer surface of the test piece. It turned out to be. Furthermore, considering only the outer part (the part from the outer surface to a depth of 7 mm), the test having the lowest chloride ion concentration among the test bodies IA, IB, and IC16 subjected to the immersion treatment was the test. Body IC16 (test specimen immersed in 16% lithium nitrite aqueous solution) (more specifically, IC16 <IB <IA), and therefore, when 16% lithium nitrite aqueous solution is used, lime water and anions. It was confirmed that a higher salt removal effect can be expected than when an aqueous solution containing an exchange resin is used.

Next, an experiment was conducted to confirm the salt removal effect when a water-retaining sheet (water-retaining material) impregnated with an aqueous solution of lithium nitrite was attached. In this experiment, the same test body as the test body used in the immersion experiment (Example 1) was used.

First, water is applied from the outer surface to bring each test piece into a wet state (humidity 98% or more), and a water-retaining sheet impregnated with an aqueous solution of lithium nitrite is attached to the outer surface thereof and housed in a container. It was sealed and allowed to stand in a room not exposed to direct sunlight for 26 weeks, after which the chloride ion concentration inside each test piece was measured.

As the water-retaining sheet, two sheets having a thickness of 6 mm and a water absorption capacity of 5000 g / m ² were used in a stacked state. Further, as an aqueous solution to impregnate the water-retaining sheet, an aqueous solution of lithium nitrite having a concentration of 16% (solvent: lime water (pH 12 or more)) was used.

In addition, one group (test body S) of the test bodies was newly impregnated with a new water-retaining sheet impregnated with an aqueous solution of lithium nitrite (a new aqueous solution of lithium nitrite) every 4 weeks. It was carried out while exchanging with a new water-retaining sheet), and for the other group (test body N), it was carried out without exchanging the water-retaining sheet.

Each of the test specimens S and N is taken out from the container, and the intermediate portion 2b of the specimen is separated into the outer portion 2d and the inner portion 2e (see FIG. 3) in the same manner as in Example 1, and a sample is collected to obtain chloride. The bodily ion concentration was measured. The value of the chloride ion concentration in the outer portion 2d of the test body S in which the water-retaining sheet was replaced is the value of the outer portion 2d of the test body IC16 (test body immersed in 16% lithium nitrite aqueous solution) of Example 1. It was lower than (2.77 kg / m ³ , see FIG. 4) (S <IC16). On the other hand, the value of the chloride ion concentration in the outer portion 2d of the test body N in which the water-retaining sheet was not replaced was higher than the value in the outer portion 2d of the test body IC16 of Example 1 (S <IC16 < N).

Therefore, when a water-retaining sheet impregnated with a 16% lithium nitrite aqueous solution is attached to the outer surface of the test piece and the water-retaining sheet is replaced regularly, the test piece is immersed in the 16% lithium nitrite aqueous solution. However, it was confirmed that a high salt removal effect can be expected.

The same experiment was conducted using an aqueous solution of lithium nitrite having a concentration of 16% and an aqueous solution of lithium nitrite having a concentration of 4% and a concentration of 8% as the aqueous solution to be impregnated in the water-retaining sheet. It was confirmed that the higher the concentration of lithium nitrate, the higher the salt removal effect can be expected.

In order to verify the salt removal mechanism of lithium nitrite, the equilibrium relative humidity of the lithium nitrite aqueous solution was measured, and in order to confirm the effectiveness as a preventive maintenance measure, it penetrated into the test body IC of Example 1. The nitrite ion was analyzed.

The inventors of the present invention assume that the humidity difference between the inside and the outside of concrete promotes salt removal (chloride ions move from the inside of concrete with high humidity to the outside with low humidity). When the above experiments (Example 1 and Example 2) were carried out, it was confirmed that a certain salt removing effect was obtained. Then, as shown in Table 1, it was confirmed that the equilibrium relative humidity of the 16% concentration lithium nitrite aqueous solution used in the experiment was 90% in an environment at a temperature of 20 ° C. This fact is consistent with the above assumptions. However, other effects were also identified between the equilibrium relative humidity and the salt removal rate.

FIG. 5 is a graph showing the correlation between the chloride ion concentrations of the outer portion 2d and the inner portion 2e of the test bodies of Example 1 and Example 2 (excluding the test body IB and the test body ID). As shown in this graph, the chloride ion concentrations of the two showed a negative correlation. That is, it was found that as the chloride ion concentration in the outer portion 2d decreases, the chloride ion concentration in the inner portion 2e tends to increase from the initial chloride ion concentration (see the test piece R in FIG. 4). ..

At the stage when the nitrite ion in the aqueous solution to be brought into contact with the test piece permeates the inside of the test piece (outer part 2d and inner part 2e), a part of the chloride ion existing in the outer part 2d of the test piece is released. It is considered that while the other part moved to the outside of the test piece, it may have moved to the inner part 2e of the test piece. In other words, it is presumed that both "equilibrium theory" and "kinetics" were involved in the factors that affected the movement rate of chloride ions by the coexistence of nitrite ions and chloride ions.

The analysis results of nitrite ion in the test body IC of Example 1 are as shown in the above table. NO specimens in IC ₂ ^- / Cl ^- molar ratio, 2.39 at the outer portion 2d, was 0.50 at the inner portion 2e. Nitrite ions have the effect of repairing the passivation film of steel materials destroyed by chloride ions and suppressing the corrosion reaction. According to previous studies, it is reported that the corrosion suppressing effect is high when the molar ratio of nitrite ion to chloride ion inside concrete is 0.6 or more.

Since it was confirmed that nitrite ions permeated to the inner portion 2e in the test body IC16 having a diameter of 50 mm, when the salt removal method according to the present invention was carried out using an aqueous solution of lithium nitrite, it was observed from the outer surface of the concrete. It is considered that the corrosion suppressing effect by nitrite ion can be expected in the range of about 25 mm depth, and therefore, it was confirmed that it can be effective as a preventive maintenance measure.

Experiments were conducted to confirm how to moisten the inside of concrete by giving water from the outer surface. In this experiment, a concrete member (length 3.7 m, height 1.7 m) that was removed due to salt damage was prepared as a test body, and there was no damage such as cracks, and a sound outer surface (test surface, test target surface, Area: 30 x 30 cm) was selected at four locations, and the following four methods were individually performed (one method for one test target surface) on each test target surface to give water (tap water). The mixture was allowed to stand for 1 day with a wrap to prevent it from drying out.
Method A Watering (spraying 500g / m ² of water with a spray)
Method a. Attaching a water-retaining sheet (thickness 2 mm, water volume 1500 g / m ² ) Method C. Attaching a water-retaining sheet (thickness 4 mm, water volume 3000 g / m ² ) D. Attaching a water-retaining sheet (thickness 6 mm, water volume 5000 g) / M ² ) paste

After that (after 1 day), the wrap (wrap and water-retaining sheet in methods (a) to (d)) was removed. Then, holes were drilled inward from each test target surface, a humidity sensor was fixed at a position at a depth of about 20 mm, and the humidity inside was measured with the drilled holes sealed. The experiment was carried out indoors, and the temperature at the time of measurement was 24 ° C. and the humidity was 65%.

As a result of the measurement, the humidity inside the test target surface on which method A was carried out was 88%, and the humidity inside the test target surface on which methods a to d were carried out was 98% or more. From this experimental result, it was confirmed that the inside of concrete can be made wet (humidity 98% or more) by using a means capable of retaining ^{1500 g / m 2 or more of water for one day or more.}

1: Container,
2, 2': Specimen,
2a: Upper part,
2b: middle part,
2c: bottom,
2d: outer part,
2e: Inner part,
3: Aqueous solution,
3': Electrolyte solution,
4: Carbon rod,
5: Mesh material,
6: Power supply,
11: Concrete structure,
12: Water tank

Claims (14)

The inside of the target concrete is kept wet with a humidity of 98% or more.
A concrete structure characterized in that a hygroscopic aqueous solution having an equilibrium relative humidity of 95% or less is brought into contact with the surface of the concrete and allowed to stand, and chloride ions inside the concrete are moved to the outside of the concrete. How to remove salt from things. The method for removing salt from a concrete structure according to claim 1, wherein an aqueous solution of lithium nitrite is used as the aqueous solution. The method for removing salt from a concrete structure according to claim 2, wherein the concentration of lithium nitrite in the aqueous solution of lithium nitrite is 16% or more. By adhering the water-retaining material containing the aqueous solution to the surface of the concrete, or by impregnating the water-retaining material adhering to the surface of the concrete with the water-retaining material, the aqueous solution can be applied to the concrete. The method for removing salt from a concrete structure according to any one of claims 1 to 3, wherein the concrete structure is brought into contact with a surface. The method for removing salt from a concrete structure according to claim 4, wherein as the water-retaining material, a material ^{capable of retaining 1000 g / m 2 or more of the aqueous solution is used.} The fifth aspect of the present invention is characterized in that, as the water-retaining material, a material obtained by molding a fibrous material having water retention into a sheet shape or a material obtained by molding a porous material having water retention into a board shape is used. The method for removing salt from a concrete structure according to the description. The concrete structure according to claim 5, wherein as the water-retaining material, an organic polymer material having water retention is housed in a bag having water permeability and molded into a sheet shape. How to remove salt from things. As the water-retaining material, a porous material having water retention or an organic polymer material having water retention is used, and they are sprayed onto the surface of the concrete to adhere to the surface of the concrete to form a water-retaining layer. , The method for removing salt from a concrete structure according to claim 5. The method for removing salt from a concrete structure according to claim 5, wherein a material whose water retention performance does not deteriorate when the aqueous solution is used is used as the water retention material. The water-retaining material is periodically replaced with a water-retaining material newly containing the aqueous solution, or the water-retaining material is regularly replaced with a new one, and the aqueous solution is newly contained. The method for removing salt from a concrete structure according to any one of claims 4 to 9, wherein the method is characterized by. A water tank is installed so as to cover the surface of the concrete.
The method for removing salt from a concrete structure according to any one of claims 1 to 3, wherein the aqueous solution is stored in the water storage tank so as to be brought into contact with the surface of the concrete. The method for removing salt from a concrete structure according to claim 4, wherein the aqueous solution in the water storage tank is replaced regularly. The method for removing salt from a concrete structure according to any one of claims 4 to 12, wherein a film or a cover is attached so as to cover the outside of the water-retaining material or the water storage tank as a drying prevention means. A method for repairing a concrete structure, which comprises performing the method for removing salt from a concrete structure according to any one of claims 1 to 13 and then applying a coating to the surface of the concrete.

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