JP3310115B2 - Concrete treatment method using electrochemical treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrochemically treating concrete structures, and more particularly to a method for electrochemically removing salt from concrete, a method for supplying an alkaline solution to neutralized concrete, and a method for electrochemically treating concrete. And a method for infiltrating concrete with an alkali-aggregate reaction inhibitor.

[0002]

2. Description of the Related Art Concrete is generally
Because of its strong resistance to various environments and strong alkalinity, the steel inside it is protected from corrosion by forming a passive film on the surface of the steel, so that the concrete structure is durable. It has been considered a certain permanent structure. However, the durability of the concrete structure, which has been considered as a permanent structure, has been reduced due to the cause of neutralization, salt damage, and the like, and the life of the structure has been questioned.

[0003] As a method of repairing such a deteriorated concrete structure, a reinforcing bar in a concrete structure is used as a negative electrode, and a concrete surface is coated with an electrolyte retaining material impregnated with an electrolyte solution. Temporarily set the mesh-shaped electrode using a positive electrode, etc., and apply a current between the two electrodes to remove chloride ions in the concrete, or to desalinate the neutralized concrete again. A repair method using an electrochemical method such as a re-alkalization treatment method is disclosed (Japanese Patent Laid-Open No.
-176287, JP-A-2-302384).

[0004] However, when the energization treatment of concrete is performed by using these methods, the following reactions occur as an electrode reaction (anode reaction) at a positive electrode which is an external electrode provided in an electrolyte solution outside the concrete.・ H ₂ O → H ⁺ + OH ⁻ (electrolysis of water) ・ 2OH ⁻ → H ₂ O + 1 / 2O ₂ + 2e (generation of oxygen gas) Among hydrogen ions and hydroxyl ions generated by electrolysis of water, hydroxyl Ions are not accumulated in the electrolyte solution because they are consumed in the oxygen gas generation reaction, but hydrogen ions continue to accumulate in the electrolyte solution as long as the energization process is continued, and the pH in the electrolyte solution is maintained. The value changes to the acidic side. When the pH value of the electrolyte solution becomes acidic,
Adverse effects such as deterioration of the concrete surface are inevitable. In other words, cement plays a role as a binder for aggregate in concrete, and the main components of the cement are calcium silicate hydrate, calcium hydroxide, calcium aluminate hydrate, calcium aluminate ferrite Hydrate and the like. Taking hydrochloric acid as an example, the reaction with cement hydrate can be represented by a chemical formula: Ca (OH) ₂ + HCl → CaCl ₂ + H ₂ O 3CaO .2SiO ₂ .3H ₂ O + HCl → CaCl ₂ + SiO ₂ + H ₂ O 3CaO · Al ₂ O ₃ · 3CaSO ₄ · 32H ₂ O + HCl → CaCl ₂ + Al ₂ O ₃ · nH ₂ O + CaSO ₄ · 2H ₂ O By such a reaction, cement hydrate is decomposed and loses its binding ability. . Calcium chloride generated by the reaction is easily eluted because it is easily soluble in water. The above mechanism causes concrete erosion.

[0005] When desalination treatment is performed using this method, chlorine ions from inside the concrete move to the outside of the concrete and dissolve in the electrolyte solution outside the concrete. At this time, if the pH value of the electrolyte solution is on the acidic side,
There is a problem in the working environment because it is released into the atmosphere as chlorine gas.

According to the present invention, as a result of various studies to solve the above-mentioned problems, by controlling the pH value of the electrolyte solution,
The present inventors have obtained knowledge that can solve the above problems, and have completed the present invention.

[0007]

Means for Solving the Problems That is, the present invention provides (1) an electrode placed on the concrete surface as an external electrode, a steel material inside the concrete as an internal electrode, and between the external electrodes, and / or
Alternatively, in a method in which a current is applied between an external electrode and an internal electrode through an electrolyte solution held on a concrete surface , an alkaline aqueous solution is continuously or intermittently applied to the electrolyte solution.
To the addition method of processing concrete and controlling the pH value of the electrolyte solution 7 above, (2) processing method of the concrete, characterized by using a high concentration alkaline aqueous solution as an electrolyte solution It is.

Hereinafter, the present invention will be described in detail. As a control range of the pH value of the electrolyte solution, the pH value is preferably 7 or more, more preferably 9 or more, and most preferably 11 or more. Next, as a method of controlling the pH value of the electrolyte solution to 7 or more,. A method in which an alkaline aqueous solution having a higher concentration than at the start of energization is used as an electrolyte solution to prevent the pH value from dropping to less than 7; A method of measuring the pH value in the electrolyte solution during the energization treatment, adding an alkaline solution continuously or intermittently according to the measured value, and maintaining the pH value at or above a specified value. There is a control method based on a combination with the above.

[0009] In the method of using an alkaline aqueous solution having a higher concentration than that at the start of energization as an electrolyte solution and suppressing the pH value from dropping to less than 7, the electrolyte solution contains hydroxyl ions, The solution is not particularly limited as long as it is a solution containing a compound soluble in water or a solution containing a carbonate having alkalinity by hydrolysis. For example, monovalent compounds containing hydroxide ions include sodium hydroxide, potassium hydroxide and lithium hydroxide, and divalent compounds include barium hydroxide and calcium hydroxide. Further, examples of the carbonate having alkalinity by hydrolysis include potassium carbonate, sodium carbonate, lithium carbonate and the like. The concentration of the electrolyte solution, which is a high-concentration alkaline aqueous solution, is preferably as high as possible, but is usually preferably 0.1 N or more, more preferably 1 N or more, and most preferably 5 N or more.

Next, the pH of the electrolyte solution during
The alkaline aqueous solution used in the method of measuring the value, continuously or intermittently adding the alkaline aqueous solution according to the measured value, and maintaining the pH value at or above a specified value includes pH.
There is no particular limitation as long as the alkaline aqueous solution has a value of 10 or more. Examples thereof include a solution containing a compound that contains hydroxyl ions and is soluble in water, or a solution of a carbonate or a nitrite that has alkalinity by hydrolysis.

The concentration of the alkaline aqueous solution to be added continuously or intermittently is not particularly limited, but it is added to the electrolyte solution according to the measurement result of the pH value. There is a need to.

As the method of the alkaline aqueous solution to be added continuously or intermittently, a method of adding the aqueous solution continuously or intermittently, a feedback control using a device such as a constant flow rate pump, and a feedforward control May be added continuously or intermittently.

With respect to a device for measuring pH in an electrolyte solution,
There is no particular limitation as long as it is a commercially available general pH meter.

In any of the above methods, in order to maintain the stability of the solution against a sudden change in the pH value,
It is preferable to use a buffer in combination, and examples thereof include boric acid.

As the material of the external electrode to be installed on the concrete surface, ordinary reinforcing steel and metal can be used.
Considering the efficiency and reuse of resources, those having high resistance to electrical corrosion are preferable. Specifically, titanium,
Titanium alloy, platinum and / or metal plated with them, carbon such as carbon fiber and carbon rod, volume resistivity is 10
Organic polymer having conductivity of ³ Ω · cm or less. Titanium and platinum are stable against electric corrosion, and carbon and organic polymers are almost stable. The volume resistivity of ordinary concrete is preferably 10 ³ to 10 ⁴ Ω · cm or less, and most preferably 10 Ω · cm or less.

The shape of the external electrode provided on the concrete surface may be any of a grid, a turtle, a rhombus, a ribbon, a line, a bar, and a sheet, and particularly preferably a grid or a turtle. It is.

As a method of applying an electrolyte solution to concrete, there is a method in which a container for holding the electrolyte solution is provided on the concrete surface, and the electrolyte solution is stored in the container. Further, there is a method of supplying the electrolyte solution to a concrete surface while adsorbing or holding the electrolyte solution to some substance.

Materials for adsorbing or holding the electrolyte solution include fibrous substances such as pulp, cloth and non-woven fabric and sheets thereof, zeolite, shirasu balloons, inorganic and organic porous materials such as foam beads, water-absorbing materials. Organic polymer and the like. Further, a combination thereof or the use of a molded product is preferred.

The current density used is 0.1 A / m
² or more is preferable, and 0.5 A / m ² is more preferable.
Most preferably, it is 1.0 A / m ² or more.

[0020]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these examples. Example 1 As shown in FIG. 1, a cylindrical PVC container 2 was used, and a device in which a disk-shaped concrete specimen 5 cut to a thickness of 30 mm was inserted was used. For the purpose of preventing liquid leakage, the concrete specimen 5 was installed by inserting the PVC container 2 with bolts 8 and nuts 9 and tightening.
As the electrode, a titanium / platinum-plated electrode 6 was set for both the positive electrode and the negative electrode. As the electrolyte solution 3, the positive electrode side was filled with three kinds of liquids, that is, an aqueous solution of lithium hydroxide, an aqueous solution of sodium hydroxide, and an aqueous solution of potassium carbonate. The solution concentration is 0.01% for each electrolyte solution.
The test was carried out for three levels: regulation, 0.1 regulation, and 10 regulation.
The negative electrode side was filled with ion-exchanged water 4 under all conditions.
The electrolyte solution 3 and the ion-exchanged water 4
A rubber lid 10 was provided on the upper part of the PVC container 2 in order to suppress the natural evaporation. A current density of 1.0 A / m ² was used for energization between the ^two electrodes, and the energization treatment was performed for about one month.
The pH value on the positive electrode side during the energization treatment was measured. Table 1 shows the results.

[0021]

[Table 1]

As a comparative example, Experiment Nos. In 1-10,
This was performed under the condition that the positive electrode side was filled with ion-exchanged water as an electrolyte solution. From Table 1, for the aqueous solution in which the solution concentration of the comparative example and the electrolyte solution on the positive electrode side is 0.01 N, the pH value significantly decreases, and after energization for 28 days,
While the pH has dropped to around 1, the solution concentration is 0.1.
Regarding the 1N and 10N electrolyte solutions, the pH value hardly decreased even after energization for 28 days,
By using a high-concentration alkaline aqueous solution as an electrolyte solution from the start of energization, it is possible to suppress a decrease in the pH value of the electrolyte solution.

Example 2 As shown in FIG. 2, fine aggregate 2 was added to 100 parts by weight of cement.
50 parts by weight and 350 parts by weight of coarse aggregate were mixed, and a concrete containing NaCl was mixed at a water-cement ratio of 54% so that chloride ion became 2 parts by weight with respect to 100 parts by weight of cement. Using this concrete, φ1 inside
10cm × 10 incorporating one 3mm deformed reinforcing bar 13
A cm × 40 cm salt-containing concrete specimen 11 was prepared. The surface excluding the lower surface of the prepared salt-containing concrete specimen 11 was subjected to insulation treatment with an epoxy paint 12. The salt-containing concrete specimen 11 is placed on a wooden gantry 15 with the surface on which the epoxy paint 12 is not applied as the lower surface, and set in a container 14 with a space of 5 cm at the lower part. In the space, a titanium / platinum-plated electrode 6 was set as an external electrode. As the electrolyte solution, ion-exchanged water and a 0.01 N aqueous potassium hydroxide solution were used, and the volume of the electrolyte solution was filled to 10 liters. The pH of the electrolyte solution was measured using a KCl-supplemented composite electrode (pH meter manufactured by Yokogawa). The pH value was controlled to 12 or more. Also, pH
As an added alkaline aqueous solution for value control, sodium hydroxide was used, and addition was performed using 5 ml and 1 ml hole pipettes for two kinds of liquid concentrations of 0.1 N and 1 N, respectively. In order to make the diffusion after the addition of the alkaline aqueous solution uniform, a magnetic stirrer 16 was provided at the lower part of the container, and the electrolyte solution was always stirred. The energization treatment was performed at a current density of 0.01 A / dm ² for about one month as in Example 1, and the amount of added alkaline aqueous solution and the pH value during the energization treatment were measured. The addition amount indicates the cumulative addition amount. For example, 50 ml before energization and 96 ml after 10 days means that 46 ml was added after 10 days. Table 2 shows the results.

<Material for Concrete Specimen> Cement: Ordinary Portland cement manufactured by Denki Kagaku Kogyo Co., Ltd. Water: Tap water Fine aggregate: Himekawa-produced sand sand Specific gravity = 2.62 M. = 2.75 Coarse aggregate: crushed stone from Himekawa Specific gravity = 2.65 M. = 6.26 NaCl: purified table salt NaCl purity 99.0%

[0025]

[Table 2]

As a comparative example, ion exchange water was used as the electrolyte solution, and the test was carried out under the condition without pH control.
From Table 2, in the comparative example, chlorine gas was generated due to a decrease in the pH value of the electrolyte solution, thereby changing the working environment and deteriorating the concrete surface. Even if ion-exchanged water or a low-concentration alkaline aqueous solution is used as the solution, no chlorine gas is generated, and deterioration of the concrete surface itself can be prevented.

[0027]

According to the present invention, it is possible to suppress a decrease in the pH value of the electrolyte solution due to energization, and to prevent deterioration of the concrete surface. Also, the pH of the electrolyte solution
By controlling the value to 7 or more, generation of chlorine gas at the time of desalination treatment can be prevented, so that the safety of the working environment can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a test apparatus used in Example 1.

FIG. 2 is a schematic diagram of a test apparatus used in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 PVC container 3 Electrolyte solution 4 Ion exchange water 5 Concrete specimen 6 Titanium / platinum plating electrode 7 Lead wire 8 Bolt 9 Nut 10 Rubber lid 11 Salt-containing concrete specimen 12 Epoxy paint 13 Deformed reinforcing bar 14 Container 15 Wooden stand 16 Magnetic stirrer 17 Stirrer 18 pH electrode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-93682 (JP, A) JP-A-5-148061 (JP, A) JP-A-5-178678 (JP, A) JP-A-5-178678 294758 (JP, A) JP-A-6-24871 (JP, A) JP-A-3-93681 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 40/00-40 / 06 C04B 41/60-41/72 C04B 2/00-32/00 E04G 23/02-23/03

Claims (2)

(57) [Claims] An electrode placed on a concrete surface is used as an external electrode, a steel material inside the concrete is used as an internal electrode, and an electrolyte solution held on the concrete surface is interposed between external electrodes and / or between external electrodes and internal electrodes. The method of applying an electric current by applying an alkaline aqueous solution to the electrolyte solution.
A method for treating concrete, characterized in that the pH value of the electrolyte solution is controlled to 7 or more by being added continuously or intermittently . 2. The method for treating concrete according to claim 1, wherein a high-concentration alkaline aqueous solution is used as the electrolyte solution.