JPH05178678A - Method for repairing concrete - Google Patents

Abstract

PURPOSE:To provide a method for repairing a reinforced concrete structure wherein reinforcing steel and PC steel are used as the reinforcing material and a prestressed concrete structure especially a concrete structure which has been deteriorated by incorporating salt into concrete. CONSTITUTION:Steel in the inside of concrete containing chlorine ions is made to an inner electrode. An electrode provided on the surface part of the concrete is made to a surface electrode. An alkaline or neutral electrolyte solution containing a corrosion retarder is made present between the concrete and the surface electrode. DC current is allowed to flow between the inner electrode and the surface electrode. When the method is used, chlorine ions are removed from a concrete structure subjected to salt damage. Therefore, formation of the passive film of steel is enabled again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for repairing a reinforced concrete structure and a prestressed concrete structure having reinforcing bars or PC steel as a reinforcing material, and in particular, repairing a concrete structure deteriorated by containing salt in concrete. Regarding the method.

[0002]

2. Description of the Related Art Concrete structures such as reinforced concrete structures and prestressed concrete structures are mechanically balanced by combining concrete with high compressive strength and steel with high tensile strength. The resulting structure has been widely used in a variety of important structures.

Further, concrete has a strong resistance to the environment such as water, fire, and sunlight, and since the alkalinity of concrete is 11 to 14 at pH, the surface of the steel material inside the concrete has a passivation film. Formation, the steel is protected from corrosion, which is why concrete structures have been considered to be durable permanent structures.

However, the durability of the concrete structure, which has been considered to be the permanent structure, is lowered due to various causes, and the life of the concrete structure is questioned.

One of the causes of deterioration of concrete structures is the phenomenon of concrete salt damage. In general, when seawater splashes onto a concrete structure on the coast and adheres to the concrete surface, salt contained in seawater penetrates into the concrete through voids in the concrete. Then, when that portion reaches the position of the internal rebar, the immobilizing body coating of the steel material is broken by the chlorine ions and corrosion occurs. Also, when sea sand is used as the fine aggregate used as a concrete material, if the salt removal is insufficient, a large amount of chloride will be contained from the time of concrete production, and the immobilization film formation of steel will occur. Is insufficient and corrosion occurs.

Corrosion occurs in the steel due to the above reasons,
The phenomenon in which the crack develops, cracks, peels off, etc. of concrete and greatly deteriorates the durability as a concrete structure is generally called "salt damage".

As a general method for repairing a concrete structure deteriorated by such salt damage, the rust of the steel material is the surrounding concrete, and the cracked or missing part of the concrete is the concrete of the part.
The main purpose was to repair so-called cross-sections, which consisted of removing "chips" and then filling them with new concrete or mortar.

This cross-section restoration is a repair only for visible deterioration phenomena such as rust of steel materials and cracking or loss of concrete, and a part where deterioration phenomena cannot be confirmed at the time of repair, that is, potentially of concrete. No treatment could be performed on the dangerous part where the deterioration is progressing but is not apparent on the surface.

In addition, this method does not take any measures against the fundamental cause of deterioration of concrete, and a fundamental solution to the deterioration phenomenon could not be expected.

A repairing method using an electrochemical method has been proposed for the purpose of solving the problems of such a potentially dangerous portion and the problems of the root cause (Japanese Patent Laid-Open No. 302384/1990).

In this repair method, hydroxides of sodium, potassium, and calcium are used as electrolytes between the steel material in the concrete portion damaged by salt and the electrodes on the concrete surface, and a direct current is passed through the electrolyte. ,
This is a method to reduce the salt concentration inside the concrete by electrically attracting chlorine ions existing inside the concrete to the concrete surface.

However, in this method, chlorine ions move to the surface of the concrete and cations sodium, potassium, and calcium move to the inside of the concrete.

Since the use of sodium or potassium hydroxide as the electrolyte promotes the alkali-aggregate reaction, even if the deterioration phenomenon due to salt damage is solved, another deterioration phenomenon called the alkali-aggregate reaction is newly introduced. The purpose of improving the overall durability of the concrete structure is not achieved.

In addition, when calcium hydroxide is used, there is no problem in the alkaline aggregate reaction, but the concrete structure is placed even in the concrete in which the salt content is removed with calcium hydroxide. Since the environmental conditions do not change, it will eventually suffer salt damage over time, at which point the steel inside the concrete will start to rust again and there will be a problem that requires similar repairs. Couldn't be.

On the other hand, there has been proposed a method of preventing corrosion of a steel material by applying nitrite or the like to deteriorated concrete in order to prevent rusting of the steel material inside the concrete (JP-A-60-231478).

However, nitrite and the like cannot penetrate into the concrete simply by coating it on the concrete, and the result is that the effect of the nitrite and the like is poor in the end.

As a result of various studies to solve the above problems, the present inventors solved the problems by adopting a specific method, and sufficiently repaired a concrete structure containing chlorine ions inside. The knowledge that can be obtained has been obtained, and the present invention has been completed.

[0018]

Means for Solving the Problems That is, according to the present invention, a steel material inside concrete containing chlorine ions is used as an internal electrode, an electrode installed on the surface of the concrete is used as a surface electrode, and between the concrete and the surface electrode. A method for repairing concrete containing chlorine ions, characterized in that an alkaline or neutral electrolyte solution containing a corrosion inhibitor is present and a direct current is passed between the internal electrode and the surface electrode.

The present invention will be described in detail below.

Generally, inside hardened concrete,
Sufficient interstitial water, which is a saturated calcium hydroxide aqueous solution, is present. Therefore, when a voltage is applied to the concrete, the pore water acts as an electrolyte and a current flows according to the resistance of the concrete itself and the applied voltage.

However, in order to make the current flow easier,
Alternatively, it is necessary to apply an electrolyte solution in order to flow the electric current more uniformly.

By passing an electric current through the concrete holding the electrolyte solution, the salt content in the concrete gradually moves to the outside of the concrete, but conversely, the electrolyte moves to the inside.

The electrolyte solution according to the present invention is an alkaline solution or a neutral solution. Usually, since the surface area of the target concrete structure is large, a large amount of alkali is required in the alkaline electrolyte solution, and it is necessary to pay attention to the health effects and storage when using the solution. The use of a polar electrolyte solution is preferred.

Here, the neutral electrolyte solution has a pH of 6
It is a solution of 10 or more. If the pH is less than 6, there is a risk that components in the hardened cement will elute and the concrete structure will collapse, and if the pH is 10 or more, care must be taken as an alkali for handling. Further, for the purpose of the present invention, pH
Even if the solution is 6 or more and less than 10, a solution containing chlorine is not preferable.

Examples of the alkali salt in the electrolyte solution include various alkali salts, for example, alkali metal salts such as sodium and potassium, alkaline earth metal salts such as calcium and magnesium, and sodium and potassium salts. However, it is not preferable because it may promote the alkali-aggregate reaction, and the use of salts such as calcium, lithium, magnesium, and aluminum is preferable. Also, ammonia or the like can be used. Further, water added with an electrolyte agent such as glycerin or ethylene glycol can also be used.

The corrosion inhibitor according to the present invention (Corrosion inhib
Itor) is usually called a rust preventive agent, and is a substance that remarkably reduces metal corrosion when added in a corrosive environment.

As the corrosion inhibitor, inorganic compounds such as nitrite, chromate, silicate and phosphate, and
Examples of the organic system include organic phosphates, ester salts, organic acids, sulfonic acids, amines, alkylphenols, mercaptans, and nitro compounds.

In the present invention, these corrosion inhibitors are adjusted to a suitable pH with hydroxides or carbonates of calcium, lithium, magnesium, aluminum, ammonia, etc., and among the above corrosion inhibitors. Although alkaline or neutral ones can be used, it is preferable to use ones that have little effect on the physical properties of concrete, for example, inorganic ones, and particularly preferable to use nitrites. Of these, calcium nitrite, which has a corrosion inhibiting effect, is usually
Since it is difficult to use it for concrete repair by kneading it together with cement because it causes pseudo-setting of cement when kneading with cement, the method of the present invention causes such a problem because it is directly used for hardened concrete. Absent. Further, from the viewpoint of suppressing the alkali-aggregate reaction, lithium, calcium, magnesium, aluminum salts and the like are preferable as the salt. As a specific example, the product name "LN-25" manufactured by Nissan Chemical Industries, Ltd. may be mentioned. The amount of the corrosion inhibitor used varies depending on the type of the corrosion inhibitor used and the length of the energizing time, but normally, the concentration of the corrosion inhibitor contained in the electrolyte aqueous solution is preferably 0.01 to 10 mol / liter, and 0.1 to 5 mol / liter. L is more preferred. If it is less than 0.01 mol / liter, the effect of suppressing corrosion is poor even if the energization time is lengthened, and if it is used in excess of 10 mol / liter, improvement of the effect cannot be expected.

The present invention is a method of forcibly permeating an electrolyte solution given to the surface of concrete into the inside of the concrete while utilizing the phenomenon of "electric induction" of the liquid. Electrode (+)
Is attracted to and moves from inside to outside.

At this time, the diffusion rate of chlorine ions in the hardened cement product is generally several to ten times higher than the diffusion rate of cationic ions such as alkali metal ions. Even if it moves to the inside, chlorine ions easily move to the outside.

Therefore, by simply applying the corrosion inhibitor to the concrete, the electric "force" of electric induction of the liquid is generated rather than the conventional method of relying on the moisture absorption of the concrete or the capillary phenomenon to permeate the inside. It can be understood that the present invention in which the electrolyte solution is forcibly moved by utilizing the present invention is more effective.

In the present invention, the electric current flowing between the electrodes is preferably 0.5 to 10 A, and 0.75 to 7.5 A per 1 m ^{2 of} concrete surface area.
Is more preferable, and 1-5A is the most preferable.

As a method for applying the electrolyte solution used in the present invention to concrete, a container for holding the electrolyte solution is provided on the concrete surface, and the electrolyte solution is stored in the container, or the electrolyte solution is stored in pulp or pulp. Examples thereof include a method of adsorbing it on an adsorbent such as cloth, or holding it.

By the above method, an electric current is applied to the concrete containing chlorine ions to allow the electrolyte solution to penetrate into the concrete, and the chloride ions inside are guided to the outside to remove chloride from the concrete. It becomes possible to eliminate the phenomenon of "salt damage" by re-forming the immobile body coating of the steel material inside.

Further, by using the corrosion inhibitor in the electrolyte solution, the corrosion of the steel material is suppressed even when a large amount of chloride again invades the concrete structure once repaired,
The rust phenomenon can be prevented, and as a result, the damage caused by salt damage can be stopped.

[0036]

EXAMPLES Hereinafter, description will be given based on examples of the present invention.

Example 1 Normal cement / sand was 1/2, water / cement ratio was 60%, and sodium chloride was 1.5 with respect to 100 parts by weight of cement.
Using a mortar containing parts by weight, the cover thickness is 2 cm
A steel rod having a diameter of 10 mm was installed at the center of the cylinder to prepare a cylindrical body having a diameter of 5 cm and a height of 10 cm. This column was subjected to room curing at 20 ° C. and 80% RH until the 28th day of age, and then the upper and lower surfaces of this column were coated with an epoxy paint to electrically insulate them to obtain a test body. The amount of sodium chloride contained in this test body is 1,650 mg. This test piece is shown in FIG.
As shown in (3), it was immersed in an electrolyte solution of 0.5 mol / liter of lithium nitrite, and a direct current having a current density shown in Table 1 was flown for 4 weeks in an electric device. The electrolyte solution was 2 liters for each test body, and distilled water was added every week for the amount of evaporated water. At the end of energization, the concentration of chloride ions eluted in this electrolyte solution was analyzed and the weight of NaCl removed from the test body was calculated. The results are shown in Table 1. Similarly, for 8 weeks,
Table 1 also shows the results when a direct current having a predetermined current density was applied.

<Materials used> Cement: Ordinary Portland cement, sand produced by Denki Kagaku Kogyo Sand: Himekawa production sand bar Steel bar: Polished steel bar Lithium nitrite: Nissan Chemical Co., Ltd. trade name “LN-2
5 ", pH = 11.5, 25% solution Sodium chloride: Wako Pure Chemical Industries, Ltd., reagent grade 1

[0039]

[Table 1]

In Table 1, the current density indicates the amount of current per surface area excluding the part insulated by the paint in the part of the test body immersed in the electrolyte solution.

Example 2 The kind of electrolyte solution was changed as shown in Table 2, and the current density was changed.
Using a test body containing 1.5 A / m ² and the same chloride as in Example 1, a direct current was applied for 6 weeks to remove most of the salt content and to allow the electrolyte solution to permeate the test body. .. After that, the test sample was placed in a salt water spray device using natural sea water, and salt water at 20 ° C was sprayed for 6 hours, followed by warm air drying at 60 ° C for 6
The spray-drying was repeated for 3 months. Three
After a month, the test piece was split and the rust condition of the polished steel rod inside was observed. The results are also shown in Table 2.

<Materials to be used> Calcium nitrite: manufactured by Nissan Kagaku Kagaku Kogyo Calcium hydroxide: manufactured by Wako Pure Chemical Industries, Reagent 1st grade

[0043]

[Table 2]

Example 3 An aqueous calcium nitrite solution was used as a corrosion inhibitor, the concentration was changed as shown in Table 3, and the current density was 2.0 A / m ^2.
The same procedure as in Example 2 was performed except for the above, and the rust condition of the polished steel rod inside the test body was observed. The results are also shown in Table 3.

[0045]

[Table 3]

Example 4 Wall of a room for storing rock salt made of reinforced concrete, which is about 10 years old and has a considerable salt content in concrete and is 2.5 m in height, 10 m in length, and 25 cm in thickness. Was tested. For salinity measurements, this wall was cored at 1.5 m intervals, samples were taken and analyzed. Further, this concrete was partially suspended, and the reinforcing steel inside the concrete was used as an internal electrode.Furthermore, a mesh with a nominal distance of 10 mm was formed on the surface of the concrete with a spacing of 15 cm and fixed to this wall, and an aqueous solution of lithium nitrite was contained. The remaining paper pulp was sprayed on the wall where the mesh was fixed to form an external electrode. Between this internal electrode and external electrode, the current density
A 1.25 A / m ² direct current was applied for 2.5 months to electrically permeate the electrolyte solution into the concrete and remove chlorine ions inside. After 2.5 months, remove the external electrodes and paper pulp on the concrete surface, and put the concrete wall to 1.so that the position of the first coring is in the middle of the gap.
As a result of coring at 5 m intervals and taking out concrete samples, and analyzing the amount of chlorine contained therein, the chlorine content in all concrete samples was 1/1 of the average value in the initial state before electrification work. It was confirmed that the number was reduced to 3 or less. Therefore, it became possible to make concrete damaged by salt damage sound.

[0047]

EFFECTS OF THE INVENTION By using the method of the present invention, chlorine ions can be removed from a concrete structure damaged by salt.
It is possible to re-form an unmoving film of steel. Therefore, it is possible to almost completely restore the durability of the concrete structure that is formed by combining the concrete and the steel material. In addition, since the concrete structure whose durability has been restored does not change the environmental conditions in which the structure is placed, the immobile body coating of steel is retained even for concrete in which chlorine ions have infiltrated again. It is possible to prevent the phenomenon of salt damage deterioration starting from rusting, and it is possible to provide a highly reliable repairing method that has never existed before.

[Brief description of drawings]

 FIG. 1 shows a method of passing a current when used in a test. Reference numeral 1: Polished steel bar 2: Hardened mortar 3: Container 4: Electrolyte solution 5: Surface electrode of concrete 6: DC power supply 7: Variable resistor 8: Ammeter

Claims (1)

[Claims] 1. A steel material inside concrete containing chlorine ions is used as an internal electrode, an electrode installed on the surface of the concrete is used as a surface electrode, and an alkaline or neutral corrosion inhibitor is contained between the concrete and the surface electrode. 2. A method for repairing concrete containing chlorine ions, characterized in that the electrolyte solution is present and a direct current is passed between the internal electrode and the surface electrode.