JPH06212814A - Method of recovering concrete - Google Patents

Abstract

PURPOSE:To recover alkalinity in concrete, remove chlorine ions in concrete and protect a reinforcing material in concrete from corrosion by using a reinforcement and PC steel materials as the reinforcing material and flowing currents to the concrete surface and concrete of a reinforced concrete structure, a prestressed concrete structure, etc. CONSTITUTION:Electrodes are installed at the two places or more of a concrete surface and employed as external electrodes, and at least one position or more of the electrodes are used as anodes and the remainder as cathodes. Reinforcements contained in concrete are connected to the cathodes, and DC currents are made to flow among the anodes and the cathodes. Accordingly, DC currents are made to flow while using the internal reinforcements of concrete and parts of the external electrodes of the concrete surface as the cathodes and other external electrodes as the anodes, thus uniformly reducing salt contained in concrete in a treating surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for regenerating concrete, such as reinforced concrete structures and prestressed concrete structures, which uses reinforcing steel or PC steel as a reinforcing material, and in particular, by applying an electric current to the concrete surface and the concrete, Restores alkalinity in concrete,
The present invention relates to a method of removing chlorine ions in concrete and preventing corrosion of a reinforcing material inside the concrete.

[0002]

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

Further, concrete is generally made of water,
Strong resistance to fire and sunlight.

Further, the alkalinity of concrete is p
It is a strong alkaline of H11-14, and a passivation film is formed on the surface of the steel material inside the concrete, and the steel material is protected from corrosion. Therefore, the concrete structure is considered to be a durable permanent structure. Came.

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 structure is questioned.

One of the causes of deterioration of concrete structures is the neutralization of concrete, for example, a phenomenon called "carbonation".

Carbonation is a phenomenon in which calcium hydroxide produced by the hydration reaction of cement reacts with carbon dioxide in the atmosphere to form calcium carbonate. Then, due to this carbonation, the alkalinity of the concrete becomes normal pH.
Lower than 11-14. When the pH is lowered to about 10, the passivation film of the steel material is destroyed, corrosion of the steel material starts, the strength balance of the concrete structure is lost, and its durability is greatly reduced.

Deterioration of a concrete structure such as neutralization of concrete causes phenomena such as rusting of steel material inside the concrete, cracking of concrete, and lack of concrete, and both structurally and externally It is a big issue.

Such a phenomenon of carbonation of concrete is
Other than carbonation, it is also caused by sulfur oxide (SO _X ) and nitric oxide (NO _X ).

In addition, in the concrete structure around the coast, the seawater splashes and adheres to the concrete surface, and the salt contained in the seawater penetrates into the concrete through the voids in the concrete. However, when it comes into contact with the reinforcing bar, there is a problem that the passive film of the steel material is destroyed and corrosion occurs.

Furthermore, 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 mixing the concrete, and As a result, there is a problem that the passivation film formation of the steel material becomes insufficient and corrosion occurs.

[0012] As described above, a phenomenon in which corrosion occurs in a steel material, which further progresses to cracking, chipping, peeling, etc. of concrete and greatly deteriorates durability as a concrete structure is generally referred to as "salt damage". I am calling.

The method of repairing a concrete structure deteriorated by "salt damage" is to remove the concrete around it for rust of steel materials and "crack" the concrete for cracks and missing parts of the concrete. ,
Filling with new concrete or mortar, so-called
The section restoration method was the main method.

This cross-section restoration method repairs only visible deterioration phenomena such as rusting of steel materials and cracking and lack of concrete, and the deterioration phenomenon cannot be confirmed at the time of repair, that is, latent Concretely, the deterioration of concrete is progressing, but on the surface, the deterioration is not manifested, and so-called dangerous parts could not be treated at all.

Further, this construction method does not take any measures for the root cause of deterioration of concrete,
A fundamental solution to the deterioration phenomenon was not expected.

[0016] For the purpose of solving such a problem of the potential dangerous portion and fundamentally solving the deterioration phenomenon, a repairing method applying an electrochemical method or a concrete reinforcing bar is used as a cathode to electrically prevent corrosion. A construction method is disclosed (JP-A-1
-176287).

However, in these methods, since only the reinforcing steel of concrete is used as a cathode and a direct current is passed,
The processing area in the depth direction is limited from the surface to the vicinity of the internal rebar,
Furthermore, there is a problem that the treatment effect between the internal reinforcing bars deteriorates because the current density decreases as the distance from the reinforcing bars increases.

In order to overcome this problem, it has been proposed to install a plurality of external electrodes on the surface of concrete and use the external electrodes as a cathode and an anode.

However, with this method, the treatment area can be expanded, but since the electrodes are installed only on the concrete surface and the internal rebars are kept in an electrically floating state, corrosion of the internal rebars is prevented. There was a problem such as the risk of causing it.

The present inventor has made various studies in order to solve the above problems in view of such circumstances, and as a result, by adopting a specific method, the above problems can be solved and the concrete structure can be sufficiently repaired. The present invention has been completed based on the knowledge obtained.

[0021]

That is, according to the present invention, electrodes are provided at two or more locations on a concrete surface to serve as external electrodes, at least one location of the electrodes is used as an anode, and the rest is used as a cathode. A method for recycling concrete is characterized in that a rebar is connected to the cathode and a direct current is passed between the anode and the cathode.

The present invention will be described in detail below.

Generally, inside hardened concrete,
A sufficient amount of aqueous solution containing calcium hydroxide or sodium hydroxide is present. Therefore, when a voltage is applied to the concrete, this aqueous solution acts as an electrolyte and a current flows according to the resistance of the concrete itself and the applied voltage. If only the reinforcing material such as the reinforcing bar inside the concrete is used as the cathode, the treatment area is limited. Also,
If the electrodes are installed only on the concrete surface, there is a risk that corrosion will occur in the reinforcing material of the reinforcing bar inside the concrete.

According to the present invention, a cathode installed outside the concrete and a reinforcing material inside the concrete are provided in order to expand the treatment area in the concrete and increase the treatment efficiency and prevent corrosion of the internal reinforcing bars during the treatment period. It is a method of electrically connecting and processing.

That is, two kinds of electrodes, an anode and a cathode, are installed on the surface of concrete, the cathode and the reinforcing material inside the concrete are electrically connected, and a direct current is passed.

First, the electrodes used in the present invention will be described.

The anode provided on the surface of the concrete can be used as a rebar mesh or a wire mesh, but since it has an electrical corrosion action, it is effective in terms of resource utilization and reuse, and therefore has a resistance to electrical corrosion. It is preferable to use those having high properties.

Specifically, titanium, titanium alloys, platinum or metals plated with platinum, carbon such as carbon fibers and carbon rods, and conductivity having a volume electric resistivity of 10 ³ Ω · cm or less. Organic polymers and the like.

Titanium and platinum are stable against electrical corrosion, and carbon and organic polymers are almost stable.

Since the volume resistivity of ordinary concrete is about 10 ³ to 10 ⁴ Ω · cm, the volume resistivity of the conductive organic polymer is preferably 10 ³ Ω · cm or less. , 10 ² Ω · cm or less is more preferable, and 10 Ω · cm or less is most preferable.

Further, since the cathode does not have an electric corrosion effect, it is possible to use not only the material used for the anode but also a conductive material other than that.

The method of installing the electrodes and the distance between the electrodes are not particularly limited, but it is necessary to install so that the effective current flowing through the concrete flows widely. When the concrete has a polygonal shape or a circular shape, it is preferable to install the anode and the cathode on the surfaces facing each other as much as possible. As a specific example, the case of a concrete wall or the like will be described, but the present invention is not limited thereto.

In the case of a concrete wall, it is preferable to provide a cathode on one surface and an anode on the other surface so as to sandwich the wall. In the case of a prism, one or more surfaces have an anode and the other surface has another surface. It is preferable to provide a cathode. In the case of a floor, it is preferable to provide an anode on the upper surface and a cathode on the lower surface. In either case, it is possible to install the electrodes on the contrary, but it is necessary to electrically connect the cathode of the external electrode and the reinforcing bar as a reinforcing material inside the concrete.

Here, the term “reinforcing bar” refers to round steel, deformed reinforcing bar, PC steel bar, or the like.

According to the present invention, it is possible to treat the electrodes installed on the surface and prevent rusting of the internal reinforcing bars existing between the surface electrodes.

Further, in the present invention, it is preferable to allow the electrolyte solution to exist around the electrodes placed on the surface of the concrete because the electric current easily flows.

Here, a preferable electrolyte solution is
Although it is an alkaline solution or a neutral solution, a weakly acidic solution having a pH of 5 or more can also be used.

Examples of sources of alkali ions in the alkaline solution include various alkali salts such as alkali metal salts such as sodium and potassium and alkaline earth metal salts such as calcium and magnesium. Of which
It is preferable to use salts of calcium, lithium, magnesium, aluminum, etc., which are less likely to promote the alkaline aggregate reaction.

Furthermore, it is preferable to use a corrosion inhibitor together with the electrolyte solution of the present invention.

The corrosion inhibitor is usually called a rust preventive agent, and is a substance that remarkably reduces metal corrosion when used together in a corrosive environment.

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

In the present invention, among these corrosion inhibitors, alkaline, neutral, and weakly acidic ones having a pH of 5 or more can be used, but the influence on the physical properties of concrete is small, for example, the use of an inorganic corrosion inhibitor is preferable. Preference is given to the use of nitrite.

Those which become ions when dissolved in water are
It is preferable because it electrically penetrates into concrete.

Next, a method for allowing the electrolyte solution to exist on the concrete surface will be described.

As a method of allowing the electrolyte solution to exist on the concrete surface, generally, a method of providing a container for holding the electrolyte solution on the concrete surface and storing the electrolyte solution therein can be considered.

However, considering that not only the surface of the concrete faces upward horizontally but also the vertical surface and the ceiling surface, it is difficult to provide a container for storing the electrolyte solution which is a liquid without leaking.

Therefore, a method of adsorbing or holding the electrolyte solution on some substance to form an electrolyte solution holding layer and supplying it to the concrete surface is more preferable. According to this method, it is possible to allow the electrolyte solution to sufficiently exist on the concrete surface not only in the horizontal upward direction but also in the vertical surface or the ceiling surface.

An electrolyte solution holding material is used to form an electrolyte solution holding layer that adsorbs or holds an electrolyte solution.

Materials for the electrolyte solution holding material include fibrous substances such as pulp, cloth, and non-woven fabric or a sheet thereof, inorganic or organic porous materials such as zeolite, shirasu balloon, and foam beads, and water-absorbing materials. Examples thereof include organic polymers and the like, or a combination thereof.

Among them, the sheet of fibrous material is preferable because it can be used simply by fixing it to the concrete surface with nails or squares. Further, by processing the sheet surface, evaporation or freezing of the electrolytic solution is prevented. It is possible to prevent it.

When the fibrous substance or the porous material is installed as an electrolyte holding material on the surface of concrete, the electrolyte solution holding layer can be formed by spraying it with water or an electrolyte solution regardless of the surface shape of the concrete.

When the electrolyte holding material is used, it is possible to add a component that increases the adhesiveness or tackiness, a thickener, etc. in order to improve the adhesiveness.

As the water-absorbing organic polymer, for example, polyacrylic acid-based ones can be mentioned, and like the porous material, by spraying, an electrolyte solution holding layer is formed on the concrete surface, or a non-woven fabric or the like. It is possible to form a sheet with.

Further, it is possible to calculate the amount of water evaporated from the electrolyte solution during the construction period and make the electrolyte solution holding material absorb water in advance to reduce the amount of water supply work during the construction. .

[0055]

EXAMPLES The present invention will be further described below based on examples.

Example 1 Cement 280 kg / m ³ , water 168 kg / m ³ , fine aggregate 860 kg / m ³ , coarse aggregate 1,002 kg / m ³ , AE water reducing agent 0.7 kg / m ³ , and sodium chloride 10 kg / m ^The concrete was adjusted using the concrete mixture of ³ and a deformed rebar having a nominal diameter of 19 mm was embedded at a distance of 30 cm at a depth of 7.5 cm, and a concrete test body of 120 cm in length, 120 cm in width, and 15 cm in thickness was prepared. . Attach a sponge with a thickness of 20 mm to one side of the prepared concrete test body,
The titanium mesh was placed in the center, and a sponge with a thickness of 20 mm was attached to the opposite surface so that the rebar mesh was placed in the center. Each sponge was supplemented with a 1N lithium nitrite aqueous solution so as to always keep a wet state. Next, using titanium mesh as the anode and the reinforcing steel mesh and the reinforcing steel inside the concrete as the cathode, the concrete surface area of 1 m ²
A direct current was passed for 4 weeks so that the current would be 1 A. As a result, the amount of salt in the concrete decreased uniformly on the surface of the concrete, becoming 1/10 of the original amount. After the treatment, when the state of the internal reinforcing bars of the concrete test body was inspected, the internal reinforcing bars were covered with the passive film. Furthermore, in the concrete test body, nitrite ions from the reinforcing steel mesh side that is the cathode, and lithium ions electrically permeate from the titanium mesh side that is the anode. The higher ion concentration has improved the effect of suppressing the alkali-silica reaction and the anticorrosive effect of deformed reinforcing bars.

<Materials used> Cement: Denki Kagaku Kogyo Co., Ltd., ordinary Portland cement Water: Tap water Fine aggregate: Himekawa produced river sand Coarse aggregate: Himekawa produced crushed stone, Gmax = 20mm AE Water reducing agent: MMB Product name: Pozzolith N
o.70 ”Sodium chloride: Wako Pure Chemical Industries, Ltd., first-grade reagent Lithium nitrite: Nissan Chemical Industries, Ltd. Titanium mesh: Eltec Corporation, trade name“ Elgard mesh # 210 ”Reinforcing bar mesh: nominal diameter 3 mm Welded rebar at 5 cm intervals

Comparative Example 1 The procedure of Example 1 was repeated except that only the internal reinforcing bars of the concrete test body were used as the cathode. As a result, the amount of salt in the concrete sandwiched between the titanium mesh and the internal rebar was 1/10 of the initial value in the area of less than 10 cm centering on the internal rebar, but 10% centering on the internal rebar.
In the area from 15 cm to 15 cm, there was only a decrease to 1/8 of the initial value. Further, the salt content from the surface where the titanium mesh was not installed to the internal rebar was hardly reduced.

Comparative Example 2 The same procedure as in Example 1 was carried out except that only the reinforcing bar mesh installed on the surface of the concrete test body was used as the cathode. As a result, the salinity concentration decreased uniformly within the surface of the concrete test body and became 1/10 of the initial value, as in Example 1. After the completion of the treatment, when the internal reinforcing bars of the concrete test body were examined, rusting of several centimeters was observed at several places.

[0060]

INDUSTRIAL APPLICABILITY According to the present invention, since a direct current is caused to flow by using the internal rebar of concrete and a part of the external electrode on the concrete surface as a cathode and the other external electrodes as an anode, corrosion of the internal rebar due to the treatment current does not occur It is possible to uniformly reduce the salt content contained in concrete within the treated surface. In addition, since both positive and negative cations useful for concrete can be electrically permeated into the interior of the concrete, it is possible to improve the concrete.

Claims (1)

[Claims] 1. An electrode is provided at two or more locations on a concrete surface to serve as an external electrode, at least one location of the electrode is used as an anode, and the rest is used as a cathode. Reinforcing rods contained in concrete are connected to the cathode. A method for recycling concrete, characterized in that a direct current is passed between the anode and the cathode.