JPH06200636A - Recovery treatment of deteriorated concrete - Google Patents

Abstract

PURPOSE:To recover and treat concrete deteriorated by lowering of alkalinity or neutralization by making steel materials in concrete as the inside electrode to supply electric current into the concrete at specific current density. CONSTITUTION:Steel materials such as reinforcing bars or PC steel materials, etc., existing in concrete as the inside electrode are constituted of materials having high resistance against electrical corrosion, and an electrode provided to the surface of the concrete are the outside electrode. Electric current density per surface area of the concrete is 0.5A/m<2>, and electric current is made to flow so that current density per surface area of the steel materials of the inside electrode is less than 10A/m<2>. Pore water in the concrete plays a part of electrolyte, current by resistance possessed by the pore water and applied voltage flows, and various kinds of ion are moved. In order to supply current easily to the concrete, alkaline electrolytic solution is supplied, if necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering deteriorated concrete from a reinforced concrete structure or a prestressed concrete structure using reinforcing steel or PC steel as a reinforcing material, and in particular, it is neutralized by decreasing the alkalinity of the concrete. The present invention relates to a method for recovering concrete structure or concrete deteriorated by salt damage.

The concrete in the present invention means
It is a generic term for cement paste, mortar, and concrete.

[0003]

2. Description of the Related Art Concrete structures such as reinforced concrete structures and prestressed concrete structures are mechanically balanced by combining concrete having high compressive strength and steel having high tensile strength. It has a well-structured structure, and thus has been widely used for various important structures.

Further, the alkalinity of concrete is pH.
Being strongly alkaline of 11-14, the steel material inside the concrete is protected from corrosion by forming a passivation film on its surface, which makes the concrete structure a durable permanent structure. Has been considered.

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, for example, a phenomenon of carbonation of concrete called "carbonation" and a phenomenon called salt damage.

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. Due to carbonation, the alkalinity of concrete is normal. pH lower than 11-14. When the pH drops to about 10, the steel film that has been formed up to that point is destroyed, corrosion of the steel begins, and the balance between compressive strength and tensile strength as a concrete structure collapses, and its durability Will be greatly reduced.

The deterioration of such a concrete structure is caused by
It causes the phenomenon of rust of steel inside concrete, cracking of concrete, and lack of concrete,
It is a major issue both structurally and in appearance.

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

Further, in many cases, seawater splashes fly to the concrete structures around the coast and adhere to the concrete surface. Then, the salt content contained in the seawater penetrates into the concrete through the voids in the concrete, and when it reaches the position of the internal rebar, the salt destroys the steel immovable body film and causes corrosion. To do.

When sea sand is used as the fine aggregate used as the concrete material, if the salt removal is insufficient, a large amount of chloride will be contained from the time the concrete is made, and As a result, the immobilization film of the steel material is insufficiently formed and corrosion occurs.

Due to the above-mentioned causes, corrosion occurs in steel materials, further progresses to cracking, chipping, peeling, etc. of concrete, and the durability as a concrete structure is greatly reduced. I am calling.

As a method for repairing concrete deteriorated due to such neutralization and salt damage, a direct current is passed through the concrete to allow an alkaline solution to permeate into the concrete or to remove chlorine ions or the like from outside the concrete. There has been proposed a repairing method using an electrochemical method, such as moving to another location (JP-A-1-176287, JP-A-2-302384).

However, when a direct current is applied to the concrete by using these methods, the effect becomes more remarkable as the current applied to the concrete is increased in order to move the alkaline solution and chlorine ions. However, the interstitial water in the concrete is electrolyzed, and hydrogen gas is generated around the steel material inside the concrete that serves as the internal electrode and the cathode. As a result, there is a problem that the generated gas pressure causes cracks in the concrete and hydrogen embrittlement in the steel material.

Moreover, the larger the current value, the more
These problems were remarkable.

Further, in order not to generate these gases,
There is also a method of suppressing the voltage applied to concrete to a low level, but reducing the voltage reduces the current density, which has the adverse effect of reducing the effect of moving the alkaline solution, chloride ions, and the like.

As described above, the effect of preventing cracking of concrete and the effect of moving an alkaline solution or chlorine ions are contradictory, and a technique that makes them compatible has been urgently desired.

As a result of various studies to solve the above-mentioned problems, the present inventor found that not only the concrete surface area around the external electrode but also the surface area of the steel material of the internal electrode has an appropriate current density. It was found that a stable effect can be obtained by passing an electric current through, and the present invention has been completed.

[0019]

[Means for Solving the Problems] That is, the present invention is that the steel material inside the concrete is the internal electrode, the electrode installed on the surface of the concrete is the external electrode, and the current density per surface area of the concrete is 0.5 A / m ² or more. The method for recovering deteriorated concrete is characterized in that an electric current is applied so that the electric current density per surface area of the steel material of the internal electrode is 10 A / m ² or less.

The present invention will be described in detail below.

Generally, inside hardened concrete,
Sufficient interstitial water, which is a saturated aqueous solution of calcium hydroxide, 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.

Since various ions such as alkaline solution and chlorine ions are eluted in the pore water in the concrete,
It is possible to move them by passing an electric current.

As the internal electrode according to the present invention, a steel material existing in concrete, particularly a reinforcing bar, a PC steel rod or a sheath can be used. Usually, these are assembled in a basket shape or a mesh shape, and thus the internal electrodes may also be in a basket shape or a mesh shape. Furthermore, when there are a plurality of internal electrodes assembled in a mesh shape, it is possible to energize only one internal electrode or energize a plurality of internal electrodes.

The external electrodes according to the present invention are generally positive electrodes.
Since it is the (+) side, an electrical corrosion action works. In the present invention, since the period in which an electric current is applied is relatively short, it is possible to use ordinary reinforcing bars, wire mesh, etc., but considering the effective use and reuse of resources, the use of those with high resistance to electrical corrosion Is preferred. Specifically, titanium, titanium alloys, platinum, or other metals plated therewith, carbon such as carbon fibers or carbon rods, and organic high organic materials having a volume electric resistivity of 10 ³ Ω · cm or less. Molecule, etc. Of these,
Titanium and platinum are preferable because they are stable against electrical corrosion. Also, carbon and organic polymers are almost stable.
Note that the volume resistivity of ordinary concrete is 10 ³ to 1
Since it is about 0 ⁴ Ωcm, the organic polymer having conductivity is preferably less than that value, that is, 10 ³ Ωcm or less,
It is more preferably 10 ² Ω · cm or less, most preferably 10 Ω · cm or less.

In the present invention, in particular, the external electrode can be installed at all times, but it is easy to remove it immediately after the recovery process of the deteriorated concrete is finished and to install it again as needed. It is possible.

In the present invention, the current applied to the concrete is 0.5 A or more, preferably 0.75 A or more, and more preferably 1.0 A or more, per 1 m ² of the surface area of the concrete in the range of the current application. If it is less than 0.5 A, the effect of migrating various ions in concrete, especially chlorine ions, is poor.
In terms of moving the ions, the larger the current value is, the greater the effect of moving the ions is. Therefore, there is no upper limit of the current value at this time.

On the other hand, the amount of hydrogen gas generated around the steel material inside the concrete is related to the magnitude of the current density with respect to the surface area of the steel material. The greater the current density, the greater the amount of gas generated.

Therefore, in the present invention, the value of the electric current passed through the concrete is 10 A or less, preferably 8.0 A or less, and more preferably 7.0 A or less, per 1 m ² of the surface area of the steel material of the internal electrode. If the current density exceeds 10 A, concrete may crack or the adhesion strength may decrease.

As described above, in the present invention, the upper limit of the current value flowing between the inner electrode and the outer electrode is determined by the upper limit value of the current with respect to the surface area of the steel material of the inner electrode, and the lower limit is the surface area of the concrete around the outer electrode. Is determined by the lower limit of the current for.

Further, in the present invention, it is preferable to supply an electrolyte solution to the concrete in order to facilitate the flow of electricity into the concrete.

The preferred electrolyte solution here is
Although it is an alkaline solution, a solution in a neutral range can be used, and tap water, well water, river water, etc. can also be used.

Examples of the alkali ion in the alkaline solution include various alkali salts, for example, alkali metal salts such as sodium and potassium, alkaline earth metal salts such as calcium and magnesium, calcium, lithium, and The use of magnesium salts is particularly preferred. It is also possible to use aluminum salts.

Further, in the present invention, in order to easily supply the electrolytic solution to the concrete, it is preferable to bring the electrolytic solution into contact with the concrete and hold it.

As a method of holding the electrolyte solution, a method of providing a container for holding the electrolyte solution on the concrete surface and storing the electrolyte solution therein can be used. Further, a method of using an electrolyte solution holding material that adsorbs or holds an electrolyte solution can also be used. This method
This is a preferable method in that not only horizontal upper and lower surfaces but also vertical surfaces can sufficiently supply the electrolyte solution to the concrete surface.

Here, as the material for adsorbing or holding the electrolyte solution, fibrous substances such as pulp, cloth, and non-woven fabric, inorganic and organic porous materials such as zeolite, shirasu balloon, and foam beads, and , Water-absorbing organic polymers and the like. Further, it is preferable to use a combination thereof or a molded product.

When a fibrous substance is used, the electrolyte solution holding material can be installed on the concrete surface by spraying or painting. It is also possible to process it into a panel or sheet and use it. The electrolyte solution holding material in the form of a panel or sheet can be used simply by fixing it to the concrete surface with nails or square timbers. further,
It is also possible to prevent evaporation or freezing of the electrolyte solution by processing the surface of the panel or sheet-shaped electrolyte solution holding material. The fibrous substance and the porous material can be sprayed or applied together with water or the electrolyte solution to form the electrolyte solution holding layer when the electrolyte solution holding material is installed on the surface of the concrete, so that the surface shape of the concrete is not affected. ,
It is possible to work. In this case, in order to improve the adhesion, it is possible to add a material that improves the adhesiveness or tackiness, and a thickener. Examples of water-absorbing organic polymers include polyacrylic acid-based ones and swelling rubbers. As with the porous material, these materials can be sprayed to form a holding layer on the concrete surface, or can be formed into a panel or sheet with another material.

Further, during the construction period, it is possible to supply the electrolyte solution or calculate the water content to be evaporated from the electrolyte solution and to absorb the water content in advance. This has the advantage of reducing the work of replenishing water during construction.

[0038]

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

Example 1 100 parts by weight of cement was mixed with 200 parts by weight of sand, and the mortar contained NaCl in a water cement ratio of 50% so that the amount of chloride ions was 0.2 parts by weight with respect to 100 parts by weight of cement. Was kneaded. Using this mortar, diameter 10 cm, height 20 cm
It has a cylindrical shape with a diameter of 22 mm and a length of 30 at the center.
A cylindrical specimen having one cm polished steel rod was prepared.
Next, an epoxy-based paint was applied to the upper and lower surfaces of the cylindrical test body to electrically insulate it. In a container containing tap water,
This cylindrical test body is dipped, an electrode is installed at a position 2 cm away from the cylindrical test body as an external electrode, and a constant current DC power supply is used between the cylindrical test body and the internal electrode of the polished steel rod.
As shown in Table 1, the current was applied for 4 weeks. At the end of the energization, the amount of chloride ions contained in the mortar in a portion 1 cm around the reinforcing bar was measured. The results are also shown in Table 1.

<Materials used> Cement: ordinary Portland cement manufactured by Denki Kagaku Kogyo Co., Ltd., water: tap water sand: Himekawa-produced river sand, specific gravity 2.62, FM2.75 NaCl: table salt, purified NaCl 99.0%

[0041]

[Table 1]

From Table 1, when the current density per mortar surface area is 0.5 A / m ² or more, the residual rate of chlorine ions is small,
It is possible to remove chloride ions from mortar.

Example 2 Unit cement amount 280 kg / m ³ , unit water amount 168 kg / m ³ , and NaCl
Using concrete with a unit of 5 kg / m ³ and a fine aggregate ratio of 48%, as shown in Table 2, at the center, there is one polished steel rod with a prescribed rebar diameter and a length of 50 cm. 15 cm, height 30
A cylindrical test body of cm was manufactured. Next, an epoxy-based paint was applied to the upper and lower surfaces of the cylindrical test piece to completely electrically insulate it. Using this cylindrical test body, it was immersed in a calcium hydroxide aqueous solution, and a constant current DC power source was used in the same manner as in Example 1, and an electric current was applied for 4 weeks so that the electric current was 1 A per concrete surface area. At the end of energization, a concrete test piece was subjected to a one-sided pulling test to examine the bond strength of the reinforcing bars. The results are also shown in Table 2. Further, during the energization treatment, it was also observed whether or not cracks were generated in this cylindrical test body. The results are also shown in Table 2.

<Materials used> Gravel: Hikawa river gravel, Gmax = 20mm, specific gravity 2.65, F.
M. = 6.26 Calcium hydroxide: Wako Pure Chemical Industries, Ltd. reagent 1st grade

[0045]

[Table 2]

As is clear from Table 2, when the current density per surface area of the reinforcing bar exceeds 10 A / m ² , the adhesive strength is drastically reduced, which also causes cracks.

Example 3 A test was conducted using a reinforced concrete wall having a height of 2 m, a length of 20 m and a thickness of 30 cm, about 20 years after construction, and a neutralization depth of about 30 mm. Partially suspend the concrete of this reinforced concrete wall, use the reinforcing bars inside the concrete as internal electrodes,
After fixing a wire mesh having a diameter of 4 mm and an interval of 10 cm on the surface of concrete, a paper pulp containing an aqueous solution of sodium carbonate as an electrolyte solution was sprayed to form an external electrode. A direct current with a current density of 1.0 A / m ² was applied to the concrete surface area around the external electrodes for 2 weeks to electrically permeate the electrolyte solution into the concrete. The ratio of the surface area of concrete to the surface area of rebar is 1.
Since it is 7: 1, the current density per surface area of the reinforcing bar is 1.7 A / m ²
Is. After 2 weeks, the external electrode and the paper pulp on the concrete surface were removed, and the neutralization depth of the concrete was measured. As a result, phenolphthalein turned red throughout the entire concrete. Therefore, it was confirmed that it was possible to improve the neutralized part.

Example 4 L of reinforced concrete having a height of 2 m, a length of 2 m and a thickness of 15 cm
The test was conducted using a mold retaining wall. Chloride ions of 5 kg / m ³ were mixed in this retaining wall when kneading concrete. This retaining wall was partially suspended, the reinforcing steel inside the concrete was used as an internal electrode, and further, Elguard Asia Service Co., Ltd. Elgard mesh was fixed to the concrete surface, and then paper pulp was soaked in tap water. Was used as an external electrode. A direct current with a current density of 1.2 A / m ² was applied to the surface area of the concrete for 4 weeks to electrically remove chlorine ions inside the concrete. Since the ratio of the surface area of concrete to the surface area of reinforcing bars is 2.3: 1, the current density per surface area of reinforcing bars is 2.8 A / m ² . After 4 weeks, the external electrodes on the concrete surface and the paper pulp were removed, and the amount of chlorine ions contained in the concrete was analyzed. As a result, it was 0.8 to 1.2 kg / m ³ , and most of the chlorine ions were removed. There was found.

[0049]

INDUSTRIAL APPLICABILITY In the method of the present invention, chlorine ions and alkaline solutions in concrete can be electrically moved, and the hydrogen gas pressure generated near the cathode can be suppressed, so that concrete cracks occur. It has the effect of being safe, reliable, and non-dangerous. In addition, it also has the effect of being able to safely restore concrete that has deteriorated due to salt damage or neutralization.

Claims (1)

[Claims] 1. A steel material inside concrete is used as an internal electrode, an electrode installed on the surface of the concrete is used as an external electrode, and the current density per surface area of the concrete is 0.5 A / m ^2.
With the above, the current density per surface area of the steel material for the internal
A method for recovering and treating concrete, characterized in that an electric current is applied so that the current becomes A / m ² or less.