JP6951053B2 - Monitoring method of sacrificial anode method in concrete structure - Google Patents

Description

The present invention relates to a monitoring method of a sacrificial anode method for preventing corrosion of reinforcing bars in a cross-section restoration method for concrete structures mainly used in the fields of civil engineering and construction.

In a concrete structure, a steel material is embedded inside the concrete structure, and the concrete and the steel material are integrated to take charge of an external force, but early deterioration is currently a problem.

Deterioration factors of concrete structures include salt damage, neutralization, frost damage, alkaline aggregate reaction, chemical concrete corrosion, etc., and selectable repair methods for these deteriorations include cross-section repair method, surface protection method, and so on. The crack repair method, the salt removal method, the alkali re-applying method, etc. are mentioned.

As a repair method for concrete structures deteriorated due to salt damage or the like, a cross-section repair method is generally widely used.

The cross-section repair method is a method of scraping the deteriorated concrete of a concrete structure and backfilling the scraped portion with a material having high durability against deterioration such as polymer cement mortar and a cross-section repair material.
However, in the reinforcing bar penetrating the joint interface between the cross-section repair material and the hardened concrete, the concentration of the deterioration factor is different on the same reinforcing bar surface. For example, salt damage causes a difference in the amount of chloride ions, and neutralization causes a difference in pH. It is known that if there is a difference in the concentration of these deterioration factors on the same reinforcing bar surface, macrocell corrosion will occur mainly on the reinforcing bar surface on the concrete hardened body side near the joint interface, and as a result, the cross-section repair part will be constructed after construction. It may deteriorate again in a few years.

That is, macrocell corrosion of reinforcing bars occurs when the amount of deterioration factors is partially different on the same surface of continuous reinforcing bars, and is between the anode part (corroded part) and the cathode part (non-corroded part) at distant positions. This is a phenomenon in which a macrocell current flows and the anode part corrodes.

Therefore, in the field of civil engineering and construction, a construction method for preventing macrocell corrosion is known by installing a sacrificial anode material having a metal having a higher ionization tendency than iron as an anode material in the cross-section repair portion (Patent Document 1). ~ 8).
However, the conventional method is premised on embedding the sacrificial anode material inside the cross-section repair material, and it is difficult to confirm the reinforcing bar anticorrosion performance of the sacrificial anode material after embedding the sacrificial anode material in the cross-section repair material. rice field.

Japanese Patent No. 5388435 Japanese Patent No. 4801051 Japanese Patent No. 5437044 Japanese Patent No. 5631024 Japanese Patent No. 4091953 Japanese Patent No. 4648389 Japanese Patent No. 4574013 Japanese Patent No. 3099830

As a result of diligent efforts, the present inventor has found that by using a specific material and a specific construction method, it is possible to solve the problems of the prior art and monitor the anticorrosion performance of the reinforcing bar in the sacrificial anode construction method of the concrete structure. The present invention was completed.

The present invention employs the following means to solve the above problems.
(1) A sacrificial anode composed of an anode material 3 made of zinc or a zinc alloy and a backfill material containing an electrolyte solution having a pH sufficient to avoid the formation of anode immobility around the anode material 3. A sacrificial anode construction method in which the material 4 is installed on the surface of the hardened concrete body 2 and the reinforcing bars 1 inside the hardened concrete body 2 and the sacrificial anode material 4 are electrically connected to each other to prevent corrosion of the reinforcing bars in the cross-sectional restoration method of the reinforced concrete structure. In this monitoring method, the position of the joint interface side end 5 of the anode material 3 inside the sacrificial anode material 4 is within 30 cm from the joint interface 7 of the cross-sectional restoration material 6 and the hardened concrete body 2. The sacrificial anode material 4 is installed on the surface of the hardened concrete body 2, and the reinforcing bar 1 and the sacrificial anode material 4 are connected via the lead wire 9, and a part of the lead wire 9 repairs the surface and / or cross section of the hardened concrete body 2. The lead wire 9 exposed on the surface of the material 6 is provided with a connection terminal 10 capable of opening and closing an electrical connection, and is a monitoring method of the sacrificial anode method of a reinforced concrete structure for performing electrochemical measurement. be.
(2) Disconnect Succoth connection reinforcing bars 1 and the sacrificial anode material 4, the releasing shi disconnected from the installed concrete cured body 2 of the surface of the sacrificial anode material 4 on the surface of the concrete hardened body 2, the surface The reference electrode 11 and the potential difference meter 12 are connected to the connection terminal 10 of the lead wire 9 exposed to the surface, and one point on the surface of the hardened concrete body 2 within 30 cm from the joint interface 7 on which the sacrificial anode material 4 is installed is measured. As point 13, the monitoring method of (1) above, in which the instant-off potential immediately after disconnection and the potential after 24 hours have elapsed are measured.
(3) The monitoring method according to (1) above, wherein an ammeter is connected to the connection terminal 10 of the lead wire 9 exposed on the surface, and the amount of current flowing between the reinforcing bar 1 and the sacrificial anode material 4 is measured.
(4) A polarization resistance measuring device is connected to the connection terminal 10 of the lead wire 9 exposed on the surface, and the polarization resistance value of the surface of the reinforcing bar 1 and / or the sacrificial anode material 4 having continuity with the lead wire 9 is measured. This is the monitoring method of (1) above.

In the monitoring method of the sacrificial anode method of the present invention, the performance of the sacrificial anode material 4 can be easily evaluated and the replacement time of the sacrificial anode material 4 can be easily grasped in the sacrificial anode method for corrosion-preventing the reinforcing bar 1 in the cross-section repair method. It works.

FIG. 1 is a cross-sectional view of an outline of the apparatus used in the method of the present invention.

FIG. 2 is a plan view of an outline of an apparatus used in the method of the present invention in which the sacrificial electrode 4 is installed on the surface of the hardened concrete body 2.

FIG. 3 is a layout diagram of an outline of the potential measuring device.

Hereinafter, the present invention will be described in detail.
Parts and% used in the present invention are based on mass unless otherwise specified.
The concrete referred to in the present invention is a general term for cement paste, cement mortar, and cement concrete.

In the present invention, the reinforcing bar 1 inside the hardened concrete body 2 is used as a cathode, and the sacrificial anode material 4 is installed on the surface of the hardened concrete body 2 to serve as an anode. Is supplied to protect the reinforcing bar 1.

The sacrificial anode material 4 is a type used in the electrochemical corrosion protection method, but it does not require adjustment of the current amount or maintenance of the external power supply, the burden of maintenance after installation is small, and the concrete structure is damaged by salt. It is considered that the durability can be improved by using it together with the cross-section restoration method of.

Here, the sacrificial anode material 4 is a material containing a metal having a higher ionization tendency than iron and ionizing before iron to prevent corrosion of the reinforcing bar 1.
Examples of the anode material 3 constituting the sacrificial anode material 4 include zinc or an aluminum and / or magnesium alloy of zinc, and it is preferable to use zinc as the anode material 3 for ease of use.

In order to avoid passivation of the anode material 3, it is necessary to keep the circumference of the anode material 3 at a sufficient pH with a backfill material (not shown). For example, when the anode material 3 is zinc or a zinc-aluminum alloy, the pH value is preferably 13.3 or more, and the pH value for suppressing passivation differs depending on the metal used, but the pH value is usually 12. That is all.

Since the pH of the electrolyte solution contained in the backfill material attached around the anode material 3 is high, there is a concern about alkali-silica reaction in the concrete portion in contact with the backfill material. Therefore, it is preferable to have an alkali silica reaction inhibitor present in the electrolyte solution.

As the alkali-silica reaction inhibitor, lithium ions are preferable, and lithium hydroxide, lithium carbonate, or lithium-type zeolite is preferably used in order to avoid a decrease in the pH of the electrolyte solution.

In the present invention, the method of electrically connecting the reinforcing bar 1 and the sacrificial anode material 4 is performed via a lead wire 9 in which the reinforcing bar 1 and the anode material 3 are electrically conductive.
The reinforcing bar 1 and the lead wire 9 can be connected by a winding method or a welding method.
The end of the lead wire 9 needs to be exposed on the surface of the hardened concrete body 2 and / or the cross-section restoration material 6.

The type of the lead wire 9 is not particularly limited, but in consideration of durability, the lead wire 9 is stainless-processed or surface-treated such as titanium-plated, galvanized, or chromate-treated. And / or, it is preferable to use a lead wire 9 covered with a coating film such as vinyl resin, fluororesin, or chloroprene rubber.

Further, in the present invention, it is preferable that the lead wire 9 exposed on the surface is provided with a connection terminal 10 capable of opening and closing an electrical connection. Any known connection terminal 10 can be used as long as the object of the present invention is not impaired, but in consideration of durability, it is preferable to use a connection terminal or a connector with a waterproof crimp terminal.

In the present invention, after scraping off the deteriorated portion of the deteriorated concrete structure, the lead wire 9 is electrically connected to the reinforcing bar 1, the cross-section repair material 6 is placed, and the sacrificial anode is placed after the cross-section repair material 6 is placed. The position of the joint interface side end 5 of the anode material 3 inside the material 4 is on the joint interface 7 between the cross-sectional restoration material 6 and the concrete hardened body 2, or within 30 cm from the joint interface 7 of the concrete hardened body 2. A sacrificial anode material 4 is installed so as to be on the surface, and the anode material 3 and the lead wire 9 are electrically connected, or the anode material 3 and the reinforcing bar 1 inside the cross-section repair portion where the cross-section repair material 6 is placed are placed. The surface of the anode material 3 is covered with a backfill material containing an electrolyte solution having a pH sufficient to avoid the formation of a dynamic film, and then the sacrificial anode material 4 is wrapped with mortar or the like. By installing it on the surface of the hardened concrete body 2, an anticorrosion current flows between the reinforcing bar 1 and the sacrificial anode material 4, and the reinforcing bar 1 inside the concrete is protected from corrosion.

In the present invention, the anticorrosion effect of the reinforcing bar of the sacrificial anode material 4 is monitored by measuring the potential of the reinforcing bar 1 and / or the sacrificial anode material 4, the current flowing from the sacrificial anode material 4, and / or the polarization resistance value of the reinforcing bar 1. can do.

When a metal having a lower standard electrode potential is electrically connected to the reinforcing bar 1 inside the hardened concrete body 2, the potential of the reinforcing bar 1 itself becomes low. Therefore, by measuring the electric potential, the effectiveness of the reinforcing bar anticorrosion can be judged from the numerical value.

The potential is measured by a potentiometer 12 using a reference electrode 11 using saturated copper sulfate, with one point on the surface of the hardened concrete body 2 on which the sacrificial anode material 4 is installed as a measurement point 13 . At this time, the connection between the sacrificial anode material 4 and the reinforcing bar 1 can be disconnected, and the instant off potential immediately after the connection is disconnected and the potential after 24 hours (off potential after 24 hours) are measured, and the difference between them is measured. The amount of repolarization is calculated from. The larger the amount of repolarization, the greater the effect of anticorrosion of the reinforcing bar. Generally, it is said that anticorrosion is achieved if the amount of repolarization of 100 mV or more is obtained in the reinforcing bar of concrete.

Further, since the current value flowing through the lead wire 9 is greatly affected by the environmental conditions of concrete, a clear threshold value has not been established, but the current flowing through the lead wire 9 connected to the reinforcing bar 1 and the sacrificial anode material 4 is the reinforcing bar. By confirming that the current flows from 1 to the sacrificial anode material 4, it is possible to determine whether or not the sacrificial anode material 4 is effectively acting on the reinforcing bar corrosion protection.
The current can be measured with any existing ammeter, but it is preferable to use a non-resistive ammeter because the current value may be small.

In the present invention, it is possible to monitor the anticorrosion effect of the reinforcing bar by measuring the polarization resistance value of the reinforcing bar 1 inside the hardened concrete body 2.

The polarization resistance value means the reaction resistance on the surface of the reinforcing bar 1, that is, the reaction resistance to the corrosion reaction. The larger the resistance value, the less likely the corrosion reaction to occur, that is, the passivation.
Known methods for measuring the polarization resistance value include a DC resistance polarization method and an AC impedance method.

The direct current resistance polarization method is a method in which a minute direct current (i) is applied to the reinforcing bar 1 and the polarization resistance value (ΔV / i) is calculated from the amount of potential change (ΔV) at that time.

On the other hand, in the AC impedance method, an AC current from a low frequency (about 0.1 mHz) to a high frequency (about 100 kHz) is energized, and the difference in impedance (resistance) at both frequencies is used as the polarization resistance value. Measuring instruments based on the principle of the AC impedance method are commercially available, and it is preferable to use them.

Polarization resistance values, from the reference value by the European Concrete Committee, "passivated state" when the 130~260kΩcm ² in the polarization resistance value, when the 52~130kΩcm ² "corrosion rate of low to moderate", 26 to When it is 52 kΩcm ² , it is said to be "medium to high corrosion rate", ^{and when it is less than 26 kΩ cm 2} , it is said to be "severe and high corrosion rate". (Concrete Diagnostic Technology '15 [Basic], p.195, Japan Concrete Engineering Society)

In the present invention, by defining the installation position of the sacrificial anode material 4, monitoring is possible while maintaining the effect of preventing the corrosion of the reinforcing bars. Specifically, starting from the joint interface 7 between the cross-sectional restoration material 6 and the hardened concrete body 2, the position of the end portion 5 on the joint interface side of the anode material 3 inside the sacrificial anode material 4 is 30 cm on the side of the hardened concrete body 2. The sacrificial anode material 4 is installed on the surface of the hardened concrete body 2 so as to be within the range of. If all or part of the sacrificial anode material 4 is covered within this range, the effect of preventing macrocell corrosion of the predetermined reinforcing bar can be obtained. The effect of preventing corrosion generated on the reinforcing bar 1 on the side may not be obtained.

In the present invention, when the sacrificial anode material 4 is installed on the surface of the hardened concrete body 2, it is preferable to wrap it with the sacrificial anode material covering material 8.

The material used for the sacrificial anode material coating material 8 is not particularly limited as long as it satisfies the specific resistance described later, but it is preferably cement mortar.

Cement used for cement mortar includes various Portland cements such as ordinary, early-strength, ultra-fast-strength, low-heat, and moderate heat, and various mixed cements in which blast furnace slag, fly ash, or silica is mixed with these Portland cements. Examples include filler cement mixed with limestone powder and blast furnace slow-cooled slag fine powder, and Portland cement such as environment-friendly cement (eco-cement) manufactured from municipal waste incineration ash and sewage sludge incineration ash. One or more of these can be used.

In the present invention, the specific resistance of the sacrificial anode material covering material 8 can be expected to be durable without excessive supply of the anticorrosion current from the anode material 3, and the amount of the anticorrosion current required to prevent macrocell corrosion is supplied. From the viewpoint of being able to be formed, 1 to 300 kΩ · cm is preferable, and 10 to 100 kΩ · cm is more preferable.

The cross-sectional restoration material 6 used in the present invention is not particularly limited, and any existing material can be used, but for admixture of an appropriate amount of cement in consideration of long-term durability and integrity with the hardened concrete body 2. A polymer cement mortar mixed with a polymer is preferable.

Hereinafter, the contents will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Experimental Example 1
A specimen with a thickness of 150 mm was prepared to simulate the wall surface of a reinforced concrete structure damaged by salt, and a cross-section restoration method was carried out in a range of 500 x 500 mm.
FIG. 1 shows a cross-sectional view of an outline of the apparatus used in the method of the present invention, and FIG. 2 shows a plan view.
As shown in FIG. 2, a reinforcing bar 1 having a diameter of 16 mm at a pitch of 150 mm is arranged inside to prepare a specimen having a length of 1,500 mm, a width of 1,500 mm, and a thickness of 150 mm. Was carried out.

The specimen was prepared in a constant temperature room at 20 ° C. After placing the concrete so that the cover of the reinforcing bar is 40 mm, the mold is removed the next day, and at the age of 28 days, the cross-section repair part (500 x 500 mm) is lifted with a water jet at a cross-section repair depth of 60 mm, and the reinforcing bar 1 The lead wire 9 was connected to the vertical and horizontal intersections by welding. A waterproof crimp connection terminal 10 was attached to the lead wire 9, and a cross-section repair material 6 was placed. A commercially available polymer cement mortar was cast as the cross-section restoration material 6. This cross-sectional view is shown in FIG.

The sacrificial anode material 4 was installed the day after the cross-section restoration material 6 was placed.
As the sacrificial anode material 4, a zinc metal as an anode material 3 and a mortar mixed with lithium hydroxide as a backfill material were used, and the sacrificial anode material 4 was further coated with the sacrificial anode material covering material 8. The size after coating with the sacrificial anode material coating material 8 is a plate shape having a length of 14 cm, a width of 4.5 cm, and a thickness of 1.3 cm. As shown in FIGS. 1 and 2, the sacrificial anode material 4 coated with the sacrificial anode material covering material 8 is placed close to the upper and lower ends of the cast cross-section repair portion, and is formed in the sacrificial anode material 4 from the joint interface 7. The anode material 3 was installed on the surface of the hardened concrete body 2 so that the distance to the joint interface side end 5 was 30 mm (3 cm).
The sacrificial anode material coating material 8 was a polymer cement mortar having a specific resistance of 50 kΩ · cm, and the sacrificial anode material coating material 8 was adjusted so that the thickness of the polymer cement mortar was 20 mm.

Concrete formulation, so that the compressive strength is 24N / mm ^2, cement 300 kg / cm ^3, fine aggregate 757kg / cm ^3, coarse aggregate 1,047kg / cm ^3, admixture 3.0kg / cm ^3, NaCl8.2kg At / cm ³ , water 165 kg / cm ³ , W / C was 55%, Gmax was 25 mm, s / a was 42.7%, and Air was 4.5 ± 1%. The amount of chloride ions to be mixed was 5 kg / m ^3, and the reagent NaCl was mixed by external division. The target slump was 12 ± 2.5 cm.

After compressing the polymer cement mortar up to the age of 28 days, the reinforcing bar 1 and the sacrificial anode material 4 were connected via the lead wire 9, and the specimen was allowed to stand outdoors to start monitoring. The measurement was carried out at four places, and the average value was calculated.
Monitoring was performed every two months immediately after the start of the test.
In the potential measurement, as shown in FIG. 3, a saturated copper sulfate reference electrode is used as the reference electrode 11, and the sacrificial anode material 4 is connected from the surface of the hardened concrete body 2 (connection between the reinforcing bar 1 and the sacrificial anode material 4). The instant off potential immediately after disconnection and the potential after 24 hours (off potential after 24 hours) were measured, and the amount of repolarization was calculated from these differences.
As for the current, the current value flowing through each lead wire 9 was measured with a non-resistive ammeter, and the average value of the current values was obtained.
The polarization resistance value was measured at the target reinforcing bar position using a portable reinforcing bar corrosion diagnostic machine "CM-V" manufactured by Shikoku Research Institute Co., Ltd.
From striking passage surface 7 was performed 3 cm, 10 cm, 30 cm, and the measurement results of recovery maximal dose calculated from the results of the electrostatic level measured just above the rebars 1 that put the position of 50 cm, the measurement of the polarization resistance The results are shown in Table 1. Table 2 shows the results of measuring the current value flowing through each lead wire 9. The direction in which the lead wire 9 flows from the reinforcing bar 1 to the sacrificial anode material 4 is the current on the anticorrosion side, and is in the positive direction.

<Material used>
Cement (C): Ordinary Portland cement, commercial product, density 3.15 g / cm ³
Fine aggregate (S): River sand from Himekawa, Niigata Prefecture, density 2.62 g / cm ³
Coarse aggregate (G): Crushed stone from Himekawa, Niigata Prefecture, Gmax15mm, density 2.66g / cm ³
Admixture (Add): Naphthalene sulfonic acid-based high-performance AE water reducing agent
NaCl: Reagent first-class sacrificial anode material: A disk-shaped zinc mass of 3.9 cm in diameter x 0.7 cm in height is conducted by two mild steel wires, and the sand / cement ratio is 3/1 and the water / cement ratio is 60%. In the mortar, the mixing water was coated with a backfill material having a pore solution containing LiOH so that the pH inside the mortar was always 13 or higher, using a saturated aqueous solution of lithium hydroxide, and the diameter was 6 cm x height. 3.5 cm columnar sacrificial anode material Coating material: A mortar using ordinary cement with sand / cement ratio = 1/1 and water / cement ratio = 60%, with a specific resistance of 20 kΩ · cm at 28 days of age.
Cross-section restoration material: Commercially available polyacrylic acid ester (PAE) -based polymer cement mortar, polymer / cement ratio (P / C) = 5%, water / cement ratio (W / C) = 45%.

From Table 1, from the start of the test to 24 months later, the amount of polarization and the polarization resistance value are large from the junction interface 7 to the position 30 cm, and from Table 2, the current flows from the start of the test to 24 months later. It is confirmed that it is possible to monitor that the high reinforcing bar anticorrosion effect is maintained from the start of the test to 24 months later.

Experimental Example 2
An experiment was conducted in which the consumption of the sacrificial anode material 4 was simulated. The same test as in Experimental Example 1 was carried out except that the consumed sacrificial anode material 4 was connected to a DC external power source so as to serve as an anode, and a current of 10 mA was forcibly applied for 2 months. The monitoring results are shown in Tables 3 and 4.

From Tables 3 and 4, when the sacrificial anode material 4 simulating wear is used from the start of the test to 24 months later, the reinforcing bar anticorrosion effect of the sacrificial anode material 4 is limited, and at 24 months from the start of the test, the impact is applied. It is confirmed that there is concern about reinforcing bar corrosion at the position of the joint interface 7 to 30 cm, and monitoring is possible.

The monitoring method of the sacrificial anode method of the present invention facilitates the performance evaluation of the sacrificial anode material 4 for the sacrificial anode method performed in association with the cross-section repair method, and makes it easy to grasp the replacement time of the sacrificial anode material 4. Suitable for civil engineering and construction fields.

1: Reinforcing bar 2: Concrete hardened body 3: Anode material 4: Sacrificial anode material 5: End of joint interface side of anode material 6: Cross section restoration material 7: Joint interface 8: Sacrifice anode material coating material 9: Lead wire 10 : Connection terminal 11: Reference electrode 12: Potentiometer 13: Potential measurement point

Claims (4)

A sacrificial anode material 4 composed of a zinc or zinc alloy anode material 3 and a backfill material containing an electrolyte solution having a pH sufficient to avoid the formation of anode immobility around the anode material 3. , A monitoring method of the sacrificial anode method that protects the reinforcing bars in the cross-sectional restoration method of the reinforced concrete structure that is installed on the surface of the hardened concrete body 2 and electrically connects the reinforcing bar 1 inside the hardened concrete body 2 and the sacrificial anode material 4. The sacrificial anode material is such that the position of the joint interface side end portion 5 of the anode material 3 inside the sacrificial anode material 4 is within 30 cm from the joint interface 7 of the cross-sectional restoration material 6 and the hardened concrete body 2. 4 is installed on the surface of the hardened concrete body 2, and the reinforcing bar 1 and the sacrificial anode material 4 are connected via the lead wire 9, and a part of the lead wire 9 is the surface and / or the cross-section repair material 6 of the hardened concrete body 2. Monitoring of the sacrificial anode method of a reinforced concrete structure characterized in that the lead wire 9 exposed on the surface and the lead wire 9 exposed on the surface is provided with a connection terminal 10 capable of opening and closing an electrical connection to perform electrochemical measurement. Method. The disconnect Succoth connection reinforcing bars 1 and the sacrificial anode material 4, the releasing shi disconnected from the concrete hardened body 2 of the surface of the sacrificial anode material 4 installed at the surface of the concrete hardened body 2 and exposed to the surface A reference electrode 11 and a potential difference meter 12 are connected to the connection terminal 10 of the lead wire 9, and one point on the surface of the hardened concrete body 2 within 30 cm from the joint interface 7 on which the sacrificial anode material 4 is installed is set as a measurement point 13. The monitoring method according to claim 1, wherein the instant-off potential immediately after the disconnection and the potential after the lapse of 24 hours are measured. The monitoring method according to claim 1, wherein an ammeter is connected to the connection terminal 10 of the lead wire 9 exposed on the surface, and the amount of current flowing between the reinforcing bar 1 and the sacrificial anode material 4 is measured. A polarization resistance measuring device is connected to the connection terminal 10 of the lead wire 9 exposed on the surface, and the polarization resistance value of the surface of the reinforcing bar 1 and / or the sacrificial anode material 4 having continuity with the lead wire 9 is measured. The monitoring method according to claim 1.

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