JP7483190B2 - Sacrificial anode monitoring sensor and monitoring method - Google Patents

Description

The present invention relates to a sacrificial anode monitoring sensor and a monitoring method for monitoring an anode buried inside a concrete structure.

Conventionally, cathodic protection has been known as an effective means of preventing corrosion of reinforcing bars in reinforced concrete structures, i.e., RC (Reinforced Concrete) structures. Cathodic protection is a maintenance method that is said to be the ultimate measure against corrosion of reinforcing bars, and is a method that controls corrosion of reinforcing bars by supplying a corrosion-preventing current to the reinforcing bars. Cathodic protection methods are broadly divided into the external current method, which uses an external power supply device to pass a corrosion-preventing current, and the galvanic anode method, which uses the difference in the ionization tendency between a sacrificial anode and the reinforcing bars to pass a corrosion-preventing current. In both methods, it is important to supply a stable corrosion-preventing current, so the external power supply method requires that the external power supply device be maintained so that it does not stop. In addition, compared to cathodic protection using an external power supply method, the galvanic (sacrificial) anode method does not require a power supply device, so the management effort and running costs after installation can be reduced.

Various methods have been proposed for cathodic protection using galvanic anodes. These include installing a panel or sheet that acts as a sacrificial anode on the surface of the concrete structure, installing it on the surface such as by applying a coating to the surface by thermal spraying, and connecting a component containing a metal that acts as a sacrificial anode in a backfill material to rebar and burying it inside the concrete.

Compared to installing sacrificial anodes on the surface, burying sacrificial anodes inside concrete can be done at the same time as reinforcing bar arrangement work during new construction, reducing construction labor. Also, when making corrections such as repairing cross sections, even if a polymer-containing material with high electrical resistance is used as the repair material, it is possible to supply anticorrosive current by maintaining a certain level of conductivity using the mortar material, which is the backfill material that contains the sacrificial anodes. For these reasons, there are a variety of application examples.

Patent Document 1 describes an electrochemical protection method in which a corrosion sensor is provided near the rebar in an RC structure made of concrete and reinforcing bars, and the corrosion sensor and an anode system are connected in parallel to the rebar.

JP 2019-066300 A

When sacrificial anodes are embedded inside concrete, the anodes are consumed as an anticorrosive current is applied to the rebar, so it is desirable to be able to grasp the consumption state of the sacrificial anodes to some extent, but this is not possible to do directly. In other words, there is an issue that it is difficult to confirm the anticorrosive effect of the sacrificial anodes or to determine when the sacrificial anodes themselves need to be replaced.

In addition, in the cathodic protection method of Patent Document 1, the corrosion sensor is very small compared to the reinforcing bars and has a small electrical resistance. Therefore, if the corrosion sensor is directly connected to the anode system and the reinforcing bars, the corrosion sensor will be in a state of over-protection, and the anti-corrosion effect of the anode material will be greater on the corrosion sensor than on the reinforcing bars. Once the anti-corrosion effect of the anode material has decreased to a certain level, the reinforcing bars will corrode first, and there is a high possibility that the corrosion sensor will hinder preventive maintenance risk detection of the reinforcing bars.

The present invention was made in consideration of these circumstances, and aims to connect a sacrificial anode to a corrosion sensor, perform electrochemical protection of the corrosion sensor, and grasp the corrosion occurrence status of the anode and rebar inside a concrete structure without connecting it to the rebar.

(1) In order to achieve the above object, the present invention takes the following measures. That is, the sacrificial anode monitoring sensor of the present invention is a sacrificial anode monitoring sensor that monitors an anode buried inside a concrete structure based on a cathodic protection method, and is characterized by comprising a corrosion sensor that detects corrosion of steel material, and an anode member connected to the corrosion sensor.

This allows the sacrificial anode monitoring sensor to be installed inside the concrete structure without the need to connect it to the rebar, preventing over-protection of the corrosion sensor and making it possible to grasp the anode consumption status and rebar corrosion status inside the concrete structure.

(2) In addition, in the sacrificial anode monitoring sensor, the anode member is a metal less noble than iron. This allows for proper electrochemical protection of the corrosion sensor, making it possible to grasp the anode consumption status and rebar corrosion status inside the concrete structure.

(3) In addition, in the sacrificial anode monitoring sensor, the sacrificial anode is made of the same type of metal as the anode. This allows for proper electrochemical protection of the corrosion sensor, making it possible to grasp the anode consumption status and rebar corrosion status inside the concrete structure.

(4) In addition, in the sacrificial anode monitoring sensor, the thickness or diameter of the anode member is 1 mm or more. This makes it possible to prevent the anode portion of the sacrificial anode monitoring sensor from wearing out and breaking earlier than expected.

(5) The monitoring method of the present invention is a monitoring method for monitoring an anode buried inside a concrete structure based on a cathodic protection method, and is characterized by including at least the steps of: a corrosion sensor for detecting corrosion of steel material; a step of connecting a sacrificial anode to the corrosion sensor with a cable to prepare a sacrificial anode monitoring sensor; a step of embedding the prepared sacrificial anode monitoring sensor in the concrete structure; and a step of monitoring a decrease in the anticorrosive effect of the sacrificial anode based on a change in resistance or a change in the electrostatic capacitance of the corrosion sensor that detects corrosion of the steel material, or a step of estimating the anticorrosive status of the buried anode based on a change over time in the current density of the sacrificial anode or a change over time in the amount of depolarization of the corrosion sensor that detects corrosion of the steel material.

This makes it possible to prevent over-protection of the corrosion sensor and accurately grasp the progress of corrosion of the reinforcing bars inside the concrete structure.

According to the present invention, by connecting a sacrificial anode to a corrosion sensor and performing electrochemical protection of the corrosion sensor, it is possible to grasp the anode consumption status and the corrosion status of reinforcing bars inside a concrete structure.

FIG. 2 is a schematic diagram of a sacrificial anode monitoring sensor. FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. FIG. 1 is a diagram showing an outline of a corrosion sensor. 1A to 1C are diagrams showing examples of installation of a sacrificial anode. FIG. 1 is a schematic diagram of a sacrificial anode monitoring sensor. FIG. 1 is a diagram showing an outline of an immersion test (Case 1) using artificial seawater. 1 is a graph showing the change in current density of a sacrificial anode monitoring sensor over time. 1 is a graph showing the results of measuring the potential of a corrosion sensor and a zinc wire at the 1 mmΦ zinc wire level. 4 is a graph showing the resistance change of a corrosion sensor. FIG. 1 is a diagram showing an outline of an immersion experiment (Case 2) using a concrete simulant solution. 1 is a graph showing the change in potential of a zinc wire having a diameter of 1 mm. 4 is a graph showing the resistance change of a corrosion sensor. 1 is a graph showing the change over time in the amount of depolarization in immersion test case 1. 13 is a graph showing the change over time in the amount of depolarization in immersion test case 2. FIG. 4 is a diagram showing the surface state of the corrosion sensor after each immersion test.

The inventors focused on the fact that in electrochemical protection, the consumption of anode members cannot be accurately determined when they are buried inside a concrete structure, and that corrosion sensors cannot accurately determine the progress of corrosion of reinforcing bars. They discovered that by connecting a sacrificial anode to a corrosion sensor and performing electrochemical protection of the corrosion sensor, it is possible to simulate electrochemical protection of reinforcing bars inside a concrete structure and accurately estimate the status of electrochemical protection, which led to the invention.

In other words, the sacrificial anode monitoring sensor of the present invention is a sacrificial anode monitoring sensor that monitors an anode buried inside a concrete structure, and is characterized by having a corrosion sensor that detects corrosion of steel materials and an anode member connected to the corrosion sensor.

This makes it possible to prevent over-protection of the corrosion sensor and accurately grasp the corrosion protection status of the reinforcing steel inside the concrete structure. Below, an embodiment of the present invention will be specifically described with reference to the drawings.

[Sacrificial anode monitoring sensor]
Fig. 1A is a schematic diagram of a sacrificial anode monitoring sensor. Fig. 1B is a cross-sectional view taken along line A-A in Fig. 1A. The sacrificial anode monitoring sensor 1 includes a corrosion sensor 10 and a sacrificial anode 20 (hereinafter also referred to as an anode member 20), and mortar 115 is provided between the corrosion sensor 10 and the sacrificial anode 20. The corrosion sensor 10 and the sacrificial anode 20 are connected by soldering a cable 111.

Figure 2 is a diagram showing an outline of the corrosion sensor. The corrosion sensor 10 includes a substrate 121 formed into a plate shape from a non-conductive material, a detection section 123 formed from an iron foil material produced by rolling iron, and a precious metal film 125 formed from a precious metal (e.g., gold) provided on a part of the detection section.

Typically, the corrosion sensor 10 is embedded in the covering of a concrete structure, and the corrosion progress is evaluated by the corrosion sensor itself corroding and breaking, to determine whether the environment near the corrosion sensor is one in which corroding factors can invade and corrode iron. The electrical resistance is measured to determine if the corrosion sensor 10 has broken due to corrosion, and if the sensor is in a healthy state, it will show an extremely low resistance of a few Ω to 20 Ω. However, if corrosion occurs and the sensor breaks, it will show a resistance of 100 Ω or more.

As shown in FIG. 1B, the corrosion sensor 10 is typically embedded inside a ceramic housing 113, the surface of the corrosion sensor 10 is covered with mortar 115, and RFID, a short-range wireless technology, is used to measure electrical resistance. The corrosion sensor is applied to many concrete structures where salt damage and neutralization are a concern.

The sacrificial anode 20 is made of a metal less base than iron, such as zinc alloy or aluminum. It is preferable that the sacrificial anode 20 is made of the same metal as the anode connected to the reinforcing bar in order to accurately estimate the corrosion protection status of the anode. The sacrificial anode 20 may have a rod-like shape as shown in FIG. 1, but is not limited to this. It may also be plate-like, wire-like, or mesh-like. The size of the sacrificial anode 20 is designed based on the useful life (service period) calculated in advance based on the mass. The preferred thickness of the sacrificial anode 20 is preferably wire with a diameter of 1 mm or more, or plate material with a thickness of 1 mm or more, or mesh-like steel material.

The corrosion sensor is installed inside a ceramic housing, and a corrosion protection current is supplied from the zinc wire, which is the sacrificial anode 20, through a 2 mm thick mortar layer. The zinc wire, which is the sacrificial anode 20, can be adjusted to any length depending on the design service life, or can be composed of multiple zinc wires. The corrosion sensor may be a capacitance corrosion sensor. In the case of a capacitance sensor, a detection section made of iron foil material, a counter electrode at a position opposite the detection section, and a dielectric between the iron foil section and the counter electrode are provided to measure changes in electrical characteristics such as capacitance caused by corrosion of the iron foil section. The mortar 115 can be, for example, cement mortar with a water-cement ratio of 50% or more so that it can detect corrosion factors and penetrate, just like conventional corrosion sensors.

Figures 3(a) to (c) are diagrams showing examples of installation of the sacrificial anode 20. Figure 3(a) is an example of installing a linear anode member 20 around the mortar. In the case of the installation example of Figure 3(a), the thickness of the anode member 20 and the number of installed anode members, as well as the length of the anode members, are changed to design the service life. It can be used even if one of the two anode members breaks. Figure 3(b) is an example of installing a plate-shaped anode member 20. In the case of the installation example of Figure 3(b), the service life is designed by changing the thickness of the plate material. The lead wires connecting to the plate material are made of a corrosion-resistant metal such as titanium, and by embedding the lead wires in a ring shape inside the plate material, electrical continuity is maintained even if the anode material is consumed in stripes. Figure 3(c) is an example of installing the anode member by applying it to the surface of a ceramic housing 113. In the case of the installation example of Figure 3(c), the service life is designed by changing the application area and thickness. Furthermore, by distributing the anode components over a wide area and forming a mesh, the connection is maintained even if the anode components corrode in islands.

The sacrificial anode monitoring sensor is installed so that its positional relationship is the same with the rebar buried inside the concrete structure and with the surface of the concrete. Installation is easy by fixing it to the rebar using a special jig, band, or wire. Note that care should be taken not to allow contact between the rebar and the steel or anode parts of the sacrificial anode monitoring sensor. The sensor can be buried either during new construction or repair work.

Monitoring measures changes in the electrical properties of the sacrificial anode and steel of the sacrificial anode monitoring sensor. By measuring the degree of decrease in current density of the sacrificial anode of the sacrificial anode monitoring sensor, the degree of damage to the anode in the cathodic protection method can also be estimated. Furthermore, by measuring the degree of increase in resistance value and the degree of decrease in capacitance value of the steel of the sacrificial anode monitoring sensor, it can be estimated whether the rebar has reached a state where it will corrode.

[Example]
4 is a schematic diagram of the sacrificial anode monitoring sensor 100. In the sacrificial anode monitoring sensor 100, a corrosion sensor 310 and a zinc wire 320 serving as a sacrificial anode are connected by a soldered cable 411. The zinc wire 320 used in this embodiment has a purity of 99.99%, and the amount of anode required during corrosion protection in the sea was calculated using the following formula (1), and two levels of 0.5 mmΦ and 1 mmΦ were set. In addition, the planned corrosion protection current density (Ii) in formula (1) was substituted with 100 mA/ ^m2 used for soft iron, and the effective amount of electricity (C) of the anode was set to 780 A·h/kg.

The exposed portion of the zinc wire 320 was adjusted to 6 mm, and the remaining exposed portion was coated with resin to make it waterproof.

The design value of the corrosion protection period calculated using formula (1) is 288 hours for a zinc wire with a diameter of 1 mm and 72 hours for a zinc wire with a diameter of 0.5 mm.

The following two immersion tests were conducted using the above-mentioned sacrificial anode monitoring sensor 100. Table 1 shows the types of solutions used in the two immersion tests. In case 1, an immersion test was conducted using artificial seawater, and in case 2, an immersion experiment was conducted using a concrete simulant solution.

[1. Immersion test using artificial seawater]
5 is a diagram showing an outline of an immersion test (case 1) using artificial seawater. As immersion test case 1, an accelerated corrosion test was carried out on the anticorrosive effect of the connection state of the corrosion sensor 310 and the zinc wire 320 in artificial seawater. As a test method, air was pumped into ion-exchanged water (pH: 7.7) adjusted to a salinity of 3% in a solution tank, and three each of the corrosion sensor 310 alone (non-corrosive) and the corrosion sensor with a sacrificial anode connected to the zinc wire 320 (sacrificial anode monitoring sensor 100) were immersed (n=3).

In immersion test case 1, the natural potential and depolarization amount of the corrosion sensor 310 and zinc wire 320 were periodically measured using a saturated silver-silver chloride electrode, and the anticorrosive current generated between the zinc wire and the corrosion sensor was also measured. The anticorrosive current was measured using a zero-resistance ammeter. The surface condition was also visually confirmed when the corrosion sensor 310 reached the resistance value used to determine corrosion. The dissolved oxygen concentration and pH were also periodically measured to confirm that there were no changes in the aqueous solution environment during the test period.

(Test results)
[1-1. Current density behavior]
6 is a graph showing the change over time in the current density measured between the zinc wire and the corrosion sensor of the sacrificial anode monitoring sensor 100. The current density was determined by dividing the measured current value by the surface area of the detection portion of the corrosion sensor, i.e., the current density in the area to be protected from corrosion.

As shown in Figure 6, the current density behavior was highest immediately after immersion in the aqueous solution and showed a tendency to decrease over time. For the 1 mm diameter zinc wire, the current density was maintained at the start of the test for approximately 60 hours, after which it showed a decreasing tendency, reaching its lowest value after 130 hours. For the 0.5 mm diameter zinc wire, the current density began to decrease rapidly immediately after the start of the test, reaching almost the lowest value between 45 and 60 hours. For the 0.5 mm diameter zinc wire, the current density also decreased rapidly immediately after the start of the test in line with the change in potential of the zinc wire, suggesting that a stable anti-corrosion environment could not be maintained.

[1-2. Corrosion sensor - potential change of zinc wire]
Figure 7 is a graph showing the potential measurement results of the corrosion sensor and zinc wire at the 1 mmΦ zinc wire level. The corrosion sensor potential showed -600 mV vs SHE until about 100 hours, similar to immediately after the start, and then showed a downward trend. The zinc wire potential gradually increased with a noble tendency from immediately after the start until 100 hours, and then remained flat without any significant change. In addition, compared to the 0.5 mmΦ shown in Figure 7, there was less variation due to individual differences, so it is considered that the corrosion prevention environment was maintained stably.

In both the 0.5 mm Φ and 1 mm Φ cases, the results were significantly shorter than the corrosion prevention design time of 72 hours and 288 hours. The reason for this is believed to be that the air pumped into the solution created a flow velocity within the solution, which accelerated the corrosion rate.

[1-3. Resistance change of corrosion sensor]
Figure 8 is a graph showing the resistance change of the corrosion sensor. The resistance change of the corrosion sensor connected to the 0.5 mmΦ and 1 mmΦ zinc wires shown in Figure 7 shows that all the sensors connected to the corrosion sensor alone (without corrosion protection) showed a corroded state within a few to 35 hours, while the 0.5 mmΦ zinc wire corrosion protection reached corrosion in 50 to 100 hours. For the 1 mmΦ zinc wire level, all the sensors reached corrosion in 140 to 160 hours.

Regardless of whether corrosion protection was used or not, the results show that the time to detect corrosion varies for each individual sample. However, the time it took to show a resistance value exceeding 100 Ω was longer in the order of no corrosion protection → 0.5 mmΦ zinc wire corrosion protection → 1 mmΦ zinc wire corrosion protection, with the 1 mmΦ taking approximately three times as long as no corrosion protection. In other words, it is believed that a corrosion effect was achieved.

[1-4. Anti-corrosion effect of zinc wire on corrosion sensor]
The relationships between the measurement results of current density, potential change, and corrosion sensor resistance change are discussed below.

In artificial seawater, an unprotected corrosion sensor becomes corroded within approximately 40 hours. A corrosion sensor protected with 0.5 mm diameter zinc wire shows signs of corrosion after 50 to 100 hours, which, subtracting the corrosion detection time of the unprotected corrosion sensor, gives an anti-corrosion effect of approximately 10 to 60 hours. The anti-corrosion effect obtained using a 1 mm diameter zinc wire is 90 to 120 hours. When we look at the current density and zinc potential at the respective anti-corrosion times of 10 to 60 hours and 90 to 120 hours, we obtain the results shown in Table 2.

電流密度で８５～１３０ｍＡ／ｍ^２以下および亜鉛電位が初期値より１５０ｍＶ程度貴化したところが防食終了の時点と予測される。

It is predicted that the end of corrosion protection will occur when the current density is 85 to 130 mA/ ^m2 or less and the zinc potential becomes nobler by about 150 mV from the initial value.

[2. Immersion experiment using concrete simulant solution]
FIG. 9 is a diagram showing an outline of an immersion experiment (case 2) using a concrete simulant solution. As immersion test case 2, a test was conducted to confirm the anticorrosive effect using a concrete simulant solution. The test environment was a saturated calcium hydroxide solution (pH: 12.3) with a salt concentration adjusted to 10%, with air from which carbon dioxide had been removed by pumping through the saturated calcium hydroxide solution, and three corrosion sensors (n=3) each with a sacrificial anode connected to zinc wires of 0.5 mmΦ and 1 mmΦ (sacrificial anode monitoring sensor 100) were immersed in the solution. The zinc wires are not shown in the figure.

The measurement items were the same as those in immersion test case 1, with attention focused on the change in anode potential and the corrosion judgment time of the corrosion sensor.

(Test results)
[2-1. Potential change of zinc wire]
FIG. 10 is a graph showing the potential change of a zinc wire having a diameter of 1 mm.

The 1 mmΦ zinc wire maintained a stable state throughout the test period, and, like immersion test case 1, showed a gradual tendency for the potential to become more noble, but only the 1 mmΦB zinc wire showed a large tendency for the potential to become more noble from around 270 hours.

[2-2. Resistance change of corrosion sensor]
FIG. 11 is a graph showing the change in resistance of the corrosion sensor. The corrosion of the non-protected and 0.5 mmΦ zinc wires was judged at almost the same time. It is presumed that the 0.5 mmΦ zinc wire itself fell off the connecting cable after 150 hours of testing due to consumption of the zinc wire and adhesion of calcium hydroxide, and the corrosion prevention effect was extremely reduced after that. The non-protected corrosion sensor reached corrosion in about 300 to 350 hours, and required about 10 times the corrosion judgment time of immersion test case 1. However, for the 1 mmΦ zinc wire, even after 350 hours, although corrosion spots were appearing on the surface, the resistance value for judging corrosion had not been reached, and it can be said that the corrosion prevention effect is sustained.

[3. Measurement results of depolarization amount]
Since a stable anticorrosion effect could not be obtained with the 0.5 mmΦ zinc wire, the depolarization amount was evaluated for immersion test case 1 and immersion test case 2 with a 1 mmΦ zinc wire. Figure 12 is a graph showing the change over time in the depolarization amount for immersion test case 1. Figure 13 is a graph showing the change over time in the depolarization amount for immersion test case 2. In both immersion tests, the depolarization amount decreased after the start of the test, and the decrease in the depolarization amount due to the consumption of the anode was confirmed. It can also be seen that the voltage did not exceed 1000 mV, at which hydrogen embrittlement of steel is a concern.

In immersion test case 1, the value rapidly decreased after 120 hours, which was roughly the same time as the decrease in the corrosion protection effect mentioned above, and this resulted in a decrease in the amount of depolarization due to a decrease in the corrosion protection current caused by the zinc potential becoming nobler.

It can be seen that for immersion test case 2, a value above 100 mV, the corrosion protection standard in concrete, continues to be maintained. Furthermore, after reaching a value of approximately 850 mV, which is the value for complete corrosion protection, a gradual downward trend is observed. Also, from approximately 270 hours, the amount of depolarization only for the 1 mm ΦB zinc wire decreased, falling below the 100 mV corrosion protection standard for concrete. On the other hand, for the 1 mm ΦA and 1 mm ΦC, although they were able to maintain a value above 100 mV even after 350 hours had passed, the clear downward trend indicates that the corrosion protection effect is declining.

Figure 14 shows the surface condition of the corrosion sensors in immersion test case 1 and immersion test case 2 after corrosion assessment, and the condition of corrosion sensor C corroded with a 1 mm Φ zinc wire at the same time.

In immersion test case 1, the corrosion area is widespread, with rust occurring over the entire surface of the corrosion sensor. On the other hand, in immersion test case 2, part of the corrosion sensor is locally pitted, and corrosion is progressing in that area.

Although fine pitting was observed in the corrosion sensor protected with 1 mm diameter zinc wire, there were clearly fewer corroded areas than in the non-corrosion-protected corrosion sensor.

[4. Consideration of application methods to actual structures]
When considering the application of a corrosion sensor to monitoring of sacrificial anodes, it is considered easy to directly connect the sacrificial anodes that are actually attached to rebars to the corrosion sensor. However, the sacrificial anodes installed in real structures are designed to supply corrosion current to rebars that have a higher resistance than the corrosion sensor through a backfill material of a certain thickness. Therefore, if the corrosion sensor is connected to the sacrificial anodes that are actually used, it is assumed that an excessive anticorrosive current will be supplied. From the viewpoint of preventive maintenance of sacrificial anodes, it is desirable to be able to make some kind of judgment just before the anticorrosive effect of the sacrificial anodes to be installed decreases, and it is desirable to monitor the anticorrosive effect separately and independently from the sacrificial anodes installed in the real structure. In addition, since the size and number of sacrificial anodes to be installed vary depending on conditions such as the target concrete area, the amount of rebar, and the salt concentration, it is also desirable to be able to arbitrarily control the amount of sacrificial anodes in the monitoring sensor.

As described above, according to the present invention, by connecting a sacrificial anode to a corrosion sensor and performing electrochemical protection of the corrosion sensor, it is possible to accurately grasp the progress of corrosion of reinforcing bars inside a concrete structure.

Reference Signs List 1, 100 Sacrificial anode monitoring sensor 10 Corrosion sensor 20 Sacrificial anode, anode member 111 Cable 113 Housing 115 Mortar 121 Base material 123 Detection unit 125 Noble metal film 310 Corrosion sensor 320 Zinc wire 411 Cable

Claims (5)

A sacrificial anode monitoring sensor that monitors an anode buried inside a concrete structure based on an electric corrosion protection method,
A corrosion sensor that detects corrosion of steel materials;
A sacrificial anode monitoring sensor comprising: an anode member connected to the corrosion sensor. The sacrificial anode monitoring sensor according to claim 1, characterized in that the anode member is a metal less noble than iron. 2. The sacrificial anode monitoring sensor of claim 1, wherein the anode member is made of the same metal as the anode. A sacrificial anode monitoring sensor according to any one of claims 1 to 3, characterized in that the thickness or diameter of the anode member is 1 mm or more. A monitoring method for monitoring an anode buried inside a concrete structure based on an electric corrosion protection method, comprising:
A step of preparing a sacrificial anode monitoring sensor by connecting a corrosion sensor for detecting corrosion of a steel material and a sacrificial anode to the corrosion sensor via a cable;
embedding the fabricated sacrificial anode monitoring sensor in the concrete structure;
a step of monitoring a decline in the anticorrosive effect of the sacrificial anode based on a change in resistance or a change in capacitance of a corrosion sensor that detects corrosion of steel material, or a step of estimating the anticorrosive status of the buried anode based on a change in the current density of the sacrificial anode over time or a change in the amount of depolarization of the corrosion sensor that detects corrosion of steel material.

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