JP2022154471A - Moisture sensor, moisture level detection method, and method of manufacturing moisture sensor - Google Patents

Abstract

To easily grasp an accurate moisture level without destroying a cementum hardened body.SOLUTION: A moisture sensor 100 for detecting a moisture level of a cementum hardened body is provided, the moisture sensor comprising a columnar dielectric body 3, one or more pairs of electrodes 5 provided in close contact with opposing points on a surface of the dielectric body 3, and conductors 7 electrically connected to each of the electrodes 5. At least one of the electrodes 5 is made of a flexible metal thin film. The dielectric body 3 is a cementum hardened body or ceramics.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a moisture sensor for detecting the amount of moisture on the surface and inside of a hardened cementitious body, a method for detecting the amount of moisture, and a method for manufacturing the moisture sensor.

Conventionally, water content in concrete plays an important role in determining properties such as cement hydration, concrete shrinkage and creep progress. In addition, since moisture intruding from the outside becomes a corrosive factor of internal reinforcing bars and promotes the penetration of chloride ions, understanding the distribution and condition of moisture in concrete is important information that determines the durability of concrete. is. In addition, the water content of concrete structures is involved in strength development, drying shrinkage, etc., and greatly affects the workability and quality of finishing work and waterproofing work. In finishing work, if the finishing material is applied in a state of high water content, sufficient adhesive strength cannot be obtained, and blistering, peeling, cracking, etc. may occur. For these reasons, it is important to know the amount of water in concrete.

As a method for grasping the water content state in concrete, for example, Patent Document 1 discloses a method of predicting the water content of concrete from the measured value of electrical resistance based on the relationship between the water content of concrete and the electrical resistance value (electrical resistance formula ) has been disclosed. Further, Patent Document 2 discloses a technique (capacitance method) for predicting the moisture content of concrete from the measured value of capacitance based on the relationship between the moisture content and capacitance of concrete. In addition, other methods for grasping the water content in concrete include measuring the humidity inside small holes made in the concrete, measuring the humidity by attaching a moisture-impermeable sheet to the concrete surface, and discoloring the concrete surface. A method of attaching paper to measure the moisture content and humidity, and the like are used. In measuring the moisture content of concrete, it is desirable to use a simple method that does not take much time at a building construction site or the like where measurement conditions vary.

Further, Patent Document 3 discloses a technique related to a moisture sensor that is installed in a concrete structure and measures the amount of moisture in the concrete structure. A water content sensor having electrodes formed thereon measures the amount of water in the concrete by using the electrical characteristics of the dielectric portion when AC electrolysis is applied to the water sensor as an index.

JP-A-62-087841 JP 2013-250215 A JP 2021-025793 A

However, the methods described in Patent Documents 1 and 2 are widely used in construction sites such as floor construction because they are simple and quick to measure the moisture content of concrete. Alternatively, since the water content of the concrete is measured by pressing the electrode against the concrete surface, the data is only for the vicinity of the concrete surface, and the water content at a depth of several cm or more from the surface cannot be measured accurately (Fig. 10 (a) (b)). In addition, since the method described in Patent Document 1 is of the embedded electrode type, it not only damages the object to be measured, but also requires repairing the hole in which the electrode is embedded after the measurement (FIG. 10(a)). In addition, in the method described in Patent Document 2, since the water content is measured by pressing the electrode against the concrete surface, dirt may adhere to the sensor portion when measuring a large amount, and reliability is poor. In addition, a method of measuring humidity inside a small hole provided in concrete, a method of measuring humidity by attaching a moisture-impermeable sheet to the surface of concrete, a method of measuring moisture content and humidity by attaching discolored paper to the surface of concrete. However, since it takes time to measure, the measurement cannot be performed quickly.

In addition, in the moisture sensor described in Patent Document 3, it is preferable to use a material having a coefficient of thermal expansion close to that of concrete or mortar as the material of the electrode portion. , SUS304, SUS316, SUS430, and other bulk materials such as stainless steel. As for the method of forming the electrode on the dielectric portion, for example, the space of the ring-shaped electrode is filled with cement paste, mortar, concrete cement, or the like before hardening, and hardened to achieve integration. However, in this electrode forming method, the hardened cementitious material has a characteristic of shrinking during hardening, and there is a possibility that minute voids may occur between the electrode portion and the dielectric portion. Also, in use in a real environment, due to seasonal fluctuations, for example, there is a possibility of receiving a thermal history from below freezing to over 40°C. Under such an environment, even if a material with a coefficient of thermal expansion similar to that of concrete or mortar is used for the electrodes, the coefficient of thermal expansion of the electrodes and the dielectric will be Even if the volume change due to the difference in .theta.

Therefore, in the moisture sensor described in Patent Document 3, due to the curing shrinkage of the mortar material and the difference in thermal expansion due to the material difference between the electrode and the mortar, as shown in FIG. A gap occurs. When water enters this gap, it becomes difficult to accurately measure the electrical properties of the dielectric portion, and as a result, it may not be possible to accurately detect the amount of water in the concrete. Further, when the dielectric portion is made of ceramics, the difference in thermal expansion with the electrode portion is larger than that of mortar, so the minute gap becomes conspicuous.

The present invention has been made in view of such circumstances. It is possible to suppress the occurrence of minute gaps in the cementitious material to be measured, and to stably acquire the electrical properties of the dielectric over a long period of time without destroying the hardened cementitious material to be measured. It is an object of the present invention to provide a moisture sensor and a method for detecting the amount of moisture that can more accurately ascertain the amount of moisture on the surface or inside a hardened body.

(1) In order to achieve the above objects, the present invention takes the following measures. That is, the moisture sensor of the present invention is a moisture sensor for detecting the moisture content of a hardened cementitious material, comprising a pair of dielectrics formed in a columnar shape and a pair of dielectrics provided so as to be in close contact with the facing surfaces of the dielectrics. It is characterized by comprising the above electrodes and current-carrying parts electrically connected to each of the electrodes, wherein at least one of the electrodes is formed of a flexible metal thin film.

As a result, it is possible to suppress the occurrence of minute gaps between the dielectric and the electrode even when subjected to thermal history due to hardening shrinkage of the hardened cementitious material that forms the dielectric and temperature changes in the actual environment. Without destroying the hardened cementitious material, it is possible to stably acquire the electrical properties of the dielectric over a long period of time, and to easily and accurately measure the water content on the surface or inside the hardened cementitious material. It is possible to comprehend. In addition, since the moisture sensor can be placed anywhere on the hardened cementitious material to be measured, it is possible to measure not only the surface of the hardened cementitious material to be measured, but also the deep part of the hardened cementitious material. It becomes possible to grasp the distribution of the moisture content of the entire cured body.

(2) Further, in the moisture sensor of the present invention, the dielectric is cementitious hardening material or ceramics. As a result, it has the same water absorbency as the hardened cementitious material to be measured, and it becomes possible to measure the water content with high accuracy.

(3) Further, in the moisture sensor of the present invention, the dielectric is formed in a hollow cylindrical body, and the pair of electrodes are provided on the outer surface and the inner surface of the hollow cylindrical body. . This makes it possible to measure the electrical characteristic value more accurately. Furthermore, the uniformity of moisture permeating into the dielectric is ensured.

(4) Further, the water content detection method of the present invention is a method for detecting the water content of the hardened cementitious material, which is installed on the surface or inside of the hardened cementitious material, and comprises: (3) The moisture sensor according to any one of (3) is installed on the surface of or inside the hardened cementitious body, and an alternating electric field is applied to the moisture sensor. The method is characterized by detecting the water content of the cementitious hardened body based on the correlation with the water content.

As a result, it is possible to suppress the occurrence of minute gaps between the dielectric and the electrode even when subjected to thermal history due to hardening shrinkage of the hardened cementitious material that forms the dielectric and temperature changes in the actual environment. Without destroying the hardened cementitious material, it is possible to stably acquire the electrical properties of the dielectric over a long period of time, and to easily and accurately measure the water content on the surface or inside the hardened cementitious material. It is possible to comprehend. In addition, since the moisture sensor can be placed anywhere on the hardened cementitious material to be measured, it is possible to measure not only the surface of the hardened cementitious material to be measured, but also the deep part of the hardened cementitious material. It becomes possible to grasp the distribution of the moisture content of the entire cured body.

(5) Further, a method for manufacturing a moisture sensor according to the present invention is a method for manufacturing the moisture sensor according to any one of (1) to (3) above, wherein a paste-like substance is applied to the surface of the dielectric. It is characterized by forming a flexible metal thin film by applying an electrode material, sputtering, vapor deposition, or plating.

As a result, it is possible to suppress the occurrence of minute gaps between the dielectric and the electrode even when subjected to thermal history due to hardening shrinkage of the hardened cementitious material that forms the dielectric and temperature changes in the actual environment, and the hardening of the cementitious material. It is possible to stably acquire the electrical properties of the dielectric over a long period of time without destroying the body, and to more accurately grasp the water content on the surface or inside of the hardened cementitious body simply and with high accuracy. .

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to grasp easily and correctly the distribution of the water content of the whole cementitious hardened body to be measured, without destroying the cementitious hardened body to be measured.

It is a figure which shows schematic structure of the water|moisture content sensor which concerns on this embodiment. It is a figure which shows the mode of penetration|permeation of the water|moisture content in a dielectric. It is a figure which shows the process of the manufacturing method of a water|moisture content sensor. It is a figure which shows schematic structure of the water|moisture content sensor used in an Example. It is a figure which shows schematic structure of the conventional moisture sensor. 5 is a graph showing the relationship between water content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a water sensor using the electrode of the example. 7 is a graph showing the relationship between the water content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz of a water sensor using conventional electrodes of Comparative Example. It is a photograph which shows the state of the electrode interface of the water|moisture content sensor of an Example. It is a photograph which shows the state between the dielectric of the conventional moisture sensor, and an electrode. It is a figure which shows the outline|summary of the moisture content measurement by the conventional moisture sensor.

The inventors of the present invention have found that a moisture sensor installed on the surface or inside of the hardened cementitious material to be measured receives thermal history due to curing shrinkage of the hardened cementitious material that forms the dielectric and temperature changes in the actual environment. Focusing on the fact that a minute gap is generated between the dielectric and the electrode, making it impossible to measure the water content accurately, by using a thin-film electrode as the electrode, the generation of a minute gap between the dielectric and the electrode was investigated. It is possible to stably obtain the electrical properties of the dielectric over a long period of time without destroying the hardened cementitious material to be measured, and to easily and accurately measure the surface or inside of the hardened cementitious material to be measured. The inventors have found that the water content can be more accurately determined, and have completed the present invention.

This embodiment will be described with reference to the drawings. A cementitious hardened body is a hardened body containing at least cement, and is a concept including cement paste, mortar, and concrete.

[Configuration of Moisture Sensor]
FIG. 1 is a diagram showing a schematic configuration of a moisture sensor 100 according to this embodiment. The moisture sensor 100 includes a columnar dielectric 3, a pair or more of electrodes 5 provided in close contact with the facing surfaces of the dielectric 3, and lead wires connected to each electrode 5 to form a current-carrying part. 7, and detects electric characteristic values such as capacitance, impedance, and dielectric loss tangent that change according to the moisture content of the dielectric. The lead wire 7 is adhered to the electrode 5 with solder. By connecting the lead wire 7 to a measuring instrument 9 and applying an AC electric field, the electrical characteristic value of the dielectric 3 is detected.

The dielectric 3 is a columnar body having a ring-like shape, a so-called hollow cylinder (annular cylinder). In this embodiment, as an example, the shape of a hollow cylindrical body is used for description, but the present invention is not limited to this. For example, it may be a prismatic body or a cylindrical body whose bottom surface is a polygon with no hollow.

The distance between the electrodes formed on the dielectric 3 is preferably 3 mm or more and 50 mm or less. If the inter-electrode distance is shorter than 3 mm, there is a possibility of short-circuiting, and if it is longer than 50 mm, uneven water content may affect measurement accuracy. Moreover, the thickness of the dielectric 3 is preferably 3 mm or more and 50 mm or less. If the thickness of the dielectric 3 is less than 3 mm, the strength may be weak and it may be damaged.

Any material may be used for the dielectric 3 as long as it contains water, and it is preferable to use a material having water absorption equivalent to that of the hardened cementitious material to be measured. For example, similar to the object to be measured, cementitious hardened bodies such as cement paste, mortar, and concrete, ceramics, and the like are preferable. A hardened cementitious material partially impregnated with a resin may also be used.

The hardened cementitious material may be made of any type of cement, such as ordinary Portland cement or high-early-strength cement. The material age of the cementitious hardened body is preferably 28 days or longer, which is when the hydration reaction is almost completed.

When mortar is used for the dielectric 3, it is preferable to have a composition that has water absorption equivalent to that of the hardened cementitious material to be measured. Specifically, the water/cement ratio (W/C) is 15 to 70%. The ratio of cement to fine aggregate is preferably 1 part cement to 2 to 3 fine aggregates. If the water/cement ratio is less than 15%, the pore volume in the mortar will become too small, and if it is greater than 70%, the water absorption will increase and the water content will no longer approximate that of the hardened cementitious material. , unfavorable. If the ratio of fine aggregate is less than 2 cement ratio, the pore volume in the mortar becomes too small. It is not preferable because it is no longer similar to cementitious hardened body. In addition, since fine aggregates are susceptible to the water absorption of fine aggregates, the physical properties of fine aggregates are preferably water absorption of 3.0% or less and specific surface area of 400 cm ² /g or less. As the fine aggregate, for example, dense artificial sand is preferable.

When concrete is used for the dielectric 3, it is preferable to use a mixture having water absorption equivalent to that of the hardened cementitious material to be measured.

By using a hardened cementitious material or ceramics for the dielectric 3, it is possible to increase the adhesion to the hardened cementitious material to be measured, and the strength and durability of the hardened cementitious material to be measured are less likely to be affected. .

By controlling the composition of the hardened cementitious material of the dielectric 3 in this way, it is possible to improve the consistency between the water content sensor 100 and the amount of moisture inside the hardened cementitious material to be measured. That is, by making the water absorption of the hardened cementitious material used for the dielectric 3 equal to that of the hardened cementitious material to be measured, the water content of the hardened cementitious material to be measured can be properly grasped.

The pair of electrodes 5 are in close contact with the facing surfaces of the dielectric 3 formed in a hollow cylinder (annular cylinder) body, and are provided so as to have the same central axis, forming concentric cylindrical electrodes.

A metal thin film formed in the form of a paste has a lower rigidity (Young's modulus) than a metal formed in the form of a bulk, and can follow minute changes in volume due to cure shrinkage of the dielectric. In addition, the pasty thin film electrode can be completely adhered to the surface of the dielectric after being applied to the dielectric due to the effect of the binder. As a result, it is possible to suppress the occurrence of minute gaps between the dielectric and the electrodes.

When the dielectric 3 has a shape of a rectangular parallelepiped, a prism or a cylinder which is a hollow column having a polygonal bottom surface, parallel plate electrodes may be formed on the top surface and the bottom surface. In the case of parallel plate electrodes, it is preferable that a pair of opposing electrodes have the same shape and size. Moreover, from the viewpoint of measurement accuracy, it is preferable that the distance between the electrodes is constant.

2(a) and 2(b) are diagrams showing how moisture permeates into the dielectric. As shown in FIG. 2(b), in the case of the parallel plate-like electrodes, since the side surfaces are open, the permeation of water may become non-uniform. On the other hand, as shown in FIG. 2(a), in the structure in which the dielectric is a hollow cylinder and the electrodes are formed on the curved surface, the side surfaces of the dielectric are closed, and the uniformity of water permeating into the dielectric is poor. Most preferred because it is guaranteed. Part of the surface of the exposed portion of the dielectric of the moisture sensor may be covered with resin or the like.

Since the moisture sensor is embedded in the hardened cementitious body for use, the electrode 5 is preferably made of a corrosive material. Furthermore, in order to further improve the followability of the electrode 5 to minute volume changes due to curing shrinkage of the dielectric and heat history in the actual environment, the paste-like electrode 5 is formed by forming a film by sputtering, vapor deposition, plating, or the like. It is preferable to use a material having flexibility and having a coefficient of thermal expansion close to that of concrete or mortar. Here, the flexibility means that the paste-like electrode 5 should be flexible enough to follow changes in volume due to thermal history due to hardening shrinkage of the dielectric and temperature changes in the actual environment while being in close contact with the dielectric. For example, a material having ductility and flexibility that can follow the dielectric while being in close contact with the dielectric can be used. For example, noble metals such as gold, platinum, and palladium, as well as silver, titanium, and carbon are preferred.

[Manufacturing method of moisture sensor]
FIG. 3 is a diagram showing the steps of the manufacturing method of the moisture sensor. First, a dielectric is produced (S1). A dielectric forming material such as cement paste, mortar, concrete, ceramics, or the like is poured into the dielectric mold and hardened. For example, when mortar is used as the dielectric material, the mortar to be poured into the mold is cement: fine aggregate=1:3, the cement is ordinary Portland cement, and the fine aggregate is artificial sand with a specific surface area of 300 cm ² /g. was used. W/C is preferably 55% and the material age period is preferably 28 days. The material used for the dielectric is not limited to mortar, as described above. A hardened cementitious material (cement paste, concrete) other than mortar, ceramics, or the like may also be used.

The hardened dielectric is removed from the mold, and a paste-like thin film metal, which is an electrode material, is applied to the inner and outer surfaces of a hollow cylinder (annular cylinder) to produce an electrode (S2). The method of forming the thin film metal is not limited to coating. For example, the film may be formed by sputtering, vapor deposition, plating, or the like.

Next, lead wires are soldered to the two electrodes produced in S2 (S3) to produce a moisture sensor.

[How to install the moisture sensor]
A moisture sensor is installed on the surface or inside the hardened cementitious material to be measured. At the time of installation, the lead wires connected to the electrodes are protruded from the side surface of the hardened cementum to be measured. Connect the leads to a measuring instrument such as an LCR meter. Also, the moisture sensor may be installed by fixing it with bolts to the surface of the hardened cementitious material to be measured.

[Calculation of moisture content]
The water content sensor according to the present embodiment detects the water content of the hardened cementitious material to be measured from the correlation between the capacitance (C) of the dielectric and the water content under an alternating voltage and a constant frequency. . It is also possible to detect the water content of the hardened cementitious material to be measured from the correlation between the relative permittivity (ε _r ), impedance (Z), dielectric loss tangent (tan δ) and the water content.

In addition, in the frequency range of 10 Hz to 100 MHz, the capacitance (C) of the dielectric is measured, and from the correlation with the slope of each measured value (logarithm) with respect to the frequency (logarithm), the hardened cementitious material to be measured Detect moisture content. Similarly, for the dielectric constant (ε _r ), the water content of the hardened cementitious material to be measured can also be detected from the correlation with the slope of each measured value (logarithm) with respect to the frequency (logarithm).

As for the latter detection method, since the slope is derived from the measurement data for a wide range of frequencies, the measurement accuracy is higher than the measurement under a constant frequency.

[Example]
[1] Fabrication of Moisture Sensor A moisture sensor was actually fabricated, and the amount of moisture inside a concrete specimen was measured. FIG. 4 is a diagram showing a schematic configuration of a moisture sensor used in Examples.

(1) Preparation of dielectric A mortar was poured into a ring-shaped mold with an outer diameter of 28 mm, an inner diameter of 10 mm, and a thickness of 10 mm and cured. The mortar poured into the mold was cement:fine aggregate=1:3, the cement was ordinary Portland cement, and the fine aggregate was artificial sand with a specific surface area of 300 cm ² /g. W/C was set to 55%, and the material age period was set to 28 days.

(2) Preparation of thin-film electrodes Next, the hardened mortar is removed from the formwork, and a paste-like thin-film metal that will be the electrode material is applied to the inner and outer surfaces of the hollow cylinder (annular cylinder) and hardened. to form an electrode.

(3) Finishing A lead wire was soldered to the two produced electrodes to produce a moisture sensor.

(4) Fabrication of Conventional Moisture Sensor FIG. 5 is a diagram showing a schematic configuration of a conventional moisture sensor. As a comparative example, a conventional moisture sensor made of a metal plate having electrodes without holes was fabricated. The moisture sensor of the comparative example uses a metal plate of SUS304 material, thickness of 2.0 mm, and width of 10 mm. A ring-shaped inner electrode 15b having a width of 10 mm and an outer diameter of 8.2 mm was produced, and the inner electrode 15b was placed in the center of the outer electrode 15a. Next, the space formed between the two electrodes 15 (15a, 15b) was filled with mortar to form the dielectric 13. As shown in FIG. The mortar used for filling was the same as the mortar used in the examples, and after the mortar had hardened, the lead wires were bonded to the two electrodes with solder.

[2] Correlation Between Moisture Content and Electrical Characteristic Value of Moisture Sensor Next, the correlation between the moisture content and electrical characteristic value of the moisture sensor will be described. Correlation data between the moisture content and electrical characteristics of the moisture sensor was collected under the following conditions.

(i) The moisture sensor was placed in an absolute dry state, and the initial weight (W0) was obtained by subtracting the weight of the electrodes and lead wires from the total weight of the moisture sensor in the absolute dry state. Next, the moisture sensor was immersed in water in a vacuum environment to make the inside of the dielectric saturated with water. Then, it was allowed to stand for 24 hours under an environment with a temperature of 20° C. and a humidity of 60%, and the water content 1 (W1) was measured. Furthermore, it was left in the same environment for 12 hours, the water content 2 (W2) was measured, and it was confirmed that W1 = W2, and it was confirmed that it was in an equilibrium state.

(ii) Next, the water content (A60) in the dielectric was calculated by content 2 (W2)/initial weight (W0) x 100. For this moisture sensor, the capacitance (C) of the moisture sensor was measured at frequencies of 100 Hz, 1 kHz, and 100 kHz using a measuring instrument (LCR meter) connected to the lead wire.

The operations (i) and (ii) were repeated in an environment with a constant temperature (20° C.) and a humidity of 20% as well as the humidity of 60%. As a result, the moisture content of the moisture sensor in the absolutely dry state (A0), the environment of 20% humidity (A20), the environment of 60% humidity (A60), and the saturated water content state (A100) are each approximately 2.0 wt%. , 4.0 wt % and 6.0 wt %.

Next, the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz was measured at each moisture content of the moisture sensor. FIG. 6 is a graph showing the relationship between the water content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for the water sensor using the electrode of the example. FIG. 7 is a graph showing the relationship between the water content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a water sensor using a conventional electrode as a comparative example. As shown in FIGS. 6 and 7, it was found that the moisture content and the capacitance of the moisture sensor had a proportional relationship, and the moisture content could be measured accurately.

[3] Consistency between the dielectric and the external electrode The heating and cooling was repeated 100 times. After that, the electrode interface of each moisture sensor was observed with an optical microscope. FIG. 8 is a photograph showing the state of the electrode interface of the moisture sensor of the example. As shown in FIG. 8, it was confirmed that the dielectric and the external electrode were in close contact with each other without forming a micro gap between the dielectric and the electrode even after the thermal history was applied. On the other hand, as shown in FIG. 9, a minute gap was observed between the dielectric and the electrode in the moisture sensor of the comparative example.

Furthermore, when the capacitance was measured in the same manner as in [2], the moisture sensor of the example showed no change in the numerical value before and after the heat history was applied, while the moisture sensor of the comparative example showed no change. was different. In other words, in the moisture sensor of the comparative example, a minute gap was formed between the dielectric and the electrode, and moisture entered the minute gap, making it impossible to accurately measure the capacitance.

As described above, the moisture sensor according to the present embodiment is installed on or inside the hardened cementitious material to be measured, and by monitoring the change in the electrical property value, the surface of the hardened cementitious material to be measured and the internal moisture content can be measured simply and with high accuracy. In addition, since the moisture sensor can be installed at any location in the hardened cementitious body to be measured, it is possible to measure not only near the surface of the hardened cementitious body to be measured, but also to the deep part. It becomes possible to grasp the distribution of the water content of the entire cementitious hardened body.

100 Moisture Sensors 3, 13 Dielectrics 5, 15 Electrode 7 Lead Wire, Conducting Part 9 Measuring Instrument, LCR Meter 15a Outer Electrode 15b Inner Electrode

Claims (5)

A moisture sensor for detecting the moisture content of hardened cementum,
a columnar dielectric;
a pair or more of electrodes provided so as to be in close contact with the facing surfaces of the dielectric;
and a current-carrying part electrically connected to each of the electrodes,
A moisture sensor, wherein at least one of said electrodes is formed of a flexible metal thin film. 2. A moisture sensor according to claim 1, wherein said dielectric is cementitious hardening material or ceramics. The dielectric is formed in a hollow cylindrical body,
3. The moisture sensor according to claim 1, wherein the pair of electrodes are provided on the outer surface and the inner surface of the hollow cylindrical body. A water content detection method for detecting the water content of the hardened cementitious material, which is installed on the surface or inside the hardened cementitious material, comprising:
installing the moisture sensor according to any one of claims 1 to 3 on the surface or inside the hardened cementitious body,
applying an alternating electric field to the moisture sensor;
A moisture content detection method, comprising: detecting the moisture content of the hardened cementitious material based on a correlation between a change in the electrical characteristic value of the moisture sensor and the moisture content of the hardened cementitious material. A manufacturing method for manufacturing the moisture sensor according to any one of claims 1 to 3,
A manufacturing method characterized by forming a flexible metal thin film on the surface of the dielectric by applying a paste-like electrode material, sputtering, vapor deposition, or plating.

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