Moisture sensor and moisture amount detection method

Abstract

To allow for easily grasping 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 (5a, 5b) provided on or in the dielectric body 3 and arranged to face each other, and conductors 7 electrically connected to each of the electrodes 5 (5a, 5b). At least one electrode 5b of the pair of electrodes 5 (5a, 5b) has a plurality of holes. The electrode 5b with the holes is closely bonded to the dielectric body 3 by a dielectric material filling the holes.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a moisture sensor and a moisture detection method for detecting the amount of moisture on the surface and inside of a cementitious hardened body.

[0002] Traditionally, moisture in concrete plays an important role in determining properties such as the hydration reaction of cement, and the progress of concrete shrinkage and creep. In addition, moisture entering from the outside can cause corrosion of internal reinforcing bars and promote the penetration of chloride ions, so understanding the distribution and state of moisture in concrete is important information that determines the durability of concrete. The moisture state of concrete structures is also involved in strength development and drying shrinkage, and also has a significant impact on the workability and quality of finishing and waterproofing work. In finishing work, if finishing materials are applied in a high moisture state, sufficient adhesive strength cannot be obtained, and swelling, peeling, cracks, etc. may occur. For these reasons, it is important to understand the moisture content in concrete.

[0003] As a method for grasping the moisture content in concrete, for example, Patent Document 1 discloses a technique for predicting the moisture content of concrete from a measured value of electrical resistance based on the relationship between the moisture content of concrete and the electrical resistance value (electrical resistance type). Patent Document 2 discloses a technique for predicting the moisture content of concrete from a measured value of electrostatic capacitance based on the relationship between the moisture content of concrete and electrostatic capacitance (electrostatic capacitance type). Other methods for grasping the moisture content in concrete include a method for measuring the humidity inside a small hole provided in the concrete, a method for measuring the humidity by attaching an impermeable sheet to the surface of the concrete, and a method for measuring the moisture content and humidity by attaching discoloration paper to the surface of the concrete. In measuring the moisture content of concrete, it is desirable to use a simple method that does not take much time at construction sites of buildings where the measurement conditions vary.

[0004] Furthermore, Patent Document 3 discloses technology relating to a moisture sensor that is installed inside a concrete structure to measure the moisture content of the concrete structure. This moisture sensor uses a mortar material as the dielectric part, on which a counter electrode is formed, and measures the moisture content inside the concrete by using the electrical characteristics of the dielectric part when an AC field is applied to the moisture sensor as an indicator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 62-087841 [Patent Document 2] JP 2013-250215 A [Patent Document 3] Patent Publication No. 2021-025793 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the methods described in Patent Document 1 and Patent Document 2 are widely used in construction sites such as floor construction because they can measure the moisture content of concrete quickly and easily. However, since the electrodes are embedded in the concrete surface or pressed against the concrete surface to measure the moisture content of concrete, the data is only from the vicinity of the concrete surface, and the moisture content at a depth of several centimeters or more from the surface cannot be accurately measured (FIGS. 18(a)(b)). In addition, since the method described in Patent Document 1 uses embedded electrodes, not only does it damage the object to be measured, but it is also necessary to repair the holes in which the electrodes are embedded after measurement (FIG. 18(a)). In addition, since the method described in Patent Document 2 measures the moisture content by pressing the electrodes against the concrete surface, dirt may adhere to the sensor when measuring a large amount, and the reliability is poor (FIG. 18(b)). In addition, the method of measuring the humidity inside a small hole provided in concrete, the method of measuring humidity by attaching a moisture-impermeable sheet to the concrete surface, and the method of measuring the moisture content and humidity by attaching discolored paper to the concrete surface take time to measure, so it is not possible to perform the measurement quickly.

[0007] In addition, in the moisture sensor described in Patent Document 3, since it is preferable to use a material with a thermal expansion coefficient close to that of concrete or mortar as the material of the electrode part, bulk materials such as precious metals such as gold, platinum, palladium, etc., and stainless steel materials such as SUS304, SUS316, and SUS430 are used. In addition, as a method of forming an electrode on the dielectric part, for example, a cement paste, mortar, concrete cement, etc. before hardening is filled into the space of the ring-shaped electrode and hardened to integrate it. However, in this electrode formation method, the cementitious hardened body has a characteristic of shrinking when hardened, and there is a risk of a minute gap being generated between the electrode part and the dielectric part. In addition, in use in an actual environment, there is a possibility that it will be subjected to a thermal history of, for example, from below freezing to exceeding 40°C due to seasonal fluctuations. In such an environment, even if a material with a thermal expansion coefficient close to that of concrete or mortar is used as the material of the electrode part, it is difficult to reliably suppress a minute gap between the electrode part and the dielectric part when considering the load due to repeated temperature fluctuations, even if the volume change caused by the difference in the thermal expansion coefficient between the electrode part and the dielectric part is minute.

[0008] Therefore, in the moisture sensor described in Patent Document 3, due to the hardening shrinkage of the mortar material and the difference in thermal expansion caused by the difference in material between the electrode and mortar, a small gap occurs between the electrode part and the dielectric part as shown in Fig. 17. When moisture penetrates into this gap, it becomes difficult to accurately measure the electrical characteristics of the dielectric part, and as a result, there are cases where the accurate amount of moisture inside the concrete cannot be detected. Furthermore, when the dielectric part is made of ceramics, the difference in thermal expansion between the electrode part and the dielectric part is larger than that of mortar, so the small gap becomes more noticeable.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a moisture sensor and a moisture detection method which can suppress the occurrence of minute gaps between the dielectric and an electrode even when subjected to hardening shrinkage of the cementitious hardened body that forms the dielectric or thermal history due to temperature changes in an actual environment, and which can stably obtain the electrical characteristics of the dielectric over a long period of time without destroying the cementitious hardened body to be measured, and which can more accurately grasp the moisture amount on the surface or inside of the cementitious hardened body to be measured in a simple and highly accurate manner. [Means for solving the problem]

[0010] (1) In order to achieve the above object, the present invention provides the following means. That is, the moisture sensor of the present invention is a moisture sensor for detecting the moisture content of a cementitious hardened body, and includes a dielectric body formed in a columnar shape, one or more pairs of electrodes provided on the surface or inside of the dielectric body so as to face each other, and a current-carrying portion electrically connected to each of the pair of electrodes. each has a plurality of holes, and the electrode having the holes is in close contact with the dielectric material by means of a dielectric material filled in the holes.

[0011] This makes it possible to suppress the generation of minute gaps between the dielectric and the electrodes even when the dielectric is subjected to a thermal history due to hardening shrinkage of the cementitious hardened body forming the dielectric or temperature changes in an actual environment, and to stably obtain the electrical characteristics of the dielectric over a long period of time without destroying the cementitious hardened body to be measured, and to easily and accurately grasp the moisture content on the surface or inside of the cementitious hardened body to be measured. In addition, since the moisture sensor can be installed at any location of the cementitious hardened body to be measured, it becomes possible to measure not only the surface of the cementitious hardened body to be measured but also deep inside, and it becomes possible to grasp the distribution of the moisture content throughout the cementitious hardened body to be measured.

[0012] (2) In the moisture sensor of the present invention, the plurality of holes are preferably in a mesh shape, which allows the electrode to follow the volumetric change of the dielectric and prevents minute gaps from occurring between the dielectric and the electrode.

[0013] (3) In the moisture sensor of the present invention, the mesh forming the mesh shape has an opening of 0.1 to 0.5 mm and a void ratio of 35 to 50%, which allows the electrode to more easily follow the volumetric changes of the dielectric while maintaining its function as an electrode, and makes it possible to prevent minute gaps from occurring between the dielectric and the electrode.

[0014] (4) In the moisture sensor of the present invention, the dielectric material is a cementitious hardened body or a ceramic. This allows the dielectric material to have the same water absorption as the cementitious hardened body to be measured, making it possible to measure the moisture content with high accuracy.

[0015] (5) Furthermore, a moisture detection method of the present invention is a method for detecting the moisture content of a cementitious hardened body by installing a moisture sensor on or inside the cementitious hardened body, the method comprising installing a moisture sensor described in any one of (1) to (4) above on the surface or inside the cementitious hardened body, applying an AC electric field to the moisture sensor, and detecting the moisture content of the cementitious hardened body based on a correlation between a change in an electrical characteristic value of the moisture sensor and the moisture content of the cementitious hardened body.

[0016] This makes it possible to suppress the generation of minute gaps between the dielectric and the electrodes even when the dielectric is subjected to a thermal history due to hardening shrinkage of the cementitious hardened body forming the dielectric or temperature changes in an actual environment, and to stably obtain the electrical characteristics of the dielectric over a long period of time without destroying the cementitious hardened body to be measured, and to easily and accurately grasp the moisture content on the surface or inside of the cementitious hardened body to be measured. In addition, since the moisture sensor can be installed at any location of the cementitious hardened body to be measured, it becomes possible to measure not only the surface of the cementitious hardened body to be measured but also deep inside, and it becomes possible to grasp the distribution of the moisture content throughout the cementitious hardened body to be measured. Effect of the Invention

[0017] According to the present invention, it is possible to easily and accurately grasp the distribution of moisture content throughout the entire cementitious hardened body to be measured, without destroying the cementitious hardened body to be measured. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a schematic configuration of a moisture sensor according to an embodiment of the present invention; [Diagram 2] 2A and 2B are front and side views of a dielectric and electrodes of the moisture sensor according to the embodiment. [Diagram 3] FIG. 1 is a diagram showing the permeation of moisture into a dielectric. [Figure 4] 1A to 1C are diagrams illustrating steps in a method for manufacturing a moisture sensor. [Diagram 5] FIG. 1 is a diagram showing a schematic configuration of a moisture sensor used in Examples 1 to 4 and Comparative Examples 1 to 3. [Figure 6] 3 is a photograph of the outer electrode used in Example 1. [Figure 7] 1 is a photograph of a metal mesh (material: SUS304) used as an electrode in Examples 1 to 3. [Figure 8] FIG. 1 is a diagram showing a schematic configuration of a conventional moisture sensor. [Figure 9]1 is a graph showing the relationship between moisture content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using the electrode of Example 1. [Figure 10] 13 is a graph showing the relationship between moisture content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using the electrode of Example 2. [Figure 11] 13 is a graph showing the relationship between moisture content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using the electrode of Example 3. [Figure 12] 13 is a graph showing the relationship between moisture content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using the electrode of Example 4. [Figure 13] 13 is a graph showing the relationship between the moisture content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using an electrode of Comparative Example 2. [Figure 14] 13 is a graph showing the relationship between the moisture content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using an electrode of Comparative Example 3. [Figure 15] 13 is a graph showing the relationship between moisture content and capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for a moisture sensor using a conventional electrode of Comparative Example 4. [Figure 16] 11 is a photograph showing a cross section (part of the outer electrode and dielectric) of the moisture sensor of Example 3. [Figure 17] 1 is a photograph showing the state between a dielectric and an electrode of a conventional moisture sensor. [Figure 18] FIG. 1 is a diagram showing an outline of moisture amount measurement using a conventional moisture sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The inventors focused on the fact that a moisture sensor installed on the surface or inside of a cementitious hardened body to be measured is subjected to thermal history due to the hardening shrinkage of the cementitious hardened body and temperature changes in an actual environment, which causes tiny gaps to form between the dielectric and the electrode, making it impossible to measure the moisture content accurately. They discovered that by providing a hole in the electrode, the formation of tiny gaps between the dielectric and the electrode can be suppressed, the electrical characteristics of the dielectric can be stably obtained over a long period of time without destroying the cementitious hardened body to be measured, and the moisture content on the surface or inside of the cementitious hardened body to be measured can be grasped simply and accurately, and thus completed the present invention.

[0020] The present embodiment will be described with reference to the drawings. The cementitious hardened body is a hardened body containing at least cement, and is a concept including cement paste, mortar, and concrete.

[0021] [Moisture sensor configuration] FIG. 1 is a diagram showing a schematic configuration of a moisture sensor 100 according to this embodiment. FIGS. 2(a) and 2(b) are a front view and a side view of a dielectric 3 and electrodes 5 (5a, 5b) of the moisture sensor 100 according to this embodiment. The moisture sensor 100 includes a dielectric 3 formed in a columnar shape, a pair or more of electrodes 5 (5a, 5b) provided on the surface or inside of the dielectric 3 so as to face each other, and a lead wire 7 connected to each electrode 5 (5a, 5b) constituting a current-carrying part, and detects electrical 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 bonded to the electrodes 5 (5a, 5b) by solder. The lead wire 7 is connected to a measuring instrument 9, and an AC electric field is applied to detect the electrical characteristic value of the dielectric 3.

[0022] The dielectric 3 is a cylindrical body. In this embodiment, the cylindrical shape is described as an example, but is not limited to this. For example, the dielectric 3 may be a rectangular parallelepiped or a prismatic body having a polygonal bottom, or a ring-shaped hollow cylinder (annular cylinder) having a hollow center.

[0023] The diameter of the dielectric 3 should be sufficient to contain the electrode 5, and is preferably 15 mm or more and 110 mm or less. 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, it may be weak and may be damaged, and if it is more than 50 mm, it may take a long time for water to penetrate, which may reduce responsiveness.

[0024] The electrode 5 is a hollow cylinder. The diameter of the electrode 5 may be smaller than the diameter of the dielectric 3, but is preferably smaller than the diameter of the dielectric 3 by 10 mm or more. The height of the electrode 5 may be the same as the thickness of the dielectric 3, but is preferably smaller by 2 mm or more. This is to prevent the electrode 5 from being exposed from the dielectric.

[0025] The material used for the dielectric 3 may be any material that contains water, and it is preferable to use a material that has the same water absorption as the cementitious hardened body to be measured. For example, it is preferable to use a cementitious hardened body such as cement paste, mortar, concrete, etc., or ceramics, etc., similar to the measurement object. Also, a cementitious hardened body partially impregnated with resin may be used.

[0026] The cement type of the cementitious hardened body may be any type, such as ordinary Portland cement or early-strength cement, but from the viewpoint of hydration reaction, it is preferable to use early-strength cement. The age of the cementitious hardened body is preferably 28 days or more, at which time the hydration reaction is almost completed.

[0027] When mortar is used as the dielectric 3, it is preferable to use a mixture that has the same water absorption as the cementitious hardened body to be measured. Specifically, the water / cement ratio (W / C) is 15 to 70%, and the ratio of cement to fine aggregate is preferably 1 part cement to 2 to 3 parts fine aggregate. If the water / cement ratio is less than 15%, the amount of porosity in the mortar becomes too small, and if it is more than 70%, the amount of water absorption increases, so the amount of water does not approximate that of the cementitious hardened body, which is not preferable. If the ratio of fine aggregate is less than 2, the amount of porosity in the mortar becomes too small, and if it is more than 3, it is susceptible to the influence of the water absorption of the fine aggregate, so the amount of water does not approximate that of the cementitious hardened body, which is not preferable. In addition, since the fine aggregate is susceptible to the influence of the water absorption of the fine aggregate, the physical properties of the fine aggregate should be such that the water absorption rate is 3.0% or less and the specific surface area is 400 cm. 2 / g or less is preferable. As the fine aggregate, for example, dense artificial sand is preferable.

[0028] When concrete is used as the dielectric 3, it is preferable that the mixture has a water absorption property equivalent to that of the concrete structure to be measured.

[0029] By using a cementitious hardened body or ceramics for the dielectric 3, the adhesion to the cementitious hardened body to be measured can be increased, and the strength and durability of the cementitious hardened body to be measured are less likely to be affected.

[0030] In this way, it is possible to improve the consistency between the moisture sensor 100 and the moisture content inside the cementitious hardened body to be measured by controlling the blending ratio of the cementitious hardened body of the dielectric 3. In other words, by making the water absorption rate of the cementitious hardened body used in the dielectric 3 equivalent to that of the cementitious hardened body to be measured, it is possible to appropriately grasp the moisture content of the cementitious hardened body to be measured.

[0031] A pair of electrodes 5 (5a, 5b) are provided inside the dielectric 3 formed into a cylindrical body so that they have the same central axis and face each other, forming concentric cylindrical electrodes. Here, the electrode provided on the outer periphery inside the dielectric 3 is referred to as the outer electrode 5a, and the electrode provided on the inner periphery inside the dielectric 3 is referred to as the inner electrode 5b. The distance between the outer electrode 5a and the inner electrode 5b, i.e., the inter-electrode distance, 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 a short circuit, and if it is longer than 50 mm, there is a possibility that uneven moisture content will affect the measurement accuracy.

[0032] The electrode 5 has a plurality of holes. In this embodiment, the plurality of holes are formed by a mesh (woven net) structure, but the present invention is not limited to this as long as the electrode 5 has a plurality of holes. For example, the holes may be formed by punching. In addition, the mesh (woven net) structure may be a plain weave, a twill weave, a plain tatami weave, a patterned tatami weave, or the like, and any weaving method may be used.

[0033] The inner electrode 5b may be formed as a dense electrode and provided inside the dielectric 3. Since compressive stress is applied due to the thermal expansion difference, even if the inner electrode 5b is a dense electrode, there is a low possibility that a minute gap will occur between the dielectric and the electrode. Here, dense refers to a shape in which no holes are formed on the surface. In addition, when the dielectric 3 is a hollow cylinder, the inner electrode 5b may be provided so as to be in close contact with the inner surface of the dielectric 3.

[0034] Metal formed in a mesh shape has a lower rigidity than metal formed in a bulk shape, and can follow minute volume changes caused by hardening and shrinking of the dielectric. In addition, by providing a mesh-shaped electrode inside the dielectric, the surface of the electrode is in close contact with the dielectric material, and the inner circumferential surface forming the region that becomes the void of the hole of the electrode is in close contact with the dielectric material filled in the hole. This allows the electrode and the dielectric to be completely integrated. Therefore, it is possible to suppress the occurrence of minute gaps between the dielectric and the electrode.

[0035] Furthermore, when the shape of the dielectric 3 is a rectangular parallelepiped or polygonal columnar or cylinder without a hollow space, parallel plate electrodes may be formed on the top and bottom surfaces. In the case of parallel plate electrodes, it is preferable that the pair of opposing electrodes have the same shape and size. From the viewpoint of measurement accuracy, it is preferable that the distance between the electrodes is constant.

[0036] Figures 3(a) and (b) are diagrams showing the state of moisture penetration into a dielectric. As shown in Figure 3(b), in the case of parallel plate electrodes, the sides are open, which may result in non-uniform moisture penetration. On the other hand, as shown in Figure 3(a), in a structure in which the dielectric is shaped as a hollow cylinder and electrodes are formed on the curved surfaces, the sides of the dielectric are closed, which is the most preferable, as it ensures uniformity of moisture penetration into the dielectric. Note that some surfaces of the exposed part of the dielectric of the moisture sensor may be covered with resin or the like.

[0037] Since the moisture sensor is used by being embedded inside the cementitious hardened body, the electrode 5 is preferably made of a corrosive material. Furthermore, in order to improve the ability of the electrode 5 to follow minute volume changes caused by the hardening shrinkage of the dielectric and thermal history in the actual environment, it is preferable that the electrode 5 is made of a flexible material with a thermal expansion coefficient close to that of concrete or mortar. For example, precious metals such as gold, platinum, palladium, etc., as well as stainless steel materials such as SUS304, SUS316, and SUS430 are preferable.

[0038] The size of the holes provided in the electrode 5 is not preferred because if the holes are too large, the electrode area is insufficient and the electrical characteristics cannot be accurately measured. Also, if the holes are too small, the material forming the dielectric cannot enter the holes, and integration and adhesion are reduced, which is not preferred. Therefore, the size of the holes provided in the electrode 5 is preferably mesh 40 (#40) or more from the viewpoint of functioning as an electrode. Also, from the viewpoint of integration with the dielectric, mesh 100 (#100) or less is preferred. Here, mesh refers to the number of lines or meshes per 25.5 mm (1 inch), and mesh size is an index indicating the combination of wire diameter and mesh. In the case of stainless steel mesh, a size that satisfies a wire diameter of 0.1 to 0.25 mm and a mesh size of 0.1 to 0.5 mm is preferred.

[0039] [Manufacturing method of moisture sensor] Figure 4 shows the steps of the method for manufacturing a moisture sensor. First, cylindrical rings that will become the outer and inner electrodes are made of mesh-shaped metal (S1). The inner electrode may be dense. In addition, in the case of parallel plate electrodes rather than concentric cylindrical electrodes, it is preferable to make both electrodes from mesh-shaped metal.

[0040] Next, lead wires are attached to the two electrodes (outer electrode and inner electrode) with solder (S2). Next, the dielectric is prepared (S3). The two electrodes (outer electrode and inner electrode) with the lead wires attached prepared in (S2) are arranged concentrically in a formwork for the dielectric. Then, the material for forming the dielectric, such as cement paste, mortar, or concrete, is poured into the formwork and allowed to harden. For example, when mortar is used as the dielectric material, the mortar poured into the formwork has a cement:fine aggregate ratio of 1:3, with the cement being ordinary Portland cement and the fine aggregate being a material with a specific surface area of ​​300 cm. 2 Artificial sand with a molecular weight of 1000 / g was used. The W / C ratio was set to 55%, and the material age was preferably 28 days. As mentioned above, the material used for the dielectric is not limited to mortar. Cementitious hardened materials other than mortar (cement paste, concrete), ceramics, etc. may also be used. The hardened dielectric is removed from the formwork to prepare a moisture sensor.

[0041] [How to install the moisture sensor] The moisture sensor is installed on the surface or inside of the cementitious hardened body to be measured. When installing, the lead wire connected to the electrode is extended from the side of the cementitious hardened body to be measured. The lead wire is connected to a measuring device such as an LCR meter. The moisture sensor may also be installed by fixing it with a bolt to the surface of the cementitious hardened body to be measured.

[0042] [Calculating moisture content] The moisture sensor according to this embodiment detects the moisture content of the cementitious hardened body to be measured from the correlation between the capacitance (C) of the dielectric and the moisture content under an AC voltage and constant frequency. r It is also possible to detect the moisture content of the hardened cementitious material being measured from the correlation between the moisture content and the electrical conductivity (Tc), impedance (Z), and dielectric tangent (tan δ).

[0043] In addition, the capacitance (C) of the dielectric is measured in the frequency range of 10 Hz to 100 MHz, and the moisture content of the cementitious hardened body to be measured is detected from the correlation between the slope of each measured value (logarithm) and the frequency (logarithm). r ) the moisture content of the hardened cementitious body being measured can also be detected from the correlation between the slope of each measured value (logarithm) and the frequency (logarithm).

[0044] The latter detection method derives the slope from measurement data over a wide range of frequencies, and therefore has higher measurement accuracy than when measurements are taken at a constant frequency.

[0045] [Example] [1] Making a moisture sensor A moisture sensor was actually fabricated and the amount of moisture inside a concrete test specimen was measured. Fig. 5 is a diagram showing a schematic configuration of the moisture sensor used in Examples 1 to 4 and Comparative Examples 1 to 3.

[0046] (1) Preparation of electrodes In Examples 1 to 4 and Comparative Examples 1 to 3, an outer electrode having a diameter of 28 mm and a thickness of 10 mm was prepared, and an inner electrode having a diameter of 10 mm and a thickness of 10 mm was prepared. Fig. 6 is a photograph of the outer electrode used in Example 1. Figs. 7(a) to (c) are photographs of metal (material: SUS304) meshes used as electrodes in Examples 1 to 3. As shown in Fig. 6, the outer and inner electrodes prepared in each Example and Comparative Example were cylindrical ring electrodes in a mesh shape made of material SUS304 (hereinafter referred to as mesh electrodes).

[0047] Table 1 shows a summary of the mesh, wire diameter, mesh opening, and void ratio of the mesh electrodes used in each of the Examples and Comparative Examples.

[0048] [Table 1]

[0049] (2) Preparation of the dielectric Lead wires were soldered to the outer and inner electrodes prepared in (1), and the two electrodes were arranged concentrically in a formwork with an outer diameter of 38 mm and a thickness of 10 mm, as shown in Figure 5. Mortar was then poured into the formwork and allowed to harden. The mortar poured into the formwork had a cement:fine aggregate ratio of 1:3, with the cement being ordinary Portland cement and the fine aggregate being 0.01 mm thick with a specific surface area of ​​300 cm. 2 The artificial sand was used with a W / C ratio of 55% and the age of the material was 28 days.

[0050] (3) Finishing After the mortar hardened, it was removed from the formwork and a moisture sensor was fabricated.

[0051] (4) Fabrication of a conventional moisture sensor FIG. 8 is a diagram showing a schematic configuration of a conventional moisture sensor. As Comparative Example 4, a conventional moisture sensor was produced in which the electrodes were formed of a metal plate without holes. In the moisture sensor of Comparative Example 4, a ring-shaped outer electrode 15a with an outer diameter of 32 mm and a ring-shaped inner electrode 15b with an outer diameter of 8.2 mm, a thickness of 1.0 mm, a width of 10 mm, and an outer diameter of 8.2 mm were produced using a metal plate made of SUS304 material, thickness of 2.0 mm, and width of 10 mm, and the inner electrode 15b was placed at the center of the outer electrode 15a. Next, mortar was filled in the space formed between the two electrodes 15 (15a, 15b) to form a dielectric 13. The filled mortar was the same as the mortar used in Examples 1 to 4 and Comparative Examples 1 to 3, and after the mortar hardened, lead wires were attached to the two electrodes by soldering.

[0052] [2] Correlation between moisture content and electrical characteristics of moisture sensors Next, the correlation between the moisture content and the electrical characteristics of the moisture sensor will be described. Correlation data between the moisture content and the electrical characteristics of the moisture sensor was collected under the following conditions.

[0053] (i) The moisture sensor was dried, and the weight obtained by subtracting the weight of the electrodes and lead wires from the total weight of the moisture sensor in the dried state was determined as the initial weight (W0). Next, the moisture sensor was immersed in water in a vacuum environment, and the inside of the dielectric was saturated with water. It was then left for 24 hours in an environment with a temperature of 20°C and a humidity of 60%, and moisture content 1 (W1) was measured. It was then left for 12 hours in the same environment, and moisture content 2 (W2) was measured, and it was confirmed that W1 = W2, confirming that the sensor was in an equilibrium state.

[0054] (ii) Next, the moisture content (A60) in the dielectric was calculated by content 2 (W2) / initial weight (W0) × 100. The capacitance (C) of this moisture sensor was measured at frequencies of 100 Hz, 1 kHz, and 100 kHz using a measuring instrument (LCR meter) connected to the lead wires.

[0055] Similar to the 60% humidity condition, steps (i) and (ii) were repeated in a constant temperature (20°C) and 20% humidity environment. As a result, the moisture content of the moisture sensor in the bone dry condition (A0), 20% humidity environment (A20), 60% humidity environment (A60), and saturated moisture condition (A100) were approximately 0%, 2.0wt%, 4.0wt%, and 6.0wt%, respectively.

[0056] Next, the capacitance of the moisture sensor was measured at frequencies of 100 Hz, 1 kHz, and 100 kHz for each moisture content. Figs. 9 to 15 are graphs showing the relationship between the moisture content and the capacitance at frequencies of 100 Hz, 1 kHz, and 100 kHz for moisture sensors using electrodes of Examples 1 to 4 and Comparative Examples 2 to 4, respectively. As shown in Figs. 9 to 15, in Examples 1 to 4 and Comparative Examples 2 to 4, the moisture content and the capacitance of the moisture sensor are proportional to each other, and it was found that the moisture content could be measured accurately. Furthermore, the capacitance could not be measured for Comparative Example 1 (mesh 30). This is thought to be because the mesh openings of the mesh electrode were too large and it did not function as an electrode.

[0057] [3] Integrity of the dielectric and outer electrode Next, each moisture sensor was placed in a constant temperature and humidity bath, and the temperature was raised and lowered 100 times at a rate of 10°C / hr in the temperature range of -5 to 50°C. After that, the electrode interface of each moisture sensor was observed with an optical microscope. FIG. 16 is a photograph showing a cross section (part of the outer electrode and the dielectric) of the moisture sensor of Example 3. As shown in FIG. 16, even after the thermal history was applied, no minute gap was generated between the dielectric and the outer electrode, and it was confirmed that the dielectric and the outer electrode were in close contact with each other. Note that, as with Example 3, in Examples 1, 2, and 4 and Comparative Example 1, even after the thermal history was applied, no minute gap was generated between the dielectric and the outer electrode, and it was confirmed that the dielectric and the outer electrode were in close contact with each other.

[0058] In the moisture sensors of Examples 1 to 4 and Comparative Example 1, the dielectric and the electrode were completely integrated even after a thermal history was applied, whereas minute gaps were observed in the moisture sensors of Comparative Examples 2 to 4. In other words, even if the outer electrode has holes, as in the moisture sensors of Comparative Examples 2 and 3, if the openings are too small, the material forming the dielectric cannot penetrate into the holes, and integration and adhesion are reduced, resulting in minute gaps as a result of the thermal history.

[0059] Furthermore, when the capacitance was measured using the same method as in [2], the moisture sensors of Examples 1 to 3 showed no change in the values ​​before and after the thermal history was applied, whereas the moisture sensors of Comparative Examples 2 to 4 showed a difference. In other words, the moisture sensors of Comparative Examples 2 to 4 could not accurately measure the capacitance because a minute gap was created between the dielectric and the electrode, allowing moisture to enter the minute gap. That is, it was found that Examples 1 to 4 have a mesh opening of 0.1 to 0.5 mm and a void ratio of 35 to 50%, and the size and proportion of the holes provided in the electrode are suitable for close contact with the dielectric.

[0060] As described above, by installing the moisture sensor according to this embodiment on the surface or inside of the cementitious hardened body to be measured and monitoring the change in the electric characteristic value, it becomes possible to measure the moisture content on the surface and inside of the cementitious hardened body to be measured easily and with high accuracy. In addition, since the moisture sensor can be installed at any position in the cementitious hardened body to be measured, it becomes possible to measure not only near the surface of the cementitious hardened body to be measured but also deep inside, and it becomes possible to grasp the distribution of the moisture content throughout the cementitious hardened body to be measured. [Explanation of symbols]

[0061] 100 Moisture Sensor 3, 13 Dielectric 5, 15 electrodes 5a outer electrode 5b Inner electrode 7 Lead wire, current carrying part 9 Measuring Instruments, LCR Meters 15a outer electrode 15b Medial electrode

Claims

1. A moisture sensor for detecting the moisture content of a cementitious hardened body, A dielectric material formed in a columnar shape; A pair or more of electrodes provided on a surface or inside of the dielectric material and facing each other; a current-carrying portion electrically connected to each of the electrodes, Each of the pair of electrodes has a plurality of holes; A moisture sensor, characterized in that the electrode having the hole is in close contact with the dielectric material by means of a dielectric material filled in the hole.

2. 2. The moisture sensor according to claim 1, wherein the plurality of holes are in a mesh shape.

3. 3. The moisture sensor according to claim 2, wherein the mesh forming the mesh shape has an opening of 0.1 to 0.5 mm and a void ratio of 35 to 50%.

4. 4. The moisture sensor according to claim 1, wherein the dielectric material is a cementitious hardened material or a ceramic material.

5. A moisture detection method for detecting a moisture content of a cementitious hardened body by installing a moisture sensor on a surface or inside the cementitious hardened body, comprising: A moisture sensor according to any one of claims 1 to 4 is installed on a surface or inside of the cementitious hardened body, Applying an AC electric field to the moisture sensor; A moisture detection method comprising: detecting a moisture content of the cementitious hardened body based on a correlation between a change in an electrical characteristic value of the moisture sensor and the moisture content of the cementitious hardened body.

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