DO and pH measurement sensors in concrete

Abstract

To provide an embedded DO and pH measurement sensor in concrete capable of operating in concrete.SOLUTION: A DO and pH measurement sensor 10 in concrete is embedded in reinforced concrete and detects corrosion of reinforcing bars inside the reinforced concrete, and the DO and pH measurement sensor 10 comprises a DO sensor 20, a pH sensor 30, and a cylindrical substrate 40 containing the DO sensor 20 and the pH sensor 30. The pH sensor 30 has an insulating substrate, and a pH measurement electrode arranged on one surface of the insulating substrate and a solid contact reference electrode arranged on the other surface of the insulating substrate.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to DO and pH measurement sensors in concrete.

Background Art

[0002] As one of the deterioration phenomena of reinforced concrete structures, corrosion deterioration of internal steel bars can be mentioned. Reinforced concrete structures built in the ocean or along the coast are affected by seawater and undergo corrosion deterioration. In addition, reinforced concrete structures built inland are subject to corrosion deterioration due to salt damage caused by the use of freeze-thaw agents. Thus, there is a concern about corrosion deterioration in reinforced concrete structures. When the degree of corrosion deterioration is severe, in addition to a decrease in structural load-bearing capacity, peeling of concrete pieces may occur. Therefore, for reinforced concrete structures with a concern about corrosion deterioration, it is necessary to appropriately evaluate the corrosion of steel bars in order to prevent a decrease in structural durability.

[0003] Conventionally, as methods for evaluating the corrosion of steel bars, a method for determining the presence or absence of corrosion generation by the natural potential method, a method for determining the corrosion rate by the polarization resistance method, etc. have generally been used. However, since these methods involve infiltrating an electrolytic solution into the concrete for measurement and performing electrochemical measurements with the concrete in a wet state, accurate measurement results cannot be obtained when the infiltration of the electrolytic solution is insufficient. In addition, for measurement, operations such as infiltrating the electrolytic solution into the concrete and installing electrodes are required by the measurer at the measurement position.

[0004] Considering the laboriousness of measurement, as a corrosion evaluation method, a method that can be monitored without special operations during measurement is desirable. The corrosion reaction of steel bars occurs when moisture penetrates to the steel bars in the concrete, and the surface of the steel bars becomes wet and electron exchange becomes possible. The reaction rate of the corrosion reaction is affected by the dissolved oxygen (hereinafter referred to as "DO") and the hydrogen ion concentration index (hereinafter referred to as "pH") in the concrete. That is, for the corrosion evaluation of steel bars, it is important to grasp the presence or absence of water penetration into the concrete and the DO and pH of the reaction system when water penetrates into the concrete.

[0005] General DO and pH detection devices are designed for liquid samples and cannot be applied to the measurement of DO and pH in concrete. As a pH sensor for concrete, for example, there is one that includes an electrode embedded in the concrete and a reference electrode brought into contact with the concrete surface from the outside, and calculates the pH from the potential difference between the two electrodes (see, for example, Patent Document 1). In addition, as a method for evaluating the pH inside the concrete, for example, there is a method targeting samples obtained during drilling or core sampling of the concrete (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the measurement system of the pH sensor of Patent Document 1, not only is it necessary to install a reference electrode on the concrete surface, but the measured value is also affected by the moisture condition of the concrete between the electrodes. That is, if the concrete between the electrodes is dry, the noise generated in the measured value will increase. Further, the pH evaluation method of Patent Document 2 is a test method involving the destruction of concrete and is not suitable for monitoring the corrosion of reinforced concrete structures.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide an embedded type DO and pH measurement sensor in concrete that can operate in concrete.

Means for Solving the Problems

[0009] The present invention has the following aspects. [1] A DO and pH measurement sensor in concrete that is embedded inside reinforced concrete and detects the corrosion of the reinforcing bars inside the reinforced concrete, comprising a DO sensor, a pH sensor, and a cylindrical base material that encloses the DO sensor and the pH sensor, wherein the pH sensor has an insulating substrate, a pH measurement electrode disposed on one surface of the insulating substrate, and a solid contact type reference electrode disposed on the other surface of the insulating substrate. [2] The DO and pH measurement sensor in concrete according to [1], wherein the DO sensor and the pH sensor are spaced apart inside the base material. [3] The DO and pH measurement sensor in concrete according to [1] or [2], wherein the solid contact type reference electrode has a solid reference membrane made of a porous body.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an embedded type DO and pH measurement sensor in concrete that can operate in concrete.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, the DO and pH measurement sensor in concrete (hereinafter, may also be referred to as "DO / pH measurement sensor") according to the embodiment of the present invention will be described with reference to FIGS. 1 to 10. FIG. 1 is a plan view showing the DO / pH measurement sensor according to the embodiment of the present invention. FIG. 2 is a side view showing the DO / pH measurement sensor according to the embodiment of the present invention. FIG. 3 shows the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view taken along line A-A of FIG. 2. FIG. 4 shows the DO sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view perpendicular to the longitudinal direction. FIG. 5 shows the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view perpendicular to the longitudinal direction. FIG. 6 is a plan view showing the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention. FIG. 7 is a plan view showing the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention. FIG. 8 shows the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view parallel to the longitudinal direction. FIG. 9 shows the pH measurement electrode of the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view perpendicular to the longitudinal direction. FIG. 10 shows the solid-contact type reference electrode of the pH sensor constituting the DO / pH measurement sensor according to the embodiment of the present invention and is a cross-sectional view perpendicular to the longitudinal direction. Note that this embodiment is specifically described to better understand the gist of the invention, and unless otherwise specified, it does not limit the present invention.

[0013] [DO and pH Measurement Sensors in Concrete] As shown in FIGS. 1 to 3, the DO / pH measurement sensor 10 of this embodiment includes a DO sensor 20, a pH sensor 30, and a cylindrical base material 40. As shown in FIGS. 1 and 3, the base material 40 encloses the DO sensor 20 and the pH sensor 30. In other words, the DO sensor 20 and the pH sensor 30 are arranged on or near the inner surface 40a of the base material 40. Also, inside the base material 40, it is preferable that the DO sensor 20 and the pH sensor 30 are arranged separately. For example, the DO sensor 20 and the pH sensor 30 are preferably separated by 10 mm or more, and more preferably separated by 20 mm or more. In this way, the DO sensor 20 and the pH sensor 30 do not interfere with each other, and the measurement of dissolved oxygen (DO) in concrete by the DO sensor 20 and the measurement of the hydrogen ion concentration index (pH) in concrete by the pH sensor 30 can be measured more accurately. Furthermore, the other ends (rear ends, parts other than the measurement parts) of the DO sensor 20 and the pH sensor 30 are adhered and fixed inside the base material 40 by an epoxy resin 50.

[0014] As will be described later, when the concrete is driven, the mortar 100 of the concrete is filled into the base material 40. In other words, the mortar 100 is filled into the space (the space inside the base material 40 that is inside the inner surface 40a) where the DO sensor 20 and the pH sensor 30 are arranged inside the base material 40. That is, the measurement parts (electrodes described later) of the DO sensor 20 and the pH sensor 30 are in contact with the mortar 100 filled in the base material 40.

[0015] "DO Sensor" As shown in FIG. 4, the DO sensor 20 has a first electrode 21, a second electrode 22, an epoxy resin 23, and a tubular body 24. One end 20a of the DO sensor 20 is the measurement part of the DO sensor 20 and is inside the base material 40, closer to the inside of the base material 40 than one end face (the end face on the side where the base material 40 is open) 40b of the base material 40. On one end face 20b of the DO sensor 20, the first electrode 21 and the second electrode 22, which are the measurement parts, are exposed.

[0016] The first electrode 21 is disposed at the center of the DO sensor 20 and extends in the longitudinal direction of the DO sensor 20. The first electrode 21 has a platinum wire and a glass capillary that embeds the platinum wire. That is, in the first electrode 21, the outer periphery of the platinum wire is surrounded by the glass capillary. The platinum wire and the glass capillary extend in the same axial direction. The diameter of the first electrode 21 is preferably as small as possible. For example, it is preferably 5 μm or more and 100 μm or less. When the diameter of the first electrode 21 is equal to or greater than the lower limit value, it is easy to install the first electrode 21. When the diameter of the first electrode 21 is equal to or less than the upper limit value, it operates based on the principle described later (see paragraph 0045).

[0017] The second electrode 22 is wound around the outer periphery of the first electrode 21. That is, the second electrode 22 is wound around the outer periphery of the glass capillary of the first electrode 21. The second electrode 22 is composed of a platinum wire. The area of the second electrode 22 is larger than that of the first electrode 21.

[0018] The epoxy resin 23 is filled between the glass tube 24 and the second electrode 22.

[0019] The material of the tubular body 24 is not particularly limited as long as it is insulating, does not deform in concrete, and has low solubility and alkali resistance. Examples of the material of the tubular body 24 include glass such as Pyrex (registered trademark) glass; resins such as epoxy resin and polyvinyl chloride; silicone resin; rubber, etc.

[0020] As shown in FIGS. 1 and 3, a lead wire 25 is connected to the other end (rear end) 20c of the DO sensor 20.

[0021] The DO sensor 20 is manufactured, for example, as follows. The first electrode 21, the glass capillary embedding the first electrode 21, and the second electrode 22 are arranged in the glass tube 24. Next, the epoxy resin 23 is filled between the glass tube 24 and the second electrode 22. Next, the epoxy resin 23 is cured to obtain a composite body in which the first electrode 21, the second electrode 22, the epoxy resin 23, and the glass tube 24 are integrated. Next, the end face of the composite body is polished, and the first electrode 21 and the second electrode 22 are exposed on one end face 20b. Next, a lead wire 25 is connected to the other end 20c to obtain the DO sensor 20.

[0022] "pH sensor" As shown in FIGS. 5 to 8, the pH sensor 30 includes an insulating substrate 31, a pH measurement electrode 60 disposed on one surface 31a of the insulating substrate 31, and a solid contact type reference electrode 70 disposed on the other surface 31b of the insulating substrate 31. The pH measurement electrode 60 and the solid contact type reference electrode 70 are disposed so as to face each other with the insulating substrate 31 interposed therebetween. One end face 30a of the pH sensor 30 is on the same plane as one end face (the end face on the opening side of the base material 40) 40b of the base material 40.

[0023] The material of the insulating substrate 31 is not particularly limited, and examples thereof include polyvinyl chloride. The distance (distance between electrodes) between the pH measurement electrode 60 and the solid contact type reference electrode 70 is preferably short from the viewpoint of avoiding the influence of the liquid junction potential difference due to the concrete between the electrodes. Therefore, the thickness of the insulating substrate 31 is preferably small, for example, preferably 1 mm or more and 5 mm or less, and more preferably 1 mm or more and 2 mm or less. When the thickness of the insulating substrate 31 is equal to or greater than the lower limit value, the durability of the sensor can be ensured. When the thickness of the insulating substrate 31 is equal to or less than the upper limit value, the influence of the liquid junction potential difference is small, and the potential difference can be measured more accurately.

[0024] The pH measurement electrode 60 is disposed on one surface 31a of the insulating substrate 31 and extends in the longitudinal direction of the insulating substrate 31. As shown in FIGS. 5, 6, and 8, the pH measurement electrode 560 includes a proton selective electrode 61 and an insulating film 62.

[0025] The proton selective electrode 61 is not particularly limited as long as it is an electrode having a proton selective function, and examples thereof include a tungsten oxide electrode and an iridium oxide electrode.

[0026] When the proton selective electrode 61 is a tungsten oxide electrode, as shown in FIG. 9, the proton selective electrode 61 includes a tungsten 63 serving as a core portion and a tungsten oxide 54 covering the outer periphery of the tungsten 63.

[0027] The cross-sectional shape of the proton selective electrode 61 in a direction perpendicular to its longitudinal direction is not particularly limited, and may be, for example, a square shape, a rectangular shape, a circular shape, or the like. When the cross-sectional shape of the proton selective electrode 61 in a direction perpendicular to its longitudinal direction is circular, its diameter is preferably 10 μm or more and 5000 μm or less, and more preferably 100 μm or more and 2000 μm or less. When the diameter of the proton selective electrode 61 is equal to or greater than the lower limit value, the durability of the electrode can be ensured. When the diameter of the proton selective electrode 61 is equal to or less than the upper limit value, it is suitable for space occupation when a large number of sensors are installed.

[0028] As shown in FIGS. 6 and 8, the insulating film 62 covers, on one surface 31a of the insulating substrate 31, portions other than the measurement portion (the portion for measuring pH) of the proton selective electrode 61. That is, the insulating film 62 is composed of a first insulating film 62A and a second insulating film 62B that are separated from each other. The proton selective electrode 61 is exposed at a portion where the first insulating film 62A and the second insulating film 62B are separated (the portion where the insulating film 62 is not provided) to form a measurement portion 61A. The length of the insulating substrate 31 of the measuring part 61A of the proton selection electrode 61 along the longitudinal direction is preferably 5 mm or more and 20 mm or less, and more preferably 10 mm or more and 20 mm or less. When the length of the measuring part of the proton selection electrode 61 is equal to or greater than the lower limit value, it is easy to fabricate the sensor. When the length of the measuring part of the proton selection electrode 61 is equal to or less than the upper limit value, the amount of metal wire used for fabricating the electrode can be reduced.

[0029] The material of the insulating film 62 is not particularly limited, and examples thereof include polyimide, polyvinyl chloride, and silicone.

[0030] The solid contact type reference electrode 70 is disposed on the other surface 31b of the insulating substrate 31 and extends in the longitudinal direction of the insulating substrate 31. As shown in FIGS. 5, 7, 8, and 10, the solid contact type reference electrode 70 includes a silver wire 71, a solid reference film 72, and an insulating film 73.

[0031] The cross-sectional shape of the silver wire 71 in the direction perpendicular to the longitudinal direction is not particularly limited, and may be a square shape, a rectangular shape, a circular shape, or the like. When the cross-sectional shape of the silver wire 71 in the direction perpendicular to the longitudinal direction is circular, its diameter is preferably 10 μm or more and 1000 μm or less, and more preferably 100 μm or more and 200 μm or less. When the diameter of the silver wire 71 is equal to or greater than the lower limit value, it is easy to fabricate the electrode and the durability of the electrode can be ensured. When the diameter of the silver wire 71 is equal to or less than the upper limit value, the material cost is low.

[0032] The solid reference film 72 is provided on the other surface 31b of the insulating substrate 31 so as to cover the silver wire 71. The solid reference film 72 is preferably composed of a porous body. By configuring the solid reference film 72 from a porous body, the pH of the moisture penetrated into the mortar 100 can be measured more accurately.

[0033] The porosity of the solid reference film 72 is the ratio of the cavity portion (pore 72B) of the solid reference film 72 composed of a porous body to the total volume of the solid reference film 72.

[0034] The thickness of the solid reference film 72 based on the other surface 31b of the insulating substrate 31 is preferably 0.1 mm or more and 0.5 mm or less, and more preferably 0.3 mm or more and 0.5 mm or less. When the thickness of the solid reference film 72 is equal to or greater than the lower limit value, a sufficient solid reference film can be formed on the silver wire 71. When the thickness of the solid reference film 72 is equal to or less than the upper limit value, the time required for the output value to stabilize during measurement can be shortened.

[0035] The solid reference film 72 contains a resin as the main material, a plasticizer, silver chloride (AgCl) and potassium chloride (KCl), or silver bromide (AgBr) and potassium bromide (KBr).

[0036] The material of the resin is not particularly limited, and examples thereof include polyvinyl chloride. The material of the plasticizer is not particularly limited, and examples thereof include bis(2-ethylhexyl) sebacate.

[0037] As shown in FIGS. 7 and 8, the insulating film 73 covers the portions other than the measurement portion of the solid reference film 72 on the other surface 31b of the insulating substrate 31. That is, the insulating film 73 is composed of a third insulating film 73A and a fourth insulating film 73B that are separated from each other. The portion where the third insulating film 73A and the fourth insulating film 73B are separated (the portion where the insulating film 73 is not provided) is the measurement portion 72A where the silver wire 71 is covered with the solid reference film 72. The length of the measurement portion 71A along the longitudinal direction of the insulating substrate 31 is preferably 5 mm or more and 20 mm or less, and more preferably 10 mm or more and 20 mm or less. When the length of the measurement portion of the solid reference film 72 is equal to or greater than the lower limit value, it is easy to fabricate the sensor. When the length of the measurement portion of the solid reference film 72 is equal to or less than the upper limit value, less raw material is required for fabricating the solid reference film.

[0038] The material of the insulating film 73 is not particularly limited, and examples thereof include polyimide, polyvinyl chloride, and silicone.

[0039] As shown in FIGS. 1 and 3, a lead wire 32 is connected to the other end 30b of the pH sensor 30.

[0040] The pH sensor 30 is manufactured, for example, as follows. On one surface 31a of the insulating substrate 31, a proton selective electrode 61 is arranged along the longitudinal direction of the insulating substrate 31. Next, on one surface 31a of the insulating substrate 31, a first insulating film 62A and a second insulating film 62B spaced apart from each other are formed at a predetermined interval so as to cover the proton selective electrode 61, and the proton selective electrode 61 is fixed on one surface 31a of the insulating substrate 31. Next, on the other surface 31b of the insulating substrate 31, a silver wire 71 is arranged along the longitudinal direction of the insulating substrate 31. Next, on the other surface 31b of the insulating substrate 31, a paste for forming a solid reference film containing a resin, a plasticizer, silver chloride (AgCl) and potassium chloride (KCl), or silver bromide (AgBr) and potassium bromide (KBr), and a solvent is applied to form a coating film, and the coating film is dried to form a solid reference film 72. Next, on the other surface 31b of the insulating substrate 31, a third insulating film 73A and a fourth insulating film 73B spaced apart from each other are formed so as to cover the silver wire 71 at a portion where the solid reference film 72 is not formed, and the silver wire 61 is fixed on the other surface 31b of the insulating substrate 31. Next, a lead wire 32 is connected to the other end 30b to obtain the pH sensor 30.

[0041] "Method of Using DO and pH Measurement Sensors in Concrete" A method of using the DO / pH measurement sensor 10 of this embodiment will be described. The DO / pH measurement sensor 10 is embedded inside the reinforced concrete and is for detecting the corrosion of the reinforcing bars inside the reinforced concrete. Specifically, before the concrete is placed, the DO / pH measurement sensor 10 is installed at the position of the reinforcing bar where corrosion is expected to be a problem (usually the position of the outermost reinforcing bar). When concrete is driven, the mortar 100 of the concrete is filled into the base material 40. When the moisture contained in the concrete penetrates up to the DO / pH measurement sensor 10, the mortar 100 filled in the base material 40 is filled with water, and a battery is formed in the DO sensor 20 and the pH sensor 30. At that time, the dissolved oxygen (DO) in the concrete can be obtained from the current value I between the first electrode 21 and the second electrode 22 of the DO sensor 20. Also, the hydrogen ion concentration index (pH) in the concrete can be obtained from the potential difference E between the pH measurement electrode 50 of the pH sensor 30 and the solid contact type reference electrode 60.

[0042] The DO / pH measurement sensor 10 of the present embodiment can be embedded in concrete to measure the dissolved oxygen (DO) in the concrete and the hydrogen ion concentration index (pH) in the concrete. By measuring the dissolved oxygen (DO) in the concrete and the hydrogen ion concentration index (pH) in the concrete, the presence or absence of water penetration into the concrete can be evaluated. As a result, the corrosion evaluation of the reinforcing bar can be performed.

[0043] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited to the above embodiments. Each configuration and their combinations in the above embodiments are examples, and additions, omissions, substitutions, and other changes of the configuration are possible without departing from the spirit of the present invention.

Example

[0044] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples.

[0045] [Example 1] The dissolved oxygen (DO) in the aqueous solution was measured by a DO sensor. As the DO sensor, a platinum disk electrode (diameter: 100 μm) was used as the sample electrode (first electrode), and a platinum wire was used as the counter electrode (and pseudo-reference electrode: second electrode). A working electrode and a counter electrode were immersed in an aqueous solution into which argon, air, and oxygen were blown, and potentiodynamic cathodic polarization was performed. The results are shown in Fig. 11. As shown in Fig. 11, a cathodic current flowed in the DO sensor in the potential region of -0.4 V or lower. This cathodic current is derived from the reduction reaction of dissolved oxygen (DO) in the aqueous solution represented by the following formula (1). O2 + 2H2O + 4e - → 4OH - (1) In the potential region of -0.5 V or lower, since the reaction of formula (1) is rate-determined by mass transfer, the cathodic current (limiting current) when the platinum disk electrode is potentiostatically polarized at the potential within this potential region is proportional to the dissolved oxygen (DO). The limiting current I lim of the microdisk electrode is represented by the following formula (2). I lim = 4nFDC b a (2) In the above formula (2), n is the number of moving electrons involved in the reaction, F is the Faraday constant, D and C b are the diffusion coefficient of the reaction species and the concentration in the bulk solution, and a is the electrode radius. Based on the above formula (2), the result of calculating the limiting current I lim is shown in Fig. 12. As shown in Fig. 12, it was found that a good linear relationship holds between the limiting current at -0.6 V and the dissolved oxygen concentration.

[0046] [Example 2] The dissolved oxygen (DO) in the cement paste (w / c = 40%) was measured using a DO sensor. As the DO sensor, one using a platinum disk electrode (diameter 100 μm) as the working electrode (first electrode) and a platinum wire as the counter electrode (and pseudo-reference electrode: second electrode) was used. The working electrode and the counter electrode were immersed in the cement paste (w / c = 40%), and potentiodynamic cathodic polarization was performed in an air-saturated environment. The results are shown in Fig. 13. Also, after potentiodynamic cathodic polarization in an air-saturated environment, oxygen aeration was performed for 12 hours, and then potentiodynamic cathodic polarization was performed. The results are shown in Fig. 13. From the results shown in Fig. 13, when comparing the limiting current values at -0.6 V, it was found that in an oxygen-saturated environment, the limiting current value increased significantly compared to an air-saturated environment, indicating that the DO sensor can detect the increase in oxygen concentration.

[0047] [Example 3] As the pH sensor, a tungsten oxide (100 μm in diameter) sample electrode (first electrode) and a silver (100 μm in diameter) reference electrode (second electrode) with a solid reference film made of silver / silver chloride / potassium chloride formed on its surface were used. Regarding the pH sensor, its operation in an aqueous solution and in cement paste was confirmed. Potential difference measurements were carried out in an aqueous solution using boric acid buffer solutions (pH 7.15, pH 8.42), carbonate buffer solution (pH 10.6), and sodium hydroxide aqueous solutions (pH 12, pH 13). The results are shown in Fig. 14. From the results shown in Fig. 14, although there is variation for each sensor, the natural potential of the tungsten oxide electrode shows a good linear relationship with pH, and it was confirmed that it operates normally in a wide pH range of neutral to alkaline.

[0048] [Example 4] As the pH sensor, a tungsten oxide (100 μm in diameter) sample electrode (first electrode) and a silver (100 μm in diameter) reference electrode (second electrode) with a solid reference film made of silver / silver chloride / potassium chloride formed on its surface were used. Potential measurement (electrometry) in cement paste (w / c = 40%) was carried out using the pH sensor. The results are shown in Fig. 15. From the results shown in Fig. 15, it was found that from the start of measurement, the pH was alkaline, indicating that the alkaline environment of the cement paste could be measured. For the pH sensor used, a calibration curve was obtained in advance and used to calculate the pH.

[0049] [Example 5] As the pH sensor, a tungsten oxide (diameter 100 μm) sample electrode (first electrode) and a silver (diameter 100 μm) reference electrode (second electrode) with a solid reference membrane made of silver / silver chloride / potassium chloride formed on its surface were used. Cement paste was placed in a room at a temperature of 20 °C and a humidity of about 30% RH, and water was supplied every week to verify the output fluctuation of the pH sensor due to the wetting and drying state of the cement paste. The results are shown in Fig. 16. From the results shown in Fig. 16, it was confirmed that when the cement paste became dry due to the vaporization of water, the potential of the pH sensor deteriorated, but it showed the original potential again for several days after water supply. That is, even if the pH measurement became temporarily impossible due to the dry state, it was confirmed that the pH could be measured again when it became wet again. At the same time, the penetration of water into the sensor position could also be grasped.

Explanation of symbols

[0050] 10 DO and pH measurement sensor (DO / pH measurement sensor) in concrete 20 DO sensor 21 First electrode 22 Second electrode 23 Epoxy resin 24 Glass tube 25 Lead wire 30 pH sensor 31 Insulating substrate 32 Lead wire 40 Base material 50 Epoxy resin 60 pH measurement electrode 61 Proton selective electrode 62 Insulating film 62A First insulating film 62B Second insulating film 63 Tungsten 64 Tungsten oxide 70 Solid contact type reference electrode 71 Silver wire 72 Solid reference membrane 73 Insulating film 73A Third insulating film 73B Fourth insulating film 100 mortar

Claims

Claim 1 A DO and pH measurement sensor in concrete that is embedded inside reinforced concrete and detects corrosion of the reinforcing bars inside the reinforced concrete, comprising: a DO sensor, a pH sensor, and a cylindrical base material enclosing the DO sensor and the pH sensor; The pH sensor has an insulating substrate, and a pH measurement electrode and a solid-contact type reference electrode disposed on both surfaces of the insulating substrate, respectively. The DO and pH measurement sensor in concrete. Claim 2 The DO and pH measurement sensor in concrete according to claim 1, wherein the DO sensor and the pH sensor are spaced apart inside the base material. Claim 3 The DO and pH measurement sensor in concrete according to claim 1 or 2, wherein the solid-contact type reference electrode has a solid reference membrane made of a porous body.

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