Chloride ion concentration measurement device and method for measuring concentration of chloride ion

Abstract

To provide a chloride ion concentration measurement device and a method for measuring the concentration of chloride ions that enable simple and rapid measurement of the concentration of chloride ions by using near-infrared light.SOLUTION: A chloride ion concentration measurement device 1 includes: a light source 11 that irradiates near-infrared light L1 onto a surface 111 of a coating film 110 that covers a concrete structure 100 and includes a resin having a hydroxy group; a photometric unit 14 that measures reflected light L2 of the near-infrared light L1 reflected by the surface 111 of the coating film 110; a calculation device 21 that calculates the concentration of chloride ions present in the surface 111 of the coating film 110 on the basis of the absorption spectrum of the hydroxy group of the reflected light L2 measured by the photometric unit 14; and an output device 22 for outputting the chloride ion concentration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a chloride ion concentration measuring device and a chloride ion concentration measuring method. [Background technology]

[0002] Salt damage is one of the causes of deterioration of concrete structures. Salt damage is a deterioration phenomenon in which salt airborne from the sea or salt contained in antifreeze and snow-melting agents penetrates concrete, causing corrosion of steel. In order to efficiently maintain and manage concrete structures, it is preferable to understand which areas of the concrete structure have a high level of salt adhesion and which parts are prone to deterioration or have already deteriorated, depending on the location, environmental conditions, and structural type.

[0003] Conventionally, a known method for quantitatively measuring the amount of salt adhering to the surface of a concrete structure is the gauze wiping method, as described in Patent Document 1. In the gauze wiping method, the surface of a concrete structure with a defined measurement range is wiped with gauze, the wiped gauze is immersed in a specified amount of water, and the salt concentration is determined by titration or electrical conductivity. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] "Study on the amount of salt adhering to concrete bridges using the gauze wiping method", Abstracts of the 68th Annual Conference of the Japan Society of Civil Engineers, September 1, 2013, V-495, pp. 989-990 Summary of the Invention [Problem to be solved by the invention]

[0005] In areas near coastlines where there is a lot of salt drifting in from the sea, and in cold regions where antifreezing agents and snow-melting agents are used, concrete structures are painted with a resin coating to prevent salt damage. However, even when such a coating is formed, scratches and cracks may appear in the coating due to deterioration over time, which may allow salt to penetrate into the concrete structure. Therefore, in order to efficiently maintain and manage concrete structures, it is preferable to also understand the salt concentration on the coating surface of the concrete structure.

[0006] However, the gauze wipe method requires a lot of preparation and steps to measure salinity, and the gauze used must be brought back for analysis, which makes it time-consuming and laborious to measure a wide area.

[0007] Therefore, an object of the present disclosure is to provide a chloride ion concentration measuring device and a chloride ion concentration measuring method that can measure chloride ion concentration simply and quickly by using near-infrared light. [Means for solving the problem]

[0008] The chloride ion concentration measuring device according to the present disclosure includes a light source that irradiates near-infrared light onto the surface of a coating film that covers a concrete structure and contains a resin having a hydroxy group. The chloride ion concentration measuring device includes a photometric unit that measures the near-infrared light reflected from the surface of the coating film. The chloride ion concentration measuring device includes a computing unit that calculates the chloride ion concentration present on the surface of the coating film based on the absorption spectrum of the hydroxy group of the reflected light measured by the photometric unit. The chloride ion concentration measuring device includes an output device that outputs the chloride ion concentration.

[0009] The calculation device may calculate the chloride ion concentration using an absorption spectrum including a wavelength region of 1350 nm to 1500 nm.

[0010] The calculation device may calculate the chloride ion concentration based on an absorption spectrum including a first peak which is a peak due to hydroxy groups on the surface of the coating film and a second peak which is a peak due to water.

[0011] The calculation device may calculate the chloride ion concentration based on the absorption spectrum including a first peak having a wavelength of 1.39 μm and a second peak having a wavelength of 1.42 μm.

[0012] The calculation device may calculate the chloride ion concentration based on an absorption spectrum including a first peak present in a wavelength range of 1350 nm or more and less than 1420 nm and a second peak present in a wavelength range of 1420 nm or more and 1500 nm or less.

[0013] The calculation device may calculate the chloride ion concentration by chemometrics.

[0014] The calculation device may calculate the chloride ion concentration based on the absorption spectrum of the unit concentration when moisture is attached to the surface of the coating film and the absorption spectrum of the unit concentration when the surface of the coating film is dry.

[0015] The chloride ion concentration measurement method according to the present disclosure includes a step of irradiating near-infrared light from a light source onto the surface of a coating film that covers a concrete structure and contains a resin having hydroxy groups. The chloride ion concentration measurement method also includes a step of measuring, with a photometric unit, the near-infrared light reflected from the surface of the coating film. The chloride ion concentration measurement method also includes a step of calculating, with a computing device, the chloride ion concentration present on the surface of the coating film based on the absorption spectrum of the hydroxy groups of the reflected light measured with the photometric unit. The chloride ion concentration measurement method also includes a step of outputting the chloride ion concentration from an output device. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a chloride ion concentration measuring device and a chloride ion concentration measuring method that can measure chloride ion concentration simply and quickly by using near-infrared light. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a chloride ion concentration measuring device according to one embodiment. [Figure 2] This is the spectrum A(λ) of unit concentration when sodium chloride is ionized and attached to the surface of the paint film. [Figure 3] This is the spectrum B(λ) of unit concentration when sodium chloride is dissolved in water and attached to the surface of the paint film. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, several exemplary embodiments will be described with reference to the drawings. Note that the dimensional proportions of the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0019] The chloride ion concentration measuring device 1 according to this embodiment is a device that measures chloride ion concentration by irradiating near-infrared light L1 onto a surface 111 of a coating film 110 that covers a concrete structure 100. Since the chloride ion concentration can be measured using near-infrared light L1, the chloride ion concentration can be measured simply and quickly.

[0020] The concrete structure 100 may include at least one selected from the group consisting of a hardened cement paste, a hardened mortar, and a hardened concrete. The hardened cement paste is a hardened product obtained by hardening a composition containing cement and water. The hardened mortar is a hardened product obtained by hardening a composition containing cement, water, and fine aggregate. The hardened concrete is a hardened product obtained by hardening a composition containing cement, water, fine aggregate, and coarse aggregate.

[0021] The concrete structure 100 is coated with a coating film 110. By coating the concrete structure 100 with the coating film 110, salt damage can be suppressed even in areas near coastlines where there is a lot of salt drifting in from the sea, or in cold regions where antifreezing agents and snow-melting agents are used. The coating film 110 may or may not have scratches and cracks.

[0022] The coating film 110 contains a resin having a hydroxy group. The hydroxy group interacts with chloride ions to absorb near-infrared light L1 in a predetermined wavelength range. Therefore, the chloride ion concentration measuring device 1 according to this embodiment can measure the chloride ion concentration on the surface 111 of the coating film 110. The coating film 110 having a hydroxy group may contain at least one resin selected from the group consisting of urethane resin, epoxy resin, fluororesin, urea resin, and phthalic acid resin.

[0023] 1, the chloride ion concentration measuring device 1 includes a probe head 10 and a controller 20. The probe head 10 is electrically connected to the controller 20 via a cable. In this embodiment, the probe head 10 and the controller 20 are connected by a cable in a wired manner, but input and output of electrical signals may also be performed by a wireless connection.

[0024] The probe head 10 includes a light source 11 , a light receiving unit 12 , a spectroscopic unit 13 , a photometer unit 14 , wheels 15 , and a grip unit 16 .

[0025] The light source 11 irradiates the surface 111 of the coating film 110 with near-infrared light L1. The wavelength range of light contained in the near-infrared light L1 may be 800 nm or more and 2500 nm or less. The wavelength range of light contained in the near-infrared light L1 may be 1000 nm or more or 1350 nm or more. The wavelength range of light contained in the near-infrared light L1 may be 2000 nm or less or 1500 nm or less. The light source 11 may be any light source capable of irradiating near-infrared light L1, and any known light source capable of emitting light including wavelengths in the near-infrared range, such as a halogen lamp, a tungsten lamp, a light-emitting diode, or a laser, may be used.

[0026] The light receiving unit 12 receives reflected light L2 of the near-infrared light L1 reflected by the surface 111 of the coating film 110. The light receiving unit 12 may include an optical system such as a condenser lens or a condenser mirror. The reflected light L2 received by the light receiving unit 12 may be input to the spectroscopic unit 13 via, for example, an optical fiber.

[0027] The spectroscopic unit 13 separates the reflected light L2 of the near-infrared light L1 reflected by the surface 111 of the coating film 110. Of the light separated by the spectroscopic unit 13, light containing at least wavelengths in the near-infrared region is input to the photometric unit 14. The spectroscopic unit 13 is not particularly limited as long as it can separate light, and may include a dispersive element such as a diffraction grating or a prism. However, when a light source 11 such as a tunable laser is used, the chloride ion concentration measuring device 1 does not need to include the spectroscopic unit 13.

[0028] The photometer 14 measures reflected light L2 of the near-infrared light L1 reflected by the surface 111 of the coating film 110. Specifically, the photometer 14 measures the light intensity of the reflected light L2. The photometer 14 may include, for example, a detector and an amplifier. The detector converts the incident light into an electrical signal such as a current or voltage corresponding to the intensity of the light. The amplifier amplifies the electrical signal from the detector.

[0029] The wheels 15 are configured to enable the probe head 10 to move along the surface 111 of the coating film 110. Since the wheels 15 enable the probe head 10 to move over the surface 111 of the coating film 110, the chloride ion concentration can be measured while scanning the surface 111 of the coating film 110. The probe head 10 may include an encoder (not shown) that detects the number of rotations of the wheels 15. With this configuration, the movement distance of the probe head 10 can be detected from the output of the encoder. Therefore, the chloride ion concentration measuring device 1 according to this embodiment can easily output a contour diagram as described below.

[0030] The grip portion 16 is configured to be grippable by a user. With this configuration, the user can grip the grip portion 16 and move the probe head 10. The grip portion 16 is provided on the upper surface of the probe head 10 and extends upward. The grip portion 16 may be configured to be extendable so that measurements can be made at high altitudes.

[0031] The controller 20 is a general-purpose microcomputer and includes an arithmetic unit 21 and an output unit 22.

[0032] The arithmetic unit 21 calculates the chloride ion concentration present on the surface 111 of the coating film 110 based on the absorption spectrum of the hydroxyl group of the reflected light L2 measured by the spectroscopic unit 13. The arithmetic unit 21 includes a storage device such as a CPU (central processing unit) and a nonvolatile memory, and can calculate the chloride ion concentration on the surface 111 of the coating film 110 based on a program stored in the storage device.

[0033] When measuring the chloride ion concentration of a concrete structure not coated with a paint film, the chloride ion concentration can be determined from the absorption of Friedel's salt immobilized on the concrete. However, because Friedel's salt is not present on the surface of the paint film, the chloride ion concentration cannot be determined in the same manner as for a concrete structure not coated with a paint film. Therefore, the chloride ion concentration measuring device 1 according to this embodiment calculates the chloride ion concentration based on the absorption spectrum of the hydroxyl group in the resin of the paint film 110.

[0034] The calculation device 21 may calculate the chloride ion concentration using an absorption spectrum including a wavelength range of 1350 nm to 1500 nm. By using an absorption spectrum including such a wavelength range, it is possible to calculate the chloride ion concentration when moisture is attached to the surface 111 of the coating film 110 and when the surface 111 of the coating film 110 is dry. Therefore, even when moisture is attached to the surface 111 of the coating film 110, it is possible to measure the chloride ion concentration with high accuracy.

[0035] The calculation device 21 may calculate the chloride ion concentration based on an absorption spectrum including a first peak, which is a peak due to hydroxy groups on the surface 111 of the coating film 110, and a second peak, which is a peak due to water. By using an absorption spectrum including such a wavelength range, it is possible to calculate the chloride ion concentrations in a state where water is adhering to the surface 111 of the coating film 110 and in a state where the surface 111 of the coating film 110 is dry. Therefore, even in a state where water is adhering to the surface 111 of the coating film 110, it is possible to measure the chloride ion concentration with high accuracy.

[0036] The calculation device 21 may calculate the chloride ion concentration based on an absorption spectrum including a first peak having a wavelength of 1.39 μm and a second peak having a wavelength of 1.42 μm. The first peak is a peak whose absorption spectrum changes depending on the chloride ion concentration. The second peak is a peak whose absorption spectrum changes when water is applied to the surface 111 of the coating film 110. By using an absorption spectrum including such a wavelength range, it is possible to calculate the chloride ion concentrations in a state where the surface 111 of the coating film 110 is wet and in a state where the surface 111 of the coating film 110 is dry. In this specification, the term "peak" does not refer only to the peak top, but also to the peak top and the region from the peak top to the baseline.

[0037] The calculation device 21 may calculate the chloride ion concentration based on an absorption spectrum including a first peak in the wavelength range of 1350 nm or more but less than 1420 nm and a second peak in the wavelength range of 1420 nm or more but less than 1500 nm. By using an absorption spectrum including such wavelength ranges, the chloride ion concentrations in a state where the surface 111 of the coating film 110 is wet and in a state where the surface 111 of the coating film 110 is dry can be calculated. The peak top of the first peak may be at 1380 nm or more or at 1385 nm or more. The peak top of the first peak may be at 1410 nm or less or at 1400 nm or less. The peak top of the second peak may be at 1470 nm or less or at 1440 nm or less.

[0038] The calculation device 21 may calculate the chloride ion concentration using chemometrics. Chemometrics is a method that applies mathematical and statistical techniques. Chemometrics allows the influence of chloride ion concentration to be extracted from multiple factors by analyzing not only changes in absorbance at a specific wavelength but also changes in absorbance at many wavelengths in a spectrum. Chemometrics may include multivariate analysis. The multivariate analysis may include regression analysis. The regression analysis may include at least one selected from the group consisting of multiple regression analysis such as CLS (Classical Linear Regression) and factor analysis. The factor analysis may include at least one selected from the group consisting of principal component regression analysis and PLS (Partial Least Squares) regression analysis.

[0039] The calculation device 21 may calculate the chloride ion concentration based on the absorption spectrum of the unit concentration when moisture is attached to the surface 111 of the coating film 110 and the absorption spectrum of the unit concentration when the surface 111 of the coating film 110 is dry. With this configuration, it is possible to improve the measurement accuracy of the chloride ion concentration in various states.

[0040] The output device 22 outputs the chloride ion concentration. In this embodiment, the output device 22 is a touch panel, and also serves as an input device that can be operated by a user. However, the input device may be a separate component from the output device 22. For example, the input device may be a keyboard and a mouse, and the output device 22 may be a display device such as an LCD monitor or a printer.

[0041] As described above, the chloride ion concentration measuring device 1 according to this embodiment includes a light source 11 that irradiates near-infrared light L1 onto the surface 111 of a coating film 110 that coats a concrete structure 100 and contains a resin having hydroxy groups. The chloride ion concentration measuring device 1 also includes a photometric unit 14 that measures reflected light L2 of the near-infrared light L1 that is reflected by the surface 111 of the coating film 110. The chloride ion concentration measuring device 1 also includes a computing device 21 that calculates the chloride ion concentration present on the surface 111 of the coating film 110 based on the absorption spectrum of the hydroxy groups in the reflected light L2 measured by the photometric unit 14. The chloride ion concentration measuring device 1 also includes an output device 22 that outputs the chloride ion concentration.

[0042] The chloride ion concentration measuring method according to this embodiment includes a step of irradiating near-infrared light L1 from light source 11 onto surface 111 of coating film 110, which coats concrete structure 100 and contains a resin having hydroxy groups. The chloride ion concentration measuring method also includes a step of measuring reflected light L2 of near-infrared light L1 reflected by surface 111 of coating film 110 with photometry unit 14. The chloride ion concentration measuring method also includes a step of calculating, with calculation device 21, the chloride ion concentration present on surface 111 of coating film 110 based on the absorption spectrum of hydroxy groups in reflected light L2 measured with photometry unit 14. The chloride ion concentration measuring method also includes a step of outputting the chloride ion concentration from output device 22.

[0043] According to the chloride ion concentration measuring device 1 and the chloride ion concentration measuring method of this embodiment, the chloride ion concentration present on the surface 111 of the coating film 110 is calculated based on the absorption spectrum of the hydroxy group in the reflected light L2 of the near-infrared light L1. Therefore, by using the near-infrared light L1, the chloride ion concentration can be measured simply and quickly.

[0044] The chloride ion concentration measuring device 1 according to this embodiment can measure the chloride ion concentration while moving the probe head 10 on the surface 111 of the coating film 110. This allows measurements to be made at multiple locations over a wide range. Therefore, the chloride ion concentration measuring device 1 according to this embodiment can also output a contour diagram showing the shade of the chloride ion concentration at each measurement position.

[0045] In this embodiment, the probe head 10 includes the spectroscopic unit 13 and the photometric unit 14, but the spectroscopic unit 13 and the photometric unit 14 may be devices disposed outside the probe head 10. [Example]

[0046] The present embodiment will be described in more detail below with reference to the following examples, but the present embodiment is not limited to these examples.

[0047] Near-infrared absorption is often affected by hydroxyl groups. It was thought that the absorption spectrum of the surface of a coating film made of a resin containing hydroxyl groups would change due to the adhesion of chloride ions. We investigated whether it would be possible to measure the chloride ion concentration on the surface of a coating film by utilizing this change in absorption.

[0048] Furthermore, outdoors, due to the influence of humidity and rainwater, it was predicted that two states would exist on the surface of the paint film: State A, where sodium chloride is ionized and attached to the surface of the paint film, and State B, where sodium chloride is dissolved in water and attached to the surface of the paint film. It was also thought that both states would be affected by the attachment of chloride ions, resulting in different absorption spectra. Therefore, it was thought that the concentration of chloride ions attached to the surface of the paint film could be measured by preparing multiple samples with different chloride ion concentrations on the surface of the paint film and calculating Y(λ) from the following formula (1).

[0049] Y(λ)=a1×A(λ)+a2×B(λ) (1)

[0050] In the above formula (1), Y(λ) is the absorption spectrum of a unit concentration of chloride ions, including states A and B. In the above formula (1), a1 is the chloride ion concentration in state A, A(λ) is the absorption spectrum of a unit concentration of chloride ions in state A, a2 is the chloride ion concentration in state B, and B(λ) is the absorption spectrum of a unit concentration of chloride ions in state B.

[0051] Here, in order to estimate a1 and a2 in the above formula (1) by regression analysis, A(λ) and B(λ) must be known. Therefore, as shown below, sample A was prepared in a state A where sodium chloride was ionized and attached to the surface of the coating film, and sample B was prepared in a state B where sodium chloride was dissolved in water and attached to the surface of the coating film, and A(λ) and B(λ) were calculated.

[0052] (Production of test specimens) Concrete containing ordinary Portland cement, mixed sand, pit sand, crushed sand, and crushed stone as aggregates was poured into a 200mm x 450mm x 40mm formwork, and the formwork was removed four days after pouring to create a concrete structure. Next, Toughguard ED intermediate coat (epoxy resin paint, manufactured by Nippon Paint Co., Ltd.) was applied as an intermediate coat with a roller and allowed to cure on one side of the removed concrete structure. Next, Toughguard UD intermediate coat (polyurethane resin paint, manufactured by Nippon Paint Co., Ltd.) was applied as a top coat with a roller on top of the epoxy resin paint and allowed to cure.

[0053] (Application of sodium chloride solution to the surface of the coating) Aqueous sodium chloride solutions were prepared to the concentrations listed in Table 1. Samples A1 to A9 were then prepared in State A, where sodium chloride was ionized and attached to the surface of the coating film, and Samples B1 to B9 were prepared in State B, where sodium chloride was dissolved in water and attached to the surface of the coating film. Specifically, Samples A1 to A9 were prepared by applying the prepared aqueous sodium chloride solution to the surface of the coating film to the target concentrations listed in Table 1 and drying it indoors for three days. Samples B1 to B9 were prepared by applying the prepared aqueous sodium chloride solution to the surface of the coating film to the target concentrations listed in Table 1 and drying it indoors for three days, and then spraying water droplets onto the surface of the coating film with a sprayer.

[0054] [Table 1]

[0055] (Measurement of sample in condition A) The surfaces of the coating films of Samples A1 to A9 were measured by near-infrared spectroscopy to obtain the absorption spectra of Samples A1 to A9. The absorption spectrum A(λ) of the unit concentration of chloride ions in State A was then calculated using the following formula (2). A(λ) is shown in Figure 2. The peak at 1391 nm in the absorption spectrum shown in Figure 2 is due to the hydroxyl groups of the coating film. Furthermore, by performing CLS regression analysis, a1 of 0.989215 was obtained. Furthermore, when the absorption spectra of Samples A1 to A9 were examined, it was confirmed that the absorption spectrum changed depending on the chloride ion concentration.

[0056] Y1(λ)=a1×A(λ) (2)

[0057] In the above formula (2), Y1(λ) is the absorption spectrum of samples A1 to A9, a1 is the chloride ion concentration in samples A1 to A9, and A(λ) is the absorption spectrum of the unit concentration of chloride ions in state A.

[0058] (Measurement of sample in condition B) The surfaces of the coating films of Samples B1 to B9 were measured by near-infrared spectroscopy to obtain absorption spectra for Samples B1 to B9. Then, using the a1 and A(λ) obtained as described above and the absorption spectra of Samples B1 to B9, the following mathematical formula (3) was calculated to obtain the absorption spectrum B(λ) of the unit concentration of chloride ions in State B. B(λ) is shown in Figure 3. In the absorption spectrum shown in Figure 3, the peak with a top at 1391 nm is due to the hydroxyl groups of the coating film. In addition, in the absorption spectrum shown in Figure 3, the broad peak with a top at 1420 nm is due to the hydroxyl groups of water. Furthermore, by performing CLS regression analysis, a2 of 1.108617 was obtained. Furthermore, when the absorption spectra of Samples B1 to B9 were examined, it was confirmed that the absorption spectrum changed depending on the chloride ion concentration.

[0059] Y2(λ)=a1×A(λ)+a2×B(λ) (3)

[0060] In the above formula (3), Y2(λ) is the absorption spectrum of samples B1 to B9. In the above formula (3), a1 is the chloride ion concentration in samples A1 to A9, and A(λ) is the absorption spectrum of the chloride ion unit concentration in state A. In the above formula (3), a2 is the chloride ion concentration in samples B1 to B9, and B(λ) is the absorption spectrum of the chloride ion unit concentration in state B.

[0061] From the above results, it was possible to determine Y(λ) in the above formula (1). It was also found that the chloride ion concentration can be output by measuring the absorption spectrum of a sample with an unknown chloride ion concentration on the surface of the coating film and calculating the chloride ion concentration based on the measured absorption spectrum and Y(λ).

[0062] Although several embodiments have been described, the embodiments can be modified or varied based on the above disclosure. All components of the above embodiments and all features described in the claims may be individually extracted and combined, unless they contradict each other.

[0063] This disclosure can contribute, for example, to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation." [Explanation of symbols]

[0064] 1. Chloride ion concentration measuring device 11 Light source 14 Photometry section 21 Arithmetic unit 22 Output Devices 100 Concrete Structures 110 Paint film 111 Surface L1 near-infrared light L2 reflected light

Claims

1. a light source that applies near-infrared light to a surface of a coating film that covers a concrete structure and contains a resin having a hydroxy group; a photometry unit that measures the near-infrared light reflected by the surface of the coating film; a calculation unit that calculates a chloride ion concentration present on the surface of the coating film based on the absorption spectrum of the hydroxyl group of the reflected light measured by the photometry unit; and an output device that outputs the chloride ion concentration; A chloride ion concentration measuring device comprising:

2. 2. The chloride ion concentration measuring device according to claim 1, wherein the calculation device calculates the chloride ion concentration using the absorption spectrum including a wavelength region of 1350 nm to 1500 nm.

3. 3. The chloride ion concentration measuring device according to claim 1, wherein the calculating device calculates the chloride ion concentration based on an absorption spectrum including a first peak which is a peak attributable to the hydroxyl groups on the surface of the coating film and a second peak which is a peak attributable to water.

4. 3. The chloride ion concentration measuring device according to claim 1, wherein the calculation device calculates the chloride ion concentration based on the absorption spectrum including a first peak having a wavelength of 1.39 μm and a second peak having a wavelength of 1.42 μm.

5. 3. The chloride ion concentration measuring device according to claim 1, wherein the calculation device calculates the chloride ion concentration based on an absorption spectrum including a first peak present in a wavelength range of 1,350 nm or more and less than 1,420 nm and a second peak present in a wavelength range of 1,420 nm or more and 1,500 nm or less.

6. 3. The chloride ion concentration measuring device according to claim 1, wherein the calculation device calculates the chloride ion concentration by chemometrics.

7. 3. The chloride ion concentration measuring device according to claim 1, wherein the calculation device calculates the chloride ion concentration based on an absorption spectrum of a unit concentration when moisture is attached to the surface of the coating film and an absorption spectrum of a unit concentration when the surface of the coating film is dry.

8. a step of coating a concrete structure and irradiating a surface of a coating film containing a resin having a hydroxy group with near-infrared light from a light source; measuring the near-infrared light reflected by the surface of the coating film with a photometry unit; calculating, by a computing device, the concentration of chloride ions present on the surface of the coating film based on the absorption spectrum of the hydroxyl group of the reflected light measured by the photometric unit; outputting the chloride ion concentration from an output device; A method for measuring chloride ion concentration, comprising:

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