Method of measuring state of concrete

The present application is based on and claims priority to Japanese Patent Application No. 2015-254407, filed on Dec. 25, 2015, the disclosure of which is hereby incorporated by reference in its entirety.

This disclosure relates to a method of measuring a state of concrete. The method is capable of optically detecting chloride content contained in the concrete and a degree of neutralization thereof.

Conventionally, a method of measuring a state of concrete which can optically detect chloride content contained in the concrete and a degree of neutralization thereof has been taught by, for example, JP 5031281 B (Patent Literature 1). The method of Patent Literature 1 detects deterioration of concrete based on absorption spectrum in a predetermined wavelength range of near infrared light reflected by a concrete building.

The method of Patent Literature 1 uses a wavelength range of 900 nm to 1700 nm of the absorption spectrum to detect concentration of calcium hydroxide so as to determine or measure the neutralization of the concrete, as the neutralization has correlation with the deterioration of the concrete. The method also uses a wavelength range of 1700 nm to 2500 nm of the absorption spectrum to detect concentration of chloride ion so as to determine or measure the salt damage, as the salt damage has correlation with the deterioration of the concrete.

According to the technique taught by Patent Literature 1, it is possible to accurately determine or measure the deterioration of concrete using a nondestructive method.

Technical Problem

The method disclosed by Patent Literature 1 executes spectroscopic analysis on a predetermined wavelength range of absorption spectrum using a spectroscopy to detect concentration of calcium hydroxide and ion concentration of a chloride. Thus, it is possible to accurately detect concentration of calcium hydroxide and/or ion concentration of a chloride, but it makes the measuring device complex and increases the manufacturing cost of the measuring device, disadvantageously.

This disclosure has been developed in view of the above problem. That is, an object of the disclosure is to provide a method of measuring concrete capable of easily determining or measuring deterioration of the concrete without using a spectroscopy while maintaining the estimation accuracy.

A method of measuring a state of concrete of this disclosure emits an irradiation light to the concrete, the irradiation light including a wavelength range of near infrared light related to concrete measurement; receives a reflection light of the irradiation light reflected on the concrete; determines at least five wavelengths different from each other by PLS regression analysis within a wavelength of 900 nm to 2500 nm of absorption spectrum; and estimates a degree of neutralization of the concrete caused by calcium hydroxide and a concentration of chloride ion.

FIG. 1 is a block diagram illustrating a schematic configuration of a measuring device which is used for a method of measuring a state of concrete according to the disclosure. FIG. 2 is a graph of characteristic curves showing changes of absorption spectrum in response to deterioration of the concrete, particularly a graph showing spectral distribution curves for different concentrations of calcium hydroxide. FIG. 3 is a graph of characteristic curves showing changes of absorption spectrum in response to deterioration of the concrete, particularly a graph showing spectral distribution curves for different concentrations of chloride ion. FIG. 4 is an explanatory view showing wavelengths determined by partial least squares regression analysis (PLS regression analysis).

Embodiment

A method of measuring a state of concrete according to the present disclosure will be described hereinafter with reference to drawings.

FIG. 1 to FIG. 4 are explanatory views for the method of measuring concrete according to an embodiment of the present invention.

FIG. 1 is an optical block diagram of a measuring device which is used for the method of measuring a state of concrete according to an embodiment of the disclosure.

In FIG. 1 , the concrete measuring device is annotated by a reference sign 1 , and concrete is annotated by a reference number 2 . The measuring device 1 includes at least a computer CPU, a light source 3 , and a light receiving part 4 .

The light source 3 emits an irradiation light P having a wavelength range of near infrared light (e.g., a wavelength range of 780 nm to 2500 nm) to the concrete 2 in order to measure a state of the concrete 2 . The light source 3 includes, for example, a halogen lamp 3 a , a reflection mirror 3 b , an aperture member 3 c , and a condenser lens L to collect the irradiation light P to emit the collected light as a parallel light flux.

The irradiation light P is reflected by the concrete 2 , and the reflected light P′ is received by the light receiving part 4 . The light receiving part 4 receives the reflected lights P′ of at least five different wavelengths within a wavelength range of 900 nm to 2500 nm of an absorption spectrum.

The above-mentioned five different wavelengths or more are used to estimate a degree of neutralization caused by calcium hydroxide, which has an influence to the neutralization, and to estimate concentration of chloride ion, which has an influence to salt damage. Here, the degree of neutralization may be determined by estimating the concentration of the calcium hydroxide or by estimating a pH value thereof.

The at least five different wavelengths are determined by PLS regression analysis. FIG. 2 is an explanatory view showing a spectral distribution curve acquired from normal concrete 2 and a spectral distribution curve acquired from neutralized concrete 2 .

In FIG. 2 , the broken line represents the spectral distribution curve acquired from the normal concrete 2 , and the dash-dotted line represents the spectral distribution curve acquired from the neutralized concrete 2 .

The spectral distribution curve Q 1 acquired from the neutralized concrete 2 varies in response to the degree of neutralization (e.g., concentration of calcium hydroxide or pH). Wavelengths λ 1 to λ 5 are determined or selected using the PLS regression analysis by acquiring multiple spectral distribution curves Q 1 .

Similarly, the spectral distribution curve Q 2 acquired from the concrete 2 containing salt varies in response to the salinity concentration thereof, as shown in FIG. 3 . Wavelengths λ 6 to λ 10 are determined or selected using the PLS regression analysis by acquiring multiple spectral distribution curves Q 2 .

As shown in FIG. 4 , the degree of neutralization caused by calcium hydroxide is estimated in accordance with the two wavelengths λ 1 , λ 2 within the wavelength range of 900 nm to 1700 nm of the absorption spectrum as well as with the three wavelengths λ 3 to λ 5 within the wavelength range of 1700 nm to 2500 nm of the absorption spectrum. The concentration of chloride ion is estimated in accordance with the wavelength λ6 within the wavelength range of 900 nm to 1700 nm of the absorption spectrum as well as with the four wavelengths λ 7 to λ 10 within the wavelength range of 1700 nm to 2500 nm of the absorption spectrum.

On the basis of a true value of the degree of neutralization of the concrete 2 , a true value of the concentration of chloride ion, as well as the determined wavelengths λ 1 to λ 5 and λ 6 to λ 10 ; a calibration curve related to the degree of neutralization and a calibration curve related to the concentration of the chloride ion are drawn through multiple regression analysis. An estimation coefficient related to the degree of neutralization and an estimation coefficient related to the concentration of chloride ion are then determined. Here, the true value of the degree of neutralization represents an ion concentration value of the calcium hydroxide obtained from a method used in a known quantitative analysis or a pH value thereof. The true value of the concentration of chloride ion represents a concentration value of the chloride ion. In FIG. 2 to FIG. 4 , the horizontal line represents wavelengths and the vertical line represents reflectance or transmittance.

The light receiving part 4 includes light receiving sections 4 a and 4 b . For example, the light receiving section 4 a is to estimate the degree of neutralization of the concrete 2 caused by calcium hydroxide, and the light receiving section 4 b is to estimate the concentration of the chloride ion contained in the concrete 2 .

The light receiving section 4 a includes filters Fi 1 to Fi 5 . The filters Fi 1 to Fi 5 allow the reflection lights P′ having the wavelengths λ 1 (λ 1 =920 nm), λ 2 (λ 2 =1410 nm), λ 3 (λ 3 =1970 nm), λ 4 (λA=2010 nm), and λ 5 (λ 5 =2225 nm), and thereabout to pass through, respectively.

The reflection lights P′ passed through the corresponding filters Fi 1 to Fi 5 are collected by the corresponding condenser lenses L 1 to L 5 , respectively. The collected lights are then photoelectrically converted by corresponding Pin-photodiodes Pin 1 to Pin 5 , amplified by corresponding amplifiers AMP 1 to AMPS, digitally converted by analog-digital converters A/D 1 to A/D 5 , and inputted to the CPU as signals NK to detect the degree of neutralization of the concrete 2 , respectively.

The light receiving part 4 b includes filters Fi 6 to Fi 10 . The filters Fi 6 to Fi 10 allow the reflection lights P′ having the wavelengths λ 6 (λ 6 =1430 nm), λ 7 (λ 7 =1723 nm), λ 8 (λ 8 =1960 nm), λ 9 (λ 9 =1967 nm), and λ 10 (λ 10 =2245 nm), and thereabout to pass through, respectively.

The reflection lights P′ passed through the corresponding filters Fi 6 to Fi 10 are collected by the corresponding condenser lenses L 6 to L 10 , respectively. The collected lights are then photoelectrically converted by corresponding Pin-photodiodes Pin 6 to Pin 10 , amplified by corresponding amplifiers AMP 6 to AMP 10 , digitally converted by analog-digital converters A/D 6 to A/D 10 , and inputted to the CPU as signals CK to detect the concentration of the chloride ion of the concrete 2 , respectively.

The CPU stores the estimation coefficient to estimate the degree of neutralization of the concrete 2 and the estimation coefficient to estimate the concentration of chloride ion thereof. The CPU estimates the degree of neutralization and the concentration of chloride ion in accordance with the signals NK, CK, and the estimation coefficients.

In this embodiment, the degree of neutralization caused by calcium hydroxide and the concentration of chloride ion are estimated based on the lights within the wavelength range of 900 nm to 2500 nm, which are used to measure the deterioration of the concrete, without classifying the wavelength ranges of the absorption spectrum. As a result, it is possible to measure the deterioration of the concrete 2 without using a spectroscopy to spectrally disperse the absorption spectrum while maintaining the accuracy.