Reinforcing bar inspection device and reinforcing bar inspection method

Abstract

To provide a reinforcing bar inspection device and a reinforcing bar inspection method capable of inspecting a corrosion state of a reinforcing bar buried in a deeper position.SOLUTION: The reinforcing bar inspection device 1 of the present embodiment includes a radiation source 2 that radiates electromagnetic waves EM having a sub-terahertz frequency, and a detector 3 that detects electromagnetic waves EM reflected from a concrete surface CS when the electromagnetic waves EM are irradiated on the concrete surface CS, and the reinforcing bar inspection device 1 is configured to determine a corrosion state of the reinforcing bar based on a reinforcing bar partial reflection intensity that is an intensity of the electromagnetic waves EM reflected from the concrete surface corresponding to a position where the reinforcing bar is buried, and the frequency of the electromagnetic waves EM is set to a frequency suitable for each cover thickness of the reinforcing bar according to the cover thickness of the reinforcing bar.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a reinforcing bar inspection device and a reinforcing bar inspection method. [Background technology]

[0002] In order to ensure the long-term and safe use of buildings and civil engineering structures that use reinforced concrete, it is important to inspect and maintain the reinforced concrete before its deterioration becomes apparent. One example of deterioration of reinforced concrete is the corrosion of rebars in the concrete. Until now, methods such as the half-cell potential method and polarization resistance method have been investigated as non-destructive methods for inspecting the corrosion state of rebars in concrete, but they have not yet achieved sufficient accuracy.

[0003] As a new non-destructive inspection method for the corrosion state of reinforcing bars in concrete, an inspection method that applies sub-terahertz waves is being considered in Non-Patent Document 1. The inspection method in Non-Patent Document 1 makes it possible to inspect the corrosion state of reinforcing bars based on the intensity of the electromagnetic waves reflected when electromagnetic waves having a sub-terahertz frequency are irradiated onto the surface of reinforced concrete. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Proceedings of the Annual Meeting of the Concrete Engineering Society, Vol. 45, No. 1, pp. 1282-1287 Summary of the Invention [Problem to be solved by the invention]

[0005] The inspection method of Non-Patent Document 1 can non-destructively inspect the corrosion state of rebars in concrete, but is limited to inspecting rebars buried at a depth (cover depth) of about 10 mm. In actually used reinforced concrete, rebars are sometimes buried not only at a depth of about 10 mm from the concrete surface, but also at depths of more than 10 mm, about 30 to 50 mm. The inspection method of Non-Patent Document 1 is difficult to apply to inspect rebars buried at such a depth greater than 10 mm from the concrete surface.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a reinforcing bar inspection device and a reinforcing bar inspection method that can inspect the corrosion state of reinforcing bars buried at greater depths. [Means for solving the problem]

[0007] The reinforcing bar inspection device of the present invention is a reinforcing bar inspection device for inspecting the corrosion state of reinforcing bars buried in concrete, and is equipped with a radiation source that emits electromagnetic waves having a sub-terahertz frequency and a detector that detects electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface.The reinforcing bar inspection device is configured to determine the corrosion state of the reinforcing bar based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic waves reflected from the concrete surface corresponding to the position where the reinforcing bar is buried, and the frequency of the electromagnetic waves is set to a frequency appropriate for each cover thickness of the reinforcing bar depending on the cover thickness of the reinforcing bar.

[0008] The reinforcing bar inspection method of the present invention is a reinforcing bar inspection method for inspecting the corrosion state of reinforcing bars embedded in concrete, and includes the steps of: irradiating the concrete surface with electromagnetic waves having a sub-terahertz frequency; detecting the electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface; and determining the corrosion state of the reinforcing bar based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic waves reflected from the concrete surface corresponding to the position where the reinforcing bar is buried, wherein the frequency of the electromagnetic waves is set to a frequency appropriate for each cover thickness of the reinforcing bar, depending on the cover thickness of the reinforcing bar. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a reinforcing bar inspection device and a reinforcing bar inspection method that can inspect the corrosion state of reinforcing bars buried at deeper positions. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a reinforcing bar inspection device according to an embodiment of the present invention. [Figure 2A] FIG. 1 is a side view of concrete with reinforcing bars embedded therein. [Figure 2B] FIG. 1 is a top view of concrete with rebar embedded therein. [Figure 3] FIG. 2 is a block diagram of a control device included in the reinforcing bar inspection device of FIG. [Figure 4] 1 is a flow diagram of a reinforcing bar inspection method according to an embodiment of the present invention. [Figure 5] 1 is a graph showing the frequency characteristics of reflected electromagnetic waves obtained from reinforced concrete having different amounts of water in the concrete and different cover thicknesses of the reinforcing bars. [Figure 6] 1 is a graph showing the frequency characteristics of reflected electromagnetic waves obtained from reinforced concrete having different amounts of chloride ions in the concrete and different cover thicknesses of the reinforcing bars. [Figure 7] 10 is a graph showing the relationship between the cover thickness of reinforcing bars and the differential reflected intensity. [Figure 8]10 is a graph showing the relationship between the corrected differential reflected intensity and the mass reduction rate of the reinforcing bar. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a reinforcing bar inspection device and a reinforcing bar inspection method according to an embodiment of the present invention will be described with reference to the accompanying drawings. However, the embodiment shown below is merely an example, and the reinforcing bar inspection device and reinforcing bar inspection method of the present invention are not limited to the following example.

[0012] The reinforcing bar inspection device 1 and reinforcing bar inspection method 100 of this embodiment are used to inspect the corrosion state of reinforcing bars R embedded in concrete C. As shown in FIGS. 2A and 2B , the reinforcing bar inspection device 1 and reinforcing bar inspection method 100 are applied to reinforced concrete RC in which reinforcing bars R are embedded to a predetermined depth (cover thickness) CD from the concrete surface CS. The reinforced concrete RC to which the reinforcing bar inspection device 1 and reinforcing bar inspection method 100 are applied is not particularly limited, and examples thereof include reinforced concrete used in buildings and other structures, bridges spanning rivers or the sea, bridge piers for highways and the like, and large civil engineering structures such as dams. Furthermore, the reinforcing bars R to which the reinforcing bar inspection device 1 and reinforcing bar inspection method 100 are applied are not particularly limited, and examples thereof include well-known round bars and deformed reinforcing bars.

[0013] <Rebar inspection device> 1, the rebar inspection device 1 includes a radiation source 2 that emits electromagnetic waves EM having a frequency of sub-terahertz (for example, 0.01 to 0.3 THz), and a detector 3 that detects the electromagnetic waves EM reflected from the concrete surface CS when the electromagnetic waves EM are irradiated onto the concrete surface CS. In this embodiment, the rebar inspection device 1 further includes a position adjustment device 4 that adjusts the relative positions between the concrete surface CS and the radiation source 2 and detector 3, and a control device 5 that controls the radiation source 2, detector 3, and position adjustment device 4.

[0014] The radiation source 2 emits electromagnetic waves EM having a sub-terahertz frequency and irradiates the electromagnetic waves EM onto the concrete surface CS. In this embodiment, the radiation source 2 is configured to emit electromagnetic waves EM having a predetermined frequency within the sub-terahertz frequency range (for example, frequencies at approximately 0.1 GHz intervals). However, the radiation source 2 may be configured to emit electromagnetic waves having a narrower or wider frequency range within the sub-terahertz frequency range. Furthermore, in this embodiment, the radiation source 2 focuses the electromagnetic waves EM at a predetermined focal depth to a predetermined diameter, for example, a diameter approximately equal to the width W of the rebar R, preferably a diameter smaller than the width W of the rebar R, more preferably a diameter smaller than 1 / 2 the width W of the rebar R, even more preferably a diameter smaller than 1 / 3 the width W of the rebar R, or a diameter approximately equal to the wavelength of the electromagnetic waves EM (for example, 1 mm to 3 cm). However, the electromagnetic waves EM can be irradiated at least onto the concrete surface CS corresponding to the position where the rebar R is buried (directly above the position where the rebar R is buried), and it is sufficient that the irradiation area is large enough so that it does not extend beyond the concrete surface CS, and it does not necessarily have to be concentrated. Furthermore, in this embodiment, the radiation source 2 is configured to irradiate the concrete surface CS with s-polarized electromagnetic waves EM. By irradiating the concrete surface CS with s-polarized electromagnetic waves EM, it is possible to suppress the influence of impurities contained in the concrete C on the intensity of the reflected electromagnetic waves EM. However, the irradiated electromagnetic waves EM are not limited to those in this embodiment, and p-polarized waves may also be used.

[0015] The configuration of the radiation source 2 is not particularly limited as long as it can irradiate the concrete surface CS with electromagnetic waves EM having a sub-terahertz frequency. In this embodiment, as shown in Fig. 1, the radiation source 2 includes an oscillator 21 that generates electromagnetic waves EM having a sub-terahertz frequency, an antenna (e.g., a horn antenna) 22 that radiates the electromagnetic waves EM into space, and a lens (e.g., a Teflon lens) 23 that focuses the electromagnetic waves EM to a predetermined focal depth. The oscillator 21, antenna 22, and lens 23 are not particularly limited, and known oscillators, antennas, and lenses can be used.

[0016] The radiation source 2 may be disposed symmetrically with the detector 3 with respect to the normal NL of the concrete surface CS, as long as it can irradiate the concrete surface CS with electromagnetic waves EM having a sub-terahertz frequency. In this embodiment, as shown in FIG. 1 , the radiation source 2 is disposed symmetrically with the detector 3 with respect to the normal NL of the concrete surface CS so that the incident angle θ1 of the incident electromagnetic waves EM with respect to the normal NL of the concrete surface CS is substantially the same as the reflection angle θ2 of the reflected electromagnetic waves EM with respect to the normal NL of the concrete surface CS. The incident angle θ1 can be appropriately set so as to increase the intensity of the reflected electromagnetic waves EM, and is set, for example, within a range of 20° to 45°, preferably within a range of 25° to 40°, more preferably within a range of 30° to 35°, and even more preferably approximately 33°. However, the radiation source 2 may also be disposed with respect to the detector 3 so that the incident angle θ1 is different from the reflection angle θ2.

[0017] 1, the radiation source 2 is communicatively connected to the control device 5 and configured to emit electromagnetic waves EM having a sub-terahertz frequency under the control of the control device 5. Furthermore, in this embodiment, the radiation source 2 is configured to be able to irradiate the electromagnetic waves EM to a desired position on the concrete surface CS under the control of the control device 5. Details of the control device 5 will be described below.

[0018] The detector 3 detects the electromagnetic waves EM reflected from the concrete surface CS when the electromagnetic waves EM emitted by the radiation source 2 are irradiated onto the concrete surface CS. Here, the electromagnetic waves EM reflected from the concrete surface CS refer to the electromagnetic waves EM emitted from the concrete surface CS when the concrete surface CS is irradiated with electromagnetic waves EM, and include not only the concrete surface CS but also electromagnetic waves EM reflected from the interior of the concrete C. In this embodiment, the detector 3 is configured to detect the intensity of the electromagnetic waves EM reflected from the concrete surface CS without frequency decomposition. However, the detector 3 may also be configured to frequency decompose the reflected electromagnetic waves EM and detect the intensity of the reflected electromagnetic waves EM for each frequency.

[0019] The detector 3 is not particularly limited in its configuration as long as it can detect electromagnetic waves EM reflected from the concrete surface CS. In this embodiment, as shown in Fig. 1, the detector 3 includes a detector main body 31 that detects electromagnetic waves EM and outputs the intensity of the electromagnetic waves EM as a detection signal (for example, a voltage value), an antenna (for example, a horn antenna) 32 that collects the electromagnetic waves EM and guides them to the detector main body 31, and a lens (for example, a Teflon lens) 33 that diverges the electromagnetic waves EM. The detector main body 31, antenna 32, and lens 33 are not particularly limited, and known detectors, antennas, and lenses can be used.

[0020] The detector 3 may be positioned symmetrically with respect to the radiation source 2 with respect to the normal NL of the concrete surface CS, as long as it can detect the electromagnetic waves EM reflected from the concrete surface CS. In this embodiment, as shown in FIG. 1 , the detector 3 is positioned symmetrically with respect to the radiation source 2 with respect to the normal NL of the concrete surface CS so that the reflection angle θ2 of the reflected electromagnetic waves EM with respect to the normal NL of the concrete surface CS is substantially the same as the incident angle θ1 of the incident electromagnetic waves EM with respect to the normal NL of the concrete surface CS. The reflection angle θ2 can be appropriately set so as to increase the intensity of the reflected electromagnetic waves, and is set, for example, within a range of 20° to 45°, preferably within a range of 25° to 40°, more preferably within a range of 30° to 35°, and even more preferably approximately 33°. However, the detector 3 may also be positioned with respect to the radiation source 2 so that the reflection angle θ2 is different from the incident angle θ1.

[0021] In this embodiment, as shown in Fig. 1, the detector 3 is communicatively connected to the control device 5 and is configured to detect electromagnetic waves EM reflected from the concrete surface CS under the control of the control device 5. Furthermore, the detector 3 is configured to transmit a detection signal of the electromagnetic waves EM to the control device 5. Details of the control device 5 will be described below.

[0022] The position adjustment device 4 adjusts the relative position of the concrete surface CS with respect to the radiation source 2 and the detector 3, thereby adjusting the irradiation position of the electromagnetic waves EM on the concrete surface CS. In this embodiment, as shown in FIG. 1 , the position adjustment device 4 is configured as a mounting table on which the reinforced concrete RC is placed, and is configured to move the reinforced concrete RC placed on the position adjustment device 4 relative to the radiation source 2 and the detector 3. The movement directions of the reinforced concrete RC can be, for example, two directions that are substantially perpendicular to each other in a plane substantially parallel to the concrete surface CS, namely, the X direction (e.g., the extension direction of the rebars R) and the Y direction (e.g., a direction substantially perpendicular to the extension direction of the rebars R), as well as the Z direction substantially perpendicular to the concrete surface CS. The position adjustment device 4 is configured to be able to move the relative position at intervals of, for example, ½ or less, preferably ⅓ or less, more preferably ⅕ or less, and even more preferably ⅙ or less of the width W of the rebars R. In this embodiment, the position adjustment device 4 is configured to move the reinforced concrete RC relative to the radiation source 2 and the detector 3, but it may also be configured to move the radiation source 2 and the detector 3 relative to the reinforced concrete RC, or it may be configured to move both the reinforced concrete RC and the radiation source 2 and the detector 3 relative to each other.

[0023] The control device 5 is communicatively connected to the radiation source 2, the detector 3, and the position adjustment device 4 via connection means such as a general-purpose serial bus cable, a wired / wireless LAN, or an internet line, and controls the radiation source 2, the detector 3, and the position adjustment device 4. The control device 5 further processes the detection signal of the electromagnetic waves EM detected by the detector 3, and determines the corrosion state of the reinforcing bar R based on the processed detection signal. The reinforcing bar inspection device 1 is configured to determine the corrosion state of the reinforcing bar R under the control of the control device 5.

[0024] 3, the control device 5 in this embodiment includes an electromagnetic wave emission control unit 51, an electromagnetic wave detection control unit 52, a position control unit 53, a detection signal processing unit 54, a corrosion state determination unit 55, and a memory unit 56. The control device 5 is not particularly limited, and can be configured, for example, as an electronic calculator such as a computer including an arithmetic processing unit such as a CPU that can mainly configure the electromagnetic wave emission control unit 51, the electromagnetic wave detection control unit 52, the position control unit 53, the detection signal processing unit 54, and the corrosion state determination unit 55, a memory that can mainly configure the memory unit 56, a storage device such as a hard disk, a communication interface such as a serial bus terminal or a network port, an input device such as a keyboard and a mouse, a display device such as an LCD display, and the like.

[0025] The electromagnetic wave radiation control unit 51 controls the radiation source 2 to emit electromagnetic waves EM from the radiation source 2. In this embodiment, the electromagnetic wave radiation control unit 51 controls the radiation source 2 to emit electromagnetic waves EM having a predetermined frequency (for example, a frequency approximately every 0.1 GHz) among sub-terahertz frequencies. At this time, the frequency of the electromagnetic waves EM is set to a frequency appropriate for each cover thickness CD of the reinforcing bars R, depending on the cover thickness CD of the reinforcing bars R. The frequency appropriate for each cover thickness CD of the reinforcing bars R is a frequency of the electromagnetic waves EM appropriate for determining the corrosion state of the reinforcing bars R for each cover thickness CD of the reinforcing bars R, and can be determined taking into account the frequency characteristics of the electromagnetic waves EM, which differ for each cover thickness CD of the reinforcing bars R. In this embodiment, the frequency appropriate for each cover thickness CD differs for each cover thickness CD, but it may be the same for all cover thicknesses CD. By selecting a frequency appropriate for each cover thickness CD of the reinforcing bars R as the frequency of the electromagnetic waves EM, information regarding the corrosion state of the reinforcing bars R can be extracted with high sensitivity from the reflected electromagnetic waves EM, making it possible to inspect the corrosion state of reinforcing bars R buried at greater depths.

[0026] The frequency of the electromagnetic waves EM can be selected as a frequency appropriate for each cover thickness CD of the rebars R, for example, from a frequency range in which the influence of impurities (e.g., water and / or chloride ions) contained in the concrete C on the intensity of the reflected electromagnetic waves EM is small for each cover thickness CD of the rebars R. More specifically, the frequency of the electromagnetic waves EM can be selected from a frequency range in which the difference in the intensity of the reflected electromagnetic waves EM obtained from multiple reinforced concrete structures RC with different concentrations of impurities contained in the concrete C is small. Examples of the "intensity of the reflected electromagnetic waves EM" here include the rebar partial reflection intensity, which is the intensity of the electromagnetic waves EM reflected from the concrete surface CS1 (see FIG. 2B) corresponding to the location where the rebars R are embedded, and other parameters calculated from the rebar partial reflection intensity, as described below, such as the differential reflection intensity, which is the difference between the rebar partial reflection intensity and the concrete partial reflection intensity, which is the intensity of the electromagnetic waves EM reflected from the concrete surface CS2 (see FIG. 2B) corresponding to the location where the rebars R are not embedded. In this embodiment, the differential reflection intensity is used as the intensity of the reflected electromagnetic waves EM. Furthermore, the terms "frequency range with less influence" and "frequency range with small difference" refer to a frequency range with less influence and a frequency range with small difference compared to other frequency ranges, respectively. For example, if other frequency ranges show an intensity difference greater than a predetermined intensity difference, the frequency of the electromagnetic waves EM can be selected from a frequency range showing an intensity difference smaller than the predetermined intensity difference. Table 1 below shows examples of frequencies suitable for each cover thickness CD when the impurity is water, and Table 2 below shows examples of frequencies suitable for each cover thickness CD when the impurity is chloride ions.

[0027] In addition to or instead of selecting the frequency of the electromagnetic waves EM from a frequency range in which the influence of impurities contained in the concrete C on the intensity of the reflected electromagnetic waves EM is minimized, as described above, the frequency can be selected from a frequency range in which the differential reflection intensity is large, as a frequency with high permeability through concrete for each cover thickness CD of the rebar R. Note that the "frequency range in which the differential reflection intensity is large" refers to a frequency range in which the differential reflection intensity is large compared to other frequency ranges, and preferably also refers to a frequency range in which the differential reflection intensity is at least positive. For example, if other frequency ranges show differential reflection intensities smaller than a predetermined intensity, the frequency of the electromagnetic waves EM can be selected from a frequency range in which the differential reflection intensity is large. For example, 11.9 GHz can be selected for a cover thickness of 10 mm, 14.3 GHz for a cover thickness of 30 mm, and 14.8 GHz for a cover thickness of 50 mm as frequencies in which the influence of impurities (water and chloride ions) contained in the concrete C on the intensity of the reflected electromagnetic waves EM is minimized and the differential reflection intensity is large.

[0028] The electromagnetic wave detection control unit 52 controls the detector 3 to detect the electromagnetic waves EM reflected from the concrete surface CS. The electromagnetic wave detection control unit 52 transmits a detection signal (e.g., a voltage value) corresponding to the intensity of the detected electromagnetic waves EM to the detection signal processing unit 54, the corrosion state determination unit 55, and / or the memory unit 56.

[0029] The position control unit 53 controls the position adjustment device 4 to adjust the relative position of the concrete surface CS with respect to the radiation source 2 and the detector 3 within a plane (XY plane) substantially parallel to the concrete surface CS (see FIG. 1). In this embodiment, the rebar inspection device 1 is configured to adjust the irradiation position of the electromagnetic waves EM on the concrete surface CS under the control of the electromagnetic wave emission control unit 51 and the position control unit 53. As a result, the rebar inspection device 1 can selectively irradiate the electromagnetic waves EM onto a concrete surface CS1 corresponding to a position where the rebar R is buried (directly above the position where the rebar R is buried) and a concrete surface CS2 corresponding to a position where the rebar R is not buried (directly above the position where the rebar R is not buried), as shown in FIG. 2B, for example. The concrete surface CS2 corresponding to the position where the rebar R is not buried is not particularly limited, but is preferably set to a concrete surface CS2 at a position at least a distance corresponding to the width W of the rebar R from the concrete surface CS1 corresponding to the position where the rebar R is buried. This makes it possible to prevent the electromagnetic waves EM reflected when irradiated onto the concrete surface CS2 corresponding to a position where the rebar R is not buried from being affected by the rebar R. From the same perspective, it is more preferable that the concrete surface CS2 corresponding to a position where the rebar R is not buried be separated from the concrete surface CS1 corresponding to a position where the rebar R is buried by a distance of at least twice the width W of the rebar R, and even more preferable that the distance be at least three times the width W of the rebar R. The position control unit 53 can also control the position adjustment device 4 to continuously move the relative position of the concrete surface CS with respect to the radiation source 2 and the detector 3 two-dimensionally at equal intervals within the XY plane. This allows the rebar inspection device 1 to examine the two-dimensional distribution of reflected electromagnetic waves EM within the XY plane.

[0030] The position control unit 53 can also control the position adjustment device 4 to adjust the relative position of the concrete surface CS with respect to the radiation source 2 and the detector 3 in a direction (Z direction) approximately perpendicular to the concrete surface CS. In this embodiment, the rebar inspection device 1 is configured to adjust the position of the focal depth of the electromagnetic waves EM emitted from the radiation source 2 relative to the position of the rebar R in the Z direction under the control of the electromagnetic wave emission control unit 51 and the position control unit 53. This makes it possible, for example, to align the position of the focal depth of the electromagnetic waves EM emitted from the radiation source 2 so that it approximately coincides with the position of the rebar R in the Z direction. By aligning the position of the focal depth of the electromagnetic waves EM for each cover thickness CD, the intensity of the electromagnetic waves EM reflected from the rebar R can be increased, allowing for more accurate determination of the corrosion state of the rebar R. However, the position of the focal depth of the electromagnetic waves EM may be different from the position of the rebar R in the Z direction. In addition, for reinforced concrete RC where the cover thickness CD is unknown, the reinforcing bar inspection device 1 can determine the position of the focal depth at which the intensity of the reflected electromagnetic waves EM is maximum, and can also determine the cover thickness CD of the reinforcing bar R from the determined position of the focal depth.

[0031] The detection signal processing unit 54 processes the detection signal of the electromagnetic wave EM transmitted from the electromagnetic wave detection control unit 52 and transmits the processed detection signal to the corrosion state determination unit 55 and / or the memory unit 56. In this embodiment, the detection signal processing unit 54 calculates a differential reflection intensity, which is the difference between the rebar partial reflection intensity, which is the intensity of the electromagnetic wave EM reflected from the concrete surface CS1 (see FIG. 2B) corresponding to the position where the rebar R is embedded, and the concrete partial reflection intensity, which is the intensity of the electromagnetic wave EM reflected from the concrete surface CS2 (see FIG. 2B) corresponding to the position where the rebar R is not embedded. The differential reflection intensity of the electromagnetic wave EM can suppress the influence of the concrete C and obtain information that more fully reflects the state of the rebar R. The detection signal processing unit 54 can also calculate the average intensity of the electromagnetic wave EM reflected from multiple positions on the concrete surface CS. For example, the detection signal processing unit 54 calculates the average intensity (rebar partial reflection intensity) of the electromagnetic wave EM reflected from multiple positions on the concrete surface CS1 corresponding to the position where the rebar R is embedded (e.g., three positions in the example shown in FIG. 2B). Furthermore, the detection signal processing unit 54 calculates the average intensity (concrete partial reflection intensity) of the electromagnetic waves EM reflected from multiple positions (e.g., six positions in the example shown in FIG. 2B) on the concrete surface CS2 corresponding to positions where no reinforcing bars R are buried. The detection signal processing unit 54 can calculate the differential reflection intensity from the averaged reinforcing bar partial reflection intensity and the averaged concrete partial reflection intensity. However, the detection signal processing unit 54 may transmit the reinforcing bar partial reflection intensity and the concrete partial reflection intensity directly to the corrosion state determination unit 55 and / or the memory unit 56 without processing them.

[0032] The detection signal processing unit 54 can determine the relationship between the cover thickness CD and the differential reflection intensity. The relationship between the cover thickness CD and the differential reflection intensity can be obtained, for example, from the relationship between the differential reflection intensity obtained from each of a plurality of reinforced concrete RCs containing reinforcing bars R buried at different known cover depths CD and the corresponding cover thickness CD. FIG. 7 illustrates the relationship between the cover thickness CD and the differential reflection intensity obtained for reinforced concrete RCs containing reinforcing bars R buried at different cover depths CD. As can be seen from FIG. 7, the differential reflection intensity varies depending on the cover thickness CD, and this variation also varies depending on the type of reinforcing bars R. The detection signal processing unit 54 can perform regression analysis on the plurality of data points shown in FIG. 7 for each type of reinforcing bars R, and can determine a regression equation (a linear regression equation in the illustrated example) as the relationship between the cover thickness CD and the differential reflection intensity.

[0033] The detection signal processing unit 54 can correct the differential reflection intensity obtained for concrete C in which reinforcing bars R with known or unknown corrosion states are embedded, based on the relationship (regression equation) between cover depth CD and differential reflection intensity determined in advance as described above. This correction corrects the differential reflection intensity obtained from reinforced concrete RC with different cover depths CD to the differential reflection intensity obtained when the reinforcing bars R have the same cover depth CD (e.g., 0 mm). As shown in FIG. 7, the differential reflection intensity varies depending on the cover depth CD. Therefore, correcting the differential reflection intensity in this manner makes it possible to directly compare the differential reflection intensities of reinforcing bars R embedded with different cover depths CD. In this embodiment, this correction can be performed using the relational equation (corrected differential reflection intensity = differential reflection intensity + a × cover depth). Note that a is the absolute value of the slope of the regression equation, and in the example shown in FIG. 7, it is 0.547 when the reinforcing bars are round steel bars and 0.578 when the reinforcing bars are deformed steel bars. However, this relational expression is changed as appropriate depending on the relationship between the cover thickness CD and the differential reflection intensity.

[0034] The detection signal processing unit 54 can determine the relationship between the corrected differential reflection intensity obtained by correcting the differential reflection intensity as described above and the mass reduction rate of the reinforcing bar R. The mass reduction rate of the reinforcing bar R represents the ratio of the mass of the reinforcing bar R reduced by corrosion to the mass of the uncorroded reinforcing bar R. The relationship between the corrected differential reflection intensity and the mass reduction rate of the reinforcing bar R can be obtained from the relationship between the corrected differential reflection intensity obtained from each of multiple reinforced concrete RCs in which reinforcing bars R with different known mass reduction rates are embedded and the corresponding mass reduction rate of the reinforcing bar R. FIG. 8 illustrates an example of the relationship between the corrected differential reflection intensity and the mass reduction rate of the reinforcing bar R obtained for reinforced concrete RCs containing reinforcing bars R with known mass reduction rates. As can be seen from FIG. 8, the corrected differential reflection intensity changes depending on the mass reduction rate of the reinforcing bar R, and this change also changes depending on the type of reinforcing bar R. The detection signal processing unit 54 performs regression analysis on the multiple data points shown in Figure 8 for each type of reinforcing bar R, and can obtain a regression equation (a linear regression equation in the illustrated example) as the relationship between the corrected differential reflection intensity and the mass reduction rate of the reinforcing bar R.

[0035] The detection signal processing unit 54 can calculate the mass loss rate of the reinforcing bar R in the concrete C from the corrected differential reflected intensity obtained for the concrete C in which the reinforcing bar R, whose corrosion state is known or unknown, is embedded, based on the relationship (regression equation) between the corrected differential reflected intensity and the mass loss rate of the reinforcing bar R determined in advance as described above. Calculating the mass loss rate of the reinforcing bar R using the corrected differential reflected intensity makes it possible to quantitatively determine the corrosion state of the reinforcing bar R embedded with various cover depths CD. In this embodiment, this calculation is performed using the relational equation (mass loss rate of reinforcing bar = cb × corrected differential reflected intensity). Note that b is the absolute value of the slope of the regression equation, which in the example shown in FIG. 8 is 0.046 when the reinforcing bar is a round steel bar and 0.130 when the reinforcing bar is a deformed steel bar. Furthermore, c is the intercept of the regression equation, which in the example shown in FIG. 8 is 1.88 when the reinforcing bar is a round steel bar and 3.53 when the reinforcing bar is a deformed steel bar. However, this relational expression is changed as appropriate depending on the relationship between the corrected differential reflection intensity and the mass reduction rate of the reinforcing bar R.

[0036] The corrosion state determination unit 55 determines the corrosion state of the reinforcing bar R based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic wave EM reflected from the concrete surface CS1 (see FIG. 2B ) corresponding to the location where the reinforcing bar R is embedded. The greater the degree of corrosion of the reinforcing bar R, the smaller the reinforcing bar partial reflection intensity. For example, the corrosion state determination unit 55 determines that the reinforcing bar R is corroded when the reinforcing bar partial reflection intensity is equal to or less than a predetermined threshold, and determines that the reinforcing bar R is not corroded when the reinforcing bar partial reflection intensity is greater than the predetermined threshold. The determination result of the corrosion state of the reinforcing bar R (including the determination results described below) may be transmitted to the memory unit 56, displayed on a display device (not shown) of the control device 5, or transmitted to an external computer, mobile device, or the like via a communication interface (not shown) of the control device 5. Note that the term “based on the reinforcing bar partial reflection intensity” used herein means that the criteria for determining the corrosion state of the reinforcing bar R include at least the reinforcing bar partial reflection intensity. Therefore, the criterion for determining the corrosion state of the reinforcing bar R may be the reinforcing bar partial reflection intensity, or may be another parameter such as the differential reflection intensity calculated from the reinforcing bar partial reflection intensity, as described below.

[0037] The corrosion state determination unit 55 may determine the corrosion state of the reinforcing bar R based on the differential reflection intensity, which is the difference between the reinforcing bar partial reflection intensity and the concrete partial reflection intensity. The greater the degree of corrosion of the reinforcing bar R, the smaller the differential reflection intensity. For example, the corrosion state determination unit 55 determines that the reinforcing bar R is corroded when the differential reflection intensity is equal to or less than a predetermined threshold, and determines that the reinforcing bar R is not corroded when the differential reflection intensity is greater than the predetermined threshold. By using the differential reflection intensity to determine the corrosion state of the reinforcing bar R, the corrosion state of the reinforcing bar R can be determined based on information that more fully reflects the state of the reinforcing bar R, thereby enabling more accurate determination of the corrosion state of the reinforcing bar R. However, in addition to the differential reflection intensity, the corrosion state determination unit 55 may also use the quotient of the reinforcing bar partial reflection intensity and the concrete partial reflection intensity, or the difference or quotient between the reinforcing bar partial reflection intensity and the intensity of the electromagnetic wave reflected from the back surface of the concrete C when an electromagnetic wave is irradiated onto the back surface.

[0038] The corrosion state determination unit 55 may determine the corrosion state of the reinforcing bar R based on the corrected differential reflected intensity obtained by correcting the differential reflected intensity as described above. The greater the degree of corrosion of the reinforcing bar R, the smaller the corrected differential reflected intensity. For example, the corrosion state determination unit 55 determines that the reinforcing bar R is corroded when the corrected differential reflected intensity is equal to or less than a predetermined threshold, and determines that the reinforcing bar R is not corroded when the corrected differential reflected intensity is greater than the predetermined threshold. By using the corrected differential reflected intensity to determine the corrosion state of the reinforcing bar R, the corrosion state of reinforcing bars R with different cover depths CD can be determined using the same criteria, and the corrosion state of the reinforcing bar R can be determined more accurately.

[0039] The corrosion state determination unit 55 may determine the corrosion state of the reinforcing bar R based on the mass loss rate of the reinforcing bar R calculated from the corrected differential reflected light intensity as described above. The greater the degree of corrosion of the reinforcing bar R, the greater the mass loss rate of the reinforcing bar R. For example, the corrosion state determination unit 55 determines that the reinforcing bar R is corroded when the mass loss rate of the reinforcing bar R is equal to or greater than a predetermined threshold, and determines that the reinforcing bar R is not corroded when the mass loss rate of the reinforcing bar R is smaller than the predetermined threshold. By using the mass loss rate of the reinforcing bar R to determine the corrosion state of the reinforcing bar R, the corrosion state of the reinforcing bar R can be evaluated more quantitatively and the corrosion state of the reinforcing bar R can be determined more accurately.

[0040] The memory unit 56 can store the above-mentioned rebar partial reflection intensity, concrete partial reflection intensity, differential reflection intensity, relationship between cover thickness CD and differential reflection intensity, corrected differential reflection intensity, relationship between corrected differential reflection intensity and mass reduction rate of rebar R, mass reduction rate of rebar R, and / or the judgment result of the corrosion state of rebar R. The detection signal processing unit 54 and corrosion state judgment unit 55 can retrieve the above information from the memory unit 56 as needed. The memory unit 56 can also store computer programs described below, and the electromagnetic wave emission control unit 51, electromagnetic wave detection control unit 52, position control unit 53, detection signal processing unit 54, and corrosion state judgment unit 55 can retrieve and execute the computer programs from the memory unit 56 as needed.

[0041] <Rebar inspection method> Next, the reinforcing bar inspection method 100 of this embodiment will be described using an example in which it is implemented using the reinforcing bar inspection device 1 of this embodiment. The matters described above regarding the reinforcing bar inspection device 1 can be applied to the reinforcing bar inspection method 100 described below, and the matters described below regarding the reinforcing bar inspection method 100 can be applied to the reinforcing bar inspection device 1 described above. However, the reinforcing bar inspection method of the present invention is not limited to the following example and can also be implemented using devices other than the reinforcing bar inspection device 1 of this embodiment. Furthermore, the reinforcing bar inspection method 100 of this embodiment is not particularly limited and can be executed by human operation or by a computer program including computer-executable instructions that, when executed on a computer, cause the computer to execute the reinforcing bar inspection method 100 of this embodiment. Note that, although several steps will be described below, the order of the steps is not limited to the order described below.

[0042] As shown in Figures 1 and 4, the rebar inspection method 100 of this embodiment includes a step 101 of irradiating a concrete surface CS with electromagnetic waves EM having a frequency of sub-terahertz (e.g., 0.01 to 0.3 THz), and a step 102 of detecting the electromagnetic waves EM reflected from the concrete surface CS when the electromagnetic waves EM are irradiated onto the concrete surface CS.

[0043] In this embodiment, the frequency of the electromagnetic waves EM in step 101 is set to a frequency appropriate for each cover thickness CD of the rebar R, depending on the cover thickness CD of the rebar R. The frequency appropriate for each cover thickness CD of the rebar R can be determined taking into consideration the frequency characteristics of the electromagnetic waves EM, which differ for each cover thickness CD of the rebar R. For example, the frequency of the electromagnetic waves EM can be selected for each cover thickness CD of the rebar R from within a frequency range in which the effect of impurities (e.g., water and / or chloride ions) contained in the concrete C on the intensity of the reflected electromagnetic waves EM is reduced. Additionally or alternatively, for example, the frequency of the electromagnetic waves EM can be selected from within a frequency range in which the differential reflection intensity, which is represented by the difference between the rebar partial reflection intensity and the concrete partial reflection intensity, is increased.

[0044] As shown in FIG. 4, the reinforcing bar inspection method 100 of this embodiment includes a step 103 of determining the corrosion state of the reinforcing bar R based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic wave EM reflected from the concrete surface CS1 (see FIG. 2B) corresponding to the location where the reinforcing bar R is embedded. For example, if the reinforcing bar partial reflection intensity is equal to or less than a predetermined threshold, it can be determined that the reinforcing bar R is corroded, and if the reinforcing bar partial reflection intensity is greater than the predetermined threshold, it can be determined that the reinforcing bar R is not corroded. Note that the term "based on the reinforcing bar partial reflection intensity" used herein means that the criteria for determining the corrosion state of the reinforcing bar R include at least the reinforcing bar partial reflection intensity. Therefore, the criteria for determining the corrosion state of the reinforcing bar R may be the reinforcing bar partial reflection intensity, or may be other parameters such as a differential reflection intensity calculated from the reinforcing bar partial reflection intensity, as described below.

[0045] The step 103 of determining the corrosion state of the reinforcing bar R may include a step of determining the corrosion state of the reinforcing bar R based on a differential reflection intensity, which is the difference between the reinforcing bar partial reflection intensity and the concrete partial reflection intensity, which is the intensity of the electromagnetic wave EM reflected from the concrete surface CS2 (see FIG. 2B ) corresponding to the position where the reinforcing bar R is not buried. For example, if the differential reflection intensity is equal to or less than a predetermined threshold, it can be determined that the reinforcing bar R is corroded, and if the differential reflection intensity is greater than the predetermined threshold, it can be determined that the reinforcing bar R is not corroded. By using the differential reflection intensity to determine the corrosion state of the reinforcing bar R, the corrosion state of the reinforcing bar R can be determined based on information that more fully reflects the state of the reinforcing bar R, thereby enabling more accurate determination of the corrosion state of the reinforcing bar R. However, other than the differential reflection intensity, the criterion for determining the corrosion state of the reinforcing bar R may also be the quotient of the reinforcing bar partial reflection intensity and the concrete partial reflection intensity, or the difference or quotient between the reinforcing bar partial reflection intensity and the intensity of the electromagnetic wave reflected from the back surface of the concrete C when the electromagnetic wave is irradiated onto the back surface.

[0046] Here, the concrete surface CS2 corresponding to the position where the rebar R is not buried is not particularly limited, but is preferably set at a concrete surface CS at a position at least a length corresponding to the width W of the rebar R away from the concrete surface CS1 corresponding to the position where the rebar R is buried, as shown in FIG. 2B . By setting the concrete surface CS2 corresponding to the position where the rebar R is not buried at a distance at least a length corresponding to the width W of the rebar R from the concrete surface CS1 corresponding to the position where the rebar R is buried, it is possible to prevent the electromagnetic waves EM reflected when the electromagnetic waves EM are irradiated onto the concrete surface CS2 corresponding to the position where the rebar R is not buried from being affected by the rebar R. From a similar perspective, the concrete surface CS2 corresponding to the position where the rebar R is not buried is more preferably set at a distance of at least twice the width W of the rebar R from the concrete surface CS1 corresponding to the position where the rebar R is buried, and even more preferably at least three times the width W of the rebar R.

[0047] The step 103 of determining the corrosion state of the reinforcing bar R may include a step of correcting the differential reflection intensity obtained for the concrete C in which the reinforcing bar R, the corrosion state of which is unknown, based on a predetermined relationship between the cover thickness CD and the differential reflection intensity, and determining the corrosion state of the reinforcing bar R based on the corrected differential reflection intensity. For example, if the corrected differential reflection intensity is equal to or less than a predetermined threshold, it can be determined that the reinforcing bar R is corroded, and if the corrected differential reflection intensity is greater than the predetermined threshold, it can be determined that the reinforcing bar R is not corroded. By using the corrected differential reflection intensity to determine the corrosion state of the reinforcing bar R, the corrosion state of the reinforcing bar R with different cover thicknesses CD can be determined using the same criteria, and the corrosion state of the reinforcing bar R can be determined more accurately.

[0048] The step 103 of determining the corrosion state of the reinforcing bar R may include a step of calculating a mass loss rate of the reinforcing bar R in the concrete C from the corrected differential reflection intensity obtained for the concrete C in which the reinforcing bar R is embedded, based on a predetermined relationship between the corrected differential reflection intensity and the mass loss rate of the reinforcing bar R. The mass loss rate of the reinforcing bar R represents the ratio of the mass of the reinforcing bar R reduced by corrosion to the mass of the non-corroded reinforcing bar R. The corrosion state of the reinforcing bar R can be determined based on the mass loss rate of the reinforcing bar R calculated from the corrected differential reflection intensity. For example, if the mass loss rate of the reinforcing bar R is equal to or greater than a predetermined threshold, it can be determined that the reinforcing bar R is corroded, and if the mass loss rate of the reinforcing bar R is less than the predetermined threshold, it can be determined that the reinforcing bar R is not corroded. By using the mass loss rate of the reinforcing bar R to determine the corrosion state of the reinforcing bar R, the corrosion state of the reinforcing bar R can be evaluated more quantitatively and the corrosion state of the reinforcing bar R can be determined more accurately.

[0049] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Note that the above-described embodiments mainly describe the invention having the following configurations.

[0050] (1) A reinforcing bar inspection device for inspecting the corrosion state of reinforcing bars embedded in concrete, a radiation source that emits electromagnetic waves having a sub-terahertz frequency; a detector that detects electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface; Equipped with The reinforcing bar inspection device is configured to determine the corrosion state of the reinforcing bar based on a reinforcing bar partial reflection intensity, which is the intensity of an electromagnetic wave reflected from a concrete surface corresponding to a position where the reinforcing bar is embedded; The frequency of the electromagnetic wave is set to a frequency suitable for each cover thickness of the reinforcing bar according to the cover thickness of the reinforcing bar. Rebar inspection equipment.

[0051] (2) The frequency of the electromagnetic wave is selected from a frequency range in which the influence of water contained in the concrete on the intensity of the reflected electromagnetic wave is small. (1) The reinforcing bar inspection device described above.

[0052] (3) The reinforcing bar inspection device is configured to determine the corrosion state of the reinforcing bar based on a differential reflection intensity represented by the difference between the reinforcing bar partial reflection intensity and a concrete partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to a position where the reinforcing bar is not buried. A reinforcing bar inspection device according to (1) or (2).

[0053] (4) The concrete surface corresponding to the position where the reinforcing bar is not embedded is set on the concrete surface at a position away from the concrete surface corresponding to the position where the reinforcing bar is embedded by at least a length corresponding to the width of the reinforcing bar. The reinforcing bar inspection device according to any one of (1) to (3).

[0054] (5) The reinforcing bar inspection device is configured to correct the differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded based on a predetermined relationship between the cover depth and the differential reflection intensity, and to determine the corrosion state of the reinforcing bar based on the corrected differential reflection intensity. The reinforcing bar inspection device according to any one of (1) to (4).

[0055] (6) The reinforcing bar inspection device is configured to calculate a mass reduction rate of the reinforcing bar in the concrete from the corrected differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded, based on a predetermined relationship between the corrected differential reflection intensity and the mass reduction rate of the reinforcing bar. The reinforcing bar inspection device according to any one of (1) to (5).

[0056] (7) A reinforcing bar inspection method for inspecting the corrosion state of reinforcing bars embedded in concrete, comprising: irradiating a concrete surface with electromagnetic waves having a sub-terahertz frequency; a step of detecting electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface; a step of determining the corrosion state of the reinforcing bar based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to the position where the reinforcing bar is embedded; Including, The frequency of the electromagnetic wave is set to a frequency suitable for each cover thickness of the reinforcing bar according to the cover thickness of the reinforcing bar. Rebar inspection methods.

[0057] (8) The frequency of the electromagnetic wave is selected from a frequency range in which the influence of water contained in the concrete on the intensity of the reflected electromagnetic wave is small. (7) A reinforcing bar inspection method as described above.

[0058] (9) The step of determining the corrosion state of the reinforcing bar includes a step of determining the corrosion state of the reinforcing bar based on a differential reflection intensity represented by the difference between the reinforcing bar partial reflection intensity and a concrete partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to the position where the reinforcing bar is not buried. (7) or (8) a reinforcing bar inspection method.

[0059] (10) The concrete surface corresponding to the position where the reinforcing bar is not embedded is set on the concrete surface at a position away from the concrete surface corresponding to the position where the reinforcing bar is embedded by at least a length corresponding to the width of the reinforcing bar. The reinforcing bar inspection device according to any one of (7) to (9).

[0060] (11) The step of determining the corrosion state of the reinforcing bar includes a step of correcting the differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded based on a predetermined relationship between the cover depth and the differential reflection intensity, and determining the corrosion state of the reinforcing bar based on the corrected differential reflection intensity. The reinforcing bar inspection method according to any one of (7) to (10).

[0061] (12) The step of determining the corrosion state of the reinforcing bar includes a step of calculating a mass reduction rate of the reinforcing bar in the concrete from the corrected differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded, based on a predetermined relationship between the corrected differential reflection intensity and a mass reduction rate of the reinforcing bar. The reinforcing bar inspection method according to any one of (7) to (11). [Example]

[0062] The reinforcing bar inspection device and reinforcing bar inspection method of the present embodiment will be described below using examples, but the reinforcing bar inspection device and reinforcing bar inspection method of the present invention are not limited to the following examples.

[0063] <Electromagnetic wave measurement conditions> Electromagnetic waves were irradiated onto the concrete surface at an incident angle of approximately 33 degrees relative to the normal to the concrete surface, and the electromagnetic waves reflected from the concrete surface at a reflection angle of approximately 33 degrees relative to the normal to the concrete surface were detected (see Figure 1). The electromagnetic waves irradiated onto the concrete surface were s-polarized and varied in 0.1 GHz increments from 7.5 to 15 GHz. The focal depth of the electromagnetic waves irradiated onto the concrete surface was adjusted to correspond to the cover thickness of the rebar. The irradiated positions on the concrete surface were the concrete surface corresponding to the positions where the rebar was embedded (three positions on the concrete surface CS1 in Figure 2B) and the concrete surface corresponding to the positions where the rebar was not embedded (six positions on the concrete surface CS2 in Figure 2B). The intensity of the electromagnetic waves reflected from the concrete surface was measured as a voltage value. The difference between the average value of the intensity of the electromagnetic waves reflected from the concrete surface at three locations corresponding to the positions where the rebars were buried (rebar partial reflection intensity) and the average value of the intensity of the electromagnetic waves reflected from the concrete surface at six locations corresponding to the positions where the rebars were not buried (concrete partial reflection intensity) (rebar partial reflection intensity - concrete partial reflection intensity) was calculated as the differential reflection intensity.

[0064] <Measurement sample> Reinforced concrete with a cover thickness of 10 mm, 30 mm, and 50 mm was used for measuring electromagnetic waves. Round steel bars and deformed steel bars with a diameter of 13 mm were used as reinforcing bars, which were buried so as to extend approximately parallel to the concrete surface. The concrete was made of cement with a density of 3.16 g / cm. 3 Ordinary Portland cement, fine aggregate with a surface dry density of 2.54 g / cm 3 , land sand from Kakegawa, Shizuoka Prefecture, with a water absorption rate of 1.89%, and coarse aggregate with a surface dry density of 2.64 g / cm 3 The concrete was made of crushed hard sandstone from Ome, Tokyo, with a water absorption rate of 0.65% and a maximum particle size of 20 mm. A lignin sulfonate-based AE water reducer (standard type) was used as a chemical admixture, and the cement was 306 kg / m 3 , water 168kg / m 3 , fine aggregate 857kg / m 3 , coarse aggregate 951kg / m 3 The cement was mixed with 1.0% chemical admixture.

[0065] To investigate the effect of the concentration of water in concrete on the intensity of reflected electromagnetic waves, electromagnetic waves were measured for reinforced concrete with different moisture contents. The moisture contents were 1.1%, 2.1%, and 3.3%, as well as a saturated state in which the concrete's pores are filled with water and the concrete has absorbed the maximum amount of water. In addition, to investigate the effect of the concentration of chloride ions in concrete on the intensity of reflected electromagnetic waves, electromagnetic waves were measured for reinforced concrete with different concentrations of chloride ions. The concentration of chloride ions in the concrete was adjusted with a 10% sodium chloride aqueous solution, and 0 kg / m 3 , 1.2 kg / m 3 , 2.5 kg / m 3 In addition, to investigate the effect of the corrosion state of rebar on the intensity of reflected electromagnetic waves, measurements of electromagnetic waves were carried out on reinforced concrete containing rebars with different mass reduction rates due to different corrosion states.

[0066] <The effect of rebar cover thickness and impurities in concrete on the frequency characteristics of electromagnetic waves> We investigated the effect of water impurities on the frequency characteristics of reflected electromagnetic waves for reinforced concrete with different cover thicknesses. The reinforced concrete used was uncorroded round steel reinforcing bars. Figure 5 shows the frequency characteristics of the differential reflected intensity of electromagnetic waves obtained for reinforced concrete RC with different water content conditions: (a) 10 mm, (b) 30 mm, and (c) 50 mm cover thicknesses. In Figure 5, the horizontal axis represents the frequency of the incident electromagnetic wave, and the vertical axis represents the differential reflected intensity of the reflected electromagnetic wave. Figure 5 shows that the frequency characteristics of the differential reflected intensity differ depending on the cover thickness CD of the reinforcing bars and the moisture content of the concrete. However, Figure 5 also reveals that there are frequency ranges in which the differential reflected intensity does not change significantly even when the moisture content of the concrete is different. By measuring reinforced concrete using electromagnetic waves in this frequency range, we can minimize the effect of water and obtain differential reflected intensity that closely reflects the condition of the reinforcing bars. For example, frequencies that are less susceptible to the influence of water can be selected when the difference in differential reflection intensity between different water content states is smaller than a predetermined intensity difference (for example, about 10 mV).Frequencies selected as being less susceptible to the influence of water are shown in Table 1 below.

[0067] [Table 1]

[0068] We investigated the effect of chloride ion impurities on the frequency characteristics of reflected electromagnetic waves for reinforced concrete with different cover thicknesses. The reinforced concrete used was uncorroded round steel reinforcing bars. Figure 6 shows the frequency characteristics of the differential reflected intensity of electromagnetic waves obtained for reinforced concrete RC with different chloride ion concentrations (a) 10 mm, (b) 30 mm, and (c) 50 mm cover thicknesses. In Figure 6, the horizontal axis represents the frequency of the incident electromagnetic wave, and the vertical axis represents the differential reflected intensity of the reflected electromagnetic wave. Figure 6 shows that the frequency characteristics of the differential reflected intensity differ depending on the cover thickness CD of the reinforcing bars and the chloride ion concentration in the concrete. However, Figure 6 also shows that there is a frequency range in which the differential reflected intensity does not change significantly even when the chloride ion concentration is different. By measuring reinforced concrete using electromagnetic waves within this frequency range, we can reduce the effect of chloride ions and obtain differential reflected intensity that closely reflects the condition of the reinforcing bars. For example, frequencies that are less susceptible to the influence of chloride ions can be selected when the difference in differential reflection intensity between different chloride ion concentrations is smaller than a predetermined intensity difference (for example, about 10 mV).Frequencies selected as being less susceptible to the influence of chloride ions are shown in Table 2 below.

[0069] [Table 2]

[0070] As described above, the frequency characteristics of reflected electromagnetic waves vary depending on the cover thickness, and the content of impurities such as water and chloride ions also influence the frequency characteristics. Therefore, it is preferable to select an electromagnetic wave frequency that can suppress the effects of impurities such as water and chloride ions for each cover thickness. In this case, a frequency range that can suppress the effects of water, a frequency range that can suppress the effects of chloride ions, or a frequency range that can suppress the effects of both water and chloride ions may be selected. Additionally or alternatively, a frequency range that has high permeability through concrete and high reflection intensity from rebar is preferably selected as the frequency of the electromagnetic wave. More specifically, it is preferable to select an electromagnetic wave frequency that maximizes the differential reflection intensity. For example, the following frequencies can be selected to satisfy all of the above conditions: 11.9 GHz for a 10 mm cover thickness, 14.3 GHz for a 30 mm cover thickness, and 14.8 GHz for a 50 mm cover thickness (see the frequencies indicated by the arrows in Figures 5 and 6).

[0071] <Relationship between rebar cover thickness and differential reflection intensity> The relationship between the rebar cover thickness and the differential reflection intensity was investigated. The frequencies of the electromagnetic waves irradiated onto the concrete surface were selected as described above: 11.9 GHz for a 10 mm cover thickness, 14.3 GHz for a 30 mm cover thickness, and 14.8 GHz for a 50 mm cover thickness. The reinforced concrete samples used were round steel and deformed steel bars, with no corrosion. Figure 7 shows the relationship between the rebar cover thickness and the differential reflection intensity, with the horizontal axis representing the cover thickness and the vertical axis representing the differential reflection intensity. Figure 7 also shows that for both round steel and deformed steel bars, the differential reflection intensity decreases as the cover thickness of the rebar increases, indicating a correlation between the cover thickness and the differential reflection intensity. Figure 7 also shows that differential reflection intensity was observed up to a 50 mm cover thickness for round steel bars, and up to a 30 mm cover thickness for deformed steel bars. This indicates that it is possible to determine the corrosion state of rebars up to a cover thickness of at least 50 mm when the rebars are round steel, and up to a cover thickness of at least 30 mm when the rebars are deformed steel. Furthermore, because the differential reflection intensity differs depending on the type of rebar, it is also possible to determine the type of rebar based on this difference in differential reflection intensity.

[0072] Figure 7 shows the regression equations obtained by regression analysis for each type of rebar. Using this regression equation, the differential reflection intensities obtained from reinforced concrete with different cover thicknesses can be corrected to the differential reflection intensities assumed to be the same cover thickness (e.g., 0 mm). This allows for direct comparison of the differential reflection intensities obtained from reinforced concrete with different cover thicknesses. Furthermore, differential reflection intensities obtained from reinforced concrete with cover thicknesses other than 10 mm, 30 mm, and 50 mm can also be directly compared by correcting the differential reflection intensities using the cover thickness determined by a known rebar detection device. When using the relationship shown in Figure 7, this correction can be performed using the relational equation (corrected differential reflection intensity = differential reflection intensity + a × cover thickness). Note that a is the absolute value of the slope of the regression equation; in the example shown in Figure 7, it is 0.547 for round steel and 0.578 for deformed steel.

[0073] <Relationship between corrected differential reflection intensity and rebar mass reduction rate> The relationship between the corrected differential reflection intensity after correcting the differential reflection intensity using the method described above and the mass reduction rate of the rebar was investigated. The frequencies of the electromagnetic waves irradiated onto the concrete surface were selected as 11.9 GHz for a 10 mm cover thickness, 14.3 GHz for a 30 mm cover thickness, and 14.8 GHz for a 50 mm cover thickness, as described above. The reinforced concrete samples used were round steel and deformed steel bars, whose mass had been reduced by the mass reduction rates shown in Figure 8 due to corrosion. Figure 8 shows the relationship between the corrected differential reflection intensity and the mass reduction rate of the rebar, with the horizontal axis representing the corrected differential reflection intensity and the vertical axis representing the mass reduction rate of the rebar. Figure 8 indicates that for both round steel and deformed steel bars, a decrease (increase) in the mass reduction rate of the rebar tends to increase (decrease) the corrected differential reflection intensity, indicating a correlation between the corrected differential reflection intensity and the mass reduction rate of the rebar. This indicates that by using the corrected differential reflection intensity, it is possible to evaluate the mass loss rate of reinforcing bars whose corrosion state is unknown, and to quantitatively determine the corrosion state of the reinforcing bars.

[0074] Figure 8 shows the regression equations obtained by regression analysis for each type of rebar. Using this regression equation, the rebar mass reduction rate can be calculated from the corrected differential reflected intensity. When using the relationship shown in Figure 8, this calculation can be performed using the following equation: (rebar mass reduction rate = cb × corrected differential reflected intensity). Note that b is the absolute value of the slope of the regression equation; in the example shown in Figure 8, it is 0.046 for round rebars and 0.130 for deformed rebars. Furthermore, c is the intercept of the regression equation; in the example shown in Figure 8, it is 1.88 for round rebars and 3.53 for deformed rebars. Using the rebar mass reduction rate to assess the state of corrosion of rebars allows for a more quantitative evaluation of the state of corrosion and a more accurate assessment of the state of corrosion of rebars. [Explanation of symbols]

[0075] 1. Rebar inspection equipment 2 Radiation source 21 Oscillator 22 Antenna 23 Lens 3. Detector 31 Detector body 32 Antenna 33 Lens 4 Position adjustment device 5. Control device 51 Electromagnetic wave radiation control section 52 Electromagnetic wave detection control unit 53 Position control section 54 Detection signal processing section 55 Corrosion condition determination unit 56 Memory section 100 Reinforcement Inspection Method 101 A process of irradiating a concrete surface with electromagnetic waves having a frequency of sub-terahertz 102. A process for detecting electromagnetic waves reflected from a concrete surface. 103 Process for determining the corrosion state of reinforcing bars based on the partial refraction intensity of reinforcing bars C. Concrete CD Cover Thickness CS Concrete Surface CS1 Concrete surface corresponding to the location where the rebar is embedded CS2 Concrete surface corresponding to the location where the rebar is not embedded EM electromagnetic waves NL Normal to concrete surface R rebar RC reinforced concrete W Width of rebar θ1 Incident angle θ2 Reflection angle

Claims

1. A reinforcing bar inspection device for inspecting the corrosion state of reinforcing bars embedded in concrete, a radiation source that emits electromagnetic waves having a sub-terahertz frequency; a detector that detects electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface; Equipped with The reinforcing bar inspection device is configured to determine the corrosion state of the reinforcing bar based on a reinforcing bar partial reflection intensity, which is the intensity of an electromagnetic wave reflected from a concrete surface corresponding to a position where the reinforcing bar is embedded; The frequency of the electromagnetic wave is set to a frequency suitable for each cover thickness of the reinforcing bar according to the cover thickness of the reinforcing bar. Rebar inspection equipment.

2. The frequency of the electromagnetic wave is selected from a frequency range in which the influence of water contained in the concrete on the intensity of the reflected electromagnetic wave is small. The reinforcing bar inspection device according to claim 1.

3. The reinforcing bar inspection device is configured to determine the corrosion state of the reinforcing bar based on a differential reflection intensity represented by the difference between the reinforcing bar partial reflection intensity and a concrete partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to a position where the reinforcing bar is not buried.

3. The reinforcing bar inspection device according to claim 1 or 2.

4. The concrete surface corresponding to the position where the reinforcing bar is not embedded is set on the concrete surface at a position away from the concrete surface corresponding to the position where the reinforcing bar is embedded by at least a length corresponding to the width of the reinforcing bar.

3. The reinforcing bar inspection device according to claim 1 or 2.

5. The reinforcing bar inspection device is configured to correct the differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded based on a predetermined relationship between the cover depth and the differential reflection intensity, and to determine the corrosion state of the reinforcing bar based on the corrected differential reflection intensity. The reinforcing bar inspection device according to claim 3.

6. The reinforcing bar inspection device is configured to calculate a mass reduction rate of the reinforcing bar in the concrete from the corrected differential reflected light intensity obtained for the concrete in which the reinforcing bar is embedded, based on a predetermined relationship between the corrected differential reflected light intensity and a mass reduction rate of the reinforcing bar. The reinforcing bar inspection device according to claim 5.

7. A reinforcing bar inspection method for inspecting the corrosion state of reinforcing bars embedded in concrete, comprising: irradiating a concrete surface with electromagnetic waves having a sub-terahertz frequency; a step of detecting electromagnetic waves reflected from the concrete surface when the electromagnetic waves are irradiated onto the concrete surface; a step of determining the corrosion state of the reinforcing bar based on the reinforcing bar partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to the position where the reinforcing bar is embedded; Including, The frequency of the electromagnetic wave is set to a frequency suitable for each cover thickness of the reinforcing bar according to the cover thickness of the reinforcing bar. Rebar inspection methods.

8. The frequency of the electromagnetic wave is selected from a frequency range in which the influence of water contained in the concrete on the intensity of the reflected electromagnetic wave is small. The reinforcing bar inspection method according to claim 7.

9. The step of determining the corrosion state of the reinforcing bar includes a step of determining the corrosion state of the reinforcing bar based on a differential reflection intensity represented by the difference between the reinforcing bar partial reflection intensity and a concrete partial reflection intensity, which is the intensity of the electromagnetic wave reflected from the concrete surface corresponding to a position where the reinforcing bar is not buried. The reinforcing bar inspection method according to claim 7 or 8.

10. The concrete surface corresponding to the position where the reinforcing bar is not embedded is set on the concrete surface at a position away from the concrete surface corresponding to the position where the reinforcing bar is embedded by at least a length corresponding to the width of the reinforcing bar. The reinforcing bar inspection device according to claim 7 or 8.

11. The step of determining the corrosion state of the reinforcing bar includes a step of correcting the differential reflection intensity obtained for the concrete in which the reinforcing bar is embedded based on a predetermined relationship between the cover depth and the differential reflection intensity, and determining the corrosion state of the reinforcing bar based on the corrected differential reflection intensity. The reinforcing bar inspection method according to claim 9.

12. The step of determining the corrosion state of the reinforcing bar includes a step of calculating a mass reduction rate of the reinforcing bar in the concrete from the corrected differential reflected light intensity obtained for the concrete in which the reinforcing bar is embedded, based on a predetermined relationship between the corrected differential reflected light intensity and a mass reduction rate of the reinforcing bar. The reinforcing bar inspection method according to claim 11.

Images