JP5583934B2 - Evaluation method of chemical degradation of concrete - Google Patents

Description

  The present invention relates to a method for evaluating the degree of chemical deterioration of concrete, and more particularly to a method for evaluating the degree of deterioration of concrete to be inspected in the field.

  Structures made of concrete, such as tunnels, bridges, dikes, buildings, etc., are maintained and managed by performing various inspections to identify deteriorated parts and repairing the deteriorated parts. As an inspection mode, there are an inspection of a physical deterioration state such as concrete floating, peeling and cracking, and an inspection of a chemical deterioration state such as neutralization and salt damage of a concrete structure. For the inspection of the physical deterioration state, an ultrasonic method, a radar method, an infrared method, an X-ray method, a sounding method, or the like is used. In addition, the chemical deterioration state is inspected by drilling a concrete structure, collecting a sample from the structure, analyzing the collected sample, and using a reagent or the like on the sample. A method to investigate is proposed. Here, chemical deterioration includes neutralization of concrete and salt damage. Examples of the inspection method for neutralization include an analysis method using a phenolphthalein method, differential thermogravimetry, an X-ray diffractometer, and an X-ray microanalyzer (EPMA). Examples of the inspection method for salt damage include a simple analysis method (JCCI-SC5) of the total salt contained in the hardened concrete and an analysis method (JCI-SC4) of the salt contained in the hardened concrete.

  However, the method of collecting the sample in this way damages the structure even if it is backfilled with new concrete after the sample is collected. Moreover, when it applies to the structure which has not progressed deterioration, it becomes a meaningless inspection and the inspection cost increases, and the structure is damaged. Furthermore, even in a structure where deterioration is progressing, the degree of progress of deterioration generally differs depending on the part, so collecting samples randomly does not necessarily sample the part that is progressing, There is a problem that the accuracy of inspection is lacking.

  Therefore, development of an apparatus capable of detecting a chemical deterioration state of a concrete structure without taking a sample is desired. In Patent Document 1, based on the absorbance at a predetermined wavelength of near infrared light reflected from the concrete structure, A deterioration detection device capable of detecting the deterioration state of a concrete structure has been proposed. The invention of Patent Document 1 seeks to detect the difference between concrete that has undergone neutralization and salt damage and concrete that has not progressed by the difference in absorbance at a predetermined wavelength of near infrared rays.

JP 2005-2919881 A

However, it is known that the high frequency band after infrared is absorbed by the vibration energy of molecules and atoms inside the concrete, and the information obtained is limited to the vicinity of the concrete surface, and the chemical degradation state inside the concrete Is difficult to evaluate.
Then, an object of this invention is to provide the evaluation method of the deterioration degree of concrete which can detect the chemical deterioration state inside concrete.

  In order to achieve the above object, a concrete deterioration evaluation method according to the present invention is firstly a method for evaluating the chemical deterioration degree of concrete using the absorbance of terahertz waves irradiated on the concrete. Forming a pair of boring holes in the concrete, introducing the terahertz wave to a predetermined depth position of one boring hole by a first optical fiber, irradiating the terahertz wave toward the other boring hole, A second optical fiber introduced into the other boring hole is used to detect the transmitted wave of the terahertz wave to calculate the absorbance, and the concrete having the same composition as the absorbance and the degree of deterioration is known. It is characterized by contrasting the absorbance of.

The second is a method for evaluating the degree of chemical degradation of concrete using the absorbance of terahertz waves irradiated to concrete, wherein the concrete is irradiated with terahertz waves generated by pulsed pump light , The reflected wave is detected by a detecting means capable of detecting the terahertz wave only when pulsed probe light synchronized with the pump light is received, and the absorbance is calculated. The absorbance has the same composition as the concrete. with deterioration degree and is compared with the absorbance of known concrete, the said detection means, said probe light wave reflected by a predetermined depth position in accordance with the time to reach the detection means of the concrete The reflected wave is selectively detected by causing the detection means to receive light .

Third, there is a method for evaluating the degree of chemical deterioration of concrete using the absorbance of terahertz waves irradiated on the concrete, wherein a boring hole is formed in the concrete, and the boring hole is predetermined by a first optical fiber. Only when the terahertz light generated by the pulsed pump light is introduced to the depth position of the bore, the terahertz wave is irradiated on the inner wall of the borehole, and the pulsed probe light synchronized with the pump light is received. The detection means capable of detecting the terahertz wave detects the reflected wave of the terahertz wave through the second optical fiber introduced into the boring hole, calculates the absorbance, and has the same composition as the absorbance and the concrete. Contrast with the absorbance of concrete having a known deterioration level, and the detection means is separated from the inner wall by a predetermined distance. By receiving the detecting means said probe light in accordance with the time at which the wave reflected by position reaches the detection means, chemical degradation of the concrete, characterized by selectively detecting the reflected wave Degree evaluation method.
Fourth, the reflected wave is a reflected wave from an aggregate surface embedded in the concrete.

Fifth, the deterioration degree is evaluated by comparing the absorbance of the absorption band of chloride ions in the concrete with the absorbance of the absorption band of chloride ions of concrete having a known chloride ion concentration. It is characterized by being.
Sixth, the evaluation of the degree of deterioration is performed by comparing the absorbance of the absorption band due to the neutralization in the concrete with the absorbance of the absorption band due to the neutralization of the concrete with a known neutralization degree. It is performed by doing.

  According to the method for evaluating the degree of deterioration of concrete according to the present invention, since a terahertz wave that can be transmitted through the concrete to some extent is used as a means for measuring the absorbance, it transmits a good absorbance without being affected by the surface condition of the concrete. It can be obtained by measurement. Moreover, since it is sufficient for the boring hole to have an inner diameter required for inserting an optical fiber for introducing a terahertz wave, damage to the concrete can be reduced. Further, by introducing the tip of the optical fiber to a predetermined depth position of the borehole, it is possible to evaluate the degree of deterioration of the concrete at a predetermined depth position.

Even when the absorbance is obtained by reflection measurement, the reflected wave of the terahertz wave reflected from a predetermined depth position can be selectively detected by making the terahertz wave into a pulse shape. Reflection measurement that is not performed can be performed, and the depth distribution of the degree of deterioration of concrete with high reliability can be evaluated without changing the optical system. In addition, since the reflected wave from the aggregate surface inside concrete has high reflection intensity, the light absorbency with a high S / N ratio is computable by selectively detecting this reflected wave.
Furthermore, since the chloride ion concentration and the neutralization degree are used as an index for evaluating the absorbance, it is possible to evaluate the chemical deterioration degree with good reproducibility.

It is a layout view of the evaluation method according to the first embodiment. It is a schematic diagram of the terahertz-TDS apparatus which comprises the evaluation method which concerns on 1st Embodiment. It is a schematic diagram of a terahertz wave generation device and a terahertz wave detection element that constitute a terahertz-TDS device. It is a flowchart of the evaluation method which concerns on 1st Embodiment. It is a conceptual diagram of the evaluation method which concerns on 2nd Embodiment. It is a layout view of the evaluation method according to the third embodiment. It is a figure which shows the light absorbency by the transmission measurement of each concrete material. It is a figure which shows the light absorbency by the transmission measurement of each concrete material. It is a figure which shows the relationship between the transmittance | permeability and chloride ion concentration in 68 GHz and 100 GHz.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .

An evaluation system for the degree of deterioration of concrete according to the first embodiment is shown in FIG.
The evaluation system 10 according to the first embodiment includes a terahertz-TDS device 18, an analysis device 48, a first optical fiber 42, a second optical fiber 46, a mounting jig 16, and the like.

  The evaluation method of the deterioration degree of the concrete according to the first embodiment using the evaluation system 10 described above is an evaluation method of the chemical deterioration degree of the concrete using the absorbance of the terahertz wave irradiated on the concrete 12, A pair of boring holes 14 is formed in the concrete 12, and a terahertz wave 50 is introduced to a predetermined depth position of one boring hole 14a by the first optical fiber 42, and the terahertz wave 50 is directed toward the other boring hole 14b. And the absorbance is calculated by detecting the transmitted wave of the terahertz wave 50 through the second optical fiber 46 introduced into the other boring hole 14b. The absorbance and the same composition as the concrete 12 are calculated. This is performed by comparing the absorbance of concrete having a known deterioration level.

  A pair of boring holes 14 are formed in the concrete 12 to be inspected, and the intervals between the boring holes 14 are formed in parallel with each other while maintaining a distance through which the terahertz wave 50 (30 GHz to 3 THz) can be transmitted. The boring hole 14 has a diameter into which a mounting jig 16 described later can be introduced.

  In order to allow the first optical fiber 42 and the second optical fiber 46 to propagate the terahertz wave 50, for example, as shown in FIG. 1 (see FIG. 6), a hollow glass or plastic tube is formed with a metal or resin on the inner wall. A thin film is used. With this structure, the propagation wavelength range is not only the terahertz range but also an optical fiber that covers a wide range of soft X-ray ranges. One end of the first optical fiber 42 is connected to the terahertz wave generating element 22, and a mirror 42 b is disposed at the other end opposite to the one end. Similarly, one end 46 of the second optical fiber is connected to the terahertz wave detecting element 24, and a mirror 46a is disposed on the other end opposite to the one end.

  The attachment jig 16 is a member having a fork shape that can be inserted into the pair of bore holes 14 at the same time, and can be fixed at a predetermined height position from the concrete 12 surface. The attachment jig 16 has a first optical fiber 42 attached to one branch and a second optical fiber 46 attached to the other branch. At this time, the mirror 42a at the tip of the first optical fiber 42 and the mirror 46a at the tip of the second optical fiber 46 are mounted at the same height and facing each other. Accordingly, the terahertz wave 50 emitted from the mirror 42a of the first optical fiber 42 can be detected (received) by the mirror 46a of the second optical fiber 46. Then, by inserting the mounting jig 16 into the boring hole 14 and fixing it at a predetermined position, the terahertz wave 50 emitted from the mirror 42a at the predetermined depth position of the boring hole 14a passes through the concrete 12 to be inspected, The mirror 46a in the other boring hole 14b can detect (receive) the transmitted wave (transmitted light) of the terahertz wave 50.

  As a configuration for generating, detecting (receiving) and analyzing the terahertz wave 50, for example, as shown in FIG. 2, a terahertz-TDS apparatus 18 used in terahertz time-resolved spectroscopy (terahertz-TDS) can be used.

  The terahertz-TDS apparatus 18 includes a femtosecond laser 20 that generates a femtosecond pulse width in the time direction, a terahertz wave generating element 22 that serves as a terahertz wave oscillation source, and terahertz wave detection that serves as a terahertz wave detecting unit (light receiving unit). It comprises an element 24, a lock-in amplifier 26, and the like.

  The femtosecond laser 20 emits an optical pulse having a time width of about 100 femtoseconds, and the optical pulse is divided into a pump light 30 and a probe light 32 by a beam splitter 28. The pump light 30 is guided to the terahertz wave generating element 22, and the probe light 32 is guided to the terahertz light detecting element 24 via a movable mirror 34 that delays the time on the optical path.

  As shown in FIG. 3A, the terahertz wave generating element 22 includes a semiconductor substrate 22a that generates a terahertz wave 50 and a super hemispherical lens 22b that collimates the generated electromagnetic wave. The material of the super hemispherical lens 22b is generally made of high resistance silicon (Si) with little absorption loss. As the semiconductor substrate 22a, gallium arsenide (low-temperature grown GaAs, LT-GaAs) grown at low temperature on semi-insulating gallium arsenide (semi-insulating GaAs, SI-GaAs) is used. Furthermore, the parallel transmission line made of an alloy (also serving as an electrode) is attached on LT-GaAs. The portion protruding to the center of the electrode acts as a minute dipole antenna 22c. There is a minute gap 22d (several μm) in the center of the antenna, and a voltage of several tens of volts is applied between the gaps. When the pump light 30 having a photon energy higher than the band gap of the semiconductor is converged and irradiated to the minute gap 22d using the lens 38, photoexcited carriers (electrons and holes) are generated in the semiconductor, and the gap between the minute gaps 22d is generated. Carriers are accelerated by voltage, and instantaneous current flows. The oscillating electric field of the terahertz wave 50 radiated from the minute dipole antenna 22c is proportional to the time derivative of the current flowing in the semiconductor. The terahertz wave 50 is strongly radiated to the SI-GaAs substrate side having a large dielectric constant. The pulse width of the radiated terahertz wave 50 is about 1 picosecond. A first optical fiber 42 that is an optical fiber that transmits the terahertz wave 50 through the off-axis parabolic mirror 36 and the lens 40 that converges the emitted terahertz wave 50 is provided at the subsequent stage of the super hemispherical lens 22b. The terahertz wave 50 is introduced from the end of the first optical fiber 42, and the terahertz wave 50 is propagated to the mirror 42a side opposite to the end while reflecting inside the fiber.

  As shown in FIG. 3B, the terahertz wave detecting element 24 has the same configuration as the semiconductor substrate 22a of the terahertz wave generating element 22, but an ammeter 24d is connected to the minute dipole antenna 24c. Has been. The terahertz wave 50 propagating through the second optical fiber 46 from the semiconductor substrate side of the minute dipole antenna 24c of the terahertz wave detecting element 24 is converged by the lens 44, and the femtosecond probe light 32 from the opposite side is made minute by the minute dipole antenna 22c. Irradiation is performed while converging on the gap 22d. Here, since the terahertz wave detecting element 24 is configured to operate only when the probe light 32 is struck, the probe light 32 is moved by the movable mirror 34 so that the terahertz wave 50 reaches the micro dipole antenna 24c at the same time. Has been adjusted. Since the carriers generated in the semiconductor substrate by the probe light 32 are accelerated by the oscillating electric field accompanying the terahertz wave 50, an instantaneous current flows in proportion to the oscillating electric field of the terahertz wave 50. The output side of the terahertz wave detecting element 24 is connected to the lock-in amplifier 26.

  In order to improve the S / N ratio of the instantaneous current, the lock-in amplifier 26 performs synchronous detection by modulating the pump light 30 with an optical chopper by several kHz and inputting a reference signal to the lock-in amplifier 26. is there. Absorbance can be obtained by subjecting the output current of the lock-in amplifier 26 to AD conversion and Fourier transform using an analyzer.

  The analysis device 48 performs AD conversion on the instantaneous current from the terahertz wave detection element 24 via the lock-in amplifier 26, and then performs Fourier transform to calculate and analyze the absorbance (absorption spectrum) of the terahertz wave 50.

Here, in the absorbance, an absorption peak appears in a specific frequency band due to chloride ions contained in the concrete 12 to be measured and neutralization of the concrete 12.
In the case of chloride ions, the absorbance increases in the range of 2220 nm to 2280 nm with a wavelength of about 2264 nm as the center. Neutralization occurs when the calcium hydroxide concentration in concrete decreases. Therefore, since non-neutralized concrete contains a large amount of calcium hydroxide, the absorbance increases in the range of 1380 nm to 1430 nm, centering on the wavelength of about 1415 nm, but when the concentration of calcium hydroxide decreases, the above range is reached. Absorbance decreases.

  Therefore, the analysis device 48 includes a first standard absorbance at various chloride ion concentrations of a concrete material having a known chloride ion concentration and composition, and a concrete material having a known calcium hydroxide concentration (degree of neutralization) and composition. The second standard absorbances at various calcium hydroxide concentrations are stored in a storage medium (not shown).

  The analysis device 48 stores first standard data indicating the chloride ion concentration dependency of the chloride ion absorption peak in the first standard absorbance in a storage medium (not shown) for each concrete material having a predetermined composition. doing. Similarly, the second standard data indicating the calcium hydroxide concentration dependency of the calcium hydroxide absorption peak of the second standard absorbance is stored in a storage medium (not shown) for each concrete material having a predetermined composition. .

  And the analysis apparatus 48 will calculate the 1st measurement absorption peak value (2nd measurement absorption peak value) of chloride ion (calcium hydroxide), if the composition information of the concrete 12 to be measured is input and the absorbance is calculated, A first standard absorption peak value group (second standard absorption peak value group) having the same composition is read, and a first absorption peak value (second absorption) is selected from the first standard peak value group (second standard peak value group). The chloride ion concentration (calcium hydroxide concentration) relating to the first standard absorption peak value (second standard absorption peak value) that matches or is closest to the peak value) can be output. Here, the analysis device 48 can process either the first measured absorption peak value or the second measured absorption peak value by operating the keyboard, the mouse, or the like, or both can be performed simultaneously. .

  Further, the analysis device 48 reads the first standard absorbance or the second standard absorbance corresponding to the first standard absorption peak value and the second standard absorption peak value, displays them on the display 48a, and the measured absorbance and the first standard absorbance. The first standard absorbance or the second standard absorbance can be simultaneously output on the same coordinates on the display 48a. As a result, the operator can confirm the measured chloride ion concentration and calcium hydroxide concentration of the concrete on the display 48a, see the overall shape of the absorbance, and measure the measured chloride ion concentration of the concrete. Alternatively, the calcium hydroxide concentration can be visually confirmed, and the deterioration degree of concrete can be evaluated using the chloride ion concentration of concrete and the degree of neutralization as indexes.

  FIG. 4 shows a flowchart of the first embodiment. First, the composition information of the concrete 12 is input to the analysis device 48. Then, the analysis device 48 activates the terahertz-TDS device 18 to irradiate the concrete 12 to be measured with the terahertz wave 50 and detects the transmitted wave (a reflected wave in the second and third embodiments described later). . The detected transmitted wave is AD-converted and Fourier-transformed by the analysis device 48, and the absorbance is derived. The analyzer 48 calculates a first measured absorption peak value (second measured absorption peak value) from the peak of the absorption band of chloride ions (calcium hydroxide) from the absorbance. And it agrees with the first absorption peak value (second absorption peak value) from the first standard absorption peak value group (second standard absorption peak value group) having the same composition as the composition related to the composition information inputted previously. The first standard absorption peak value (second standard absorption peak value) having the closest value is selected from the storage medium, and the first measured absorption peak value (second measured absorption peak value) and the first standard absorption peak are selected. The value (second standard absorption peak value) and the chloride ion concentration (calcium hydroxide concentration) corresponding to the first standard absorption peak value are output on the display 48a. Further, the analysis device 48 reads the first standard absorbance (second standard absorbance) of the concrete material corresponding to the first standard absorption peak value (second standard absorption peak value) from the storage medium, and displays the measured absorbance on the display 48a. Output. The first standard absorbance and the second standard absorbance can be output simultaneously.

  In FIG. 5, the conceptual diagram of the evaluation method of the chemical degradation degree of the concrete which concerns on 2nd Embodiment is shown. The method for evaluating the degree of chemical deterioration of concrete according to the second embodiment is a method for evaluating the degree of chemical deterioration of concrete using the absorbance of terahertz waves irradiated on the concrete 12, and is generated in a pulse shape. The concrete 12 is irradiated with the terahertz wave 50 and the reflected wave is detected by a detection means (terahertz detection element 24) to calculate the absorbance. The absorbance and the deterioration of the concrete 12 are the same. While comparing the absorbance of the known concrete, the detection means controls the opening and closing of the detection means in accordance with the time when the reflected wave 54 reflected at a predetermined depth position of the concrete 12 reaches the detection means. It is intended to detect the reflected wave 54 by performing. The basic apparatus configuration and flow for realizing this are the same as those in the first embodiment, but are characterized in that the terahertz wave 50 is applied to the surface of the concrete 12 and the reflected wave 54 is selectively detected.

  The concrete 12 often has a layered structure, and the reflected wave is reflected not only from the surface of the concrete 12 but also from a predetermined depth position (boundary of each layer). Therefore, in the second embodiment, the reflected wave reflected from the predetermined depth position is selectively detected. Similar to the first embodiment, the terahertz-TDS device 18 used in the present embodiment generates a pulsed terahertz wave. The pulse width is 1 picosecond, so the length is about 0.3 mm. . On the other hand, since the terahertz wave can be transmitted through the concrete 12 in the milli-order, the reflected wave of the terahertz wave from the depth position of the milli-order can be measured. Therefore, the reflected wave 52 reflected by the surface with the same irradiation pulse and the reflected wave 54 reflected from the depth position in the milli-order are not spatially overlapped, and they are separated as described below. It can be measured.

  Here, as shown in FIG. 5, consider a case where a terahertz wave 50 incident at an angle θ is reflected at a position of depth d. It is assumed that the terahertz wave 50 does not refract when incident. Then, the optical path difference between the reflected wave 52 reflected on the surface and the reflected wave 54 reflected at the position of the depth d is d / cos θ. At this time, the reflected wave 54 reaches the terahertz wave detection surface (the minute dipole antenna 24 c) by d / (c · cos θ) (c: speed of light) behind the reflected wave 52, but is movable in the terahertz-TDS device 18. If the delay length of the optical path formed by the mirror 34 is adjusted to be longer by the above-described optical path difference d / cos θ than in the first embodiment, the terahertz wave detection element 24 detects the reflected wave 52. Without this, only the reflected wave 54 can be detected. Therefore, the reflected wave 54 can be selectively detected by opening / closing the terahertz wave detecting element 24 according to the time when the reflected wave 54 arrives as described above. In this embodiment, since the surface of the concrete 12 is irradiated with the terahertz wave 50, it is not necessary to use the first optical fiber 42 and the second optical fiber 46. That is, after the terahertz wave generating element 22 is installed so that the emission direction of the terahertz wave 50 is at an angle θ with respect to the normal of the concrete 12, the terahertz wave 50 is irradiated onto the concrete 12, and the reflected wave 52 of the terahertz wave 50 is reflected. The terahertz wave detecting element 24 may be disposed on the optical path 54 with the terahertz wave light receiving side facing the concrete 12 side. At this time, the reflected wave 54 is detected as a terahertz wave that has passed through the concrete 12 by a length of 2d / cos θ.

  FIG. 6 shows a layout according to the third embodiment. 6A is a schematic diagram, and FIG. 6B is a partial detail view of FIG. 6A. The method for evaluating the degree of chemical degradation of concrete according to the third embodiment selectively detects the reflected wave 58 reflected from a predetermined depth position, as in the second embodiment. 12, a boring hole 14c is formed, and a terahertz wave 50 is irradiated to the wall surface of the boring hole 14c through a first optical fiber 42 introduced into the boring hole 14c at a predetermined depth position, and a reflected wave of the terahertz wave 50 is irradiated. 58 is received through the second optical fiber 46 introduced into the boring hole 14c. As shown in FIG. 6, the first optical fiber 42 and the second optical fiber 46 are fixed to a mounting jig 56 that can be fixed at a predetermined height position, and the heights of the tips of the first optical fiber 42 and the second optical fiber 46 are fixed. By changing the position and setting the mirror 42a and the mirror 46a to a predetermined angle, the inner wall of the boring hole 14c is irradiated from the first optical fiber 42 at a predetermined angle. Therefore, the terahertz wave detecting element 24 can detect the reflected wave 58 reflected from the inner wall of the boring hole 14c from a predetermined depth position via the mirror 46a of the second optical fiber 46.

  In the second embodiment and the third embodiment, the reflected waves 52 and 58 have been described on the premise that they are reflected at the boundary between concrete layers having a layered structure. However, an aggregate (for example, metal) that reinforces the strength of the concrete 12 is embedded in the concrete 12. Such aggregate is stronger than concrete and can effectively reflect the reflected wave of terahertz waves. Therefore, by selectively detecting the reflected wave reflected from such an aggregate, the reflected wave can be easily detected, and the absorbance having a high S / N ratio can be calculated.

  As described above, according to the concrete deterioration evaluation method according to the first to third embodiments, the terahertz wave 50 that can be transmitted through the concrete 12 to some extent is used as a means for measuring the absorbance. A good absorbance can be obtained by transmission measurement without being affected by the surface condition of the concrete 12. Further, the bore hole 14 is sufficient if it has an inner diameter necessary for inserting the optical fibers (the first optical fiber 42 and the second optical fiber 46) for introducing the terahertz wave 50. Can be reduced. Further, by introducing the tip of the optical fiber to a predetermined depth position of the boring hole 14, the degree of deterioration of the concrete 12 at the predetermined depth position can be evaluated.

Further, even when the absorbance is obtained by reflection measurement as in the second and third embodiments, the terahertz wave 50 reflected from a predetermined depth position is obtained by making the terahertz wave 50 into a pulse shape. , 58 can be selectively detected, so that reflection measurement independent of the surface state can be performed, and the depth distribution of the degree of deterioration of the concrete 12 with high reliability can be evaluated without changing the optical system. In addition, since the reflected wave from the aggregate surface inside the concrete 12 has high reflection intensity, the light absorbency with a high S / N ratio is computable by selectively detecting this reflected wave.
Furthermore, since the chloride ion concentration and the neutralization degree are used as an index for evaluating the absorbance, it is possible to evaluate the chemical deterioration degree with good reproducibility.

This inventor investigated the change by the chloride ion concentration of the spectrum of concrete. The materials used were Material 1: Cement paste (COP), Material 2: Cement paste 50% substituted with blast furnace slab (COS), Material 3: Mortar (MOP), Material 4: Mortar 50% with blast furnace slab. Substitution (MOS) was used. All materials used had chloride ion concentrations of 0.0, 1.2, 4.8, 9.6, and 19.2 (kg / m ³ ). The thickness of all materials was 3 mm.

  FIG. 7 and FIG. 8 show the absorbance of each concrete material as measured by transmission. 7A shows COP, FIG. 7B shows COS, FIG. 8A shows MOP, and FIG. 8B shows MOS. In addition, the absorbance when neutralized in any material is displayed for reference. As shown in FIGS. 7 and 8, it can be seen that any concrete material having a thickness of 3 mm can transmit terahertz waves. Therefore, this transmission spectrum can be used as the above-mentioned first standard absorbance and second standard absorbance. Note that the vibration appearing in the entire spectrum is interference fringes generated by multiple reflection of terahertz waves inside the concrete.

  It is known that absorption peaks relating to chloride ions exist at 68 GHz and 100 GHz among the absorbance measured by the transmission measurement. FIG. 9 shows the relationship between transmittance (absorption peak value) and chloride ion concentration at 68 GHz and 100 GHz. As shown in the figure, although the transmittance varies depending on the material, it can be seen that the chloride ion concentration and the transmittance have a certain relationship, so the data indicating this relationship is used as the first standard absorption peak value group described above. can do. Although it is desirable that the transmittance decreases monotonically as the chloride ion concentration increases, extreme values can be seen in the plot in the data of FIG. This may be because the position of the interference fringes described above is shifted in the frequency direction due to variations in the measured concrete thickness, or a measurement error. Therefore, it is considered that a monotonously decreasing curve can be obtained by accurately controlling the thickness of the measurement sample to eliminate the displacement of the interference fringe position and improving the measurement error.

  On the other hand, since such interference fringes do not occur in the reflection measurement, it is considered that the first absorption peak value corresponding to the chloride ion concentration can be extracted more accurately from the first standard absorption peak value group. Although not shown as data, the relationship between permeability and calcium hydroxide concentration is expected to have a certain relationship as well as chloride ion concentration, and the data showing this relationship is also the degree of neutralization of concrete. The inventor of the present application considers that it can be used as the second standard peak value group that serves as an index of.

  It can be used as a method for evaluating the degree of chemical deterioration of concrete, which can be evaluated by in-situ observation with a simple configuration and the degree of deterioration of the concrete to be inspected.

10 ......... Evaluation system, 12 ......... Concrete, 14 ......... Boring hole, 16 ...... Mounting jig, 18 ...... Terahertz-TDS device, 20 ...... Femtosecond laser, 22 ......... Terahertz wave Generating element, 24... Terahertz wave detecting element, 26... Lock-in amplifier, 28... Beam splitter, 30 ... Pump light, 32 ... Probe light, 34 ... Movable mirror, 36 ...... Off-axis parabolic mirror, 38 ......... Lens, 40 ......... Lens, 42 ......... First optical fiber, 44 ...... Lens, 46 ......... Second optical fiber, 48 ......... Analysis Equipment: 50 ......... Terahertz wave, 52 ......... Reflected wave, 54 ......... Reflected wave, 56 ......... Mounting jig, 58 ......... Reflected wave.

Claims (3)

A method for evaluating the degree of chemical degradation of concrete using the absorbance of terahertz waves irradiated on the concrete,
Forming a pair of boring holes in the concrete;
Introducing the terahertz wave to a predetermined depth position of one boring hole by the first optical fiber and irradiating the terahertz wave toward the other boring hole,
Detecting the transmitted wave of the terahertz wave through the second optical fiber introduced into the other boring hole, and calculating the absorbance;
A method for evaluating the degree of chemical degradation of concrete, comprising comparing the absorbance with the absorbance of concrete having the same composition as the concrete and having a known degradation level. The evaluation of the degree of deterioration is performed by comparing the absorbance of the absorption band of chloride ions in the concrete with the absorbance of the absorption band of chloride ions of concrete having a known chloride ion concentration. The method for evaluating the degree of chemical deterioration of concrete according to claim 1. The evaluation of the degree of deterioration is performed by comparing the absorbance of the absorption band caused by the neutralization in the concrete with the absorbance of the absorption band caused by the neutralization of the concrete having a known neutralization degree. evaluation method of chemical degradation of the concrete according to claim 1, characterized in that.

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