JP4919396B2 - Nondestructive inspection method for the degree of corrosion of reinforcing bars in concrete structures - Google Patents

Description

  The present invention relates to a nondestructive inspection method for the degree of corrosion of reinforcing bars in a concrete structure.

JP 2006-3288 A

  In recent years, deterioration of concrete structures 1 (FIG. 15) such as tunnels and bridges constructed during a high growth period has become serious, and maintenance of the concrete structures 1 has become an important social issue. . Among the deterioration phenomenon of the structure portion, the corrosion of the reinforcing bars 3 in the concrete structure 1 is particularly serious.

  FIG. 15 shows the pattern. FIG. 15A is a schematic diagram of a sound concrete structure 1 in which the reinforcing bars 3 are not corroded. FIG. 15B is a schematic diagram of the concrete structure 1 when the reinforcing bar 3 is corroded. When the reinforcing bar 3 corrodes, the volume of the reinforcing bar expands. For this reason, a crack 7 is generated around the reinforcing bar. When the corrosion of the reinforcing bars 3 progresses, the concrete peels and finally the concrete peels as shown in FIG. In this state, the strength of the concrete composition 1 cannot be maintained, and immediate repair is required. Since the peeled portion can be confirmed visually or by hitting with a hammer or the like, and the peeled portion can be visually confirmed, repair is often performed only around the peeled or peeled portion.

  As a typical method used for corrosion detection of the reinforcing bar 3, there is a natural potential method defined in (ASTM C876). The measurement pattern is shown in FIG. First, a part of the reinforcing bar 3 is exposed artificially except for concrete. Thereafter, the electrode A is attached to the exposed portion of the reinforcing bar 3. The electrode B is installed on the surface 2 of the concrete structure. The natural potential measuring device 9 measures the potential between the electrode A and the electrode B. The corrosion of the reinforcing bar 3 is inspected by the measured value.

In addition, a technique for measuring and diagnosing a deteriorated portion of a concrete structure using ultrasonic waves has been developed, and a commercially available apparatus for that purpose exists. The present inventor has established a macroscopic detection theory and technique and developed a highly accurate concrete exploration device (Patent Document 1).
The measurement principle using ultrasonic waves is shown in FIG. The transmission probe 12 and the reception probe 13 are installed on the concrete structure surface 2 to generate an ultrasonic wave 21. The received waveform is processed by the calculation unit 18 and the result is displayed on the display unit 20.

  By the way, it is necessary to repair the part where concrete peels off due to corrosion of reinforcing bars. As a repair area, it is currently carried out only around the area where peeling or peeling occurs. However, even if the concrete is not peeled off or peeled off, very many cases are observed when the reinforcing bars are corroded. Therefore, there are many cases where concrete peels and peels again after 1 to 3 years after repair. For this reason, the cost required for repair is enormous.

In the natural potential method (ASTM C876) for measuring corrosion of reinforcing bars,
(1) No corrosion with a probability of 90% or more
(2) Uncertain
(3) It is judged that there is corrosion with a probability of 90% or more, and it is very vague, qualitative and can be judged only on the presence or absence of corrosion.

  In order to know the appropriate corrosion range, initial to moderate corrosion inspection is also required. Moreover, it is necessary to attach an electrode directly to a reinforcing bar for the measurement by the natural potential method. Therefore, it is necessary to expose the reinforcing bars artificially, not a nondestructive inspection. Since holes are made in concrete artificially, there is also a concern that water will infiltrate from that position and rebar corrosion will occur.

  Further, if the ultrasonic method is used, it is possible to measure the reinforcing bar depth do, the concrete thickness, etc., but there is a problem that the corrosion of the reinforcing bar cannot be inspected.

  An object of the present invention is to provide a non-destructive inspection method for the degree of corrosion of reinforcing bars in a concrete structure capable of quantitatively inspecting corrosion of reinforcing bars in concrete by non-destructive.

The invention according to claim 1 is a step of installing a transmitting probe and a receiving probe at a distance L ₀ on a reinforcing bar in reinforced concrete;
Transmitting ultrasonic waves from the transmission probe and receiving a propagation waveform fo (t) at the reception probe;
Extracting a waveform fp (t) from time t = Ts to Te from the propagation waveform fo (t);
Obtaining a spectrum S (f) of a frequency function from the waveform fp (t);
Obtaining a frequency Su corresponding to a point that is 1 / Z of the normalized peak intensity of the spectrum peak frequency Sm of the spectrum S (f);
This is a nondestructive inspection method for the degree of corrosion of reinforcing bars in concrete structures.
Ts: time from transmission to reception Te: constant Z: any positive number greater than or equal to 1

Claim 1 according the invention is characterized and to Turkey Nkurito nondestructive inspection method about Corrosion within the structure to inspect the degree of corrosion of the reinforcing bars by comparing Sua and Sub and magnitude.
Sua: Su for healthy rebar
Sub: Su in inspection object

The invention according to claim 2 is L _{0 /} d 0 ≧ 10 and non-destructive inspection method of about Corrosion in claim 1 concrete structure of wherein a is.
d ₀ : Reinforcing bar depth , L ₀ : Distance between probes

Billing invention according to claim 1 is characterized and to Turkey Nkurito structure Corrosion about nondestructive inspection method in object to seek Ts by the following equation.
Ts = 2 × (d ₀ / cos θ) × (1 / Vc) + (L ₀ −2d ₀ · tan θ) × (1 /
V _R )
θ: Transmission angle Vc: Sound velocity in concrete V _R : Sound velocity in rebar

The invention according to claim 3 is the nondestructive inspection method for the degree of corrosion of reinforcing bars in the concrete structure according to claim 1 or 2, wherein the spectral frequency Su is obtained at a plurality of measurement positions m.
According to a fourth aspect of the present invention, the spectral frequency Su is graphed as the measured frequency m on the horizontal axis and the normalized spectral frequency Suo (Sub / Sua) on the vertical axis, and the upper limit of the vertical axis is set to Sua / It is set to Sua = 1, and the corrosion state of the reinforcing bar is determined in stages according to the numerical value of the frequency Suo, and the degree of corrosion of the reinforcing bar in the concrete structure according to any one of claims 1 to 3 is determined. Destructive inspection method.

ADVANTAGE OF THE INVENTION According to this invention, the nondestructive inspection method of the reinforcement corrosion degree in the concrete structure which can test | inspect quantitatively the corrosion of the reinforcement in concrete by nondestructive is attained.
<Action>

  In order to carry out nondestructive inspection of the degree of corrosion of reinforcing bars in concrete structures by the ultrasonic method, the transmitting probe and the receiving probe are placed on the reinforcing bar at a distance Lo, and ultrasonic waves are transmitted from the transmitting probe. The waveform fo (t) transmitted and propagated by the receiving probe is received, the waveform fp (t) between time t = Ts and Te is extracted, and the spectrum S (f) of fp (t) is calculated. The spectrum peak frequency Sm of the spectrum S (f) is calculated, the normalized intensity of the spectrum peak frequency Sm is calculated, the value of 1 / Z of the normalized intensity is calculated, and the calculated Z minute By calculating the spectral frequency Su for the intensity of 1 and evaluating the spectral frequency Su at each measurement position m, a non-destructive inspection of the degree of corrosion of reinforcing bars in the concrete structure can be performed.

  The present invention will be described below with reference to the drawings. The present invention is a technique that enables measurement of the degree of corrosion of the reinforcing bar 3, which has been impossible by the ultrasonic method.

<Basic processing flowchart until I waveform collection and spectrum calculation>
FIG. 1 shows a basic processing flowchart of the present invention up to waveform collection and spectrum calculation. Description will be made along this flowchart.

(STEP1)
The transmission probe 12 and the reception probe 13 are installed on the reinforcing bar 3 at a distance Lo. The pattern is shown in FIG. 2A is a side view and FIG. 2B is a top view. It is preferable that the inter-probe distance Lo be sufficiently longer than the reinforcing bar depth do. For example, it is preferable that L ₀ / d ₀ ≧ 10.

(STEP2)
An ultrasonic wave is transmitted from the transmission probe 12, and the propagated waveform fo (t) is received by the reception probe 13. In FIG. 2A, an ultrasonic propagation path from the transmission probe 12 to the reception probe 13 is shown. The ultrasonic wave transmitted from the transmission probe 12 propagates through the concrete and enters the reinforcing bar 3. The ultrasonic wave incident on the reinforcing bar 3 propagates through the reinforcing bar 3 as shown in FIG. The propagated ultrasonic wave is finally received by the receiving probe 13. An example of the received waveform is shown in FIG. The time Ts on the horizontal axis shown in FIG. 4 is the time from when the ultrasonic wave is transmitted from the transmission probe 12 until the propagation wave is received by the reception probe 13 in FIG. Details are described below.

FIG. 3 is a detailed drawing regarding the propagation path of ultrasonic waves. As shown in FIG. 3, the ultrasonic wave transmitted from the transmission probe 12 propagates inside the concrete. Among them, an ultrasonic wave with an angle θ is incident on the reinforcing bar 3. The propagation wave at this time is referred to as a concrete propagation wave 23. The propagation distance from the transmission probe 12 to the reinforcing bar 3 is L1, and the propagation time corresponding to L1 is called Tc. The ultrasonic wave incident on the reinforcing bar propagates through the reinforcing bar. Then, it is received by the receiving probe 13 at an angle θ as in the case of incidence. The distance between the receiving probe and the reinforcing bar is L1, and the propagation time corresponding to L1 is called Tc. The distance propagating in rebar and L2, the propagation time corresponding to the L2 and T _R.

The distance Ls until the ultrasonic wave transmitted from the transmission probe 12 is received by the reception probe 13 can be expressed by the following equation.
Ls = 2L1 + L2 (1)
L1 = d ₀ / cos θ (2)
L2 = L _o −2d ₀ · tan θ
(D ₀ : depth of rebar, L _o : distance between probes)

The time Ts until the reception probe 13 receives the ultrasonic wave transmitted from the transmission probe 12 can be expressed by the following equation.
Ts = 2Tc + T _R (4)
Tc = (d ₀ / cos θ) × (1 / Vc) (5)
T _R = (L ₀ −2d ₀ tan θ) × (1 / V _R ) (6)
Vc: Speed of sound in concrete
V _R : Speed of sound in the reinforcing bar

In the present invention, it is necessary to calculate the time Ts until the reception probe 13 receives the ultrasonic wave transmitted from the transmission probe 12 according to the equation (4). The variables in equation (4) are the speed of sound Vc in the concrete, the speed of sound V _R in the reinforcing bar, and the angle θ. It is known that the sound speed of iron is about 5900 m / s. However, it is known that the sound speed of the reinforcing bars embedded in concrete is smaller than the above value. In this embodiment, it is obtained by measurement with a test piece.
Sound velocity Vc in the concrete, the acoustic velocity V _R in a reinforcing bar is determined by experiments. The pattern is shown in FIG. As shown in FIG. 5A, the transmission probe 12 and the reception probe 13 are installed at both ends of the reinforcing bar 3.

  Similarly, in order to obtain the sound velocity Vc in the concrete, a transmission / reception probe is installed as shown in FIG. In this state, ultrasonic waves are transmitted, and the received waveforms are shown in FIGS. FIG. 5B shows a waveform propagating through the reinforcing bar, and time T20 corresponds to the time when it was first received. FIG. 5B shows a waveform propagating through the concrete, and time T30 corresponds to the time when it was first received.

The sound velocity V _R in the reinforcing bar and the sound velocity Vc in the concrete are calculated by the following equations.
V _R = L ₁₀ / T ₂₀ (7)
Vc = L ₁₀ / T ₃₀ (8)

Sound velocity Vc in the concrete in the present embodiment is 4300 m / s, the speed of sound _{V R} in a rebar was 5400 m / s.
In this embodiment, calculation of the time Ts shown in FIG. 4 is important. What is unknown in the equation (4) is the angle θ. Therefore, the change in time Ts with respect to the angle θ is shown in FIG. Here probe distance Lo is 300 mm, the depth _{d 0} of the rebar 30 mm, sound velocity Vc in a concrete 4300 m / s, the speed of sound _{V R} in a reinforcing bar is set to 5400 m / s.

As shown in FIG. 6, the time Ts until the ultrasonic wave transmitted from the transmission probe 12 is received by the reception probe 13 decreases as the angle θ increases. In the present embodiment, description will be made by adopting the propagation time when the angle θ is 45 degrees.
Further, as shown in FIG. 3, the ultrasonic wave propagates in the concrete and the reinforcing bar. On the other hand, as the inter-probe distance Lo increases, the propagation time of the ultrasonic wave in the concrete becomes relatively smaller than the propagation time of the ultrasonic wave inside the reinforcing bar. Therefore, for convenience of explanation, the propagation wave received by the reception probe 13 is hereinafter referred to as an actual reinforcing bar propagation wave.

(STEP3)
In the received waveform fo (t), a waveform fp (t) between time t = Ts and Te is extracted. The extracted pattern is shown in FIG. Here, the time Ts is calculated by Equation 4. Te is a constant value set to extract the entire actual reinforcing bar propagation waveform. The value depends on conditions such as the depth of the reinforcing bar, the diameter of the reinforcing bar, the type of reinforcing bar, and the surface roughness of the concrete. Accordingly, these conditions can be set and obtained in advance experimentally and experimentally.

(STEP4)
The spectrum S (f) of the extracted waveform fp (t) is calculated using FFT. The pattern is shown in FIG.
FIG. 8 shows a spectrum Sa (f) obtained by converting the waveform of FIG. 7 into the frequency domain using FFT.
The above is the basic processing content of the present invention. An example of a method for evaluating the converted spectrum will be described later.

<II waveform signal processing method>
[II-1] Ultrasonic wave propagation pattern in corroded rebar and influence on ultrasonic wave FIG. 9 shows an ultrasonic wave propagation pattern in corroded steel bar 4. FIG. 9B shows a pattern in which ultrasonic waves are scattered inside the corroded rebar 4. The incident ultrasonic waves are attenuated by these scattering phenomena. In particular, the attenuation of high frequency component waves becomes significant. A spectrum of the received waveform is obtained for the corroded reinforcing bar according to the flowchart of FIG. The pattern is shown in FIG. The spectrum Sa (f) corresponds to the received waveform when there is no reinforcing bar corrosion. The spectrum Sb (f) corresponds to the received waveform when the reinforcing bar is corroded. It can be seen that the spectrum Sb (f) is attenuated or severe at high frequencies.

[II-2] Spectrum Determination Method A method for calculating the above-described spectrum feature amount and determining the degree of corrosion of the reinforcing bars will be described.
FIG. 10 shows the pattern. First, the spectrum peak frequency Sm of the spectrum S (f) is calculated. For the spectra Sa (f) and Sb (f), spectrum peak frequencies Sma and Smb are calculated. Then, the normalized intensity Po of each spectrum peak frequency Sma, Smb is calculated.
The spectrum peak frequency Sma of Sa (f) is set to a normalized intensity 1 (1 = Sma / Sma). This is because Sa (f) corresponds to the case where there is no rebar corrosion. The normalized intensity Po for the spectral peak frequency Smb of Sb (f) is Psc (= Sma / Smb).

  Next, as shown in FIG. 10, the intensity corresponding to 1 / Z is calculated with respect to the normalized intensity (1, Psc). The normalized strength 1 is 1 / Z, and the normalized strength Psc is Psc / Z. In this embodiment, the description will be made assuming that Z = 10.

The spectral frequency Su for the intensity corresponding to 1/10 calculated above is calculated. As a result, the spectrum frequency Su in the spectrum Sa (f) is obtained as Sua, and the spectrum Sub is obtained in the spectrum Sb (f).
The above values indicate the degree of corrosion of reinforcing bars. Since the frequency Sub is much smaller than the frequency Sua, it is determined that the reinforcing bar corresponding to the spectrum of Sb (f) is corroded.

[II-3] Specific Measurement / Judgment Example FIG. 11A is a schematic diagram of an actual concrete structure surface 2. A region D is a portion where the crack 7 is observed directly above and around the reinforcing bar. A region where only one crack 7 can be observed just above the reinforcing bar is a region C, and a region where no crack 7 can be observed is a region B and A. Moreover, sectional drawing of the concrete structure in each area | region is shown to FIG.11 (b) to (e). FIG. 11B shows a cross-sectional view in the A region. The rebar 3 is in a healthy state that is not corroded. FIG. 11C shows a cross-sectional view in the B region. Although the rebar 3 is in a slightly corroded state and the crack 7 is generated from the rebar 3, the crack has not reached the surface 2 of the concrete structure. FIG. 11D shows a cross-sectional view in the C region. The rebar 3 is in a moderately corroded state, and the crack 7 reaches the concrete structure surface 2. Moreover, the corroded part 5 exists around a reinforcing bar.

  FIG. 11E shows a cross-sectional view of the D region. The rebar 3 is in a severely corroded state, and three cracks 7 reach the concrete structure surface 2. Moreover, the corrosion part 5 exists notably around a reinforcing bar. The healthy part described here indicates a state in which the reinforcing bar is not corroded, and the slight corrosion indicates a state in which the crack 7 is generated from the reinforcing bar but does not reach the concrete structure surface 2. Corrosion indicates a state in which the crack 7 generated from the reinforcing bar 3 reaches the concrete structure surface 2, and severe corrosion indicates that a large number of cracks 7 are generated from the reinforcing bar 3. Shows a state where the surface reaches the surface 2 of the concrete structure.

  FIG. 12 shows a method of actually measuring the concrete structure surface 2 shown in FIG. In consideration of the surface state, the measurement position m is divided into seven in this embodiment. Measurement position 1 in the D area, measurement position 2 in the C area, measurement positions 3 and 4 in the B area, and measurement positions 5, 6, and 7 in the A area. The inter-probe distance Lo is the same value at each measurement position.

  The spectral frequency Su is calculated in accordance with the above-mentioned item [II-2] at each measurement position. The calculated value is graphed as a measurement frequency m on the horizontal axis and a normalized spectral frequency Suo on the vertical axis. The result is shown in FIG. In this embodiment, the reference value used for normalization is the frequency Su corresponding to the actual waveform propagation wave Sa (f) without rebar corrosion, that is, the frequency Sua shown in FIG. Therefore, 1 on the vertical axis in FIG. 13 is a value obtained by dividing the frequency Sua by Sua, that is, 1.

  As shown in FIG. 13, it can be observed that the normalized spectral frequency Suo increases as the measurement position increases to 1, 2, and 3. At the measurement positions 5, 6, and 7 which are sound portions, the normalized spectral frequency Suo becomes 1 and becomes saturated. This state is called a stable state. It can be determined that the reinforcing bar is healthy at the measurement position in the stable state.

If the measurement position m is determined as shown in FIG. 12 and measurement is performed in order at the measurement position m and the graph of FIG. 13 is created, a region where the reinforcing bars are healthy can be inspected nondestructively. The values ε1 and ε2 shown on the vertical axis in FIG. 13 will be described. In the vertical axis of FIG. 13, it can be determined that the reinforcing bar is healthy at the measurement position where the vertical axis value is 1 or substantially coincides with 1. At the measurement position corresponding to the range of less than 1 to ε1, it can be determined that the reinforcing bar is slightly corroded. Further, on the vertical axis in FIG. 11, it can be determined that the reinforcing bar is moderately corroded at the measurement position corresponding to the range of ε1 to ε2, and further, at ε2 to 0, the reinforcing bar is severely corroded. . ε1 and ε2 are values found through numerous experiments and field measurements. ε1 is around 0.6 and ε2 is around 0.3.
As described above, according to the present invention, the corrosion state of the reinforcing bar 3 of the concrete structure 1 using ultrasonic waves is divided into four stages, for example, healthy, minor corrosion, moderate corrosion, and severe corrosion. Discrimination is possible.

[II-4] Application measurement example The inter-probe distance Lo is normally set to about 30 cm to 40 cm. On the other hand, as shown in FIG. 14, a method of setting the inter-probe distance Lo from 1 to 2 m is conceivable. In FIG. 14, it seems that a plurality of probes are arranged in a mesh shape, but in reality, a pair of transmission / reception probes is arranged for one reinforcing bar. Then, after the measurement is completed, the transmission / reception probe is moved to the adjacent reinforcing bar to perform the measurement. The above measurement is performed in the vertical direction and the horizontal direction in FIG. If the measurement waveform is analyzed by the method according to the present invention, it is possible to know the degree of corrosion of a wide range of reinforcing bars.

According to the above embodiment, the following effects can be obtained.
1. It is possible to non-destructively inspect corrosion of reinforcing steel in concrete structures.
2. Non-destructive inspection is possible by dividing the corrosion level of reinforcing bars into four stages, for example, healthy, minor corrosion, moderate corrosion, and severe corrosion.
3. If the crack growing from the reinforcing bar does not reach the surface of the concrete structure, it is impossible to visually observe the crack, but the corrosion of the reinforcing bar can be inspected nondestructively by using this method.
4). When the crack growing from the reinforcing bar does not reach the surface of the concrete structure, it is impossible to observe the crack visually. For this reason, it has been excluded from repair work in the past. For this reason, concrete peeling and cracking occurred again one or two years after the repair work was carried out, and it was forced to carry out the repair work again. As a result, the maintenance cost was enormous. If the present invention is used, even if cracks growing from the reinforcing bar do not reach the surface of the concrete structure, the corrosion degree of the reinforcing bar can be inspected nondestructively, and a truly appropriate repair range can be selected and repair work can be executed. Therefore, the maintenance cost can be greatly reduced.
5. In the past, it was usual to repair after the concrete on the surface of the concrete structure peeled off. The repair range was such that only the peeled portion or a little around the peeled portion was included. However, even if the concrete does not peel off, the corrosion of the reinforcing bars is progressing, and the proof stress of the concrete structure as a whole decreases. If this strength is significantly reduced, various effects will occur, such as the collapse of roads, the inclination of ground buildings, etc. due to partial damage of concrete structures and partial damage of underground structures. There is a possibility of becoming a social problem. By using the present invention, it is possible to non-destructively inspect the degree of corrosion of reinforcing bars even if the concrete is not peeled off. If the concrete structure is regularly inspected and repaired using this method, the strength of the entire concrete structure can be significantly maintained as compared with the conventional case.
6). The conventional repair methods are large-scale, such as excavating concrete to a depth greater than the depth of the reinforcing bar and placing a new reinforcing bar, and the cost is also significant. If the present invention is used, the degree of corrosion of the reinforcing bars can be measured non-destructively, so that an appropriate repair method according to the degree of corrosion of the reinforcing bars can be selected, and the repair cost can be reduced.
7). Cracks also occur when a strong stress is applied to a concrete structure due to an earthquake or construction failure. In this case, cracks often occur from the reinforcing bars. Although the reinforcing bars are healthy, cracks are visually observed on the surface of the concrete structure. Since cracks have occurred, there is a high possibility that the reinforcing bars will corrode after several years or decades, but it is a simple repair method. A method, for example a water stop treatment of the concrete surface, is sufficient. However, since corrosion of reinforcing bars could not be detected in the past, full-scale repair has been performed even in the above case. If the present invention is used, it can be measured non-destructively that the reinforcing bars are not corroded even if cracks occur, so that a simple repair method can be selected and the repair / maintenance cost is greatly reduced.

It is a flowchart of a basic process in a present Example until a waveform collection and the spectrum of the extracted waveform are calculated. It is a layout view of a transmission probe and a reception probe, (a) is a side view, (b) is a top view. It is a conceptual diagram which shows the propagation path figure of an ultrasonic wave. The received waveform is f0 (t). It is a schematic diagram of sound speed measurement. In (a), the probe at the time of sound velocity measurement is ceaseless. (B) is a reinforcing bar propagation waveform. (C) is a concrete propagation waveform. It is a graph which shows the change of propagation time with respect to angle theta. It is a figure which shows the extracted actual reinforcing bar propagation waveform fp (t). It is a spectrum figure of a real reinforcing bar propagation waveform fp (t). It is a conceptual diagram which shows the measurement schematic diagram in the corroded reinforcing bar, and the pattern of scattering in the reinforcing bar. It is a schematic diagram which calculates | requires frequency Sua and Sub. It is a schematic diagram which shows the corrosion degree of the reinforcing bar vicinity which performs a measurement. It is a schematic diagram which shows the measurement position m. The normalized spectrum state at each measurement position m is a graph showing nest Suo. It is a conceptual diagram which shows the example of applied measurement. It is a conceptual diagram which shows the pattern of concrete peeling by rebar corrosion. It is a conceptual diagram which shows the measurement pattern by a natural potential method. It is a measurement block diagram of ultrasonic measurement.

Explanation of symbols

1: Concrete structure 2: Concrete structure surface 3: Reinforcing bar 4: Corroded reinforcing bar 5: Corroded part 6: Peeling of concrete 7: Crack 8: Concrete specimen 9: Natural potential measuring instrument 10: Electrode A
11: Electrode B
12: Transmitting probe 13: Reception probe 14: Voltage generator 15: Receiver 16: Piezoelectric element 17: Contact medium 18: Control unit 19: Calculation unit 20: Display unit 21: Ultrasound 22: Rebar propagation wave 23: Concrete propagation wave 24: Super wave propagation path 25: Vertical line 26: Angle θ
27: Real rebar propagation wave

Claims (4)

A step of placing the transmitting probe and the receiving probe at a distance L ₀ on the reinforcing bar in the reinforced concrete;
Transmitting ultrasonic waves from the transmission probe and receiving a propagation waveform fo (t) at the reception probe;
Extracting a waveform fp (t) from time t = Ts to Te from the propagation waveform fo (t);
Obtaining a spectrum S (f) of a frequency function from the waveform fp (t);
Obtaining a frequency Su corresponding to a point that is 1 / Z of the normalized peak intensity of the spectrum peak frequency Sm of the spectrum S (f);
Have a, Ts is expressed by the following equation
Ts = 2 × (d ₀ / cos θ) × (1 / Vc) + (L ₀ −2d ₀ · tan θ) × (1 / V _R )
A nondestructive inspection method for the degree of corrosion of reinforcing bars in a concrete structure, characterized in that the degree of corrosion of reinforcing bars is quantitatively expressed by obtaining Sub / Sua .
Ts: time from transmission to reception Te: constant Z: any positive number greater than or equal to 1
Sua: Su for healthy rebar
Sub: Su in inspection object
θ: Transmission angle
Vc: speed of sound in concrete
V _R : Speed of sound in the reinforcing bar
d ₀ : Reinforcing bar depth, L ₀ : Distance between probes L _{0 /} d 0 ≧ 10 and non-destructive inspection method of about Corrosion in claim 1 concrete structure of wherein a is. 3. The nondestructive inspection method for the degree of corrosion of reinforcing bars in a concrete structure according to claim 1, wherein spectrum frequencies Su are obtained at a plurality of measurement positions m. The spectral frequency Su is graphed as the measurement position m on the horizontal axis and the normalized spectral frequency Suo (Sub / Sua) on the vertical axis,
The upper limit of the vertical axis is Sua / Sua = 1, and the numerical value of the frequency Suo
The non-destructive inspection method for the degree of corrosion of reinforcing bars in a concrete structure according to any one of claims 1 to 3, wherein the corrosion state of the reinforcing bars is determined in stages.

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