JP6678562B2 - AE detection method and device for reinforcing steel corrosion - Google Patents

Description

  The present invention relates to a method and an apparatus for detecting AE of reinforcing steel corrosion, which detects AE caused by corrosion of reinforcing steel inside concrete.

It is known that AE is generated due to corrosion of reinforcing steel inside concrete.
AE (Acoustic Emission) is an elastic wave generated in a process in which a solid undergoes deformation, destruction, or corrosion.

AE generated inside concrete has a frequency band of several tens of kHz to several hundreds of kHz, and can be detected by an AE sensor (for example, a piezoelectric element sensor) in principle.
Further, corrosion of reinforcing steel inside the concrete can be evaluated from the detected maximum amplitude value, count number, energy, signal duration time, rise time, and the like of the AE.

  For example, Patent Document 1 has already been proposed as a method for evaluating corrosion of reinforcing steel inside concrete using AE.

Patent Literature 1 discloses a method for quantitatively evaluating the amount of reinforcing steel corrosion of a concrete structure by AE, in which a piezoelectric element sensor is installed in a reinforced concrete structure to detect AE generated. The number of hits where the peak frequency f of the AE satisfies f ₁ ≦ f <f ₂ with respect to arbitrary frequencies f ₁ , f ₂ , f ₃ , f ₄ (f ₁ <f ₂ ≦ f ₃ <f ₄ ). The steel bar corrosion is evaluated based on the ratio of Hl to the number of hits Hh that satisfies f ₃ ≦ f <f ₄ .

JP 2011-133448 A

  Corrosion of reinforcing steel in concrete involves volumetric expansion of oxides during corrosion and generates compressive stress between the reinforcing steel and concrete, thereby generating AEs due to destruction and rubbing of oxidized corrosives. Furthermore, as the corrosion of the reinforcing bars progresses, cracks occur in the concrete, leading to more serious damage.

  However, AE due to corrosion of reinforcing steel inside the concrete is weak, and it is difficult to distinguish it from noise (noise due to wind or rain), especially in the initial state of corrosion of reinforcing steel.

  For example, in Patent Literature 1, the AE detected from the concrete surface determines that a remarkable change in frequency in each loading cycle cannot be confirmed, and exposes a part of a reinforcing bar of a concrete structure, and installs a piezoelectric element sensor in that part. doing.

  The present invention has been made to solve the above-mentioned problems. That is, an object of the present invention is to provide a method and an apparatus for detecting AE of reinforcing steel corrosion, which can accurately detect an AE generated by an AE source on the reinforcing steel from noise without exposing the reinforcing steel in the concrete. To provide.

According to the present invention, a sensor arrangement step of arranging a plurality of AE sensors at a sensor interval from each other on a surface of a concrete in which a reinforcing bar is arranged inside,
A delay time calculating step of calculating an individual delay time of an AE arriving at each AE sensor from an AE source on a reinforcing bar;
A reception waveform storing step of receiving the AE generated at the AE generation source by the plurality of AE sensors and storing a plurality of reception waveforms,
A waveform synthesizing step of generating a synthesized waveform by delaying and synthesizing the received waveforms based on the individual delay times, respectively.

Further, according to the present invention, a plurality of AE sensors arranged on a surface of a concrete in which a reinforcing bar is arranged inside with a sensor interval therebetween,
A delay time calculating device that calculates an individual delay time of an AE arriving at each AE sensor from an AE source on a reinforcing bar;
A reception waveform storage device configured to receive the AE generated at the AE generation source by the plurality of AE sensors and store a plurality of reception waveforms;
An AE detecting device for reinforcing steel corrosion, comprising: a waveform synthesizing device that delays the received waveforms based on the individual delay times to create a synthesized waveform.

  According to the present invention, based on the individual delay time of the AE arriving at each AE sensor from the AE source on the reinforcing bar, a composite waveform is created by delaying and synthesizing the received waveform. As a result of this synthesis, AEs (referred to as “received AE waveforms”) included in each received waveform are added synchronously based on the individual delay time, so that the synthesized waveform is emphasized (amplified) in proportion to the number of AE sensors. ) Received AE waveform. In addition, noise included in each received waveform is canceled out and attenuated because its generation position is different from that of the AE source.

  Therefore, according to the present invention, the AE generated at the AE source on the reinforcing bar can be identified from the noise without exposing the reinforcing bar in the concrete, and the initial state of corrosion of the reinforcing bar can be accurately detected.

FIG. 3 is an explanatory diagram of an AE detection method. It is a schematic diagram of the reception waveform of AE. 1 is an embodiment of an AE detection apparatus for reinforcing steel corrosion according to the present invention. 1 is an overall flowchart showing an embodiment of an AE detection method for reinforcing steel corrosion according to the present invention. It is a schematic diagram of a reception waveform and a synthetic waveform. It is a figure showing the case where a plurality of sensors are arranged on a straight line perpendicular to the length direction of a reinforcing bar. FIG. 4 is a diagram showing a simulation waveform of an AE used in the simulation. FIG. 7 is a diagram showing a combined waveform obtained by combining the pseudo AE generated on the upper surface (source) of the reinforcing bar of FIG. 6 by the method of the present invention. FIG. 7 is a diagram showing a synthesized waveform synthesized by the method of the present invention based on a pseudo AE generated at a different depth from the generation source of FIG. 6. FIG. 4 is a relationship diagram between a sound source depth and an amplitude value ratio. FIG. 4 is a diagram illustrating a relationship between a width direction position of a sound source and an amplitude value ratio. It is a figure which shows the example of arrangement | positioning of the sensor with respect to the support | pillar of a road bridge. FIG. 7 is a diagram illustrating a relationship between a sensor interval and an amplitude value ratio. 9 shows a composite waveform of noise coming from a long distance from a support when the distance between sensors satisfies Expression (3).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the drawings, common parts are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is an explanatory diagram of an AE detection method.
In this figure, 1 is a concrete surface, 2 is an AE generation source of reinforcing bar B, and 4 is an AE sensor. This figure shows a two-dimensional cross section that passes through the AE source 2 and is orthogonal to the reinforcing bar B.

In this figure, the position of the surface 1 closest to the AE source 2 (directly above in the figure) is the origin O, one axis along the surface 1 is the X axis, and the axis orthogonal to the surface 1 is the Z axis.
The AE generation source 2 is located on the Z-axis at a depth d from the position of the reinforcing bar B, that is, the origin O. The AE sensor 4 is located on the X axis at a surface distance L from the origin O.

In this case, the propagation distance R from the AE generation source 2 to the receiving surface (the position of the surface 1) of the AE sensor 4 is geometrically obtained by Expression (1).
R ² = d ² + L ² (1)
Further, from the sound speed v of the AE 3, the individual delay time t from the occurrence of the AE 3 to the detection by the AE sensor 4 can be obtained by Expression (2).
t = R / v (2)
The sound speed v of the AE3 is a sound wave in the concrete, for example, about 4250 to about 5250 m / s.

The position of the reinforcing bar B in the concrete is usually known from drawings and the like. Further, even if it is not known, the position of the reinforcing bar B can be actually measured by a radar or the like. Further, the sound speed v in the concrete can be measured in advance. Further, the surface distance L of the AE sensor 4 from the origin O can be set freely.
Therefore, by setting the position of the AE source 2 on the reinforcing bar in advance, the individual delay time t can be calculated from the equations (1) and (2).

FIG. 2 is a schematic diagram of the AE reception waveform 5, in which the horizontal axis represents time and the vertical axis represents AE intensity.
In this figure, S is a threshold, T1 is a duration, T2 is a rise time, Hm is a maximum amplitude value, a black circle (●) is a count point, and a hatched area is energy.
As shown in this figure, the received waveform 5 includes noise 8 in addition to the waveform of the AE 3 (“received AE waveform 5a”). Therefore, as described above, when the AE3 is weak, it is difficult to distinguish the received AE waveform 5a from the noise 8.

FIG. 3 is an embodiment diagram of the AE detecting apparatus 10 for reinforcing steel corrosion according to the present invention.
In this figure, the AE detection device 10 has a plurality of AE sensors 12, a delay time calculation device 14, a received waveform storage device 16, a waveform synthesis device 18, and an evaluation device 20.

  The plurality of AE sensors 12 are, for example, piezoelectric element sensors, and are arranged at intervals on the concrete surface 1 in which the reinforcing bar B is arranged. Hereinafter, the AE sensor 12 will be simply referred to as “sensor 12” unless necessary.

FIG. 3 is a view of the surface 1 of the concrete as viewed from above (in a direction perpendicular to the surface 1). The surface position closest to the AE source 2 on the reinforcing bar is defined as the origin O, and axes orthogonal to each other along the surface 1. Are the X axis and the Y axis.
In this example, eleven sensors 12 are arranged on the X-axis with the sensor interval ΔL from the origin O centered on the origin O. The sensor interval ΔL may be constant or random.
Further, the plurality of sensors 12 are not limited to the X-axis, and if the surface distance L from the origin O is the same (on a circle centered on the origin O), as shown by a broken line in the drawing, the Y-axis Above, or any other position.

The delay time calculating device 14, the received waveform storage device 16, the waveform synthesizing device 18, and the evaluating device 20 are configured by, for example, one computer (PC) as a whole. This computer has an input / output device, an arithmetic device, and a storage device.
Note that a part of the delay time calculation device 14, the reception waveform storage device 16, the waveform synthesis device 18, and the evaluation device 20 may be configured by another device. The evaluation device 20 is not essential, and may be omitted.

  The delay time calculating device 14 calculates an individual delay time t of the AE 3 arriving at each sensor 12 from the AE source 2 on the reinforcing bar.

  When the position of the AE generation source 2 on the reinforcing bar is known or predetermined, the individual delay time t is calculated based on the known or actually measured position of the reinforcing bar B and the sound velocity v, using the above-described equations (1) and (2). Can be calculated in advance.

The reception waveform storage device 16 receives the AE 3 generated by the AE generation source 2 by the plurality of sensors 12 and stores a plurality of reception waveforms 5.
The waveform synthesizing device 18 creates a synthesized waveform 6 obtained by delaying and synthesizing the received waveform 5 based on the individual delay time t.
The evaluation device 20 evaluates the corrosion of the reinforcing steel inside the concrete from the maximum amplitude value, the count number, the energy, the signal continuation time, the rise time and the like of the created composite waveform 6.

In FIG. 3, when the position of the AE source 2 on the reinforcing bar is unknown, it is preferable that the AE detection device 10 further includes a position locating device 15. The position locating device 15, like the delay time calculating device 14, is configured by, for example, one computer (PC) as a whole.
The position locating device 15 locates the position of the AE source 2 from the detection time difference of the AEs 3 arriving at three or more AE sensors 12.
The delay time calculating device 14 calculates the individual delay time t based on the position of the located AE source 2, and the waveform synthesizing device 18 generates the synthesized waveform 6.

FIG. 4 is an overall flowchart showing an embodiment of the AE detection method for reinforcing steel corrosion according to the present invention.
In this figure, the AE detection method has steps S1 to S6.

  In the sensor arrangement step S1, a plurality of sensors 12 are arranged from the origin O at a sensor interval ΔL on the concrete surface 1 in which the reinforcing bar B is arranged.

This arrangement is not limited to the X-axis as shown in FIG. 3, and if the surface distance L from the origin O is the same (on a circle centered on the origin O), as shown by a broken line in the figure. Alternatively, the position may be on the Y axis or another position.
That is, the AE sensors 12 may be respectively arranged on a plurality of circles on the surface where the propagation distances R from the AE source 2 to the AE 3 are different from each other.

In the delay time calculation step S2, the individual delay time t of the AE 3 arriving at each AE sensor 12 from the AE source 2 on the reinforcing bar is calculated.
As described above, when the position of the AE source 2 on the reinforcing bar is known or predetermined, the position is calculated in advance from the above-described equations (1) and (2). In this case, step S2 is performed prior to step S3.

When the position of the AE source 2 on the reinforcing bar is unknown, a position locating step S6 is provided, and the position of the AE source 2 is located from the detection time difference of the AEs 3 arriving at three or more AE sensors 12. In this case, the individual delay time t is calculated in step S2 based on the located position of the AE generation source 2, and the composite waveform 6 is created in step S3.
Step S6 may be omitted.

  In the received waveform storage step S3, the AEs 3 generated by the AE generation source 2 are received by the plurality of sensors 12 and the plurality of received waveforms 5 are stored.

FIG. 5 is a schematic diagram of the reception waveform 5 and the composite waveform 6. FIG. 5A is a schematic diagram of two reception waveforms 5, each including the waveform of the AE 3 (reception AE waveform 5 a) and noise 8.
The two reception AE waveforms 5a are obtained by detecting the same reception waveform 5 generated by a single AE generation source 2. Therefore, the two received AE waveforms 5a have the same waveform, although the delay time ta between them is different.
On the other hand, the noises 8 included in the two received waveforms 5 are generated from various positions and have different delay times to reach the AE sensors 12, so that the waveforms of the respective noises 8a to 8d are different. .

  In the waveform synthesizing step S4, a synthesized waveform 6 is created by delaying and synthesizing the received waveform 5 based on the individual delay time t.

  By combining the two received waveforms 5 in FIG. 5A based on the delay time ta between the two, the received AE waveforms 5a having the same waveform are added and emphasized (amplified). In addition, since the waveforms of the noises 8a to 8c are different due to the combination, the noises are canceled and attenuated.

Therefore, as shown in FIG. 5B, the composite waveform 6 includes the reception waveform (reception AE waveform 5a) of the AE 3 emphasized (amplified) in proportion to the number of sensors 12 (for example, five). Become.
In this example, for the sake of explanation, the occurrence time of the received AE waveform 5a and the noise 8 are different, but the same applies to the case where the occurrence times overlap.

In the evaluation step S5, the corrosion of the reinforcing steel inside the concrete is evaluated from the maximum amplitude value, the count number, the energy, the signal continuation time, the rise time and the like of the created composite waveform 6.
This step S5 is preferably performed using the evaluation device 20, but may be performed artificially without using this.

  Hereinafter, effects of the present invention will be described based on simulation results.

FIG. 6 is a diagram illustrating a case where a plurality of sensors 12 are arranged on a straight line orthogonal to the length direction of the reinforcing bar B.
The AE 3 generated by the AE generation source 2 on the reinforcing steel in the concrete reaches the plurality of sensors 12 linearly as shown in this figure, and at this time, corresponds to the difference in the propagation distance R of the AE 3 (ie, sound wave). A time difference is created by each sensor 12.

  With the depth d (cover depth) of the AE source 2 on the reinforcing bar set to 70 mm, a simulation was performed in which 11 sensors 12 were arranged at a sensor interval ΔL (50 mm) in a direction perpendicular to the reinforcing bar B.

  FIG. 7 is a diagram illustrating a simulation waveform of AE3 (hereinafter, referred to as “pseudo AE7”) used in the simulation. The pseudo AE 7 has a wavelength of 32 mm and a maximum amplitude value Hm of about 1.0.

FIG. 8 is a diagram showing a synthetic waveform 6 obtained by synthesizing the pseudo AE 7 generated on the upper surface (the AE generation source 2) of the reinforcing bar B in FIG. 6 by the method of the present invention. In this simulation, the noise 8 is not assumed, and it is assumed that the pseudo AE 7 (the AE 3 generated by the AE source 2) reaches each sensor 12 without attenuating.
In this figure, the maximum amplitude value Hm of the composite waveform 6 is amplified to about 11. That is, when the pseudo AE 7 is generated by the AE generation source 2 set in advance, it is understood that the composite waveform 6 includes the reception AE waveform 5a emphasized (amplified) in proportion to the number of the sensors 12. .

FIG. 9 is a diagram showing a synthesized waveform 6 synthesized by the method of the present invention based on the pseudo AE 7 generated at a different depth from the AE source 2 of FIG. That is, the pseudo AE 7 in this case corresponds to the noise 8 generated at a position (200 mm) deeper than the AE source 2.
In this figure, the maximum amplitude value Hm of the composite waveform 6 is attenuated to about 2. That is, when the pseudo AE 7 is generated at a different depth from the preset AE source 2, even if the plurality of reception waveforms 5 have the same waveform, the delay time is different from the AE source 2, so the phase is different. In contrast, it can be seen that the plurality of received waveforms 5 cancel and attenuate due to the combination.

FIG. 10 is a relationship diagram between the depth of the sound source and the amplitude value ratio, and shows a change in the maximum amplitude value Hm depending on the depth.
In this figure, point A is a case where the pseudo AE 7 is generated at a preset depth d (= 70 mm) of the AE generation source 2, and the other is a case where the pseudo AE 7 is generated at a different depth. The width direction position X is the same (X = 0 in FIG. 3).
The horizontal axis in the figure is the depth at which the pseudo AE 7 occurs, and the vertical axis is the ratio of the maximum amplitude value Hm to the point A.

  In this figure, the amplitude value ratio is maximum at the point A, and sharply decreases at other depths. That is, even when the AE 3 (or the noise 8) of the same level is generated from a depth different from the depth d of the AE generation source 2 set in advance, the plurality of reception waveforms 5 are canceled by each other and attenuated. Accordingly, it can be seen that only the received AE waveform 5a generated at the preset depth d (= 70 mm) of the AE source 2 can be emphasized.

FIG. 11 is a relationship diagram between the width direction position of the sound source and the amplitude value ratio, and shows how the maximum amplitude value Hm changes when the sound source position is shifted in the width direction.
In this figure, point A is a case where a pseudo AE7 occurs at a preset width direction position X (X = 0 in FIG. 3), and the other is a case where a pseudo AE7 occurs at a different width direction position X. The depth at which the pseudo AE 7 occurs is the same (d = 70 mm).
The horizontal axis in the figure is the width direction position X where the pseudo AE 7 occurs, and the vertical axis is the ratio of the maximum amplitude value Hm to the point A.

  In this figure, the amplitude value ratio is maximum at point A, and sharply decreases at other width direction positions X. That is, even when the AE 3 (or the noise 8) of the same level is generated from the position X in the width direction different from the AE generation source 2 set in advance, the plurality of received waveforms 5 are canceled and attenuated by the combination. Therefore, it can be seen that only the received AE waveform 5a generated at the preset width direction position X (= 0 mm) can be emphasized.

  According to the first embodiment described above, the received AE waveform 5a based on the AE source 2 set in advance is emphasized by the method according to the present invention, and the AE 3 (or noise 8) generated at a position where the depth or width direction is different is attenuated. Can be done. Therefore, according to the present invention, it was confirmed that the target received AE waveform 5a can be accurately detected by distinguishing it from the noise 8.

  FIG. 12 is a diagram illustrating an example of the arrangement of the sensor 12 with respect to the support 9 of the road bridge. In this figure, (A) shows an example in which a plurality of sensors 12 are arranged on a straight line in the axial direction and the orthogonal direction to the reinforcing bar B, respectively, and (B) shows a plurality of sensors 12 on a straight line in the orthogonal direction to the reinforcing bar B. This is an example in which 12 is arranged.

In a road bridge or the like, the columns 9 are elongated in the vertical direction (longitudinal direction), and the reinforcing bars B are often arranged in the longitudinal direction. In this case, for the noise 8 propagating in the concrete from above (or below), signal processing by the sensor 12 arranged in the width direction of the reinforcing bar B is not very effective, as shown in FIG. . This is because each sensor 12 detects the noise 8 almost simultaneously.
In this case, it is effective to arrange a plurality of sensors 12 along the reinforcing bar B.

In particular, as shown in FIG. 12A, it is preferable to arrange a plurality of sensors 12 on straight lines in the axial direction and the orthogonal direction to the reinforcing bar B, respectively.
In this case, in the plurality of sensors 12 in the axial direction and the orthogonal direction of the reinforcing bar B, the signal processing of the present invention is performed, and the AE3 is intended as an AE3 only for the case where both the axial and orthogonal synthetic waveforms 6 exceed the threshold value. The counting method is effective.

  In the second embodiment, the optimum sensor interval ΔL for discriminating the noise 8 propagating from a far distance (above or below) of the support 9 from the AE 3 generated by the AE source 2 set in advance will be discussed. The wavelength of AE3 (pseudo AE7) assumed here is 32 mm.

  First, the sensor 12 is arranged as shown in FIG. In this case, the noise 8 from a distance travels through the concrete and is simultaneously transmitted to the plurality of sensors 12 arranged.

FIG. 13 is a relationship diagram between the sensor interval ΔL and the amplitude value ratio. This figure shows a case where the sensor interval ΔL for identifying the noise 8 from an infinite distance is changed by the plurality of sensors 12 arranged on a straight line perpendicular to the reinforcing bar B when the depth d of the reinforcing bar B is 70 mm. Is a result of simulating the state of reduction of the noise 8 of FIG.
From this figure, it can be seen that the effect of reducing the noise 8 changes periodically depending on the sensor interval ΔL. From this, it can be said that the noise 8 is most effectively reduced when the propagation distance R to the reinforcing bar B changes by a half wavelength.

That is, in the sensor arrangement step S1, it is preferable to set the sensor interval ΔL such that the difference between the propagation distance R of the AE generation source 2 and the adjacent sensor 12 is a half wavelength of the sound wave in the concrete.
In this case, the following equation (3) holds.
R ² = d ² + L (n) ² = {d + (λ / 2) (2n−1)} ² (3)
Here, λ is the wavelength of the sound wave in the concrete, L (n) is the n-th surface distance from the center, and n is an integer.

  FIG. 14 shows a composite waveform 6 of the noise 8 coming from the far side of the support 9 when the sensor interval ΔL satisfies Expression (3). It is assumed that the noise 8 from a distance has no attenuation.

  In this figure, the maximum amplitude value Hm of the composite waveform 6 is attenuated to about 1. In this case, the detection waveforms of the sensors 12 of n (1) to n (5) and the sensors 12 of n (-1) to n (-5) in FIG. 6 have opposite phases. That is, even if the noise 8 coming from the far side of the support 9 is detected by a plurality of (11) sensors 12 and the received waveforms 5 have the same waveform without attenuating, the combined waveforms 6 cancel each other because the phases are different. It is attenuating together.

As described above, in the present invention, the reception waveform of the AE3 due to corrosion is emphasized and measured by synthesizing the waveform by providing the individual delay time t associated with the shortest time difference between each sensor position and the reinforcing bar B.
Therefore, when the AE3 is received by one sensor, the waveform of the other sensor 12 is synthesized in consideration of the predicted individual delay time t, so that the reception waveform of the AE3 associated with the corrosion using the reinforcing bar B as a sound source becomes The noise 8 is emphasized and can be easily distinguished from the noise 8 generated from other parts.

  According to the above-described embodiment of the present invention, based on the individual delay time t of the AE 3 arriving at each sensor 12 from the AE source 2 on the reinforcing bar, the received waveform 5 is delayed and synthesized to create a synthesized waveform 6. . By this combination, the reception AE waveform 5a included in each reception waveform is added synchronously based on the individual delay time t, so that the composite waveform 6 is emphasized (amplified) in proportion to the number of sensors 12 in the reception. AE waveform 5a is included. Further, the noise 8 included in each received waveform is canceled out and attenuated because its generation position is different from that of the AE generation source 2.

  Therefore, according to the present invention, the AE 3 generated by the AE source 2 on the reinforcing bar can be identified from the noise 8 without exposing the reinforcing bar B in the concrete, and the initial state of the reinforcing bar corrosion can be accurately detected.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the spirit of the present invention.

B rebar, d depth, Hm maximum amplitude value, L, L (n) surface distance,
ΔL sensor interval, O origin, R propagation distance, S threshold, t individual delay time,
ta delay time, T1 duration time, T2 rise time, v sound speed, λ wavelength,
1 concrete surface, 2 AE sources, 3 AE, 4 AE sensors,
5 reception waveform, 5a reception AE waveform, 6 composite waveform, 7 pseudo AE,
8 (8a-8c) noise, 9 props, 10 AE detector,
12 AE sensor (sensor), 14 delay time calculation device,
16 received waveform storage device, 18 waveform synthesis device, 20 evaluation device

Claims (8)

A sensor arrangement step of arranging a plurality of AE sensors at a sensor interval from each other on a surface of a concrete in which a reinforcing bar is arranged;
A delay time calculating step of calculating an individual delay time of an AE arriving at each AE sensor from an AE source on a reinforcing bar;
A reception waveform storing step of receiving the AE generated at the AE generation source by the plurality of AE sensors and storing a plurality of reception waveforms,
An AE detection method for reinforcing steel corrosion, comprising: a waveform synthesizing step of delaying the received waveforms based on the individual delay times to create a synthesized waveform.   The AE detection method for reinforcing bar corrosion according to claim 1, wherein in the sensor arranging step, a plurality of the AE sensors are arranged on a straight line in the axial direction or the orthogonal direction to the reinforcing bar of the AE source. In the sensor disposing step, a plurality of AE sensors are disposed on straight lines in the axial direction and the orthogonal direction with respect to the rebar of the AE source,
In the waveform synthesizing step, the synthesized waveform is created from each of the plurality of reception waveforms in the axial direction and the orthogonal direction,
The AE detection method for reinforcing steel corrosion according to claim 1, wherein when both of the combined waveforms in the axial direction and the orthogonal direction exceed a threshold, one or both of the combined waveforms are output.   2. The AE detection method for reinforcing steel corrosion according to claim 1, wherein in the sensor arranging step, the AE sensors are arranged on a plurality of circles on surfaces having different propagation distances from the AE source to the AE, respectively.   2. The sensor interval according to claim 1, wherein in the sensor disposing step, the sensor interval is set such that a difference in propagation distance from the AE generation source to an adjacent AE sensor is a half wavelength of a sound wave in the concrete. 3. AE detection method for steel corrosion.   The AE detection method for reinforcing steel corrosion according to claim 1, further comprising a position locating step of locating the position of the AE source based on a detection time difference of the AE arriving at three or more of the AE sensors. A plurality of AE sensors arranged on the surface of the concrete in which the reinforcing bar is arranged at a distance from each other,
A delay time calculating device that calculates an individual delay time of an AE arriving at each AE sensor from an AE source on a reinforcing bar;
A reception waveform storage device configured to receive the AE generated at the AE generation source by the plurality of AE sensors and store a plurality of reception waveforms;
An AE detecting device for reinforcing steel corrosion, comprising: a waveform synthesizing device that delays the received waveforms based on the individual delay times to create a synthesized waveform.   The AE detecting device for reinforcing steel corrosion according to claim 7, further comprising a position locating device for locating the position of the AE source based on a detection time difference of the AE arriving at three or more of the AE sensors.

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