JP6305860B2 - Nondestructive inspection method and nondestructive inspection device - Google Patents

Description

  The present invention relates to a nondestructive inspection method and a nondestructive inspection device for detecting the presence or absence of a broken portion of a reinforcing bar provided in a reinforced concrete structure such as a bridge, a building, or a concrete pole.

Conventionally, a nondestructive inspection method for detecting a fracture portion of a reinforcing bar provided in a concrete body is known.
For example, in the nondestructive inspection method described in Japanese Patent No. 3734822 (Patent Document 1), the permanent magnet is moved on the surface of the concrete along the longitudinal direction of the reinforcing bar to be inspected embedded in the concrete. Is used to magnetize the reinforcing bar, then measure the magnetic flux density leaking from the concrete surface, and calculate the differential value of the obtained measurement value to detect the presence or absence of breakage of the reinforcing bar.

  However, generally, a ferromagnetic body such as a large number of reinforcing bars and metal fittings having different positions and arrangement directions is embedded in the concrete body. For this reason, when the magnetic force of the reinforcing bar to be inspected is detected by the magnetic sensor outside the concrete body, the magnetism from reinforcing bars other than the reinforcing bar to be inspected is often detected at the same time. However, in the nondestructive inspection method described in Patent Document 1, since there is no means for removing the influence of magnetism emitted from other than the inspection target reinforcing bars, the detection of the fractured portion lacks accuracy. There is a fear.

  Japanese Patent Laid-Open No. 2013-130552 (Patent Document 2) magnetizes the inspection target rebar by moving the magnet on the surface of the concrete along the longitudinal direction of the inspection target rebar embedded in the concrete. Next, the magnet to be inspected is remagnetized by moving the magnet along the longitudinal direction of the inspected reinforcing bar at a position away from the magnetized position of the inspecting reinforcing bar, and then the surface of the concrete Describes a non-destructive inspection method for detecting the presence or absence of breakage of a rebar to be inspected by measuring the magnetic flux density leaking from the steel.

  According to such an inspection method, when the concrete cover on the inspection reinforcing bar is shallow, accurate fracture detection that occurs from the inspection target reinforcing bar due to the distance between the magnet and the inspection reinforcing bar being too close during magnetization. It is possible to reduce the magnetism that becomes an obstacle. However, it is not described that the influence of magnetism emitted from other than the inspection target reinforcing bars can be removed.

Japanese Patent No. 3734822 JP 2013-130552 A

As described above, the conventional non-destructive inspection method has a problem that the influence of magnetism generated from reinforcing bars other than the inspection target reinforcing bars cannot be removed, and has a problem in terms of detection accuracy of a fractured portion.
Therefore, the present invention reduces the influence of magnetism from ferromagnetic materials other than the inspection target rebar, and in particular, the installation quantity is generally large, and the influence of magnetism from the cross rebar provided substantially orthogonal to the inspection target rebar is remarkable. Non-destructive inspection method and non-destructive method that can detect the presence or absence of a rupture portion with high accuracy by utilizing the property of magnetic flux density change that appears characteristically when the rebar to be inspected has a rupture portion. The purpose is to provide an inspection method.

1st invention of this application magnetizes this inspection object reinforcing bar with a magnet from the outside of the concrete body in which inspection object reinforcement was embed | buried, and measures the magnetic flux density of the said concrete body outside with a magnetic sensor after that, The said inspection A non-destructive inspection method for detecting the presence or absence of a broken portion of the target reinforcing bar,
The magnetized surface of the magnet is placed close to the surface of the concrete body so that both magnetic poles of the magnet are along the longitudinal direction of the inspection object reinforcing bar, and then the magnet is moved along the longitudinal direction of the inspection object reinforcing bar. A first magnetizing step of removing the magnet after magnetizing the rebar to be inspected by
A first magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then the magnet is substantially the same as the first magnetizing step. A second magnetization step of moving the same trajectory in the opposite direction and re-magnetizing the rebar to be inspected, and then removing the magnet;
A second magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
A non-inspection magnetic flux removal step of canceling and removing the magnetic flux density from the non-inspection object by adding both of the magnetic flux densities measured in the first and second magnetic flux density measurement steps to obtain a sum of both magnetic flux densities; ,
It is a nondestructive inspection method characterized by including the fracture | rupture part detection process which detects the presence or absence of the fracture part of the said test | inspection reinforcing bar based on the sum of the said both magnetic flux density obtained by the non-inspection magnetic flux removal process.

  In order to arrange the magnetized surface of the magnet close to the surface of the concrete body when the reinforcing bar is magnetized in the first magnetizing step and the second magnetizing step of the first invention, the magnetized surface of the magnet is placed on the concrete body. It is only necessary to temporarily approach a predetermined position in the vicinity of the surface, and it is not always necessary to bring the magnetized surface of the magnet into direct contact with the surface of the concrete body, and it is not necessary to be stationary.

Here, the magnetized surface of the magnet refers to the one surface of the magnet that is closest to the concrete body when the reinforcing bar is magnetized. Such a magnetized surface is not limited to a single plane as long as both magnetic poles of the magnet can be aligned with the longitudinal direction of the reinforcing bar to be inspected.
In the first and second magnetizing steps, the magnet is moved along substantially the same track. In order to perform the work easily and accurately, for example, a guide rail is provided on the surface of the concrete body, or marking is performed. You may go.

  Next, in the first and second magnetic flux density measurement steps, in order to place the magnetic sensor close to the surface of the concrete body, the magnetic sensor is placed at a predetermined position near the surface of the concrete body as in the case of the magnet. It only needs to be brought close temporarily, and does not need to be brought into direct contact with the surface of the concrete body.

However, in order to obtain the magnetic flux density along the longitudinal direction of the inspection target reinforcing bar, it is necessary to measure the magnetic flux density up to the inspection range of the fracture portion of the inspection target reinforcing bar and, if necessary, the peripheral range.
For this purpose, the magnetic flux density may be measured while appropriately moving one or a plurality of magnetic sensors. For example, the magnetic sensor is moved near the surface of the concrete body along the longitudinal direction of the reinforcing bar to be inspected. Magnetic flux density can be measured. Alternatively, the magnetic sensor disposed on the surface of the concrete body is moved back and forth in a direction perpendicular to the longitudinal direction of the inspection target rebar while being close to the concrete body surface, and gradually shifted in the longitudinal direction of the inspection target rebar. Thus, the magnetic flux density of the inspection target reinforcing bar can be measured, and the magnetic flux density along the longitudinal direction of the inspection target reinforcing bar can be calculated from the measurement result.

  For example, when using a long magnetic sensor unit in which a large number of magnetic sensors are connected in a straight line, the magnetic sensor unit is placed on the surface of the concrete body along the longitudinal direction of the reinforcing bar to be inspected. The magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected can be measured only by placing them close to each other and without moving them thereafter.

Next, in the second invention of the present application, both the reinforcing bars are magnetized by magnets from the outside of the concrete body in which the reinforcing bars to be inspected and the crossing reinforcing bars intersecting with the reinforcing bars to be inspected are embedded, and then the concrete body is detected by a magnetic sensor. Is a non-destructive inspection method for detecting the presence or absence of a fracture portion of the inspection target reinforcing bar by measuring the magnetic flux density outside
The magnetized surface of the magnet is placed close to the surface of the concrete body so that both magnetic poles of the magnet are along the longitudinal direction of the inspection object reinforcing bar, and then the magnet is moved along the longitudinal direction of the inspection object reinforcing bar. A first magnetizing step of removing the magnet after magnetizing both the reinforcing bars by
In a predetermined position separated from the position where the magnet is arranged in the first magnetizing step by a distance D or more determined by a “distance D determination method” described later in the width direction of the inspection reinforcing bar, the magnetized surface of the magnet is By placing the magnet close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then moving the magnet along the longitudinal direction of the rebar to be inspected A first additional magnetization step of removing the magnet after magnetizing the rebars again;
A first magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then the magnet is substantially the same as the first magnetizing step. A second magnetizing step of moving the same track in the opposite direction and magnetizing the rebars again, and then removing the magnets;
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first additional magnetization step, and then the magnet is placed in the first additional magnetization step. And a second additional magnetization step of removing the magnet after moving the same orbit in the opposite direction and magnetizing the rebars again,
A second magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
By adding both of the magnetic flux densities measured in the first and second magnetic flux density measurement steps to obtain the sum of both magnetic flux densities, the magnetic flux density from the cross reinforcing bars and other non-inspected objects is canceled out. Inspection magnetic flux removal process,
It is a nondestructive inspection method characterized by including the fracture | rupture part detection process which detects the presence or absence of the fracture part of the said test | inspection reinforcing bar based on the sum of the said both magnetic flux density obtained by the non-inspection magnetic flux removal process.

The “distance D determination method” is as follows.
When the S-pole side direction in the straight line connecting the center portions of both magnetic poles of the magnet is the X direction, the magnetized surface of the magnet is parallel to the magnetized surface when facing downward, and the left side in the X direction The direction perpendicular to the Y direction is the Y direction, the direction perpendicular to the X direction and the Y direction, and the direction of the magnetized surface side of the magnet is the Z direction.
In such a case, the position separated from the magnetized surface of the magnet by 100 mm from the center position of the straight line connecting the central portions of the two magnetic poles of the magnet in the Z direction is defined as P1, and separated from the position P1 in the Y direction, A position where the X direction component of the magnetic flux density shows a value of about ¼ of the X direction component of the magnetic flux density at the position P1 is determined as P2, and the separation distance between the position P1 and the position P2 is determined as “distance D”.

Here, the position where the magnet is arranged in the first and second magnetizing steps and the position where the magnet is arranged in the first and second additional magnetizing steps need to be separated by “distance D” or more. The value of “distance D” is an eigenvalue determined for each magnet that differs depending on the shape and size of the magnet. Therefore, the value of “distance D” needs to be obtained by the “determination method of distance D” for each magnet.
In the first and second magnetizing steps and the first and second additional magnetizing steps, the magnet is moved by a substantially parallel track at a position separated by “distance D” or more, but the operation is easy and accurate. For example, a guide rail may be provided on the surface of the concrete body or marking may be performed.

Next, a third invention of the present application is the nondestructive inspection method according to the first or second invention, wherein each of the first and second magnetic flux density measuring steps is in a longitudinal direction of the reinforcing bar to be inspected. Measure the vertical component of the magnetic flux density along
In the non-inspection magnetic flux removal step, by adding both of the vertical components of the magnetic flux density measured in the first and second magnetic flux density measurement steps to obtain the sum of both magnetic flux densities, the crossed reinforcing bars and other non-inspection bars It is characterized in that the vertical component of the magnetic flux density from the inspection object is canceled out.

  Here, the vertical component of the magnetic flux density is a component in the direction perpendicular to the surface of the concrete body in the magnetic flux density.

  Next, a fourth invention of the present application is the nondestructive inspection method according to any one of the first to third inventions, wherein, in the breaking portion detection step, a differential value of a sum of the two magnetic flux densities or A differential value of an average value of both magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2 is calculated, and these differential values are compared with a predetermined threshold value. It is characterized by detecting the presence or absence.

  Similarly, a fifth invention of the present application is the nondestructive inspection method according to any one of the first to third inventions, wherein, in the fracture portion detection step, a differential approximation of the sum of the two magnetic flux densities or the A differential approximation value of an average value of both magnetic flux densities obtained by dividing the sum of both magnetic flux densities by 2 is calculated, and these differential approximation values are compared with a predetermined threshold value, and the fracture portion of the inspection reinforcing bar It is characterized by detecting the presence or absence of.

Next, the sixth invention of the present application is to magnetize the inspection target reinforcing bar with a magnet from the outside of the concrete body in which the inspection reinforcing steel bar is embedded, and then measure the magnetic flux density outside the concrete body with a magnetic sensor. , A nondestructive inspection device for detecting the presence or absence of a fracture portion of the inspection target rebar,
Both magnetic poles are arranged along the longitudinal direction of the inspected reinforcing bar so that the magnetized surface is arranged close to the surface of the concrete body and the relative position of both magnetic poles is not changed. A magnet that magnetizes the rebar to be inspected by moving substantially the same trajectory in the forward and reverse directions,
A magnetic sensor for detecting a detection signal based on the magnetic flux density by placing it close to the surface of the concrete body and moving it appropriately or without moving;
An arithmetic means for calculating a magnetic flux density along a longitudinal direction of the inspection reinforcing bar on the surface of the concrete body from a detection signal detected by the magnetic sensor;
Rupture determination means for detecting the presence or absence of a rupture portion of the rebar to be inspected based on the magnetic flux density calculated by the calculation means,
The magnetic sensor is based on a first detection signal based on a magnetic flux density generated when the magnet is moved in the forward direction by the track and a magnetic flux density generated when the magnet is moved in the reverse direction by the track. Detecting a second detection signal;
The calculation means calculates a magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected on the surface of the concrete body from the first and second detection signals, and further adds both of these magnetic flux densities. By canceling out the magnetic flux density from the non-inspected object,
The break determination means is a non-destructive inspection apparatus that detects the presence or absence of a broken portion of the inspection target reinforcing bar based on the sum of both magnetic flux densities.

Similarly, a seventh invention of the present application is the nondestructive inspection device according to the sixth invention, wherein the calculation means is configured to detect the first and second detection signals on the surface of the concrete body, respectively. By calculating the vertical component of the magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected and further adding both of the vertical components of the magnetic flux density to obtain the sum of both magnetic flux densities, the magnetic flux from the non-inspecting object is obtained. Cancel out the vertical component of density,
The rupture determining means detects the presence or absence of a rupture portion of the inspection target reinforcing bar based on the sum of the two magnetic flux densities.

Next, an eighth invention of the present application is the nondestructive inspection apparatus according to the sixth or seventh invention, wherein the calculation means further includes a differential value of the sum of the two magnetic flux densities or the two magnetic flux densities. The differential value of the average value of both magnetic flux densities obtained by dividing the sum of 2 by 2 is calculated,
The rupture determination means compares these differential values with a predetermined threshold value, and detects the presence or absence of a rupture portion of the inspection target reinforcing bar.

Similarly, a ninth invention of the present application is the nondestructive inspection apparatus according to the sixth or seventh invention, wherein the calculation means further includes a differential approximation of the sum of the magnetic flux densities or the magnetic flux densities. The differential approximation of the average value of both magnetic flux densities obtained by dividing the sum of 2 by 2,
The rupture determination means compares these differential approximation values with a threshold value provided in advance, and detects the presence or absence of a rupture portion of the inspection target reinforcing bar.

According to the nondestructive inspection method according to the first invention of the present application, by adding both of the magnetic flux densities measured in the first and second magnetic flux density measuring steps and obtaining the sum of both magnetic flux densities, the inspection target reinforcing bar Since the magnetic flux density from non-inspection objects other than the above can be canceled out, the influence can be eliminated or greatly reduced. As a result, it is possible to accurately determine the change state of the magnetic flux density of the magnetic flux generated from the inspection target reinforcing bar, and the presence / absence of the fracture portion can be detected with high accuracy.
The non-inspection object is mainly a ferromagnetic material such as a crossed reinforcing bar or a metal fitting other than the inspection object reinforcing bar embedded in the concrete body, and its shape, size, arrangement position, etc. are not particularly limited.

Further, according to the nondestructive inspection method of the second invention of the present application, the first additional magnetization process is performed after magnetizing the reinforcing bar to be inspected and the crossing reinforcing bar which is not the inspection object in the first magnetization process. Thereby, the magnetic flux density by the magnetism emitted from a crossing rebar can be made remarkably small among the magnetic flux density by the magnetism each emitted from the inspection object reinforcing bar and the crossing reinforcing bar magnetized by the 1st magnetization process.
Similarly, after magnetizing the inspected reinforcing bar and the crossed reinforcing bar in the second magnetizing step, the second additional magnetizing step is performed, so that the inspected reinforcing bar and the crossed reinforcing bar magnetized in the second magnetizing step can be used. Of the magnetic flux density generated by the magnetism, the magnetic flux density generated by the cross rebar can be significantly reduced.
Therefore, coupled with the effect that the magnetic flux density from the non-inspection object other than the inspection target reinforcing bar in the first invention can be canceled out, it is possible to more accurately determine the change state of the magnetic flux density of the magnetic flux generated from the inspection target reinforcing bar. This makes it possible to detect the presence or absence of a broken portion with extremely high accuracy.

  Next, according to the nondestructive inspection method of the third invention of the present application, in the first and second magnetic flux density measurement steps, the magnetic flux density from the non-inspection object is determined by measuring the vertical component of the magnetic flux density. It can be captured more clearly. Therefore, it is possible not only to improve the detection accuracy of the presence / absence of the broken portion of the inspection target reinforcing bar, but also to detect the presence / absence and position of the non-inspection target with high accuracy.

According to the nondestructive inspection method according to the fourth or fifth invention of the present application, based on the sum of the two magnetic flux densities or the average value of the two magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2. For example, when these are represented in a graph, the peak value is increased by emphasizing the rapid change in magnetic flux density caused by the presence of a fracture in the reinforcing bar. Since it appears, it is possible to more accurately detect the presence or absence of a fractured portion by comparing this peak value with a predetermined threshold value.
In particular, as in the third aspect of the invention, the “vertical component” of the magnetic flux density is measured, and a differential value or differential approximation value based on the sum or average value of the “vertical component” of the two magnetic flux densities is calculated and displayed on the graph. In this case, since only one peak value due to the broken portion of the reinforcing bar appears, it is difficult for erroneous recognition to occur in the comparison between the peak value and the threshold value, so that the detection accuracy of the broken portion can be further increased. .

Note that calculating a differential value or a differential approximation value based on the sum or average value of both magnetic flux densities is nothing but obtaining a difference between the two magnetic flux densities at two adjacent locations. It is significant that the magnetic flux density caused by the environmental magnetic field such as geomagnetism contained in the magnetic flux density measured by the first and second magnetic flux density measurement steps is subtracted and removed.
Therefore, by calculating the differential value or the differential approximation value, it is very convenient because it is not necessary to consider the magnetic flux density of the environmental magnetic field when providing a threshold value for comparison with these values. It can contribute to improvement of detection accuracy.

  Furthermore, according to the nondestructive inspection apparatus according to the sixth to ninth inventions of the present application, the nondestructive inspection method according to the first to fifth inventions can be carried out efficiently and surely, It is possible to accurately detect the presence or absence of a fractured portion.

It is explanatory drawing which shows the X direction cross section at the time of arrange | positioning a magnet on the surface of the concrete body by which the main reinforcement (reinforcement object inspection) and three crossing reinforcing bars which do not contain a fracture | rupture part are embed | buried. Explanation showing a cross section in the X direction when a magnet arranged substantially directly above the main reinforcing bar is moved in the X direction on the surface of the concrete body in which the main reinforcing bar and the three crossing reinforcing bars are not embedded. FIG. The X direction cross section at the time of moving the magnet arrange | positioned in the position substantially right above the main reinforcing bar in the -X direction on the surface of the concrete body in which the main reinforcing bar and the three crossing reinforcing bars not including the fracture portion are embedded is shown. It is explanatory drawing. It is a graph which shows the measurement result of the perpendicular | vertical component of the magnetic flux density on the surface of the concrete body by which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. Explanatory drawing which shows the X direction cross section at the time of moving the magnet arrange | positioned in the position substantially right above the main rebar on the surface of the concrete body in which the main rebar including the fracture part and three cross rebars are embedded. It is. It is explanatory drawing which shows the state of the magnetic flux on a magnetic field line and a concrete body surface when the main reinforcement containing a fracture | rupture part is magnetized. It is a graph which shows the measurement result of the perpendicular | vertical component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is explanatory drawing which shows the Y direction cross section at the time of moving the magnet arrange | positioned on the surface of the concrete body with which the main reinforcement and the crossing reinforcement were embedded substantially right above the main reinforcement in the X direction (direction toward this side). is there. A cross section in the Y direction when a magnet arranged at a position 250 mm apart in the Y direction from a position substantially directly above the main rebar is moved in the X direction on the surface of the concrete body in which the main reinforcing bar and the crossing reinforcing bar are embedded is shown. It is explanatory drawing. A cross section in the Y direction when a magnet arranged at a position 500 mm apart in the Y direction from a position substantially directly above the main rebar is moved in the X direction on the surface of the concrete body in which the main reinforcing bar and the crossing reinforcing bar are embedded is shown. It is explanatory drawing. A cross section in the Y direction when a magnet arranged at a position 750 mm apart in the Y direction from a position substantially directly above the main reinforcing bar on the surface of the concrete body in which the main reinforcing bar and the crossing reinforcing bar are embedded is shown in the Y direction. It is explanatory drawing. It is a graph which shows the measurement result of the perpendicular | vertical component of the magnetic flux density on the surface of the concrete body by which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. It is a graph which shows the differential value of the perpendicular | vertical component of the magnetic flux density on the surface of the concrete body in which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. It is a graph which shows the measurement result of the horizontal component of the magnetic flux density on the surface of the concrete body by which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. It is a graph which shows the differential value of the horizontal component of the magnetic flux density on the surface of the concrete body in which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. It is a graph which shows the measurement result of the perpendicular | vertical component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a graph which shows the differential value of the perpendicular component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a graph which shows the measurement result of the horizontal component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a graph which shows the differential value of the horizontal component of the magnetic flux density on the surface of the concrete body with which the main reinforcing bar containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is explanatory drawing which shows the main processes contained in the nondestructive inspection method of 1st Embodiment of this invention. It is a graph which shows the differential value of the perpendicular component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a graph which shows the measurement result of the horizontal component of the magnetic flux density on the surface of the concrete body by which the main reinforcing bar which does not include a fracture | rupture part, and seven crossing reinforcing bars were embed | buried. It is a graph which shows the measurement result of the horizontal component of the magnetic flux density on the surface of the concrete body with which the main reinforcement containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a graph which shows the differential value of the horizontal component of the magnetic flux density on the surface of the concrete body with which the main reinforcing bar containing a fracture | rupture part and seven crossing reinforcing bars were embed | buried. It is a Y direction section explanatory view showing an example of the 1st and 2nd additional magnetization processes. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing rebar (cover thickness 100mm) in the concrete body after the 1st magnetization. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing reinforcing bar (cover thickness 100mm) in the concrete body when additional magnetization is performed at a position separated by 100mm in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing reinforcing bar (cover thickness 100mm) in the concrete body when additional magnetization is performed at a position separated by 200mm in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing reinforcing bar (cover thickness 100mm) in the concrete body when additional magnetization is performed at a position 400mm apart in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing reinforcing bar (cover thickness of 100 mm) in the concrete body when additional magnetization is performed at a position separated by 600 mm in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing reinforcing bar (cover thickness 75mm) in the concrete body when additional magnetization is performed at a position separated by 200mm in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing rebar (cover thickness 75mm) in the concrete body when additional magnetization is performed at a position 400mm apart in the Y direction after the first magnetization. is there. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density along the longitudinal direction of the crossing rebar (cover thickness 75mm) in the concrete body when additional magnetization is performed at a position separated by 600mm in the Y direction after the first magnetization. is there. It is a side view which shows an example of a rectangular parallelepiped magnet. It is a top view of the said rectangular parallelepiped magnet. It is explanatory drawing which shows the relative positional relationship of a magnet and the position P1. It is explanatory drawing which shows the relative positional relationship of a magnet, the position P1, and the position P2. It is a graph which shows the magnetic flux density along the X direction straight line separated from the magnetization surface of the magnet by 100 mm in the Z direction, and the magnetic flux density along the parallel line separated from the X direction straight line by a predetermined distance in the Y direction. It is a perspective view which shows an example of a U-shaped magnet. It is explanatory drawing which shows the main processes contained in the nondestructive inspection method of 2nd Embodiment of this invention. It is a schematic block diagram which shows an example of a nondestructive inspection apparatus.

  Embodiments of a nondestructive inspection method and a nondestructive inspection apparatus according to the present invention will be described below.

A: Principle of nondestructive inspection method
Aa: Main rebar and cross rebar The principle of the nondestructive inspection method according to the present invention will be described.
FIG. 1 to FIG. 3 show a cross section in the X direction of a concrete body 1 in which main reinforcing bars (inspection reinforcing bars) 2 having no fracture portion are embedded, and FIG. 4 is concrete in which main reinforcing bars without a fracture portion are embedded. It is a graph which shows the measurement result of the perpendicular | vertical component of the magnetic flux density on the surface of a body. 5 and 6 show a cross section in the X direction of the concrete body 1 in which the main rebar 2 (2N, 2P) having the fracture portion H is embedded, and FIG. 7 shows the main rebar having the fracture portion embedded therein. It is a graph which shows the measurement result of the perpendicular component of the magnetic flux density in the surface of the done concrete body.
In these figures, a main rebar 2 as an inspection object and a cross rebar 3 as a non-inspection object arranged substantially orthogonal to the main rebar 2 are embedded in the concrete body 1.

  Here, the reinforcing bar is not limited to a round steel having a round cross-sectional shape frequently used for a general reinforced concrete structure or a deformed steel bar having protrusions on its surface, but a rectangular cross-sectional shape, other polygonal steel, H It may be a shape steel. Moreover, the inside of the pipe used for water flow or ventilation may be a hollow steel pipe, and further, PC steel material such as PC steel rod, PC steel wire or PC steel twisted wire used for prestressed concrete construction method, or these inside It may be a sheath tube used through a PC steel material in the sheath tube.

Ab: When the main reinforcing bar has no fracture
A-b-1: The case where there is no fracture portion in the magnetized main rebar 2 of the rebar by the magnet will be described.
As shown in FIG. 1, the magnet 5 is placed on the surface 1 </ b> A of the concrete body 1 so that both magnetic poles are along the longitudinal direction of the main rebar 2, and the N pole is on the left side of the figure and the S pole is on the right side of the figure. If the magnetized surfaces 5A are arranged close to each other, the main rebar 2 is magnetized to the S pole on the left side of the figure and to the N pole on the right side of the figure due to the influence of the magnetic force lines 51 from the magnet 5, so Produces a magnetic flux 2A oriented in the X direction.
Further, the portion near the magnet 5 of the cross rebar 3L on the left side of the figure is magnetized to the south pole by the influence of the magnetic field lines 51, so that a magnetic flux 3LA directed in the Z direction is generated on the concrete body surface 1A. Since the portion of the reinforcing bar 3R close to the magnet 5 is magnetized to the N pole, a magnetic flux 3RA directed in the -Z direction is generated on the concrete body 1A.

Here, the position where the magnet 5 is arranged is preferably a position where the separation distance between the magnetized surface 5A of the magnet 5 and the main rebar 2 is the shortest in order to sufficiently magnetize the main rebar 2 to be inspected. In such an example, the magnet 5 is positioned just above the main rebar 2 on the surface 1A of the concrete body 1 (that is, the position of the magnet 5 in the Y direction is the same as the position of the main rebar 2 in the Y direction). It is preferable to arrange in.
However, if the distance between the magnet 5 and the main reinforcing bar 2 is too short, extra magnetism that hinders inspection may occur. If there is such a fear, the magnet 5 is slightly above the concrete body surface 1A. What is necessary is just to arrange | position in the separated position.
Further, the orientations of the two magnetic poles of the magnet 5 to be arranged may be the S pole on the left side and the N pole on the right side, contrary to the present embodiment.

  The magnet 5 in the present embodiment is a rectangular parallelepiped (100 mm in length, 100 mm in width, 60 mm in height) made of a rare earth metal such as Nd, but is not limited to this, for example, an electromagnet instead of a permanent magnet. The shape is not limited to a rectangular parallelepiped, and may be a U shape or a U shape. Further, the magnet 5 may be in a bare state as it is, but is housed in a case having a function for facilitating movement while being close to the surface of the concrete body, or is unitized by combining a plurality of magnets. There may be.

A-b-2: the first magnetized and second magnetized Next, as shown in FIGS. 2 and 8, a magnet 5 which is arranged substantially directly above the main reinforcement 2 on the concrete surface 1A, the main reinforcing bars 2 is moved to the X direction side along the longitudinal direction of “2” to perform “first magnetization” (hereinafter, the movement of the main rebar 2 in the X direction side along the longitudinal direction is referred to as “forward movement”). Also called.)
FIGS. 2 and 8 both show an implementation state of “first magnetization”, and FIG. 2 shows a cross section in the X direction, which is the longitudinal direction of the main rebar 2 of the concrete body 1. FIG. 8 is a cross section in the Y direction that is the width direction of the main reinforcing bar 2 of the concrete body 1, and the magnet 5 has its S pole on the near side in the figure and the N pole on the far side in the figure, The state moved toward (the direction from the back side to the near side in FIG. 3) is shown.
At this time, the main reinforcing bar 2 is magnetized, and a magnetic flux 2A in the X direction is generated therein. Further, a portion of the crossing reinforcing bar 3 that is located immediately below the trajectory to which the magnet 5 has moved is magnetized to the S pole under the influence of the N pole of the magnet 5 that has finally passed through the vicinity thereof. Therefore, the magnetic flux density is relatively large on the concrete body surface 1A above the portion magnetized to the S pole of the crossed rebar 3 (the portion of the crossed rebar 3 positioned directly above the main rebar 2). The magnetic flux 3A (3A1) is generated.

2 and 8, in order to facilitate understanding of the present invention, the magnetic flux 3A (3A1) and the crossing reinforcing bar 3 are shown to overlap each other, but precisely, the magnetic flux 3A (3A1) is, for example, as shown in FIG. Is the magnetic flux in the Z direction generated on the concrete body surface 1A.
Similarly, in FIGS. 3, 5, 9 to 11, and 40, the magnetic flux 3 </ b> A and the magnetic flux 3 </ b> A <b> 1 to magnetic flux 3 </ b> A <b> 4 that are represented so as to overlap with the cross rebar 3 are precisely Magnetic flux generated on the body surface 1A.
In addition, the direction of the arrow showing each magnetic flux has shown the direction of each magnetic flux.

  Here, the trajectory for moving the magnet 5 does not necessarily have to be directly above the main rebar 2. Similarly, the description “along the longitudinal direction of the reinforcing bar” does not necessarily mean that it should always be along the reinforcing bar. However, in order to sufficiently magnetize the main rebar 2 of the inspection object, it is desirable that the moving trajectory has the shortest separation distance between the magnet 5 and the main rebar 2. It is desirable to move the magnetized surface 5A of the magnet 5 close to the concrete body surface 1A and move it directly above the main rebar 2 along its longitudinal direction.

  Next, as shown in FIG. 3, when “second magnetization” is performed by moving the magnet 5 in the reverse direction (−X direction) along the same orbit as in FIG. 2 (hereinafter, the main reinforcing bar 2). The movement in the −X direction along the longitudinal direction of the wire is also referred to as “movement in the reverse direction.”) The direction of the magnetic flux 2A generated inside the main reinforcing bar 2 is the X direction as in FIG. On the other hand, the direction of the magnetic flux 3A generated from the crossed reinforcing bar 3 is -Z direction (surface direction of the concrete 1) opposite to that shown in FIG. 2 due to the influence of the south pole of the magnet 5 that has finally passed through the vicinity. Facing.

Therefore, for example, in the concrete body 1 in which the main reinforcing bar 2 and the seven crossed reinforcing bars 3 having no fracture portion are embedded, as shown in FIG. 2, on the concrete body surface 1A along the longitudinal direction of the main reinforcing bar 2, N When the magnet 5 with the poles on the left side and the S poles on the right side is moved in the X direction to perform “first magnetization” and the rebar 2 and the crossed rebar 3 are magnetized, a concrete body is obtained using a magnetic sensor. When the vertical component (Z-direction or -Z-direction component) of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the surface 1A is measured, a curve S1 in FIG. 4 is obtained.
That is, the curve S1 represents a change according to the X-direction position of the vertical component of the magnetic flux density on the concrete body surface 1A along the longitudinal direction directly above the main reinforcing bar 2 after the “first magnetization”. .

Further, as shown in FIG. 3, the magnet 5 having the same relative position of both magnetic poles as in the case of FIG. 2 is moved in the −X direction along the same orbit as in FIG. When the main rebar 2 and the crossed rebar 3 are magnetized, the vertical component of the magnetic flux density along the longitudinal direction of the main rebar 2 on the concrete body surface 1A is measured using a magnetic sensor. A curve S2 is obtained.
That is, the curve S2 represents a change according to the X-direction position of the vertical component of the magnetic flux density on the concrete body surface 1A along the longitudinal direction directly above the main reinforcing bar 2 after the “second magnetization”. .
In addition, the horizontal axis of the graph of FIG. 4 represents the position (unit: mm) in the X direction on the concrete body surface 1A, and the vertical axis represents the vertical component (unit: μT) of the magnetic flux density at the position. ing.

Comparing the curves S1 and S2, it can be seen that the change in the magnetic flux density is different due to the influence of the direction of the magnetic flux 3A generated in the crossing reinforcing bar 3 due to the difference in the moving direction of the magnet 5. Specifically, since seven cross rebars 3 are buried one by one at each position of −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm, and 750 mm on the horizontal axis of FIG. At each position, a downward convex portion appears on the curve S1, and an upward convex portion appears on the curve S2.
In the example of FIG. 4, the main reinforcing bar 2 is a reinforcing bar (deformed bar) having a diameter of 16 mm, and the concrete cover thickness is 100 mm. Moreover, the crossing reinforcing bar 3 is a reinforcing bar (deformed bar) having a diameter of 13 mm embedded so as to be substantially orthogonal to the main reinforcing bar 2, and the concrete cover thickness is 62 mm.
Moreover, the concrete cover thickness is the shortest distance from the surface of the concrete body to the surface of the reinforced steel bar.

Ab-3: Elimination of magnetic flux density from non-inspected object Next, curve S3 in the graph of FIG. 4 is obtained by adding both magnetic flux densities (vertical components) shown in curves S1 and S2. An average value of both magnetic flux densities obtained by further dividing the sum of magnetic flux densities by 2 (number of measurements) is shown.

The curve S3 does not have a large convex portion as compared with the curves S1 and S2, and shows a gentle upward shape.
The reason is that the magnet 5 is moved in the X direction as shown in FIG. 2, and the magnetic flux density of the magnetic flux 3A in the Z direction generated from the crossing reinforcing bar 3 is moved, and the magnet 5 is moved in the -X direction as shown in FIG. Since the magnitude (absolute value) of the magnetic flux 3A in the −Z direction generated in step S is substantially the same, the sum of both magnetic flux densities shown in the curves S1 and S2 is added to This is because most of them are canceled out. That is, since the downward convex shape portion of the curve S1 and the upward convex shape portion of the curve S2 cancel each other, no large convex shape portion appears in the curve S3.

On the other hand, since the direction of the magnetic flux 2A inside the main rebar 2 is the same regardless of the moving direction of the magnet 5, the main rebar is the sum of both magnetic flux densities obtained by adding the magnetic flux densities of the curves S1 and S2. The magnetic flux density from 2 is about twice as large.
Therefore, the average value obtained by dividing the sum of the two magnetic flux densities by 2 represents an approximate value of the magnetic flux density from the main rebar 2 in which the influence of the magnetic flux density of the crossing reinforcing bars 3 is eliminated or greatly reduced. It can be said.

Ab-4: Main magnetization As described above, as shown in FIG. 2 and FIG. 8, the magnet 5 arranged on the concrete body surface 1 </ b> A substantially directly above the main rebar 2 is arranged in the longitudinal direction of the main rebar 2. By moving to the X direction side along the “first magnetization”, the magnetic flux 2 </ b> A in the X direction is generated inside the main rebar 2. The portion located at is magnetized into the south pole, and a magnetic flux 3A (3A1) in the Z direction having a relatively large magnetic flux density is generated on the concrete body surface 1A above it.

Further, as shown in FIG. 3, the main rebar 2 is obtained by performing the “second magnetization” by moving the magnet 5 in the reverse direction (−X direction) along the same orbit as in the case of FIG. 2 and FIG. 2, the magnetic flux 2 </ b> A in the X direction is generated as in FIGS. 2 and 8, whereas the magnetic flux 3 </ b> A in the −Z direction is generated from the cross reinforcing bar 3.
Hereinafter, the “first magnetization” and the “second magnetization” are collectively referred to as “main magnetization”.

Here, the curve B0 shown in the graph of FIG. 12 is the same as that in the example of FIGS. 2 and 8 in the concrete body 1 in which the main reinforcing bar 2 and the seven crossing reinforcing bars 3 without the fracture portion are embedded. After the main rebar 2 and the crossed rebar 3 are magnetized by performing “one magnetization” (main magnetization), the longitudinal direction directly above the main rebar 2 on the concrete body surface 1A using a magnetic sensor (not shown) The result of having measured the perpendicular component of the magnetic flux density along is shown.
That is, this curve B0 represents the change according to the position in the X direction of the vertical component of the magnetic flux density on the concrete body surface 1A along the longitudinal direction directly above the main reinforcing bar 2 after the first magnetization.
In addition, the horizontal axis of the graph of FIG. 12 represents the position (unit: mm) of the concrete body surface 1A in the X direction, and the vertical axis represents the vertical component (unit: μT) of the magnetic flux density at the position. Yes.

In FIG. 12, a total of seven cross reinforcing bars 3 are embedded at each position of −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm, and 750 mm on the horizontal axis of the graph. In the curve B0, a downward convex portion appears.
In the example of FIG. 12, the main reinforcing bar 2 is a reinforcing bar (deformed bar) having a diameter of 16 mm, and the concrete cover thickness is 150 mm. Moreover, the crossing reinforcing bar 3 is a reinforcing bar (deformed bar) with a diameter of 13 mm embedded so as to be substantially orthogonal to the main reinforcing bar 2, and the cover thickness of the concrete is 112 mm.

Ab-5: Reduction of magnetic flux density from crossed reinforcing bar by additional magnetization Next, as shown in FIG. 9, from the position directly above the main reinforcing bar 2 on the concrete body surface 1A, in the width direction of the main reinforcing bar 2. At a position 250 mm apart in a certain Y direction, the magnet 5 is arranged in the same direction as in the examples of FIGS. 2 and 8 and then moved in the X direction, which is the longitudinal direction of the main rebar 2. Perform “first additional magnetization”.
Then, as in the case of the “first magnetization” (main magnetization), the portion of the crossing rebar 3 that is located directly below the trajectory to which the magnet 5 has moved is the magnet 5 that has passed through its vicinity last. Since the magnet is magnetized to the S pole under the influence of the N pole, the Z-direction magnetic flux 3A2 having a relatively high magnetic flux density is placed on the concrete body surface 1A above the portion magnetized to the S pole of the crossed reinforcing bar 3. Will occur. At the same time, the magnetic flux density of the magnetic flux 3A1 generated from the portion of the crossed reinforcing bar 3 located immediately above the main reinforcing bar 2 by the first magnetization is significantly reduced.

Here, the reason why the magnetic flux density of the magnetic flux 3A1 is reduced is as follows.
In general, when a part of a long rebar is magnetized to the south pole, the rebar has the properties of a magnet, and the peripheral part of the rebar that is magnetized to the south pole will be magnetized to the opposite north pole. This produces the action. Therefore, when the first additional magnetization is performed, the portion of the crossed reinforcing bar 3 positioned immediately below the moving trajectory of the magnet 5 is magnetized to the south pole, and a magnetic flux 3A2 having a relatively large magnetic flux density is generated. In a portion that is magnetized to the S pole by the first magnetization of the crossed reinforcing bar 3 separated by 250 mm in the -Y direction (a portion that is located directly above the main reinforcing bar 2 in the crossed reinforcing bar 3), go to the opposite N pole It is considered that the magnetic flux density of the magnetic flux 3A1 generated from this portion is reduced because the magnetization of the S pole causes the magnetism of the south pole to be reduced.

  In the example of FIG. 9, when the vertical component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A is measured using a magnetic sensor (not shown), it is shown in the graph of FIG. Curve B25 is obtained. This curve B25 shows a gentle upward rising shape as a whole because the height difference of the downward convex shape portion is smaller than that of the curve B0.

  In the example of FIG. 10, “first magnetization” (main magnetization) is performed by the same method as in the examples of FIGS. 2 and 8, and “first additional magnetization” is performed by the same method as in the example of FIG. After magnetizing the main rebar 2 and the crossed rebar 3, the magnet 5 is placed at a position 500 mm away from the position directly above the main rebar 2 on the concrete body surface 1A in the Y direction, and the orientations of both magnetic poles are as shown in FIG. In the same manner as in the above, “second first additional magnetization” is performed by moving in the X direction which is the longitudinal direction of the main reinforcing bar 2.

In such a case, the magnetic flux 3A1 emitted from the portion of the crossed reinforcing bar 3 located immediately above the main reinforcing bar 2 is more than the magnetic flux 3A1 (see FIG. 8) emitted from the same portion after the first magnetization. The magnitude of the magnetic flux density is remarkably reduced, and the direction of the magnetic flux is the opposite -Z direction.
This is because, by performing the first additional magnetization of the second time, the portion of the crossed rebar 3 positioned directly below the moving trajectory of the magnet 5 is magnetized to the S pole, and a magnetic flux 3A3 having a relatively large magnetic flux density is generated. This is because, in the portion located just above the main reinforcing bar 2 in the crossed reinforcing bar 3 separated by 500 mm in the −Y direction, the magnetizing action to the opposite N pole is received. In the portion of the crossed reinforcing bar 3, the S pole magnetism having a small magnetic flux density remained after the first additional magnetization. However, the magnetizing action on the N pole by the second first additional magnetization is performed. By receiving, it is considered that the south pole magnetism disappeared and the north pole magnetism was reversed.

  In addition, in this invention, when comparing the magnitude | size of magnetic flux density, unless it refuses, the positive / negative direction of the magnetic flux shall not be considered. That is, the magnitude of the magnetic flux density is determined based on the absolute value in principle.

  In the example of FIG. 10, when the perpendicular component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A is measured using the magnetic sensor, a curve B50 shown in the graph of FIG. 12 is obtained. . The curve B50 is different from the curves B0 and B25 in the direction in which the convex portion appears, and is, for example, −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm on the horizontal axis of the graph of FIG. An upward convex portion appears at the position where the crossing reinforcing bars 3 are buried.

  In the example of FIG. 11, “first magnetization” (main magnetization) is performed by the same method as the examples of FIGS. 2 and 8, and “first additional magnetization” is performed by the same method as the examples of FIGS. And after performing the first additional magnetization of the second time and magnetizing the main reinforcing bar 2 and the crossed reinforcing bar 3, at a position spaced 750 mm in the Y direction from the position directly above the main reinforcing bar 2 on the concrete body surface 1A. In the case where the “first first additional magnetization” is performed by moving the magnet 5 in the X direction which is the longitudinal direction of the main rebar 2 with the direction of both magnetic poles being the same as in the example of FIG. is there.

In such a case, the magnetic flux 3A1 emitted from the portion of the crossed reinforcing bar 3 located immediately above the main reinforcing bar 2 is more than the magnetic flux 3A1 (see FIG. 8) emitted from the same portion after the first magnetization. The magnitude of the magnetic flux density is remarkably reduced, and the direction of the magnetic flux is the opposite -Z direction.
This is because by performing the first additional magnetization for the third time, the portion of the crossed reinforcing bar 3 located immediately below the moving trajectory of the magnet 5 is magnetized to the S pole, and the magnetic flux 3A4 in the Z direction having a relatively large magnetic flux density is generated. This is because the portion of the crossed reinforcing bar 3 located just above the main reinforcing bar 2 and separated by 750 mm in the −Y direction receives the magnetizing action to the opposite N pole.

  Furthermore, although the N pole magnetism having a small magnetic flux density remains after the second first additional magnetization in the portion directly above the main reinforcing bar 2 in the crossed reinforcing bar 3 (see FIG. 10). After the third first additional magnetization, the magnetic flux density is further reduced. This is because the third first additional magnetization is performed at a position further 250 mm apart in the Y direction than the second first additional magnetization, and therefore, the N pole with respect to the portion directly above the main reinforcing bar 2 in the crossing reinforcing bar 3 This is thought to be due to the decay of the magnetizing force on the.

  In the example of FIG. 11, when the perpendicular component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A is measured using the magnetic sensor, a curve B75 shown in the graph of FIG. 12 is obtained. . The curve B75 has the same appearance direction as the curve B50, but the height difference is smaller, and the curve B75 shows a generally gentle upward shape.

  The effect that the magnetic flux density from the crossed reinforcing bars 3 generated by the “first magnetization” (main magnetization) can be reduced by the “first additional magnetization” has the effect of “second magnetization” (main magnetization). This also occurs in the relationship between the magnetism) and “second additional magnetization”. That is, the magnetic flux density from the crossed reinforcing bars 3 generated by the “second magnetization” can be reduced by the “second additional magnetization”.

Ac: When there is a fracture in the main reinforcing bar
A-c-1: the first magnetizing Next, the case where there is a break portion in the main reinforcing bar 2.
FIG. 5 shows a cross section in the X direction of the concrete body 1 when the main reinforcing bar 2 has a fracture H.

First, as shown in FIG. 5, on the concrete body surface 1A along the longitudinal direction of the main reinforcement 2 (2N and 2P), the magnet 5 with the N pole on the left side and the S pole on the right side of the main reinforcement 2N After being arranged at a position almost directly above, it is moved in the X direction to perform “first magnetization”, and the main reinforcing bars 2N and 2P and the crossing reinforcing bar 3 are magnetized. Then, portions other than the rupture portion H of the main reinforcing bar 2 are magnetized, but the rupture portion H is not magnetized, and the main rebar 2N located on the negative side in the X direction with the rupture portion H as the origin position has X A magnetic flux 2AN in the direction is generated, and a magnetic flux 2AP in the X direction is generated in the main reinforcing bar 2P located on the positive side in the X direction.
Further, a portion of the crossing reinforcing bar 3 that is located immediately below the trajectory to which the magnet 5 has moved is magnetized to the S pole under the influence of the N pole of the magnet 5 that has finally passed through the vicinity thereof. Therefore, a magnetic flux 3A in the Z direction is generated on the concrete body surface 1A above the portion magnetized to the south pole of the crossed rebar 3 (the portion of the crossed rebar 3 positioned immediately above the main rebar 2).

  In FIG. 5, in order to facilitate understanding of the present invention, the magnetic flux 3A and the crossing reinforcing bar 3 are shown to overlap each other. However, the magnetic flux 3A is precisely the magnetic flux in the Z direction generated on the concrete body surface 1A. .

FIG. 6 shows the state of the lines of magnetic force generated from the main reinforcing bars 2N and 2P after the first magnetization. The magnetic lines of force 61 are generated from the main reinforcing bar 2N, and the magnetic lines of force 62 are generated from the main reinforcing bar 2P. In this case, a magnetic flux 6N1 in the Z direction is generated on the concrete body surface 1A above the left end of the main reinforcing bar 2N, while a magnetic flux 6N2 opposite to 6N1 is generated above the right end of the main reinforcing bar 2N. Further, a magnetic flux 6P1 in the Z direction is generated above the left end of the main reinforcing bar 2P, while a magnetic flux 6P2 opposite to 6P1 is generated above the right end of the main reinforcing bar 2P.
Therefore, the vertical component of the magnetic flux density on the concrete body surface 1A above the main reinforcing bar 2N is affected by the magnetic flux in the Z direction such as 6N1 near the end of the moving range of the magnet 5 away from the fracture H. It appears strongly, and at the position close to the fracture portion H, the influence of magnetic flux in the −Z direction such as 6N2 appears strongly. Similarly, the vertical component of the magnetic flux density on the concrete body surface 1A above the main reinforcing bar 2P is influenced by the magnetic flux in the −Z direction like 6P2 in the vicinity of the end of the moving range of the magnet 5 away from the fracture portion H. Appears strongly, and at the position close to the fracture portion H, the influence of the magnetic flux in the Z direction as in 6P1 appears strongly.

Therefore, when the perpendicular component of the magnetic flux density on the concrete body surface 1A along the entire main reinforcing bar 2 including the main reinforcing bars 2N and 2P is measured, as shown in the graph of FIG. On the left and right of (0 mm position), a curve having convex portions I1 and I2 due to a change in magnetic flux density is obtained. Further, the slope of the line segment I3 connecting these convex portions I1 and I2 is very steep. That is, in the vicinity of the position of the fracture portion H, a large change in magnetic flux density of a substantially S shape that appears from the convex portions I1 to I2 occurs.
As described above, when the main reinforcing bar 2 has the fracture portion H, the vertical component of the magnetic flux density on the concrete body surface 1A changes abruptly. Therefore, by detecting this characteristic sudden change, The presence or absence can be determined.

  The example of FIG. 7 has the same conditions as the example of FIG. 4 except that the main reinforcing bar 2 has a fracture H at the 0 mm position on the horizontal axis of the graph. That is, the main rebar 2 is a 16 mm diameter rebar (deformed bar), the concrete cover thickness is 100 mm, the cross rebar 3 is a 13 mm diameter rebar (deformed bar), and the concrete cover thickness is 62 mm. In addition, the crossed reinforcing bars 3 are embedded in the respective positions of −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm, and 750 mm on the horizontal axis of the graph so that a total of seven bars are substantially orthogonal to the main reinforcing bar 2. Yes.

Ac-2: Elimination of magnetic flux density from non-inspection object Curve D1 in FIG. 7 is a concrete body along the longitudinal direction substantially directly above main reinforcing bar 2 (2N and 2P) as shown in FIG. On the surface 1A, the main rebar on the concrete body surface 1A when the main rebar 2 and the crossed rebar 3 are magnetized by moving the magnet 5 with the N pole on the left side and the S pole on the right side in the X direction. 2 shows the magnetic flux density (vertical component) along the longitudinal direction directly above 2.
Curve D2 magnetizes main rebar 2 and crossed rebar 3 by moving magnet 5 in which the relative positions of both magnetic poles are the same as those of curve D1 in the -X direction along the same orbit as in curve D1. The magnetic flux density (vertical component) along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A is shown.
Further, a curve D3 indicates an average value of both magnetic flux densities obtained by dividing the sum of both of the magnetic flux densities shown in the curves D1 and D2 by 2.

In the curve D3, there are fewer large convex portions compared to the curves D1 and D2, there is one large upward convex portion I1 slightly on the negative side from the 0 mm position on the horizontal axis of the graph, and a little from the 0 mm position on the horizontal axis. There is only one large downward convex portion I2 on the positive side.
The reason is the same as in the case of the curve S3 in FIG. 4 described above. When the magnetic flux densities shown in the curves D1 and D2 are added together to obtain the sum of both magnetic flux densities, the crossed reinforcing bars 3 included in the curve D1 This is because the magnetic flux density of the generated magnetic flux 3A in the Z direction and the magnetic flux density of the magnetic flux 3A in the -Z direction generated from the crossed reinforcing bar 3 included in the curve D2 are canceled out.
On the other hand, the magnetic flux density from the main rebar 2 (2N and 2P) is about twice as large without being canceled out in the sum of both magnetic flux densities. Therefore, the average value obtained by dividing the sum of the two magnetic flux densities by 2 represents an approximate value of the magnetic flux density from the main rebar 2 in which the influence of the magnetic flux density of the crossed reinforcing bars 3 is eliminated or greatly reduced. .

From this, it can be seen that the convex portions I1 and I2 of the curve D3 and the steep line segment I3 connecting these appear due to the presence of the fracture portion H in the main reinforcing bar 2.
In the curves D1 and D2, a large number of upward and downward convex portions appear due to the influence of the magnetic flux density of the crossing reinforcing bars 3, and therefore it is difficult to determine the presence or absence of the fracture portion H in the main reinforcing bars 2 only from these. It is. However, by adding them together to obtain the sum of both magnetic flux densities, or by dividing the sum of both magnetic flux densities by 2 to obtain an average value, the fracture portion H can be detected accurately and easily. It is.

A-c-3: curve G0 in the graph of the main magnetized Figure 16, for example in FIG. 5, substantially at the right above of the concrete surface 1A of the main reinforcing bars 2N and 2P, S pole N pole in FIG left The first magnetizing (main magnetizing) is performed by moving the magnet 5 with the right side in the figure in the X direction, and the main reinforcing bars 2N and 2P and the crossing reinforcing bar 3 are magnetized on the concrete body surface 1A. The vertical component of the magnetic flux density along the longitudinal direction directly above the main reinforcing bars 2N and 2P is shown.

  The example of FIG. 16 has the same conditions as the example of FIG. 12 except that the main reinforcing bar 2 has a fracture H at the 0 mm position on the horizontal axis of the graph. That is, the main rebar 2 is a 16 mm diameter rebar (deformed bar), the concrete cover thickness is 150 mm, the cross rebar 3 is a 13 mm diameter rebar (deformed bar), and the concrete cover thickness is 112 mm. In addition, the crossed reinforcing bars 3 are embedded in the respective positions of −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm, and 750 mm on the horizontal axis of the graph so that a total of seven bars are substantially orthogonal to the main reinforcing bar 2. Yes.

  The curve G0 in FIG. 16 shows a large upward convex portion and a downward convex portion due to a sudden change in magnetic flux density caused by the fracture portion H on the left and right of the location of the fracture portion H (0 mm position on the horizontal axis of the graph). However, at the same time, a large number of large downward convex portions appear due to the magnetic flux density from the crossing reinforcing bars 3, so the rapid change in the magnetic flux density caused by the fracture H of the main reinforcing bars 2 can be accurately determined. It is difficult to distinguish.

Ac-4: Reduction of magnetic flux density from crossed reinforcing bars by additional magnetization Next, as shown in FIG. 9, from the position directly above main reinforcing bars 2N and 2P on the concrete body surface 1A, the length of the crossed reinforcing bars 3 By moving the magnet 5 in the X direction, which is the longitudinal direction of the main reinforcing bars 2N and 2P, with the direction of both the magnetic poles being the same as in FIGS. “First additional magnetization” is performed.
Then, as in the case of the “first magnetization” (main magnetization), the portion of the crossing rebar 3 that is located directly below the trajectory to which the magnet 5 has moved is the magnet 5 that has passed through its vicinity last. Since the magnet is magnetized to the S pole under the influence of the N pole, the Z-direction magnetic flux 3A2 having a relatively high magnetic flux density is placed on the concrete body surface 1A above the portion magnetized to the S pole of the crossed reinforcing bar 3. Will occur. At the same time, the magnetic flux density of the magnetic flux 3A1 generated from the portion directly above the main reinforcing bars 2N and 2P in the crossed reinforcing bar 3 by the first magnetization is significantly reduced.

When the first additional magnetization is performed, the vertical component of the magnetic flux density along the longitudinal direction directly above the main reinforcing bars 2N and 2P on the concrete body surface 1A is measured using the magnetic sensor. A curve G25 shown in FIG.
The curve G25 is larger than the curve G0 except for a large upward convex portion appearing near −150 to −100 mm on the horizontal axis of the graph and a large downward convex portion appearing near 100 to 150 mm. The height difference of each convex shape part is small. This is because the magnetic flux density of the magnetic flux generated from the portion directly above the main reinforcing bars 2N and 2P in the crossed reinforcing bar 3 is reduced by the first additional magnetization.

  Therefore, by performing the first additional magnetization, a large upward convex portion appearing in the vicinity of −150 to −100 mm on the horizontal axis of the curve G25 caused by the fracture portion H of the main reinforcing bar 2; A sudden change in the magnetic flux density between the large downward convex portion appearing in the vicinity of ~ 150 mm can be found more reliably, and the detection accuracy of the presence or absence of the fracture portion H can be improved.

  Further, the curve G50 in the graph of FIG. 16 shows that after performing the “first magnetization” (main magnetization) and the “first additional magnetization” to magnetize the main reinforcing bars 2N and 2P and the crossing reinforcing bars 3, By moving the magnet 5 in the X direction at the position 500 mm away from the position directly above the main reinforcing bars 2N and 2P on the concrete body surface 1A in the Y direction with the direction of both magnetic poles being the same as in the example of FIG. The vertical component of the magnetic flux density along the longitudinal direction directly above the main reinforcing bars 2N and 2P on the concrete body surface 1A in the case of performing “second first additional magnetization” is shown.

  Similarly, the curve G75 in FIG. 16 shows the surface of the concrete body after performing the “first magnetization” (main magnetization), “first additional magnetization”, and “second first additional magnetization”. By moving the magnet 5 in the X direction at a position 750 mm away from the position directly above the main reinforcing bars 2N and 2P on 1A in the Y direction, the direction of both magnetic poles is the same as in the example of FIG. The vertical component of the magnetic flux density along the longitudinal direction directly above the main reinforcing bars 2N and 2P on the concrete body surface 1A when the "first additional magnetization of" is performed.

  Further, the curve G100 of the graph of FIG. 16 indicates the “first magnetization” (main magnetization), “first additional magnetization”, “second first additional magnetization”, and “third first magnetization”. After performing “additional magnetization”, the magnet 5 is positioned at a position 1000 mm away from the position directly above the main reinforcing bars 2N and 2P on the concrete body surface 1A in the Y direction, and the directions of both magnetic poles are the same as in the example of FIG. The vertical component of the magnetic flux density along the longitudinal direction of the main reinforcing bars 2N and 2P on the concrete body surface 1A when the “fourth first additional magnetization” is performed by moving in the X direction. Is shown.

  These curves G50, G75 and G100 all appear in the vicinity of −150 to −100 mm on the horizontal axis of the graph and a large upward convex portion appearing in the vicinity of the graph horizontal axis and in the vicinity of 100 to 150 mm, similarly to the curve G25. Except for the large downward convex portion, the height difference of each convex portion is smaller than that of the curve G0.

Furthermore, the height difference of each convex shape part of these curves becomes small in order of curve G0, G25, G50, G75, and G100. That is, “first additional magnetization”, “second first additional magnetization”, “third first additional magnetization”, “fourth first additional magnetization”, and multiple additional magnetizations. The distance between the main reinforcing bars 2N and 2P on the concrete body surface 1A and the position of the main reinforcing bars 2N and 2P on the concrete body surface 1A is increased by sequentially separating the reinforcing bars in the width direction (Y direction). From the magnetic flux density along the upper longitudinal direction, the influence of the magnetic flux density from the crossing reinforcing bars 3 can be gradually reduced.
Therefore, since the rapid change of the magnetic flux density caused by the broken portion H of the main reinforcing bar 2 can be found more reliably, the detection accuracy of the presence or absence of the broken portion H can be increased.

  The effect that the magnetic flux density from the crossed reinforcing bars 3 generated by the “first magnetization” (main magnetization) can be reduced by the “first additional magnetization” has the effect of “second magnetization” (main magnetization). This also occurs in the relationship between the magnetism) and “second additional magnetization”.

B: Non-destructive inspection method
Ba: First Embodiment As shown in FIG. 20, the first embodiment of the nondestructive inspection method of the present invention is a first magnetization step 101, a first magnetic flux density measurement step 102, and a second magnetization step. 103, a second magnetic flux density measurement step 104, a non-inspection magnetic flux removal step 105, and a fracture portion detection step 106.

B-a-1: First magnetization step 101
In the first magnetization step 101, the magnetized surface 5A of the magnet 5 is arranged close to the concrete body surface 1A so that both magnetic poles of the magnet 5 are along the longitudinal direction of the rebar 2 to be inspected, and then the magnet 5 is inspected. This is a step of removing the magnet 5 after magnetizing the rebar 2 to be examined by moving it along the longitudinal direction of the rebar 2.

For example, as shown in FIG. 2 or FIG. 5, the magnet 5 has its N pole on the left side of the figure and the S pole on the right side of the figure, and the magnetized surface 5A is brought close to the concrete surface 1A. 2 is arranged so as to be along the longitudinal direction (X direction) substantially above 2. Next, after moving the magnet 5 in the X direction to magnetize the main rebar 2, the magnet 5 is removed from the concrete body surface 1 </ b> A and moved away.
By this first magnetizing step 101, a magnetic flux 2 </ b> A in the X direction is generated inside the main reinforcing bar 2. Further, not only the main reinforcing bar 2 but also non-inspected objects such as a crossed reinforcing bar 3 and other metal fittings embedded substantially orthogonally to the main reinforcing bar 2 in the concrete body 1 are magnetized in the same manner. As a result, for example, the three crossed reinforcing bars 3 in FIG. 2 generate a magnetic flux 3A directed in the Z direction on the concrete body surface 1A.

The moving trajectory of the magnet 5 does not necessarily have to be directly above the main reinforcing bar 2 (that is, when the position of the magnet 5 in the Y direction and the position of the main reinforcing bar 2 in the Y direction are the same). Similarly, the description “along the longitudinal direction of the reinforcing bar” does not necessarily mean that it should always be along the reinforcing bar.
The reason why the magnet 5 is removed after magnetization is to prevent the magnet 5 from directly affecting the magnetic sensor when the magnetic flux density is measured in the next first magnetic flux density measuring step 102. Therefore, the distance to be removed and moved away may be determined as appropriate according to the strength of the magnetic force of the magnet and the conditions such as whether it is a permanent magnet or an electromagnet.

B-a-2: First magnetic flux density measurement step 102
Next, in the first magnetic flux density measuring step 102, after the first magnetizing step 101, the magnetic sensor is placed close to the concrete body surface 1 </ b> A, moved appropriately, or moved in the longitudinal direction of the rebar 2 to be inspected without moving. It is the process of measuring the magnetic flux density along.

In the first magnetic flux density measurement step 102, in order to arrange the magnetic sensor close to the surface 1A of the concrete body, the magnetic sensor may be temporarily brought close to a predetermined position on the concrete body surface 1A. There is no need to abut the surface and no need to be stationary.
However, in order to obtain the magnetic flux density along the longitudinal direction of the inspection target reinforcing bar 2, it is necessary to measure the magnetic flux density up to the inspection range of the fractured portion of the inspection target reinforcing bar 2 and, if necessary, the peripheral range.
For this purpose, the magnetic flux density may be measured while appropriately moving one or a plurality of magnetic sensors. For example, the magnetic sensor is moved near the surface of the concrete body along the longitudinal direction of the rebar 2 to be inspected. The magnetic flux density can be measured. Alternatively, the magnetic sensor arranged on the surface of the concrete body is moved back and forth in a direction (Y direction) perpendicular to the longitudinal direction of the inspection target reinforcing bar while being close to the concrete body surface 1A, and the inspection target reinforcing bar is gradually moved. By shifting in the longitudinal direction (X direction), the magnetic flux density from the inspection target reinforcing bar 2 can be measured, and the magnetic flux density along the longitudinal direction of the inspection target reinforcing bar 2 can be calculated from the measurement result.

  Further, for example, when using a long magnetic sensor unit in which a large number of magnetic sensors are continuously arranged in a straight line, the surface of the concrete body 1A is arranged along the longitudinal direction of the rebar 2 to be inspected. It is possible to measure the magnetic flux density along the longitudinal direction of the rebar to be inspected without being moved after that, by simply placing it close to.

In the first magnetic flux density measuring step 102, the magnetic flux density from the crossed reinforcing bar 3 other than the main reinforcing bar 2 and other non-inspection objects is also measured.
Further, in the first magnetic flux density measuring step 102, it is preferable that the magnetic flux density from the non-inspected object such as the crossed reinforcing bar 3 can be grasped more clearly by measuring the vertical component of the magnetic flux density. Therefore, it is possible not only to improve the detection accuracy of the presence / absence of the broken portion of the inspection target reinforcing bar, but also to detect the presence / absence and position of the non-inspection target with high accuracy.

Here, when the main reinforcing bar 2 does not have the fracture portion H, the curve S1 of FIG. 4 appears as a vertical component of the magnetic flux density on the concrete body surface 1A. Further, when the main reinforcing bar 2 has a fracture H, a curve D1 in FIG. 7 appears as a vertical component of the magnetic flux density on the concrete body surface 1A.
As described above, the curved line D1 includes the convex portions I1 and I2 on the left and right of the 0 mm position in the X direction due to the influence of the fracture portion H, and a line segment I3 indicating a rapid decrease in the magnetic flux density connecting the both convex portions. include. However, at the same time, a large number of convex portions other than the convex portions I1 and I2 appear in the curve D1 due to the influence of the seven crossed reinforcing bars 3 embedded in the concrete body 1. It is difficult to accurately find a sudden change in magnetic flux density caused by the portion H.

B-a-3: Second magnetization step 103
Next, in the second magnetizing step 103, the magnetized surface 5A of the magnet 5 is arranged close to the concrete body surface 1A so that the relative positions of both magnetic poles of the magnet 5 are the same as those in the first magnetizing step 101. Next, the magnet 5 is moved in the opposite direction along the orbit substantially the same as that in the first magnetizing step and magnetized again on the inspection target reinforcing bar 2, and then the magnet 5 is removed.

Here, it is necessary to arrange the magnet 5 so that the relative positions of the two magnetic poles are the same as those in the first magnetizing step. For example, in the first magnetizing step 101, the N pole of the magnet 5 is on the left side of the figure. In the second magnetizing step 103, the N pole of the magnet 5 is arranged on the left side of the figure and the S pole is on the right side of the figure without changing it.
Thereafter, the main rebar 2 is magnetized by moving the magnet 5 in the reverse direction (−X direction) along the same orbit as in the first magnetization step 101. Here, a magnetic flux 2A facing in the X direction is generated inside the main reinforcing bar 2 as in the first magnetizing step 101 (see FIG. 3).

  Similarly to the case of the first magnetizing step 101, non-inspected objects such as crossed reinforcing bars 3 and other metal fittings arranged substantially orthogonal to the main reinforcing bar 2 in the concrete body 1 are also magnetized. However, the magnetized non-inspection object generates a magnetic flux in the opposite direction to that in the first magnetization step 101. For example, for the three crossed reinforcing bars 3 in FIG. 3, a magnetic flux 3 </ b> A directed in the −Z direction is generated on the concrete body surface 1 </ b> A.

In this embodiment, the moving direction of the magnet 5 in each magnetization step is the X direction in the first magnetization step 101 and the -X direction in the second magnetization step 103, but this is reversed. The first magnetization step 101 may be in the −X direction, and the second magnetization step 103 may be in the X direction.
In each magnetization step, the magnet 5 may be reciprocated in the X direction and the −X direction a plurality of times along the longitudinal direction of the main rebar 2 in order to sufficiently magnetize the main rebar 2. However, in each magnetizing step, the direction in which the magnet 5 is finally moved determines the direction of the magnetic flux 3A of the crossing reinforcing bar 3. For example, in this embodiment, the magnet 5 in the first magnetizing step 101 is used. The last moving direction of the magnet 5 needs to be the X direction, and the last moving direction of the magnet 5 in the second magnetizing step 103 needs to be the −X direction.

Ba-4: Second magnetic flux density measurement step 104
Next, in the second magnetic flux density measuring step 104, after the second magnetizing step 103, the magnetic sensor is disposed close to the concrete body surface 1 </ b> A, and then moved appropriately or without being moved. It is a step of measuring the magnetic flux density along the direction.

In the second magnetic flux density measuring step 104, similarly to the first magnetic flux density measuring step 102, the magnetic flux density from the non-inspected object such as the crossed reinforcing bar 3 other than the main rebar 2 and other metal fittings is also measured.
When the main reinforcing bar 2 does not have the fracture portion H, a curve S2 in FIG. 4 appears as a vertical component of the magnetic flux density on the concrete body surface 1A. Further, when the main reinforcing bar 2 has a fracture H, a curve D2 in FIG. 7 appears as a vertical component of the magnetic flux density on the concrete body surface 1A.
The curve D2 is a line segment indicating the rapid change in the magnetic flux density connecting the convex portions I1 and I2 at the left and right of the 0 mm position in the X direction and the convex portions due to the influence of the fracture portion H, similarly to the curve D1 described above. I3 is included. However, since a large number of convex shape portions other than the convex shape portions I1 and I2 appear in the curve D2 due to the influence of the seven crossed reinforcing bars 3 embedded in the concrete body 1, from the curve D2, the fracture portion It is difficult to accurately find a sudden change in magnetic flux density caused by H.

Ba-5: Non-inspection magnetic flux removal step 105
Next, the non-inspection magnetic flux removal step 105 adds the magnetic flux densities measured by the first magnetic flux density measurement step 102 and the second magnetic flux density measurement step 104 to obtain the sum of both magnetic flux densities. This is a step of canceling and removing the magnetic flux density from the inspection object.

As described above, the curve D1 (FIG. 7) obtained by the first magnetic flux density measurement step 102 or the curve D2 (FIG. 7) obtained by the second magnetic flux density measurement step 104 has many undulations. Since it appears, it is difficult to detect the presence or absence of the fracture portion H of the main reinforcing bar 2 only from these curves.
However, when the vertical components of both magnetic flux densities shown in the curves D1 and D2 are added to obtain the sum of both magnetic flux densities, the Z-direction magnetic flux density generated from the crossed reinforcing bar 3 included in the curve D1 and the curve D2 are included. The magnetic flux density in the −Z direction generated from the crossed reinforcing bars 3 can be canceled out. Accordingly, the influence of the magnetic flux density from the crossing reinforcing bars 3 is eliminated or greatly reduced, and the convex part I1 representing the change in magnetic flux density caused by the fracture part H of the main reinforcing bar 2 as shown by the curve D3 (FIG. 7). , I2 and line segment I3 can be clearly expressed, and therefore the presence or absence of the fracture portion H can be detected very accurately.

  As long as the magnetic flux density from the non-inspected object is canceled out by adding both magnetic flux densities, the average of both magnetic flux densities is calculated by dividing the sum of both magnetic flux densities by 2. Or any other additional calculation process.

Ba-6: Breaking portion detection step 106
Next, the broken portion detection step 106 is a step of detecting the presence or absence of the broken portion H of the inspection target reinforcing bar 2 based on the sum of both magnetic flux densities obtained by the non-inspection magnetic flux removing step 105.
As described above, based on the result obtained by dividing the sum of both magnetic flux densities by 2 to calculate the average value of both magnetic flux densities or performing other additional calculation processing, It is also possible to detect the presence or absence of the broken portion H of the reinforcing bar 2.

Even if the sum of both magnetic flux densities is obtained by the non-inspection magnetic flux removal step 105, the influence of the crossing reinforcing bars 3 may remain to some extent. For example, the curve S3 in FIG. Shape portions (C1, C2 in FIG. 4 or K1, K2, etc. in FIG. 7) often appear. In that case, when these convex-shaped parts are large, there is a possibility of being mistaken for being caused by the fractured part H.
Therefore, it is preferable to obtain the sum of the two magnetic flux densities or the average value of the two magnetic flux densities and further calculate the differential value thereof, whereby the change in the magnetic flux density due to the fracture portion H can be found more reliably.

  The differential value of the vertical component of the magnetic flux density represented by the curve D3 in FIG. 7 is shown in the curve T3 in FIG. On the curve T3, a convex peak value J3 appears downward at the 0 mm position on the horizontal axis of the graph. On the other hand, a peak value L3 having a convex shape appears in the downward direction in the vicinity of the -300 mm position. In this way, a plurality of peak values may appear in the curve indicating the differential value of the vertical component of the magnetic flux density. In such a case, whether or not the peak value is caused by the fracture portion H. It is only necessary to provide a threshold value for determining whether or not the fracture portion H is present by comparing the threshold value with the peak value.

For example, when the threshold value is −0.5 μT / mm, the peak value J3 is approximately −1.1 μT / mm and thus exceeds the threshold value. Therefore, it can be determined that the main reinforcing bar 2 includes the fracture portion H.
Here, since the portion where the fracture portion H exists in the curve T3 has a downward convex shape, “beyond the threshold value” means that the peak value is smaller than the threshold value (in the negative direction of the vertical axis of the graph). Large).
On the other hand, since the peak value L3 is about 0 μT / mm and does not exceed the threshold value, the peak L3 is not a change in magnetic flux density caused by the fractured portion H, and other non-inspections such as the crossed reinforcing bars 3 It is determined that it is caused by the object.
Thus, since the change of the magnetic flux density due to the fracture portion H can be easily determined by comparing the sum of the magnetic flux densities or the differential value of the average value with a preset threshold value, the fracture portion H It is possible to more accurately detect the presence or absence.

  Moreover, in the fracture | rupture part detection process 106, you may obtain | require a differential approximate value instead of calculating | requiring the differential value which is a change rate of magnetic flux density. As a method for obtaining a differential approximate value, for example, two magnetic sensors that are close to each other at a predetermined distance are arranged along the longitudinal direction of the reinforcing bar, and the difference in magnetic flux density obtained from each of the two magnetic sensors is determined. A method of dividing by the distance between them can be considered. In the present embodiment, the magnetic flux density is differentiated once (floor), but may be differentiated twice (floor) or more as necessary. The same applies to the differential approximation value.

In the embodiment of the nondestructive inspection method, the magnetic flux density on the concrete body surface 1A is measured by measuring the vertical component thereof, but can also be performed by measuring other arbitrary direction components. it can. As an example, an embodiment for measuring the horizontal component of the magnetic flux density on the concrete body surface 1A will be described next.
Here, the horizontal component of the magnetic flux density is a component in the horizontal direction with respect to the concrete body surface 1A in the magnetic flux density, and in the present embodiment, is a component in the X direction or the -X direction.
The difference between the embodiment in which the horizontal component of the magnetic flux density on the concrete body surface 1A is different from the embodiment in which the vertical component is measured is that the magnetic flux to be measured in the first and second magnetic flux density measuring steps 102 and 104. The point that the direction component of density is the horizontal direction and the point that the sum of both magnetic flux densities becomes the sum of the horizontal components of both magnetic flux densities in the non-inspection object magnetic flux removing step 105 and the fracture portion detecting step 106.

  FIG. 22 shows the horizontal component of the magnetic flux density along the longitudinal direction of the main rebar 2 on the concrete body surface 1A in the concrete body 1 in which the main rebar 2 without the fracture portion H and the seven crossed reinforcing bars 3 are embedded. It is a graph which shows. Here, the horizontal axis of the graph represents the position in the X direction on the concrete body surface 1A, and the vertical axis represents the value of the horizontal component of the magnetic flux density at the position. Note that the seven crossed reinforcing bars 3 are embedded at positions of −750 mm, −500 mm, −250 mm, 0 mm, 250 mm, 500 mm, and 750 mm on the horizontal axis of the graph, as in the example of FIG. 4. Further, the diameters of the main reinforcing bars 2 and the crossed reinforcing bars 3 and the cover thickness of the concrete are the same as in the example of FIG.

The curve U1 in FIG. 22 shows the horizontal component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A when the magnet 5 is moved in the X direction, as shown in FIG. The change according to the position is shown.
Further, as shown in FIG. 3, the curve U <b> 2 indicates the horizontal component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1 </ b> A when the magnet 5 is moved in the −X direction of the main reinforcing bar 2. The change according to the position in the X direction is shown.
Furthermore, a curve U3 shows an average value of horizontal components of both magnetic flux densities shown in the curves U1 and U2.

In the curve U <b> 1, a downward convex shape portion and an upward convex shape portion appear in pairs on the left and right of each position of the cross reinforcing bar 3. For example, a downward convex portion U1v appears at a position of about -300 mm and an upward convex portion U1m appears at a position of about -200 mm before and after the crossed reinforcing bar 3 embedded at a position of -250 mm on the horizontal axis of the graph. .
On the other hand, in the curve U2, as in the case of the curve U1, the downward convex portion and the upward convex portion appear in pairs on the left and right of each position of the crossing reinforcing bar 3. An upward convex shape portion appears at substantially the same position in the X direction as the convex shape portion, and a downward convex shape portion appears at substantially the same position in the X direction as the upward convex shape portion on the curve U1. For example, an upward convex portion U2m appears at a position of about -300 mm and a downward convex portion U2v appears at a position of about -200 mm before and after the crossed reinforcing bar 3 embedded at a position of -250 mm on the horizontal axis of the graph.

  As a result, the curve U3 indicating the average value of the horizontal component of the magnetic flux density indicated by the curve U1 and the horizontal component of the magnetic flux density indicated by the curve U2 is the downward convex shape portion of the curve U1 and the upward convex shape portion of the curve U2. Further, the upward convex shape portion of the curve U1 and the downward convex shape portion of the curve U2 cancel each other, thereby showing a gentle shape with few undulations.

On the other hand, FIG. 23 shows the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A in the concrete body 1 in which the main reinforcing bar 2 having the fracture portion H and the seven crossing reinforcing bars 3 are embedded. It is a graph which shows the horizontal component of.
A curve Q1 in FIG. 23 shows the horizontal component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A when the magnet 5 is moved in the X direction, as shown in FIG. The change according to the position is shown.
Further, as shown in FIG. 3, the curve Q2 indicates the horizontal component of the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A when the magnet 5 is moved in the -X direction. The change according to the position is shown.
Furthermore, the curve Q3 shows the average value of the horizontal components of both magnetic flux densities shown in the curves Q1 and Q2. Here, the position of the fracture portion H is the 0 mm position on the horizontal axis of the graph.

  In the curves Q1 and Q2 in FIG. 23, as in the curves U1 and U2 in FIG. 22, upward convex portions and downward convex portions alternately appear. However, the magnetic flux densities shown in the curves Q1 and Q2 are the same. In the curve Q3 indicating the average value of the horizontal components, unlike the curve U3 in FIG. 22, a convex peak value M3 appears downward at the position of 0 mm on the horizontal axis where the fracture portion H is present. Therefore, it is possible to detect the presence or absence of the fracture portion H in the main reinforcing bar 2 depending on whether or not the peak value M3 appears.

Note that the differential value of the horizontal component of the magnetic flux density represented by the curve Q3 in FIG. 23 is shown in the curve F3 in FIG. On the curve F3, large convex portions W1 and W2 appear on the left and right of the position of the fracture portion H (0 mm position on the horizontal axis of the graph). Therefore, it is possible to detect the presence or absence of the fracture portion H in the main reinforcing bar 2 depending on whether or not such a large convex portion W1 or W2 appears.
Further, a threshold for determining whether or not the convex shape portion W1 or W2 is due to the fracture portion H is provided, and this threshold value is compared with the peak value of the convex shape portion W1 or W2. Or you may make it detect the presence or absence of the fracture | rupture part H by comparing a threshold value and the difference of the convex-shaped parts W2 and W1.

As described above, in the first embodiment of the nondestructive inspection method of the present invention, in the measurement of the magnetic flux density in the first and second magnetic flux density measurement steps 102 and 104, not only the vertical component of the magnetic flux density but also any arbitrary It is also possible to detect the fracture H by measuring the direction component.
However, it is preferable to measure the vertical component of the magnetic flux density because the detection accuracy of the broken portion H of the main reinforcing bar 2 can be further increased. That is, when the differential value based on the average value of the vertical components of both magnetic flux densities measured by the first and second magnetic flux density measuring steps 102 and 104 is calculated and represented in the graph, the fracture portion H exists in the main reinforcing bar 3. In this case, as shown by a curve T3 in FIG. 21, only one peak value J3 having a large downward convex shape appears at the position of the fracture portion H (0 mm position on the horizontal axis of the graph). For this reason, in the comparison between the peak value J3 and the threshold value, since erroneous recognition is not particularly likely to occur, the detection accuracy of the fracture portion H can be improved.

BB: Second Embodiment As shown in FIG. 40, the second embodiment of the nondestructive inspection method of the present invention is the first magnetization step 101, the first additional magnetization step 101A, and the first magnetic flux density measurement. The process 102, the 2nd magnetization process 103, the 2nd additional magnetization process 103A, the 2nd magnetic flux density measurement process 104, the non-inspection object magnetic flux removal process 105, and the fracture | rupture part detection process 106 are included.

The second embodiment of the present invention differs from the first embodiment in that in the second embodiment, “first additional magnetization step 101A” and “second additional attachment” that are not in the first embodiment. The magnetic process 103A ”is included.
That is, in the second embodiment, the first additional magnetization step 101A is provided after the first magnetization step 101, and the second additional magnetization step 103A is provided after the second magnetization step 103. Except for the points provided, the process consists of the same steps as in the first embodiment, so the following mainly describes the “first additional magnetization step 101A” and the “second additional magnetization step 103A”. The description of other processes is omitted, and the corresponding explanation part in the first embodiment is used.

B-b-1: First additional magnetization step 101A
In the first additional magnetization step 101A, as shown in FIG. 25, the “distance D determination method” described later in the width direction (Y direction) of the main reinforcing bar 2 from the position where the magnet 5 is arranged in the first magnetization step 101 is used. The magnetized surface 5A of the magnet 5 is arranged close to the concrete body surface 1A so that the relative positions of both magnetic poles of the magnet 5 are the same as those in the first magnetizing step 101 at a predetermined position separated by the obtained “distance D” or more. Then, the magnet 5 is moved again along the longitudinal direction (X direction) of the main rebar 2 to magnetize the main rebar 2 and the crossed rebar 3 again, and then the magnet 5 is removed.

  As in the case of the first magnetizing step 101, the first additional magnetizing step 101A, as in the case of the first magnetizing step 101, the portion of the cross rebar 3 that is located directly below the trajectory to which the magnet 5 has moved has passed through its vicinity last. Since the magnet 5 is magnetized to the south pole under the influence of the north pole, the magnetic flux density is relatively large in the Z direction on the concrete body surface 1A above the portion magnetized to the south pole of the crossed reinforcing bar 3. Magnetic flux 3A2 is generated. At the same time, the magnetic flux density of the magnetic flux 3A1 generated from the portion directly above the main reinforcing bar 2 in the crossed reinforcing bar 3 by the first magnetizing step 101 can be significantly reduced. (See FIG. 9).

  As described above, by appropriately performing the first additional magnetization step 101A, the magnetic flux density of the magnetic flux 3A1 generated from the portion directly above the main reinforcing bar 2 in the crossed reinforcing bar 3 can be significantly reduced. It becomes possible to more accurately determine the magnetic flux density. Therefore, a sudden change in the magnetic flux density caused by the fracture portion H of the main reinforcing bar 2 can be found more reliably, and the detection accuracy of the presence or absence of the fracture portion H can be increased.

  The movement of the magnet 5 from the arrangement position of the magnet 5 in the first magnetization step 101 to the arrangement position of the magnet 5 in the first additional magnetization step 101A is, for example, as shown by an arrow 4A in FIG. 5 is temporarily removed from above the concrete body surface 1A after the first magnetization, and the magnet 5 can be placed again close to the concrete body surface 1A at a predetermined position where the first additional magnetization is performed. .

B-b-2: Reduction of magnetic flux density by the first additional magnetizing step 101A As described above, the magnetic flux generated from the portion directly above the main reinforcing bar 2 in the crossed reinforcing bar 3 by appropriately performing the first additional magnetizing step 101A. Although the magnetic flux density of 3A1 can be reduced and the detection accuracy of the presence or absence of the rupture portion H can be increased, in what position should the magnet 5 be arranged in the first additional magnetization step? is important.
In this regard, the inventor of the present application may reduce the magnetic flux density of the magnetic flux 3A1 (see FIG. 8) from the crossed reinforcing bar 3 generated as a result of the first magnetizing step 101 to about 1/2 or less. If possible, it is possible to determine the magnetic flux density of the magnetic flux generated from the main rebar 2 almost accurately and experience the knowledge that a sudden change in the magnetic flux density caused by the fracture H of the main rebar 2 can be found almost certainly. Acquired.

Here, an example in which the magnetic flux density from the crossed reinforcing bar 3 generated as a result of the first magnetization step 101 is reduced by the first additional magnetization step 101A will be described based on the graphs of FIGS.
First, the curve shown in the graph of FIG. 26 shows the magnet 5 on the surface 1A of the concrete body 1 in which only the crossing reinforcing bars 3 extending in the Y direction are embedded and the main reinforcing bars 2 are not embedded, and the S poles in the X direction. After the N pole is directed to the -X direction side and the magnetized surface 5A is arranged close to the concrete body surface 1A, the magnet 5 is moved in the X direction so as to pass right above the crossing rebar 3 at a substantially right angle. The first magnetization is performed, and then the result of measuring the vertical component of the magnetic flux density along the longitudinal direction (Y direction) just above the crossed reinforcing bar 3 on the concrete body surface 1A by the magnetic sensor is obtained. Show.
Here, the position where the first magnetization was performed (the position where the magnet 5 crossed right above the crossing reinforcing bar 3) is the 0 mm position on the horizontal axis of the graph, and the vertical component of the magnetic flux density at this position is about −200 μT. It has become.

  In the example of FIG. 26, the crossing reinforcing bars 3 are deformed steel bars having a diameter of 13 mm, and the cover thickness of the concrete is 100 mm. The magnet 5 used for magnetization is a permanent magnet having the above-mentioned rectangular parallelepiped shape (length 100 mm, width 100 mm, height 60 mm).

Next, the curve shown in the graph of FIG. 27 performs “first magnetization” under the same conditions and method as in the example of FIG. 26, and then in the Y direction from the position where the magnet 5 is arranged during the first magnetization. At a position separated by 100 mm, the magnet 5 is arranged in the same manner as in the case of the first magnetization and then moved in the X direction to perform “first additional magnetization”, and then the surface of the concrete body 1A by the magnetic sensor. The result of having measured the perpendicular | vertical component of the magnetic flux density along the longitudinal direction (Y direction) just above the crossing reinforcing bar 3 on the upper side is shown.
In the example of FIG. 27, the vertical component of the magnetic flux density at the position where the first magnetization is performed (the 0 mm position on the horizontal axis of the graph) is about −160 μT, and this value is the first magnetization at the same position. It is a value (absolute value) larger than about -100 μT which is ½ of the later value (about -200 μT). That is, it can be said that the effect of reducing the magnetic flux density by the first additional magnetization is not sufficient.

Next, the curve shown in the graph of FIG. 28 performs “first magnetization” under the same conditions and method as in the example of FIG. 26, and then in the Y direction from the position where the magnet 5 is arranged at the time of the first magnetization. In the position separated by 200 mm, the “other additional magnetization” was performed under the same conditions and method as in the example of FIG. 27, and the result of measuring the vertical component of the magnetic flux density along the longitudinal direction of the crossed reinforcing bar 3 is shown. Yes.
In the example of FIG. 28, the vertical component of the magnetic flux density at the position where the first magnetization is performed (position of 0 mm on the horizontal axis of the graph) is about −100 μT, and this value is the first magnetization at the same position. It is the same as about -100 μT which is 1/2 of the later value (about −200 μT). That is, it can be said that the effect of reducing the magnetic flux density by the first additional magnetization is exhibited.

Further, the curves shown in the graphs of FIG. 29 and FIG. 30 are the positions where the “first magnetization” is performed under the same conditions and method as in the example of FIG. 26, and then the magnet 5 is disposed at the time of the first magnetization. 27, at the positions separated from each other by 400 mm and 600 mm, respectively, the “first additional magnetization” is performed under the same conditions and method as in the example of FIG. 27, and the perpendicular magnetic flux density along the longitudinal direction of the crossed reinforcing bars 3 The result of measuring the components is shown.
In each example of FIG. 29 and FIG. 30, the vertical components of the magnetic flux density at the position where the first magnetization was performed (0 mm position on the horizontal axis of the graph) are about 10 μT and about −10 μT, respectively. Is a value (absolute value) smaller than about −100 μT which is ½ of the value after the first magnetization (about −200 μT) at the same position. That is, it can be said that the effect of reducing the magnetic flux density by the first additional magnetization is sufficiently exhibited.

  Next, the curves shown in the graphs of FIGS. 31, 32 and 33 are the same as the examples of FIGS. 28 and 32 except that the concrete cover thickness with respect to the crossing reinforcing bars 3 is 75 mm. The example of FIG. 29 performs the “first magnetization” and the “first additional magnetization” under the same conditions and methods as in the example of FIG. 29 and the example of FIG. 33, respectively. The result of having measured the perpendicular component of the magnetic flux density along the longitudinal direction is shown.

  Further, except that the concrete cover thickness with respect to the crossed reinforcing bar 3 is 75 mm, “first magnetization” is performed under the same conditions and method as in the example of FIG. 26, and the magnetic flux along the longitudinal direction of the crossed reinforcing bar 3 is also the same. When the perpendicular component of the density was measured, the perpendicular component of the magnetic flux density at the position where the first magnetization was performed (the position where the magnet 5 crossed right above the crossing rebar 3) was about −340 μT (not shown). ).

  In each of the examples of FIGS. 31, 32, and 33, the vertical components of the magnetic flux density at the position where the first magnetization is performed (0 mm position on the horizontal axis of the graph) are about 150 μT, about 20 μT, and about 10 μT, respectively. These values are values (absolute values) smaller than about −170 μT which is ½ of the value after the first magnetization (about −340 μT) at the same position. That is, it can be said that the effect of reducing the magnetic flux density by the first additional magnetization is sufficiently exhibited.

26 to 33, when the first magnetizing step 101 and the first additional magnetizing step 101A are performed using the magnet 5 in the present embodiment, the crossing reinforcing bars are started from the position where the first magnetizing is performed. By performing the first additional magnetization at a position separated by 200 mm or more in the longitudinal direction (Y direction) 3, the magnetic flux density is set to 1 regardless of whether the cover thickness of the concrete with respect to the crossed reinforcing bar 3 is 100 mm or 75 mm. It is clear that it can be reduced to less than / 2.
Further, the most distant position in the longitudinal direction of the crossed reinforcing bar 3 where the first additional magnetization can be effectively performed is not necessarily clear, but from the examples of FIGS. It is clear that when the first additional magnetization is performed at a position separated by 600 mm from the position where the magnetization is performed, the effect of reducing the magnetic flux density by the first additional magnetization is sufficiently exhibited.

B-b-3: Distance D and its determining method The position at which the magnet 5 is arranged in the first additional magnetization step 101A is the width direction of the main reinforcing bar 2 (Y (Distance) must be separated by “Distance D” or more.
As described above, the distance D is about ½ or less of the magnetic flux density of the magnetic flux 3A1 (see FIG. 8) generated from the portion directly above the main reinforcing bar 2 in the crossed reinforcing bar 3 by the first magnetization step 101. It is desirable that the distance be able to be reduced.

As described above, when the portion immediately below the moving track of the magnet 5 in the crossed reinforcing bar 3 is magnetized to the S or N pole by the first additional magnetization step 101A, the peripheral portion deviated from the position immediately below the moving track of the magnet 5 In this case, a magnetization action to the north pole or south pole opposite to the position immediately below occurs.
Therefore, in the portion located immediately above the main reinforcing bar 2 in the crossed reinforcing bar 3 that has already been magnetized to the S pole or the N pole by the first magnetizing step 101 due to the magnetization action by the first additional magnetizing step 101A, the magnetic flux It is thought that the density is reduced and reduced.

  The way in which the result of the magnetizing action in the first additional magnetization step 101A appears is as follows: the distance between the arrangement position of the magnet 5 in the first magnetization step 101 and the arrangement position of the magnet in the first additional magnetization step 101A. Although it differs depending on the distance, the separation distance (distance D) necessary for exerting the effect of reducing the magnetic flux density by the first additional magnetization step 101A differs depending on the size and shape of the magnet 5 used for magnetization. To do. For example, when the wide magnet 5 is used, the portion magnetized by the S pole or the N pole located just below the moving track of the magnet 5 in the crossing reinforcing bar 3 is also wide.

Next, the “distance D determination method” will be described.
First, as shown in FIGS. 34 and 35, the S pole side direction in the straight line (both magnetic pole center lines C) connecting the central portions of both magnetic poles of the magnet 5 is the X direction, and the magnetized surface 5A of the magnet 5 is on the lower side. The direction parallel to the magnetized surface 5A of the magnet 5 and orthogonal to the left side in the X direction is defined as the Y direction, the direction orthogonal to the X direction and the Y direction, and the magnetized surface 5A side of the magnet 5 is defined as Z. The direction.
In this case, as shown in FIG. 36 and FIG. 37, a position 100 mm away from the magnetized surface 5A of the magnet 5 from the center position of both magnetic pole center lines C of the magnet 5 in the Z direction is P1, and the positions P1 to Y The position where the X direction component of the magnetic flux density is about 1/4 of the X direction component of the magnetic flux density at the position P1 is P2, and the separation distance between the position P1 and the position P2 is “distance”. D ”.
When the magnet 5 has a shape other than the rectangular parallelepiped shape, for example, when the magnet 5 has a U-shape, both magnetic pole center lines C are as shown in FIG.

  When magnetizing the main reinforcing bar 2 and the crossed reinforcing bar 3 using the magnet 5, the strongest magnetic flux acting on both the reinforcing bars is the direction of the magnetic pole center lines C generated immediately below the magnetized surface 5 A of the magnet 5 (X Direction). Therefore, in the “determination method of the distance D”, the X-direction component of the magnetic flux density at the position P1 that is 100 mm directly below the magnetization surface 5 (Z direction) of the magnet 5 is used as the reference value.

  Further, as it moves away from the portion directly below the magnetized surface 5A of the magnet 5 in the Y direction, the influence of the magnetic force of the magnet 5 decreases and the X direction component of the magnetic flux density also decreases, but the magnitude is about 1 of the value of the position P1. At the position P2 that decreases to / 4, for example, when the cross rebar 3 is present at the position P2, the direct magnetizing action on the cross rebar 3 from the magnet 5 is relatively weak. On the other hand, however, a magnetizing action to a pole opposite to the position immediately below the magnet 5 appears prominently in the peripheral portion of the crossing reinforcing bar 3 that is off from the position immediately below the magnet 5. Therefore, the effect of the first additional magnetization step 101A that the magnetic flux density of the magnetic flux 3A1 (see FIG. 8) generated from the crossed reinforcing bars 3 by the first magnetization step 101 can be reduced can be exhibited.

Here, the curve M0 shown in the graph of FIG. 38 represents the result of measuring the X direction component of the magnetic flux density of the magnetic flux generated from the magnet 5 on the X direction straight line passing through the position P1. Curves M100, M200, and M400 shown in the figure are on the X direction straight line that passes through the X direction component of the magnetic flux density of the magnetic flux generated from the magnet 5 by 100 mm, 200 mm, and 400 mm apart from the position P1 in the Y direction, respectively. The measurement results are shown.
Note that the 0 mm position on the horizontal axis of the graph in the curve M0 corresponds to the position P1.

The X direction component of the magnetic flux density at the 0 mm position on the horizontal axis of the graph indicated by these curves is about 22 mT (reference value at the position P1) for the curve M0, about 13 mT for the curve M100, about 5 mT for the curve M200, and about 1 mT for the curve M400. It is.
Therefore, since the value (about 5 mT) indicated by the curve M200 is about 1/4 of the reference value (about 22 mT) indicated by the curve M0, the position corresponding to the 0 mm position on the horizontal axis of the curve M200 (positions P1 to Y) The position P2 is a position separated by 200 mm in the direction).
In this case, since the separation distance between the position P1 and the position P2 is 200 mm, the “distance D” for the magnet 5 in this embodiment is determined as “200 mm”.

In this embodiment, the conclusion that the “distance D” is “200 mm” is that the first magnetizing step 101 and the first additional magnetization using the magnet 5 in this embodiment according to the example of FIGS. 26 to 33 described above. When the magnetic step 101A is performed, the magnetic flux density is reduced to 1 / percent by performing the first additional magnetization at a position separated by “200 mm” or more in the longitudinal direction (Y direction) of the crossed reinforcing bar 3 from the position where the first magnetization is performed. This is consistent with the conclusion that it can be reduced to 2 or less.
Further, as described above, the most distant position in the longitudinal direction of the crossed reinforcing bar 3 where the first additional magnetization can be effectively performed is not necessarily clear, but at least from the examples of FIG. 30 and FIG. When the first additional magnetization is performed at a position separated by 600 mm from the position where one magnetization is performed, the effect of reducing the magnetic flux density is sufficiently exhibited. In this embodiment, the “distance D” is “200 mm”. Therefore, at least “distance D + 400 mm” from the position where the first magnetization was performed
In the case where the first additional magnetization is performed at a separated position, it is considered that the effect of reducing the magnetic flux density is sufficiently exhibited.

  The above-mentioned “determination method of the distance D” is generally applicable to magnetizing magnets other than the magnet 5 of the present embodiment, and can be applied not only to permanent magnets but also to electromagnets. It can also be applied to a magnet unit in which a plurality of magnets are combined.

B-b-4: Second additional magnetization step 103A
As shown in FIG. 40, the second additional magnetization step is a step provided after the second magnetization step 103 described above.
First, the magnetized surface 5A of the magnet 5 is disposed close to the concrete body surface 1A so that the relative positions of both magnetic poles of the magnet 5 are the same as those in the first additional magnetizing step 101A, and then the magnet 5 is placed in the first position. The magnet 5 may be removed after the main rebar 2 and the crossed rebar 3 are re-magnetized by moving in the opposite direction on the orbit substantially the same as that of the 1 additional magnetizing step 101A.

According to the second additional magnetizing step 103A, the magnetic flux density from the crossed reinforcing bars 3 generated by the second magnetizing step 103 can be reduced.
That is, the moving trajectory of the magnet 5 in the first magnetizing step 101 and the second magnetizing step 103 is the same except that the moving direction of the magnet 5 is opposite, and the first additional magnetizing step 101A and Since the moving trajectory of the magnet 5 in the second additional magnetizing step 103A is the same except that the moving direction of the magnet 5 is reverse, the second additional magnetizing step 103A is performed to perform the second magnetization. It is possible to obtain the same effect as that of the first additional step 101A that the magnetic flux density generated from the crossed reinforcing bars 3 can be reduced by the step 103.

  In the first additional magnetization step 101A and the second additional magnetization step 103A, the second, third, and more additional magnetizations are performed as in the examples of FIGS. 9 to 11 described above. It is also possible to carry out continuously.

BB-5: Directional component and differential value of magnetic flux density Next, how the magnetic flux density appears in the first magnetic flux density measuring step 102 after the first additional magnetization step 101A will be described.

  In the second embodiment of the present invention, in order to increase the detection accuracy of the fracture portion H, for example, the magnetic flux 3A generated from the crossed reinforcing bar 3 from the measured value of the magnetic flux density obtained by the first magnetic flux density measuring step 102. Therefore, it is preferable to calculate a differential value or a differential approximation value of the magnetic flux density, and to thereby emphasize a sudden change in the magnetic flux density due to the fracture portion H. Can do.

With respect to the vertical component of the magnetic flux density represented by the curves B25, B50, and B75 in FIG. (Hereinafter also referred to as “curve B25d etc.”).
Further, when the main reinforcing bar 2 includes the fracture portion H, the differential values of the vertical components of the magnetic flux density represented by the curves G25, G50, G75, and G100 in FIG. , G75d and G100d (hereinafter also referred to as “curve G25d etc.”).

  Here, in the curve B25d or the like (FIG. 13) in the case where the main reinforcing bar 2 does not include the fracture portion H, a particularly large convex portion does not appear, whereas the main reinforcing bar 2 includes the fracture portion H. In the curved line G25d and the like (FIG. 17), a particularly large convex portion appears downward at the 0 mm position on the horizontal axis of the graph. Therefore, a threshold for determining whether or not the convex shape portion is caused by the fracture portion H is provided, and by comparing this threshold value with the peak value of the convex shape portion, it is easy and highly accurate. The presence or absence of the fracture portion H can be detected.

  In the second embodiment described above, the magnetic flux density on the concrete body surface 1A is measured by measuring the vertical component thereof, but can also be measured by measuring other arbitrary direction components. . As an example, an embodiment for measuring the horizontal component of the magnetic flux density on the concrete body surface 1A will be described next.

FIG. 14 shows the magnetic flux density along the longitudinal direction directly above the main reinforcing bar 2 on the concrete body surface 1A in the concrete body 1 in which the main reinforcing bar 2 without the breaking portion H and the seven crossed reinforcing bars 3 are embedded. It is a graph which shows the result of having measured a horizontal component.
Here, the horizontal axis of the graph represents the position in the X direction on the concrete body surface 1A, and the vertical axis represents the value of the horizontal component of the magnetic flux density at the position. In addition, the seven crossed reinforcing bars 3 are embed | buried in each position of -750mm, -500mm, -250mm, 0mm, 250mm, 500mm, 750mm of a graph horizontal axis like the example of FIG. Further, the diameters of the main reinforcing bars 2 and the crossed reinforcing bars 3 and the cover thickness of the concrete are the same as in the example of FIG.

As shown in FIG. 2, the curve E0 in FIG. 14 shows the longitudinal direction directly above the main rebar 2 on the concrete body surface 1A after moving the magnet 5 in the X direction and performing "first magnetization". It is the result of measuring the horizontal component of the magnetic flux density along.
In this curve E0, on the left and right of each position of the crossing reinforcing bar 3, an upward convex portion and a downward convex portion appear as a pair. For example, on the left and right sides of the crossed reinforcing bars 3 embedded in the 250 mm position on the horizontal axis of the graph, an upward convex shape portion appears at a position of about 200 mm, and a downward convex shape portion appears at a position of about 300 mm.

On the other hand, FIG. 18 shows, in the concrete body 1 in which the main reinforcing bar 2 having the broken portion H and the seven crossing reinforcing bars 3 are embedded, along the longitudinal direction directly above the main reinforcing bar 2 on the concrete body surface 1A. It is a graph which shows the result of having measured the horizontal component of the magnetic flux density.
Further, as shown in FIG. 2, the curve R0 in FIG. 18 indicates the longitudinal length directly above the main reinforcing bar 2 on the concrete body surface 1A after the magnet 5 is moved in the X direction and “first magnetization” is performed. It is the result of measuring the horizontal component of the magnetic flux density along a direction. Here, the position of the fracture portion H is the 0 mm position on the horizontal axis of the graph.

  In the curve R0, as in the case of the curve E0 in FIG. 14, the upward convex portion and the downward convex portion appear alternately. However, the horizontal direction of the magnetic flux density after the “first additional magnetization” is performed. In the curves R25, R50, R75 and R100 showing the components, the height difference of the convex portions appearing alternately becomes small, and the peak value of the upward convex portion at the position of 0 mm on the horizontal axis where the fracture portion H is present appears more clearly. ing. Therefore, it is possible to detect the presence or absence of the fracture portion H in the main reinforcing bar 2 depending on whether or not this peak value appears.

For the horizontal component of the magnetic flux density represented by the curves E25, E50 and E75 in FIG. It is also referred to as “curve E25d etc.”).
Further, with respect to the horizontal component of the magnetic flux density represented by the curves R25, R50, R75, and R100 in FIG. 18 when the main reinforcing bar 2 has the fracture portion H, the differential values thereof are represented by the curves R25d, R50d, R75d and R100d (hereinafter also referred to as “curve R25d etc.”).

In the curve E25d and the like in FIG. 15, upward convex portions and downward convex portions alternately appear, but the height difference between these convex portions is smaller than that of the curve E0d, and the entire curve E25d and the like. As a comparatively gentle curve.
On the other hand, in the curve R25d of FIG. 19 and the like, large upward convex portions and downward convex portions appear in pairs on the left and right of the position of the fracture portion H (0 mm position on the horizontal axis of the graph). Therefore, it is possible to detect the presence or absence of the fracture portion H in the main reinforcing bar 2 depending on whether or not such a pair of large convex portions appear.

As described above, in the second embodiment of the nondestructive inspection method of the present invention, in the measurement of the magnetic flux density in the first magnetic flux density measuring step 102, not only the vertical component of the magnetic flux density but also the component in an arbitrary direction is measured. By doing so, it is possible to detect the fracture H.
However, it is preferable to measure the vertical component of the magnetic flux density because the detection accuracy of the broken portion H of the main reinforcing bar 2 can be further increased. That is, when the differential value based on the vertical component of the magnetic flux density measured in the first magnetic flux density measuring step 102 is calculated and represented in the graph, the curved line G25d in FIG. As described above, at the position of the fracture portion H (0 mm position on the horizontal axis of the graph), only one large downward convex peak value appears. For this reason, in the comparison between the peak value and the threshold value, since erroneous recognition is not particularly likely to occur, it is possible to further increase the detection accuracy of the fracture portion H.

B-b-6: Synergistic effect of second magnetization and additional magnetization According to the second embodiment of the nondestructive inspection method of the present invention, the main rebar 2 to be inspected in the first magnetization step 101 and After magnetizing the cross rebar 3 that is not the object to be inspected, the first additional magnetization step 101A is performed, whereby the magnetic fluxes generated from the main rebar 2 and the cross rebar 3 magnetized in the first magnetization step 101, respectively. Of the densities, the magnetic flux density from the crossing reinforcing bars 3 can be significantly reduced.
Similarly, after the main reinforcing bar 2 and the crossed reinforcing bar 3 are magnetized in the second magnetizing step 103, the second additional magnetizing step 103A is performed, so that the main reinforcing bar 2 magnetized in the second magnetizing step 103 is obtained. Among the magnetic flux densities of the magnetic fluxes respectively generated from the cross reinforcing bars 3, the magnetic flux density from the cross reinforcing bars 3 can be remarkably reduced.

Therefore, in the non-inspection object magnetic flux removal step 105, when the magnetic flux density from the crossed reinforcing bar 3 is canceled and removed by adding both magnetic flux densities measured by the first magnetic flux density measurement step 102 and the second magnetic flux density measurement step 104, Since the magnetic flux density from the crossing rebar 3 included in both magnetic flux densities can be greatly reduced in advance, the magnetic flux density from the crossing rebar 3 can be surely canceled by this synergistic effect.
Therefore, the change state of the magnetic flux density from the inspection target reinforcing bar 2 can be more accurately determined, and the presence / absence of the fracture portion H can be detected with extremely high accuracy.

C: Nondestructive inspection apparatus FIG. 41 is a schematic configuration diagram of the nondestructive inspection apparatus of the present invention.
The nondestructive inspection apparatus is a magnet separate from the main body 20, and both magnetic poles are arranged along the longitudinal direction of the rebar 2 to be inspected, and the magnetized surface 5 </ b> A is disposed close to the concrete body surface 1 </ b> A to be inspected. The magnet 5 (refer FIG. 2 and FIG. 3) which magnetizes the test | inspection reinforcement 2 etc. by moving along the longitudinal direction of the reinforcement 2 is provided.

The nondestructive inspection apparatus (main body) 20 includes a magnetic detection unit 210, and the magnetic detection unit 210 is provided with a magnetic sensor 211 that detects a detection signal based on the magnetic flux density on the concrete body surface 1A.
The magnetic sensor 211 has a first detection signal based on the magnetic flux density generated when the magnet 5 is moved in the forward direction by the track and the magnetic flux density generated when the magnet 5 is moved in the reverse direction by the track. And a function of detecting the second detection signal based thereon.

Further, the nondestructive inspection apparatus (main body) 20 calculates a magnetic flux density along the longitudinal direction of the reinforcing bar 2 to be inspected on the concrete body surface 1A from the detection signal detected by the magnetic sensor 211. Is provided.
The calculation unit 220 calculates the magnetic flux density along the longitudinal direction of the inspection target reinforcing bar 2 on the concrete body surface 1A from the first and second detection signals, and further adds both of these magnetic flux densities. Thus, it has a function of canceling and removing the magnetic flux density from the non-inspected object by obtaining the sum of both magnetic flux densities.

Furthermore, the nondestructive inspection device (main body) 20 is based on the sum of the two magnetic flux densities calculated by the calculation unit 220 and detects the presence or absence of the rupture portion H of the rebar 2 to be inspected (rupture determination means). 230.
Further, the nondestructive inspection device (main body) 20 preferably includes a memory 250 that holds and reads / writes various data used in detecting a broken portion.

Hereinafter, each component of the nondestructive inspection apparatus will be described.
The magnet 5 magnetizes the main reinforcing bar 2 and the crossed reinforcing bar 3 embedded in the concrete body 1, and as described above, the first magnetizing step 101, the first additional magnetizing step 101A, and the second magnetizing. Used in step 103 and second additional magnetization step 103A.
For example, in the first magnetization step 101, as shown in FIG. 2, the magnet 5 is disposed close to the concrete body surface 1A so that both magnetic poles are along the longitudinal direction of the main reinforcing bar 2, and then forward (X direction). Move to. In the second magnetizing step, as shown in FIG. 3, the magnet 5 is arranged close to the concrete body surface 1A so that the relative positions of both magnetic poles are the same as in the forward movement, A trajectory that is substantially the same as the trajectory when moving in the direction is moved in the reverse direction (−X direction).

Next, the magnetism detection unit 210 is disposed close to the concrete body surface 1A after the magnet 5 is removed, and measures the magnetic flux density from the main reinforcing bar 2, the crossed reinforcing bar 3, and the like. The magnetic detection unit 210 includes a magnetic sensor 211, and detects a detection signal based on the magnetic flux density on the concrete body surface 1A.
Here, among the detection signals detected by the magnetic sensor 211, the magnet 5 is moved in the forward direction along the longitudinal direction of the main reinforcing bar 2 in the first magnetization step 101 and the first additional magnetization step 101A. The detection signal obtained in this case is referred to as “first detection signal”. Further, a detection signal obtained when the magnet 5 is moved in the opposite direction in the second magnetizing step 103 and the second additional magnetizing step 103A in substantially the same orbit as that of the first magnetizing step 101 is referred to as “second”. Is called a "detection signal".
The magnetic sensor 211 is a highly sensitive MI sensor, fluxgate sensor, Hall element, superconducting quantum interference element, or the like.

Further, since the distance traveled by the magnetic detection unit 210 can be measured by incorporating the distance sensor 212 into the magnetic detection unit 210, the position of the magnetic detection unit 210 and the magnetic flux density at that position can be calculated.
When the nondestructive inspection apparatus (main body) 20 according to the present invention has a high-precision positioning mechanism, the position of the magnetic detection unit 210 and the magnetic flux density at the position are detected without the distance sensor 212. can do.

Next, the calculation unit 220 calculates the magnetic flux density along the longitudinal direction of the main reinforcing bar 2 on the concrete body surface 1A from the detection signal detected by the magnetic sensor 211, and generates a graph of the calculated magnetic flux density. To do.
For example, when the detection signal detected by the magnetic sensor 211 is the “first detection signal”, the calculation unit 220 has a vertical component of the magnetic flux density along the longitudinal direction of the main rebar 2 on the concrete body surface 1A. As shown in FIG. 4, the curve S1 in FIG. 4 (when the main reinforcing bar 2 has no fracture portion) or the curve D1 in FIG. 7 (when the main reinforcing bar 2 has a fracture portion) is generated. Similarly, when the detection signal detected by the magnetic sensor 211 is the “second detection signal”, the calculation unit 220 has the curve S2 in FIG. 4 (when the main reinforcing bar 2 has no fracture portion) or FIG. Curve D2 (when the main reinforcing bar 2 has a fracture portion) is generated.

Further, the arithmetic unit 220 adds the vertical component (curve S1 or D1) of the magnetic flux density based on the first detection signal and the vertical component (curve S2 or D2) of the magnetic flux density based on the second detection signal. It has a function of calculating the sum of both magnetic flux densities and further dividing the sum by 2 to calculate an average value. The curve S3 in FIG. 4 (when the main rebar 2 has no fracture portion) or the curve D3 in FIG. If there is a broken part in the
In this way, by obtaining the average value of the vertical components of both magnetic flux densities calculated based on the first and second detection signals, the influence of the magnetic flux density due to the crossing reinforcing bars 3 is eliminated or greatly reduced. The change state of the vertical component of the magnetic flux density from the reinforcing bar 2 can be accurately determined. Therefore, the presence or absence of the rupture portion H in the main reinforcing bar 2 can be detected with high accuracy.

  Moreover, it is desirable that the calculation unit 220 has a function of calculating a differential value of an average value of both magnetic flux densities and generating a graph. Thereby, for example, the curve T3 of FIG. 21 showing the differential value of the curve D3 of FIG. 7 can be generated, and in the vicinity of the 0 mm position on the horizontal axis where the fracture portion H exists in the curve T3, the vertical axis of the graph Since the large peak value J3 can be expressed in the minus direction, the presence or absence of the fracture portion H of the main reinforcing bar 2 can be accurately detected by comparing the peak value J3 with a preset threshold value.

Next, the fracture determination unit 230 determines whether or not the fracture portion H is included in the main reinforcing bar 2 based on the average value of both magnetic flux densities calculated by the calculation unit 220 and information on the differential value thereof. At the same time, the position of the fracture portion H in the main reinforcing bar 2 is specified.
When determining the presence or absence of the rupture part H from the average value of both magnetic flux densities, a curve of the change in magnetic flux density indicating this (S3 in FIG. 4 when there is no rupture part H, D3 in FIG. 7 when there is a rupture part H) ), If a large change in magnetic flux density is recognized, it can be determined that the main reinforcing bar 2 has a fracture H.
Further, when determining the presence or absence of the rupture portion H from the differential value of the average value of both magnetic flux densities, the differential value calculated by the calculation unit 220 is compared with a predetermined threshold value, and the differential value exceeds the threshold value. In addition, it can be determined that the main reinforcing bar 2 has the fracture portion H. In the present embodiment, information regarding the threshold value is held in the memory 250.
In addition, you may obtain | require a differential approximate value instead of the above-mentioned differential value, and in that case, for example, two magnetic sensors 211 which are separated from each other by a predetermined distance are used, and detection signals obtained from the respective magnetic sensors are used. What is necessary is just to calculate the difference of the magnetic flux density based on.

The display unit 240 displays a graph of magnetic flux density generated by the arithmetic unit 220 and a graph of differential values of magnetic flux density.
In addition, although embodiment of the above-mentioned nondestructive inspection apparatus calculates the vertical component of magnetic flux density, you may calculate the other direction component of magnetic flux density, for example, a horizontal component.
Further, the invention of the present application is not limited to the above-described embodiment, and design changes and additions are permitted without departing from the gist of the invention according to each claim of the claims.

  The nondestructive inspection method and nondestructive inspection apparatus of the present invention can be used for nondestructive inspection for detecting the presence or absence of a broken portion of a reinforcing bar provided in a concrete body such as a bridge, a building, or a concrete pole.

DESCRIPTION OF SYMBOLS 1 Concrete body 1A Concrete body surface 2 Main rebar 2A Magnetic flux generated inside magnetized main rebar 3 Cross rebar 3A Magnetic flux generated from magnetized cross rebar 4A Magnet trajectory 5 Magnet 5A Magnetized surface 101 First magnetizing step 101A 1st additional magnetization process 102 1st magnetic flux density measurement process 103 2nd magnetization process 103A 2nd additional magnetization process 104 2nd magnetic flux density measurement process 105 Non-inspection magnetic flux removal process 106 Breaking part detection process 20 Nondestructive inspection device (Body)
210 Magnetic detection unit 211 Magnetic sensor 220 Calculation unit (calculation means)
230 Break determination unit (break determination means)
240 display portion 250 memory C center line of both magnetic poles H broken portion

Claims (9)

By magnetizing the inspected reinforcing bar from the outside of the concrete body in which the inspected reinforcing bar is embedded, and then measuring the magnetic flux density outside the concrete body by a magnetic sensor, the presence or absence of a fracture portion of the inspected reinforcing bar is determined. A non-destructive inspection method to detect,
The magnetized surface of the magnet is placed close to the surface of the concrete body so that both magnetic poles of the magnet are along the longitudinal direction of the inspection object reinforcing bar, and then the magnet is moved along the longitudinal direction of the inspection object reinforcing bar. A first magnetizing step of removing the magnet after magnetizing the rebar to be inspected by
A first magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then the magnet is substantially the same as the first magnetizing step. A second magnetization step of moving the same trajectory in the opposite direction and re-magnetizing the rebar to be inspected, and then removing the magnet;
A second magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
A non-inspection magnetic flux removal step of canceling and removing the magnetic flux density from the non-inspection object by adding both of the magnetic flux densities measured in the first and second magnetic flux density measurement steps to obtain a sum of both magnetic flux densities; ,
A nondestructive inspection method, comprising: a fracture portion detection step of detecting the presence or absence of a fracture portion of the inspected reinforcing bar based on the sum of both magnetic flux densities obtained by a non-inspection magnetic flux removal step. By magnetizing the reinforcing bars from the outside of the concrete body in which the inspection reinforcing bars and the crossing reinforcing bars that cross the inspection reinforcing bars are embedded, and then measuring the magnetic flux density outside the concrete body by a magnetic sensor, A non-destructive inspection method for detecting the presence or absence of a fracture portion of the inspection target reinforcing bar,
The magnetized surface of the magnet is placed close to the surface of the concrete body so that both magnetic poles of the magnet are along the longitudinal direction of the inspection object reinforcing bar, and then the magnet is moved along the longitudinal direction of the inspection object reinforcing bar. A first magnetizing step of removing the magnet after magnetizing both the reinforcing bars by
In a predetermined position separated from the position where the magnet is arranged in the first magnetizing step by a distance D or more determined by a “distance D determination method” described later in the width direction of the inspection reinforcing bar, the magnetized surface of the magnet is By placing the magnet close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then moving the magnet along the longitudinal direction of the rebar to be inspected A first additional magnetization step of removing the magnet after magnetizing the rebars again;
A first magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first magnetizing step, and then the magnet is substantially the same as the first magnetizing step. A second magnetizing step of moving the same track in the opposite direction and magnetizing the rebars again, and then removing the magnets;
The magnetized surface of the magnet is arranged close to the surface of the concrete body so that the relative positions of both magnetic poles of the magnet are the same as in the first additional magnetization step, and then the magnet is placed in the first additional magnetization step. And a second additional magnetization step of removing the magnet after moving the same orbit in the opposite direction and magnetizing the rebars again,
A second magnetic flux density measuring step of measuring the magnetic flux density along the longitudinal direction of the rebar to be inspected by appropriately moving or after moving the magnetic sensor close to the surface of the concrete body; and
By adding both of the magnetic flux densities measured in the first and second magnetic flux density measurement steps to obtain the sum of both magnetic flux densities, the magnetic flux density from the cross reinforcing bars and other non-inspected objects is canceled out. Inspection magnetic flux removal process,
A nondestructive inspection method, comprising: a fracture portion detection step of detecting the presence or absence of a fracture portion of the inspected reinforcing bar based on the sum of both magnetic flux densities obtained by a non-inspection magnetic flux removal step.
[Determination method of distance D]
When the S-pole side direction in the straight line connecting the center portions of both magnetic poles of the magnet is the X direction, the magnetized surface of the magnet is parallel to the magnetized surface when facing downward, and the left side in the X direction The direction perpendicular to the Y direction is the Y direction, the direction perpendicular to the X direction and the Y direction, and the direction of the magnetized surface side of the magnet is the Z direction.
In such a case, the position separated from the magnetized surface of the magnet by 100 mm from the center position of the straight line connecting the central portions of the two magnetic poles of the magnet in the Z direction is defined as P1, and separated from the position P1 in the Y direction, A position where the X direction component of the magnetic flux density shows a value of about ¼ of the X direction component of the magnetic flux density at the position P1 is determined as P2, and the separation distance between the position P1 and the position P2 is determined as “distance D”. In the first and second magnetic flux density measurement steps, the vertical component of the magnetic flux density along the longitudinal direction of the test reinforcing bar is measured,
In the non-inspection magnetic flux removal step, by adding both vertical components of the magnetic flux density measured in the first and second magnetic flux density measurement steps, a sum of both magnetic flux densities is obtained, thereby The nondestructive inspection method according to claim 1 or 2, wherein the vertical component of the magnetic flux density from the inspection object is canceled out.   In the fracture portion detection step, the differential value of the sum of the two magnetic flux densities or the average value of the two magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2 is calculated, and these differential values are provided in advance. The non-destructive inspection method according to any one of claims 1 to 3, wherein the presence or absence of a fracture portion of the inspection target reinforcing bar is detected by comparing with a determined threshold value.   In the broken portion detection step, the differential approximation of the sum of the two magnetic flux densities or the differential approximation of the average of the two magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2 is calculated. The non-destructive inspection method according to claim 1, wherein the presence or absence of a fracture portion of the inspection target reinforcing bar is detected by comparing a predetermined threshold value with a predetermined threshold value. By magnetizing the inspected reinforcing bar from the outside of the concrete body in which the inspected reinforcing bar is embedded, and then measuring the magnetic flux density outside the concrete body by a magnetic sensor, the presence or absence of a fracture portion of the inspected reinforcing bar is determined. A non-destructive inspection device for detecting,
Both magnetic poles are arranged along the longitudinal direction of the inspected reinforcing bar so that the magnetized surface is arranged close to the surface of the concrete body and the relative position of both magnetic poles is not changed. A magnet that magnetizes the rebar to be inspected by moving substantially the same trajectory in the forward and reverse directions,
A magnetic sensor for detecting a detection signal based on the magnetic flux density by placing it close to the surface of the concrete body and moving it appropriately or without moving;
An arithmetic means for calculating a magnetic flux density along a longitudinal direction of the inspection reinforcing bar on the surface of the concrete body from a detection signal detected by the magnetic sensor;
Rupture determination means for detecting the presence or absence of a rupture portion of the rebar to be inspected based on the magnetic flux density calculated by the calculation means,
The magnetic sensor is based on a first detection signal based on a magnetic flux density generated when the magnet is moved in the forward direction by the track and a magnetic flux density generated when the magnet is moved in the reverse direction by the track. Detecting a second detection signal;
The calculation means calculates a magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected on the surface of the concrete body from the first and second detection signals, and further adds both of these magnetic flux densities. By canceling out the magnetic flux density from the non-inspected object,
The nondestructive inspection apparatus, wherein the break determination means detects the presence or absence of a broken portion of the inspection target reinforcing bar based on the sum of both magnetic flux densities. The computing means calculates a vertical component of the magnetic flux density along the longitudinal direction of the rebar to be inspected on the surface of the concrete body from the first and second detection signals, respectively, and further, the vertical component of these magnetic flux densities By adding both of these, the vertical component of the magnetic flux density from the non-inspected object is canceled out by calculating the sum of both magnetic flux densities.
The nondestructive inspection apparatus according to claim 6, wherein the break determination means detects the presence or absence of a broken portion of the inspection target reinforcing bar based on the sum of the two magnetic flux densities. The computing means further calculates a differential value of the sum of the two magnetic flux densities or an average value of the two magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2.
The nondestructive inspection apparatus according to claim 6 or 7, wherein the fracture determination means compares these differential values with a predetermined threshold value to detect the presence or absence of a fracture portion of the inspection target reinforcing bar. The computing means further calculates a differential approximation of the sum of the two magnetic flux densities or a differential approximation of the average of the two magnetic flux densities obtained by dividing the sum of the two magnetic flux densities by 2.
The nondestructive inspection apparatus according to claim 6 or 7, wherein the fracture determination means compares these differential approximation values with a predetermined threshold and detects the presence or absence of a fracture portion of the inspection target reinforcing bar. .