Non-destructive testing methods

Abstract

To provide a nondestructive inspection method capable of accurately detecting presence or absence of a fracture portion of a steel bar to be inspected.SOLUTION: A nondestructive inspection method detects presence or absence of a fracture portion of inspection object steel bars 21 to 25 embedded in a concrete body 1 from outside of the concrete body 1, and includes: a magnetization step for magnetizing the inspection object steel bars 21 to 25 and a cross steel bar 3; a post-demagnetization magnetic flux density measuring step for demagnetizing the cross steel bar 3 at a position near a surface of the concrete body 1 by using an AC type demagnetization device and measuring magnetic flux density of the inspection object steel bars 21 to 25 by a magnetic sensor after completion of a demagnetization step to prepare a post-demagnetization magnetic flux density graph; and a fracture portion detection step for detecting presence or absence of a fracture portion of the inspection object steel bars 21 to 25 based on the post-demagnetization magnetic flux density graph. Since detection of presence or absence of the fracture portion of the inspection object steel bars 21 to 25 is performed based on the post-demagnetized magnetic flux density graph from which influence of magnetic force of the cross steel bar 3 is eliminated, the fracture portion can be accurately detected.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a non-destructive inspection method for detecting the presence or absence of a broken part of a reinforcing bar provided in a reinforced concrete structure such as a bridge, a building, or a concrete pole.

Background Art

[0002] Conventionally, a non-destructive inspection method for detecting a broken part of a reinforcing bar provided in concrete has been known. For example, the non-destructive inspection method described in Japanese Patent Application Laid-Open No. 2006-177747 (Patent Document 1) magnetizes a reinforcing bar by moving a permanent magnet along the longitudinal direction of the reinforcing bar to be inspected embedded in concrete on the surface of the concrete, and then measures the magnetic flux density leaking from the surface of the concrete, and further calculates the differential value of the obtained measurement value to detect the presence or absence of a break in the reinforcing bar.

[0003] However, generally, magnetic bodies having different positions and arrangement directions are embedded in the concrete body. Therefore, when the magnetism of the reinforcing bar to be inspected is detected by a magnetic sensor outside the concrete body, the magnetism from magnetic bodies other than the reinforcing bar to be inspected is also detected at the same time. However, in the non-destructive inspection method described in Patent Document 1, since there is no means for removing the influence of the magnetism emitted from magnetic bodies other than the reinforcing bar to be inspected, there is a risk of lacking accuracy in detecting the broken part. Here, the magnetic body is a member having a property that can be magnetized by a magnet, and specifically, crossing reinforcing bars, reinforcing bars such as main reinforcing bars, which are located at a shallower position of the concrete covering than the reinforcing bar to be inspected, separators for maintaining the reinforcing bar interval, PC sheaths into which PC steel materials are inserted, PC sheath couplers, accessories of PC steel materials such as PC steel material support fittings, metal fittings embedded in the concrete body, binding wires (wires) for binding reinforcing bars, metal pipes such as electric wire pipes and drain pipes, etc. correspond to this.

[0004] Furthermore, Japanese Patent Publication No. 2013-130452 (Patent Document 2) describes a non-destructive testing method in which a magnet is moved along the longitudinal direction of the reinforcing bar to be inspected embedded in concrete on the surface of the concrete to magnetize the reinforcing bar to be inspected, then the magnet is moved again along the longitudinal direction of the reinforcing bar to be inspected at a position a certain distance away from the position where the reinforcing bar to be inspected was magnetized, and then the presence or absence of fracture of the reinforcing bar to be inspected is detected by measuring the magnetic flux density leaking from the surface of the concrete.

[0005] This inspection method can reduce the magnetic field generated from the reinforcing bar during magnetization, which can hinder accurate detection of fractures, especially when the concrete cover over the reinforcing bar is shallow, causing the magnet to get too close to the reinforcing bar. However, it does not mention whether the method can eliminate the influence of magnetic fields emitted from sources other than the reinforcing bar being inspected.

[0006] Furthermore, Japanese Patent Publication No. 2015-42975 (Patent Document 3) describes a non-destructive testing method that includes a first magnetization step of moving a magnet along the longitudinal direction of the reinforcing bar to be inspected to magnetize the reinforcing bar; a first magnetic flux density measurement step of measuring the magnetic flux density on the surface of the concrete body thereafter; a second magnetization step of moving the magnet in the opposite direction to the first magnetization step to magnetize the reinforcing bar; a second magnetic flux density measurement step of measuring the magnetic flux density on the surface of the concrete body thereafter; a non-inspection object magnetic flux removal step of adding up both magnetic flux densities measured in the first and second magnetic flux density measurement steps to obtain the sum of both magnetic flux densities and canceling out the magnetic flux density from the non-inspection object; and a fracture detection step of detecting the presence or absence of fractures in the reinforcing bar based on the sum of both magnetic flux densities obtained in the non-inspection object magnetic flux removal step.

[0007] However, in this non-destructive testing method, the magnetic flux densities measured in the first and second magnetic flux density measurement steps are added together to obtain the sum of both magnetic flux densities, and the magnetic flux density from the object not being inspected is canceled out. Therefore, the process of removing the magnetic flux density is complicated, which may lead to higher inspection costs. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2006-177747 [Patent Document 2] Japanese Patent Publication No. 2013-130452 [Patent Document 3] Japanese Patent Publication No. 2015-042975 [Overview of the project] [Problems that the invention aims to solve]

[0009] As mentioned above, conventional non-destructive testing methods have problems such as being unable to eliminate the influence of magnetism emitted from reinforcing bars other than the target reinforcing bar, or the cost of eliminating such influence being high, thus posing challenges in ensuring the accuracy of fracture detection.

[0010] Therefore, the present invention aims to provide a non-destructive testing method that can detect the presence or absence of fractures with extreme accuracy by reducing the influence of magnetic materials such as cross reinforcement bars, which are generally installed in large quantities and are positioned approximately perpendicular to the reinforcement bars being inspected, and by utilizing the properties of changes in magnetic flux density that characteristically appear when the reinforcement bars being inspected have fractures. Technical background of the present invention

[0011] The present invention involves magnetizing the reinforcing bar to be inspected and the magnetic material, which are embedded in the concrete body and located closer to the surface of the concrete body than the reinforcing bar to be inspected, using a magnet from the outside of the concrete body, and then measuring the magnetic flux density on the outside of the concrete body with a magnetic sensor to detect the presence or absence of fractures in the reinforcing bar to be inspected. However, there are three background technologies that serve as prerequisites for detecting the presence or absence of fractures in the reinforcing bar to be inspected.

[0012] One such characteristic is the peculiarity of magnetic flux density when there is a fracture in the reinforcing bar being inspected. Specifically, if a magnet is moved along the longitudinal direction of the reinforcing bar to be inspected and magnetized, and the magnetic flux density in a direction perpendicular to the magnet's movement plane is measured with a magnetic sensor, a magnetic flux density graph showing an upward trend is obtained. However, at the fracture in the reinforcing bar being inspected, the flow of magnetic flux within the reinforcing bar is interrupted at the fracture. As a result, at this fracture, the polarity of the magnetic flux changes abruptly from the polarity upstream of the fracture (e.g., north pole) to the polarity downstream (e.g., south pole). This abrupt change in polarity allows for the determination that "a fracture is present."

[0013] The next factor is the influence of magnetic flux density emitted from intersecting reinforcing bars (i.e., magnetic materials) that intersect with the reinforcing bar being inspected. When a magnet is moved along the longitudinal direction of the reinforcing bar being inspected to magnetize it, if there are intersecting reinforcing bars that intersect with the reinforcing bar being inspected at a close position, the intersecting reinforcing bar will inevitably be magnetized as well when the reinforcing bar is magnetized by the magnet, and magnetic flux will be generated. This magnetic flux density generated by the intersecting reinforcing bar affects the magnetic flux density generated in the reinforcing bar being inspected, and in the area corresponding to the intersecting reinforcing bar, the magnetic flux density of the reinforcing bar being inspected will change in a valley-like or mountain-like pattern, corresponding to the polarity of the intersecting reinforcing bar.

[0014] However, in a magnetic flux density graph, it is difficult to distinguish from the shape of the graph the portion of the magnetic flux change caused by the fracture of the reinforcing bar under inspection and the portion of the magnetic flux density change caused by the magnetization of the intersecting reinforcing bars. Therefore, in order to improve the accuracy of determining whether or not the reinforcing bar under inspection is fractured, it is considered effective to minimize the influence of the magnetic flux caused by the magnetization of the intersecting reinforcing bars on the magnetic flux generated from the reinforcing bar under inspection, thereby improving the ability to confirm the portion of the magnetic flux change caused by the fracture of the reinforcing bar under inspection.

[0015] The last point concerns the demagnetization characteristics of AC-type demagnetizers. These AC-type demagnetizers are equipped with a demagnetizing coil that uses an AC power source, and the strong magnetic field generated by this coil demagnetizes the magnetized material. However, because this demagnetizer is AC-type, it has the characteristic that the demagnetization effect decreases rapidly the further you are from the internal demagnetizing coil. Moreover, the distance over which the demagnetization effect is exerted can be adjusted by adjusting the frequency and strength of the AC power supply flowing through the demagnetizing coil. Therefore, by making these adjustments, it is possible to demagnetize only the magnetic material located at a shallow depth from the concrete surface (i.e., close to the demagnetizing coil), that is, "selective demagnetization".

[0016] In other words, by utilizing the demagnetization characteristics of this AC-type demagnetizer, only magnetic materials with little cover from the concrete surface can be reliably demagnetized without affecting the magnetism of the reinforcing bars being inspected, which are located deeper within the concrete. As a result, the influence of the magnetic flux emitted from the magnetic materials on the magnetic flux density of the reinforcing bars being inspected can be reduced as much as possible.

[0017] Based on this background technology, the inventor of this invention has conceived of a technology that significantly reduces the influence of magnetic flux from magnetic materials, thereby enabling accurate and easy detection of fractures in reinforcing bars under inspection. [Means for solving the problem]

[0018] The present invention employs the following configuration as a specific means to solve the above-mentioned problems.

[0019] The first invention of this application provides a non-destructive testing method for detecting the presence or absence of fractures in a concrete bar, wherein a reinforcing bar to be inspected is embedded in a concrete body, and a magnetic material is embedded closer to the surface of the concrete body than the reinforcing bar to be inspected is magnetized from the outside of the concrete body using a magnet, and then the magnetic flux density on the outside of the concrete body is measured using a magnetic sensor, wherein the magnetized surface of the magnet is positioned close to the surface of the concrete body such that both magnetic poles of the magnet are aligned along the longitudinal direction of the reinforcing bar to be inspected, and then the magnet is moved along the longitudinal direction of the reinforcing bar to be inspected to magnetize the reinforcing bar and the magnetic material, and then the magnet is removed, and the magnetization process The method is characterized by including: a demagnetization step in which, after the completion of the above process, an AC-type demagnetizing device is placed close to the surface of the concrete body and moved as appropriate, or without moving, to demagnetize the magnetic material located close to the surface of the concrete body; a post-demagnetization magnetic flux density measurement step in which, after the completion of the demagnetization step, the magnetic sensor is placed close to the surface of the concrete body and moved as appropriate, or without moving, to measure the magnetic flux density of the reinforcing bar to be inspected, and a post-demagnetization magnetic flux density graph of the reinforcing bar to be inspected is created from the measurement results; and a fracture detection step in which the presence or absence of fractures in the reinforcing bar to be inspected is detected based on the post-demagnetization magnetic flux density graph obtained in the post-demagnetization magnetic flux density measurement step.

[0020] In the magnetization process of this first invention, when magnetizing the reinforcing bar to be inspected, in order to position the magnetized surface of the magnet close to the surface of the concrete body, it is sufficient to temporarily bring the magnetized surface of the magnet close to a predetermined position near the surface of the concrete body, and it is not necessarily required to directly contact the surface of the concrete body with the magnetized surface, nor is it necessary to keep it stationary.

[0021] Furthermore, the magnetized surface of the magnet refers to the side of the magnet that is closest to the concrete body when magnetizing the reinforcing bar being inspected. This magnetized surface only needs to have both magnetic poles aligned along the longitudinal direction of the reinforcing bar being inspected, and its shape is not limited to a single plane.

[0022] On the one hand, in the demagnetization process, an alternating current demagnetization device is used. For example, a demagnetization device equipped with a demagnetization coil through which an AC power supply of 100 V with a frequency of 50 Hz and a rated current of 3 A, or a frequency of 60 Hz and a rated current of 2.5 A flows can be used, and it is desirable that the power supply frequency and current value are adjustable.

[0023] In addition, in the demagnetization process, it is common practice to perform demagnetization by placing the above demagnetization device close to the surface of the concrete body and appropriately moving it. Performing demagnetization without moving the demagnetization device is limited to cases such as performing spot demagnetization on specific parts.

[0024] Furthermore, in the post-demagnetization magnetic flux density measurement process, to place the magnetic sensor close to the surface of the concrete body, similar to the case of the above magnet, the magnetic sensor can be temporarily brought close to a predetermined position near the surface of the concrete body, and there is no need to directly contact the surface of the concrete body, nor is there a need to keep it stationary. Various known magnetic sensors can be used as the magnetic sensor. For example, a Hall element sensor, an MR sensor, a MI sensor, a TMR sensor, etc. can be used as the magnetic sensor.

[0025] In the second invention of the present application, in the non-destructive inspection method according to the first invention, after the magnetization process is completed, the magnetic sensor is placed close to the surface of the concrete body, and by appropriately moving it or without moving it, the magnetic flux density of the inspection target reinforcing bar is measured, and a post-magnetization magnetic flux density graph of the inspection target reinforcing bar is created from this measurement result. In the breakage detection process, based on the post-demagnetization magnetic flux density graph obtained in the post-demagnetization magnetic flux density measurement process and the post-magnetization magnetic flux density graph obtained in the post-magnetization magnetic flux density measurement process, the presence or absence of a breakage in the inspection target reinforcing bar is detected.

Effects of the Invention

[0026] (a) According to the non-destructive testing method of the first invention of the present application, in the magnetization step, the reinforcing bars to be inspected and the magnetic material are magnetized, in the demagnetization step, the magnetic material located near the surface of the concrete body is demagnetized, and thereafter, in the post-demagnetization magnetic flux density measurement step, the magnetic flux density of the reinforcing bars to be inspected is measured by a magnetic sensor, and a post-demagnetization magnetic flux density graph of the reinforcing bars to be inspected is created from this measurement result. Then, in the fracture detection step, the presence or absence of fractures in each of the reinforcing bars to be inspected is detected based on the post-demagnetization magnetic flux density graph. At this time, in the post-demagnetization magnetic flux density graph, the influence of the magnetic flux density generated from the magnetic material is reduced as much as possible due to the demagnetization action in the demagnetization step, and the post-demagnetization magnetic flux density graph is flattened, so that the portion of the magnetic flux density that changes abruptly due to the fracture of the reinforcing bars to be inspected can be easily and accurately detected, thereby improving the reliability of the fracture inspection.

[0027] (b) In the non-destructive testing method according to the second invention of the present application, after magnetization is completed in the magnetization step, the magnetic flux density of the reinforcing bar to be inspected is measured in the post-magnetization magnetic flux density measurement step to create a post-magnetization magnetic flux density graph. Furthermore, in the fracture detection step, the presence or absence of a fracture in the reinforcing bar to be inspected is detected based on the post-demagnetization magnetic flux density graph obtained in the post-demagnetization magnetic flux density measurement step and the post-magnetization magnetic flux density graph obtained in the post-magnetization magnetic flux density measurement step. Therefore, when detecting the presence or absence of a fracture in the reinforcing bar to be inspected based on the post-demagnetization magnetic flux density graph, the positional information of the magnetic material can be taken into account based on the post-magnetization magnetic flux density graph, thereby improving the accuracy of detecting fractures in the reinforcing bar to be inspected. [Brief explanation of the drawing]

[0028] [Figure 1] This is a side view of a concrete body to which the non-destructive testing method according to the first embodiment of the present invention is applied. [Figure 2] This is an enlarged cross-sectional view AA of Figure 1. [Figure 3] This is a view along the BB arrow in Figure 2 (partially a cross-sectional view looking upwards). [Figure 4] Figure 3 is a cross-sectional view of CC. [Figure 5] Figure 3 is a cross-sectional view of the DD. [Figure 6] This graph shows the vertical component of the magnetic flux density on the bottom surface of the concrete body after the magnetization process according to the first embodiment of the present invention, for each reinforcing bar being inspected. [Figure 7] This graph shows the vertical component of the magnetic flux density on the bottom surface of the concrete body after the demagnetization process according to the first embodiment of the present invention, for each reinforcing bar being inspected. [Figure 8] This is a partial cross-sectional view (corresponding to Figure 3 in the first embodiment) of a concrete body to which the non-destructive testing method according to the second embodiment of the present invention is applied. [Figure 9] Figure 8 is an enlarged cross-sectional view of the EE. [Figure 10] Figure 8 is an enlarged cross-sectional view of the FF. [Figure 11] This graph shows the vertical component of the magnetic flux density on the bottom surface of the concrete body after the magnetization process according to the second embodiment of the present invention, for each reinforcing bar being inspected. [Figure 12] This graph shows the vertical component of the magnetic flux density on the bottom surface of the concrete body after the demagnetization process according to the second embodiment of the present invention, for each reinforcing bar being inspected. [Modes for carrying out the invention]

[0029] "First Embodiment" Figure 1 shows a concrete body 1 to which the non-destructive testing method according to the first embodiment of the present invention is applied. This concrete body 1 is used as a girder bridge and comprises a main body 1A that constitutes the road surface side and a lower flange portion 1B located below it. As shown in Figures 2 to 5, five reinforcing bars 21 to 25, which function as PC steel, are embedded in the lower flange portion 1B at a predetermined depth position (90 mm cover in this embodiment) from the bottom surface 1a, each inserted through a sheath pipe 20, parallel to the bottom surface 1a and at predetermined intervals in the width direction (85 mm pitch in this embodiment). These five reinforcing bars 21 to 25 constitute the group of reinforcing bars to be inspected 2.

[0030] Here, "reinforcement" is not limited to round steel bars with a circular cross-section or deformed steel bars with protrusions on the surface, which are commonly used in general reinforced concrete structures, but may also refer to steel materials with a rectangular or other polygonal cross-section, or H-beams. Furthermore, it may refer to hollow steel pipes used for water passage or ventilation, and may also refer to PC steel materials such as PC steel bars, PC steel wires, or PC steel strands used in prestressed concrete construction, or sheath pipes or PC steel materials inside sheath pipes through which these are passed.

[0031] Furthermore, at a predetermined depth position (in this embodiment, a position with a core cover of 50 mm) between the bottom surface 1a and the group of reinforcing bars 2 to be inspected, the horizontal portion 3a of the crossing reinforcing bar 3, which is an example of a magnetic material, is embedded at predetermined intervals (in this embodiment, unequal intervals of 120 to 340 mm) in the longitudinal direction of the group of reinforcing bars 2 to be inspected. Note that the ends of the horizontal portion 3a of the crossing reinforcing bar 3 are corner portions 3c, and a rising portion 3b is continuous with these corner portions 3c.

[0032] The lateral portion 3a of the above-mentioned group of reinforcing bars 2 and the above-mentioned intersecting reinforcing bars 3 are spaced 40 mm apart. When the reinforcing bars 21 to 25 of the group of reinforcing bars 2 are magnetized using the magnet 5 as described later, the lateral portion 3a of the intersecting reinforcing bars 3 will inevitably also be magnetized.

[0033] As described above, each of the reinforcing bars 21-25 embedded in the concrete body 1 is an extremely important element for ensuring the strength of the concrete body 1, and it is important to confirm whether or not they have fractured. Here, this is done by the non-destructive testing method according to the first embodiment described below.

[0034] "Structure of Non-Destructive Testing Methods" The above non-destructive testing method includes a magnetization step, a post-magnetization magnetic flux density measurement step, a demagnetization step, a post-demagnetization magnetic flux density measurement step, and a fracture detection step, and the inspection is performed using a magnet 5, a magnetic sensor 6, and a demagnetization device 7.

[0035] "Magnetization process" The magnetization process is a process of magnetizing the reinforcing bars to be inspected using the magnet 5 described above. The number of reinforcing bars to be magnetized may be one, or it may be each of the reinforcing bars in a group of reinforcing bars. In other words, this magnetization process is not limited by the number of reinforcing bars to be magnetized. In this embodiment, as shown in Figures 3 to 5, an example is given in which each of the reinforcing bars in a group of reinforcing bars 2 consisting of five reinforcing bars 21 to 25 is magnetized.

[0036] First, as shown in Figure 3, a magnet 5 is placed midway between the first reinforcing bar 21 and the second reinforcing bar 22, with the front side being the north pole and the front side being the south pole. Then, the magnet 5 is moved from the front side to the front side, and then moved from the front side to the front side while maintaining its polarity. During this one round trip of the magnet 5, the first reinforcing bar 21 and the second reinforcing bar 22, as well as the intersecting reinforcing bars 3 that cross them in the longitudinal direction, are magnetized.

[0037] Next, the magnet 5 is placed between the third reinforcing bar 23 and the fourth reinforcing bar 24, and it is moved back and forth once between the near side and the front side to magnetize the third reinforcing bar 23 and the fourth reinforcing bar 24.

[0038] Furthermore, the magnet 5 is placed to the right of the fifth reinforcing bar 25 to be inspected, and it is moved back and forth once between the front and back sides to magnetize the fifth reinforcing bar 25 to be inspected.

[0039] Furthermore, when the magnetization operation is performed on the reinforcing bars to be inspected from the first to the fifth reinforcing bars 25 using the magnet 5, the lateral portions 3a of each crossing reinforcing bar 3 are also magnetized at the same time. This magnetization of the crossing reinforcing bars 3 is performed as the magnet 5 passes over the lateral portions 3a of the crossing reinforcing bars 3. In this case, the lateral portions 3a are magnetized with the opposite pole of the magnet 5 to the pole that passed over them last, so the lateral portion 3a of the crossing reinforcing bar 3 near one end of the first reinforcing bar 21 is magnetized with the S pole, and the lateral portion 3a of the crossing reinforcing bar 3 near the other end of the first reinforcing bar 21 is magnetized with the N pole. Depending on the magnetic pole of each of these crossing reinforcing bars 3, the direction of change in the magnetic flux of the crossing reinforcing bars 3 in the magnetic flux density graph after magnetization (valley-shaped change and mountain-shaped change) is determined (see Figure 6).

[0040] "Magnetic flux density measurement process after magnetization" The post-magnetization magnetic flux density measurement process involves, after the completion of the magnetization process, positioning the magnetic sensor 6 close to the surface of the concrete body 1, and then measuring the magnetic flux density along the longitudinal direction of the reinforcement bar to be inspected, either by moving it as appropriate or without moving it. A post-magnetization magnetic flux density graph of the reinforcement bar to be inspected is then created from these measurement results.

[0041] Furthermore, this post-magnetization magnetic flux density measurement process, like the magnetization process described above, is not limited by the number of reinforcing bars to be inspected, and can be applied without any problems whether there is one reinforcing bar or multiple reinforcing bars to be inspected. In this embodiment, as shown in Figures 3 to 5, an example is given in which the magnetic flux density measurement operation is performed for each of the five reinforcing bars 21 to 25 in the group of reinforcing bars to be inspected.

[0042] Furthermore, in addition to the Z-axis direction perpendicular to the surface of the concrete body 1 (i.e., the moving surface of the magnetic sensor 6) (see Figure 4), the measurement direction for the magnetic flux density to be measured can also be the X-axis direction along the longitudinal direction of the reinforcement bar being inspected (see Figure 4), or the Y-axis direction along the width direction of the reinforcement bar being inspected (see Figure 4). It is arbitrary which of these three axial directions to adopt. In this embodiment, the Z-axis direction is adopted as the measurement direction for the magnetic flux density.

[0043] When measuring magnetic flux density, first, a magnetic sensor 6 is placed midway between the first reinforcing bar 21 and the second reinforcing bar 22. Then, the magnetic sensor 6 is moved from the near side to the front side, and then from the front side back to the near side, and the magnetic flux density of the first reinforcing bar 21 and the second reinforcing bar 22 is measured during one round trip of the magnetic sensor 6. At the same time, the magnetic flux density of the intersecting reinforcing bars 3 that intersect these in the longitudinal direction is also measured.

[0044] Next, the magnetic sensor 6 is placed between the third and fourth reinforcing bars 23 and 24, and it is moved back and forth once between the near and far sides to measure the magnetic flux density of the third and fourth reinforcing bars 23 and 24. This also measures the magnetic flux density of the intersecting reinforcing bars 3 that cross them in the longitudinal direction.

[0045] Furthermore, the magnetic sensor 6 is placed to the right of the fifth reinforcing bar 25 to be inspected, and it is moved back and forth once between the near side and the front side to measure the magnetic flux density of the fifth reinforcing bar 25 to be inspected. As a result, the magnetic flux density of the intersecting reinforcing bar 3 that intersects it in its longitudinal direction is also measured.

[0046] Furthermore, in this post-magnetization magnetic flux density measurement process, changing the order of the magnetic flux density measurement operations for the inspected reinforcing bars 21-25 will not affect the resulting post-magnetization magnetic flux density graph.

[0047] Figures 6(a) to (e) show the magnetic flux density graphs for each of the inspected reinforcing bars 21 to 25, as well as the magnetic flux density graphs for each of the inspected reinforcing bars 21 to 25, as well as the magnetic flux density graphs for the crossing reinforcing bars 3.

[0048] "Demagnetization process" In the above demagnetization process, an AC-type demagnetizing device is used to demagnetize the already magnetized magnetic material (in this embodiment, not the individual reinforcing bars 21-25 to be inspected, but the lateral portions 3a of the intersecting reinforcing bars 3 that are arranged at predetermined intervals (unequal intervals of 120-340 mm in this embodiment) in a direction perpendicular to the surface of the concrete body 1 (the Z-axis direction shown in Figures 4 and 5) relative to the individual reinforcing bars 21-25 to be inspected). The demagnetizing device 7 is equipped with a demagnetizing coil that uses a 100V AC power supply with a frequency of 60 Hz and a rated current of 2.5 A. In this case, the power supply frequency and applied current to the demagnetizing device 7 are set in advance so that only the depth portion of the lateral portions 3a of the intersecting reinforcing bars 3, which are covered by 50 mm from the surface of the concrete body 1, can be effectively demagnetized, and the demagnetizing effect does not extend to the individual reinforcing bars 21-25 to be inspected.

[0049] The above demagnetization operation is performed in three stages. Specifically, the demagnetization device 7 is placed midway between the first reinforcing bar 21 and the second reinforcing bar 22 to be inspected. First, the demagnetization device 7 is moved from the near side to the front side, and then again from the front side to the near side. During one round trip of this demagnetization device 7, the portion of the intersecting reinforcing bar 3 that intersects with the first reinforcing bar 21 and the second reinforcing bar 22 is demagnetized.

[0050] Next, the demagnetizing device 7 is placed between the third reinforcing bar 23 and the fourth reinforcing bar 24, and it is moved back and forth once between the front and back sides to demagnetize the intersection of the third reinforcing bar 23 and the fourth reinforcing bar 24.

[0051] Furthermore, the demagnetizing device 7 is placed to the right of the fifth reinforcing bar 25 to be inspected, and it is moved back and forth once between the front and back sides to demagnetize the intersection portion of the intersecting reinforcing bar 3 with the fifth reinforcing bar 25 to be inspected.

[0052] Furthermore, as mentioned above, this demagnetization process can demagnetize magnetic materials positioned across multiple reinforcing bars under inspection, as well as magnetic materials positioned in relation to a single reinforcing bar under inspection.

[0053] "Demagnetization and Magnetic Flux Density Measurement Process" In the demagnetized magnetic flux density measurement process, after the completion of the demagnetization process, the magnetic sensor 6 is placed close to the surface 1a of the concrete body 1, and then the magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected is measured by moving it as appropriate or without moving it, and a demagnetized magnetic flux density graph of the reinforcing bar to be inspected is created from this measurement result.

[0054] In this embodiment, as shown in Figures 3 to 5, three magnetic flux density measurements are performed on a group of five reinforcing bars 21 to 25 to be inspected. Specifically, a magnetic sensor 6 is placed midway between the first reinforcing bar 21 and the second reinforcing bar 22. First, the magnetic sensor 6 is moved from the near side to the front side, and then from the front side back to the near side. During this one round trip of the magnetic sensor 6, the magnetic flux density of the first reinforcing bar 21 and the second reinforcing bar 22 is measured. At the same time, the magnetic flux density of the intersecting reinforcing bars 3 that cross these bars in the longitudinal direction is also measured.

[0055] Next, the magnetic sensor 6 is placed between the third and fourth reinforcing bars 23 and 24, and it is moved back and forth once between the near and far sides to measure the magnetic flux density of the third and fourth reinforcing bars 23 and 24. This also measures the magnetic flux density of the intersecting reinforcing bars 3 that cross them in the longitudinal direction.

[0056] Furthermore, the magnetic sensor 6 is placed to the right of the fifth reinforcing bar 25 to be inspected, and it is moved back and forth once between the near side and the front side to measure the magnetic flux density of the fifth reinforcing bar 25 to be inspected. As a result, the magnetic flux density of the intersecting reinforcing bar 3 that intersects it in its longitudinal direction is also measured.

[0057] Figures 7(a) to 7(e) show the demagnetized magnetic flux density for each of the inspected reinforcing bars 21 to 25 and the crossing reinforcing bars 3, as measured in this manner, and represent them as demagnetized magnetic flux density graphs for each inspected reinforcing bar 21 to 25. Comparing the demagnetized magnetic flux density graphs shown in Figures 7(a) to 7(e) with the magnetized magnetic flux density graphs shown in Figures 6(a) to 7(e), the following can be observed.

[0058] In the magnetized magnetic flux density graphs in Figures 6(a) to (e), each inspected reinforcing bar generally shows an upward sloping basic shape, with valley-shaped or mountain-shaped abrupt changes in magnetic flux observed in the portions corresponding to each intersecting reinforcing bar 3. In this example, as indicated by the arrows in Figures 6(a) and 6(e), the first inspected reinforcing bar 21 and the fifth inspected reinforcing bar 25 are used as examples where fractures exist. Therefore, in the portions corresponding to the fractures in the first inspected reinforcing bar 21 and the fifth inspected reinforcing bar 25, the polarity changes abruptly due to the characteristics of the fractures.

[0059] Therefore, if the abrupt change in polarity described above can be clearly identified in Figures 6(a) and 6(e), it becomes possible to detect the fracture. However, in the magnetized magnetic flux density graphs of Figures 6(a) to (e), there is little visual difference between the abrupt change in magnetic flux caused by the magnetic flux of the intersecting reinforcing bars 3 and the abrupt change in polarity corresponding to the fracture. As a result, it is extremely difficult to accurately detect the fracture of the reinforcing bar being inspected using the magnetized magnetic flux density graphs of Figures 6(a) to (e).

[0060] On the other hand, in the demagnetized magnetic flux density graphs shown in Figures 7(a) to (e), the magnetic flux of the intersecting reinforcing bars 3 is demagnetized in the demagnetization process. Therefore, the basic shape of the demagnetized magnetic flux density graph is relatively flat and slopes upward to the right, making it easy to identify the abrupt change in polarity caused by the fracture in the fracture determination described below. Consequently, the fracture of the reinforcing bar under inspection can be detected more accurately.

[0061] The demagnetized magnetic flux density measurement process involves obtaining the demagnetized magnetic flux density graphs shown in Figures 7(a) to (e) above based on the demagnetized magnetic flux density graphs acquired in the demagnetized magnetic flux density measurement process described above. However, since the content of this process is almost the same as that of the magnetized magnetic flux density measurement process described above, the relevant explanation for the magnetized magnetic flux density measurement process will be used, and the explanation here will be omitted.

[0062] "Fracture detection process" In the fracture detection step described above, the presence or absence of fractures in each of the reinforcing bars to be inspected is detected based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step described above and the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step described above, and the detection method is as described above.

[0063] In this embodiment, as described above, the presence or absence of fractures in each of the reinforcing bars to be inspected is detected based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step and the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step. However, in other embodiments of the present invention, the presence or absence of fractures in each of the reinforcing bars to be inspected can also be detected based solely on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step.

[0064] As described above, the reason for referring to the post-magnetization magnetic flux density graph obtained in the post-magnetization magnetic flux density measurement process is to confirm the position of the intersecting reinforcing bars 3 in the longitudinal direction of each reinforcing bar under inspection based on the change in magnetic flux density of the intersecting reinforcing bars 3, to supplement the confirmation of the location of the fracture in the post-demagnetization magnetic flux density graph, and to detect the fracture more accurately. However, from the perspective of the original purpose of accurately detecting the location of the fracture in the post-demagnetization magnetic flux density graph, it is not necessarily required to refer to the post-magnetization magnetic flux density graph in the fracture detection process.

[0065] "Second Embodiment" Figures 8 to 10 show a state in which five reinforcing bars 21 to 25 to be inspected are embedded at predetermined intervals near the bottom surface 1a of the concrete body 1, and numerous intersecting reinforcing bars 3 are positioned to intersect each of the five reinforcing bars 21 to 25. After magnetizing these five reinforcing bars 21 to 25 using a magnet 5, the magnetic flux density after magnetization is measured using a magnetic sensor 6. Subsequently, each magnetic material is demagnetized using a demagnetizing device 7, and the magnetic flux density after demagnetization is measured again using the magnetic sensor 6. In particular, in this embodiment, when the magnet 5, magnetic sensor 6, and demagnetizing device 7 are positioned directly above a specific reinforcing bar to be inspected, magnetization, magnetic flux density measurement, and demagnetization can be performed simultaneously on that reinforcing bar and a total of three reinforcing bars adjacent to both sides of it. For this purpose, the magnet 5, magnetic sensor 6, and demagnetizing device 7 are selected to have the capability to accommodate the above usage configuration.

[0066] "Magnetization process" The magnetization process may involve magnetizing just one reinforcing bar, or it may involve magnetizing each individual reinforcing bar in a group of multiple reinforcing bars. In other words, this magnetization process is not restricted by the number of reinforcing bars to be magnetized.

[0067] In this embodiment, as shown in Figures 8 to 10, an example is given in which each of the five reinforcing bars 21 to 25 to be inspected in the reinforcing bar group 2 is magnetized. Two positions for setting the magnet 5 during the magnetization operation are set: a first position directly above the second reinforcing bar 22 and a second position directly above the fourth reinforcing bar 24, and a total of two magnetization operations are performed, a first magnetization operation and a second magnetization operation (see Figure 8).

[0068] "First magnetization operation" In the first magnetization operation, the magnet 5 is placed at the first position such that the front side is the north pole and the front side is the south pole. Then, the magnet 5 is moved back and forth from one end of the group of reinforcing bars 2 to the other end in the longitudinal direction, and while maintaining the polarity of the magnet 5, it is moved back from the other end to the first end. This back-and-forth movement of the magnet 5 simultaneously magnetizes the first reinforcing bar 21, the second reinforcing bar 22, and the third reinforcing bar 23. Furthermore, when the first reinforcing bar 21, the second reinforcing bar 22, and the third reinforcing bar 23 are magnetized, the intersecting reinforcing bars 3 that intersect these three reinforcing bars at predetermined intervals are also magnetized.

[0069] In the second magnetization operation, the magnet 5 is placed at the second position with the front side being the north pole and the front side being the south pole. Then, the magnet 5 is moved back and forth from one end of the group of reinforcing bars 2 to the other end in the longitudinal direction, and while maintaining the polarity of the magnet 5, it is moved back from the other end to the first end. Through this back-and-forth movement of the magnet 5, the third reinforcing bar 23, the fourth reinforcing bar 24, and the fifth reinforcing bar 25 are magnetized simultaneously. Furthermore, when the third reinforcing bar 23, the fourth reinforcing bar 24, and the fifth reinforcing bar 25 are magnetized, the intersecting reinforcing bars 3 that intersect them sequentially at predetermined intervals are also magnetized.

[0070] Furthermore, when the magnet 5 is used to magnetize the reinforcing bars to be inspected from the first to the fifth reinforcing bars 25, the lateral portions 3a of each crossing reinforcing bar 3 are also magnetized simultaneously. This magnetization of the crossing reinforcing bars 3 is performed as the magnet 5 passes over the lateral portions 3a of the crossing reinforcing bars 3. In this case, the lateral portions 3a are magnetized to the opposite pole of the magnet 5 that passed over them last, so the lateral portion 3a of the crossing reinforcing bar 3 near one end of the first reinforcing bar 21 is magnetized to the S pole, and the lateral portion 3a of the crossing reinforcing bar 3 near the other end of the first reinforcing bar 21 is magnetized to the N pole. Depending on the magnetic pole of each of these crossing reinforcing bars 3, the direction of change in the magnetic flux of the crossing reinforcing bars 3 in the magnetic flux density graph after magnetization (valley-shaped change pattern and mountain-shaped change pattern) is determined (see Figure 11).

[0071] "Magnetic flux density measurement process after magnetization" The above-described post-magnetization magnetic flux density measurement process involves, after the completion of the magnetization process, positioning the magnetic sensor 6 close to the surface of the concrete body, and then measuring the magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected, either by moving it as appropriate or without moving it, and creating a post-magnetization magnetic flux density graph for each reinforcing bar to be inspected from these measurement results.

[0072] In this embodiment, two magnetic flux density measurements are performed on a group of reinforcing bars 2 consisting of five reinforcing bars 21 to 25. Specifically, a magnetic sensor 6 is placed directly above the second reinforcing bar 22. First, the magnetic sensor 6 is moved from the front to the front, and then from the front to the front. During this one round trip of the magnetic sensor 6, the magnetic flux density of the second reinforcing bar 22 and the first and third reinforcing bars 21 and 23 located on either side of it is measured. The magnetic flux density of the intersecting reinforcing bars 3 that cross these in the longitudinal direction is also measured.

[0073] Next, the magnetic sensor 6 is placed directly above the fourth reinforcing bar 24, and it is moved back and forth once between the near side and the front side to measure the magnetic flux density of the third reinforcing bar 23, the fourth reinforcing bar 24, and the fifth reinforcing bar 25. At the same time, the magnetic flux density of the intersecting reinforcing bars 3 that intersect these in the longitudinal direction is also measured.

[0074] Figures 11(a) to (e) show the magnetic flux density graphs after magnetization of each of the inspected reinforcing bars 21 to 25, and the magnetization of the crossing reinforcing bars 3 mentioned above, for each of the inspected reinforcing bars 21 to 25.

[0075] "Demagnetization process" In the above demagnetization process, an AC-type demagnetizing device is used to demagnetize the already magnetized bodies, specifically the lateral portions 3a of the intersecting reinforcing bars 3, which are arranged at predetermined intervals (unequal intervals of 120 to 340 mm in this embodiment) in a direction perpendicular to the surface of the concrete body 1 (the Z direction shown in Figures 9 and 10) relative to each of the reinforcing bars 21 to 25 to be inspected. In this embodiment, a demagnetizing device 7 is used, which is equipped with a demagnetizing coil with a rated current of 2.5 A and uses an AC power supply with a frequency of 60 Hz. In this case, the power supply frequency and applied current to the demagnetizing device 7 are set in advance so that only the depth portion of the lateral portions 3a of the intersecting reinforcing bars 3, which are covered by 50 mm from the surface of the concrete body 1, can be effectively demagnetized, and the demagnetizing effect does not extend to each of the reinforcing bars 21 to 25 to be inspected.

[0076] The above demagnetization operation is performed in two stages. Specifically, the demagnetization device 7 is placed directly above the second reinforcing bar 22 to be inspected, and first the demagnetization device 7 is moved from the near side to the front side, and then moved again from the front side to the near side. During this one round trip of the demagnetization device 7, the portion of the intersecting reinforcing bar 3 that intersects with the first reinforcing bar 21, the second reinforcing bar 22, and the third reinforcing bar 23 to be inspected is demagnetized.

[0077] Next, the demagnetizing device 7 is placed directly above the fourth reinforcing bar 24, and it is moved back and forth once between the front and back sides to demagnetize the intersection portion of the intersecting reinforcing bar 3 between the third reinforcing bar 23, the fourth reinforcing bar 24, and the fifth reinforcing bar 25.

[0078] "Demagnetization and Magnetic Flux Density Measurement Process" In the demagnetized magnetic flux density measurement process, after the completion of the demagnetization process, the magnetic sensor 6 is placed close to the surface 1a of the concrete body 1, and then the magnetic flux density along the longitudinal direction of the reinforcing bar to be inspected is measured by moving it as appropriate or without moving it, and a demagnetized magnetic flux density graph of each reinforcing bar to be inspected is created from these measurement results.

[0079] In this embodiment, as shown in Figures 8 to 10, two magnetic flux density measurements are performed on the group of reinforcing bars 2 consisting of five reinforcing bars 21 to 25. Specifically, first, the magnetic sensor 6 is placed directly above the second reinforcing bar 22. Then, the magnetic sensor 6 is moved from the front to the front, and then from the front to the front, and the magnetic flux density of the first reinforcing bar 21, the second reinforcing bar 22, and the third reinforcing bar 23 is measured during one round trip of the magnetic sensor 6. At the same time, the magnetic flux density of the intersecting reinforcing bars 3 that intersect these in the longitudinal direction is also measured.

[0080] Next, the magnetic sensor 6 is placed directly above the fourth reinforcing bar 24, and it is moved back and forth once between the near side and the front side to measure the magnetic flux density of the third reinforcing bar 23, the fourth reinforcing bar 24, and the fifth reinforcing bar 25. At the same time, the magnetic flux density of the intersecting reinforcing bars 3 that intersect these in the longitudinal direction is also measured.

[0081] Figures 12(a) to (e) show the demagnetized magnetic flux density for each of the inspected reinforcing bars 21 to 25 and the crossing reinforcing bars 3, as measured in this manner, represented as demagnetized magnetic flux density graphs for each inspected reinforcing bar 21 to 25. Comparing the demagnetized magnetic flux density graphs shown in Figures 12(a) to (e) with the magnetized magnetic flux density graphs shown in Figures 11(a) to (e), the following can be observed.

[0082] In the magnetized magnetic flux density graphs in Figures 11(a) to (e), each of the reinforcing bars under inspection generally shows a basic shape that slopes upward to the right, with valley-shaped or mountain-shaped abrupt changes in magnetic flux observed in the parts corresponding to each intersecting reinforcing bar 3. In this example, as indicated by the arrows in Figures 11(a) and 11(e), fractures are present in the intermediate positions of the first reinforcing bar 21 and the fifth reinforcing bar 25, respectively.

[0083] Therefore, in the portion corresponding to the fracture of the first reinforcing bar 21 and the portion corresponding to the fracture of the fifth reinforcing bar 25, the polarity changes abruptly due to the characteristics of the fracture. For this reason, if the abrupt change in polarity can be clearly recognized in Figures 11(a) and 11(e), the fracture can be detected. However, in the magnetized magnetic flux density graphs of Figures 11(a) to (e), there is little visual difference between the abrupt change in magnetic flux due to the magnetic flux of the intersecting reinforcing bars 3 and the abrupt change in polarity corresponding to the fracture. As a result, it is extremely difficult to accurately detect the fracture of the reinforcing bar in the magnetized magnetic flux density graphs of Figures 11(a) to (e).

[0084] The demagnetized magnetic flux density measurement process described above involves obtaining the demagnetized magnetic flux density graphs shown in Figures 12(a) to (e) based on the demagnetized magnetic flux density graphs acquired in the demagnetized magnetic flux density measurement process described above. However, since the content of this process is almost the same as that of the magnetized magnetic flux density measurement process described above, the relevant explanation for the magnetized magnetic flux density measurement process will be used, and the explanation here will be omitted.

[0085] "Fracture detection process" In the fracture detection step described above, the presence or absence of fractures in each of the reinforcing bars to be inspected is detected based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step described above and the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step described above, and the detection method is as described above.

[0086] In this embodiment, as described above, the presence or absence of fractures in each of the reinforcing bars to be inspected is detected based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step and the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step. However, in other embodiments of the present invention, the presence or absence of fractures in each of the reinforcing bars to be inspected can also be detected based solely on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step. As described above, the reason for referring to the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step is to confirm the position of the intersecting reinforcing bars 3 in the longitudinal direction of each of the reinforcing bars to be inspected from the state of change in magnetic flux density of the intersecting reinforcing bars 3, to supplement the confirmation of the position of fractures in the demagnetized magnetic flux density graph, and to detect the fractures more accurately. However, from the perspective of the original purpose of accurately detecting the position of fractures in the demagnetized magnetic flux density graph, it is not necessarily required to refer to the magnetized magnetic flux density graph in the fracture detection step. [Explanation of Symbols]

[0087] 1. Concrete body 2. Reinforcement bars to be inspected 3 ··Crossing reinforcement bars 5. Magnets 6. Magnetic Sensor 7 ···Demagnetizing device 21-25 ··Reinforcement bars subject to inspection

Claims

1. A non-destructive testing method for detecting the presence or absence of fractures in a concrete reinforcement bar, comprising: magnetizing the concrete reinforcement bar and the magnetic material embedded in the concrete body, located closer to the surface of the concrete body than the concrete reinforcement bar, using a magnet from the outside of the concrete body; and then measuring the magnetic flux density on the outside of the concrete body using a magnetic sensor. The magnetization process involves positioning the magnetized surface of the magnet so that both magnetic poles of the magnet are aligned with the longitudinal direction of the reinforcing bar to be inspected, then moving the magnet along the longitudinal direction of the reinforcing bar to be inspected, magnetizing the reinforcing bar and the magnetic material, and then removing the magnet. After the completion of the above magnetization process, a demagnetization process is performed in which an AC-type demagnetizing device is placed close to the surface of the concrete body and moved as appropriate, or without moving, to demagnetize the magnetic material located close to the surface of the concrete body. After the completion of the above demagnetization process, the magnetic sensor is placed close to the surface of the concrete body, and the magnetic flux density of the reinforcing bar to be inspected is measured by moving it as appropriate or without moving it, and a demagnetized magnetic flux density graph of the reinforcing bar to be inspected is created from the measurement results, in a post-demagnetization magnetic flux density measurement process. Based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step described above, a fracture detection step is performed to detect the presence or absence of fractures in the reinforcing bar to be inspected, A non-destructive testing method characterized by including the following.

2. In the non-destructive testing method described in claim 1, After the completion of the magnetization process described above, the magnetic sensor is positioned close to the surface of the concrete body, and the magnetic flux density of the reinforcing bar to be inspected is measured by moving it as appropriate or without moving it, and a post-magnetization magnetic flux density graph of the reinforcing bar to be inspected is created from the measurement results, comprising a post-magnetization magnetic flux density measurement process. The fracture detection step is characterized by detecting the presence or absence of fractures in the reinforcing bar to be inspected based on the demagnetized magnetic flux density graph obtained in the demagnetized magnetic flux density measurement step and the magnetized magnetic flux density graph obtained in the magnetized magnetic flux density measurement step.

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