JP4304121B2 - Reinforcing bar breakage detection method for concrete structures - Google Patents

Description

  The present invention relates to a method for detecting breakage of a reinforcing bar in a concrete structure for detecting breakage of a reinforcing bar disposed in the concrete.

  In recent years, alkaline aggregate reaction (ASR) has become a problem in concrete structures such as bridges. The alkali-aggregate reaction is a phenomenon in which alkali metal ions in the concrete and a specific mineral in the aggregate cause a chemical reaction, and the alkali silica gel produced by the reaction expands when water is supplied.

  The damage to the concrete structure due to this reaction appears as a crack due to the expansion of the concrete or a phenomenon in which the reinforcing bar inside the concrete is torn off and broken.

  It is extremely dangerous in terms of structural strength to leave the rupture of the reinforcing bar as it is, and it is strongly desired to detect it by nondestructive inspection without destroying the concrete.

  At present, however, there is no device that can effectively detect the breakage of the reinforcing bar in a non-destructive manner, and the following method is used for investigation by destructive inspection.

  (1) Find cracks in concrete through regular inspections.

  (2) Estimate whether an alkali-aggregate reaction has occurred from characteristics such as precipitation of a white gel-like substance.

  (3) A detailed investigation such as measurement of the crack width is performed on the site where the alkali-aggregate reaction is determined to have occurred.

  (4) Based on the detailed investigation, the number of cracks in the parts that are judged to have an effect on the durability structurally, if the crack width is more than a certain value, remove the concrete by sampling, otherwise remove the internal rebar. Check the breaking condition.

  The applicant has already filed a nondestructive measurement method using a magnetic sensor. However, it is necessary to move the magnetic sensor during measurement, and it takes time for the measurement or a plurality of expensive magnetic sensors must be used. There is a problem of not becoming.

  In general, the reinforcing bars are often arranged in a grid, and when measuring the magnetic force by moving the magnetic sensor along the reinforcing bars to be measured, the reinforcing bars laid in a direction perpendicular to the reinforcing bars to be measured in some places. Will cross over. In addition, there is a possibility that there are reinforcing bars that are orthogonally below the fractured portion, and the measured value is affected by the magnetic force generated from these reinforcing bars, and it is very difficult to eliminate this influence.

  Furthermore, since the magnitude direction of the remanent magnetism of the reinforcing bar varies depending on factors at the time of manufacture or construction, it is difficult to detect the break even when a portion that is hardly magnetized is broken.

  In order to solve these problems of magnetic measurement, a method of magnetizing only the reinforcing bar to be measured after demagnetizing the surrounding area has also been proposed. Equipment is required.

An object of the present invention is to provide a concrete structure capable of accurately detecting the breaking point of an embedded reinforcing bar by eliminating the influence of residual magnetism caused by manufacturing and construction of reinforcing bars to be measured in a short time and reinforcing bars to be measured. An object of the present invention is to provide a method for detecting rebar breakage.

In order to achieve the above object, a method for detecting the breakage of a reinforcing bar in a concrete structure according to the present invention is based on the magnetic flux of the reinforcing bar in the concrete structure, and the breaking of the reinforcing bar between the first magnetic sensor and the second magnetic sensor. A first magnetic field detection method for detecting a magnetic field on a concrete surface due to a remanent magnetism of the reinforcing bar after the first magnetization step. step and a second-order magnetization step of magnetizing the reinforcing bars and the first-order magnetization process with reverse polarity, detecting the magnetic field on the concrete surface by the residual magnetism of the reinforcing bar after said second magnetization step Secondary magnetic field detection step, and a breakage detection step of detecting breakage of the reinforcing bar based on the detection signals obtained in the primary and secondary magnetic field detection steps, the second magnetic sensor Arranged on the magnetizing means side used in the magnetizing step, the front In the first and second magnetic field detection steps, the magnetic field of the reinforcing bar is detected at the respective positions by the first and second magnetic sensors, and in the breakage detection step, the first magnetic sensor detects the first magnetic sensor. Next, the difference D0 between the detection signals in the second and second magnetic field detection steps is obtained, the difference D1 between the detection signals in the first and second magnetic field detection steps of the second magnetic sensor is obtained, and the difference A ratio D1 / D0 of D0 and difference D1 is obtained .

According to the method for detecting the breakage of a reinforcing bar in a concrete structure according to the present invention, the broken part of the reinforcing bar in the concrete is detected nondestructively and accurately in a short time regardless of the depth, thickness and material of the reinforcing bar. be able to.

FIG. 1 shows a first reference example prior to the present invention, in which a magnetizing device 1 and a magnetic sensor 2 are arranged in a concrete C along a reinforcing bar Rx to be measured with a break point X at which breakage is expected. The magnetizing apparatus 1 has a magnetizing coil 4 connected to the magnetizing power source 3 and close to the concrete C. For convenience of explanation, it is assumed that the reinforcing bar Rx to be measured is not magnetized, and the reinforcing bar Ry orthogonal to this is magnetized.

  Note that the magnetic flux density on the concrete surface due to the residual magnetism of the reinforcing bars Rx is 5 to 500 microtesla (μT), which is extremely small. For this reason, a Hall element type magnetic sensor that is widely used is not sufficient for accurate detection. Therefore, by using a high-precision fluxgate type magnetic sensor or a magnetic inductance (MI) type magnetic sensor as the magnetic sensor 2, more accurate detection can be performed.

FIG. 2 is a block circuit configuration diagram of Reference Example 1. The output of the magnetic sensor 2 is alternatively connected to a pre-magnetization data memory 12 and a post-magnetization data memory 13 via an A / D converter 11. Yes. Outputs of the pre-magnetization data memory 12 and the post-magnetization data memory 13 are connected to a comparison circuit 15 and a display unit 16 via a subtraction circuit 14. Further, the output of the threshold memory 17 is connected to the comparison circuit 15 for comparison with the output of the subtraction circuit 14.

  The basic measurement procedure will be described. (1) First, the magnetism sensor 1 is not operated, and the residual magnetism of the rebar Rx is measured by the magnetic sensor 2.

  The magnetic sensor 2 changes the magnitude of the magnetic field on the surface of the concrete C into a voltage signal, and the A / D converter 11 obtains digital data (D1) and stores it in the pre-magnetization data memory 12.

  (2) Next, the magnetizing power source 3 temporarily energizes the magnetizing coil 4 of the magnetizing device 1 and magnetizes the rebar Rx by the magnetic flux generated from the magnetizing coil 4.

  (3) The residual magnetism of the reinforcing bar Rx is again measured by the magnetic sensor 2.

  The magnitude of the magnetic field after magnetization is detected in the same manner as (1), and the digital data (D2) is stored in the data memory 13 after magnetization.

  (4) The difference between the signals D1 and D2 obtained in (1) and (3) by the magnetic sensor 2 is obtained to detect the presence or absence of breakage of the reinforcing bar Rx.

  The subtraction circuit 14 calculates the difference D2-D1, and the comparison circuit 15 compares the difference with the threshold value of the threshold value memory 17. If the difference is smaller than the threshold value, it is determined that there is a break and is displayed on the display unit 16.

  When actually detecting the magnetic field on the surface of the concrete C, not only the magnetic field due to the residual magnetism of the reinforcing bar Rx is detected, but also the influence of external magnetic fields such as the magnetic field due to the geomagnetism or the current flowing through the nearby transmission line. Will receive. For example, the magnetic flux density due to the residual magnetism of the reinforcing bar Rx at the position of the magnetic sensor 2 100 mm away from the reinforcing bar Rx is about 5 to 500 microtesla as described above, but the magnetic flux density due to geomagnetism is 50 microtesla around Japan. There is a level that cannot be ignored.

  When the magnetic field difference D2-D1 between before and after magnetization is obtained, the magnetic field due to the geomagnetism or the orthogonal reinforcing bar Ry is constant before and after magnetization. Thus, by obtaining the difference in this way, these influences are offset, and the reinforcing bar Rx. Only the magnetic field increased by magnetizing can be obtained.

  In the case where the reinforcing bar Rx has no fracture portion, the magnitude of the magnetic field along the reinforcing bar Rx to be measured on the surface of the concrete C before the operation of the magnetizing device 1 of (1) is shown in, for example, data A in FIG. Thus, a magnetic field caused by a certain geomagnetism and a magnetic field caused by the residual magnetism of the reinforcing bars Ry orthogonal to each other are combined.

  In this state, when a direct current is temporarily passed through the magnetized coil 4 in (2) to magnetize the rebar Rx, the magnitude of the magnetic field on the surface of the concrete C is as shown in data B of FIG. Although the influence of magnetization is detected by the magnetic sensor 2, as in the case of data A, the geomagnetism and the residual magnetism of the reinforcing bar Ry are added as they are. Note that data D in FIG. 3 indicates the difference between data A and B.

  FIG. 4 shows data A before magnetization, data B after magnetization, and difference data D before and after magnetization for the magnitude of the magnetic field on the surface of the concrete C along the reinforcement Rx when the reinforcement Rx is broken. Is shown.

  Furthermore, FIG. 5 represents each difference data D in the same graph in order to compare the difference data D of FIG. 3 and FIG. As is apparent from FIG. 5, the difference between the magnetic fields before and after magnetization is substantially the same from the center of the magnetizing apparatus 1 to the vicinity of the breaking point X regardless of whether or not there is a break. However, after the break point X, the difference in the case of breakage is extremely small compared to the case of not breakage, and the size thereof is 1 or less, which is sufficient when there is no breakage. This is because when there is no breakage, the influence of magnetization reaches far through the reinforcing bar Rx, whereas when the breakage occurs, the influence from the breakage part X hardly reaches.

  As can be seen from FIG. 3 to FIG. 5, the magnetic sensor 2 is arranged at one place away from the breaking point X without measuring all the magnetic fields along the reinforcing bars Rx, and the magnitude of the magnetic field before and after magnetization. If the difference in thickness is measured, the presence or absence of breakage of the reinforcing bar Rx can be detected. According to this method, it is possible to detect the presence or absence of the breaking point X without having to move the magnetic sensor 2 or arranging a large number of magnetic sensors 2.

  However, the rebar Rx used in the concrete structure is generally magnetized in some size due to residual magnetism due to factors during manufacture or construction, and its size, direction or distribution is not necessarily constant.

  On the other hand, when magnetizing the reinforcing bar Rx by the magnetizing device 1, even if the magnitude of magnetization is increased, the magnetic saturation characteristic of the reinforcing bar Rx does not magnetize it beyond a certain value. For this reason, when the reinforcing bar Rx to be measured is already magnetized to a certain polarity and to a certain size before magnetization, the residual magnetism before and after magnetization is magnetized even if it is magnetized to the same polarity. Change will be small.

In this way, just by measuring the change in the magnitude of the magnetic field on the surface of the concrete C before and after magnetization as in Reference Example 1 , it is affected by the magnetization state of the rebar Rx before the measurement, and is accurately broken. The presence / absence may not be detected.

As a method for solving this problem, the polarity of the magnetizing coil 4, that is, the polarity of magnetization, can be arbitrarily switched by switching the direction of the current. FIG. 6 is a block circuit configuration diagram of the reference example 2. Compared with the block circuit configuration diagram of FIG. 2, the pre-magnetization data memory 12 and the post-magnetization data memory 13 are respectively connected to the positive magnetization data memory 21, The negative magnetization data memory 22 is replaced.

  The measurement procedure in this case is as follows.

(11) Similarly to the reference example 1 , the magnetizing device 1 is arranged on one side, the magnetic sensor 2 is arranged on the other side, and the polarity switching circuit of the magnetizing device 1 is arranged across the portion where the breakage of the reinforcing bar Rx is to be measured. The magnet is set to be positive, and a magnetic field having a magnitude that saturates the reinforcing bar Rx is temporarily applied by the magnetizing coil 4 to magnetize the reinforcing bar Rx. As a result, the rebar Rx is magnetized with a constant magnitude regardless of the polarity and magnitude of magnetization before magnetization.

  (12) The magnitude of the magnetic field is changed to a voltage signal by the magnetic sensor 2, and digital data (DP) is obtained by the A / D converter 11 and stored in the positive magnetization data memory 21.

  (13) The polarity switching circuit of the magnetizing apparatus 1 is set to be negative, and a current in a direction opposite to that of (11) is passed through the magnetizing coil 4 to temporarily apply a magnetic field having a magnitude that saturates the rebar Rx. In addition, it is magnetized.

  (14) The magnitude of the magnetic field after magnetization is obtained in the same manner as in (12), and the obtained digital data (DM) is stored in the negative magnetization data memory 22.

  (15) The subtraction circuit 14 calculates the difference (DM-DP) between the positive magnetization data memory 21 and the negative magnetization data memory 22.

  (17) The difference data DM-DP is compared with the threshold value of the threshold value memory 17 by the comparison circuit 15, and if it is smaller than the threshold value, it is determined that there is a break and is displayed on the display unit 16.

The difference in the magnitude of the magnetic field due to the residual magnetism of the reinforcing bar Rx due to the first and second polarity changes obtained in (15) is twice that of FIG. Just the shape of the curve is the same. Therefore, if the difference (DM-DP) in the magnitude of the magnetic field when magnetized with the positive and negative polarities measured by the magnetic sensor 2 is obtained, the presence or absence of fracture is detected regardless of the magnetization state of the rebar Rx before the measurement. be able to.

  Generally, the depth from the surface of the concrete C to the reinforcing bar Rx to be measured is not constant. For this reason, even if the same magnetizing apparatus 1 is used, the degree to which the reinforcing bar Rx is magnetized decreases as the distance to the reinforcing bar Rx increases. Further, the magnitude of the magnetic field due to the residual magnetism of the magnetized rebar Rx also decreases as the distance from the rebar Rx to the magnetic sensor 2 increases.

In addition , the magnitude of the magnetic field at a location away from the magnetism source is inversely proportional to the cube of the distance. The difference in the magnitude of the magnetic field decreases rapidly as shown in FIG.

  In addition, since the magnitude of residual magnetism due to magnetization differs depending on the thickness and material of the reinforcing bar Rx, if the depth, thickness and material of the reinforcing bar Rx are not known, only the value of the difference in magnetic field magnitude before and after magnetization Then, it is difficult to determine the presence or absence of breakage.

  However, as can be seen from FIG. 7, even if the depth is different, the difference in the magnitude of the magnetic field before and after magnetization is similar if the fracture is the same, and only the magnitude is different.

In the present embodiment , as shown in FIG. 7, the second magnetic sensor 2 ′ is arranged on the magnetizing device 1 side, for example, at the center position of the magnetizing coil 4 from the location where the fracture is measured. The magnetic sensor 2 ′ obtains the difference between the magnitudes of the magnetic fields before and after the magnetization similarly to the magnetic sensor 2, and uses the value (D0) as a reference to obtain the difference between the magnitudes of the magnetic fields before and after the magnetization obtained by the magnetic sensor 2. If a value obtained by dividing (D1) (K = D1 / D0) is obtained, it becomes a substantially constant value according to the presence or absence of the break point X regardless of the depth of the reinforcing bar Rx. The same applies when the diameter and material of the reinforcing bar Rx are different.

FIG. 8 is a block circuit configuration diagram used in this embodiment . The outputs of the magnetic sensors 2 and 2 ′ are alternatively connected to the A / D converter 11. The output of the A / D converter 11 is the sensor 2 positive magnetization data memory 31, the sensor 2 negative magnetization data memory 32, and the sensor 2 in accordance with the switching of the magnetic sensors 2, 2 ′ and the forward / reverse switching of the magnetizing coil 4. 'Positive magnetization data memory 33, sensor 2' is selectively connected to negative magnetization data memory 34. The outputs of the sensor 2 positive magnetization data memory 31 and the sensor 2 negative magnetization data memory 32 are connected to the sensor 2 subtraction circuit 35, and the sensor 2 ′ positive magnetization data memory 33 and the sensor 2 ′ negative magnetization data memory 34 The output is connected to the subtracting circuit 36 for the sensor 2 ′.

  The outputs of the sensor 2 subtraction circuit 35 and the sensor 2 'subtraction circuit 36 are connected to a division circuit 37, and the subsequent configuration is the same as the block circuit diagrams of FIGS.

The measurement procedure of this example is as follows.

  (21) The magnetizing device 1 and the second magnetic sensor 2 ′ are arranged on one side and the magnetic sensor 2 is arranged on the other side with a portion where the breakage of the reinforcing bar Rx is to be measured. The polarity switching circuit of the magnetizing apparatus 1 is set to be positive, and a large magnetic field is temporarily applied to magnetize the rebar Rx.

  (22) Digital data (D1P) is obtained from the output of the magnetic sensor 2 by the A / D converter 11 and stored in the magnetic sensor 2 positive magnetization data memory 31.

  (23) Digital data (D0P) is obtained from the output of the magnetic sensor 2 ′ by the A / D converter 11 and stored in the magnetic sensor 2 ′ positive magnetization data memory 33.

  (24) The polarity switching circuit of the magnetizing device 1 is switched to negative, a current in the opposite direction to (21) is passed through the magnetizing coil 4, and a large magnetic field is temporarily applied to magnetize the rebar Rx.

  (25) The A / D converter 11 obtains digital data (D1M) from the output of the magnetic sensor 2 and stores it in the magnetic sensor 2 negative magnetization data memory 32.

  (26) The A / D converter 11 obtains digital data (D0M) from the output of the magnetic sensor 2 ′ and stores it in the magnetic sensor 2 ′ negative magnetization data memory 34.

  (27) The sensor 2 subtraction circuit 35 calculates D1 = D1M−D1P.

  (28) The sensor 2 'subtraction circuit 36 calculates D0 = D0M-D0P.

  (29) The division circuit 37 calculates K = D1 / D0 = (D1M−D1P) / (D0M−D0P).

  (30) The obtained value K is compared with the threshold value of the threshold value memory 17 by the comparison circuit 15, and if the value K is smaller than the threshold value, it is determined that there is a break and is displayed on the display unit 16.

  The data obtained with the reinforcing bar Rx in the graph of FIG.

Table 1
D1 D0 K = D1 / D0
No break, depth 50mm -102μT 170μT -0.6
With break and depth 50mm -9μT 149μT -0.06
No break, depth 75mm -30μT 51μT -0.59
With fracture, depth 75mm -2.5μT 44μT -0.057

  Thus, the value K is a value that differs by almost an order of magnitude depending on the presence or absence of breakage, and the breakage of the rebar Rx can be easily determined.

  The value K varies depending on the characteristics of the magnetizing device 1 such as the positions of the magnetic sensors 2 and 2 'and the diameter of the magnetizing coil 4. However, if these are always kept constant, the depth and thickness of the rebar Rx are measured. Because the value is the same regardless of the material, the presence or absence of breakage can be detected correctly.

  Further, although an example in which the magnetic sensor 2 ′ is placed at the center position of the magnetizing device 1 is shown, the center position of the magnetizing device 1 is not necessarily required as long as it is closer to the magnetizing device 1 side than the break point X. .

In the embodiment , it is preferable to dispose the magnetizing device 1 and the magnetic sensors 2 and 2 ′ directly above the reinforcing bar Rx to be measured. For this reason, it is necessary to know the position of the reinforcing bar Rx in advance. In an actual inspection site, the laying direction of the reinforcing bar Rx can be easily determined from the appearance of the concrete structure, but it is often unknown where the reinforcing bar Rx is embedded.

  In this case, the magnetic sensor 2 that detects the magnetic field due to the residual magnetism of the reinforcing bar Rx is moved in a direction perpendicular to the length direction of the reinforcing bar Rx, and the magnetic field due to the residual magnetism of the reinforcing bar Rx is measured. Since the magnitude of the magnetic field obtained is inversely proportional to the cube of the distance between the magnetic sensor 2 and the reinforcing bar Rx, the magnetizing coil 4 and the magnetic sensor 2 are arranged and moved in an integral housing as shown in FIG. When the line connecting the magnetizing coil 4 and the magnetic sensor 2 coincides with the longitudinal direction of the reinforcing bar Rx, the output of the magnetic sensor 2 becomes the largest.

  Therefore, by obtaining the position where the output is maximized while moving the magnetizing coil 4 and the magnetic sensor 2 in the direction perpendicular to the length direction of the rebar Rx, the position where the rebar Rx exists can be known. What is necessary is just to detect a fracture.

In addition, although the method of flowing a direct current from the magnetizing power supply 3 to the magnetizing coil 4 close to the surface of the concrete C as the magnetizing device 1 was shown, it is not always necessary to use the magnetizing coil 4. A method of moving away after temporarily approaching a strong permanent magnet may be used. In addition, the polarity of the permanent magnet can be switched easily by turning it over, for example. Furthermore, the example in which the magnetizing device 1 and the magnetic sensor 2 are arranged linearly has been explained, but the bending portion of the reinforcing bar Rx is inspected. In this case, the measurement can be performed in the same manner as in the case of a plane by arranging as shown in FIG.

It is explanatory drawing of a measurement principle. 6 is a block circuit configuration diagram of Reference Example 1. FIG. It is explanatory drawing of the data when there is no fracture in a reinforcing bar. It is explanatory drawing of the data when there exists a fracture | rupture in a reinforcing bar. It is explanatory drawing of the comparison of difference data. 6 is a block circuit configuration diagram of Reference Example 2. FIG. It is explanatory drawing of the data when the presence or absence and depth of a reinforcing bar are different. It is a block circuit block diagram of an Example . It is explanatory drawing in the case of searching for a reinforcing bar. It is explanatory drawing of the detection in a concrete corner | angular part.

DESCRIPTION OF SYMBOLS 1 Magnetization apparatus 2, 2 'Magnetic sensor 3 Power supply for magnetization 4 Magnetization coil 11 A / D converter 12, 13, 21, 22, 31-34 Data memory 14, 35, 36 Subtraction circuit 15 Comparison circuit 16 Display Part 17 Threshold memory 37 Dividing circuit

Claims (3)

A method for detecting a broken portion of the reinforcing bar between the first magnetic sensor and the second magnetic sensor based on the magnetic flux of the reinforcing bar in the concrete structure, wherein the first magnetization step magnetizes the reinforcing bar And a first magnetic field detecting step for detecting a magnetic field on the concrete surface due to the residual magnetism of the reinforcing bar after the first magnetizing step, and a first magnetizing the reinforcing bar with a polarity opposite to that of the first magnetizing step. a secondary magnetizing step, a second-order magnetic field detection step of detecting a magnetic field on the concrete surface by the residual magnetism of the reinforcing bar after said second magnetization step, the first-order, second-order magnetic field detection step A break detecting step for detecting breakage of the reinforcing bar based on the obtained detection signal, and the second magnetic sensor is disposed on the side of the magnetizing means used in the magnetizing step, and the first, first, In the secondary magnetic field detection step, the first and second magnetic sensors respectively The magnetic field of the reinforcing bar is detected in the setting, and in the fracture detection step, a difference D0 between the detection signals in the first and second magnetic field detection steps of the first magnetic sensor is obtained, and the second magnetic Reinforcing bar breakage detection method for concrete structure characterized in that difference D1 between respective detection signals in said primary and secondary magnetic field detection steps of sensor is obtained and ratio D1 / D0 of said difference D0 and difference D1 is obtained. . 2. The method for detecting rebar breakage in a concrete structure according to claim 1 , wherein the magnetizing step is performed by passing a current through the magnetizing coil. Wherein prior to each step, rebar breaking detection method for a concrete structure according to claim 1, said first magnetic sensor is characterized in that in advance detect the position of the rebar by moving the reinforcing bars a direction perpendicular to the direction.

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