Measurement device for evaluating PC grout filling state of concrete structure and evaluation method of PC grout filling state using the same

Abstract

To provide a measurement device capable of easily measuring in a short time with a simple configuration to grasp a PC grout filling state accurately.SOLUTION: A measurement device includes: an exciting coil 12 arranged so that two magnetic pole end surfaces having different polarity from each other at an excitation state face a measurement surface of a measurement object 20, or an exciting coil having a rectangular parallelepiped shape arranged so that one magnetic pole end surface faces the measurement surface of the measurement object; a pulse generation part configured to apply a pulse current to an exciting coil; a detection coil 14 arranged alienated from an axis connecting two magnetic pole end surfaces on a plane including the two magnetic pole end surfaces of the exciting coil, or arranged alienated from the exciting coil having a rectangular parallelepiped shape; and a measurement part configured to measure an induction current or an induced electromotive force generated at the detection coil. A detection coil face defined by a circulating lead wire is arranged parallel to the measurement surface. The exciting coil and the detection coil are arranged on a circuit board 5. The exciting coil and the detection coil are arranged on the circuit board in an alienated manner. At least the exciting coil is fixed to the circuit board. The circuit board is arranged on the measurement surface of the measurement object.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a measuring device for evaluating the PC grout filling state in, for example, a post-tensioned concrete structure in which a sheath and PC steel are embedded, and a method for evaluating the PC grout filling state using the same. [Background technology]

[0002] In a post-tensioned concrete structure 20 in which sheaths 21 and prestressing steel members 22 are embedded, as shown in Figure 21(A), the inside of the sheath is generally filled with PC grout 21a, which stably holds the prestressing steel members 22 in the sheaths 21, thereby suppressing corrosion of the prestressing steel members 22 and integrating the prestressing steel members 22, the sheaths 21, and the concrete members. Therefore, if the sheaths 21 are not sufficiently filled with PC grout 21a, the durability and safety of the concrete structure 20 will be impaired, as shown in Figures 21(B) and (C).

[0003] For example, Non-Patent Document 1 reports an evaluation of PC grout filling using the electromagnetic field response of sheaths and steel rods excited by an electromagnetic input method. According to this paper, a pulsed excitation current is passed through an excitation coil using a pulse current generator, which excites a steep magnetic field in the excitation coil. This magnetic field acts on the sheath and steel rod, causing an electromagnetic force to act on them, causing them to vibrate. When PC grout is filled, the steel rod is constrained and vibration is small, but when PC grout is not filled, vibration becomes large. This vibration is detected using the electromagnetic field response to evaluate the PC grout filling status. Here, the magnetic flux density near the sheath and steel rod is detected by search coils installed on the sheath and steel rod, respectively.

[0004] However, it can be difficult to fully grasp the state of grout filling inside the sheath, for example, when the sheath diameter is small compared to the buried depth. Furthermore, with the conventional method of receiving elastic waves by transmitting electromagnetic pulses, it is necessary to position and fix the excitation coil, which applies an impact to the sheath, and the detection coil, which detects the induced current based on the vibration caused by the shock wave, relative to the concrete structure. This makes the work required for measurement complicated and takes a long time to measure to grasp the state of PC grout filling.

[0005] Furthermore, in the case of Non-Patent Document 1, in order to detect the vibration of the sheath along with the vibration of the steel rod, it is necessary to process the detection signals from search coils installed at each measurement point on the concrete surface. Since the detection signals from two search coils must be processed separately, the structure becomes complex, and the work time becomes long in order to evaluate the PC grout filling condition at each of the multiple measurement points along the longitudinal direction of the sheath.

[0006] Patent Document 1 discloses a measuring device that has a simple configuration with only one detection coil placed near the excitation coil, which can perform measurements easily and quickly, and can accurately grasp the PC grout filling state even when the sheath diameter is small, and a method for evaluating the PC grout filling state using this measuring device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-59754 [Non-patent literature]

[0008] [Non-Patent Document 1] Shinichi Hattori, Daiki Kibe, Hiroki Terasawa, and Toshiro Kamata, "Evaluation of PC Grout Filling Using Electromagnetic Field Response of Sheath and Steel Bar Excited by Electromagnetic Input Method," Proceedings of the Japan Concrete Institute, Vol. 41, No. 1, 2019, pp. 1793-1798 Summary of the Invention [Problem to be solved by the invention]

[0009] In the PC grout filling state evaluation method disclosed in Patent Document 1, there was a problem in that it was difficult to accurately measure the magnetic field A3 because the vibrations caused by the excitation coil affect the detection coil, and the magnetic field of the excitation coil is larger than the magnetic field A3 generated by the vibrations of the sheath 21 and PC steel 22 caused by applying a pulse to the excitation coil to excite it, as described below.

[0010] In view of the above, the present invention aims to provide a measuring device with a simple configuration that can perform measurements easily and quickly and accurately grasp the PC grout filling state, and a method for evaluating the PC grout filling state using this measuring device. [Means for solving the problem]

[0011] In order to achieve the above object, in a first configuration of the present invention, a measurement device includes: an excitation coil arranged so that two magnetic pole tip faces of mutually opposite polarities face the measurement surface of the measurement object, or a rectangular parallelepiped excitation coil arranged so that one magnetic pole tip face faces the measurement surface of the measurement object; a pulse generating unit that applies a pulse current to the excitation coil; a detection coil disposed on a plane including the two magnetic pole tip surfaces of the excitation coil, spaced apart from an axis connecting the two magnetic pole tip surfaces, or spaced apart from the rectangular parallelepiped excitation coil; a measuring unit that measures an induced current or an induced electromotive force generated in the detection coil; Including, the detection coil is made of a surrounding conductor, and a detection surface defined by the surrounding conductor is arranged parallel to the measurement surface; the excitation coil and the detection coil are disposed on a substrate; the excitation coil and the detection coil are disposed separately on the substrate, At least the excitation coil is fixed to the substrate, and the substrate is placed on the measurement surface of the object to be measured.

[0012] In the above configuration, the end of the excitation coil is preferably fixed to the substrate via a stiffening plate. The excitation coil is preferably fixed to the substrate via an elastic member. The excitation coil having two magnetic pole end faces is preferably U-shaped. The detection coil is preferably positioned near the excitation coil so as to receive a magnetic field in the Z direction, which is perpendicular to the measurement surface of the object to be measured, or a magnetic field in the X direction, which is the longitudinal direction of the PC steel of a post-tensioned concrete structure in which PC steel is embedded in a sheath as the object to be measured and filled with grout material, on the measurement surface.

[0013] In order to achieve the above object, in a second aspect of the present invention, there is provided a method for evaluating a PC grout filling state in a concrete structure using the above-mentioned measuring device, comprising: In a state where there is no steel material within the range of influence of the excitation magnetic field, a pulse current is applied to the excitation coil by the pulse generating unit to apply a magnetic field to the surroundings in order to measure the reference point; a first step of measuring an induced current or an induced electromotive force generated in the detection coil by the measurement unit; a second step in which a pulse current is applied to the excitation coil by the pulse generating unit with both magnetic pole end faces of the excitation coil facing each other in the longitudinal direction of the sheath of a post-tensioned concrete structure, which is the object of measurement and has PC steel embedded in the sheath and filled with grout, to apply a magnetic field to the concrete structure, and measure, by the measuring unit, the induced current or induced electromotive force generated in the detection coil as an electromagnetic field response to the magnetic field; a third step of calculating a difference between the induced current or induced electromotive force obtained in the first step and the induced current or induced electromotive force obtained in the second step; A fourth step of comparing the difference measurement data with reference data on the filling state of the grout material to evaluate the quality of the PC grout filling state in the sheath of the concrete structure; The present invention is characterized by comprising: [Effects of the Invention]

[0014] This invention provides a measurement device that can easily and quickly accurately assess the grout filling status of a PC board by using an integrated configuration that allows the excitation coil and detection coil to be fixed. In a PC grout filling status evaluation method using this measurement device, in the second stage, the induced current or induced electromotive force generated in the detection coil in response to the excited magnetic field contains both a magnetic field acting directly from the excitation coil, which is a noise component in grout filling evaluation, and a magnetic field containing information useful for grout filling evaluation, with the former dominating. Therefore, by evaluating the difference between the induced current or induced electromotive force generated in the detection coil acquired in the first stage and the induced current or induced electromotive force acquired in the second stage, the magnetic field acting directly from the excitation coil, which is a noise component in grout filling evaluation, can be canceled out, thereby improving evaluation accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram showing the overall configuration of an embodiment of a measurement device according to the present invention; [Figure 2] 2A is a schematic plan view of the measuring device in FIG. 1, FIG. 2B is a schematic front view of the device in use, and FIG. 2C is a schematic perspective view showing the positional relationship of the measurement object with respect to the concrete structure. [Figure 3] In the measurement device of FIG. 1, (A) is a schematic side view of the excitation coil, (B) is a schematic bottom view of the excitation coil, and (C) is a photographic view of the top side showing an example of a detection coil. [Figure 4]1A to 1C are diagrams showing an example of the configuration of an excitation coil and a detection coil of the present invention, in which (A) is a front view, (B) is a plan view, and (C) is a side view. [Figure 5] 2 shows the positional relationship of the excitation coil and detection coil with respect to the measurement surface of the concrete structure during measurement operation of the measurement device of FIG. 1, where (A) is an enlarged side view, (B) is a front view, and (C) is an enlarged plan view of the main part. [Figure 6] 2 is a wiring diagram showing an example of the configuration of a pulse generating section in the measurement device of FIG. 1. [Figure 7] 4 is a graph showing the waveform of a pulse generated by the pulse generating unit of FIG. 3. [Figure 8] 2 is an explanatory diagram showing the processes of a measurement unit, a calculation unit, and an evaluation unit in the measurement device of FIG. 1. [Figure 9] 2A and 2B are explanatory diagrams illustrating (A) generation of a magnetic field by an excitation coil, (B) generation of an electromagnetic force, and (C) generation of an induced current during measurement by the measurement device of FIG. 1. [Figure 10] 2A is a schematic diagram showing multiple measurement points and unfilled and underfilled areas B of PC grout using the measurement device of FIG. 1, and FIG. 2B is a graph showing the two-dimensional coordinate positions of evaluation values ​​obtained by measurements at each measurement point. [Figure 11] 2A is a schematic diagram showing the distance d between the detection surface of the detection coil and the sheath of the concrete structure in the measurement device of FIG. 1, and FIG. 2B is a graph showing the relationship between the distance d and the measurement data. [Figure 12] 2 is a schematic diagram showing measurement points of the measurement device of FIG. 1 on a sheath bent-up portion of a concrete structure. [Figure 13] This figure shows examples of data measured using the manufactured excitation coil 12 and detection coil 14, where (A) shows the induced electromotive force in the first stage obtained by measuring the reference point, (B) shows the induced electromotive force in the second stage, and (C) shows the difference between the induced electromotive force obtained in the first stage and the induced electromotive force obtained in the second stage. [Figure 14] 1 is a diagram showing the receiving position of a detection coil relative to a U-shaped excitation coil of Example 1. FIG. [Figure 15]FIG. 15 is a diagram showing the magnetic flux density of the secondary magnetic field detected at each receiving position shown in FIG. [Figure 16] 10A and 10B are diagrams showing the configuration of a rectangular parallelepiped excitation coil 12A used in Example 2, where (A) is a plan view and (B) is a front view. [Figure 17] 10 is a diagram showing the magnetic flux density in the Z direction of the U-shaped excitation coil of Example 1 and the rectangular parallelepiped excitation coil of Example 2. FIG. [Figure 18] 1A and 1B are diagrams showing induced electromotive forces in the X direction of excitation coils, where FIG. 1A shows a U-shaped excitation coil of Example 1, and FIG. 1B shows a rectangular parallelepiped excitation coil of Example 2. [Figure 19] FIG. 10 is a diagram showing the receiving position of a detection coil relative to a rectangular parallelepiped excitation coil of the second embodiment. [Figure 20] FIG. 20 is a diagram showing the magnetic flux density of the secondary magnetic field detected at each receiving position shown in FIG. [Figure 21] 1A is a cross-sectional view of a known concrete structure, (B) is an example of imperfect PC grout filling, and (C) is an enlarged cross-sectional view showing another example of imperfect PC grout filling. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below based on the embodiments shown in FIGS. FIG. 1 shows the configuration of one embodiment of a measuring device 10 according to the present invention. Here, we will explain a case where this measuring device 10 is used to evaluate the PC grout filling state in a post-tensioned concrete structure in which a sheath 21 and PC steel strands 22 are embedded as the measurement object. Here, PC steel strands 22 collectively refer to materials used in post-tensioned concrete structures, such as PC steel bars and PC steel strands. As shown in FIG. 1, the measuring device 10 is composed of a housing 11, an excitation coil 12, a pulse generator 13, a detection coil 14, a measurement unit 15, a calculation unit 16, an evaluation unit 17, a memory unit 18, and a display unit 19.

[0017] 2(A) to 2(C), the housing 11 has a substantially rectangular parallelepiped outer shape and houses therein the excitation coil 12, the pulse generating unit 13, the detection coil 14, the measurement unit 15, the calculation unit 16, and the evaluation unit 17, with a display unit 19 exposed on the top surface. The housing 11 has an opening (not shown) on the bottom surface, through which the excitation coil 12 and the detection coil 14 are exposed downward.

[0018] As a result, each component is housed and integrated within a single housing 11, so when performing measurements on the measurement surface 23 (see Figure 5) of the object to be measured, the simple task of positioning the housing 11 relative to the measurement surface 23 allows each component, particularly the excitation coil 12 and detection coil 14, to be accurately positioned relative to the measurement surface 23, improving workability and reducing work time when measurements are performed sequentially at multiple measurement points.

[0019] In order to evaluate the PC grout filling state of a concrete structure 20 having a sheath 21 and PC steel members 22 embedded therein, the bottom surface of the housing 11 is abutted against a surface (hereinafter referred to as measurement surface) 23 that is close to the sheath 21 of the concrete structure 20, as shown in Fig. 2(B). As a result, as shown in Fig. 2(C), the excitation coil 12 and detection coil 14 of the measuring device 10 face the measurement surface 23 that is close to the sheath 21 of the concrete structure 20. The housing 11 may be configured as a portable type, with a handle 11a provided on its upper side, as shown in Fig. 2(B).

[0020] Here, the storage unit 18 is used as a so-called SD card 18a inserted into a slot 18c provided on the top surface of the housing 11. In addition to or instead of the SD card 18a, the storage unit 18 may be provided as a storage medium such as an HDD or SSD inside the housing 11. In the storage unit 18, measurement data 16a calculated by the calculation unit 16 (described later) is registered in a readable and writable manner, and reference data 16b is also registered in advance in a readable and writable manner. Furthermore, the storage unit 18 may include a first storage area 18a for storing reference data and a second storage area 18b for storing evaluation index values, as described later.

[0021] FIG. 3 shows an example of an excitation coil 12. As shown in FIGS. 3A and 3B, the excitation coil 12 includes a main body 12a extending laterally and magnetic pole tips 12b and 12c extending from both ends of the main body 12a to one side (the lower side in the illustrated example). Windings 12d and 12e are wound around the magnetic pole tips 12b and 12c, respectively. The excitation coil 12 is excited by applying a pulse voltage from a pulse generator 13 (described later). The excited excitation coil 12 is positioned so that its two magnetic pole tip faces, each with a different polarity, face the measurement surface of the measurement object 20. In the illustrated example, the main body 12a has a total length of 250 mm, a height of 50 mm, and a width of 50 mm, and the height of each magnetic pole tip 12b and 12c is set to 50 mm. This results in coil dimensions of 200 × 100 × 50 mm, a coil cross section of 50 × 50 mm, and a coil magnetic path length of 300 mm. The main body 12a and the magnetic pole tips 12b, 12c form a so-called U-shape, and this U-shaped coil core is manufactured by laminating electromagnetic steel sheets with high magnetic permeability and high magnetic flux density at saturation in a U-shape. Each of the windings 12d, 12e has, for example, eight turns. The excitation coil 12 shown in FIG. 3 is called a U-shaped excitation coil 12, but it can also be called a U-shaped excitation coil 12.

[0022] Furthermore, during measurement, the end faces (referred to as magnetic pole end faces) 12f, 12g of the magnetic pole ends 12b, 12c of the excitation coil 12 are positioned with a gap of a predetermined distance D from the measurement surface 23 of the object to be measured, as shown in Figures 4 and 5(A) described below, and a solid spacer 7 is placed within this gap, so that the excitation coil 12 is spaced apart from the measurement surface 23 of the object to be measured without contacting it.

[0023] Fig. 4 shows an example of the configuration of the excitation coil and detection coil of the present invention, where (A) is a front view, (B) is a plan view, and (C) is a side view. Fig. 5 shows the positional relationship of the excitation coil and detection coil of Fig. 4 with respect to the measurement surface of the concrete structure during measurement operation of the measurement device of Fig. 1, where (A) is an enlarged side view, (B) is a front view, and (C) is an enlarged plan view of the main part. As shown in FIG. 4(A), the excitation coil 12 and the detection coil 14 are disposed and fixed on a substrate 5. During measurement, which will be described later, the substrate 5 on which the excitation coil 12 and the detection coil 14 are mounted is placed on the measurement surface of the object to be measured. A resin plate can be used as the substrate 5, and if a transparent resin plate, such as an acrylic resin plate, is used, the concrete structure serving as the measurement surface can be seen. The size of the substrate must be large enough to accommodate the excitation coil 12 and the detection coil 14, and the area of ​​the substrate should be set large enough to allow the measurement surface to be seen so that the concrete structure serving as the measurement surface can be seen. While FIG. 4 shows a rectangular substrate, it may also be circular or have other shapes. Therefore, using a transparent substrate can improve the efficiency of the alignment work during measurement. In the following explanation, the substrate 5 is described as a transparent resin plate. Furthermore, the excitation coil 12 may be disposed on the substrate 5 via a solid spacer 7. In order to prevent the excitation coil 12 from rotating when a pulse, which will be described later, is applied to the excitation coil 12, the excitation coil 12 may be fixed to a stiffening plate (not shown), for example, a transparent resin plate, with an adhesive or the like.

[0024] As shown in FIG. 5(C), the detection coil 14 is disposed on a plane including the two magnetic pole tip faces 12f, 12g of the excitation coil 12, on the axis X connecting these two magnetic pole tip faces 12f, 12g. In the illustrated example, the detection coil 14 is disposed at position A on the right side, spaced apart from the magnetic pole tip face 12g, and is fixed to the transparent resin plate 5 with an adhesive or the like. Furthermore, the detection coil 14 may be arranged at position B, that is, on a plane including the two magnetic pole tip surfaces 12f, 12g of the excitation coil 12, on an axis Y perpendicular to the axis X connecting these two magnetic pole tip surfaces 12f, 12g.

[0025] The solid spacer 7 is made of, for example, a non-magnetic, non-conductive, and non-elastic material, particularly a material that does not propagate the impact of the exciting coil 12, such as polyurethane foam. When the exciting coil 12 is positioned at a distance D from the measurement surface 23, the solid spacer 7 compresses to press it against the measurement surface 23 with a constant pressure, while maintaining its compressed shape and absorbing the impact of the pulse current of the exciting coil 12. With this configuration, the magnetic pole tip faces 12f, 12g of the exciting coil 12 are reliably spaced from the measurement surface 23, allowing the measurement to be performed without contact. In particular, when the solid spacer 7 is present, the solid spacer 7 suppresses vibrations caused by the impact of the pulse current, allowing for more accurate measurement.

[0026] The distance D defined by the gap or solid spacer 7 can be adjusted appropriately depending on the distance (so-called cover) to the sheath 21 and prestressing steel members 22 embedded in the concrete structure 20, which is the object of measurement. This allows the thickness of the gap or solid spacer 7 to be adjusted appropriately depending on various factors such as the embedded depth of the steel rod in the concrete structure 20 and the diameters of the sheath 21 and prestressing steel members 22, thereby enabling optimal measurement.

[0027] 4 and 5, the excitation coil 12 is fixed to the substrate 5, so that the electromagnetic field acting directly from the excitation coil 12 on the detection coil 14 can be maintained at a constant value without fluctuations between measurements. Furthermore, by using a transparent resin plate 5, it is possible to improve the efficiency of the alignment work for determining at which parts of the concrete the excitation coil 12 and detection coil 14 should be placed, as shown in FIG. 4(A).

[0028] As described above, the detection coil 14 is disposed at a distance to one side from the axis X of the excitation coil 12. As the attenuation of the potential field induced from the excitation coil to the detection coil 14 is large, even a slight distance can provide a reduction effect, and therefore the potential field that acts directly from the excitation coil 12 on the detection coil 14 and becomes a noise component can be reduced. Furthermore, by providing the solid spacer 7, it is possible to make it difficult for vibrations due to magnetostriction caused by an electromagnetic field generated by applying a pulse to the excitation coil 12 to propagate to the detection coil .

[0029] Figure 6 is a wiring diagram showing an example of the configuration of the pulse generating unit in the measuring device of Figure 1. As shown in this diagram, pulse generating unit 13 is composed of charging circuit 13a and discharging circuit 13b. Charging circuit 13a has a known circuit configuration, and receives power from power source 13c, such as a commercial power source (100V AC) or a power supply unit, via charging control circuit 13d, step-up transformer 13e, and bridge-type rectifier circuit 13f, and voltage setting unit 13g controls charging control circuit 13d to obtain a predetermined output voltage V.

[0030] The discharge circuit 13b is composed of a charging capacitor C connected in parallel to the exciting coil 12, the exciting coil 12, and a discharge switch circuit 13i connected in series to the exciting coil 12 and the negative side of the charging capacitor C. The charging capacitor C is made up of multiple capacitors, each with a predetermined withstand voltage, connected in series and parallel. When the discharge switch circuit 13i is turned on, the charge stored in the charging capacitor C is discharged all at once to the exciting coil 12, and a pulse current is applied to the exciting coil 12.

[0031] Here, regarding the discharge circuit 13b of the pulse generating unit 13, in order to obtain a larger pulse current with the lowest possible charging voltage, the wiring resistance r of the wiring constituting the discharge circuit 13b is set to r. c and the resistance r of the excitation coil 12 coil is set as small as possible, and the capacitance C of the charging capacitor is set as large as possible. In this case, the equivalent series resistance r ESR Select a capacitor with a small capacitance and connect it in parallel if necessary to ensure sufficient capacitance.

[0032] By minimizing the wiring resistance r of the discharge circuit 13b, a low charging voltage is sufficient, and by increasing the capacitance C of the capacitor as much as possible, a larger pulse current can be obtained, making it possible to generate a strong magnetic field. Also, since the withstand voltage of the charging capacitor C must be set higher than the supply voltage V, if this withstand voltage is insufficient, a predetermined number of capacitor stages can be connected in series. In other words, the withstand voltage of the charging capacitor C is the withstand voltage (V) of the capacitor having the predetermined withstand voltage multiplied by the number of stages connected in series.

[0033] Furthermore, the critical damping condition in the discharge circuit 13b is as follows: (r / 2) 2 =L / C or (r / 2) 2 <L / C The critical damping condition must be satisfied, and multiple capacitors are connected in parallel in each stage until this condition is met. By satisfying the critical damping condition, an optimal pulse current can be obtained.

[0034] In Figure 6, charging capacitor C is made up of four capacitors C1, C2, C3, and C4 connected in parallel and in series. Generally, aluminum electrolytic capacitors are used as large-capacity capacitors, but aluminum electrolytic capacitors have the problem of high equivalent series resistance due to the electrolyte inside and the mobility of ions carrying electric charge. Therefore, charging capacitor C should be made of film capacitors, which have a lower equivalent series resistance than aluminum electrolytic capacitors, to reduce the equivalent series resistance and to ensure voltage resistance by connecting them in series in a specified number of stages. In the pulse generating unit 13 configured as described above, the charging capacitor C is charged by the charging circuit 13a, and then the discharge switch circuit 13i is turned on to discharge the current to the exciting coil 12 all at once, causing a pulse current to flow in the exciting coil 12, as shown in the graph of FIG. 7, for example.

[0035] As shown in Fig. 3(C), the detection coil 14 is composed of a surrounding conductor 14a with a predetermined number of turns and a connection cable 14b drawn out from both ends of the surrounding conductor 14a. As shown in Fig. 5, the detection coil 14 is arranged on a plane including the two magnetic pole end faces 12f, 12g of the excitation coil 12, at a distance to one side (upper side in the illustrated case) of the axis X connecting these two magnetic pole end faces 12f, 12g. In the illustrated case, the detection coil 14 is selected to have, for example, 5 turns and a coil diameter of 20 mm. The connection cable 14b shown in Fig. 3(C) uses two vinyl wires, i.e., a two-core cable.

[0036] As shown in Fig. 1, the measurement unit 15 detects the induced current i generated in the detection coil 14 and outputs it to the calculation unit 16. As shown in Fig. 8, the calculation unit 16 time-integrates the induced current i measured by the measurement unit 15 to calculate the magnetic flux density B, and also calculates an estimated electromagnetic force signal as measurement data 16a from the product of the induced current I and the magnetic flux density B. This estimated electromagnetic force signal changes depending on whether the PC grout filling state, which will be described later, is unfilled or insufficiently filled (see Non-Patent Document 1).

[0037] The evaluation unit 17 compares the measurement data 16a calculated by the calculation unit 16 with the reference data 16b read from the first memory area 18a of the memory unit 18, and evaluates the PC grout filling state of the measurement target, that is, the concrete structure 20. Specifically, the evaluation unit 17 compares the measurement data 16a with the reference data 16b, and generates a first evaluation index value 17a from the difference between the measurement data 16a and the reference data 16b.

[0038] The evaluation unit 17 registers this first evaluation index value 17a in a second memory area 18b of the memory unit 18, and compares it with a preset threshold value 17b to evaluate the PC grout filling state. That is, the evaluation unit 17 evaluates that the PC grout filling state is filled when the first evaluation index value 17a is equal to or less than the threshold value 17b, and evaluates that the PC grout filling state is unfilled or insufficiently filled when the first evaluation index value 17a exceeds the threshold value 17b, and outputs this evaluation result 17c to the display unit 19.

[0039] Furthermore, when the evaluation unit 17 performs the above-mentioned measurement and evaluation process at a plurality of measurement points along the longitudinal direction of the sheath 21 of the concrete structure 20, it generates a first evaluation index value 17a by comparing the measurement data 16a created by the calculation unit 16 with reference data 16b for each measurement point in sequence, registers the first evaluation index value 17a in a second memory area 18b of the memory unit, and compares the first evaluation index value 17a with a preset threshold value 17b to evaluate the PC grout filling state, and outputs an evaluation result 17c together with the measurement data 16a to the display unit 19. In this case, the evaluation unit 17 evaluates the PC grout filling state as unfilled or improperly filled when the first evaluation index value 17a exceeds the threshold value 17b at two consecutive measurement points.

[0040] As a result, measurements are taken at multiple measurement points along the longitudinal direction of the sheath 21 to generate a first evaluation index value 17a, and if the first evaluation index value 17a exceeds the threshold value 17b at both adjacent measurement points, the PC grout filling state is determined to be unfilled or poorly filled, so that even if an error occurs in the measurement of the induced current by the measurement unit 15, it is possible to more reliably evaluate the PC grout filling state as being unfilled or poorly filled.

[0041] Furthermore, the evaluation unit 17 acquires position information 17d at each measurement point, associates it with the first evaluation index value 17a, and outputs it as two-dimensional coordinate information 17e to the display unit 19. As a result, the display unit 19 displays a two-dimensional graph 19a based on this two-dimensional coordinate information 17e. Then, based on a change in the slope of the curve of the first evaluation index value 17a in the two-dimensional coordinate information 17e, the evaluation unit 17 generates a second evaluation index value 17f and outputs it to the display unit 19 when the slope of the curve becomes equal to or greater than a predetermined angle.

[0042] Furthermore, when the evaluation unit 17 performs the above-mentioned measurement and evaluation processing at multiple measurement points in the region 24 (see Figure 12) of the bent-up portion of the sheath 21 in the concrete structure 20, it generates a first evaluation index value 17a by comparing the measurement data 16a created by the calculation unit 16 with reference data 16b for each measurement point sequentially from the bottom to the top of the bent-up portion, and registers it in a second memory area 18b of the memory unit 18.It also evaluates the PC grout filling state based on changes in the first evaluation index value 17a and outputs the evaluation result 17c to the display unit 19 together with the measurement data 16a.

[0043] The display unit 19 is provided on the top surface of the housing 11, and displays the measurement data 17a and evaluation results 17c output from the evaluation unit 17, as well as a two-dimensional graph 19a based on the two-dimensional coordinate information 17e, and also displays a warning that the PC grout filling state is unfilled or insufficiently filled based on the second evaluation index value 17f.

[0044] Next, a description will be given of an evaluation method for evaluating the PC grout filling state of a concrete structure 20 in which a sheath 21 and PC steel members 22 are embedded as a measurement object using the measurement device 10 according to the embodiment of the present invention. As shown in Figure 2(B), the measuring device 10 is placed against the measurement surface 23 close to the sheath 21 of the concrete structure 20. By integrating the excitation coil 12 and detection coil 14 within the housing 11, there is no need to position them relative to the measurement surface 23, and all the necessary components are built into the measuring device 10, making evaluation easy.

[0045] In this state, when a pulse current from the pulse generating unit 13 is applied to the exciting coil 12, a pulsed magnetic field A1 is generated in the exciting coil 12, as shown in Fig. 9(A). Therefore, the magnetic field from the exciting coil 12 generates an induced current A2 in the sheath 21 and the PC steel 22, as shown in Figs. 9(A) and 9(B). This induced current A2 and the magnetic field A1 of the exciting coil 12 generate an electromagnetic force F in the sheath 21 and the PC steel 22.

[0046] Therefore, a difference ΔF in electromagnetic force occurs between the sheath 21 and the PC steel 22 due to the difference between the magnetic field on the exciting coil 12 side and the magnetic field on the opposite side. A force acts on the sheath 21 and the PC steel 22 on the side opposite to the exciting coil 12, causing the sheath 21 and the PC steel 22 to vibrate. This vibration generates an induced current flowing through the sheath 21 and the PC steel 22, as shown in Figure 9(C), generating a new magnetic field A3. If the sheath 21 is not filled with PC grout or is imperfectly filled, the restraining force of the PC grout 22a on the sheath 21 and the PC steel 22 is weaker than when the sheath 21 and the PC steel 22 are filled. This increases the vibration of the sheath 21 and the PC steel 22, and also increases the generated magnetic field A3. This magnetic field A3 therefore generates an induced current i in the detection coil 14.

[0047] This induced current i is measured by the measurement unit 15, and the calculation unit 16 calculates an estimated electromagnetic force signal acting on the detection coil 14 as measurement data 16a by multiplying this induced current i by the time integral of the induced current. The calculation unit 16 registers this measurement data 16a in a first storage area 18a of the storage unit 18. Thereafter, the evaluation unit 17 compares this measurement data 16a with reference data 16b previously registered in the first storage area 18a of the storage unit 18, and generates a first evaluation index value 17a from the difference between the two.

[0048] The evaluation unit 17 evaluates the PC grout filling state by comparing the first evaluation index value 17a with a threshold value 17b read out from the second memory area 18b of the memory unit 18. That is, the evaluation unit 17 evaluates that the PC grout filling state is filled when the first evaluation index value 17a is equal to or less than the threshold value 17b, and evaluates that the PC grout filling state is unfilled or insufficiently filled when the first evaluation index value 17a exceeds the threshold value 17b, and outputs this evaluation result 17c to the display unit 19.

[0049] After the evaluation of the PC grout filling condition at one measurement point is completed, the measurement device 10 is then moved sequentially to multiple measurement points, and the evaluation of the PC grout filling condition is repeated at each measurement point. Measurement data 16a and a first evaluation index value 17a are generated for each measurement point, and the first evaluation index value 17a is compared with a threshold value 17b to generate an evaluation result 17c. The measurement data 16a and the evaluation result 17c are then output to the display unit 19. The display unit 19 sequentially displays the measurement data 16a and the evaluation result 17c for each measurement point. Therefore, by moving the measurement device 10 from one measurement point to another, the operator can visually confirm the measurement data 16a and the evaluation result 17c at each measurement point as a primary evaluation. The evaluation unit 17 may also be configured to evaluate the PC grout filling condition as incomplete or improperly filled when the first evaluation index value 17a exceeds the threshold value 17b at two consecutive measurement points.

[0050] With the measurement device 10, for an object to be measured, for example, a post-tensioned concrete structure 20 having a sheath 21 and PC steel members 22 embedded therein, a surface adjacent to the PC steel members 22 inserted into the sheath 21 and filled with PC grout 22a is set as a measurement surface 23, and two magnetic pole end faces 12f, 12g of the excitation coil 12 are positioned facing this measurement surface 23. As a result, the excitation coil 12 is excited by the pulse current, and an impact is applied to the sheath 21 and PC steel members 22 of the concrete structure 20. This impact generates an induced current in the detection coil 14 in response to an electromagnetic field, and this induced current is measured by the measurement unit 15. A calculation unit 16 calculates measurement data 16a based on this induced current. The evaluation unit 17 compares the measurement data 16a with reference data 16b registered in the memory unit 18 to evaluate the PC grout filling state within the sheath 21 of the concrete structure 20, and the display unit 19 displays the evaluation result 17c and the measurement data 16a.

[0051] (Improvement of the analysis method in the detection coil 14) The magnetic field A3 generates an induced current i or an induced electromotive force that is detected by the detection coil 14. An improvement in the method for analyzing this induced current i or induced electromotive force will now be described. First step: Using the measuring device 10, measurements are taken in the absence of any target object such as steel or concrete (also called reference measurement). In this state, the electromagnetic field received by the detection coil 14 is taken as the electromagnetic field that acts directly on the detection coil 14 from the excitation coil 12. Second step: Next, the concrete and the sheath and PC steel rods embedded in the concrete are measured using the measuring device 10. In this state, the electromagnetic field received by the detection coil 14 is defined as "the electromagnetic field acting directly on the detection coil 14 from the excitation coil 12 plus the electromagnetic field generated by the eddy currents in the sheath and PC steel." Third step: By evaluating the difference between the electromagnetic field measured in the first step and the electromagnetic field measured in the second step, the electromagnetic field generated by the eddy currents in the sheath and PC steel can be obtained with noise components removed.

[0052] The method for analyzing the induced current i may be improved using the measuring device 10 in the following steps. In a state where there is no steel material within the range of influence of the excitation magnetic field, a pulse current is applied to the excitation coil 12 by the pulse generating unit 13 to apply a magnetic field to the surrounding area in order to measure the reference point. a first step of measuring an induced current or an induced electromotive force generated in the detection coil 14 by a measuring device 10; a second stage in which a measurement device 10 measures an induced current i or an induced electromotive force generated in a detection coil 14 by an electromagnetic field response caused by the magnetic field, with both magnetic pole end faces 12f, 12g of the excitation coil 12 facing the longitudinal direction of the sheath 21 of a post-tensioned concrete structure 20 in which PC steel 22 is embedded in the sheath 21 and grout material 22a is filled; a third stage in which a calculation unit 16 calculates the difference between the measurement data, the induced current generated in the detection coil 14 obtained in the first stage, and the induced current or induced electromotive force generated in the detection coil 14 obtained in the second stage; and a fourth stage in which the difference measurement data is compared with reference data on the filling state of the grout material to evaluate the quality of the filling state of the PC grout 22a in the sheath 21 of the concrete structure 20. The calculation of the difference in the third stage may be obtained by the evaluation unit 17. Furthermore, a fifth step may be provided in which the evaluation results are displayed on the display unit 19. The evaluation results may be stored as data in a storage device, or may be printed on paper using a printer or the like.

[0053] According to the above-mentioned PC grout filling condition evaluation method, in the second stage, the induced current or induced electromotive force generated in the detection coil in response to the excited magnetic field includes both the magnetic field acting directly from the excitation coil, which is a noise component in the grout filling evaluation, and the magnetic field containing information useful for the grout filling evaluation, with the former dominating. Therefore, by evaluating the difference between the induced current or induced electromotive force generated in the detection coil acquired in the first stage and the induced current or induced electromotive force acquired in the second stage, it is possible to cancel the magnetic field acting directly from the excitation coil, which is a noise component in the grout filling evaluation, and thereby improve the evaluation accuracy. In the following explanation, a first-stage reference measurement is performed in the absence of any target object such as PC steel 22 or concrete structure 20, and then the difference between this and the second-stage measurement measured using the above-mentioned measurement system targeting the sheath and PC steel rod buried in concrete is calculated and evaluated as the induced current i generated in the detection coil 14.

[0054] This makes it easy to evaluate the PC grout filling state within the sheath 21 of a post-tensioned concrete structure 20 in which the sheath 21 and PC steel members 22 are embedded. Also, even if the sheath diameter is small compared to the sheath embedding depth, the PC grout filling state within the sheath 21 can be reliably evaluated. Furthermore, because only the vibration of the PC steel members 22 needs to be detected by the induced current generated in the detection coil 14, the number of parts is reduced, and the processing content and processing time are shortened, making it possible to more efficiently evaluate the PC grout filling state.

[0055] Figure 10(A) shows the relationship between the position of each measurement point (distance from the end of the prestressing steel 22 in the concrete structure 20) and the measurement data 16a. When there is an unfilled or underfilled portion B near the end of the prestressing steel 22 (to the left in Figure 10(A)), the measurement data 16a increases dramatically compared to when the PC grout is filled (see Figure 10(B)). Therefore, by creating measurement data 16a for when the PC grout is filled as a standard value in advance and registering it in the memory unit 18 as reference data 16b, it is possible to evaluate the PC grout filling state at each measurement point by comparing the measurement data 16a at that measurement point with the reference data 16b.

[0056] Here, the difference between the measurement data 16a and the reference data 16b is defined as a first evaluation index value 17a. If the first evaluation index value 17a exceeds a threshold value 17b, the difference between the measurement data 16a and the reference data 16b is deemed to be outside the allowable range of standard values, and the PC grout filling state is evaluated as unfilled or poorly filled. Thus, evaluation at each measurement point is performed immediately upon measurement and displayed on the display unit 19. With this configuration, by comparing the difference between the measurement data 16a and the reference data 16b with the threshold value 17b at a single measurement point, the PC grout filling state at that measurement point can be evaluated as filled, poorly filled, or unfilled. Furthermore, each time a measurement is performed at each measurement point, the first evaluation index value 17a as the measurement data 16a and the evaluation result 17c are displayed on the display unit 19.

[0057] For example, as shown in Figure 11(A), when measuring with the measuring device 10, the distance d between the bottom surface of the housing 11 and the sheath 21 of the concrete structure 20 changes. This changes the induced current and magnetic flux density detected by the detection coil 14, as shown in Figure 11(B). The corresponding change in measurement data 16a at each measurement point corresponds to this change. The difference between the measurement data 16b and the reference data 16b, i.e., the first evaluation index value 17a, is then compared with the threshold value 17b. This method allows for a more accurate evaluation of the PC grout filling condition by using the measurement data 16a at measurement points where the PC grout filling condition is known in advance as the reference data 16b. Therefore, even when the sheath diameter is small relative to the sheath burial depth, the PC grout filling condition can be reliably evaluated by comparing the first evaluation index value 17a with the threshold value 17b.

[0058] Furthermore, when the evaluation unit 17 measures the above-mentioned measurement data 16a at each of a plurality of measurement points along the longitudinal direction of the sheath 21 of the concrete structure 20 to be evaluated, it acquires position information 17d of the measurement points, creates two-dimensional coordinate information 17e consisting of the measurement data 16a or the first evaluation index value 17a and the position information 17d, and after measurements at all measurement points are completed, sends the two-dimensional coordinate information 17e for all measurement points to the display unit 19. In this case, it is possible to evaluate the PC grout filling state at all measurement points, i.e., perform a secondary evaluation that provides an overview of the entire PC steel member 22.

[0059] According to the above method, measurements are taken at multiple measurement points, and position information 17d is added to the measurement data 16a to create two-dimensional coordinate information 17e. This allows the changes in the measurement data 16a at the multiple measurement points to be comprehensively analyzed along the longitudinal direction of the sheath as a distribution of first evaluation index values. Second evaluation index values ​​17f are generated from this distribution of first evaluation index values, allowing the PC grout filling state to be evaluated as filled, insufficiently filled, or not filled. In other words, the extent of PC grout filling or not filled can be evaluated based on the second evaluation index value. Furthermore, if the distribution of the first evaluation index values ​​is a curve, the second evaluation index value 17f may be generated from changes in the slope of this curve. Based on this two-dimensional coordinate information 17e, the display unit 19 displays a two-dimensional graph 19a, for example, with the horizontal axis representing the measurement positions and the vertical axis representing the measurement data 16a or the first evaluation index value 17a. Therefore, by visually checking the two-dimensional graph 19a displayed on the display unit 19 of the measuring device 10, the worker can instantly visually grasp the state of PC grout filling.

[0060] In this case, the evaluation unit 17 generates a second evaluation index value 17f when the gradient of the curve of the first evaluation index values ​​17a in the distribution of the first evaluation index values ​​or the two-dimensional coordinate information 17e becomes equal to or greater than a predetermined angle, and outputs the second evaluation index value 17f to the display unit 19. In response to this, the display unit 19 displays a warning that the PC grout filling state has become incomplete or improperly filled based on the second evaluation index value 17f. This allows the worker to visually recognize the warning display on the display unit 19 and understand that the PC grout filling state has become incomplete or improperly filled.

[0061] 12 shows measurement work in a region 24 of the bent-up portion of a sheath 21 and PC steel 22 in a concrete structure 20. It is known that in the bent-up portion region 24, the upper portion 24b (right side in FIG. 12) is more likely to be insufficiently filled with PC grout due to a phenomenon such as forward flow when filling the PC grout, compared to the lower portion 24a (left side in FIG. 12).Therefore, as shown by arrow Y in FIG. 11, measurement and evaluation are carried out at measurement points sequentially starting from the lower portion 24a.

[0062] That is, the evaluation unit 17 measures and evaluates each of the measurement points in the region 24 of the bent-up portion of the concrete structure 20, sequentially from the bottom 24a to the top 24b, and generates a first evaluation index value 17a at each measurement point. When the first evaluation index value 17a is equal to or less than the threshold value 17b, the PC grout filling state is evaluated as filled, and when the first evaluation index value 17a exceeds the threshold value 17b, the PC grout filling state is evaluated as unfilled or imperfectly filled, and the evaluation result 17c is output to the display unit 19. In response to this, the display unit 19 displays the measurement data 16a and the evaluation result 17c at each measurement point.

[0063] Here, the evaluation unit 17 may be configured to evaluate the PC grout filling state as unfilled or improperly filled when the first evaluation index value 17a exceeds the threshold value 17b at two consecutive measurement points. This prevents the PC grout filling state from being erroneously evaluated as unfilled or improperly filled due to measurement errors caused by noise or the like. By focusing on the fact that the PC grout filling state is more likely to be unfilled or improperly filled at the upper side in the region 24 of the bent-up portion of the PC steel member 22, measurements can be taken sequentially from bottom to top, making it possible to more reliably evaluate the portion where the PC grout filling state changes from filled to improperly filled or unfilled.

[0064] Example 1 The excitation coil 12 and detection coil shown in Figures 4 and 5 were fabricated using a transparent resin plate 5 as the substrate, which was made of acrylic, a stiffening plate 6, and a solid spacer made of rubber. As for post-tensioned concrete structures in which PC steel is embedded in the sheath and filled with grout, measurements were taken of concrete structures filled with grout and unfilled concrete structures that were not filled with grout.

[0065] 13 shows examples of data measured using the fabricated excitation coil 12 and detection coil 14, where (A) shows the induced electromotive force in the first stage obtained by measurement at the reference point, (B) shows the induced electromotive force in the second stage, and (C) shows the difference between the induced electromotive force obtained in the first stage and the induced electromotive force obtained in the second stage. In each figure, the horizontal axis shows time (sec) and the vertical axis shows induced electromotive force (V).

[0066] As shown in Figure 13(C), the difference between the induced electromotive force obtained in the first stage and the induced electromotive force obtained in the second stage was measured with high accuracy at the order of mV, which made it possible to cancel out the magnetic field acting directly from the excitation coil, which is a noise component, and improved the evaluation accuracy. Furthermore, the waveform shape of the difference between a concrete structure filled with grout and a concrete structure not filled with grout was significantly different, making it easy to determine whether the structure was filled with grout or not.

[0067] (Relationship between the receiving position of the detection coil and magnetic flux density) The relationship between the receiving position of the detection coil relative to the U-shaped excitation coil 12 of Example 1 and the detected magnetic flux density will be described. An induced electromotive force is generated in the detection coil in proportion to the change over time in the magnetic flux density acting on the detection coil. By performing differential processing between the induced electromotive force acquired in the first stage and the induced electromotive force acquired in the second stage, as shown in the following equation (1), the influence of the magnetic field generated by the excitation coil 12 (called the primary magnetic field) is reduced, and only the magnetic field generated by eddy currents generated near the steel sheath (called the secondary magnetic field) is detected.

[0068]

number

[0069] where f s (t) is the time-axis waveform of the induced electromotive force (V) extracted from the secondary magnetic field obtained by differential processing, and f i (t) is the time-axis waveform of the induced electromotive force (V) received by the detection coil, and f0(t) is the time-axis waveform of the induced electromotive force (V) received in the reference measurement.

[0070] f is the time-axis waveform of the induced electromotive force (V) extracted from the secondary magnetic field obtained by equation (1). s (t) can be converted into magnetic flux Φ(Wb) using the following equation (2), and then into magnetic flux density B(T) using the following equation (2).

[0071]

number

[0072]

number

[0073] where N is the number of turns in the detection coil and S is the area of ​​the detection coil (m 2 )

[0074] 14 is a diagram showing the receiving positions of the detector coils relative to the U-shaped excitation coil 12 of Example 1. As shown in this figure, the detector coils are arranged with their diameter faces in the Z direction and at measurement points 1 to 4 which are arranged in the X direction of the main body 12a of the excitation coil, and at measurement points 5 and 6 which are arranged in the X direction and 100 mm outside the magnetic pole ends 12b and 12c of the excitation coil.

[0075] Figure 15 shows the magnetic flux density of the secondary magnetic field detected at each receiving position shown in Figure 14. The horizontal axis of Figure 15 indicates the measurement point, and the vertical axis indicates the magnetic flux density (T) due to the filled and unfilled concrete structure at each measurement point. As shown in Figure 15, at measurement point 6, i.e., when the detection coil 14 was placed in the Z direction directly above the steel sheath, the magnetic flux density was higher in the unfilled case than in the filled case, and the shape of the differential waveform was significantly different, making it easy to determine whether the concrete structure was filled or unfilled with grout. Furthermore, at measurement points 1 and 2, where the detection coil 14 was placed in the X direction, the difference between the unfilled and filled cases was smaller than at measurement point 6, but it was still possible to determine whether the concrete structure was filled or unfilled with grout.

[0076] Example 2 The U-shaped excitation coil 12 of Example 1 was changed to a rectangular parallelepiped excitation coil 12A, and similarly to Example 1, differential measurements were performed on a filled concrete structure and an unfilled concrete structure using the rectangular parallelepiped excitation coil 12A and a detection coil 14 similar to that of Example 1, and the magnetic flux density was measured from the induced electromotive force detected by the detection coil 14.

[0077] 16A and 16B are diagrams showing the configuration of a rectangular parallelepiped excitation coil 12A used in Example 2, with (A) being a plan view and (B) being a front view. As shown in Fig. 16, the rectangular parallelepiped excitation coil 12A was produced by laminating the same electromagnetic steel sheets as in Example 1 into a rectangular parallelepiped shape measuring 100 mm x 40 mm x 80 mm, forming this into a coil core 12h (coil core cross section: 100 mm x 40 mm), and winding a coil 12i with 9 turns in the axial direction (80 mm portion) of the coil core 12h. In the rectangular parallelepiped excitation coil 12A, one magnetic pole tip face is positioned to face the measurement surface of the object to be measured.

[0078] Fig. 17 is a diagram showing the magnetic flux density in the Z direction of the U-shaped excitation coil 12 of Example 1 and the rectangular parallelepiped excitation coil 12A of Example 2. The horizontal axis of Fig. 17 is the distance (m) from the excitation coil surface, and the vertical axis is the magnetic flux density (T). In Fig. 17, the magnetic flux density is shown when the applied voltage of the pulse generating unit 13 is 500V and 900V, and it was found that when the applied voltage was 900V, the rectangular parallelepiped excitation coil 12A had a higher magnetic flux density than the U-shaped excitation coil 12.

[0079] 18 shows the induced electromotive force in the X direction of the excitation coil 12, where (A) shows the U-shaped excitation coil 12 of Example 1 and (B) shows the rectangular parallelepiped excitation coil 12A of Example 2. The horizontal axis of Fig. 18 is the distance (mm) from the center of the coil, and the vertical axis is the induced electromotive force (V). 18, in the U-shaped excitation coil 12 of Example 1, the magnetic field lines flow in a direction connecting the left and right magnetic pole tips 12b, 12c, and it was found that the induced electromotive force is greatest directly below the center of the main body of the U-shaped excitation coil 12. As a result, the U-shaped excitation coil 12 has the characteristic of exciting a magnetic field in the Z direction directly below the excitation coil 12 as well as a large horizontal magnetic field in the X direction at the center of the excitation coil 12. On the other hand, in the rectangular parallelepiped excitation coil 12A of Example 2, the magnetic field is concentrated in the Z direction at the center of the excitation coil 12A, and the magnetic field is dispersed to the left and right outside the excitation coil 12A due to the repulsion of magnetic field lines, so that the X-direction magnetic field is hardly acting directly below the excitation coil 12A. As a result, the rectangular parallelepiped excitation coil 12A is characterized by having a strong magnetic field in the Z direction and a magnetic field that spreads in the X direction.

[0080] Fig. 19 is a diagram showing the receiving positions of the detector coil 14 relative to the rectangular parallelepiped excitation coil 12A of Example 2. As shown in Fig. 19, the detector coil 14 is arranged at measurement points 1 and 2, with its diameter surface in the Z direction and located to the left of the rectangular parallelepiped excitation coil 12A in the X direction, measurement point 3, with its diameter surface in the Z direction and located adjacent to the center of the longitudinal direction (X direction) of the coil core of the rectangular parallelepiped excitation coil 12A, and measurement points 4 and 5, with its diameter surface in the X direction and located to the right of the rectangular parallelepiped excitation coil 12A in the X direction.

[0081] Figure 20 shows the magnetic flux density of the secondary magnetic field detected at each receiving position shown in Figure 19, with the horizontal axis representing the measurement point and the vertical axis representing the magnetic flux density (T) due to the filled concrete structure and the unfilled concrete structure at each measurement point. As shown in Figure 20, the polarity of the magnetic flux density is reversed between filled and unfilled conditions, making it easy to determine whether grout is filled or unfilled. Furthermore, the difference in magnetic flux density between filled and unfilled conditions was greatest at measurement point 3, followed by measurement point 4, which is located near the rectangular excitation coil 12A directly above the steel sheath and receives the magnetic field in the X direction. Therefore, in the case of the rectangular excitation coil 12A, when measurement point 3, i.e., the detection coil 14, is positioned so that its diametric plane is in the Z direction and adjacent to the center of the coil core of the rectangular excitation coil 12A in the longitudinal direction (X direction), the magnetic flux density in the unfilled condition is greater than that in the filled condition, and the waveform of the differential magnetic flux density is significantly different, making it easier to determine whether grout is filled or unfilled. Here, orienting the detection coil 14 so that its diametric plane is in the Z direction improves the sensitivity of the magnetic field in the Z direction.

[0082] The present invention can be embodied in various forms without departing from the spirit of the invention. While the embodiment in which the induced electromotive force detected by the detector coil 14 is measured over time has been described, the measurement unit 15 of the measurement device 10 in FIGS. 1 and 8 may measure the induced electromotive force instead of the induced current. The calculation unit 16 may then calculate the difference between the induced electromotive force generated by the detector coil 14 acquired in the first stage and the induced electromotive force acquired by the detector coil 14 in the second stage. Furthermore, the evaluation unit 17 may compare the difference between the induced electromotive force acquired in the first stage and the induced electromotive force acquired in the second stage, i.e., the measurement data 16a with the reference data 16b, and generate a first evaluation index value 17a based on the difference. This allows the measurement device 10 to compare the measurement data 16a of the difference due to the induced electromotive force using the detector coil 14 with the reference data 16b regarding the filling state of the grout material, thereby evaluating the quality of the filling state of the PC grout 22a in the sheath 21 of the concrete structure 20. [Explanation of symbols]

[0083] 5. Substrate (transparent resin board) 6 Stiffening plate 7 Solid Spacer 10. Measuring equipment 11. Housing 11a Handle 12 U-shaped excitation coil 12A rectangular excitation coil 12f,12g pole end face 12h coil core 12i coil 13 Pulse generator 13a charging circuit 13b Discharge circuit 13c power supply 13d Charging control circuit 13e Step-up transformer 13f Bridge Rectifier Circuit 13g Voltage setting section 14, 14A, 14B, 14C detection coils 14a Circulating wire 14b, 14c Connection wiring 15 Measurement section 16 Arithmetic section 16a Measurement data 16b Reference Data 17 Evaluation Section 17a First evaluation index value 17b Threshold 17c Evaluation Results 17d Location information 17e Two-dimensional coordinate information 17f Second evaluation index value 18 Memory section 19 Display section 19a Two-dimensional graphs 20 Concrete Structures 21 Sheath 22 PC steel material 22a PC grout 23 Measurement Surface 24 Bending-up area

Claims

1. an excitation coil arranged so that two magnetic pole tip faces of mutually opposite polarities face the measurement surface of the measurement object, or a rectangular parallelepiped excitation coil arranged so that one magnetic pole tip face faces the measurement surface of the measurement object; a pulse generating unit that applies a pulse current to the excitation coil; a detection coil disposed on a plane including the two magnetic pole tip surfaces of the excitation coil, and spaced apart from an axis connecting the two magnetic pole tip surfaces, or spaced apart from the rectangular parallelepiped excitation coil; a measuring unit that measures an induced current or an induced electromotive force generated in the detection coil; Including, the detection coil is made of a surrounding conductor, and a detection surface defined by the surrounding conductor is arranged parallel to the measurement surface; the excitation coil and the detection coil are disposed on a substrate; the excitation coil and the detection coil are disposed separately on the substrate, A measurement device, characterized in that at least the excitation coil is fixed to the substrate, and the substrate is placed on the measurement surface of the object to be measured.

2. 2. The measuring device according to claim 1, wherein an end of the excitation coil is fixed to the substrate via a stiffening plate.

3. 2. The measuring device according to claim 1, wherein the excitation coil is fixed to the substrate via an elastic member.

4. 2. The measuring device according to claim 1, wherein the excitation coil having the two magnetic pole end faces has a U-shape.

5. 2. The measuring device according to claim 1, wherein the detection coil is positioned in the vicinity of the excitation coil so as to receive a magnetic field in the Z direction perpendicular to the measurement surface of the object to be measured, or a magnetic field in the X direction, which is the longitudinal direction of the PC steel of a post-tensioned concrete structure in which PC steel is embedded in a sheath as the object to be measured and filled with grout, on the measurement surface.

6. Using the measurement device according to any one of claims 1 to 5, In a state where there is no steel material within the range of influence of the excitation magnetic field, a pulse current is applied to the excitation coil by the pulse generating unit to apply a magnetic field to the surroundings in order to measure the reference point; a first step of measuring an induced current or an induced electromotive force generated in the detection coil by the measurement unit; a second step in which a pulse current is applied to the excitation coil by the pulse generating unit with both magnetic pole end faces of the excitation coil facing each other in the longitudinal direction of the sheath of a post-tensioned concrete structure, which is the object of measurement and has PC steel embedded in the sheath and filled with grout, to apply a magnetic field to the concrete structure, and the measurement unit measures the induced current or induced electromotive force generated in the detection coil as an electromagnetic field response to the magnetic field; a third step of calculating a difference between the induced current or induced electromotive force obtained in the first step and the induced current or induced electromotive force obtained in the second step; A fourth step of comparing the difference measurement data with reference data on the filling state of the grout material to evaluate the quality of the PC grout filling state in the sheath of the concrete structure; A method for evaluating the filling state of PC grout in a concrete structure, comprising:

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