JP2009008521A - Inspection method and device of casted concrete - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method and device of casted concrete, which has high reliability and certainly performs inspection of the whole region of casted concrete including a sheath pipe and driven pile. <P>SOLUTION: Two wires 14 are kept in parallel with a waterproof insulator, a sensor cable 12 whose terminal end is short-circuited by a resistor 15 is buried in the longitudinal direction of the inside of the cast concrete 11, an alternating current signal such as sine wave, a rectangular pulse, or a step-like pulse is applied from a measuring device 19 to the input side of the sensor cable, the current flowing at this time is measured, the measured current data is compared with preset reference current data, and the state of the cast concrete is inspected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for inspecting cast concrete, and more specifically, whether or not there is a failure in filling when concrete (including grout) is placed on a sheath tube, cast-in-place pile, etc., and whether or not an abnormality has occurred due to ground fluctuation, etc. The present invention relates to a method and an apparatus for inspecting cast concrete for inspecting.

  As a method of inspecting the filling condition of the cast concrete, a detection unit consisting of two conductors separated by a fixed interval is embedded and fixed in the concrete, and the capacitance is different depending on whether the periphery of the detection unit is air or concrete. A method for obtaining the filling degree of concrete by utilizing the change is known. The detection unit can be formed by removing the insulation coating from a part of the electric wire that holds the pair of conductors in parallel in the insulation coating and exposing the pair of conductors (see, for example, Patent Document 1).

It is also known to detect the position of water leakage in a concrete structure by laying a twisted wire with a water-permeable coating in the concrete structure, outputting an electric pulse to the twisted wire, and observing the reflected wave. (For example, see Patent Document 2).
Japanese Patent Laid-Open No. 6-229968 JP 2004-85285 A

  However, since the method described in Patent Document 1 uses only a part of the electric wire from which the insulation coating has been removed as the detection unit, it is not possible to detect a filling failure in a portion where the insulation coating has not been removed. There is. Moreover, in the method described in Patent Document 2, if the water-permeable coating absorbs moisture at the time of placing concrete, it is difficult to distinguish it from water leakage, and there is a problem in reliability as an inspection method.

  Accordingly, an object of the present invention is to provide a method and an apparatus for inspecting cast concrete that can reliably inspect the entire area of cast concrete such as a sheath tube and a cast-in-place pile, and is excellent in reliability. Yes.

  In order to achieve the above object, the first configuration of the method for inspecting cast concrete according to the present invention is to place a sensor cable in which two electric wires are held in parallel with a water-resistant insulator and whose ends are short-circuited by resistance. Embedded in the concrete, on the input side of the sensor cable, an AC signal including not only a sine wave but also a rectangular pulse or a stepped pulse is applied and the current flowing at that time is measured. It is characterized by inspecting the condition of the placed concrete by comparing with the set reference current data.

  Further, the second configuration of the method for inspecting cast concrete according to the present invention includes a plurality of sensor cables in which two electric wires are held in parallel with a water-resistant insulating material and whose ends are short-circuited with a resistance, and the inside of the cast concrete. Embedded in parallel to each other, apply an AC signal to the input side of each sensor cable, measure the current flowing at that time, and compare the measured current data with each other to inspect the condition of the placed concrete It is characterized by doing.

  Furthermore, the third configuration of the method for inspecting cast concrete according to the present invention is a method in which two cables are held in parallel with a water-resistant insulator, and sensor cables whose ends are short-circuited by resistance are provided inside a plurality of cast concrete. Each of the sensor cables is imbedded, an AC signal is applied to the input side of each sensor cable, the current flowing at that time is measured, and the measured current data is compared with each other to check the condition of the placed concrete. It is characterized by.

  In addition, according to the method of the present invention, in each of the above configurations, the application of the AC signal, the measurement of current data, and the comparison of the current data are performed immediately after placing concrete, the application of the AC signal, the measurement of current data, the current It is characterized by comparing data periodically after placing concrete.

  Further, the casting concrete inspection apparatus of the present invention is a sensor cable embedded in the casting concrete in a state where the two electric wires are held in parallel with a water-resistant insulator and the terminal ends are short-circuited by resistance, A transmitter for applying an AC signal to the input side of the sensor cable, an ammeter for measuring the current when the AC signal is applied, and setting the current data measured by the ammeter in comparison with reference current data stored in advance And a calculation means for determining the state of the concrete.

  According to the present invention, when an AC signal (incident pulse) is applied to the input side of the sensor cable, a reflected wave is generated because the capacitance or characteristic impedance of the sensor cable changes at a point where air or water exists in the concrete. . Therefore, by detecting the state of the reflected wave by the change of the current (pulse waveform) and comparing it with the preset reference current data, or comparing the current data detected by any one sensor cable as the reference current data From the state of the reflected wave, it can be determined whether air or water is present in the cast concrete.

  Further, the size of the area where air or water exists can be obtained from the amount of change in current, and the position can be obtained by measuring the time until the reflected wave returns. In addition, by periodically inspecting every certain period, it is possible to inspect for the occurrence of cracks in the concrete and the ingress of water into the interior. Presence / absence can be determined easily and reliably.

  FIG. 1 is an explanatory view showing an example of an inspection state according to the method for inspecting cast concrete according to the present invention, FIG. 2 is a perspective view showing an example of the shape of the sensor cable, and FIG. 3 is an explanatory view showing an installation example of the sensor cable.

  In order to inspect the filling state of a long cast concrete 11 such as a sheath tube or a cast-in-place pile, a sensor is placed so that the concrete is buried in the longitudinal direction inside the cast concrete 11 before placing the concrete. The cable 12 is installed. The sensor cable 12 is obtained by holding two electric wires 14 and 14 made of a metal wire such as copper having a low resistance value in parallel by a water-resistant insulator 13 such as a synthetic resin. The typical cross-sectional shape is an ellipse or oval shape as shown in FIG. 2A, or an iron array shape as shown in FIG. 2B, and is susceptible to the influence of substances around the sensor cable 12. . In addition, a resistor 15 for short-circuiting the electric wires 14 and 14 is provided at the end of the sensor cable 12.

  For the installation of the sensor cable 12, an appropriate method can be adopted according to the situation of the object to be placed with concrete. For example, in the case of a sheath tube in which concrete is cast and filled through a steel rod or wire in the axial direction of the metal sheath, appropriate cable holders are provided at both ends of the metal sheath, and the resistance 15 is provided by the cable holder. The other end of the metal sheath is fixed to one end of the metal sheath, and the other end side of the metal sheath is connected to the sensor cable 12 in a state where the lead wire 16 having an appropriate length is drawn from the end of the metal sheath. Can be fixed. When placing concrete using the cast-in-place method, install appropriate cable holders similar to those described above at least at both ends of the reinforcing bar to be placed in the placement section before placing the concrete. The sensor cable 12 may be fixed in a state where the (termination resistor) 15 is positioned and the lead wire 16 is drawn from the upper end.

  Although the position of the sensor cable 12 can be selected as appropriate, in the case of a cast-in-place pile, a large number of reinforcing bars are arranged vertically and horizontally, so the sensor cable 12 is installed over the entire length in the longitudinal direction of the pile so as to be orthogonal to the reinforcing bars. It is preferable to do. The number of sensor cables 12 to be installed is arbitrary and can be appropriately selected according to the size of the sheath tube or cast-in-place pile.

  In addition, when the cable holder is difficult to attach or the sensor cable 12 cannot be fixed by the cable holder in terms of the placement length, as shown in FIG. The sensor cable 12 can be arranged and fixed along the reinforcing bar 17 arranged over the entire length in the direction. In this case, it is possible to directly fix the sensor cable 12 to the reinforcing bar 17, but as shown in FIG. 3B, by interposing the buffer resin 18 between the sensor cable 12 and the reinforcing bar 17, The influence from a reinforcing bar can be reduced.

  After installing the sensor cable 12 and placing concrete, the measuring device 19 is connected to the lead wire 16 extending from one end of the sensor cable 12 embedded in the placed concrete to inspect the concrete filling state. As described above, the sensor cable 12 that holds the two electric wires 14 and 14 in parallel has an impedance that depends on the frequency according to the structure and relative dielectric constant of the material constituting the cable. That is, in the low frequency region, the impedance of the sensor cable 12 depends on the conditions such as the thickness of the electric wires, the interval, the relative dielectric constant of the surrounding material, and the impedance decreases in inverse proportion to the increase in frequency. However, when a synthetic resin such as polyethylene is used as the insulation coating constituting the water-resistant insulator 13 and the distance between the wires 14 is 5 cm or less, the impedance is constant without depending on the frequency in a high frequency region of several MHz or more. It becomes.

  Thus, the frequency at which the impedance does not change as the frequency increases is called a transition frequency, and the impedance that becomes constant at a frequency equal to or higher than the transition frequency is called a characteristic impedance. As described above, the characteristic impedance and the transition frequency are the thickness and resistance value of the electric wire 14 constituting the sensor cable 12, the distance between the two electric wires 14, the shape and relative dielectric constant of the surrounding water-resistant insulator 13, Since it is determined by conditions such as the relative dielectric constant of the material outside the water-resistant insulator 13, by setting these conditions in advance, a desired transition frequency and characteristic impedance can be set.

Usually, the relative permittivity of the placed concrete is about 60, which is close to water immediately after placing, but decreases with solidification of the concrete, and after 3 days or more, the relative permittivity is about 20 descend. Therefore, the capacitance value of the sensor cable 12 embedded in the solidified concrete is calculated using the water-resistant insulation 13 holding the electric wire 14 and the relative dielectric constant of the surrounding solidified concrete, and this value is calculated as a characteristic impedance. and Z _0. Since this value Z ₀ is a pure resistance, by setting the resistance value of the resistor 15 attached to the end to Z ₀ , an AC signal is sent from the lead wire 16 connected to the input side of the sensor cable 12 after the concrete is solidified. In the case of concrete in which the periphery of the sensor cable 12 is solidified over the entire length when applied, the AC signal is consumed by the resistor 15 at the end of the sensor cable 12 and no reflected wave is generated.

  On the other hand, in concrete placement, the inflow of concrete is incomplete and air is left in the concrete as bubbles, or in the case of cast-in-place piles, the water used for drilling, the groundwater that flows from the outside, or the soil around the hole When the soil collapses and soil remains in the concrete, for example, if water is present in the solidified concrete, the dielectric constant around the sensor cable 12 increases and the capacitance also increases, so the impedance of that portion decreases. . On the contrary, when air exists around the sensor cable 12, the dielectric constant of the portion is lower than that of concrete, so that the impedance is increased.

  Therefore, if water or air is present in the solidified concrete, the current when an AC signal is applied to the sensor cable 12 changes. Therefore, basically, as shown in FIG. The transmitter 19a that generates the current and the AC ammeter 19b that measures the current when the AC signal is applied are installed, and the presence or absence of air or water in the concrete is measured by measuring the current when the AC signal is applied. Can be inspected. Since this inspection can be performed over the entire length of the sensor cable 12, it is possible to continuously inspect the entire area of the sheath tube and cast-in-place pile, and the presence of air and water in the placed concrete. Can be reliably detected.

  Judgment of the concrete filling state by the current data (including the rectangular wave shape) measured when an AC signal including a rectangular wave is applied is performed by comparing the measured current data with preset reference current data. be able to. Here, as the reference current data, current data that is theoretically calculated in advance, current data obtained by experiments, current data collected in the past in the same manner as the installation work was statistically processed. Various data such as data, current data when a plurality of sensor cables 12 are installed in one sheath tube and cast-in-place pile, current data measured in other sheath tubes and other cast-in-place piles in which concrete is placed simultaneously Current data can be used as reference current data.

  For example, by installing a plurality of sensor cables 12 in one sheath tube or cast-in-place pile and comparing the current data measured by each sensor cable 12, current data different from other current data is measured. In this case, it can be detected that an abnormality has locally occurred around the sensor cable 12.

  In addition, since the dielectric constant immediately after placing concrete is close to water, if there is a small unfilled area where air remains, sufficient detection accuracy may not be obtained due to the influence of errors. In such a case, when a certain period of time has passed since the concrete was placed, and the concrete was solidified to some extent and the dielectric constant decreased, the same AC signal was applied again to measure the current, and the measurement was performed immediately after placing. By comparing the current data as reference current data, it is also possible to determine the presence or absence of a filling failure from the change in the measured current data. Furthermore, since the electric wire 14 is covered with the water-resistant insulator 13, no abnormality occurs in the sensor cable 12 due to moisture in the concrete.

  On the other hand, the concrete immediately after placement has a large dielectric constant and capacitance, and the impedance between two adjacent wires 14 is small. For this reason, immediately after placing concrete, an alternating current signal having a frequency of 1/10 to 1/100 of the transition frequency is applied from the lead wire 16 to the sensor cable 12, and the current flowing at this time is measured. Since the impedance value of the sensor cable 12 connected in parallel to the circuit 15 is 1/10 to 1/100 compared with that after solidification, the sensitivity to changes in the surrounding conditions is large. The change in current data can be easily detected. For example, when air is present in the concrete immediately after placing, the capacitance becomes large and the current data decreases, so that a filling failure can be easily detected.

  As a means to improve measurement accuracy, install the same number of sensor cables 12 of the same structure at the same position of the sheath tube or cast-in-place pile of the same structure as the construction work prior to actual construction, and use the same concrete To create a calibration sample, using the same AC signal as the AC signal used in the actual construction inspection, and the current data immediately after placement and the current data after a certain period of time respectively. It is also possible to measure and set the measured change rate of both current data as the reference change rate of the current. In this case, by measuring the current immediately after placing with a constructed sheath tube or cast-in-place pile and after a certain period of time, and comparing the change rate of the measured current data with the reference change rate, the reference change rate When the rate of change in current measured is smaller than that of, it can be determined that air or earth and sand remains in the cast concrete.

  In addition, when the concrete has solidified and the change in dielectric constant has disappeared, the sample is disassembled and the internal state is observed, and data with no abnormalities such as the presence of air is used as the reference data for calibration. If there is no difference between the reference data and the measurement result at the time of construction, it can be determined that the placed concrete is free of defects, so that it can be guaranteed that the sheath tube and the pile are free of defects. Similarly, when multiple sheath tubes and cast-in-place piles are constructed, all sheath tubes and cast-in-place piles are checked by confirming that the data measured in each sheath tube and cast-in-place pile are the same or substantially the same. It can be assured that the concrete is placed in the same state. Therefore, the reliability of the sheath tube and the cast-in-place pile can be improved, and the occurrence of an accident due to a defect when placing concrete can be prevented.

  Furthermore, the change in capacitance immediately after placing concrete and after solidification is compared with the reference data for calibration. If the measured capacitance after placing and after solidification is smaller than the capacitance of the reference data, air is present. Can be determined. On the other hand, the capacitance measured at the time of placing is not different from the reference data, but if the capacitance measured after solidification is larger than the capacitance of the reference data, it can be determined that water is present in the concrete.

  When applying the time-of-flight measurement method as the measurement method, as shown in FIG. 5, as the measurement device 19, a rectangular pulse transmitter 21 that generates an AC signal, the impedance of the measurement device 19, and the sensor cable 12 uses an impedance conversion circuit 22 for matching 12 impedances, a boxcar integrator 23 for obtaining an average value of a large number of pulses to reduce the influence of noise, and a waveform analysis means 24 for performing waveform analysis. Then, a rectangular pulse or a stepped pulse is incident on the lead-out line 16 from the rectangular pulse transmitter 21 via the impedance conversion circuit 22 as an AC signal.

  At this time, when the concrete is completely filled over the entire length of the sheath tube or the pile, the incident rectangular pulse is absorbed by the terminal resistor 15 having a predetermined resistance value, and no reflected wave is generated. If air or earth and sand are present inside, the capacitance at that point is lowered and the characteristic impedance is increased, so that a reflected wave is generated. The state of this reflected wave is taken into the waveform analysis means 24 via the boxcar integrator 23, and the time from the incidence to the reflection is measured by the waveform analysis means 24, so that the size of the existing air (bubble) region can be reduced. From the intensity of the reflected wave, the position can be measured by the delay time from incident to reflection.

  In the time-of-flight measurement method using air as an inspection target, the value of the characteristic impedance does not match the resistance value of the termination resistor 15 when the concrete has a high dielectric constant immediately after placement. Will occur. However, since the difference in dielectric constant with respect to the presence of air increases, the sensitivity increases and the air detection capability increases. Thereby, it becomes possible to find a defect immediately after placement, and it is possible to quickly perform measures such as compaction.

  When applying the time response analysis method, as shown in FIG. 6, as the measuring device 19, the frequency variable transmitter 31, the directional coupler 32, the impedance conversion circuit 33, the reception amplifier 34, and the inverse Fourier transform circuit are used. 35, a plurality of frequencies above the transition frequency are changed from the frequency variable transmitter 31 and incident on the sensor cable 12 via the directional coupler 32 and the impedance conversion circuit 33.

  When air or water is present in the concrete due to poor placement of the concrete, a reflected wave is generated because the characteristic impedance of the sensor cable 12 changes at that portion, so that the reflected wave is reflected from the directional coupler 32 to the receiving amplifier 34. The wave signal is sent and amplified, and the amplified signal is output to the inverse Fourier transform circuit 35. The inverse Fourier transform circuit 35 performs inverse Fourier transform with reference to the signal output from the reception amplifier 34 and the signal obtained from the variable frequency transmitter 31, so that the delay time from incident to reflection and the size of the defective filling portion are large. The area where air or water exists is specified.

  Since the time-of-flight measurement method is observation of a single-shot phenomenon by a rectangular pulse or a stepped pulse, an expensive boxcar integrator must be used for noise removal, whereas the inverse Fourier transform circuit 35 is used. The time response analysis method used has a high performance for removing the influence of noise because the calculation is performed in a wide frequency range, and the apparatus price can be kept low.

  These measurement methods can be carried out independently, but can be carried out by appropriately combining a current measurement method, a time-of-flight measurement method, and a time response analysis method as necessary. At this time, since the sensor cable 12 can be used in common in each method, these measurements can be easily performed only by connecting a necessary device to the lead wire 16.

  Furthermore, by saving the data acquired by various measurement methods after construction, it is possible to easily detect any abnormality in the pile or sheath tube from the outside without destroying the pile or sheath tube due to ground fluctuation or secular change. Can be detected. For example, as shown in the construction example in FIG. 7, the sensor cable 12 is installed on the cast-in-place pile 42 that supports the building floor structure 41, and the lead wire 44 is connected to the outside from the impedance converter 43 to convert the impedance. Construction of buildings and structures is performed with the vessel 43 left. It is preferable that the lead wire 44 is gathered on the terminal board 45 so that it can be used later easily.

  After completion of the construction, the above measuring device was connected to the lead wire 44 or the terminal board 45 at any time or periodically, and each sensor cable 12 was measured and stored by the above measuring method. By comparing with the data, it is possible to non-destructively inspect that the pile 42 is broken due to ground fluctuation or the like and that water has entered the sheath tube.

  In addition to embedding a sensor cable in the longitudinal direction of a long and narrow concrete placement object such as a sheath tube or a pile as described above, for example, as shown in the construction example of FIG. Also in the flat structure 51, the sensor cable 12 similar to the above is installed as appropriate, and the lead wires 44 are respectively connected from the impedance converter 43 to the outside, so that defects at the time of placing the structure 51 can be eliminated. Discovery and long-term regular inspection can be easily and reliably performed non-destructively.

  The present invention can be applied to various concrete placing objects as long as the sensor cable as described above can be embedded therein, and is not limited to concrete placing on site, but manufactured in a factory. Is also applicable. When manufacturing a sheath tube or a pile at a factory, it is possible to easily and surely perform a periodic inspection after construction by manufacturing the sensor cable in a state where it is embedded in advance and including an impedance converter.

It is explanatory drawing which shows an example of the test | inspection state by the test | inspection method of the placement concrete of this invention. It is a perspective view which shows the example of a shape of a sensor cable. It is explanatory drawing which shows the example of installation of a sensor cable. It is explanatory drawing which shows the usage example of the measuring apparatus which uses an ammeter. It is explanatory drawing when the time of flight measuring method is applied to a measuring apparatus. It is explanatory drawing when a time response analysis method is applied to a measuring device. It is explanatory drawing which shows the construction example of the cast-in-place pile which installed the sensor cable. It is explanatory drawing which shows the construction example which installed the sensor cable in the structure of a cube or a flat plate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Casting concrete, 12 ... Sensor cable, 13 ... Water-resistant insulation, 14 ... Electric wire, 15 ... Resistance, 16 ... Lead wire, 17 ... Reinforcing bar, 18 ... Resin for buffering, 19 ... Measuring apparatus, 19a ... Transmitter , 19b ... AC ammeter, 21 ... rectangular pulse transmitter, 22 ... impedance conversion circuit, 23 ... boxcar integrator, 24 ... waveform analysis means, 31 ... variable frequency transmitter, 32 ... directional coupler, 33 ... impedance Conversion circuit 34... Receiving amplifier 35. Inverse Fourier transform circuit 41. Building floor structure 42. Cast-in-place pile 43. Impedance converter 44. Lead line 45. Terminal board 51.

Claims (6)

  A sensor cable, in which two wires are held in parallel with a water-resistant insulator and whose end is short-circuited with a resistor, is embedded in the concrete, and an AC signal is applied to the input side of the sensor cable. A method for inspecting cast concrete, comprising: measuring a flowing current and comparing the measured current data with preset reference current data to inspect the condition of the placed concrete.   A plurality of sensor cables, in which two wires are held in parallel with water-resistant insulation and whose ends are short-circuited with resistance, are buried in parallel in the cast concrete, and an AC signal is sent to the input side of each sensor cable. A method for inspecting cast concrete, wherein the current flowing at that time is measured, and the measured current data is compared with each other to check the condition of the placed concrete.   Sensor cables, in which two wires are held in parallel with water-resistant insulation and whose ends are short-circuited with resistance, are embedded in a plurality of cast concrete, and an AC signal is applied to the input side of each sensor cable. A method for inspecting cast concrete, wherein the current flowing at that time is measured, and the measured current data is compared with each other to check the condition of the placed concrete.   The method for inspecting cast concrete according to any one of claims 1 to 3, wherein the application of the AC signal, the measurement of current data, and the comparison of the current data are performed immediately after the concrete is placed.   The method for inspecting cast concrete according to any one of claims 1 to 4, wherein the application of the AC signal, the measurement of current data, and the comparison of the current data are periodically performed after the concrete is placed.   A sensor cable embedded in the cast concrete with the two wires held in parallel by a water-resistant insulator and the terminal end short-circuited by a resistor, and transmission that applies an AC signal to the input side of the sensor cable And an ammeter for measuring the current when an AC signal is applied, and an arithmetic means for determining the state of the placed concrete by comparing the current data measured by the ammeter with reference current data stored in advance. An inspection apparatus for cast concrete characterized by the above.

Images