JP2005315622A - Nondestructive inspection method and device of concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure simply on the site the object physical quantity such as the compressive strength of a concrete structure or the progression degree of an alkali aggregate reaction by determining the sound speed ratio between a longitudinal wave and a transversal wave by a one-time measuring work relative to one measuring point. <P>SOLUTION: This nondestructive inspection method of the concrete structure comprises steps for: (a) allowing an ultrasonic pulse 7 to enter the inside the structure 6 from a transmitting probe 3 for the longitudinal wave in contact with the outer surface of the concrete structure 6, and detecting a reflected wave 8 reflected by the boundary surface of the concrete structure 6 and returned by a receiving probe 4 for the longitudinal wave in contact with the outer surface of the structure 6; (b) calculating the sound speed ratio R between the longitudinal wave and the transversal wave from an arrival time of a bottom surface echo 12a in an unconverted mode acquired at first and a delay echo 12b in a converted mode acquired thereafter in a plurality of peaks 12a, 12b recognized in the waveform of the reflected wave; and (c) determining the object physical quantity corresponding to the sound speed ratio R measured on the site from the correlation between the sound speed ratio R acquired beforehand relative to the concrete structure 6 and the object physical quantity which is an inspection object. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nondestructive inspection method and apparatus for nondestructively measuring target physical quantities such as compressive strength of concrete structures and the degree of progress of alkali aggregate reaction.

Concrete structures may suffer from insufficient compressive strength due to poor construction and early deterioration due to salt damage and alkali-aggregate reaction, etc. Therefore, their measurement has been attempted by various methods. In terms of cost, nondestructive inspection of concrete structures by ultrasonic exploration is attracting attention.
Therefore, the applicant of the present application has already developed a method for measuring the progress of the alkali-aggregate reaction to the concrete structure by ultrasonic exploration, and this measurement method includes an average value of the reflected sound velocity by the ultrasonic reflection method, Measure the average value of the transmitted sound velocity measured by the ultrasonic transmission method for the part corresponding to the ultrasonic propagation path, and based on the correlation between the difference in the average value and the progress of the alkali aggregate reaction, The degree of progress of the alkali aggregate reaction at the measurement point is estimated (claim 1 of Patent Document 1).

In the above measurement method, since it is necessary to measure the transmitted sound velocity by the ultrasonic transmission method, in the case of a concrete structure in which the back surface of the retaining wall or dam is buried in the earth and sand, it is necessary to remove the core. There is room for further improvement in terms of measurement speed and cost. Therefore, a technique for measuring the target physical quantity of a concrete structure without completely removing the core from an existing concrete structure that cannot employ the ultrasonic transmission method has not yet been put into practical use.
JP 2003-302382 A

By the way, the present inventor measured the ultrasonic wave velocity of longitudinal waves and transverse waves in a laboratory by using a transmission method on a concrete core sampled from an existing concrete structure, and the sound velocity ratio, compressive strength, and alkali bones were measured. As a result of investigating the relationship with the progress of the aggregate reaction, the sound velocity ratio of the longitudinal wave and the transverse wave is proportional to the compressive strength of the concrete (see Fig. 3), and also strong against the progress of the alkali aggregate reaction It was found that there is a correlation (see FIG. 4).
Therefore, the acoustic velocity of longitudinal and transverse waves is measured on site for a concrete structure with unknown compressive strength and alkali-aggregate reaction, and the sound velocity ratio of the longitudinal and transverse waves obtained by this is measured. If applied to the above correlation diagram, even for concrete structures that cannot adopt the ultrasonic transmission method, the target physical quantities of the concrete structures in the field can be completely non-destructed without performing troublesome work such as core extraction. Can be sought.

  However, in order to measure the sound velocity of the transverse wave and longitudinal wave at a specific measuring point of a concrete structure by ultrasonic survey, measurement using a probe dedicated to longitudinal wave and measurement using a probe dedicated to transverse wave are usually used. Therefore, there is a problem that the sound speed ratio cannot be obtained immediately at the site and the work takes a very long time. In particular, the measurement using the probe exclusively for shear waves is performed by interposing a special contact medium between the probe and the object to be inspected.

  In view of the above-described conventional problems, the present invention obtains the sound velocity ratio of longitudinal waves and transverse waves in one measurement operation at one measurement point, and compresses strength and alkali bone of a concrete structure. An object of the present invention is to provide a nondestructive inspection method and apparatus for a concrete structure capable of easily measuring a target physical quantity such as a degree of progress of a material reaction on site.

The inventor of the present application has experienced many ultrasonic surveys on concrete structures using a probe dedicated to longitudinal waves. Even in the case of concrete structures, the transverse waves generated by mode conversion at the boundary surface are reflected waves. And the present invention has been completed.
That is, the present invention is a nondestructive inspection method for a concrete structure including the following steps.

(A) An ultrasonic pulse is incident on the inside of the structure from the longitudinal wave transmission probe brought into contact with the outer surface of the concrete structure, and the boundary surface of the concrete structure is reflected and returned. Detecting the reflected wave with a receiving probe in contact with the outer surface of the structure (b) Of the plurality of peaks recognized in the waveform of the reflected wave, the bottom echo without mode conversion obtained first (C) calculating the sound velocity ratio of longitudinal waves and shear waves from the arrival time of the delayed echo with mode conversion obtained thereafter and the arrival time of the delayed echo with mode conversion. A step of obtaining the target physical quantity corresponding to the sound speed ratio measured in the field from a correlation with a target physical quantity.

According to the present invention described above, the arrival time of the bottom echo without mode conversion obtained first and the arrival time of delayed echo with mode conversion obtained after that among the plurality of peaks recognized in the waveform of the reflected wave Therefore, the sound velocity ratio between the longitudinal wave and the transverse wave is calculated, so that the sound velocity ratio can be obtained with a single measurement for a specific measurement point of the concrete structure. There is no need to perform separate measurements with a probe dedicated to shear waves.
For this reason, by obtaining the target physical quantity corresponding to the sound speed ratio simply measured at the site as described above from the correlation between the sound speed ratio obtained in advance for the concrete structure and the physical quantity to be inspected, the target Physical quantities can be determined very quickly.

In the present invention, the target physical quantity of the concrete structure is not particularly limited as long as it has a correlation with the acoustic velocity ratio of the longitudinal wave and the transverse wave. However, as described later, the acoustic velocity ratio of the longitudinal wave and the transverse wave is the compressive strength of the concrete structure. It is known from the measured data in the laboratory for the concrete core that there is a strong correlation with the progress of the alkali aggregate reaction, so at least these are included in the target physical quantity .
Assuming that the concrete structure is a macroscopically homogeneous isotropic body, the elastic constant (Young's modulus) can be obtained from the density of the concrete structure, the sound velocity and sound velocity ratio of the longitudinal wave, and the Poisson's ratio is Since they can be obtained from the sound speed ratio, these are also included in the target physical quantity.

On the other hand, in the present invention, a plurality of ultrasonic pulses are incident on the concrete structure at a predetermined timing from the transmitting probe, and each reflected wave of the ultrasonic pulses is received by the receiving probe and received. By averaging the digitized waveforms of each signal on the same time axis, it is possible to amplify the reflected wave from the detection target while removing the scattering that hinders detection, and to improve the measurement accuracy. Can be improved.
In that case, if one or both of the probes is moved along the outer surface of the concrete structure and the reflected wave is detected, the inside of the point where the probe contacts Even if relatively large coarse aggregates and voids exist, each incident ultrasonic pulse does not continue to collide with these obstacles. For this reason, the influence of the reflected wave by those obstacles is maintained as it is, and the peak of the output waveform becomes clearer.

Therefore, in performing the above measurement method, in order to prevent the influence of the reflected wave due to the coarse aggregate as much as possible, the size of the coarse aggregate in the concrete (about 3.0 to 5.0 cm) is assumed. It is preferable to move the probe within a range. Further, in the case where the transmission probe and the reception probe are configured as separate and independent elements, it is preferable that the probes are moved separately.
The reason for this is that moving the transmitting probe prevents the ultrasonic pulse immediately after incidence from continuing to collide with the obstacle, and moving the receiving probe causes the echo just before reception to the obstacle. This is because the collision is prevented and the influence of the obstacles in the concrete is less than when only one of the probes is moved.

  On the other hand, in the above measurement method, the method of moving the probe is not particularly limited. For example, the probe may be reciprocated in a certain direction such as vertical or horizontal, or the surface of the concrete structure. The probe may be moved randomly within a predetermined range. However, as will become apparent in the embodiments described below, it is preferable to move the probe randomly in order to minimize the adverse effects of obstacles in the concrete.

  As described above, according to the present invention, it is possible to determine the sound velocity ratio of the longitudinal wave and the transverse wave in one measurement operation with respect to one measuring point, so that the compressive strength of the concrete structure and the progress of the alkali aggregate reaction The target physical quantity such as degree can be easily measured at the site.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a nondestructive inspection apparatus according to the present invention.
As shown in the figure, the nondestructive inspection apparatus 1 of the present embodiment includes an inspection apparatus main body 2, a transmission probe (pulsar) 3 dedicated to longitudinal waves connected to the inspection apparatus main body 2, and the transmission probe. A longitudinal wave-dedicated reception probe (receiver) 4 connected to the inspection apparatus main body 2 separately from the contact 3 and an information processing apparatus 5 including a notebook computer connected to the inspection apparatus main body 2 Has been.

Among these, the transmission probe 3 transmits an ultrasonic pulse 7 toward the inside of a concrete structure 6 made of a retaining wall, a dam or the like, and is an electroacoustic such as piezoelectric ceramics or piezoelectric polymer. An acoustic matching layer made of epoxy resin or the like is laminated on a piezoelectric element made of a conversion element.
The receiving probe 4 receives the echo 8 of the ultrasonic pulse 7 on the same surface as the transmitting side, and has the same basic structure as the transmitting probe 3. Note that the probes 3 and 4 of this embodiment are ultra-wideband that covers from an audible range of about 10 kHz to a frequency range of a normal flaw detector of about 5 MHz.

The inspection apparatus main body 2 includes a transmission control circuit that controls the transmission timing of the ultrasonic pulse 7 by the transmission probe 3, a main amplifier that amplifies the signal from the reception probe 4, and a signal amplified by this amplifier. An A / D conversion circuit for converting the digitized waveform and an adder for averaging the digitized waveforms on the same time axis.
On the other hand, the information processing apparatus 5 includes an auxiliary storage device including a hard disk to which an OS, predetermined application software, and the like are fixed, an auxiliary storage device (main ram) that temporarily stores the software and data, the software, A personal computer main body 9 composed of a CPU for calculating and controlling data and a display unit 10 composed of a liquid crystal display or the like connected to the main body 9 are provided. Application software that gives instructions to the inspection apparatus body 2 such as digital filter processing for data is installed.

For this reason, according to the nondestructive inspection apparatus 1 of the present embodiment, a plurality of ultrasonic pulses 7 are incident on the concrete structure 6 from the transmission probe 3 at a predetermined timing, and the ultrasonic pulses 7 are An output waveform 11 obtained by receiving each echo 8 by the reception probe 4 and averaging the received signals digitized on the same time axis is displayed on the display unit of the information processing device 5. 10 can be displayed.
The program stored in the auxiliary storage device of the personal computer main body 9 includes the relationship between the sound velocity ratio of the longitudinal wave and the transverse wave and the compressive strength of the concrete (FIG. 3), and the progress of the alkali-aggregate reaction of the concrete. And the sound speed ratio (FIG. 4) are included as data.

  These data are obtained by measuring the ultrasonic wave velocity of longitudinal waves in a laboratory for a large number of concrete cores (φ100 mm, H = 200 mm) sampled from a structure different from the concrete structure 6 to be measured. The ultrasonic wave velocity of the transverse wave is measured by the transmission method, and the compression strength of each core and the progress of the alkali aggregate reaction are obtained. In addition, about the compressive strength, since 3-5 cores are obtained in one sampling position, the average value was made into the compressive strength in the said sampling position.

On the other hand, since a general-purpose criterion for quantifying the progress of the alkali-aggregate reaction has not yet been probable, in this embodiment, the state of the aggregate in the cross section when each core is sliced is as follows. A method was adopted in which stages were divided and weighted at 10 locations to score.
(1) Reaction stage 1 = × 2 points (white spots are seen on the aggregate)
(2) Reaction stage 2 = × 4 points (the aggregate is surrounded by a white ring)
(3) Reaction stage 3 = × 8 points (there is a crack in the aggregate)
(4) Reaction stage 4 = × 16 points (aggregate cracks extend to the mortar)

Therefore, if all 10 points of a cross section are in stage (1), 20 points are obtained, and if all are in stage (4), 160 points are obtained.
As shown in FIG. 3, the sound velocity ratio between the longitudinal wave and the transverse wave is proportional to the compressive strength of the concrete, and as shown in FIG. 4, the compressive strength decreases as the degree of progress of the alkali aggregate reaction increases. A strong correlation is observed.
When the concrete structure 6 is assumed to be an isotropic homogeneous elastic body, the elastic constant (Young's modulus) can be obtained by the following equation (1), and the Poisson ratio can be obtained by the following equation (2). be able to. In the following equation, E is an elastic constant, R is a sound velocity ratio, ρ is a density, Vt is a sound velocity of a transverse wave, and ν is a Poisson's ratio.

Therefore, in the present embodiment, the above-described equations (1) and (2) for obtaining the elastic constant and Poisson's ratio are also stored as data in the program stored in the auxiliary storage device of the personal computer body 9.
By the way, the inventor of the present application, while measuring the plate thickness of the concrete structure 6 many times by ultrasonic exploration, even when using only the probes 3 and 4 for longitudinal waves, For example, as shown in FIG. 2, it is noticed that the second peak 12b often appears after the first peak 12a, and this second peak 12b is not the influence of the transverse wave generated by the mode conversion at the boundary surface. I guessed.

Therefore, as shown in FIG. 2, on the waveform data screen, the first cursor 13 is set at the position of the horizontal axis (arrival time) when the longitudinal wave is assumed to be a longitudinal wave (assumed sound velocity of 4000 m / s), and When the second cursor 14 is set at the position of the horizontal axis when the forward wave is a longitudinal wave and the return wave is a horizontal wave (assumed sound speed of 2350 m / s), the first cursor 13 substantially coincides with the first peak 12a, The cursor 14 substantially coincided with the second peak 12b.
Therefore, even when the concrete structure 6 is ultrasonically surveyed using only the longitudinal wave probes 3 and 4, the transverse wave echo generated by the mode conversion at the boundary surface is the reception probe dedicated to the longitudinal wave. 4 was picked up and found to be included in the waveform data of the reflected wave.

For this reason, in the present embodiment, among the plurality of peaks 12a and 12b recognized in the waveform of the reflected wave, the arrival time T1 of the bottom echo without mode conversion obtained first and the mode conversion obtained thereafter are obtained. From the arrival time T2 of the delayed echo, the sound speed ratio between the longitudinal wave and the transverse wave is calculated.
That is, the first peak 12a can be regarded as a bottom echo without mode conversion, and the second peak 12b can be regarded as a transverse wave echo generated by mode conversion at the boundary surface. If the arrival time of the latter is T2, the sound speed ratio R (= Vl / Vt) between the longitudinal wave and the transverse wave can be expressed by the following equation (3).
R = (2 × T2−T1) / T1 (3)

In the present embodiment, the above equation (3) is stored as data in the program stored in the auxiliary storage device of the personal computer main body 9, and the arrival times T1 and T2 obtained in the field are expressed by this equation ( By substituting in 3), the sound speed ratio R can be calculated.
Next, a method for measuring the target physical quantity such as the compressive strength of the concrete structure 6 and the progress of the alkali aggregate reaction using the nondestructive inspection apparatus 1 will be described.
First, an operator brings the transmitting probe 3 and the receiving probe 4 into contact with a place where the target physical quantity on the surface of the concrete structure 6 is to be measured. And the process which transmits the ultrasonic pulse 7 with a predetermined output voltage, injects into the concrete structure 6, and measures the echo 8 by each pulse 7 is repeated many times (for example, about 1000-20000 times).

While receiving the echo 8, for example, as shown in circles A to C in FIG. 1, one or both of the transmission probe 3 and the reception probe 4 are placed in the concrete structure 6. To move along the surface.
The probes 3 and 4 may be moved reciprocally in the vertical direction as shown in the circle A in FIG. 1, or in the horizontal direction as shown in the circle B. It may be reciprocated. Further, as shown in the C circle, the probe may be moved randomly within a predetermined range on the surface of the concrete structure.

Furthermore, in order to prevent the influence of the reflected wave due to the coarse aggregate in the concrete as much as possible, the movement range of the probes 3 and 4 is larger than the expected size of the coarse aggregate (about 3.0 to 5.0 cm). A large range is preferable, and in order to prevent the influence of scattered waves due to poor contact, it is preferable to apply a lubricating liquid to the measurement site of the concrete structure 6. The moving speed of the probes 3 and 4 may be about 5 to 12 cm / second.
Each echo 8 obtained by repeatedly measuring as described above is digitized by the inspection apparatus main body 2, and an output waveform 11 obtained by averaging the digital waveforms on the same time axis is an information. It is displayed on the display unit 10 of the processing device 5.

In addition, the noise contained in each echo 8 is canceled by this averaging, and an output waveform 11 having a higher S / N ratio is obtained. Also, if the amplitude is too large or too small, an appropriate amplitude can be obtained by increasing or decreasing the number of additions and the output voltage.
And by the first peak 12a appearing in the output waveform 11 of the display unit 10, the position of the boundary surface between the concrete structure 6 and the ground 13 behind it is measured, and the plate thickness of the structure 6 is determined, The arrival time T1 of the first peak 12a and the arrival time T2 of the second peak 12b are detected.

Then, by substituting these arrival times T1 and T2 into the equation (3), the sound velocity ratio R between the longitudinal wave and the transverse wave is obtained, and the compression strength corresponding to the sound velocity ratio R is a correlation diagram shown in FIG. The degree of progress of the alkali-aggregate reaction corresponding to the sound velocity ratio R is obtained from the correlation diagram shown in FIG.
In addition, when calculating | requiring an elastic constant (Young's modulus) and Poisson's ratio, it calculates | requires by substituting the said sound speed ratio R and the transverse wave sound speed Vt to said Formula (1) and (2).

  Thus, according to the nondestructive inspection method of this embodiment, the arrival time T1 of the bottom echo 12a without mode conversion obtained first among the plurality of peaks 12a and 12b recognized in the waveform of the reflected wave and thereafter Since the sound velocity ratio R between the longitudinal wave and the transverse wave is calculated from the arrival time T2 of the delayed echo 12b with mode conversion obtained in the above, one measurement operation is performed for a specific measuring point of the concrete structure 6. The sound speed ratio R can be obtained. For this reason, the target physical quantity corresponding to the sound speed ratio R is obtained from the correlation between the sound speed ratio R and the target physical quantity obtained in advance for the concrete structure 6 (FIGS. 3 and 4, and the expressions (1) and (2)). Can be determined very quickly.

  In addition, this invention is not limited to the said embodiment, For example, the probe for longitudinal waves which performs both transmission and reception by one can also be used.

It is a schematic block diagram of the nondestructive inspection apparatus for performing the method of this invention. It is an example of the output waveform at the time of actually measuring. It is a graph which shows the correlation with the sound speed ratio of a longitudinal wave and a transverse wave, and compression strength. It is a graph which shows the correlation with the progress degree of alkali-aggregate reaction, and the sound speed ratio of a longitudinal wave and a transverse wave.

Explanation of symbols

1 Nondestructive inspection device 2 Inspection device body 3 Transmitter probe (Pulsar)
4 Receiving probe (receiver)
5 Information processing equipment 7 Ultrasonic pulse 8 Echo (reflected wave)
9 PC body (calculation means, storage means, control means)
10 Display section

Claims (9)

A nondestructive inspection method for concrete structures including the following steps.
(A) An ultrasonic pulse is incident on the inside of the structure from the longitudinal wave transmission probe brought into contact with the outer surface of the concrete structure, and the boundary surface of the concrete structure is reflected and returned. (B) a mode conversion obtained first among a plurality of peaks recognized in the waveform of the reflected wave; and a step of detecting the reflected wave with a longitudinal wave receiving probe brought into contact with the outer surface of the structure. A step of calculating a sound velocity ratio of longitudinal waves and transverse waves from the arrival time of the bottom echo with no wave and the arrival time of the delayed echo with mode conversion obtained thereafter (c) The sound velocity ratio obtained in advance for the concrete structure Obtaining the target physical quantity corresponding to the sound speed ratio measured in the field from the correlation between the target physical quantity and the target physical quantity to be inspected   2. The nondestructive inspection method for a concrete structure according to claim 1, wherein the target physical quantity is a compressive strength of the concrete structure, a degree of progress of an alkali aggregate reaction, an elastic constant, or a Poisson's ratio. In the step (a), a plurality of ultrasonic pulses are incident on the concrete structure from the transmitting probe at a predetermined timing, and each reflected wave of the ultrasonic pulses is received by the receiving probe. And steps to
A nondestructive inspection method for a concrete structure according to claim 1, further comprising: adding and averaging waveforms obtained by digitizing received signals on the same time axis.   The concrete structure according to any one of claims 1 to 3, wherein the reflected wave is detected while moving either one or both of the probes along the outer surface of the concrete structure. Non-destructive inspection method. An outgoing probe for longitudinal waves for injecting ultrasonic pulses from the outer surface of the concrete structure toward the inside;
A longitudinal wave reception probe for detecting a reflected wave reflected on the boundary surface of the concrete structure and returning to the outer surface;
Of the multiple peaks observed in the waveform of the reflected wave detected by this receiving probe, the arrival time of the bottom echo without mode conversion obtained first and the arrival time of delayed echo with mode conversion obtained thereafter From the calculation means for calculating the sound velocity ratio of the longitudinal wave and the transverse wave,
Storage means for storing a correlation between a sound speed ratio obtained in advance for the concrete structure and a target physical quantity to be inspected;
Control means for obtaining the target physical quantity corresponding to the sound speed ratio measured on-site from the correlation stored in the storage means;
A non-destructive inspection device for concrete structures.   6. The nondestructive inspection device for a concrete structure according to claim 5, wherein the target physical quantity is a compressive strength of the concrete structure, a degree of progress of an alkali aggregate reaction, an elastic constant, or a Poisson's ratio.   The control means makes a plurality of ultrasonic pulses incident on the concrete structure from the transmitting probe at a predetermined timing, and receives each echo of the ultrasonic pulse by the receiving probe. The nondestructive inspection apparatus for a concrete structure according to claim 5 or 6, which has a function of averaging the waveforms obtained by digitizing received signals on the same time axis.   Concrete comprising an inspection apparatus main body, a longitudinal wave transmitting probe and a longitudinal wave receiving probe connected to the inspection apparatus main body, and a programmable information processing apparatus connected to the inspection apparatus main body A computer program for controlling a non-destructive inspection apparatus for a structure, the program causing a computer to execute each step according to claim 1.   A computer-readable storage medium storing the program according to claim 8.

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