JPH0768763B2 - METHOD AND DEVICE FOR DETECTING INTERNAL STATE OF PACKING GROUT FOR CONCRETE STRUCTURE - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The disclosed technology measures non-destructively the filling state of grout in the sheath around the PC steel rod interposed in the concrete structure in civil engineering and construction work. Belongs to the field of technology.

<Summary of summary> Therefore, the invention of this application is filled in the sheath around the PC steel rod required for the prestressed concrete member of a large concrete structure such as a mountain bridge. Input the elastic wave such as ultrasonic wave and measure the reflected wave of the presence or absence of filling of grout such as cement mortar, the solidification state over time after filling, and the state of voids and cracks caused by corrosion. It is an invention relating to a method for continuously or intermittently detecting the interposed state of the grout, and an apparatus directly used for the method, and in particular, PC steel interposed in the grout. An ultrasonic elastic wave of a high frequency pulse of several tens of kHz to several MHz is input from the oscillator of the transmitting sensor from one end on the open side of the rod, and a reflected wave from the other end is output from the oscillator of the receiving sensor and received. Ultrasonic wave transmitter Interposed state detecting method for filling grout concrete structure which is adapted to nondestructively measure the interposed state of the grout around the PC steel rod by an oscilloscope synchronized operation, and an invention relating to the apparatus.

<Prior Art> As is well known, modern civilization is supported by many kinds of instruments, mechanical devices, structures, etc. backed by science and technology.

Therefore, in order for such instruments, machines, structures, etc. to fully and reliably exhibit their original functions as designed, until their completion and at regular intervals during operation, Irregular tests, functional tests, maintenance and maintenance are essential, and some are legally obligatory.

Lid, these tools, devices and structures are initially manufactured, assembled,
Errors during construction, vibration, various external forces during operation, thermal behavior,
This is because the functions may not be fully fulfilled due to environmental changes and the like.

Of these, most of the various mechanical devices are assembly and assembly of multiple parts, so each element can be disassembled, and the assembly and assembly processes and after completion In general, it is easy to carry out tests and functional tests, and it is also relatively easy to disassemble and fully inspect during regular and irregular inspections.

However, errors, vibrations, external forces, thermal behavior, changes in the surrounding environment, etc. that make the functions of these instruments and devices insufficient are relatively small, and the main body itself is a small size, but the main body itself is a large size. Therefore, the applied external force and vibration are large, and the environment is subject to severe environmental changes, such as steel frames and concrete structures, or composite types of these structures, especially large structures, once they are constructed, they are easy to handle. It is almost impossible to inspect each one by disassembling and dismantling, and it is extremely difficult to attach and detach the inspection device and the recording device and operate them from a high place due to safety measures. It is impossible to adjust to the side, so
To deal with this, a so-called nondestructive inspection is required for the functional inspection after completion or during operation.

Therefore, for example, non-destructive inspection methods for concrete structures such as bridges constructed in mountainous areas generally include X-ray method, ultrasonic inspection method (AE inspection method), and radar inspection method. .

<Problems to be solved by the invention> By the way, in the non-destructive inspection of such a structure, especially a large structure, a set of inspection devices has a structure such as a high position construction of a mountain portion of a structure or a long and high size. Due to the structure of itself and the relationship with the surroundings, there is a high risk, and it is difficult to set in a complicated structure part, and moreover,
When the number of inspection sites is large and covers a wide area, there is a disadvantage that the inspection becomes large-scale and the cost is high.
In the case of a concrete structure, there is a drawback that it is practically impossible to set the device to necessary parts because it is embedded inside the concrete except a part of the fixing part of the PC steel rod. It was

For example, in a mode where prestressing is introduced using PC steel rods for concrete structures such as bridges, the PC steel rods may unexpectedly become cracked due to corrosion or fatigue over time. There is an extremely problematic problem in the case where the prestress is greatly reduced and the proof stress is reduced.Therefore, in concrete structures, etc. In order to transmit stress, the grout cement mortar, etc. is filled in the sheath surrounding the PC steel rod so as to achieve the adhesive force with the PC steel rod. If the adhesion between the PC steel rod and the grout is reduced or insufficient due to insufficientness, unfortunately forgetting to fill, etc., or voids due to corrosion are generated, adhesion fracture may occur. , Led to the breaking of the PC steel rod, there is a possibility that a major accident occurs.

The decrease in adhesive force due to such adhesive failure causes differences in the cracking occurrence state and concentration of cracks, and appears as an increase in deflection of the girder, and when adhesive failure reaches the fixing portion,
There is a high possibility that fatigue fracture will occur at the threaded portion.

Therefore, in order to deal with this, it is necessary to directly and after-measurement and inspect whether or not the injection and filling of grout such as cement mortar in the sheath in the outer peripheral portion of the PC steel rod is performed as designed. It will also be necessary for the management of.

Therefore, the installation of the device is relatively easy and the risk is small,
An ultrasonic flaw detection method that has high safety, is easy to handle, and is strong against noise has been put into practical use, and ultrasonic waves used for inspection of defects that are planar and at a short distance range from 1 to 10 depending on the minimum defect portion. Although a direct wave of megahertz is used, since the influence of grout such as cement mortar filled around the PC steel rod as a waveguide rod is small, the PC
There was a problem in that it was not possible to detect the time-dependent intervention state immediately after the grout was filled, such as the appropriate amount of grout around the steel rod, cracking, and the occurrence of fatigue.

In addition, if it is necessary to measure temporally the change in the solid filling state with time immediately after filling, independently of the presence or absence of pre-filled grout in the sheath around the PC steel rod of the concrete structure (void formation due to corrosion However, in such a case, the prescribed inspection cannot be performed because the influence state around the PC steel bar cannot be detected by the straight wave ultrasonic wave having the directivity of 1 to 10 MHz. There was an inconvenience.

And, it is extremely important to detect whether or not the grout is filled in the sheath, whether it is sufficient or not, and whether the grout and the PC steel rod are in good contact with each other. The technology to respond to this has not been developed, and it is the current situation that its appearance is greatly expected.

<Object of the invention> The object of the invention of this application is in the presence or absence of an appropriate filling amount of grout around the PC steel rod of the concrete structure based on the above-mentioned conventional technique or during the operation of the interposed state, or immediately after the filling. Problems of state change inspection and measurement over time, and technical issues that should be resolved by the expectations of related industries.
Tens to hundreds of kHz to generate elastic waves in a wide range of Hz
High-frequency pulse with no directivity, the attenuation by distance in the frequency range is small, and by using the ultrasonic wave of the high-frequency pulse that does not require resolution, it is input as an elastic wave at one end of the PC steel bar and the reflected wave is By receiving and measuring from the end, it is possible to grasp the installation state of the filled grout at a predetermined timing or in real time over time. It is an object of the present invention to provide an improved method for detecting the state of interposition of a filling grout of a concrete structure, and an apparatus directly used for the method.

<Means and Actions for Solving the Problem> In order to solve the above-mentioned problems, the structure of the invention of the present application, which is based on the above-mentioned object, is made of precast concrete for concrete structures such as mountain bridges. Insert and embed a PC steel rod inside the filling graph of cement mortar, etc. in the inner sheath, abut the oscillator of the transmission sensor at one end of the open part, and integrate it into a high frequency pulse of several tens of kHz to several MHz. The ultrasonic waves are input to generate a wide-band elastic wave, and the high-frequency wave of several MHz goes straight in the PC steel bar due to its directivity, and the low-frequency wave of several tens of kHz to several hundred kHz is the PC steel bar. Reflection is repeated in the inside and is received by the transducer of the receiving sensor provided at the other end.When the grout exists around the PC steel rod, the elastic wave is greatly affected by it, and when there is no grout. Produces a reflected wave (echo) that is not affected Output from the transducer of the receiving sensor and measured by an oscilloscope, and coagulation or gelation of grout with time is also observed as an effect on the reflected wave of the elastic wave. And gelation state, as well as voids, cracks, etc. are observed and measured in real time, and are taken in close-up and recorded so that appropriate measures can be taken.
The oscillator of the transmission / reception sensor can be easily attached to and detached from the open end of the PC steel rod, can be easily attached and detached, and the measurement can be performed smoothly. Also, because it is an ultrasonic measurement, it is safe and no noise is generated. It is a technical measure that makes it possible to perform measurements in a state that is difficult to pick up.

<Principle Background of the Invention> When a high-frequency pulse such as an ultrasonic wave is input to a transmission sensor installed at one end of a steel rod to generate a broadband elastic wave of several tens of kHz to several MHz, the elastic wave of the steel rod is generated. When propagating in the longitudinal direction, a wave with a high frequency of several MHz has directivity, so it travels straight, while a relatively low frequency of several tens of kHz to several hundred kHz.
Since the wave motion of is not directional, it repeats reflection inside the steel rod and is detected by the reception sensor installed on the opposite side.

It has been found that when such a wave propagates through the steel rod in the axial direction, the sound pressure decreases according to the propagation distance of the steel rod.

Thus, as shown in FIG. 1, when the unbonded steel rod 1 is in the free surface state, the elastic wave generated by the oscillator 2 is reflected inside the steel rod 1 in addition to the longitudinal wave P ₁ traveling straight. The reflected wave P _s propagating as a result of velocity dispersion due to the difference in sound velocity and becomes a plurality of wave groups.

On the other hand, as shown in FIG. 2, when the steel rod 1 in the bonded state is embedded in the grout 3 and is not a free surface, each time reflection is repeated at the boundary between the side surface of the steel rod 1 and the grout 3. The wave is dissipated to the outside of the steel rod 1, and its energy is gradually attenuated.

The state of such elastic waves in FIGS. 1 and 2 can be visually checked with a CRT of an oscilloscope through a reception sensor (not shown),
When the horizontal axis is the time axis and the vertical axis is the voltage axis, the results are as shown in Fig. 3 (corresponding to Fig. 1) and Fig. 4 (corresponding to Fig. 2) (T ₁ is from wave start to P ₁ wave reception) time of).

This phenomenon occurs in the unbonded member (without grout).
For PC steel rod, the wave is almost completely reflected due to the free surface state, while the bond member (with grout)
Regarding the PC steel rod in the inside, from the constraint by the grout in the sheath, it is known that the reflected wave in the PC steel rod is in a state of being easily absorbed in the grout from the boundary between the grout and the PC steel rod, and from this, If the received waveform of the elastic wave propagating in the PC steel rod is measured, the filling and inserting condition of the PC steel rod and the grout surrounding it can be detected from the change.

The invention of this application was developed and devised based on the above-mentioned theoretical background.

<Example> Next, regarding the invention of this application, an embodiment of the state of the existing filling state detection measurement of grout cement mortar filled with a sheath around the PC steel rod of the prestressed concrete member of the concrete structure is illustrated as an example. It will be described below with reference to.

The illustrated embodiment shows a PC prestressed concrete member for bridge girders.
It is a mode to non-destructively inspect whether or not the grout cement mortar through the sheath is filled into the PC steel rod for prestressing the girder through the sheath, as shown in FIG. In addition, a sheath 6 is coaxially arranged on the outside of the PC steel rod 5 embedded in the PC girder 4 of the bridge girder for prestressing as in the conventional manner, and the PC steel rod 5 and the sheath 6 are provided. A cement mortar 3 made of grout is filled between and.

An ultrasonic transducer 2 serving as a transmission sensor is attached to one end of the PC steel rod 5 and electrically connected to the ultrasonic generator 7 via a circuit 8.

An ultrasonic transducer 2'as a receiving sensor is attached to the other end of the PC steel rod 5 and is electrically connected to the oscilloscope 9 via a circuit 10.

The ultrasonic wave generator 7 and the oscilloscope 9 are synchronous signal circuits.
11 is connected, and the oscilloscope 9 is connected to a recording-like close-up device 12.

In the above-mentioned configuration, the output pulse signal from the ultrasonic generator 7 excites the ultrasonic transducer 2 via the circuit 8 to generate an elastic wave.
Propagate into the PC steel rod 5.

The elastic wave (including the reflected wave) propagating in the PC steel rod 5 is received by the ultrasonic transducer 2'of the receiving sensor at the other end, and the received signal is visually observed by the oscilloscope 9 via the circuit 10. It is formed and measured in a predetermined manner, and is also recorded in close-up by the close-up device 12.

Thus, the waveform formed by the oscilloscope 9 has the above-mentioned first waveform.
As shown in FIGS. 4A to 4C, in the bond state in which the grout cement mortar 3 which is basically interposed is filled, a reflected wave is not observed, a linear waveform appears, and the unfilled unbonded state appears. In this case, the reflected wave appears and the waveform is disturbed.

Therefore, by measuring the reception waveform of the elastic wave of the oscilloscope 9, the presence or absence of the grout cement mortar 3 and the state of interposition (corrosion, voids, cracks) and the like can be observed in real time in an analog manner, and the detected data is a close-up device.
Recorded at 12, the best response can be taken immediately.

In this way, the elastic wave propagating in the PC steel rod 5 can be measured for changes in the received waveform, and the interposition state of the PC steel rod 5 and the surrounding interposition grout 3 can be observed.

Next, an experimental example according to the above-mentioned embodiment will be shown.

The specimen used was a PC girder (girder height 65c as shown in Figs. 6-9).
m, width 50 cm, length 6.4 m) 4 with φ45 mm sheath 6 placed inside, and φ32 mm PC steel rod (Type B No. 2 φ32 SBPR 9
5/120) 5 post-tension type 5 bodies with a short section were used.

Incidentally, 13 is a partition plate, and 14 is an embedded bearing plate.

A prestress of 52.8 tf was introduced into the PC steel rods 5, and then four grouts 3 were injected into the sheath 6 of the PC girder 4.

Tables 1 and 2 show the formulations of concrete and grout, and Table 3 shows the compressive strength.

As the cement, early-strength cement was used.

An electrohydraulic fatigue tester with a capacity of 150 tf (50 tf range) was used for the loading test, and the loading method was a bending test by two-point concentrated loading using a load distribution girder 15 as shown in FIG. In the fatigue test, the lower limit load is 21 tf (PC steel bar stress 60 kgf / mm ² equivalent), and the upper limit load is the load added with stress fluctuation,
The repetition rate was 2 to 2.5 Hz.

Regarding the measuring method of the elastic wave measurement, the measurement was performed at an arbitrary number of repetitions before the test use of each sample 4 and during the fatigue test.

In the observation of the propagating elastic wave, the electrical signal from the receiving sensor 2'is directly received by the oscilloscope (20 MHz) 9 and observed in real time.

The situation of the received waveform was recorded by photographing the screen of the CRT with the close-up device 12.

Thereafter, work to the area of the received waveform with planimetry, the data wavefront ratio _{(s / s o × 100%} s: area of bond members, s _o:
The area of unbonded members).

The PC girder 4 is used to confirm the adhesion failure of the PC steel rod 5 and the grout 3.
Was monitored by a strain gauge attached to the fixing nuts (Dividark method) on the fixed side and the tension side of both ends.

Table 4 below shows the wavefront ratio of the PC girder specimen 4 before the test and during the fatigue test.

The wave front factor during the fatigue test was the value at the time of repeated loading that was closest to the destruction of the PC girder 4.

PC for unbonded specimen No.1 without grout 3
The attenuation of the received waveform was small in the steel rod 5 due to the perfect reflection state, and the wave group was composed of the P ₁ wave and the P ₅ wave generated by velocity dispersion.

The wavefront ratio without grout was set to 100%.

On the other hand, the received waveforms of the bond specimens No. 2 to No. 5 filled with grout before the test were only P ₁ wave (sound velocity 5540 m / s), and the existence of P _s wave was not recognized.

This is because when the P _s wave repeats reflection inside the PC steel rod 5,
Since the acoustic impedance of the steel rod 5 and the grout 3 are close,
It is judged that the energy was gradually absorbed from the boundary with the grout 3 and the amplitude of the _Ps wave was attenuated.

As described above, the wavefront ratio of the adhesion state before the test is 0.4 to 1.1.
It was found to be remarkably small.

From the above test data, the presence or absence of the filling of the grout 3 in the sheath 6 in the PC girder 4 is clearly seen as the received waveform of the propagating elastic wave in the PC steel rod 5, and the phenomenon is CRT of the oscilloscope 9. Observed above.

Therefore, it was determined that the filling degree of the grout 3 can be evaluated by performing the calibration.

Example of reception waveform according to the number of repetitions (N) of reflection of elastic wave in the PC steel bar 5 Figure 11, 12, 13 for sample No. 4 (Reception sensitivity: 20 mV / div, time axis: 0.5 msec / div).

As shown in Fig. 11 N = 0, the received waveform before the test use is P ₁
With only waves (wave front ratio 0.5%), the number of repetitions N increases (N =
16 thousand times: Fig. 12 wave front ratio 2%, N = 208,000 times: Fig. 13 wave front ratio 24%), and it was found that a lot of _Ps waves were received.

Fig. 14 shows the relationship between the strain of the nut and the number of reflection repetitions, such as the tightening and fixing of the end of the PC steel rod at each stress level.

As the number of repeated reflections increased and the adhesion failure progressed and reached the position of the fixing nut, the fluctuation due to the test load began to propagate to the nut and the strain (compression) amplitude increased,
It was found that the adhesion between the PC steel rod 5 and the grout 3 was reduced.

It was also found that the wavefront ratio increases with an increase in nut strain amplitude, as shown in Fig. 15, corresponding to Fig. 14 described above.

It can be seen that the change in the wavefront rate is in good agreement with the behavior of the strain amplitude in any of the sample Nos. 1 to 5.

Then, it was found that when the stress amplitude was high, or when the wave front ratio was large even before the test, the adhesion fracture proceeded quickly and the effect thereof appeared.

In addition, as shown in Table 4, the specimen whose fracture position is in the fixing part
In No.3, the wave front ratio was maintained at about 20% after repeated loading, and a fluctuation of about 8% was observed due to the stress amplitude.

In contrast, specimen No. 5 has a wavefront ratio of 10 when repeatedly loaded.
%, Which was small, and the variation due to stress amplitude was 2% or less.

In the received waveform of Specimen No. 2 which was once subjected to the fatigue test (without breaking), P ₁ wave and P _s wave were observed even during unloading, and a decrease in adhesion was confirmed.

As described above, the increase in the wave front ratio clearly showed the tendency of the decrease in the adhesive force between the PC steel rod 5 and the grout 3.

From these facts, it was confirmed from the test that the observation of the P _s wave in the received waveform of the propagating elastic wave in the PC steel rod 5 is an effective detection means for the evaluation of the adhesion property between the PC steel rod 5 and the grout 3. It was done.

<Effects of the Invention> As described above, according to the invention of this application, basically, an elastic wave such as an ultrasonic wave of several tens of kHz to several MHz is input from one end of a PC steel rod for prestressing a concrete structure such as a bridge. Let the PC
Good design of the grout in the sheath by observing the reflected wave from the other end due to elastic wave absorption of grout such as cement mortar around the steel rod and observing it with an oscilloscope and observing the interposed state of the grout It is possible to detect the filling state, the solidification state over time, the corrosion occurrence state, the existence state of voids, cracks, etc. Therefore, non-destructive inspection during the operation of the structure can be performed, and the data can be converted into analog digital form. Since it can be observed and memorized in real time, it is not necessary to take appropriate measures to deal with it immediately, and it can be used as reference data for other structures. It

In this way, by inputting ultrasonic waves of elastic waves into PC steel rods in concrete structures such as PC girders, it is possible to detect the presence or absence of grout filling in the sheath from the wave condition that has propagated through the PC steel rods. can, adhesion fracture in PC steel bar and the grout can be observed from the change of the wavefront rate due to the presence of P _s-wave, these things during cyclic loading is of course, load holding state or even when removing the load There are effects that are applicable.

Thus, in the detection device, by attaching an ultrasonic transducer as a transmission sensor to the end face of the open end of the fixing portion of the PC steel rod and an ultrasonic transducer of a reception sensor at the other end
There is also an effect that it can be easily attached to and detached from the steel rod, is easy to handle, and can detect the inserted state quickly and efficiently.

In addition, since ultrasonic waves are pulsed ultrasonic waves of several tens of kHz to several MHz, they are safe and do not pick up noise. Moreover, transient phenomena occur under the influence of grout without directivity. There is an effect that the reflected wave from the other end surface can be separated and received, and there is an effect that it can contribute to inspection of construction completion of concrete structures and the like, examination of durability during operation, and maintenance management.

[Brief description of drawings]

The drawings are explanatory views of an embodiment of the invention of this application, and
The figure is a schematic cross-sectional view of the propagation state of the elastic wave of the grout of the basic embodiment, FIGS. 3 and 4 are the CRT waveform diagrams of the received wave of 100 kHz of the elastic wave in the PC steel rod, and FIG. Schematic diagram of the device, No. 6
~ Fig. 9 is a plan view, side view and Fig. 7 IIX-I of the PC girder of the specimen.
IX sectional view, FIG. 7 IX-IX sectional view, FIG. 10 is a schematic side view of a loading test, FIGS. 11 to 13 are CRT diagrams of received waveforms, FIG. 14 is a characteristic graph diagram of the number of reflection repetitions and nut strain, FIG. 15 is a characteristic graph of the number of reflection repetitions and the wavefront ratio. 3 ... Grout, 5 ... PC steel rod, 6 ... Sheath

Claims (6)

[Claims] 1. A grout filled in a sheath.
In the method of applying an elastic wave to a PC steel rod and measuring the reflected wave of the elastic wave to detect the filling interposition state of the grout,
An elastic wave of several tens of kHz to several MHz is input from one end of the PC steel rod and a reflected wave is received from the other end to nondestructively measure the interposed state of the grout filling body around the PC steel rod. A method for detecting the state of insertion of a filling grout of a concrete structure, characterized by the above. 2. The method for detecting the state of interposition of a filling grout for a concrete structure according to claim 1, wherein the input elastic wave is an ultrasonic wave. 3. The method for detecting the state of interposition of a filled grout for a concrete structure according to claim 1, wherein the grout is cement mortar. 4. The method for detecting the state of interposition of a filling grout for a concrete structure according to claim 1, wherein the measurement is performed continuously or intermittently with time. 5. An interposition detecting device for a filling grout of a concrete structure in which a vibrator is provided at an end of a PC steel rod inserted into a grout of a sheath and electrically connected to a measuring device, wherein One is a transmission sensor and is electrically connected to the ultrasonic pulse oscillation device, and the other transducer is a reception sensor and is electrically connected to an oscilloscope that is synchronously connected to the ultrasonic pulse transmission device. An insertion state detecting device for a filling grout of a concrete structure, which is characterized in that 6. A device for detecting the state of interposition of a filling grout for a concrete structure according to claim 5, wherein a close-up device is connected to the oscilloscope.