JP2020041879A - Impact elastic wave measuring method of cement hardened body - Google Patents

Abstract

To provide an impact elastic wave measuring method of stably and efficiently measuring an elastic wave propagation speed only by Fourier transformation processing even when an analysis method such as auto-correlation is not applied to a cement hardened body that is relatively thick, for example a thickness of 0.6 m or more.SOLUTION: In an impact elastic wave measuring method of a cement hardened body, using a pendulum having a radius R exceeding 1.5 cm and lower than 20 cm and a spherical impact surface of a mass exceeding 0.1 kg and 100 kg or lower, an elastic wave is input to the cement hardened body at a predetermined speed of a strike speed of 0.1 m/s or more and 1.4 m/s or less. An elastic wave reciprocating in the cement hardened body is received, and the elastic wave propagation speed in the cement hardened body or the thickness of the cement hardened body is estimated by frequency analysis.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for measuring impact elastic waves of a hardened cement body such as concrete.

  Cement hardened material such as concrete is used as a basic material for construction of structures, or as a hardened material that is solidified by mixing with wastes such as incinerated fly ash and radioactive waste or filled into these wastes and stable for a long period of time. It's being used. However, while solidification by cement is a chemical reaction and the long-term strength is increased, leaching depends on the material used as concrete, such as aggregate, the components contained therein, or the components containing waste, or depending on the environment in which the hardened material is placed. Due to freezing and thawing, alkali-aggregate reaction, corrosion of reinforcing steel, drying shrinkage, crystallization of cement components, and formation of precipitates, cracks may occur, the strength of the hardened body may decrease, and deterioration such as scaling may occur.

  Usually, the progress of these deteriorations gradually progresses over a long period of several years to several tens of years, and after the progress of the deterioration becomes apparent by visual inspection or the like, it may be difficult to take measures such as repair. For such a problem, monitoring using a nondestructive inspection capable of grasping the internal deterioration state, instead of a visual inspection based on the external appearance, is expected.

  It is known that the propagation speed of elastic waves such as ultrasonic waves has a high correlation with concrete strength, and that the propagation speed of elastic waves decreases when deterioration such as cracking or expansion occurs. However, accurate measurement of the elastic wave propagation velocity has the following problems.

The elastic wave propagation velocity using ultrasonic waves is greatly attenuated due to low energy, and it is difficult to measure the velocity of hard concrete such as thick concrete or waste material such as a drum or concrete to which a steel plate is bonded.

Since the ultrasonic wave propagation velocity is usually measured with a cured body interposed, it is difficult to measure the ultrasonic wave propagation velocity when the back surface cannot be accessed. There is also a method in which a transmitter and a receiver are installed on a measurement surface to measure an elastic wave propagation velocity using bottom surface reflection. However, attenuation is increased because the propagation distance is doubled due to bottom surface reflection. . Attempts have also been made to install a transmitter and a receiver on the surface to capture elastic waves propagating inside, but no information can be obtained up to the deep inside of concrete.

In the measurement of the propagation velocity by ultrasonic waves, a difference occurs in the propagation velocity measured by an apparatus to be used or an analysis method, and an error occurs if the same apparatus is not used, which is not suitable for long-term monitoring.

There is also a measurement method using a shock elastic wave having a large energy (Non-Patent Document 1). For example, concrete can be measured clearly for concrete up to about 0.6 m, but when the cement hardened body becomes thicker than 2 m, reflection and scattering of elastic waves in the hardened body occur, making measurement difficult, and a Fourier using a cross-correlation function. When the distance is 1.2 m or more even when an analysis method based on conversion is used, a clear peak cannot be obtained, and measurement is considered to be difficult. In addition, the input frequency of conventional shock elastic waves is not stable, and the input energy is not stable when hitting with a manually input hammer, and detailed changes in the deterioration state even if data is continuously acquired It is difficult to figure out. Thus, there is a need for a non-destructive inspection method for a hardened cement body that can stably compare with past data for a long time and easily grasp the progress of deterioration.

Iwano et al. Thickness measurement of concrete structures by the impact elastic wave method. 23 No. 1 2001 547-552

  Therefore, it is possible to measure the elastic wave propagation velocity stably and efficiently by using only the Fourier transform process, without using an analysis method such as autocorrelation, for a relatively thick cement hardened body having a thickness of, for example, 0.6 m or more. It was an object to obtain an elastic wave measuring method.

  The present invention has been made in view of the above-described problems, and provides a method for measuring impact elastic waves of a hardened cement body such as concrete.

In order to solve the above problems, the method for measuring the impact elastic wave of the present invention is:
[1] A method for measuring impact elastic waves of a cured cement body, wherein the pendulum having a spherical impact surface having a radius R of more than 1.5 cm and less than 20 cm and a mass of more than 0.1 kg and 100 kg or less is used. An elastic wave is inputted to the hardened body at a predetermined speed of 0.1 m / s or more and 1.4 m / s or less, an elastic wave reciprocating in the hardened cement body is received, and an elastic wave inside the hardened cement body is analyzed by frequency analysis. Provided is a method for measuring the impact elastic wave of a hardened cement body, which comprises estimating a propagation speed or a thickness of the hardened cement body.

[2] The method for measuring the impact elastic wave of a hardened cement body according to [1], wherein a sensor for receiving the elastic wave is attached to a position on the hardened cement body hitting surface where the elastic wave is input.

[3] The method according to [1] or [2], wherein the pendulum has a mass of 1 kg or more and 100 kg or less.

[4] A suspension plate having a friction sheet attached thereto is used to suspend the impacting body having a mass of more than 1 kg and not more than 100 kg, and the suspension plate is pressed against the surface of the hardened cement body via the friction sheet. And a method for measuring the impact elastic wave of a hardened cement body according to any one of [1] to [3], wherein a fulcrum of the pendulum is secured by the frictional force of the friction sheet.

[5] Using a suspension plate having a pendulum with a mass of more than 0.1 kg and not more than 10 kg and having a friction sheet attached thereto, press the suspension plate against the impact surface of the hardened cement body via the friction sheet. Then, the fulcrum of the pendulum is secured by the frictional force of the friction sheet, and the elastic wave is input by a method of covering the surface of the hardened cement body to which the elastic wave is input with a resin sheet having a thickness of 0.02 mm or more and less than 2 mm. The present invention provides a method for measuring impact elastic waves of a cured cement body according to any one of [1] to [4].

Applicable object The hardened cement body of the present invention is a hardened cement body in which voids are filled with cement paste or mortar, in addition to cement paste, mortar, and concrete used for construction. As the filled cement hardened body, for example, a hardened body in which waste is put into a drum or the like and the periphery thereof is filled with cement paste or mortar, a hardened body obtained by solidifying incineration fly ash or the like with a cement material or a geopolymer, etc. There is. The present invention is also applicable to a state in which a steel plate or the like is adhered to the surface of a hardened cement body, or a hardened cement body filled with a drum. The thickness of the hardened cement body is 30 cm or more and about several meters, preferably 0.6 m or more, particularly 2 m or more.

The impacting body has a spherical impacting surface, but the overall shape does not matter. The striking surface is preferably spherical, but may have an elliptical diameter such as an oval or a metal ball such as a steel ball.

The material used for the striking surface of the striking body is preferably a metal having a density of 4 g / cm ³ or more and a Vickers hardness of 50 Hv or more. preferable. Steel balls, stainless steel balls, titanium balls, density 7 g / cm ³ or more 10 g / cm ³ or less of a metal sphere, or the striking face when striking the cured cement, and particularly preferably these metals .
these. For metals such as aluminum having a density of less than 4 g / cm ^3, the radius R for securing the required mass increases, and the contact area with concrete increases, so that elastic waves cannot be efficiently input to the cured body. Gold and silver having a Vickers hardness of less than 50 Hv may cause deformation of the striking body when struck.

Hitting surface R
The radius R of the striking surface is more than 1.5 cm and preferably not more than 20 cm. More preferably, it is 2.0 cm or more and 10 cm or less. This is because if the radius R is small, an input that causes a reciprocal response of the elastic wave cannot be performed, and if the radius R is large, the contact area with the concrete increases, so that the elastic wave cannot be efficiently input to the cured body.

Striking Body Mass The striking body mass is preferably more than 0.1 kg and 100 kg or less. Even if the elastic wave in the cement hardened body is attenuated, there is a minimum mass for inputting measurable energy, and the mass is more than 0.1 kg and 100 kg or less. If the mass is 0.1 kg or less, an elastic wave is generated and energy for propagating through the relatively thick cement hardened body is insufficient, and if it exceeds 100 kg, there is a possibility that the cement hardened body may be damaged at the time of impact. In addition, it is difficult to handle when hitting stably.

As a method of controlling the mass of the impacting body, when using a metal ball such as a steel ball, by changing its size or density, or when the metal ball is insufficient in mass, for example, a part of hardened concrete There is a method of embedding a hemispherical or spherical metal sphere by protruding a part of the surface of the metal sphere, or a method of joining a steel material to a hemispherical or spherical metal sphere by welding or the like and using it as a hitting body.

Elastic Wave Input Method The input of the elastic wave is hit such that the center of gravity of the hitting body is perpendicular to the surface of the hardened cement body. When the hardened cement body surface is horizontal, it can be hit by the free fall of the hit body. In this case, by setting the distance between the hitting surface of the hardened cement body and the surface of the hitting body, the speed of the hitting body at the time of hitting can be set arbitrarily, and a stable elastic wave can be input. Furthermore, in the case of horizontal, rebound by concrete after impact due to free fall may be insufficient, so a helical spring is attached to the upper part of the impact body and fixed at an arbitrary height from the concrete surface, and immediately after impact There is also a method to ensure that the impact body jumps from the concrete surface more than free fall. In the case of free fall, ignoring air resistance, the impact speed does not depend on the mass of the impact object, and the impact speed is v, the distance between the impact surface of the hardened cement body and the impact surface is h, and the gravitational acceleration is g. , Equation 1

On the vertical surface, a method can be used in which a fulcrum 12 is formed on the cement hardened body illustrated in FIG. 1 and the hitting body 11 suspended by a string is hit like a pendulum.

In this case, the preceding equation h required to determine the impact speed v can be determined by equation 2 from the string length R and the distance a between the impact surface of the hardened cement body and the impact body.

This method requires calculation of the impact speed not only for the vertical surface but also for the inclined surface. In addition, there are a method in which a metal ball is rolled using a rail or the like to collide with a hardened cement body, and a method in which a hammer is formed into a spherical hitting surface.

  The impact speed is preferably 0.1 m / s or more and 1.4 m / s or less, more preferably 0.2 m / s or more and 0.9 m / s or less. If it is slower than 0.2 m / s, the input impact force for each measurement greatly varies, and if it is slower than 0.1 m / s, the required elastic wave input energy is insufficient. If the speed is higher than 1.0 m / s, the possibility of damage to the striking surface of the hardened cement becomes high, and if the speed is higher than 1.4 m / s, secondary vibration occurs in the hardened cement due to impact force, and elastic wave propagation. Unreliable vibration occurs and stable measurement cannot be performed.

  At the fulcrum, a percussion body can be hung by drilling holes in a structure such as a post-installed anchor, but the structure is partially destroyed and drilling takes time. If the mass of the impacting body is more than 0.1 kg and not more than about 10 kg, as shown in FIG. 2, the size is not particularly limited, but a square of about 20 cm × 20 cm or a wooden suspension plate 12 of about 10 cm in diameter is used. A method of attaching a rubber sheet 14 or the like as a friction sheet and pressing against a structure such as a concrete hitting surface and securing the fulcrum 12 by the friction force is preferable because non-destructive and efficient measurement can be performed.

When an elastic wave is input by an impact body using a resin sheet, if the mass is large, the impact speed is fast, or the radius R is small, the impact surface of the hardened cement body may be damaged or damaged. At this time, a resin sheet is placed between the hardened cement and the hit object. Examples of the material of the resin sheet include vinyls such as polyethylene and polypropylene, urethane rubber, silicone rubber, butyl rubber, fluorine rubber, chloroprene rubber, rubbers such as NBR and EPDM, and foamable materials can also be used. The thickness of the resin sheet is preferably 0.02 mm or more and less than 2 mm. If the thickness is less than 0.02 mm, there is no protection effect, and the resin sheet itself is greatly damaged. On the other hand, if the thickness is more than 2 mm, the repulsive force of the resin sheet impedes the input of elastic waves generated by the impacting body.

Measurement method Propagation of the input elastic wave can be measured using the method A: a sensor arranged on the back side of the impact surface of the hardened cement body, or the method B: a piezoelectric element arranged on the impact surface of the hardened cement body, etc. Recording using an acceleration sensor using C. Method C: It is conceivable to measure by arranging a sensor at an arbitrary position that you want to measure near the impact position and through the inside of the cement hardened material and recording.

In the case of the method A and the method B, a response frequency is calculated by Fourier transform processing or the like by capturing an elastic wave that reciprocates within the hardened cement body, and the propagation speed is calculated if the thickness of the hardened cement body is known. If the propagation speed is known, the thickness of the cured cement body can be determined. Further, if a change in the deterioration state is grasped, only a successive change in the response frequency may be measured.

On the other hand, in the case of the method C, the hitting time is set to 0, the time (s) at which the elastic wave reaches the arbitrary point is detected by the sensor, and the propagation velocity is calculated from the linear distance between the hitting position and the arbitrary point. . In the method C, the time (s) may vary depending on the striking object, the striking method, and the measurement conditions such as the sensor sensitivity. It is necessary to unify these measurement conditions.

However, Method A and Method B are suitable for long-term monitoring because the differences due to the impacting body, impact method, sensor sensitivity, etc. are small, and in the case of Method B, since the measurement is performed on the impact surface, access to the back of the cement hardened body It is not necessary to perform the measurement, and it is advantageous because it is possible to efficiently measure a structure that is difficult to install on the back surface of the hardened cement body. In the present invention, the method B is basically used. And it is preferable that the sensor position is in a range of 5 to 30 cm with respect to the hit point. If the distance is less than 5 cm, the impact at the time of impact is transmitted to the sensor, causing noise or the like, and the measurement may not be performed properly.

Since the impacting body collides with the vertical plane or horizontal plane at a stable speed when elastic waves are input, it is simple, has excellent reproducibility of the impacting body impact conditions, can grasp the change of the deterioration state over a long period of time, and can harden the cement hardened body. Non-destructive inspection of strength and deterioration state, monitoring over time, and evaluation of its soundness.

It is a schematic diagram which illustrates the method of this invention which makes a fulcrum on a hardened cement body, and hits the hit body hung with a string like a pendulum. It is a schematic diagram which illustrates the method of this invention which secures a fulcrum by the frictional force which presses the suspension board with which the friction sheet was attached on a concrete hitting surface. The waveform recorded by the sensor installed on the hitting surface (left figure) and the waveform recorded by the sensor installed on the back surface (right figure) in Experimental Example 17 are shown. The waveform (left figure) recorded by the sensor installed on the hitting surface and the waveform (right figure) recorded by the sensor installed on the back surface in Experimental Example 34 are shown. The Fourier transform result (left figure) of the waveform recorded by the sensor installed on the hitting surface and the Fourier transform result (right figure) of the waveform recorded by the sensor installed on the back surface in Experimental Example 17 are shown. The Fourier transform result (left figure) of the waveform recorded by the sensor installed on the hitting surface and the Fourier transform result (right figure) of the waveform recorded by the sensor installed on the back surface in Experimental Example 34 are shown.

11: Striking body (pendulum)
12: Pendulum fulcrum 13: Suspension plate 14: Friction sheet

Next, an experimental embodiment including the best mode of the present invention will be described below with reference to the drawings.
A 1 m × 1 m × 1.2 m concrete block is used as a cement hardened body, and an elastic wave is inputted by hitting the center of the 1 m × 1 m surface with a pendulum hitting body, and a position 10 cm from the hitting position (hitting surface) ), And a sensor was arranged at the center of the surface (back surface) facing the impact surface, and the test was performed. The experimental levels are shown in Table 1.

As the impacting body, a steel ball was used in Experimental Examples 1 to 20 and Experimental Examples 33 to 38, and in Experimental Example 21, a radius of 5.times.10 cm.times.10 cm was measured on one 10 cm.times.10 cm surface of a 10 cm.times.10 cm.times.40 cm concrete. Examples in which a steel ball of 0 cm was attached and a steel spherical surface was hit on a concrete block, and Examples 22 to 25 and Example 39 in which a steel material (H-shaped steel) was hit instead of a prismatic concrete in the same manner. In Experimental Examples 26 to 29, a columnar concrete having a radius of 20 cm x height of 40 cm was attached in the same manner. In Experimental Examples 30 to 32, a boring ball was used. Instead of using a spherical shape, a columnar concrete having a radius of 20 cm was used, and the side face was directly hit on the concrete block.

  The impact method was a pendulum method. The length of the string was 50 cm from Experimental Examples 1 to 20 and from Experimental Examples 33 to 38, and 150 cm from the others, and the distance between the concrete surface and the spherical portion of the impacting body was set to a predetermined impact speed. It was controlled by adjusting. In addition, a level using a resin sheet was set for some test levels, and a polyethylene sheet having a thickness of 0.1 mm or a natural rubber sheet having a thickness of 2 mm was used as the resin sheet.

  The sensor used was NP3201 manufactured by Ono Sokki, and the sensor amplifier and data recorder used HIOKI 8947 and 8835, respectively. The recording data was set at intervals of 20 μs. , And the subsequent 4,096 data were subjected to Fourier transform to obtain a response frequency.

The results are shown in Table 1. In each of the tests, the surface properties of the samples were as follows: a level at which slight damage to the impacted surface was observed in each of the three impacts; The sample was indicated by XX, and the sample with no change was indicated by-.

  In the main peak intensity column, in the Fourier transform of the impact surface sensor, the mark x indicates that 1.58 kHz corresponding to a concrete block thickness of 1.2 m is not recognized, and the level where other figures are described indicates that the main peak is It is 1.58 kHz, which is the intensity of the main peak obtained by Fourier transform. The larger this number is, the larger the reciprocating propagation of the elastic wave is.

  The intensity ratio with respect to other peaks indicates the intensity of other appearing peaks when the main peak is set to 1 in the Fourier transform of the impact surface sensor. If this value is large, the response frequency of the reciprocally propagating elastic wave is determined. This indicates that it is difficult to do so, and that no reciprocating propagation occurs according to the concrete thickness.

  In the comprehensive evaluation, the number of circles was larger as the main peak intensity was higher, the intensity ratio with respect to other peaks was lower, and the degree of damage to the hitting surface was lower. However, the level at which the main peak intensity was not recognized or extremely weak, or the level at which the peak other than 1.58 kHz became the largest peak was marked X.

In Experimental Examples 1 to 32, 1.58 kHz corresponding to the concrete block thickness of 1.2 m was recognized as the main peak, and the intensity ratio with other peaks was 0.85 or less. When the mass of the impacting body was 4 kg or more, a slight change in the impact surface properties was sometimes observed. In particular, when the weight is 31 kg or more, it is possible to suppress damage to the hitting surface by covering a part of the hitting surface of the hardened cement body with a resin sheet or reducing the hitting speed to about 0.128 m / s.
For example, in Experimental Examples 28 and 29, although the main peak intensity was large, the impact surface peeled off. However, even in this case, the inside of the cured body was sound and effective as a nondestructive inspection. By reducing the speed to 0.128 m / s, it is possible to suppress damage to the hitting surface.

  All of the experimental examples using 0.1 mm as the resin sheet had a high main peak intensity and a low peak intensity ratio. In Experimental Example 19 in which the 0.1 mm resin sheet was not used, the impact surface slightly changed, but in Experimental Example 17 in which the 0.1 mm resin sheet was used, the impact surface did not change. In Experimental Example 38 and Experimental Example 39 using a 2.0 mm resin sheet, the main peak intensity was extremely weak or no main peak was recognized. If the resin sheet was thick, impact energy was absorbed and elastic waves were input to the concrete block. It turns out that it is difficult.

FIGS. 3 to 6 show Fourier transform of a waveform or a waveform recorded by a sensor in an experimental example. In each of the figures, the left side shows the result of the sensor installed on the striking surface, and the right side shows the result of the sensor recorded by the sensor installed on the back side. FIG. 3 shows waveforms recorded by the sensor installed on the hitting surface and the sensor installed on the back surface in Experimental Example 17. In each of the figures, it can be seen that the elastic wave propagates back and forth in the concrete block and the attenuation is small. In addition, on the impact surface on the left side of FIG. 3, the acceleration (approximately 100 m / s ² ) obtained from the sensor voltage immediately after the impact, and the acceleration (approximately 20 m / s ² ) obtained from the subsequent reciprocating propagation sensor voltage Is high, and it can be seen that the elastic wave is input efficiently. FIG. 4 shows Experimental Example 34. No clear reciprocating propagation was observed in comparison with FIG. 3, and on the left striking surface in FIG. 4, a subsequent reciprocating motion was made for the acceleration (about 30 m / s ² ) obtained from the sensor voltage immediately after the striking. The acceleration obtained from the sensor voltage for propagation is as small as several m / s ² , indicating that the input efficiency of the elastic wave is poor.

  FIG. 5 shows the result of Fourier transform of the waveform measured in Experimental Example 17. A clear response frequency is found at 1.58 kHz on both the impact surface and the back surface, and from this value and the concrete thickness of 1.2 m, the elastic wave propagation velocity can be calculated to be 3800 m / s. Further, the coefficient of variation of the main peak intensity in three measurements on the hitting surface was 13%, and stable measurement was possible. However, in the experimental example 34 shown in FIG. 6, although the response frequency was observed at around 1.58 kHz in the measurement from the back side having no influence at the time of impact shown in FIG. 6, the other frequency peaks were dominant, and the elastic wave of the concrete block was observed. The propagation speed cannot be determined. Also, almost no peak is observed in the measurement from the impact surface. As described above, in Experimental Example 17, a clear response frequency in reciprocating propagation can be confirmed even from the measurement from the impact surface, and measurement can be performed without accessing the back surface of the hardened cement body and installing a sensor. It can be seen that internal deformation of structures such as concrete can be monitored.

Claims (5)

A method for measuring the impact elastic wave of a hardened cement body, wherein a radius R is more than 1.5 cm and less than 20 cm, and a pendulum having a spherical impact surface having a mass of more than 0.1 kg and less than 100 kg is used for the hardened cement body. An elastic wave is input at a predetermined speed of 0.1 m / s or more and 1.4 m / s or less, an elastic wave reciprocating in the cement hardened body is received, and an elastic wave propagation velocity inside the cement hardened body is determined by frequency analysis. Alternatively, a method for measuring the impact elastic wave of a hardened cement body, comprising estimating the thickness of the hardened cement body. 2. The method according to claim 1, wherein a sensor for receiving the elastic wave is attached to a position on the hardened cement body hitting surface where the elastic wave is input. The method according to claim 1 or 2, wherein the mass of the pendulum is 1 kg or more and 100 kg or less. The suspension of the impacting body whose mass of the pendulum is more than 1 kg and 100 kg or less, using a suspension plate with a friction sheet attached thereto, pressing the suspension plate against the surface of the cement hardened body via the friction sheet, 4. The method for measuring the impact elastic wave of a hardened cement body according to claim 1, wherein a fulcrum of the pendulum is secured by a frictional force of the sheet. The mass of the pendulum is greater than 0.1 kg and less than 10 kg, using a suspension plate with a friction sheet attached thereto, pressing the suspension plate against the impact surface of the hardened cement body through the friction sheet, The method is characterized in that a fulcrum of the pendulum is secured by the frictional force of the friction sheet, and the elastic wave is input by a method of covering the surface of the hardened cement body for inputting the elastic wave with a resin sheet having a thickness of 0.02 mm or more and less than 2 mm. The method for measuring the impact elastic wave of a hardened cement body according to any one of claims 1 to 4.