JPS63247608A - Method for measuring thickness and internal cracking position of concrete - Google Patents

Abstract

PURPOSE:To easily and accurately measure the thickness and internal cracking position of concrete by sending ultrasonic waves of different frequencies to the concrete and receiving a resonance wave when the concrete and an ultra sonic wave enters a nearly resonance state. CONSTITUTION:A transmitter 2 and a receiver 3 which are ultrasonic wave vibrators are installed on the surface of the concrete 1 at an interval. Then while the frequency of electric vibrators (rectangular wave signal) from a variable oscillator 21 is varied, the transmitter 2 is excited to send ultrasonic wave pulses. A reflected wave A which is transmitted in the concrete 1 and reflected by the opposite surface is received by the receiver 3, amplified 31, and then displayed on a spectrum analyzer 32. When the concrete 1 almost enters the resonance state, the amplitude of the vibrations increases abruptly and a resonance wave is generated. Further, a wave of frequency almost in the beginning of an increase in the amplitude is sent and the variable oscillator 21 is adjusted finely to detect a frequency MkHz where the spectrum of the resonance wave is maximum. Then the thickness Dcm of the concrete 1 is found from D=v/2M (v: acoustic velocity m/sec).

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for measuring the thickness and location of inherent cracks in concrete.

<Conventional technology> In the case of large concrete structures such as underground petroleum and LPG storage tanks, tunnels, nuclear power plants, etc., it is necessary to measure and verify the thickness of the concrete or the location of inherent cracks from one side of the concrete. Quality is very important from the viewpoint of safety and construction methods.

Conventionally, as a method for measuring the thickness of concrete and the position of inherent cracks from one side, there is a pulse reflection method using ultrasonic waves.

In this method, as shown in FIG. 4, a transmitter 2 and a receiver B3 of an ultrasonic vibrator are installed on one surface of concrete 1 at a constant interval.

The transmitter 2 transmits an ultrasonic wave to the concrete 1, and this ultrasonic wave is transmitted through the concrete 1 and reflected at a discontinuous portion, so that it is reflected after reaching the opposing surface of the concrete 1 or an internal crack.

This reflected wave A is captured by a receiver 3, the arrival time of the reflected wave A is measured, and the thickness of the concrete 1 and the position of any inherent cracks are measured.

Problems to be Solved by the Present Invention> In the case of the above measurement method, the ultrasonic waves sent from the transmitter 2 are divided into a reflected wave A that is transmitted through the concrete 1 and reflected, and a reflected wave A that is directly received by the surface of the concrete 1. Surface wave B propagating to wave device 3
It is divided into

Therefore, this surface wave B and the reflected wave A overlap, making it difficult to accurately capture the reflected wave A.

Moreover, since concrete 1 itself is a material that does not emit wavelengths easily, the measurement error can reach ±50%.
It is not possible to accurately measure the thickness of concrete 1 and the location of inherent cracks.

OBJECT OF THE INVENTION The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to easily and accurately measure the thickness of concrete and the position of inherent cracks from one side of the concrete. The purpose of this study is to provide a method for measuring the thickness of concrete and the location of inherent cracks.

Configuration of the Present Invention> An embodiment of the present invention will be described below with reference to the drawings.

Measuring principle of the present invention When a periodic external force is applied to a single vibrating body, as the period of the external force approaches the period of the natural vibration of the vibrating body, the amplitude of the vibrating body increases rapidly and a resonant wave is generated. do.

The present invention utilizes this resonance, uses concrete as one of the rotating bodies, and uses ultrasonic waves as an external force.

The specific frequency at which resonant waves are generated differs depending on the thickness of concrete.

Therefore, ultrasonic waves are transmitted at different frequencies to the concrete object to be measured.

Then, at a certain frequency, the specific imaging number of the concrete and the frequency of the ultrasonic wave almost match, resulting in a co-imaging state.

Therefore, as described above, when a resonance state occurs, the amplitude of the ultrasonic frequency increases rapidly and a resonant wave is generated.

Therefore, by receiving the resonant wave and detecting the frequency at which the resonant wave is generated, the specific imaging number of the concrete can be determined, and the thickness of the concrete can be calculated using the calculation method described later. .

〉Method for Measuring Concrete Thickness In this example, a case will be described in which concrete 1 having a thickness of 20 cm is used as the object to be measured.

First, a transmitter 2 and a receiver 3 of an ultrasonic vibrator are installed at a distance from each other on one surface of the concrete 1 to be measured.

(1) First measurement In the first measurement, a rough resonance frequency is first found.

The transmitter 2 is excited without changing the frequency of the electric vibration from the variable transmitter 21, and ultrasonic pulses formed by the electric vibration are transmitted from the transmitter 2 toward the opposing surface of the concrete 1. .

Then, the frequency of the ultrasonic wave is found when the natural frequency of the concrete 1 and the frequency of the ultrasonic wave almost match, resulting in a resonant state.

In this embodiment, in order to avoid the influence of surface waves, for example, a rectangular wave is used instead of a sine wave for the dynamic electric signal, and pulses formed by the rectangular wave are repeatedly transmitted to the concrete 1 while changing the frequency.

The reflected wave A transmitted through the concrete 1 and reflected by the opposing surface is received by the wave receiver 3, amplified by the amplifier 31, and then displayed on the screen of the spectrum analyzer 32.

While transmitting ultrasonic pulses while changing the frequency, when the concrete 1 approaches a resonant state, the amplitude of vibration increases rapidly and a resonant wave is generated.

The resonance frequency at this time was captured and the spectrum analyzer 3
When displayed on the screen of 2, as shown in FIG. 2, many spectral peaks suddenly appear from a certain frequency.

As a result of experiments, it was found that the lowest frequency in this group of spectra was closest to the resonance frequency due to the thickness of the concrete 1.

Figure 2 shows the case where 1.5KHz ultrasonic waves are transmitted.
The lowest frequency spectrum C appeared around 10 KHz.

From the results of experiments, the lowest frequency spectrum A appears most clearly on the screen at approximately 10% to 30% of the resonant frequency.
% frequency.

Therefore, if you have an idea of the thickness of the concrete 1 to be measured, you can roughly estimate the resonant frequency from the method for calculating the thickness of the concrete 1, which will be described later, and
By transmitting a frequency of % to concrete 1,
Work can be done quickly.

Depending on the purpose of the measurement, the work may be completed with only the first measurement.

(2) Secondary measurement In the second measurement, a more accurate resonant frequency is determined.

A frequency (10K) Iz in the vicinity of the spectrum C appearing in the first measurement is transmitted, and the variable oscillator 21 is finely adjusted to find the frequency at which the spectrum C of the resonant wave has a maximum.

As shown in FIG. 3, the frequency at which the spectrum C is displayed at its maximum on the screen of the spectrum analyzer 32 is the correct resonance frequency at which the concrete 1 and the ultrasonic waves resonate.

The maximum spectrum C in this example is 10.9KHz
This value is the exact resonant frequency.

The thickness of the concrete 1 can be determined from this resonance frequency by the following calculation.

<C> Method for calculating the thickness of concrete First, the speed of ultrasonic waves propagating within the concrete 1 is determined using an ultrasonic measurement method.

Although the sound speed differs depending on longitudinal waves, transverse waves, and surface waves, since longitudinal waves are used in this embodiment, the sound speed of longitudinal waves is determined.

As a result of the experiment, the sound speed of concrete 1 is approximately 4000 m/s
It was eC.

The resonant frequency in the thickness direction of the concrete 1 corresponds to the reciprocal of the time it takes for an ultrasonic longitudinal wave to travel in the thickness direction, be reflected on the opposing surface, and return.

The resonance frequency is Ml The thickness of concrete 1 is D (cm)
Assuming that the speed of sound is v (m/sec) and the propagation time of the sound wave in the thickness direction of concrete 1 is t (μs),
The following formula holds true.

From these formulas, the following formula (1) holds true.

By substituting the numerical values of this example into this formula, the thickness of the concrete 1 can be determined from the resonance frequency in this way.

Therefore, in actual measurement, the thickness 6 of the concrete l can be easily calculated by simply substituting the resonance frequency determined by the above-mentioned measurement method into the equation (1).

<Other Examples> By applying the method for measuring the thickness of concrete 1 described above, it is possible to measure the position of a crack existing substantially parallel to the surface of concrete 1.

The ultrasonic pulse transmitted from the surface of concrete 1 is
As described above, the light passes through the concrete 1 and is reflected at the discontinuous portions, so if there are cracks existing substantially parallel to the surface of the concrete 1, the light will be reflected by the cracks.

Therefore, by capturing the resonant frequency when reflected by the crack, the distance from the surface of the concrete 1 to the crack can be determined using the calculation method described above.

Further, by bringing the transmitter 2 and the receiver 3 closer together and moving the surface of the concrete 1, the range where cracks occur can be measured.

That is, on the surface of the concrete 1, when the transmitter 2 and the receiver 3 are out of the range where an inherent crack occurs, the ultrasonic pulses reach the opposing surface of the concrete 1.
The resonance frequency spectrum of the thickness of the concrete 1 from the surface to the crack disappears.

From this, it can be seen that the range where the resonance frequency spectrum appears is the range where cracks occur, and by determining this range, the range of cracks can be measured.

Effects of the Present Invention> Since the present invention has been described above, the following effects can be expected.

In the case of the conventional pulse reflection method for measuring the thickness of concrete and the location of inherent cracks, a surface wave is generated that propagates from the transmitter directly across the concrete surface to the receiver, allowing accurate measurement. Unable to measure concrete thickness and location of inherent cracks.

In the present invention, a transmitter and a receiver of an ultrasonic vibrator are installed on the same surface of the concrete to be measured, and the transmitter emits a wave, not a sine wave, toward the opposing surface of the concrete or an internal crack. For example, by repeatedly transmitting ultrasound pulses formed by rectangular wave electrophotography while changing the frequency,
The thickness of the concrete and the position of the internal cracks are measured by detecting resonance frequencies that vary depending on the thickness of the concrete or the position of the internal cracks.

Therefore, the thickness of concrete and the position of inherent cracks can be easily and accurately measured without interference from surface waves as in the conventional method.

Therefore, even in the case of large concrete structures such as underground petroleum and LPG storage tanks, tunnels, nuclear power plants, etc., the thickness of the concrete and the location of any inherent cracks can be accurately measured from one side of the concrete, making it safe from a safety perspective. Improvements can be made in terms of construction and construction methods.

[Explanation] Since the oscillator used in the present invention can perform measurements with an output of ±IOV or less, measurements can be performed at low cost.

[Brief explanation of the drawing]

Figure 1: An explanatory diagram of one embodiment of the present invention Figure 2: An explanatory diagram showing the spectrum of the resonant frequency displayed on the screen of the spectrum analyzer by the first measurement Figure 3: The spectrum by the second measurement Explanatory diagram showing the resonance frequency spectrum displayed on the analyzer screen

Claims (1)

[Claims] A transmitter and a receiver of an ultrasonic vibrator are installed on the same surface of the concrete of the object to be measured, and the transmitter is excited by electrical vibrations other than sine waves, and the Ultrasonic pulses are repeatedly sent to the opposite surface of the concrete while changing the frequency of electric vibration, and the concrete is placed in a resonant state. Resonant waves with frequencies that vary depending on the thickness of the concrete or the location of internal cracks are received. A method for measuring the thickness of concrete and the position of internal cracks, the method comprising receiving waves with a device and measuring the thickness of concrete and the position of internal cracks from the resonant frequency.