JP2002318101A - Electric measuring method of crack depth of concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric nondestructive measuring method of the crack depth of a concrete structure from the concrete surface. SOLUTION: This method comprises conductor powder injected into the crack of the concrete, an earth plate arranged on the concrete surface, and a network analyzer. An antenna is constituted from the conductor in the crack of the concrete and the earth plate, and input impedance is measured, to thereby determine the crack depth of the concrete. Hereby, the crack depth of the concrete can be determined precisely and easily. The device used for the measuring method is simple, small and portable. In addition, the method also has a function for repairing the crack by injecting a mixture of the conductor powder, an epoxy-based resin or the like into the crack.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for non-destructively measuring the depth of cracks generated in a concrete structure from a concrete surface by an electrical method.

[0002]

2. Description of the Related Art A conventional method for measuring the depth of cracks generated in concrete is to inject red ink or a fluorescent agent into the cracks generated in concrete and then split or cut the concrete to observe cracks inside. The way has been taken. Although this method has the advantage that cracks can be directly observed with the naked eye, it is suitable for indoor experiments in a laboratory using experimental specimens, but it is not practical because cracks in actual structures cannot be detected nondestructively.

[0003] As a test method for non-destructively measuring the depth of cracks generated in concrete of an actual structure, there is an ultrasonic method. This method determines the crack depth based on the time it takes to reach the transducer by inputting ultrasonic waves into the concrete.However, in the case of a complex like concrete or a concrete bridge deck slab covered with asphalt pavement, In the case of the composite, there is a disadvantage that the propagation speed of the elastic wave is greatly different and an error is inevitably generated. In particular, in the case of reinforced concrete, the propagation speed of the elastic wave of the reinforcing bar is higher than that of concrete, and therefore, the accuracy is remarkably poor, and it may not be practically used.

[0004] The AE method is, in principle, an ultrasonic method using a measuring instrument only on the transducer side. However, as is understood from the principle, this measuring method is completely passive, and a new crack is generated. If the generation is not in progress, nothing is detected and existing internal cracks cannot be detected.

[0005] The pulse radar method is a method of incident and receiving microwaves using an antenna, and is used as an underground radar for exploring underground buried objects, and is considered applicable to measurement of internal cracks in concrete. Have been. It is under development in the field of crack measurement in concrete and has not yet been put to practical use.

In X-ray contrast radiography, which is widely used in the medical field, a contrast agent is injected into an organ to be examined, and a difference in X-ray transmittance between the organ and surrounding tissue is generated. This X-ray contrast radiography is applied to concrete, and it is possible to continuously measure minute cracks in a time series in a nondestructive manner with considerable accuracy. However, it is applicable to the measurement of cracks in concrete structures having a thickness of at most about 0.3 m from the relation of the output energy of the current X-ray generator. Measurement is not possible. In addition, the X-ray generator is too large to be transported and is difficult to apply to actual structures on the site.
This method cannot be used because line film cannot be installed. In addition, when inspecting for cracks in road bridge decks,
Since it is necessary to install an X-ray irradiation device on the road surface,
It is necessary to regulate traffic, and there is a problem of social and economic impact such as traffic congestion.

[0007]

The conventional ultrasonic method, AE
The method of non-destructive measurement of the crack depth of concrete by the radar method, radar method, and X-ray contrast imaging method has advantages and disadvantages according to each principle as described above. There is a problem that it is very difficult to make a good judgment. An object of the present invention is to provide a method for determining a crack depth by a low-cost, high-accuracy, workable, and inexpensive measurement method that is non-destructive and has a deep measurement depth for a crack from a concrete surface.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method for non-destructively and electrically measuring the crack depth of concrete. Inject conductor powder,
In addition, a conductor plate made of aluminum or the like is placed on the concrete surface to provide a grounding function, the input impedance between the conductor injected into the crack and the ground plate is measured, and the antenna is operated by the conductor and the ground plate to radiate the electric field. By measuring the distribution, the impulse voltage is further applied from the input terminal of the conductor that is cracking, and the time it takes to reflect from the crack tip and return to the input end can be determined to determine the crack depth of concrete. A possible way.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the method for electrically measuring cracks in concrete according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a main part of an electrical measurement method for concrete cracks according to an embodiment of the present invention. Let the direction of the normal line standing on the concrete surface be the Z axis,
The directions perpendicular to each other and perpendicular to each other are defined as an X direction and a Y direction. In the drawing, 1 is a concrete structure, 2 is a crack in concrete, 3 is a conductor powder injected into the crack in concrete, and 4 is an earth plate made of a conductor such as aluminum, which conducts with the conductor powder injected into the crack in concrete. Not. Reference numeral 5 denotes a connector. For example, an N-type receptacle connector is attached to the ground plate, the center pin is connected to the conductor powder injected into the concrete crack, and the outer conductor is electrically connected to the ground plate. The conductor and ground plate injected into the concrete crack form a kind of monopole antenna surrounded by concrete dielectric. The antenna and the network analyzer are connected by a coaxial cable.

Hereinafter, the above situation will be described in some detail with experimental results. FIG. 2 is a cross-sectional view taken along the XZ plane in FIG. The conductor powder is pressed into the crack to be measured from the concrete surface. At this time, let the crack depth be L. The N-type receptacle connector has, for example, a hole through which a connector center pin passes through an aluminum plate having a thickness of 1 to 2 mm, the center pin does not conduct with the conductor plate, and the connector outer conductor is attached to the aluminum plate. The center pin of the connector is inserted into the cracked conductor powder appearing on the concrete surface, and is electrically connected to the conductor powder. When the potential of the aluminum plate is zero, the aluminum plate has a grounding function and forms a monopole antenna having an antenna length L together with a conductor injected into a crack in concrete. When a voltage is applied to the monopole antenna, the current distribution becomes zero at the tip because the tip is open. If the ratio between the voltage and the flowing current is the input impedance Z, and the real part is R and the imaginary part is X, it can be expressed as follows.

If the frequency of the power supply is f and the relative permittivity of concrete is ε _s , the wavelength λ _{g in} concrete is It is represented by Here, c is the speed of light. At frequencies where the length of the antenna is about a quarter wavelength, the reactance is zero. This state is called an antenna resonance state, and an electromagnetic wave is radiated into space. That is, the input impedance Z of the monopole antenna composed of the conductor powder injected into the cracks in the concrete and the ground plate was measured, and the resonance frequency f
_If we find ₀ , the monopole antenna length L is Is required. The resonance frequency of the monopole antenna can be easily obtained by measuring the input impedance Z with a network analyzer or the like, and therefore the crack depth of concrete can be easily determined.

Next, in order to determine the crack depth of concrete by the measuring method according to the present invention, a concrete test specimen with simplified cracks was manufactured. That is, two types of slits having a thickness of 1 mm, a width of 2 mm, and a depth of 50 mm and 30 mm were formed in a concrete test piece having a diameter of 100 mm and a length of 200 mm to simulate cracking. A conductive silver paste was pressed into the crack. The ground plate is a square aluminum plate having a thickness of 2 mm and a side length of 350 mm. An N-type receptacle connector is attached substantially at the center of the ground plate, and the center pin is inserted into the cracked conductive silver paste to establish electrical conduction. The monopole antenna is composed of the ground plate and the conductive silver paste in the cracks. The monopole antenna and the network analyzer are connected by a coaxial cable having a length of 400 mm. A coaxial cable was connected to a network analyzer so that the input impedance viewed from the N-type receptacle connector of the monopole antenna could be measured, and calibration was performed.

FIG. 3 shows a measurement result of the input impedance of the monopole antenna in the case of a crack having a depth of 50 mm. The horizontal axis is frequency from 300KHz to 3,000MHz
Has changed. The vertical axis represents S ₁₁ of the scattering matrix from the input end of the monopole antenna, that is, when the incident wave at the output end is 0, represents the ratio of the incident wave to the reflected wave at the input end and is expressed in dB as the return loss. The scale is 1.93 dB. When the frequency is 300 KHz, the return loss is almost zero,
That is, the characteristic impedance 50 of the coaxial line at the input end
The input impedance of the monopole antenna is much larger than that of Ω and almost totally reflected. As the frequency increases, the return loss gradually decreases, the input impedance of the monopole antenna decreases, and approaches the characteristic impedance of the coaxial line of 50Ω. Frequency 848.022 MHz
, The minimum return loss of -12 dB is obtained, the input impedance is also minimized, and it can be seen that the device is in a resonance state.
The measured value of the resonance frequency of a 50 mm long monopole antenna in air is 1,475.5 MHz, and the measured value of the resonance frequency in concrete is 848.
Since at 022MHz, than this calculated to be about 3 the relative permittivity epsilon _s of the test concrete. When the antenna length L, that is, the crack depth is obtained from Expression (3), it is 51 mm, and the depth can be determined with sufficient accuracy. FIG. 4 shows a measurement result of the input impedance of the monopole antenna in the case of a crack having a depth of 30 mm. One scale of the return loss on the vertical axis is 5 dB. The frequency is 133.674M
It can be seen that the return loss at Hz is a minimum of -15 dB, the input impedance is also a minimum, and the device is in a resonance state. When the antenna length L, that is, the crack depth is obtained from the equation (3), it becomes 32.5 mm, and it can be seen that the depth can be determined with sufficient accuracy.

According to the present invention, a concrete crack depth can be determined nondestructively by configuring a monopole antenna composed of a conductor press-fitted into the crack and an earth plate, and measuring the input impedance. Although the experimental results were not shown here, this antenna was excited at the resonance frequency and the radiated electric field distribution was measured, or an impulse voltage was applied from the input terminal of the cracked conductor to Obviously, it is also possible to determine the crack depth of the concrete by measuring the time from the reflection to the input end to the input end. Also, for example, if the epoxy resin is mixed with the conductor powder and injected into the crack, the epoxy resin is solidified with the determination of the crack depth, and the crack is sealed.
The effect of repairing cracks can also be expected and has the effect of two birds per stone.

[0015]

Since the present invention is configured as described above, it has the following effects. First, a monopole antenna is composed of a conductor injected into a crack in concrete and an earth plate, and the input impedance of the monopole antenna is measured to determine the resonance frequency, whereby the depth of crack in concrete can be accurately determined. In general, cracks in concrete may be branched inside the concrete. In such a case, the depth of cracks in concrete can be determined by measuring the input impedance of the antenna and determining the resonance frequency. Second, the resonance frequency of the monopole antenna and the antenna length, that is, the crack depth, are inversely proportional, and the deeper the crack, the lower the resonance frequency. For example, when the crack depth is 2 m, the resonance frequency is about 22
MHz, which is a frequency band that can be easily and accurately measured by a network analyzer or the like. This makes it possible to measure the depth of very deep cracks in thick concrete structures, for example, 2 m or more. Third, even when the surface of concrete is covered with asphalt, as in the case of the roadbed of a bridge, drill holes in asphalt,
By injecting conductive powder into cracks in concrete, installing an earth plate on the asphalt surface, and measuring the resonance frequency of the monopole antenna, the crack depth can be determined from the asphalt surface. Fourth, the antenna length L, that is, the crack depth can also be determined by exciting the monopole antenna at the resonance frequency and measuring the electric field distribution radiated around the antenna. Fifth, this measurement method can also determine the crack depth from time domain measurements. That is, if a pulse voltage is applied to the input of the conductor in the crack and the pulse voltage is propagated, the light is almost totally reflected at the tip of the crack and returns to the input end. If this round-trip time is measured by the TDR method, the conductor length, that is, the crack depth can be easily determined. Even when a concrete crack is branched inside the concrete, it is reflected at each end, so that there is an advantage that the crack depth of each branch can be determined. Sixth, if the epoxy resin is mixed with the conductor powder and injected into the cracks, the crack depth is determined, and after the epoxy resin is solidified, the cracks are sealed and the cracks are repaired. Has the effect of Seventh, the measuring device according to this measuring method has features such as simple, compact, portable and quick measurement. Can be provided at cost.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a method for electrically measuring the crack depth of concrete according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a main part of a method for electrically measuring the crack depth of concrete according to an embodiment of the present invention.

FIG. 3 shows a measurement result of return loss of a monopole antenna having a length of 50 mm.

FIG. 4 is a measurement result of return loss of a monopole antenna having a length of 30 mm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Concrete 2 Crack of concrete 3 Conductor powder 4 Ground plate 5 Connector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F063 AA15 BD20 DA02 DC08 LA05 NA06 2G060 AA14 AA20 AE04 AF06 AG08 HC10 HE10

Claims (3)

[Claims] A concrete fluid is injected into a concrete crack, a ground plate is provided on the concrete surface, and the impedance between the conductor and the ground plate in the concrete crack is measured to determine the concrete crack depth. An electrical measurement method of the crack depth of concrete, characterized in that the depth is determined. 2. The concrete according to claim 1, wherein the antenna is operated by the conductor in the concrete crack and the ground plate, and the radiated electric field distribution is measured to determine the crack depth of the concrete. Method for electrical measurement of cracking depth in concrete. 3. The concrete cracking depth is determined by applying an impulse voltage from an input terminal of a conductor in a concrete crack and measuring a time required for the concrete to reflect from the crack tip and return to the input terminal. An electrical measurement method for crack depth of concrete, characterized in that: