JP3010467B2 - Non-destructive inspection method and apparatus for reinforced concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for nondestructively inspecting reinforced concrete, and more particularly to a method and apparatus for monitoring the aging of RC structures.

[0002]

2. Description of the Related Art The following methods are commonly used as nondestructive inspection methods for concrete.

(1) Impact method A method of hitting the surface of concrete and measuring the mechanical properties of the concrete, such as compressive strength, based on the rebound hardness. (2) X-ray transmission method A method of investigating the position and cavities of reinforcing bars in concrete, utilizing the fact that the rate at which X-rays are absorbed by concrete differs depending on the substance. (3) Ultrasonic method A method of measuring the propagation speed and waveform of an ultrasonic pulse and inspecting internal defects due to the thickness and waveform of concrete according to the propagation speed.

[0004]

However, the above-mentioned conventional inspection method has the following problems.

(1) Impact method This is for inspecting mechanical characteristics such as strength, and can be inspected only from the surface, and cannot be inspected inside. Further, re-inspection (re-applying to the same place) cannot be performed due to a change in surface hardness in the first inspection. (2) X-ray transmission method Since radiation that requires the management of a qualified person (chief of X-ray work) is used, it is not a simple method such as a complicated device or method. (3) Ultrasonic method Although it is used for the investigation of the state of cracks, the investigation location is determined arbitrarily, and it is difficult as a method to find the distribution of cracks in the entire target structure.

[0006] In general, the above-mentioned conventional method requires only a specified inspection such as strength (a measurement target is limited), a continuous inspection cannot be performed, or a measurement target or a measurement range is arbitrary and partial (a measurement range is narrow). However, there is a problem that the measurement is limited to the ones or the technique for the measurement and the handling require an expert.

Therefore, the present invention can be applied to a wide range of objects to be measured, such as strength and cracks, extends the measurement range to the entire structure, and allows the aging of reinforced concrete to be easily inspected without requiring an expert. To provide a non-destructive inspection method for reinforced concrete.

[0008] Another object of the present invention is that the aging of concrete refers to the water content of concrete, in other words, the aging of the concrete structure itself in addition to the environmental change due to daily changes in temperature and humidity. The present invention provides a method and an apparatus for measuring aging, such as cracking of reinforced concrete and strength development after concrete casting, by measuring these physical characteristics.

Still another object of the present invention is to measure and monitor the aging of concrete by using a simple device and measuring method by using an electrically insulating reinforcing bar which is arranged on almost the entire area of the concrete structure. No destructive inspection equipment will be provided.

In the case of a non-insulated reinforcing bar, the measurement cannot be performed because the measured current flows directly through the reinforcing bars that are in contact with each other due to the high electrical conductivity.
In addition, the rust of the rebar itself causes the rebar to lose its function as an electrode, which seriously affects the electrical characteristics between the rebars (electrodes). There were drawbacks.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its gist that at least two electrically insulated reinforcing bars in reinforced concrete are separated by a predetermined distance.
The electrodes arranged with the electrodes arranged as electrodes, and the impedance between the electrodes obtained by energizing each electrode, or the electrical characteristics such as the resistance component, the capacitance component, and the phase angle of the electrodes are periodically measured.
There is a non-destructive inspection method for reinforced concrete, in which the aging of the concrete constituting the reinforced concrete structure is grasped by analysis.

Here, the two electrically insulated rebars are two or more electrically insulated rebars, each of which is a crossed portion where a single-stage rebar arranged in a concrete structure crosses two, and a parallel portion which is parallel. Between (electrodes), two-level (upper and lower two levels are electrically insulated) or three-level rebar (all upper, middle and lower levels or only upper and lower levels are electrically insulated),
It is meant to include various forms in which a lap portion vertically overlapped, a parallel portion between upper portions and lower portions, or a lap portion or a parallel portion between upper and lower portions or between upper, middle, and lower portions is used as an electrode.

[0013] Further, as an alternative to the arrangement of the above-mentioned insulated reinforcing bars, it is possible to use electrically insulated painted metal plates.
It is also possible to use a combination with an electrically insulating reinforcing bar.

Similarly, the conductive paint applied to at least two concrete surfaces can be used, or can be used in combination with an electrically insulated reinforcing bar or an electrically insulated painted metal plate.

The distance between the electrodes can be easily measured by using a general-purpose measuring instrument such as a known impedance measuring instrument.

[0016] The above-mentioned regular measurement does not always mean a regular interval every day, every other day, every other week. For example, every two days, every other week, then every month, In addition, when the change in impedance due to a change in moisture or cracks appears remarkably, such as every three days, the measurement is finely divided, and when not, the measurement is performed at long intervals.

Furthermore, the aging of concrete refers to the state of change of concrete structures due to the progress of hardening after concrete casting, the drying / moisture absorption and the occurrence of cracks due to changes in humidity as the surrounding environment.

Next, as another aspect of the present invention, the reinforced concrete structures are Haisuji at predetermined intervals
Electrically insulating reinforcement subjected to at least two electrically insulating coating was
Connect the lead as electrodes, electrical properties placed the lead impedance between the electrodes or the resistance component and capacitance component, the structure outside of measuring the electrical characteristic value, such as phase angle, There is a non-destructive inspection device for reinforced concrete to which a measuring device is attached.

At least two electrically insulated reinforcing bars serving as electrodes can be peeled off and partially connected to an electrical characteristic measuring device directly. In this case, however, the concrete structure must be cut off until the reinforcing bars are visible. Instead, the operation is easier if the device is attached to an electrical characteristic measuring device using a lead wire. In addition, it is easier to use conductive paint applied to at least two concrete surfaces as electrodes.

The present invention is also directed to a reinforced concrete structure using an electrically insulated reinforcing bar, and is provided with an apparatus for constructing the structure or after the construction. In addition to this, even for structures using conventional reinforcing bars without insulation coating, newly laying electrically insulating reinforcing bars or electrically-insulated painted metal plates or applying conductive paint applied to the concrete surface as electrodes It can also be used as

Further, the reinforcing bars of the concrete structure may be a single-tiered one crossed in a lattice shape, a two-tiered one in the upper and lower parts, or a three-tiered one in the upper, middle and lower parts or more.
In addition, the connection of the lead wire to the rebar is performed at the intersection or parallel portion in the above-described one-stage reinforcing structure, or at the two or more stages, in addition to the lap portion or the parallel portion vertically overlapping, the upper portion or the lower portion, or the parallel portion at the middle portion Can be used as electrodes, and these arbitrary positional relationships can enable electrical measurements in most parts of the concrete structure.

[0022]

According to the method of the present invention, an electrically insulating rebar or a metal plate coated with an electrically insulating material, or a conductive paint or the like applied to a concrete surface is used as an electrode, and the impedance,
Alternatively, an electrical characteristic value such as a resistance component, a capacitance component, a phase angle, or the like is periodically measured, and the aging tendency is analyzed and determined.

The absolute value of the electrical characteristics (impedances, etc.) of a concrete structure naturally depends on the shape of the structure, the arrangement of the reinforcing bars, the measurement position, and the like.
By measuring continuously at the same place, the absolute value does not matter, and the relative change tendency is used as an index.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-destructive inspection method for reinforced concrete according to the present invention will be described below with reference to the accompanying drawings.

It is considered that the electrical characteristics of concrete vary depending on the water content of the concrete, the environment of temperature and humidity, and also with the aging such as cracking of the concrete.

Therefore, according to the present invention, the aging of concrete is measured by using an electrically insulated reinforcing bar or an electrically insulated painted metal plate,
Alternatively, a method of monitoring the electrical characteristics obtained by energizing each electrode with conductive Peyton or the like applied to the concrete surface and monitoring deterioration conditions such as cracks in the concrete structure was studied.

<Concrete monitoring test method>
Three types of concrete specimens having different young age, middle age, long age and age were left in the room, and at a frequency of 100 Hz, electrical characteristics, weight, temperature, and humidity were measured every two days for 40 days. FIG. 1 shows the concept of the test body and the measurement circuit. The young-age concrete was produced the day before the measurement start date, the medium-age concrete was approximately two and a half years ago, and the long-age concrete was approximately 80 years ago.

<Test Results> FIG. 2 shows changes in temperature, humidity, and weight of two specimens of a young-age specimen, one specimen of a medium-age specimen, and one specimen of a long-age specimen as representative examples. Is shown. FIG. 3 shows a change in absolute humidity for 40 days in an environment in which the test specimen of FIG. 1 was left based on the temperature and humidity shown in FIG. 2, and FIG. 4 shows two weak material age tests at that time. It is a measure of body impedance.

As a result, the change in weight of the above-mentioned concrete test piece is heavy immediately after the concrete is cast because of the large amount of water, gradually becomes lighter as it hardens, and thereafter changes with the humidity in the air. It was found that the impedance changed. That is, from FIGS. 3 and 4, the impedance increases almost monotonously for a while immediately after the concrete is cast due to the effect of the decrease in moisture accompanying hardening, but thereafter, in response to a change in humidity, when the humidity increases, the concrete absorbs moisture and the impedance increases. Drop,
It was found that when the humidity decreased, the concrete dried and the impedance increased.

Next, on the premise of the test using the concrete specimen described above, a long-term monitoring test using an insulated reinforced concrete specimen in which an electrically insulated reinforcing bar (epoxy resin painted reinforcing bar) is arranged in concrete will be described.

<Monitoring Test Method for Electrically Insulated Reinforced Concrete> FIG. 5 shows an outline of an epoxy resin-coated reinforced specimen. Two test pieces (A-1 and A-2) were manufactured, and a circular 100 mmφ conductive paint was applied to the electrically insulated reinforcing bar and the upper and lower surfaces to form electrodes. Once dried, the test specimen was cured with a vinyl sheet so as not to be directly exposed to rainwater, left under an outdoor eave, and the electrical characteristics, the specimen weight, and the temperature and humidity were measured once a month. The measurement was performed between the upper and lower electrodes coated with the conductive paint, between the electrically insulated reinforcing bars, and between the electrode coated with the conductive paint and the electrically insulated reinforcing bars.

<Test Results> FIG. 6 shows a change in absolute humidity in an environment in which the test specimen of FIG. 5 was left.
FIG. 7 shows the measured impedance at that time. As the number of months has elapsed, the impedance has decreased due to the moisture absorption phenomenon of the test specimen once dried. 6 and 7 show that the relationship between the change in the absolute humidity and the change in the impedance has the same tendency as in the concrete monitoring test.

Further, in the case where cracks occur in reinforced concrete in the future, when the humidity in the air increases, the cracks absorb moisture more remarkably than the solid concrete portion, and when the humidity decreases, the drying becomes remarkable. Therefore, it can be predicted that the rise and fall of the humidity at the same location after the occurrence of the crack causes a significant rise and fall of the impedance.

Therefore, the occurrence of cracks in reinforced concrete can be determined from the tendency of impedance change.

The inspection of the reinforced concrete is not limited to the measurement of the impedance, but can be predicted by measuring the electrical characteristics such as the resistance component, the capacitance component, and the phase angle of the impedance.

As described above, the electrically insulated reinforcing bars in the reinforced concrete structure, the electrically insulated painted metal plate, or the conductive paint or the like applied to the concrete surface are used as electrodes, and the same or different electrodes are used. It is possible to grasp the secular change of reinforced concrete by periodically measuring the electric characteristic value between the electrodes.

Next, the nondestructive inspection method for reinforced concrete according to the present invention was monitored on an actual structure.
An inspection apparatus provided on an actual structure will be described.

<Test Method Applying Electrically Insulated Reinforced Concrete to Actual Structure>
In a superconducting experiment building where electrical insulation performance is required, use an electrically insulated reinforcing bar and attach a measuring lead wire to the reinforcing bar between the soil, before, immediately after, and 1 month to 6 months after placing concrete.
After a month, the DC insulation resistance (applied voltage: 500 ~
1000V) and AC impedance (applied voltage: natural potential difference ± 100mV-5V, frequency: 1Hz-1KHz)
Was measured. The positional relationship of the reinforcing bars was determined for the lap portion, the intersection portion, and the parallel portion. FIG. 8 shows the concept of the measurement points.

FIG. 8 shows that the experimental room of
The lead wire 4 is connected to the upper and lower bars 2 and 3, respectively, of the insulated reinforcing bar, and the lead wire is drawn out to a measuring terminal box 6 in a column provided in the middle of the column 5, and a connector ( (Not shown) makes it possible to connect an impedance analyzer 7 which is an electric characteristic measuring device outside the pole.

Although not shown in the drawing, in the experiment, it is also possible to connect a lead wire to the lower base reinforcing bar in the column base 8 and the vacuum vessel base 9 as described above.

As shown in FIG. 10, for more specific attachment of the measurement lead wire, the insulating coating was peeled off from the upper and lower muscles, the upper and central muscles, and the central muscle, which were completely electrically insulated. Lead wires were connected and measurements were taken between these concrete sections.

<Test Results> An example of the measurement of the impedance at a frequency of 100 Hz is shown in FIG. 9, where the parallel portions of the vertical streaks between the soils show that the impedance is high before the concrete is cast and rapidly drops immediately after the concrete is cast. are doing. This is thought to be due to the effect of water during casting. Thereafter, the hydration reaction proceeds as the date and time elapse, and the impedance gradually increases. In addition, the same tendency was shown in any part such as the wrap part.

[0043]

As described above, according to the method of the present invention, the electrical properties of the concrete portion between the reinforcing bars cannot be measured due to the conventional high conductivity, or the electrical properties greatly change due to the generation of rust. For those that could not be measured, the secular change of concrete was made possible by using the electrically insulated reinforcing bars of the concrete structure as electrodes.

Further, the method of the present invention utilizes an electrically insulated reinforcing bar itself, which is a component of the structure itself, as an electrode for measurement (or an electrically insulated reinforcing bar which does not cause harm to the structure or a metal plate coated with an electrically insulated material). Buried or applying conductive paint on the concrete surface)
There is no need to seriously damage the structure itself or install new large-scale equipment.

Further, the simplification and automation of the measuring instrument for measuring the impedance or the electrical characteristic values such as the resistance component, the capacitance component, the phase angle, etc. of the impedance or the like can be achieved without any problem by applying the existing technology. It is considered feasible, and further labor saving is possible in the future.

In addition, according to the method of the present invention, it is not necessary to newly install a large-scale special device without using an expert, and anyone can easily use existing general-purpose measuring instruments (impedance measuring instruments, etc.). Can be measured.

In comparison with the conventional method of performing a test with a star on the basis of information visible from the surface using conventional impact, X-ray, or ultrasonic waves, the location of a defect that is not visible is newly added. Investigation can be performed on the entire structure, not limited to specific sites such as clarification (eliminating the disadvantage that the measurement range is narrow).

[Brief description of the drawings]

FIG. 1 is a diagram showing a concrete test body and a measurement circuit using the test body.

FIG. 2 is a graph showing changes over time in ambient temperature and humidity and weight of a test specimen of the same two young, medium and long test specimens as in FIG.

FIG. 3 is a graph showing a change in absolute humidity for 40 days from the time when concrete was cast and the test body of FIG. 1 was prepared.

FIG. 4 is a graph showing the change in impedance measured during the 40-day period shown in FIG.

FIG. 5 is a perspective plan view and a perspective side view of a test piece of electrically insulated reinforced concrete.

FIG. 6 is a graph showing a change in absolute humidity during a period when the test specimen of FIG. 5 once made absolutely dry is left outdoors.

FIG. 7 is a graph showing a change in impedance between each electrode of the electrically insulated reinforced concrete specimen measured during the period shown in FIG. 6;

FIG. 8 is a conceptual diagram showing a state where the apparatus of the present invention is installed in an experimental building.

FIG. 9 is a graph showing the impedance measured by changing the frequency over time in FIG. 8;

FIG. 10 is an explanatory diagram obtained by tracing a photograph showing a state in which lead wires are connected to upper and lower lap portions, upper and lower parallel portions, and a binding portion of the upper and lower two-step reinforcing bars of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 Soil (concrete) 2 Upper bar (electrically insulating bar) 3 Lower bar (electrically insulating bar) 4 Lead wire 5 Pillar 6 Measurement terminal box 7 Electrical characteristics measuring device

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoichi Akutsu 1221-2, Muramatsu, Tokai-mura, Naka-gun, Ibaraki Prefecture (72) Inventor Yoshinao Okawa 5--11-15 Chuo, Warabi City, Saitama Prefecture (72) Inventor Takeshi Suzuki No. 45-60 Yoshizawa-cho, Mito-shi No. 122, Yoshizawa housing complex 122 (72) Inventor Akio Nakagoe 2-5-8 Kita-Aoyama, Minato-ku, Tokyo Intra-company group (72) Inventor Koichi Yamamoto 1-3-3 Wakihama-cho, Chuo-ku, Kobe-shi No. 18 Kobe Steel, Ltd. (56) References JP-A-62-87841 (JP, A) JP-A-1-141346 (JP, A) JP-A-56-124041 (JP, A) 1-89360 (JP, U) Abstracts of the 45th Annual Scientific Meeting of the Japan Society of Civil Engineers (September 1990), Part 5, pages 774-775 (58) Fields surveyed (Int. Cl. ^7, DB name) G01N 27/00 - 27/24 G01N 33/38 JICST file (J IS)

Claims (4)

(57) [Claims] 1. A reinforcing bar in reinforced concrete
At least two electrically insulated reinforcing bars separated by a predetermined distance.
The electrodes are used as electrodes, and the impedance between the electrodes obtained by energizing each electrode, or the resistance component, the capacitance component, and the electrical characteristic values such as the phase angle are periodically measured.
A non-destructive inspection method for reinforced concrete that analyzes the aging of the concrete that composes the reinforced concrete structure by analyzing. 2. In a reinforced concrete structure , reinforcing bars are provided as reinforcement in reinforced concrete at predetermined intervals.
Electrically insulating the iron subjected to at least two electrically insulating coating that
A lead wire is connected with a streak as an electrode , and the lead wire is installed outside the structure for measuring an impedance between the electrodes, or a resistance component, a capacitance component, and an electrical characteristic value such as a phase angle. Non-destructive inspection device for reinforced concrete with a characteristic measuring device. 3. The reinforced concrete according to claim 2, wherein the electrically insulated reinforcing bar to which the lead wires are connected is a reinforcing bar between upper and lower portions arranged in two or more stages vertically or between upper and lower reinforcing bars. Non-destructive inspection equipment. 4. The non-reinforced concrete non-reinforced concrete according to claim 3, wherein the electrically insulated reinforcing bar to which the lead wire is connected is a crossing portion where a reinforcing portion is bound, an upper and lower wrap portion, or an upper and / or lower parallel portion. Destructive inspection equipment.