KR20160074186A

KR20160074186A - Method for monitering crack propagation into reinforced concrete with high conductive cement composite

Info

Publication number: KR20160074186A
Application number: KR1020140183174A
Authority: KR
Inventors: 김형기
Original assignee: 조선대학교산학협력단
Priority date: 2014-12-18
Filing date: 2014-12-18
Publication date: 2016-06-28

Abstract

The present invention relates to a method and apparatus for effectively generating cracks in a reinforced concrete by using a highly conductive cement composite material capable of being installed in the field and having the same material behavior as the surrounding concrete structure and exhibiting a high electrical conductivity, There is a main purpose in enabling you to detect.
In order to accomplish the above object, there is provided a method for detecting cracks in a reinforced concrete using a high-conductivity cement composite material according to the present invention, comprising the steps of mixing a conductive material, cement and water at a predetermined mixing ratio, Preparing a high-conductivity cement composite material; Disposing the highly conductive cementitious composite material at a position adjacent to the reinforcing bars laid in the concrete structure; Casting the concrete to produce the concrete structure; Electrically connecting measurement equipment to the electrode plate inserted on both sides of the high-conductivity cement composite material; And monitoring a change in electrical conductivity of the highly conductive cementitious composite material due to cracking in the concrete structure through the measurement equipment.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of detecting a crack in a reinforced concrete using a high-conductivity cement composite material. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a method of detecting a crack in a reinforced concrete using a high-conductivity cement composite material, and more particularly, to a method of monitoring the occurrence of cracks in a reinforced concrete using a high- .

Concrete structures may crack structurally due to external load under cracking and working load due to drying and shrinkage during curing.

These cracks cause problems in the use of concrete structures and deterioration of structural stability. Therefore, it is important to periodically check the occurrence of cracks in concrete structures to determine the location and size of cracks, and take appropriate measures to ensure that the stability of concrete structures can be maintained normally.

Methods for inspecting cracks in these concrete structures are mainly inspected using visual inspection, optical fiber, piezoelectric elements, CT scan, acoustic emission sensing, and conductive paint. However, visual inspection can easily grasp external cracks, but not internal cracks.

The method using the grating type optical fiber measures the scattering of the light passing through the optical fiber. It detects the crack from the degree of change of the wavelength of light and detects the occurrence of the crack according to the wavelength change. none.

The piezoelectric element has a short life span of a piezoelectric element, a high-priced CT scanner, and acoustic emission sensing detects a sound generated when a crack is generated.

Although CT scans or X-ray scans have the advantage of detecting internal cracks in concrete structures, it is not possible to monitor the occurrence of cracks in real time, and when the width of concrete cracks is too narrow, It is disadvantageous that measurement is possible only when using expensive equipment.

The acoustic emission sensing method measures a sound when a crack is generated by using a micro-microphone. However, there is a disadvantage that the application is limited in the actual construction site where the risk of damaging the microphone is high and the noise is high, and the microphone and the sound information processing apparatus are very expensive and complicated.

As disclosed in Korean Patent Laid-Open Publication No. 2013-0115915 (entitled "Crack Detection Device for Concrete Structures") (Patent Document 1), a method of using conductive paint has a property that electricity A conductive paint is applied and connected to a crack detecting device equipped with a signal oscillating and receiving unit to detect a crack when the concrete structure is cracked at the point where the conductive paint is cut or the resistance value of the conductive paint is changed. will be.

This method has a simple and simple structure with high reliability and can detect the crack of concrete structure. However, since the thermal expansion coefficient of concrete and paint is different, when used for more than 1 year, There is a risk of falling out of the concrete and a crack occurring inside can not be detected.

Korean Patent Laid-Open Publication No. 2013-0115915 (Title: Crack Detection Device for Concrete Structures), 2013. 10. 22. Open, Applicant:

The present invention has been developed in order to solve all the problems of the related art, and it is an object of the present invention to provide a high conductivity The main purpose of this study is to enable the effective detection of the occurrence of cracks in reinforced concrete using cement composites.

In order to accomplish the above object, there is provided a method for detecting cracks in a reinforced concrete using a high-conductivity cement composite material according to the present invention, comprising the steps of mixing a conductive material, cement and water at a predetermined mixing ratio, Preparing a high-conductivity cement composite material; Disposing the highly conductive cementitious composite material at a position adjacent to the reinforcing bars laid in the concrete structure; Casting the concrete to produce the concrete structure; Electrically connecting measurement equipment to the electrode plate inserted on both sides of the high-conductivity cement composite material; And monitoring a change in electrical conductivity of the highly conductive cementitious composite material due to cracking in the concrete structure through the measurement equipment.

In addition, the conductive material is preferably at least one conductive material selected from the group consisting of carbon nanotubes, carbon fibers, graphite, and coke.

Also, the conductive material is carbon nanotubes, and it is preferable to mix the carbon nanotubes in an amount of 0.4 to 0.6 wt% based on the weight of the cement.

In order to improve the dispersibility of the carbon nanotubes, it is preferable to mix 10 to 30% by weight of the silica fume with respect to the weight of the cement.

Further, it is preferable that the high-conductivity cement composite material is produced by further blending the fine aggregate.

In addition, the step of arranging the high-conductivity cement composite material preferably places the high-conductivity cement composite material between the reinforcing bars and the concrete surface where the crack propagates in the concrete structure.

In addition, it is preferable that the monitoring of the electrical conductivity change measures the change in electrical conductivity of the highly conductive cementitious composite material in real time or periodically with the occurrence of cracks.

According to another aspect of the present invention, there is provided a method of manufacturing a high-conductivity cement composite material, comprising: mixing a conductive material, cement, and water at a predetermined mixing ratio; Forming a cut groove having a predetermined length on a surface of a previously installed concrete structure; Inserting the highly conductive cement composite material into the cut groove and inserting an electrode plate made of a metal material on both sides of the highly conductive cement composite material; Electrically connecting measurement equipment to the electrode plate inserted on both sides of the high-conductivity cement composite material; And monitoring a change in electrical conductivity of the highly conductive cementitious composite material due to cracking in the concrete structure through the measurement equipment.

It is also preferable that the cutting grooves are formed in the cutting groove forming step so as to be disposed between the reinforcing bars laid in the concrete structure provided with the high-conductivity cement composite material and the concrete surface where cracks are to be generated .

The step of injecting the highly conductive cement composite material into the cut groove may further include finishing the concrete by placing the concrete in the cut groove.

According to the method for detecting cracks in reinforced concrete using the highly conductive cement composite material according to the present invention constructed as described above, only the electric conductivity of the highly conductive cement composite material can be measured, so that an expensive system for processing complicated data is required It can be implemented at low cost.

Also, a highly conductive cement composite material is disposed between the surface of the concrete structure and the reinforced steel disposed in the interior of the concrete structure, and the change in the electric conductivity caused by propagation of the cracks in the highly conductive cement composite material can be detected. As a result, the structural stability of the reinforced concrete is maintained because proper maintenance work can be performed by monitoring it before the crack propagates to the rebar.

Also, since the high-conductivity cement composite material is the same material as the concrete structure, it can be used for a long period of time because the thermal expansion coefficient is the same and no dropout due to thermal expansion / thermal expansion occurs.

In addition, since a high-conductivity cement composite material can be directly used in the field, it is excellent in workability and workability.

In addition, if a high-conductivity cement composite material is applied to prestressed concrete, the crack detection function can be reused due to the crack closure phenomenon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating the installation of a highly conductive cementitious composite material according to the present invention in a concrete structure; FIG.
FIG. 2 is a graph showing changes in electrical resistance according to the content of carbon nanotubes in a highly conductive cement composite material according to the present invention. FIG.
3 is a diagram illustrating a configuration in which a highly conductive cement composite material according to the present invention is disposed.
4 is a flowchart showing a crack detection method in a reinforced concrete using a high-conductivity cement composite material according to the present invention for a new concrete structure.
5 is a view of a highly conductive cement composite material provided with an electrode plate.
6 is a view showing an installation position of a highly conductive cementitious composite material according to the present invention.
7 is a flowchart showing a method of detecting a crack in a reinforced concrete using a highly conductive cement composite material according to the present invention for a pre-installed concrete structure.
8 is a view showing an example in which a high-conductivity cement composite material according to the present invention is applied to a prestressed concrete.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

The present invention provides a method for simply monitoring whether or not cracks are generated in a reinforced concrete using a highly conductive cement composite material in which changes in electrical conductivity against cracking and propagation are sensitive. For this purpose, as shown in FIG. 2, the high-conductivity cement composite material 10 is extended to a predetermined position of the concrete structure by a required length. For example, the high-conductivity cement composite material 10 may be installed vertically or horizontally on the outer wall of the high-rise concrete building 11 (upper left figure) or installed at a constant depth on the surface facing the sea in the coastal breakwater 12 (Upper right picture).

The reason for using the high-conductivity cement composite material in the present invention is that the change in the electric conductivity is exhibited only by the behavior of the crack to be measured. When cracks occur in the surrounding concrete of the high-conductivity cement composite, cracks are generated and propagated in the high-conductivity cement composite. This is because the surrounding concrete structure and the high-conductivity cement composite material are composed of the same material and exhibit the same behavior. As a result, electricity can not pass through the high-conductivity cement composite material, so that the electric conductivity is drastically lowered.

In order to achieve the object of the present invention, the conductivity of the highly conductive cementitious composite material should not be rapidly increased or decreased for reasons other than cracking. However, the electric conductivity value of concrete concrete material varies greatly depending on the shape and moisture content of the concrete concrete material. Therefore, it is necessary to distinguish between changes in electrical conductivity due to water content, boundary conditions, and structural shapes inside the concrete, and changes in electrical conductivity due to the occurrence of cracks to be measured in the present invention.

If cracks occur in the concrete material, the electrical conductivity is reduced so that monitoring can be done in any case. Therefore, if the concrete material does not sensitively increase or decrease the electric conductivity according to the shape or moisture content of the concrete, the electric conductivity change due to cracking can be independently detected. The inventors of the present invention manufactured a cement composite material having high conductivity by incorporating a conductive material such as a nano carbon tube as a method for realizing the technical idea.

To this end, the highly conductive cementitious composite material according to the present invention is prepared so as to have a higher electrical conductivity than ordinary water by mixing the conductive material, cement and water at a predetermined mixing ratio. The conductive material may be at least one conductive material selected from the group consisting of carbon nanotubes, carbon fibers, graphite, and coke.

Carbon nanotube (CNT) is one of the advanced nanomaterials. Since its discovery in 1991, CNT has been steadily researched and commercialized in various fields based on its unique structural, chemical, mechanical and electrical properties due to highly stable chemical bonding come. In other words, carbon nanotubes are as high in electrical conductivity as copper, have the same thermal conductivity as natural diamond, and have a strength 100 times higher than steel, but with an elongation of more than 15%.

However, in the course of using carbon nanotubes dispersed in various matrix materials, it is difficult to study due to low dispersion performance of carbon nanotubes, and thus, its use as a construction material has been limited. The inventors of the present invention developed a cement composite material in which carbon nanotubes, silica fume and cement were blended to improve the dispersibility of carbon nanotubes. The cement composite material was prepared in accordance with Korean Patent No. 10-1339904 A method of manufacturing a cement composite material containing a tube and a method of manufacturing a carbon nanotube-cement structure using the cement composite material). The present inventors have developed a method capable of effectively detecting the occurrence and propagation of cracks based on the technology of manufacturing cement composite materials containing such carbon nanotubes.

Carbon fiber is a fiber made by heating organic fibers (rayon, pitch, etc.) at high temperature over 1,000 ℃ to make carbon content more than 90%. Since Edison first developed Edison in 1879, It is a new material widely used in all industries such as automobile, civil engineering, architecture, electricity, electronics, sports, and leisure. The carbon fiber has properties of high electrical conductivity as well as high strength / high elasticity. Therefore, when dispersed in cement, a highly conductive cement composite material can be produced.

In addition, Graphite, which is widely used as an electrode material, and porous cokes formed by coking of coking coal at high temperature are materials having high electrical conductivity mainly composed of carbon, so when dispersed and mixed in cement, highly conductive cement A composite material can be produced.

In general concrete, electrical conductivity is greatly changed by water because there is only water that can conduct electricity. However, when a large amount of highly conductive material such as carbon nanotube or carbon fiber is incorporated into a cement composite material, electricity is conducted through a highly conductive material having a higher electric conductivity than that of water. Therefore, the electric conductivity of the cement composite material It will not be affected.

This fact can be clearly seen in FIG. 2 which shows the change in electrical resistance according to the content of carbon nanotubes in a high-conductivity cement composite material. The water / binder ratio (W / B) was 0.4, 0.5 and 0.6, and nine concrete specimens were prepared so that the contents of carbon nanotubes were 0.1, 0.3 and 0.5 wt% based on cement. FIG. 2 shows the results of measurement of electrical conductivity at the surface-saturated and surface-dried condition and the electrical conductivity at the completely dried condition (Oven Dried) for each concrete specimen.

As shown in FIG. 2, when the content of carbon nanotubes is the smallest as 0.1 wt% based on cement, the electric conductivity of the concrete in the fully dried state (SSD) and the state in the moisture saturated state (SSD) There was a difference of 10 to ⁷ times. Therefore, even if a sudden change in electric conductivity is measured, it is difficult to clearly determine whether it is due to drying or cracking.

However, when the content of carbon nanotubes is increased to contain 0.5 wt% of cement, the difference in electric resistance between the completely dry state (OD) and the moisture saturation state (SSD) decreases while the electric resistance decreases . That is, in a highly conductive cement composite material, the electric conductivity does not change drastically depending on moisture drying. Therefore, the increase in the electrical conductivity of the cement composite material due to the incorporation of carbon nanotubes can eliminate the possibility of sudden change of the electrical conductivity due to moisture drying. Therefore, the rapid decrease in the electrical conductivity in the high- It can be judged that it is caused by the occurrence.

High-conductivity cement composites have the same behavior as the surrounding concrete, so cracks occur at the same position as the concrete, so that the occurrence of cracks in the concrete can be accurately detected. Also, even if there is a deviation of the electric conductivity in the produced high-conductivity cement composite material, the electric conductivity will decrease sharply due to the occurrence of cracks, which is a reliable measurement method.

FIG. 3 illustrates a configuration in which a highly conductive cement composite material according to the present invention is disposed in a concrete structure.

The highly conductive cementitious composite material 10 can be disposed between the reinforcing bars 30 and the concrete structure 20 between the concrete surface where the cracks are to be generated and the concrete surface (lower surface in the drawing), as shown in FIG. As a result, when the crack propagates through the surface of the concrete structure 20 as shown in FIG. 3 (b), it is measured that the electric conductivity decreases rapidly in the measuring equipment 40 connected to the high-conductivity cement composite material 10, It can be detected in advance before the crack is propagated to the reinforcing bars 30. Therefore, according to the present invention, the structural stability of the reinforced concrete is improved by monitoring the cracks before they propagate through the concrete to the reinforcing bars to perform proper maintenance work.

According to the present invention, when carbon nanotubes are mixed to form a highly conductive cement composite material, it is preferable to mix the carbon nanotubes in an amount of 0.4 to 0.6 wt% based on the cement weight. When the content of the carbon nanotubes is less than 0.4 wt%, as shown in Fig. 2, the electric conductivity of the completely dry state (OD) and the moisture saturation state (SSD), except for the water / binder ratio (W / B) The resistance difference is still large, and it is difficult to clearly determine whether the electric conductivity is decreased rapidly due to moisture drying or cracking. On the other hand, when the content of the carbon nanotubes exceeds 0.6% by weight, it is difficult to mix with the cement, so that the uniform dispersibility may be lowered.

In addition, the high-conductivity cement composite material can be used immediately after being mixed at the construction site of the concrete structure, and thus has excellent workability and workability. However, when carbon nanotubes are used as a conductive material, it may not be possible to easily form a highly conductive cement composite material on site due to the low dispersibility of carbon nanotubes. According to the present invention, in order to solve this problem, when mixing carbon nanotubes, cement, etc., it is preferable to mix silica fume with 10-30 wt% based on the weight of the cement.

Carbon nanotubes exhibit low dispersibility due to their high length-to-diameter ratio, strong hydrophobicity and van der Waals attraction. When silica fume having a small particle size similar to that of carbon nanotubes of 10 to 500 nm is mixed together, Are uniformly dispersed in the concrete matrix while physically interacting with each other. As described above, when the content of silica fume is incorporated in the range of 10 to 30% by weight, the dispersibility of the carbon nanotubes at a satisfactory level capable of achieving the object of the present invention can be obtained and voids are generated in the concrete matrix By effectively dispersing the carbon nanotube aggregate by silica fume, it reduces the pores in the concrete and makes it more tight, thereby improving the compressive strength.

In other words, according to the present invention, even when cement, carbon nanotubes, and silica fumes are simply mixed in situ, the carbon nanotubes are uniformly dispersed in the concrete matrix, so that the highly conductive cement composite material can be immediately blended and placed in the field . This is one of the characteristic features of the present invention, which is compared with a conventional conductive cement composite material that has been manufactured and transported to a site for a long time in a plant having a sonication facility, not a construction site.

Also, it is preferable that the high-conductivity cement composite material according to the present invention is basically made of a cement material having properties similar to those of concrete. As a result, since they have the same thermal expansion coefficient, they do not fall off due to an additional heat shrinkage / expansion, and thus can be used for a long time. Therefore, a high conductivity cement composite material can be manufactured by further mixing fine aggregate in order to prepare the same composition ratio as that of the surrounding concrete and more accurately match the physical properties of the material.

Hereinafter, a method for detecting cracks in a reinforced concrete using a highly conductive cement composite material according to the present invention will be described in detail with reference to FIGS.

4 shows a process of installing a high-conductivity cement composite material according to the present invention on a new concrete structure.

First, a conductive material, cement, and water are mixed at a predetermined mixing ratio, and a high conductivity cement composite material is prepared by inserting an electrode plate made of metal on both sides (S10). At this time, it is already described that the conductive material uses at least one material selected from the group consisting of carbon nanotube, carbon fiber, graphite and coke.

FIG. 5 shows an example in which a pair of electrode plates 15 made of a metal material is provided at one end of a high-conductivity cement composite material 10 of a certain standard. Although not shown in FIG. 5, the highly conductive cementitious composite material 10 is provided with electrode plates 15 of the same shape at the other end after being extended by a predetermined length. As the material of the electrode plate 15, a metal having a high electrical conductivity such as a copper plate is often used, but other materials having the same level can be used.

Next, a highly conductive cement composite material is disposed at a position adjacent to the reinforcing bars laid in the concrete structure (S11). 3, the highly conductive cementitious composite 10 can be placed between the reinforcing bars 30 and the concrete structure 20 between the concrete surfaces where cracks will occur and propagate. As a result, once the crack propagates through the surface of the concrete structure 20, it is detected by the measuring equipment 40 connected to the highly conductive cementitious composite 10 before contact with the reinforcing bar 30 to perform proper maintenance work .

As shown in FIG. 6, in order to increase the accuracy of crack measurement, it is preferable that the high-conductivity cement composite material is disposed at a position where cracks are likely to occur among various types of concrete structures. For example, as shown in FIG. 6 (a), in the case of a concrete beam 21, a high-conductivity cement composite material 10 is disposed between the lower bottom surface of the beam and the reinforcing bar 31, a high conductivity cement composite material 10 is placed between the side of the lower end of the girder and the reinforcing bar 32 as shown in Figure 6 (b), and as shown in Figure 6 (c) In the case of the column 23, the high-conductivity cement composite material 10 is arranged in the horizontal direction between the outer surface of the column and the reinforcing bars 33, and as shown in FIG. 6 (d) , 24, a highly conductive cementitious composite material 10 is disposed between the surface of the joining portion of the minambuco and the reinforcing bars 34.

When the placement of the high-conductivity cement composite material is completed, a new concrete structure is prepared by pouring the concrete (S12), and the measurement equipment is electrically connected to the electrode plate inserted into both sides of the high-conductivity cement composite material (S13) , And the change in the electrical conductivity of the highly conductive cement composite material due to crack propagation in the concrete structure is monitored in real time or periodically (S14).

The real-time monitoring is configured to automatically check the change in the electrical conductivity through data processing while continuously connecting the measuring device to the electrode plate, and automatically alert the manager through an alarm when a change over a certain range is detected . On the other hand, the periodic monitoring is configured to visit the site at predetermined intervals, connect the measuring equipment to the electrode plate to check the change in electrical conductivity, and to perform maintenance work required when an abnormality is found in comparison with the previous recording .

FIG. 7 shows a process of installing a highly conductive cement composite material according to the present invention on a concrete structure installed therein.

First, a conductive material, cement, and water are mixed at a predetermined mixing ratio to produce a high-conductivity cement composite material (S20). At this time, it is already described that the conductive material uses at least one material selected from the group consisting of carbon nanotube, carbon fiber, graphite and coke.

Next, cutting grooves of a predetermined length are formed on the surface of the previously installed concrete structure using a device such as a power saw (S21). The high-conductivity cement composite material is charged into the cut-off grooves, and an electrode plate made of a metal material is inserted into both sides of the high-conductivity cement composite material (S22). As a result, as shown in FIG. 3, the high-conductivity cement composite 10 is placed between the reinforcing bars 30 and the concrete structure 20 between the concrete surface (the lower surface of the drawing) to be propagated and cracked.

According to the present invention, since carbon nanotubes, cement, and silica fume as conductive materials can be immediately mixed in the field and installed in the cut grooves, the workability and workability are excellent as described above.

When the placement of the high-conductivity cement composite material is completed, concrete is poured into the inside of the cut-off groove to protect the high-conductivity cement composite material from external temperature changes, impact, etc. (S23). However, this finishing process is not essential and may be omitted. That is, as the simplest method, the highly conductive cement composite material may be cured and fixed while being exposed to the outside of the cut groove.

Thereafter, the measurement equipment is electrically connected to the electrode plates installed on both sides of the high-conductivity cement composite material (S24), and then the high-conductivity cement composite material according to the crack generation and propagation in the concrete structure The electrical conductivity change is monitored in real time or periodically (S25).

Meanwhile, as shown in FIG. 7, when the high-conductivity cement composite material according to the present invention is used in a prestressed concrete (PSC) structure applied to a bridge or the like, the crack detection function can be reused by crack closure. More specifically, when a crack occurs due to a tendon loss in the PSC structure, the structure is usually repaired by restoring the tendon due to re-tension.

If a high-conductivity cement composite material is installed in the PSC structure, the electric conductivity decreases when cracks are generated as shown in the upper part of FIG. 7. However, as shown in the lower part of FIG. 7, Cracks in the cement composites also disappear together, so electrical conductivity is likely to recover again. Therefore, after recovering the tendon, the crack sensing using the highly conductive cement composite material can be recycled.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various changes and modifications may be made without departing from the scope of the appended claims.

10: High Conductivity Cement Composite 20: Concrete Structure
30: Rebar 40: Measuring equipment

Claims

Preparing a high-conductivity cement composite material in which conductive material, cement and water are mixed at a predetermined mixing ratio and electrode plates made of metal are inserted into both sides;
Disposing the highly conductive cementitious composite material at a position adjacent to the reinforcing bars laid in the concrete structure;
Casting the concrete to produce the concrete structure;
Electrically connecting measurement equipment to the electrode plate inserted on both sides of the high-conductivity cement composite material; And
And monitoring a change in electrical conductivity of the highly conductive cement composite material due to cracking in the concrete structure through the measurement equipment.

The method according to claim 1,
Wherein the conductive material is at least one conductive material selected from the group consisting of carbon nanotubes, carbon fibers, graphite, and cokes.

The method of claim 2,
Wherein the conductive material is carbon nanotubes and is mixed in an amount of 0.4 to 0.6% by weight based on the weight of the cement, wherein the crack is detected using the high-conductivity cement composite material.

The method of claim 3,
Wherein the silica fume is mixed in an amount of 10 to 30 wt% based on the weight of the cement to improve the dispersibility of the carbon nanotubes.

The method according to any one of claims 1 to 4,
Wherein the high-conductivity cement composite material is manufactured by further compounding a fine aggregate.

The method according to claim 1,
Wherein the step of arranging the high-
Wherein the high-conductivity cement composite material is disposed between the reinforcing bars and the concrete surface on which the cracks are to be generated, from among the concrete structures.

The method according to claim 1,
Wherein monitoring the electrical conductivity change comprises:
Wherein the change in electric conductivity of the highly conductive cement composite material due to the occurrence of cracks is measured in real time or periodically.

Mixing a conductive material, cement and water at a predetermined mixing ratio to produce a high-conductivity cement composite material;
Forming a cut groove having a predetermined length on a surface of a previously installed concrete structure;
Inserting the highly conductive cement composite material into the cut groove and inserting an electrode plate made of a metal material on both sides of the highly conductive cement composite material;
Electrically connecting measurement equipment to the electrode plate inserted on both sides of the high-conductivity cement composite material; And
And monitoring a change in electrical conductivity of the highly conductive cement composite material due to cracking in the concrete structure through the measurement equipment.

The method of claim 8,
Wherein the conductive material is at least one conductive material selected from the group consisting of carbon nanotubes, carbon fibers, graphite, and cokes.

The method of claim 9,
Wherein the conductive material is carbon nanotubes and is mixed in an amount of 0.4 to 0.6% by weight based on the weight of the cement, wherein the crack is detected using the high-conductivity cement composite material.

The method of claim 10,
Wherein the silica fume is mixed in an amount of 10 to 30 wt% based on the weight of the cement to improve the dispersibility of the carbon nanotubes.

The method according to any one of claims 8 to 11,
Wherein the high-conductivity cement composite material is manufactured by further compounding a fine aggregate.

The method of claim 8,
The cutting groove forming step may include:
Wherein the cutting groove is formed so that the cutting groove is disposed between the reinforcing bars laid in the concrete structure in which the high-conductivity cement composite material is installed, and the concrete surface in which the cracks are to be propagated among the concrete structures. Crack detection method in concrete.

The method of claim 8,
The step of injecting a high-conductivity cement composite material into the cut-
The method of claim 1, further comprising the step of applying a concrete to the inside of the cut groove to finish the cemented composite.

The method of claim 8,
Wherein monitoring the electrical conductivity change comprises:
Wherein the change in electric conductivity of the highly conductive cement composite material due to the occurrence of cracks is measured in real time or periodically.