KR101610710B1 - Self-detecting method for crack and damage with self-detecting hybrid fiber reinforced cement composite and self detecting system thereof - Google Patents

Abstract

The present invention relates to a method and a device for detecting cracked or damaged magnetic properties of a concrete structure containing hybrid fibers for more precisely and sensitively monitoring or monitoring microstructure changes such as cracks and cracks in fragile portions of concrete structures expected to be cracked or damaged A hybrid fiber including a carbon fiber and a steel fiber is used as a reinforcing material so that a concrete structure exhibits a strain hardening behavior and a system capable of detecting damage through a resistivity measurement can be provided. Only a weak portion of a concrete structure requiring special care or attention is finished or applied with a concrete composition reinforced with a hybrid fiber having conductivity, and then a certain time Interval or desired check It is possible to diagnose the degree of cracking or damage of the concrete structure effectively and economically simply by monitoring the resistivity by flowing an electric current through a simple electrode installed at the point of time.

Description

TECHNICAL FIELD [0001] The present invention relates to a self-detecting method and a self-detecting hybrid fiber reinforced cement composite and a self-

The present invention relates to a method for magnetic sensing of a crack or damage of a cracked and damaged self-sensing hybrid fiber-reinforced cement composite material in which two fibers are mixed together, and to a magnetic sensing device using the hybrid fiber- By reinforcing the conductive fibers of steel fiber and carbon fiber together, strain hardening is induced directly under tensile load, and current is flowed to measure the resistivity to separate the crack or damage of the structure. Provides a self-detecting method and apparatus that can detect without using a strain gage.

In more detail, the fragile portion of the concrete structure where cracks or damage are expected is defined as a hybrid fiber comprising steel fibers and carbon fibers in a range of 1.25 to 2.0 vol% based on the total composition The present invention relates to a method for observing or predicting cracks or damages of a concrete building in real time or in advance by measuring the change in resistivity with respect to such a vulnerable portion using the included concrete composition, and an apparatus applied to such a method.

Concrete structures made of composite materials such as cement and aggregate are the most widely used building structures for the construction of urban buildings and infrastructure. They are used for cracking and damaging the concrete structures to be maintained securely and safely for a long period of time. There is an increasing demand for a system capable of real-time or pre-detecting or predicting the risk of collapsing caused by a collision.

A system for detecting the damage of a conventional concrete structure includes a monitoring system and a safety diagnosis for measuring damage and soundness of a structure by real-time measurement by additionally installing various kinds of strain or displacement measuring devices. Also, various electrochemical methods can be applied. Among them, the electrical resistivity method is a representative example of the non-destructive corrosion diagnosis method in which electric current is flowed to the concrete structure to measure the resistivity to check damage or cracks.

Open Patent Application No. 2011-0010853 discloses a non-destructive corrosion diagnosis system capable of directly estimating the electrical resistivity related to concrete and reinforcing bars from the upper side of the reinforcing bars and evaluating the corrosion environment of the reinforcing bars and the condition thereof. Two current electrodes and two voltage electrodes inside were installed at equal intervals in parallel with the longitudinal direction of the reinforcing bars to measure the response voltage generated by the current source to determine the interlayer and average resistivity of the concrete showing the corrosion environment of the reinforcing bars, And the surface resistivity of the reinforcing bars indicating the direct corrosion state is estimated, so that regular inspection and regular monitoring of the corrosion and durability of the reinforcing steel of the concrete structure are carried out.

However, the method of monitoring the corrosion and durability of the reinforcing steel of such a concrete structure has a limitation in that it can measure only the degree of corrosion of the reinforcing steel, which is an electrically conductive material formed in the concrete, and the damage and deformation such as cracks and cracks in the whole concrete structure There is a problem that information can not be provided. Further, current monitoring systems that separately attach or embed sensors to separate structures for measuring strain or displacement have a problem in that they can not be continuously used for the entire lifetime of the structure due to the durability life of the sensor, which is short compared to the lifetime of the structure .

Open Patent Application No. 2005-0018744 discloses a method for producing a steel sheet by using polyethylene fiber (PE) fiber or polyvinyl alcohol (PVA) fiber or polypropylene (PP) fiber as a microfiber in steel cement paste or mortar, Or polyvinyl alcohol (PVA) fiber as a macro fiber, and the tough cement composite has strain hardening properties and multiple crack characteristics under the action of flexure and tensile load, Tensile strength, deformation ability and energy absorbing ability as well as suppression of penetration of various degradation factors by controlling the crack width.

Recently, it has been reported that carbon black having high conductivity is mixed into a high-strength cement composite using polyvinyl alcohol (PVA) fiber to detect cracks and damage. However, as a result of the low electrical conductivity of the polyvinyl alcohol fiber, cracking has been reported to increase the electrical resistance. Therefore, there is a need for an electrical resistance measuring device capable of measuring very low electrical conductivity.

In the case of conventional sensors measuring strain or displacement, the GF (gauge factor) value, which is defined as the ratio of the resistivity change per unit strain, is as low as about 2 and the life span of the sensors is very short. There is still a problem that the electrical conductivity of the used hard cement composite becomes very low as cracks occur. In addition, the tensile strength of the modified cementitious cement composites reinforced with steel fiber is 8-15 MPa, whereas the tensile strength of the cementitious composite using polyvinyl alcohol fiber is lower than 4-5 MPa. Therefore, there is a problem that cracks are generated even under a small external load.

Therefore, in the present invention, it is possible to provide a fiber reinforced hybrid fiber reinforced with a carbon fiber having a small diameter and a small diameter but a small diameter and a long length, The present invention provides a method for easily diagnosing and monitoring the safety of a concrete structure by continuously measuring the change of resistivity with time in a concrete structure by applying the cementitious cementitious composite material to a vulnerable portion of the concrete structure.

Also, by optimizing the type and composition of the hybrid fiber reinforcement used in the high-tensile concrete composition, it is possible to more accurately detect or monitor the change in the microstructure of the concrete structure by improving the GF value defined as the ratio of the specific resistance change per unit strain And to provide a composition of a hybrid fiber reinforcement having excellent magnetic sensing and tensile resistance behavior.

Published Patent No. 2011-0010853 Published Japanese Patent Application No. 2005-0018744

M. Li, V. Lin, J. Lynch and V.C. Li. (2012). Multifunctional carbon black engineered cementitious composites for the protection of critical infrastructure. RILEM. pp. 99-106.

As described above, the present invention overcomes the problems of the prior art and provides a method for accurately and sensitively monitoring or monitoring microstructure changes such as cracks and cracks in a vulnerable portion of a concrete structure, The present invention provides a method and an apparatus for detecting a crack or damage in a concrete structure using two kinds of hybrid fiber reinforced cement composites having excellent conductivity.

More specifically, a macro steel fiber and a micro carbon fiber are used to induce strain hardening behavior under a direct tensile load, and a cement type fiber reinforced or mixed with these two kinds of fibers It is an object of the present invention to derive the optimum compounding ratio of the matrix, thereby remarkably improving the GF value defined as the ratio of the specific resistance change per unit strain, and simultaneously exhibiting the strain hardening behavior accompanied by a plurality of microcracks.

Also, by using the hybrid fiber reinforced cement composite material having the composition of the present invention at a vulnerable portion of a concrete structure, it is possible to easily diagnose or monitor the degree of self-damage of the concrete structure, To prevent damage, breakage or collapse of the concrete structure of the concrete, and to establish countermeasures.

In order to accomplish the above-mentioned problems of the prior art and the object of the present invention, a method of cracking or damaging magnetic sensing of a hybrid fiber-reinforced cement composite material according to the present invention is a method of detecting a crack or damage in a fragile portion of a concrete structure A first step of forming a hybrid fiber including steel fibers and carbon fibers using a concrete composition containing 1.25 to 2.0 vol% based on the total composition; A second step of forming an electrode on a fragile portion of the concrete structure using the fiber-reinforced cement composite material; And a third step of supplying a current to the electrode to measure a change in resistivity of the fragile portion of the concrete structure with time.

The concrete composition includes 1.0 to 1.5 vol% of a steel fiber and 0.25 to 0.5 vol% of carbon fiber. The steel fiber used as the macro fiber is 0.25 to 0.45 mm in diameter and 25 to 45 mm in length , The diameter of the carbon fibers which are microfibers is preferably 0.005 to 0.01 mm, and the length is preferably 10 to 17 mm.

In the present invention, the composition of the cement composite material used for the construction of the fragile portion of the concrete structure is composed of 75 to 85 parts by weight of cement, 5 to 10 parts by weight of pyrolysis silica, 15 to 25 parts by weight of fly ash, 1 to 10 parts by weight of an admixture, 20 to 30 parts by weight of water, and a steel fiber and a carbon fiber are mixed together.

Preferably, the fly ash has a powdery degree of 3000 to 4000 cm 2 / g, the pyrolytic silica has an average diameter of 0.01 to 1 μm, and the silica sand has an average diameter of 0.01 to 0.5 mm.

Another embodiment of the present invention is a device for detecting a magnetic damage of a concrete structure, which comprises a concrete composition containing a steel fiber and a carbon fiber in a range of 1.25 to 2.0 vol% based on the composition, This predicted vulnerability of the concrete structure; An electrode unit electrically connecting the vulnerable portion to an external power source; A control unit for supplying a current through the electrode unit to record a change in electrical resistivity with time of a fragile portion of the concrete structure; And a connection part electrically connecting the electrode part and the control part.

The method for cracking or damaging a self-reinforced concrete structure reinforced with the hybrid fiber of the present invention is characterized in that only a vulnerable portion of a concrete structure requiring special care or attention is closed or constructed with a hybrid fiber-reinforced cement composite material having conductivity, It is possible to diagnose the degree of cracking or damage of the concrete structure effectively and economically simply by monitoring the resistivity by flowing current through the electrode which is simply installed at a predetermined time interval or at a desired inspection time point.

In addition, by partially applying a weak portion requiring attention observation within the existing concrete structure selectively using the hybrid fiber-reinforced cement composite material of the present invention, it is possible to diagnose damage by simple electric resistance measurement, It is possible to provide a method of detecting a damage of a concrete structure with a high durability through a curing behavior and at the same time being economical for a wide area.

In the present invention, by using a mixture of a steel fiber as a macro fiber and a carbon fiber as a micro fiber, even if a concrete structure undergoes initial cracking under the action of bending and tensile force, The strain hardening characteristic which increases the stress along with the increase and the multiple crack characteristic that many microcracks occur throughout the concrete structure can be induced and the ratio of the specific resistance per unit strain GF (gauge factor value to be higher than 50 so as to provide a high crack or damage detection capability. Also, the electrical conductivity is further improved after the occurrence of the cracks through the reinforcement of the highly conductive fibers, so that the specific resistance per unit strain is rapidly lowered, thereby clearly recognizing the point of occurrence of the initial crack and improving the self-sensing ability.

Therefore, the method and apparatus for cracking or damaging the concrete structure reinforced with the hybrid fiber of the present invention can be used to precisely and effectively monitor the internal state of the concrete structure and to detect the risk of cracks and the like in advance. Can be applied to the following structures.

First, the water or liquid storage tank must always withstand a high tensile load by water pressure. Since the column of this structure is also subjected to a tensile load at all times, the application of the present invention is effective.

Second, when the present invention is applied to a structure such as a roof which is always subjected to a tensile load as a thin film structure, it is effective for convenience of construction and maintenance and the like.

Third, the top tower of the cable structure is always exposed to vibration, so that when the method or apparatus for cracking or damaging the magnetic structure of the concrete structure reinforced by the hybrid fiber of the present invention is applied, the displacement of vibration can be adjusted It is effective in detecting tensile stress and deformation.

FIG. 1 shows the resistivity change behavior of a steel fiber reinforced self-reinforced concrete structure. FIG. 1 (a) shows a case without tensile strain, and FIG. 1 (b) shows a resistivity with increasing tensile strain And the tensile strength of the test specimen.
2 is a diagram schematically showing a tensile strain hardening behavior of a general strain hardening type fiber reinforced cement composite material.
3 is a photograph of the steel fiber (a) and the carbon fiber (b) used in the present invention.
Fig. 4 is a result of observing the electromechanical behavior of a concrete structure using a hybrid fiber which is a mixture of steel fiber alone or a mixture of steel fiber and carbon fiber.
5 shows the results of measuring the electromechanical behavior of concrete structures containing 1.0 vol% of steel fibers according to the amount of added carbon fibers (Fig. 5a: 0 vol% of carbon fibers, Fig. 5b: 0.5 vol% of carbon fiber, Fig. 5c: 1.0 vol% of carbon fiber, and Fig. 5d: 1.5 vol% of carbon fiber).
6 is a GF (gauge factor) value measured by varying the amount of carbon fiber for a concrete structure containing 1.0 vol% of steel fiber.
FIG. 7 shows the electromechanical behavior changes of concrete structures containing 1.5 vol% of steel fibers according to the amount of added carbon fibers (FIG. 7a: 0 vol% of carbon fibers, FIG. 7b: 0.25 vol% of carbon fiber, and Fig. 7c: 0.5 vol% of carbon fiber).
8 (a) is a GF (gauge factor) value measured by varying the amount of carbon fiber for a concrete structure containing 1.5 vol% of steel fiber, and Fig. 8 (b) And the result of measuring the change of the tensile stress value.

Hereinafter, the technical features of the present invention will be described in detail with reference to embodiments and drawings. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. shall.

In general, the cementitious composites represented by concrete have brittle properties in which the stress is rapidly lowered after initial cracking under the action of bending and tensile load, and the compressive strength is high but the bending and tensile strength are low, , There have been pointed out problems with respect to durability and toughness of concrete structures such as penetration of external deterioration factor from these cracks and induction of internal reinforcing bars.

In order to solve these problems, steel fiber reinforced concrete having increased bending strength and toughness compared to ordinary concrete has been used by mixing steel fiber into concrete. However, after initial cracking under bending and tensile loading, There is a problem that the cracks are locally localized so that it is difficult to improve the deformation capacity and to control the crack width. Therefore, There is a problem that the variation of the electrical resistivity is small according to the change of the microstructure.

Recently, a manufacturing technique of a short fiber reinforced cement composite excellent in flexure, tensile performance, crack control performance, and deformation performance has been studied more recently than fiber reinforced concrete. However, in this case, There is a disadvantage that the stress is rapidly lowered or the localization of the crack rapidly progresses in the softening zone after the maximum stress because microfibers alone are used.

In order to solve such a problem, the present invention maximizes the strain hardening characteristic of a concrete structure by simultaneously applying a macro fiber fiber and a carbon fiber to a concrete structure and experimentally confirming an optimized blending ratio, And to provide a method and an apparatus for observing minute changes such as cracks of a concrete structure more economically and accurately.

In general, in the absence of tensile deformation, as shown in FIG. 1A, the electrical resistivity of the concrete structure reinforced with steel fiber is increased at the initial stage due to the electro-polarization phenomenon, and then stabilized with time.

However, when a tensile strain is applied to a concrete structure reinforced with a steel fiber, as shown in the graph of FIG. 1B, the tensile stress also increases proportionally with increasing tensile strain, and the electrical resistivity decreases . However, when the tensile strain increases beyond the final cracking strength, the tensile stress is rather reduced, and the electrical resistivity does not change anymore even if the tensile stress is not changed any more.

The electrical resistivity can be calculated from the measured cross-sectional area (A) and the distance (L) between the measured internal electrodes by measuring the electrical resistance (R) as shown in the following equation (1).

(1)

(One)

Where ρ is the electrical resistivity, R is the electrical resistance, A is the cross-sectional area, L is the distance between the two internal electrodes, and the viewpoint distance of the specimen.

In general, electrical resistivity corresponds to the intrinsic property of a sample which is not influenced by the shape or structure of the sample. However, since the electrical resistance is affected by structural variables such as the cross-sectional area and the length between the internal electrodes, It is necessary to measure the resistance and convert it into an electrical resistivity.

In order to evaluate the self-damage detection ability by measuring the electrical resistivity of a concrete structure in which strain hardening occurs, the value of GF (gauge factor), which is a ratio of resistance change per unit strain, is used. This GF value can be calculated as an average from the time point of the tensile strain to the post cracking point as shown in the following equation (2). In the following equation (2) can be calculated by measuring the ratio of the rate of change of the electrical resistivity (or electrical resistance) value to the tensile strain up to? _pc .

(2)

(2)

Here, △ R is the amount of change in electrical resistance, R ₀ is the electrical resistance value, △ ε is the tensile strain variation, ε _pc is tensile strain value at crack initiation points, △ ρ is the electrical resistivity value when the tensile load is started change, ρ ₀ is the electrical resistivity value, ρ △ _pc is a variation, the electrical resistivity ρ _pc value at the crack initiation point when the tensile load is started shows the resistivity values at the crack initiation point.

Fig. 2 is a graphical representation of the general tensile strain behavior of a steel-reinforced concrete structure with increasing tensile strain, showing an elastic region (I region) at the beginning of strain, (III region) in which the tensile hardening behavior (II region) in which multiple cracks occur is shown and then the stress is decreased by the growth of many cracks as the strain further increases. Tensile stress and tensile strain in the initial crack at which the tensile curing occurs is denoted by σ _cc and ε _cc each, more tensile stress to tensile strain in the final cracking when the invisible tensile hardening behavior and σ _pc each ε _pc .

The strain hardening behavior of a typical reinforced concrete structure appears when σ _pc is higher than σ _cc. By detecting or monitoring the crack or microstructure change of the concrete structure in the strain hardening behavior area, cracks or damage of the concrete structure can be detected .

For the concrete structure having the strain hardening behavior used in the present invention, hybrid fibers including steel fibers and carbon fibers were used. The tensile strength and ductility of a concrete structure constructed with such a concrete mixture can be improved simultaneously by applying a small amount of a hybrid fiber composed of a carbon fiber and a steel fiber to a concrete mixture. This is because carbon fibers, which are microfibers, increase ductility and contribute effectively to improving tensile strength.

However, the amount of reinforcing fibers used in such a concrete mixture is limited due to workability. Macro fibers can be used up to 2 vol%, and microfibers can be used up to 6 vol% .

In addition, the carbon fiber used as the microfibers in the present invention is more effectively distributed in the concrete structure than the conventional metal reinforcement, and is excellent in corrosion resistance and strength, and has a very small diameter and a high aspect ratio (aspect ratio> 1500) And it can be effectively distributed in the interface between the macro fiber fiber and the concrete in the concrete structure to effectively improve the battery conductivity so that the sensitivity and the sensitivity of the method of detecting the magnetic damage of the present invention by measuring the electrical resistivity change of the concrete structure .

The method for detecting a magnetic damage of a concrete structure reinforced with such a hybrid reinforcement is characterized in that the hybrid fiber including steel fiber and carbon fiber is contained in a range of 1.25 to 2.0 vol% Forming a concrete structure, forming an electrode capable of flowing electricity to the concrete structure, and supplying a current to the electrode to measure a change in specific resistance of the concrete structure with time, It is also possible to directly select a user's required time, such as a durability test cycle of a concrete structure or a specific event such as an earthquake, in order to measure the change in resistivity with time.

The concrete composition used in the concrete composition preferably contains a steel fiber in a range of 1.0 to 1.5 vol% and a carbon fiber in a range of 0.25 to 0.5 vol%. The diameter of the steel fiber is 0.25 to 0.45 mm, Preferably 25 to 45 mm, the diameter of the carbon fiber is 0.005 to 0.01 mm, and the length is 10 to 17 mm. Although such a composition can be applied over the entire concrete structure, It is also possible to make some construction only for a specific vulnerable part of the structure.

Also, it is possible to selectively install a concrete structure using a hybrid fiber reinforcing material of the present invention only for a specific vulnerable site, and to change the position and quantity of the electrode to various types It is also possible to do.

Another embodiment of the present invention is a device for detecting a magnetic damage of a concrete structure, which comprises a hybrid fiber including a steel fiber and a carbon fiber in a range of 1.25 to 2.0 vol% A control unit for supplying a current through the electrode unit to record a change in electrical resistivity of the fragile portion of the concrete structure over time, And a connection unit for electrically connecting the control unit.

The concrete composition used for producing the concrete structure of the present invention is composed of 75 to 85 parts by weight of cement, 5 to 10 parts by weight of pyrolysis silica, 15 to 25 parts by weight of fly ash, and 1 to 25 parts by weight of high- To 10 parts by weight of water and 20 to 30 parts by weight of water, wherein the fly ash used has a powdery degree of 3000 to 4000 cm 2 / g, the pyrolytic silica has an average diameter of 0.01 to 1 μm, It is preferable that the average diameter is 0.01 to 0.5 mm.

[ Example  One]

In order to examine the cracking or damage magnetic detection performance of the concrete structure reinforced with the hybrid fiber used in the present invention, a concrete structure using only a steel fiber as a reinforcing material, a concrete composition using a hybrid fiber including a steel fiber and a carbon fiber as a reinforcing material And the GF values of these specimens were measured and compared.

The steel fiber and the carbon fiber used in the present embodiment were made of the materials shown in Table 1, and the photographs thereof are shown in FIG. In the case of using only the steel fiber as the reinforcing material, the concrete mixture was mixed into the concrete mixture such that the steel fiber content was 1.5 vol% in the entire concrete composition. When reinforced with the hybrid fiber, the steel fiber content was 1.0 vol% and the carbon fiber content was 0.5 vol% .

Type of fiber Diameter [mm] Length [mm] Density [g / cc] Tensile Strength [MPa] Elastic modulus [GPa] Carbon fiber 0.005 to 0.01 10-17 1.81 4137 240 Steel fiber 0.25 to 0.45 25 ~ 45 7.9 2580 200

The concrete steps of forming the deformation-hardened concrete structure using the concrete composition are as follows.

Cement, fly ash, silica fume, silica sand, and carbon fiber for 5 minutes; Adding water to the mixture of the first step and mixing the mixture for 3 minutes; A third step of adding a plasticizer to the mixture of the second step and mixing the resulting mixture for 5-10 minutes; A fourth step of adding a steel fiber to the mixture of the third step and mixing the same again for 5 minutes; A fifth step of pouring the mixture of the fourth step into the mold and giving a fine vibration; A sixth step of covering the mixture of the fifth step with a plastic sheet and storing at room temperature for 2 days; A seventh step of taking the molded body of the sixth step from the mold and wet-curing it for 14 days; A step 8 of drying the molded body of the seventh step at a high temperature for 12 to 36 hours and a step 9 of spraying polyurethane of 2 to 3 layers of the molded body of the eighth step.

The silica fly has an average diameter of 0.01 to 1 占 퐉 and an average diameter of the silica fly ranges from 0.01 to 0.5 mm. The silica fume is 5 to 10 parts by weight, the fly ash is 15 to 25 parts by weight, the admixture is 1 to 10 parts by weight, the water is 20 to 20 parts by weight, To 30 parts by weight.

When only the steel fiber was used as the reinforcing material, concrete specimens were prepared in the same manner except for the carbon fiber in the first step. Each of the concrete specimens thus prepared was wrapped with a silver paste as a whole, and a copper tape was attached to increase the electrical conductivity between the concrete and the tape. Then, a tensile load was applied to the concrete specimen, And the experimental results for each specimen are summarized in the following Table 2 and FIG. 4.

Tensile strain
ε _pc (%) Tensile stress
σ _pc (MPa) Average crack number
Npc GF value Steel fiber 0.53 7.64 10 99.85 Hybrid fiber 0.49 6.81 7 208.23

The results of Table 2 and the mechanical-electrical response behavior of FIG. 4 show that both concrete specimens using only steel fibers as reinforcing materials and concrete specimens using hybrid fibers containing both steel fibers and carbon fibers as reinforcing materials Although typical strain hardening behaviors were shown, the concrete specimens with hybrid fibers were slightly reduced in tensile strain and tensile stress compared to steel fiber only.

However, it was confirmed that the GF value indicating the change of the resistivity due to the unit tensile strain was increased to more than 2 times, and it was confirmed that it is more advantageous to detect the magnetic damage of the concrete structure to be solved in the present invention.

[ Example  2]

A concrete specimen was prepared using hybrid fibers in the same manner as in [Example 1], and the amount of the steel fiber used was fixed to 1.0 vol% of the total amount of the concrete composition, and the amount of carbon fiber was set to 0 vol%, 0.5 vol%, 1.0 vol%, and 1.5 vol%, and the mechanical-electrical response behavior was observed in the same manner. The results are shown in Figs. 5a to 5d.

5a shows the mechanical-electrical response behavior of a concrete specimen in which carbon fiber is not used but only 1 vol% of the steel fiber is used. Figs. 5b to 5d show carbon fiber 0.5, 1 and 1.5 vol% The mechanical - electrical response behavior of concrete specimens prepared using hybrid fibers containing.

The typical strain hardening behavior was observed only when the steel fiber contained 1.0 vol%, the steel fiber contained 1.0 vol%, and the carbon fiber contained 0.5 vol%. The use of carbon fiber was increased to 1.0 or 1.5 vol% The strain softening behavior is not suitable for detecting the magnetic damage of the concrete structure to be solved in the present invention.

As the tensile strain increases after the initial cracking, the tensile resistance decreases. Instead, many microcracks are generated, but the width of one crack increases gradually. Therefore, not only the durability life of the structure is shortened, but also the load resistance ability is lowered.

6 shows the results of comparing GF values for each case based on the above results. The GF values of the concrete specimens mixed with 1.0 vol% of the steel fiber and 0.5 vol% of the carbon fiber were the highest values As shown in Fig.

[ Example  3]

The concrete specimens were prepared using the hybrid fibers in the same manner as in Example 2 except that the amount of the steel fiber used was fixed at 1.5 vol% of the total amount of the concrete composition and the amount of the carbon fibers was adjusted to the total amount 0 vol%, 0.25 vol%, and 0.5 vol%, respectively, and the mechanical-electrical response behavior was observed in the same manner. The results are shown in FIGS. 7a to 7c.

FIG. 7A shows the mechanical-electrical response behavior of a concrete specimen in which 1.5% by volume of carbon fiber is not used, and FIG. 7B and FIG. 7C show carbon fiber 0.25 and 1.0 vol% The mechanical - electrical response behavior of concrete specimens prepared using hybrid fibers is shown.

The typical strain hardening behavior was observed only when the steel fiber contained 1.5 vol% of carbon fiber, 1.5 vol% of steel fiber, and 0.25 vol% or 0.50 vol% of carbon fiber, and the amount of carbon fiber used increased to 1.0 vol %, Strain softening behavior was confirmed as shown in Example 2, and it was not suitable for detecting the magnetic damage of the concrete structure to be solved in the present invention.

Based on the above results, the GF value for each case was calculated and the results of the comparison and the measurement results of the tensile strength were shown in FIGS. 8A and 8B, respectively. Steel fibers were mixed in an amount of 1.5 vol% and carbon fibers were mixed in an amount of 0.5 vol% The GF values of the concrete specimens were found to be the highest values, And it was confirmed that it was not significantly changed by increasing to 0.5 vol%.

Claims (10)

A method for detecting a magnetic damage of a concrete structure,
A concrete composition in which a hybrid fiber including steel fiber and carbon fiber is contained in an amount of 1.25 to 2.0 vol% based on the total composition, A first step of forming by use;
A second step of forming an electrode on a vulnerable portion of the concrete structure formed using the concrete composition; And
And a third step of supplying a current to the electrode to measure a change in resistivity of the fragile portion of the concrete structure with time,
Wherein the hybrid fiber comprises 1.0 to 1.5 vol% of a steel fiber and 0.25 to 0.5 vol% of a carbon fiber, wherein the hybrid fiber is cracked or damaged. delete The method according to claim 1,
Wherein the steel fiber has a diameter of 0.25 to 0.45 mm and a length of 25 to 45 mm and a diameter of the carbon fiber is 0.005 to 0.01 mm and a length of the reinforcing fiber is 10 to 17 mm. Cracks or damage to the magnetic sensing method. The method according to claim 1,
In the concrete composition, 75 to 85 parts by weight of cement, 5 to 10 parts by weight of pyrolysis silica, 15 to 25 parts by weight of fly ash, 1 to 10 parts by weight of high strength admixture, 20 to 20 parts by weight of water, 30 parts by weight of the reinforcing fibers are reinforced by the reinforcing fibers. 5. The method of claim 4,
Characterized in that the fly ash has a powder degree of 3000 to 4000 cm 2 / g, the pyrolytic silica has an average diameter of 0.01 to 1 μm and the silica sand has an average diameter of 0.01 to 0.5 mm. Methods of cracking or damaging magnetic detection of concrete structures. A magnetic damaging device for a concrete structure,
A fragile portion of a concrete structure in which a hybrid fiber including steel fiber and carbon fiber is formed of a concrete composition containing 1.25 to 2.0 vol% based on the total composition;
An electrode unit electrically connecting the vulnerable portion to an external power source;
A control unit for supplying a current through the electrode unit to record a change in electrical resistivity with time of a fragile portion of the concrete structure; And
And a connection unit electrically connecting the electrode unit and the control unit,
Wherein the hybrid fiber comprises 1.0 to 1.5 vol% of a steel fiber and 0.25 to 0.5 vol% of a carbon fiber, wherein the hybrid fiber is cracked or damaged by a hybrid fiber. delete The method according to claim 6,
Wherein the steel fiber has a diameter of 0.25 to 0.45 mm and a length of 25 to 45 mm and a diameter of the carbon fiber is 0.005 to 0.01 mm and a length of the reinforcing fiber is 10 to 17 mm. Crack or damage magnetic sensor. The method according to claim 6,
In the concrete composition, 75 to 85 parts by weight of cement, 5 to 10 parts by weight of pyrolysis silica, 15 to 25 parts by weight of fly ash, 1 to 10 parts by weight of high strength admixture, 20 to 20 parts by weight of water, 30 parts by weight of the reinforcing fibers are reinforced by the reinforcing fibers. 10. The method of claim 9,
Characterized in that the fly ash has a powder degree of 3000 to 4000 cm 2 / g, the pyrolytic silica has an average diameter of 0.01 to 1 μm and the silica sand has an average diameter of 0.01 to 0.5 mm. Crack or damage of a concrete structure.

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