JP2016218049A - Crack detecting sensor, and crack monitoring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crack detecting sensor and a crack monitoring method that enable detection of cracks with a simple configuration.SOLUTION: A crack detecting sensor 1 for detecting any crack cr in a hardened cement-concrete composition C is equipped with a surface protecting layer 7, at least one holding layer 6 in which a glass ball 5 is encapsulated, and a detection sheet S including a focus forming layer 4 and a specular reflection layer 3. The reverse side of the detection sheet S to the surface protecting layer 7 is pasted onto the surface of the hardened cement-concrete composition C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a crack detection sensor and a crack monitoring method for monitoring cracks and the like generated in a structure composed of a cement / concrete hardened body.

  Cement / concrete used in civil engineering and building structures undergo changes such as cracks, cracks, and unevenness due to changes in the volume of the material itself, environmental conditions such as solar radiation, and external forces during service. These changes are important signs in the maintenance of cement-concrete structures. In particular, when cracks and cracks grow beyond a certain limit, rainwater, chloride ions, carbon dioxide, etc. cause corrosion of reinforcing bars inside the structure, so it is important to properly grasp the changes. . Appropriately grasping these changes makes it possible to diagnose the cause and take appropriate countermeasures, and to increase the durability of the cement / concrete structure. Evaluation and management of deformation such as cracks in a cement / concrete structure is performed by, for example, a method in which an operator moves to an inspection target portion and directly visually observes it. The degree of growth of cracks and cracks found is determined by installing crack gauges, strain gauges, or pie-type displacement gauges between cracks, and periodically recording the crack width values detected by these sensors and instruments. ,to manage.

  In many cases, it is difficult to easily perform these operations. For example, on a bridge pier or a floor slab lower surface, it is necessary to construct a scaffold so that it can approach the inspection target part. In addition, an aerial work vehicle is used for inspection and survey of the top of the tunnel. Furthermore, since there are many cases of nighttime investigations when there is a restriction on traffic blockage, there is a problem that a deformation such as a crack may be missed. Visual inspection of cracks in the dark is extremely difficult and requires complicated work requiring skilled skills. If the crack is not accurately grasped to some extent, it may be interpreted differently from the original cause, and appropriate judgment and countermeasures may not be performed.

  Recently, with the advancement of IT technology, we have developed a method to measure cracks by image processing with a CCD video camera and to detect cracks by irradiating the concrete surface with laser light and detecting reflected light. Has been. In addition, a wide range of information can be obtained at a time by making the measuring device and the like on-vehicle. Since these methods perform complicated processing in addition to the use of expensive measuring equipment, they cannot be easily operated by field workers.

  In order to appropriately prevent and maintain concrete structures, an easy monitoring technique for cracking concrete is required. In particular, there is a need for a simple and highly accurate detection method that can be used to collect data that can be used to monitor cracks in concrete structures and determine whether or not a serious accident such as peeling occurs.

  In Patent Document 1, as a concrete crack sensor, an optical fiber is attached so as to straddle a plurality of cracks generated on the wall surface in the tunnel in order, and according to the distortion of the optical fiber generated as the crack expands. A remote monitoring system is disclosed in which a signal appearing at the end of an optical fiber is received and processed to sense the progress of a crack. In a remote monitoring system, for example, an optical fiber loss distribution measuring instrument or a strain distribution measuring instrument is connected to the starting end of an optical fiber to measure the strain at an arbitrary position in the optical fiber, and the strain change that has been associated in advance. Estimate the amount of crack growth by using the relationship between the amount of crack and the change in crack width. In order to monitor the growth of cracks in the concrete, the remote monitoring system requires precise on-site work to mount the optical fiber on the cracked part and maintaining the attitude of the optical fiber after construction, and also requires advanced measuring instruments. To do. Furthermore, when a new crack appears during the observation period, there remains a problem that it is not easy to reconstruct the sensor for including the new crack in the monitoring target.

  In Patent Document 2, a hardened rod-shaped cement body in which short fibers such as graphite powder and carbon fibers are dispersed is embedded in the concrete to be detected, and the resistance value between the ends of the hardened cement body is measured. A sensor for estimating the cracking state of concrete is disclosed. The method of measuring the resistance value between both ends of the hardened cement body can be monitored at any time or as appropriate, but only detects the cracked state in the portion in which the hardened cement body is previously embedded. Further, since a measurement signal cannot be obtained after the hardened cement body is cut by cracks, it cannot be applied to the case of detecting crack growth.

  In Patent Document 3, a plurality of metal plates are arranged on a rubber plate that stretches following the expansion of concrete cracks when pasted on the surface of a concrete structure, and the metal plates are overlaid according to the width of the cracks to be detected. A sensor disposed in a wrap is disclosed. When the crack of concrete becomes larger than the overlap width of the metal plate, the electric circuit for detection passing through the metal plate is cut, so that a crack that has grown beyond a predetermined width can be detected. However, the sensor notifies when the crack to be monitored has developed to a predetermined width or more, but does not provide a special signal before reaching the width, so it is difficult to grasp the situation on the way.

  In Patent Document 4, a fiber-containing plastic plate is affixed to a concrete surface, and when a crack in the concrete grows and tensile stress acts on the fiber-containing plastic, the fiber-containing plastic is whitened, and the crack can be visually recognized. A sensor is disclosed. This sensor is effective when there is an expansion of a crack of 1 mm or more, but it is difficult to detect a small crack.

  Patent Document 5 discloses a crack detection tape and a crack detection system that can be easily attached to a detection target in a short time and can accurately detect the occurrence of a crack. The tape includes a conductive layer whose energization state changes when a crack occurs in the detection target, a surface insulating layer that covers the surface of the conductive layer and electrically insulates the conductive layer, and the conductive layer A crack detection tape comprising a back surface insulating layer that covers the back surface and electrically insulates the conductive layer, and an adhesive layer that adheres the back surface insulating layer to the object to be detected, and requires a step of energizing. Therefore, it is difficult to use a simple method.

  Patent Document 6 discloses a strain sensor that detects a strain of a member to be detected, and includes a member to be detected and a coating film portion in which a paint is applied to the member to be detected. Cracks occur when subjected to larger strains. Thus, it is described that strain can be detected simply and inexpensively, and the soundness of the member and the degree of damage to the member after an earthquake can be easily confirmed. Since the sensitivity of the sensor is lowered depending on the coating film thickness of the paint, a skilled treatment is required and it is difficult to say that this is a simple method.

Japanese Patent Application Laid-Open No. 2001-066117 JP-A-10-238139 JP 2005-043220 A Japanese Patent No. 5570943 Japanese Patent Laying-Open No. 2005-91167 JP 2007-33050 A

Concrete cracks can be detected and monitored by conventional methods. However, in visual inspections by workers such as daily inspections, in order to observe cracks over time, it is often necessary to go directly to the vicinity of the cracks using an aerial work vehicle or the like, which places a heavy burden on measurement. In addition, in the method of measuring the crack width by installing measurement equipment such as a pie-type displacement meter, a relatively expensive sensor is installed for each crack. Spatial constraints such as securing the power supply. Furthermore, the method of calculating cracks and crack widths by image processing of images acquired with a CCD camera or the like requires analysis and diagnosis by an expert using an expensive measuring instrument, which is a limitation on the spread.
For this reason, there is a high demand for a crack detection sensor and a crack monitoring method with a simple configuration.

Accordingly, the present invention provides (1) a crack detection sensor for detecting cracks in a hardened cement / concrete, comprising a surface protective layer, at least one holding layer enclosing glass spheres, a focus forming layer, a mirror surface A detection sheet including a reflective layer is provided, and the detection sheet is characterized in that the side opposite to the surface protective layer is attached to the surface of the cement / concrete hardened body.
Moreover, this invention is a crack detection sensor of (1) whose (2) glass sphere is 10-150 micrometers in diameter.
Moreover, this invention is a crack detection sensor of (1) or (2) whose (3) specular reflection layer is a layer formed by metal vapor deposition.
Moreover, this invention is a crack detection sensor in any one of (1)-(3) in which the color of the position along the crack of a detection sheet | seat changes when the crack width is 0.1 mm or more.
The present invention is also a crack monitoring method for a cement / concrete cured body using the detection sensor according to any one of (5), (1) to (4), wherein cracks generated on the surface of the cement / concrete cured body are detected. This is a monitoring method in which a detection sheet is pasted with an adhesive so as to straddle, and a change in crack is detected by a change in reflected light of the detection sheet.

  According to the crack detection sensor and crack monitoring method of the present invention, it is possible to detect fluctuations in cracks by attaching a detection sheet to the surface of a hardened cement / concrete body without requiring skill. Play.

FIG. 1 is a diagram showing a crack detection sensor.

  Hereinafter, the present invention will be described in detail.

  FIG. 1 is a diagram showing a crack detection sensor of the present invention. As shown in FIG. 1, the crack detection sensor 1 includes a detection sheet S, and FIG. 1 shows a state in which the detection sheet S is adhered to the surface of the cement / concrete hardened body with an adhesive A.

  The detection sheet S includes a surface protective layer 7, a glass sphere 5, one or more holding layers 6 that hold the glass sphere 5, a focus forming layer 4, and a specular reflection layer 3. In this detection sheet S, the surface protective layer 7 is on the air side, and the side opposite to the surface protective layer 7 is attached to the surface of the cement / concrete hardened body with an adhesive A.

  The holding layer 6 holding the glass spheres is extended by the occurrence of cracking cr of the cement / concrete hardened body C, and the interval between the glass spheres 5 is widened, or the holding layer 6 itself holding the glass spheres 5 is cut. The specular reflection layer 3 or the member to be detected on the back surface appears, discolors along the generated crack cr, and the presence of the crack cr can be easily observed visually. That is, the reflection structure inside the detection sheet S in the part along the crack cr is partially broken and cannot be reflected, and the difference in light reflection from the healthy part in which the reflection structure is not broken along the crack cr. The surface of the partial detection sheet S is emphasized, and the presence of a crack cr can be easily visually observed.

  In the present invention, when the detection sheet is attached to the cement / concrete hardened body C, the adhesive A is applied to the surface of the cement / concrete hardened body C in advance. Although it does not specifically limit as a kind of adhesive agent A, The cyanoacrylate adhesive agent, epoxy adhesive agent, ester adhesive agent, acrylic adhesive agent, silicone adhesive agent etc. which are generally marketed can be used. . Of these, cyanoacrylate adhesives are preferred.

  In the present invention, the detection sheet S can be provided with an adhesive layer. When the detection sheet S provided with an adhesive is attached to the surface of the cement / concrete hardened body C, the above-described adhesive can be used. The type of the adhesive is not particularly limited, and for example, a commercially available acrylate adhesive can be used.

  The surface protective layer 7 of the detection sheet S used in the present invention is preferably a layer having transparency with a total light transmittance of 60% or more, and is a layer for protecting the surface of the detection sheet S. , Alkyd resin, fluororesin, vinyl chloride resin, polyester resin, urethane resin, polycarbonate resin and the like are used alone or in combination. An acrylic resin, a polyester resin, and a vinyl chloride resin are preferable from the viewpoint of weather resistance and processability, and an acrylic resin is particularly preferable in consideration of coating suitability and dispersibility of a coloring agent when coloring. Various additives such as an ultraviolet absorber, a stabilizer, a plasticizer, and a crosslinking agent can be added to the surface protective layer 7 as long as the transparency is not significantly impaired. A transparent protective film or a transparent plate can also be used as the surface protective layer 7.

The holding layer 6 for holding the glass sphere 5 of the detection sheet used in the present invention is usually an acrylic resin, an alkyd resin, a fluororesin, a vinyl chloride resin, a polyester, a urethane resin, a polycarbonate, or the like alone or in combination. Formed using. Acrylic resins, polyesters, and vinyl chloride resins are preferable from the viewpoint of weather resistance and processability, and acrylic resins are particularly preferable in consideration of coating suitability and dispersibility of colorants when coloring. The molecular weight of the resin forming the holding layer 6 is not particularly limited. The thickness of the holding layer 6 is preferably 20 to 40 μm.
The glass sphere 5 preferably has a diameter of 10 to 150 μm, more preferably 70 to 100 μm, and most preferably 80 to 90 μm. Sheets encapsulating glass balls 5 are well known, and using their reflectivity, safety signs such as road signs, construction signs, vehicle license plates, clothing, life-saving equipment, etc. It is widely used for marking of materials, signboards, various authentication stickers, reflectors for visible light, laser light or infrared light reflection type sensors. Both recognize the reflected light that comes back.

  The specular reflection layer 3 of the detection sheet S used in the present invention is formed by metal vapor deposition, and can be formed by vapor deposition of metal such as aluminum, silver, chromium, nickel, magnesium, gold, tin. The thickness of the specular reflection layer 3 is preferably 0.03 μm to 0.30 μm, more preferably 0.05 μm to 0.20 μm, and particularly preferably 0.06 to 0.15 μm, but is not limited thereto.

The focus forming layer 4 of the detection sheet S used in the present invention is a layer for disposing the specular reflection layer 3 at the focus position of the minute glass sphere, and is usually an acrylic resin, an alkyd resin, a fluororesin, or a vinyl chloride resin. , Polyester, urethane resin, polycarbonate, butyral resin, etc. are used alone or in combination, but acrylic resin and butyral resin are preferred from the viewpoint of weather resistance, coating suitability, and thermal stability. Resins are most preferred. Various additives such as a colorant, an ultraviolet absorber, a stabilizer, a plasticizer, and a crosslinking agent can be added to the focus forming layer 4 as long as the transparency is not significantly impaired.
The thickness of the focus forming layer 4 is determined in consideration of the refractive index of the resin so that the incident light beam is focused on the specular reflection layer 3, preferably 10 to 60 μm, more preferably 15 to 50 μm, Although 20-40 micrometers is especially preferable, it is not specifically limited.

  The elongation of the detection sheet S of the present invention is preferably 10 to 60%, and preferably 15 to 50%. If it is less than 10%, there is a possibility that the sheet will be cracked at the time of attachment, or the sheet may be completely broken when cracked cr is generated. If it exceeds 60%, the detection sensitivity when cracking occurs is low. There is a possibility.

  In the crack detection sensor 1 of the present invention, when the detection sheet S is pasted on the surface of the detected member so as to straddle the crack cr that has already occurred, the width of the crack cr is then expanded according to the expansion amount. The reflection structure of the detection sheet S in the portion along the crack cr is broken and cannot be reflected, and the presence of the enlarged portion of the crack cr can be easily visually observed as described above. Further, even when the crack cr is closed, since the reflection structure of the detection sheet S in the portion along the crack cr has already been broken, the history remains, so that the portion where the crack cr is generated can be visually detected.

  By using the detection sheet S, the crack detection sensor 1 of the present invention can be easily visually observed not only from the vicinity of the detected member but also from a remote position. Furthermore, since the reflection structure of the detection sheet S along the crack cr is broken even in the dark, the detection sheet S is illuminated with a commercially available flashlight or a flash is used with a digital camera. By confirming the photographed image, it is possible to easily determine the presence or absence of a crack cr. That is, in daily inspections, a normal worker can easily and accurately monitor the crack cr.

  The crack detection sensor 1 of the present invention has a relatively low manufacturing cost of the detection sheet S, and can be easily adhered to the detected member with the adhesive A, and there is no special facility such as a scaffold or an aerial work vehicle. In addition, since measurement can be performed from a distance using binoculars or the like, measurement can be performed by regular patrol monitoring by an ordinary worker.

The detection method for detecting the expansion of crack cr of the present invention is such that the detection sheet S of the present invention is such that the surface protective layer 7 is on the air layer side, and the opposite side of the surface protective layer 7 is the cement / concrete hardened body C. The holding layer 6 that is attached to the surface and holds the glass sphere 5 extends due to the generation of cracked cr, and the interval between the glass spheres 5 widens, or the holding layer 6 itself of the glass sphere 5 is cut, so that it is on the back surface. When the specular reflection layer 3 appears, the color changes along the generated crack cr, and the presence of the crack cr can be easily observed visually.
That is, the reflective structure on the surface of the detection sheet S along the crack cr is broken and cannot be reflected, and the surface of the detection sheet S along the crack cr is emphasized due to the difference in reflection from the healthy part, The presence of cr can be easily observed visually. In other words, the crack cr exists in a portion that does not reflect, and a portion that does not have the crack cr reflects, so that the crack portion that does not reflect is emphasized.

In addition, the present invention attaches the detection sheet S of the crack detection sensor 1 of the present invention so as to straddle the joint part of the cement / concrete hardened body surface, and the color density of the detection sheet S at a position along the joint part is increased. The expansion of the joint can be detected by the change.
Furthermore, the present invention is applied to the surface between adjacent different cement / concrete hardened bodies C so as to straddle the detection sheet S of the crack detection sensor 1 of the present invention, and by the change in the color intensity of the detection sheet S. The deviation between the cement / concrete hardened body C can be detected.
Furthermore, the present invention can be used as a monitoring method for capturing a change in the cement / concrete hardened body C using the crack detection sensor 1.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited thereto.

"Experiment 1"
The bending strength test of JIS A1106 was conducted using ordinary concrete with a nominal name of 24-12-20N. The tensile edge at the center of the span was provided with a notch having a height of about 5 mm in order to induce bending cracks. The detection sheet was affixed to the side surface of the concrete specimen using a commercially available cyanoacrylate-based adhesive.

The detection sheet used in the experimental example of the present invention was produced by the following procedure.
Using a transparent polyethylene terephthalate film (trade name, Teijin Tetoron Film S-75) with a thickness of 75 μm made by Teijin Limited, on top of that an acrylic resin solution (trade name, RS-1200) made by Enki Ai Thin Film Co., Ltd. To 100 parts by mass, 14 parts by mass of a methylated melamine resin solution (trade name, Nicalac MS-11) manufactured by Sanwa Chemical Co., Ltd., and 4 parts by mass of a cellulose derivative (trade name, CAB) manufactured by Tokushiki Co., Ltd. Dainippon Ink Co., Ltd. UV absorber (trade name, Seesorb 103) in 0.5 parts by mass, leveling agent (trade name, BYK-300) from Big Chemie Japan in 0.04 parts by mass A catalyst (trade name, Becamine P-198) manufactured by Kagaku Kogyo Co., Ltd. is 0.12 parts by mass, and 16.7 parts by mass so that the ratio of MIBK / toluene = 8/2 is used as a solvent In addition, to form a surface protective layer having a thickness of 36μm was coated with a stirred mixture.
On the surface protective layer, 100 parts by mass of an acrylic resin (trade name RS-3000) manufactured by Onuki Ai Thin Film Co., Ltd., and 12 isocyanate crosslinking agent (trade name, Sumidur N-75) manufactured by Sumitomo Bayer Urethane Co., Ltd. On the surface protective layer, 21 parts by mass of toluene as a solvent and 9 parts by mass of MIBK mixed and stirred are applied on the surface protective layer, dried at 80 ° C. for 5 minutes, light incident side having a thickness of 27 μm and a transmittance of 95% A retention layer of was obtained.
A glass sphere (trade name, NB-45S) manufactured by Enki Ai Thin Film Co., Ltd. was attached to the holding layer on the focus forming layer side, and heat-treated at 145 ° C. for 3 minutes and 30 seconds to submerge the glass sphere in the holding layer. . On the holding layer and the glass sphere, 100 parts by mass of an acrylic resin solution (trade name, RS-5000) manufactured by Unki Ai Thin Film Co., Ltd., and a methylated melamine resin solution (trade name, Nicarak MS) manufactured by Sanwa Chemical Co., Ltd. -11) was added to 5.5 parts by mass, 39.3 parts by mass of MIBK / toluene = 4/6 as a solvent, and the mixture was stirred and mixed, and dried to form a focus-forming layer having an average thickness of 23 μm. Formed. From the focus forming layer, aluminum was vacuum-deposited to form a specular reflection layer having an average thickness of 0.1 μm to obtain a detection sheet. The elongation of the detection sheet was 32% as a result of measuring a strip-shaped test piece (width 25 mm × length 150 mm) with a tensile tester under a tensile speed of 300 mm / min.

(Materials used)
Cyanoacrylate-based adhesive: 1 liquid, room temperature curing type, manufactured by Tokyo Sokki Co., Ltd. Product name: CN

Table 1 shows the result of visually observing the detection sheet from the crack width and a position 5 m away from the detected member.
Observation was conducted indoors in the daytime. Moreover, the detection sheet | seat of the Example of this invention is 10-150 micrometers (experiment No. 1-1, detection sensor A), 70-100 micrometers (experiment No. 1-2, detection sensor B), 80 of a glass sphere. ˜90 μm (Experiment No. 1-3, detection sensor C).
The comparative example (Experiment No. 1-4, detection sensor D) is a commercially available crack detection sensor utilizing the whitening phenomenon of the fiber-containing plastic plate, and the comparative example (Experiment No. 1-5, detection sensor E) is usually The reflective sheet which does not enclose the glass spheres, and the comparative example (Experiment No. 1-6, no detection sensor) are cases where no sheet is attached.
The evaluation is made in three stages, “◯” is easily visible, “Δ” is sheet deformation, but it is difficult to judge and skill is required, “X” is not visible.
From Table 1, it can be seen that the product of the present invention can be visually observed easily from a crack of 0.1 mm even from a location 5 m away.

"Experiment 2"
In the same test as in Experimental Example 1, the specimen was visually observed from a position of 20 m in a dark room. In addition, the visibility of a crack was compared similarly to Experimental Example 1 by irradiating light from an observer's position using a commercially available LED light.

Table 2 shows the result of visually observing the detection sheet from the crack width and a position 20 m away from the detected member. From Table 2, even if it is dark, by irradiating a commercially available LED light, the product of the present invention can be easily visually observed even from a place 20 m away from a crack of 0.1 mm.
It should be noted that the same results as in Table 2 were obtained not at the directly facing position but also at an angle of 45 ° C. Effective use for nighttime surveys is expected.

"Experiment 3"
It is the same as Experimental Example 1 except that the diameter of the glass sphere is set to 10 to 150 μm, and the presence or absence of the specular reflection layer and the focus forming layer is changed and visually observed from the positions of 5 m and 10 m. Table 3 shows the experimental results.
When visually observed from a position of 5 m, an opening of 0.1 mm can be confirmed in all cases. On the other hand, although it was difficult to see from the 10 m position, it can be visually confirmed in the same manner as in Experimental Example 2 by using irradiation with a commercially available LED light. Further, by using a pair of binoculars, a telescope, etc., it can be visually recognized from a further distance.

"Experimental example 4"
In the same test as in Experimental Example 2, the type of adhesive was changed, and the specimen was visually observed from a position of 20 m in a dark room. In addition, the visibility of cracks was compared in the same manner as in Experimental Example 1 using a commercially available LED light. Table 4 shows the experimental results.
Although there are differences depending on the type of adhesive, cracks that could not be visually recognized without a comparative product or sheet can be visually recognized from a position 20 m away in the dark by using the product of the present invention.

(Materials used)
Epoxy adhesive: Two-component room temperature curing type epoxy resin, manufactured by Konishi Co., Ltd. Product name: Bond E205
Ester adhesive: Two-component room temperature curable polyester resin manufactured by Tokyo Sokki Co., Ltd. Product name: RP-2

  The detection sensor of the present invention and the detection method using the same can detect a fluctuation with a crack width of 0.1 mm minimum by applying a detection sheet to the cement / concrete hardened body surface without requiring skill. It can be applied widely in the civil engineering / architecture field.

DESCRIPTION OF SYMBOLS 1 Crack detection sensor 3 Specular reflection layer 4 Focus formation layer 5 Glass ball 6 Retaining layer 7 Surface protective layer A Adhesive C Cement and concrete hardened body S Detection sheet cr Crack

Claims (5)

A crack detection sensor for detecting cracks in hardened cement / concrete,
A detection sheet including a surface protective layer, at least one holding layer enclosing glass spheres, a focus forming layer, and a specular reflection layer;
The crack detection sensor, wherein the detection sheet has a side opposite to the surface protective layer attached to the surface of the hardened cement / concrete. The crack detection sensor according to claim 1, wherein the glass sphere has a diameter of 10 to 150 μm. The crack detection sensor according to claim 1, wherein the specular reflection layer is a layer formed by metal vapor deposition. The crack detection sensor according to any one of claims 1 to 3, wherein the color of the position along the crack of the detection sheet changes when the crack width is 0.1 mm or more. A crack monitoring method for a hardened cement / concrete using the crack detection sensor according to any one of claims 1 to 4,
Crack detection characterized in that the detection sheet is pasted with an adhesive so as to straddle the crack generated on the surface of the cement / concrete hardened body, and a change in crack is detected by a change in reflected light of the detection sheet. Method.

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