Fixing jig and method for early detection of concrete deterioration using the same

Abstract

To allow early detection of deterioration of concrete by using a core sample of a concrete structure to be measured without going to the site.SOLUTION: A fixture 1 fixes a concrete test piece to be read to a fixed position on a reading surface of a line sensor scanner, and comprises: a plate-like member 11 that has one or more through holes 13; hollow columnar members 15 that each surround one opening end of the through hole 13 and have a hollow part for accommodating the concrete test piece; and fixing parts 17 that each are provided on the hollow columnar member 15 and fix the accommodated concrete test piece. The inner diameter of the through hole 13 is smaller than the inner diameter of the hollow columnar member 15.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a fixing jig that is attached to a line sensor type digital image acquisition scanner (full field strain measurement device), and a method for early detection of concrete deterioration using the same.

[0002] Concrete deterioration factors include alkali-silica reaction (ASR), delayed ettringite formation (DEF), freeze-thaw, drying shrinkage, and corrosion of reinforcing bars. Among these, alkali-silica reaction is a phenomenon in which silica in reactive aggregate reacts with alkali metal ions in concrete under high pH conditions to produce alkaline silica gel, which absorbs and expands, causing cracks in the concrete. Delayed ettringite formation is a phenomenon in which ettringite may concentrate and form several years after steam curing concrete, causing the concrete to expand and collapse. Freeze-thaw is a phenomenon in which moisture in concrete repeatedly freezes and thaws over many years, causing the volume expansion of moisture (ice) to cause cracks in the concrete. Drying shrinkage is a phenomenon in which moisture in concrete evaporates as the concrete dries, causing the concrete to shrink and crack. Furthermore, corrosion of reinforcing bars is a phenomenon in which the passive film on reinforcing bars is damaged by neutralization or salt damage, causing the reinforcing bars to rust and expand, resulting in cracks in the concrete.

[0003] In these concrete deterioration phenomena, cracks often become apparent and by the time they are discovered, the deterioration has already progressed too far. Therefore, in order to effectively prevent concrete deterioration, it is necessary to detect the causes of deterioration early, before cracks become apparent, and to take measures according to each cause.

[0004] Meanwhile, several methods for detecting deterioration of concrete have been proposed in the past. One method for inspecting cracks in a concrete structure is to sequentially laminate an undercoat layer, a peeling prevention sheet layer, and a topcoat layer on a base constituting a concrete structure, and then sequentially laminate a high-elasticity coating layer containing a fluorescent dye that develops color when exposed to excitation light and a low-elasticity coating layer containing a shielding agent that blocks the transmission of excitation light on the topcoat layer, and then irradiate the structure with excitation light after the concrete structure is put into service to detect cracks that have developed in the base due to deterioration over time.

[0005] As a concrete deterioration factor detection method, there is a method in which a concrete surface is imaged to obtain a visible light image, and at the same time, the concrete surface is irradiated with infrared light, and the reflected light from the concrete surface is input to a spectroscope via a scanning device, and the spectroscope detects absorbance based on the light intensity of a specific wavelength for detecting a specific deterioration factor, and the absorbance is converted into a concentration of the deterioration factor, the concentration is quantized, and based on the quantized value, a deterioration factor image is obtained by expressing the gradation or color corresponding to the concrete surface to be measured, and the deterioration factor image and the visible light image are synthesized. As a concrete deterioration detection method, there is a method in which digital images are acquired over time, and a strain distribution is obtained using a digital image correlation method. However, all of these methods are complicated and require time and effort.

[0006] In this situation, Patent Document 1 discloses a method for early detection of concrete deterioration, which uses a line sensor type digital image acquisition scanner (full-field strain measurement device) to acquire strain distribution by digital image correlation of the concrete surface before and after treatment including drying, heating, and cooling, enabling early and rapid detection of the causes of deterioration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-153784 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method for early detection of concrete deterioration described in Patent Document 1, it is necessary to directly fix a line sensor type digital image acquisition scanner (full-field strain measurement device) (hereinafter also simply referred to as a line sensor scanner) to the concrete structure to be measured and acquire images. Therefore, in order to investigate the cause of concrete deterioration, it is necessary to go to the site. In addition, since the line sensor scanner has a size of 265 x 570 mm, an area for installing the line sensor scanner is required on the measurement surface of the concrete structure, and the measurement area must be flat in order to be measured.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a fixed jig that enables early detection of concrete deterioration using a core sample (hereinafter also referred to as a concrete specimen) of the concrete structure to be measured, without having to go to the site, and a method for early detection of concrete deterioration using the same. [Means for solving the problem]

[0010] (1) In order to achieve the above object, the present invention provides the following means: That is, the fixing jig of the present invention is a fixing jig for fixing a concrete specimen to be read at a fixed position on a reading surface of a line sensor scanner, and is characterized in that it comprises a plate-like member having one or more through holes, a hollow columnar member surrounding one open end of the through hole and having a hollow portion for accommodating the concrete specimen, and a fixing portion provided in the hollow columnar member for fixing the accommodated concrete specimen, and the inner diameter of the through hole is smaller than the inner diameter of the hollow columnar member.

[0011] This eliminates the need to install a line sensor scanner directly on the concrete structure to be measured. Early detection of deterioration of the concrete structure becomes possible using core samples obtained from the concrete structure. Furthermore, while a flat, wide installation space was previously required for installing the line sensor scanner on the concrete structure to be measured, by using the fixing jig of the present invention, it becomes possible to measure the concrete structure to be measured no matter where it is located as long as a core sample can be obtained.

[0012] (2) In the fixing jig of the present invention, the plate-like member and the hollow columnar member are made of a heat-resistant material, which makes it possible to maintain the fixed state of the concrete specimen without deformation even if a treatment such as heating is performed while the concrete specimen is fixed to the fixing jig in a strain manifestation treatment (described in detail later).

[0013] (3) In addition, in the fixing jig of the present invention, the fixing part is characterized by comprising two or more locking holes formed on the side surface of the hollow columnar member and fixing members that fit into the locking holes. This makes it possible to fix the concrete specimen so that it does not move during imaging, making it possible to obtain accurate images.

[0014] (4) In addition, in the fixing jig of the present invention, the fixing portion is formed by two or more locking claws formed on the inner surface of the hollow columnar member. This makes it possible to fix the concrete specimen so that it does not move during imaging, making it possible to obtain accurate images. In addition, it becomes possible to fix the concrete specimen easily.

[0015] (5) In addition, in the fixing jig of the present invention, the fixing part is characterized by being composed of a pair of gripping parts and a biasing means for biasing the jig to a closed state so as to grip the stored concrete specimen. This makes it possible to fix the concrete specimen so that it does not move during imaging, making it possible to obtain accurate images. In addition, it becomes possible to fix the concrete specimen easily.

[0016] (6) In addition, in the fixing jig of the present invention, the fixing portion is an elastic body formed on the inner surface of the hollow columnar member. This makes it possible to fix the concrete specimen so that it does not move during imaging, making it possible to obtain accurate images. In addition, it becomes possible to fix the concrete specimen easily and without damaging it.

[0017] (7) The fixing jig of the present invention is also characterized in that a support portion is provided at the other open end of the through hole. This prevents the concrete specimen from coming into contact with the image reading surface of the line sensor scanner. Also, by maintaining a constant distance between the concrete specimen and the line sensor scanner, it becomes possible to adjust the focus on the concrete specimen when capturing an image.

[0018] (8) The method for early detection of deterioration of concrete of the present invention is a method for early detection of deterioration of concrete using a fixing jig according to any one of (1) to (7), and is characterized by including at least the steps of: placing a concrete specimen on the fixing jig and fixing it; placing the fixing jig on which the concrete specimen is placed on a line sensor scanner, and acquiring a digital image of an image acquisition target surface of the concrete specimen; removing the fixing jig on which the concrete specimen is placed from the line sensor scanner, and performing one of drying, heating, and cooling processes on the concrete specimen while the concrete specimen is placed on the fixing jig; placing the concrete specimen that has been subjected to one of the drying, heating, and cooling processes on the line sensor scanner while the concrete specimen is placed on the fixing jig, and acquiring a digital image of the acquisition target surface of the concrete specimen; calculating strain using a digital image correlation method based on the two acquired digital images, and obtaining a distribution of changes in maximum principal strain based on the strain; and estimating a factor of deterioration of concrete based on the acquired distribution of positive and negative strains.

[0019] This eliminates the need to install a line sensor scanner directly on the concrete structure to be measured. Early detection of deterioration of the concrete structure is possible using core samples obtained from the concrete structure. Conventionally, a flat and wide installation space was required for installing a line sensor scanner on the concrete structure to be measured, but the method for early detection of concrete deterioration of the present invention makes it possible to measure the concrete structure to be measured in any location as long as a core sample can be obtained. Furthermore, since the strain elicitation treatment, which is any one of drying, heating, and cooling treatments, and the image acquisition treatment of the measurement surface of the concrete specimen performed before and after the treatment, are all performed with the concrete specimen fixed to the fixing jig, it is possible to install the line sensor scanner at the same reading position and in the same direction and capture images, and it is possible to more clearly acquire changes before and after the strain elicitation treatment. Effect of the Invention

[0020] According to the present invention, it is possible to easily and accurately detect deterioration of concrete at an early stage by using a core sample of the concrete structure to be measured, without going to the site. [Brief description of the drawings]

[0021] [Figure 1A] FIG. 2 is a plan view showing a schematic configuration of a fixing jig according to the present embodiment. [Figure 1B] FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A. [Figure 1C] FIG. 1C is an enlarged view of part B in FIG. [Figure 2A] 1 is a schematic diagram showing a state in which a fixing jig according to the present embodiment is installed on a line sensor scanner. [Figure 2B] FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A. [Diagram 3] 13A and 13B are diagrams illustrating modified examples of the fixing portion. [Figure 4] 1A to 1C are diagrams illustrating the steps of a method for early detection of concrete deterioration using a fixing jig according to an embodiment of the present invention. [Diagram 5] FIG. 13 is a diagram showing the strain distribution obtained in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The inventors discovered that by using a fixture capable of fixing a concrete specimen to a line sensor scanner, it is possible to detect deterioration of concrete at an early stage using a core sample of the concrete structure to be measured without going to the site, and thus came to the present invention. An embodiment of the present invention will be described with reference to the drawings.

[0023] [Fixed fixture configuration] FIG. 1A is a plan view showing a schematic configuration of the fixing jig 1 according to this embodiment. FIG. 1B is a view showing a cross section at AA in FIG. 1A. FIG. 1C is an enlarged view of part B in FIG. 1B. The fixing jig 1 is installed on the image reading surface of a line sensor scanner and used to obtain an image of a core sample of a concrete structure. The line sensor scanner used has a planar size of 265×570 mm, but is not limited to this. The planar size may be 265×570 mm or more, or may be less than this. It goes without saying that the size and number of the fixing jig and each of the components constituting it described below can be changed according to the planar size of the line sensor scanner.

[0024] The fixing jig 1 comprises a plate-shaped member 11 having a through hole 13, a hollow columnar member 15 having a hollow portion at one open end of the through hole 13 for accommodating a concrete specimen, a fixing portion 17 for fixing the accommodated concrete specimen, and a support portion 19 at the other open end of the through hole 13.

[0025] The plate-shaped member 11 has a surface that is approximately the same size as the image reading surface of the line sensor scanner. In this embodiment, the plate-shaped member 11 is made of a heat-resistant material and has a size of approximately 242 x 550 mm. For example, aluminum can be used as the heat-resistant material from which the plate-shaped member 11 is made. Furthermore, for example, titanium, magnesium, etc. may be used as a material that can withstand heating, cooling, and drying and can be made lightweight.

[0026] Fig. 2A is a schematic diagram showing a state in which the fixing jig 1 according to this embodiment is installed on the line sensor scanner 3. Fig. 2B is a diagram showing a cross section taken along the line AA in Fig. 2A. The fixing jig 1 may be fixed to the line sensor scanner 3 by members such as bolts and screws, or the shape of the plate-like member 11 of the fixing jig 1 may be formed into a fitting shape so as to match the shape of the line sensor scanner 3, and the fixing jig may be fitted and fixed to the line sensor scanner 3, and is not particularly limited. In addition, an installation frame or a support member for fixing the fixing jig 1 may be provided on the line sensor scanner 3.

[0027] The plate-like member 11 is provided with a total of four through holes, including two through holes of φ100 mm, one through hole of φ75 mm, and one through hole of φ50 mm, and a concrete specimen is placed in each through hole 13. The number of through holes 13 is not limited to four. There may be one through hole, or two or more through holes. The size of each through hole 13 is not limited to the above-mentioned three sizes. The size of the through hole 13 may be changed depending on the size of the concrete specimen to be placed. The shape of the through hole 13 according to this embodiment is approximately circular, but is not limited to circular. For example, it may have a polygonal shape such as a triangle or a rectangle.

[0028] The hollow columnar member 15 is a member for accommodating a concrete specimen, and is provided so as to surround one open end of the through hole 13. The hollow columnar member 15 is made of a heat-resistant material. For example, aluminum can be used as the heat-resistant material for forming the plate-like member 11. Furthermore, for example, titanium, magnesium, etc. may be used as a material that can withstand heating, cooling, and drying and can be made lightweight.

[0029] The size of the inner diameter of the through hole 13 is smaller than the size of the inner diameter of the cross section of the hollow columnar member 15. The hollow columnar member 15 may be integrally molded with the plate-like member 11, or may have a structure in which it is fixed to the plate-like member 11 with bolts, screws, or the like. In this embodiment, the cross section of the hollow columnar member 15 is described as being approximately circular, but is not limited to being circular. For example, it may have a polygonal shape such as a triangle or a rectangle. In addition, the shape of the through hole 13 and the cross section of the hollow columnar member 15 are preferably the same shape, but are not limited to this.

[0030] Moreover, the hollow columnar member 15 is provided with a fixing portion 17 for fixing the concrete specimen accommodated in the hollow columnar member 15 so as not to move. The fixing portion 17 is composed of two or more locking holes 21 formed on the hollow columnar side surface of the hollow columnar member 15 and a fixing member 23 that fits into the locking holes 21. After the concrete specimen is accommodated in the hollow columnar member 15, the concrete specimen is fixed by fitting the fixing member 23 into the locking hole 21 from the outer side surface of the hollow columnar member 15. The fixing member 23 may be, for example, a bolt, but is not limited to this. Any member that can fix the concrete specimen accommodated in the hollow columnar member 15 may be used. In this way, by fixing the concrete specimen with the fixing member 23 or the like, it is possible to obtain an accurate image.

[0031] Although not shown, the fixing portion 17 may be, for example, two or more locking claws formed on the inner surface of the hollow columnar member 15, other than the locking hole 21 and the fixing member 23. By forming the fixing portion 17 with the locking claws, it becomes possible to fix the concrete specimen simply by placing it inside the hollow columnar member 15. The locking claws may be formed from the same material as the hollow columnar member 15.

[0032] Although not shown, the fixing part 17 may be composed of a biasing means for biasing the pair of gripping parts to a closed state so as to grip the contained concrete specimen, and a pair of gripping parts. When the concrete specimen is contained in the hollow columnar member, the pair of gripping parts is opened by the biasing means, and after the concrete specimen is contained, the pair of gripping parts is closed, thereby making it possible to fix the concrete specimen. The pair of gripping parts may be formed of a material having the same heat resistance as the hollow columnar member 15.

[0033] FIG. 3 is a diagram showing a modified example of the fixing part 17. FIG. 3(a) is a plan view of a modified example of the fixing part 17, and FIG. 3(b) is a cross-sectional view taken along the line AA in FIG. 3(a). For example, as shown in FIGS. 3(a) and (b), the fixing part 17 may be an elastic body formed on the inner surface of the hollow columnar member 15 so as to have an inner diameter smaller than that of the concrete specimen. In this way, by forming the fixing part 17 on the inner surface of the hollow columnar member 15 and making it an elastic body, it becomes possible to fix the concrete specimen by simply placing the concrete specimen in the hollow columnar member 15. Since it is sufficient for the elastic body to fix the concrete specimen, it is not necessary to provide the elastic body on the entire inner surface of the hollow columnar member 15, and it may be provided on a part of the inner surface of the hollow columnar member 15. In addition, the elastic body may be formed of a material such as a heat-resistant resin. Furthermore, silicone rubber or the like may be used as a material that can withstand heating, cooling, and drying.

[0034] The support portion 19 is provided at the other open end of the through hole 13, which is the surface side of the plate-like member 11 that contacts the line sensor scanner 3. The inner diameter of the support portion 19 is smaller than the inner diameter of the through hole 13 provided in the plate-like member 11. The shape of the support portion 19 is preferably the same as that of the through hole 13, but is not limited thereto. Any shape may be used as long as the concrete specimen accommodated in the hollow columnar member 15 can be supported so as not to abut against the image reading surface of the line sensor scanner 3. Also, as shown in FIG. 1C, the support portion 19 may be integrally molded with the plate-like member 11. In this way, by providing the support portion 19, it is possible to prevent the concrete specimen from abutting against the image reading surface of the line sensor scanner 3 and damaging the image reading surface of the line sensor scanner 3. Also, by providing the support portion 19, a constant distance can be maintained between the concrete specimen and the line sensor scanner 3, and as a result, it is possible to adjust the focus on the concrete specimen when capturing an image.

[0035] Furthermore, the fixing jig 1 may be provided with a handle 29 on the plate-like member 11. After the concrete specimen has been fixed, when the fixing jig 1 is to be placed on the line sensor scanner 3, the fixing jig 1 can be placed by holding the handle 29.

[0036] Furthermore, the fixing jig 1 may be provided with a light-shielding lid 31. When there is a hollow columnar member 15 that does not house a concrete specimen, the light-shielding lid 31 can be installed on the upper part of the hollow columnar member 15 to block light generated when imaging is performed by the line sensor scanner 3.

[0037] By using the fixing jig 1 configured in this manner, it is possible to perform image analysis of a concrete structure using a concrete specimen, without installing the line sensor scanner 3 directly on the concrete structure itself.

[0038] [Methods for early detection of concrete deterioration] Next, a method for early detection of concrete deterioration using the fixing jig of this embodiment will be described. Fig. 4 is a diagram showing the procedure of the method for early detection of concrete deterioration using the fixing jig of this embodiment. Concrete deterioration is detected using the pattern that appears in the image of the maximum principal strain distribution obtained through the following steps.

[0039] (procedure) (A) As a concrete specimen for measuring concrete deterioration, a core sample is obtained from the concrete structure to be measured, and a concrete specimen 5 is prepared. The obtained core sample is cut and polished so that the aggregate is visible on the measurement surface (surface to be imaged) and it is flat. If the aggregate is not visible even if it is flat, a random pattern treatment is performed. (B) The prepared concrete specimen 5 is placed on the fixing jig 1 and fixed in place (Figure 4(1)). (C) Next, the fixture 1 on which the concrete specimen 5 is placed is placed on the line sensor scanner 3, and a digital image of the target surface of the concrete specimen 5 is acquired (image acquisition process before strain manifestation process) (FIG. 4(2)) before performing a process including drying, heating, or cooling (strain manifestation process). If there is a hollow columnar member 15 that does not contain a concrete specimen 5, a light-shielding cover 31 is placed on the top of the hollow columnar member 15 to block light generated when the line sensor scanner 3 captures an image. (D) The fixing jig 1 with the concrete specimen 5 placed thereon is removed from the line sensor scanner 3, and with the concrete specimen 5 placed on the fixing jig 1, the concrete specimen 5 is subjected to one of the following processes (strain manifestation treatment process) (Figure 4 (3)). (E) After performing a process including any one of drying, heating, and cooling (strain manifestation treatment process), the fixture 1 on which the concrete specimen 5 is placed is placed again on the line sensor scanner 3, and a digital image of the target surface of the concrete specimen 5 is obtained (image acquisition process after strain manifestation treatment) (FIG. 4(4)). Note that, if a heating treatment is performed in the strain manifestation treatment process, a rubber heater 39 may be kept installed on the top of the concrete specimen 5 to prevent a drop in temperature of the concrete specimen 5. (F) Based on the digital images taken before and after treatment, the strain is calculated using a digital image correlation method, and a distribution of changes in maximum principal strain is obtained based on the strain (maximum principal strain distribution acquisition step). (G) Estimate the factors behind concrete deterioration based on the distribution of positive and negative strain.

[0040] Next, the above steps (D) to (F) will be described in detail. (D) Image acquisition process before strain elicitation treatment (F) Image acquisition process after strain elicitation treatment This step is a step of acquiring a digital image of the surface of the concrete specimen 5. Here, the concrete of the concrete specimen 5 is not particularly limited, and examples thereof include ordinary concrete, watertight concrete, hot weather concrete, cold weather concrete, mass concrete, flowable concrete, high flow concrete, high strength concrete, low heat concrete, expansive concrete, prestressed concrete, low shrinkage concrete, fiber reinforced concrete, lightweight concrete, and polymer concrete.

[0041] In order to obtain a good digital image, it is preferable to polish the target surface of the concrete. Moreover, the digital image of the target surface is obtained before and after the concrete is subjected to any one of drying, heating, and cooling processes. Moreover, the image is preferably obtained after the concrete hardens and at least before the cracks occur, since the accumulated strain is released when cracks occur. Here, if moisture is attached to the image acquisition surface of the concrete when the image of the concrete is acquired, the color contrast may be reduced and color unevenness may occur, and the correlation of the images acquired before and after the process may decrease. In order to avoid this decrease in correlation, before the image is acquired, the moisture on the imaged surface of the concrete is absorbed by a cloth or the like to remove it, or the image is left to air dry until the moisture disappears from the imaged surface. Note that this process is an optional process that is performed when moisture is attached to the image acquisition surface.

[0042] (E) Distortion manifestation treatment process This step is a step of performing a treatment including drying, heating, and cooling on the target surface of the concrete specimen 5. By performing drying over a long period of time without acquiring images over time, a change in length due to drying shrinkage is caused, and the change can be made clear by the strain distribution. The concrete surface can be dried by blowing air with an electric fan or compressed air, or by applying hot air using a jet heater, burner, or the like. The surface may also be heated and dried with a halogen heater or sunlight. The drying temperature is not particularly limited, but considering the drying speed, the concrete surface temperature is preferably 30°C or higher, more preferably 40°C or higher. The drying temperature is preferably 80°C or lower, more preferably 60°C or lower, so as not to cause deterioration of the concrete. The lower limit of the drying time depends on the drying method, but in the case of a method using hot air or heating, it is preferably 10 minutes, more preferably 1 hour, and even more preferably 3 hours, so that the strain distribution can be made clearer. Moreover, the upper limit of the drying time is preferably one week, more preferably three days, and even more preferably one day, in order to ensure the rapidity of the detection method and to prevent deterioration of the concrete.

[0043] Other drying methods include immersing the concrete in an organic solvent such as alcohol or acetone, or spraying it with water to remove (absorb) the moisture in the concrete. The dehydration time is preferably at least 30 minutes. After immersion in the organic solvent, condensation may form, so it is recommended to quickly remove the organic solvent by wiping it off, or leave it to stand under dry conditions.

[0044] Before drying, the concrete surface should be exposed to water by immersion, spraying, or covering with a wet cloth to allow it to absorb enough water, and then dried to obtain a clearer strain distribution. The water absorption time should be at least 30 minutes or more.

[0045] By heating without acquiring images over time for a long time, a change in length due to temperature strain is brought about, and the strain distribution can be made clearer. The concrete surface in the present invention can be heated by applying hot air using a jet heater, burner, etc., which also dries the concrete, or by heating with a halogen heater or sunlight. The concrete surface can also be heated by covering it with a sheet heater such as a rubber heater or hot water. The heating temperature is not particularly limited, but the concrete surface temperature is preferably 20°C or higher, more preferably 40°C or higher than the original temperature so that the strain distribution can be made clearer. The drying temperature is preferably 80°C or lower, more preferably 60°C or lower, so that the concrete surface does not deteriorate. The heating time is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more so that the concrete surface is sufficiently heated. The drying time is preferably within 1 day, more preferably within 6 hours, and even more preferably within 3 hours in order to ensure the rapidity of the detection method and to prevent deterioration of the concrete.

[0046] By cooling without acquiring images over time over a long period of time, a change in length due to temperature strain is brought about, and the strain distribution can be made clearer. The cooling of the concrete surface in the present invention can be achieved by applying cold air using a cold air generator or spraying a cooling spray. The concrete surface can also be cooled by covering it with a cold insulation material or cold water. In order to improve the cooling efficiency and eliminate the variation in cooling, it is more preferable to install an electric heating plate such as a metal on the concrete surface and then cover it with a cold insulation material. The cooling temperature is not particularly limited, but is preferably 20°C or more, more preferably 40°C or more lower than the original concrete surface temperature so that the strain distribution can be made clearer. The cooling temperature is preferably 10°C or more, more preferably 0°C or more, so that the concrete surface does not deteriorate. The cooling time is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 1 hour or more so that the concrete surface is sufficiently cooled. In order to ensure the rapidity of the detection method and to prevent deterioration of the concrete, the cooling time is preferably within one day, more preferably within six hours, and even more preferably within three hours. It is also possible to heat the concrete using the above-mentioned heating method and then expose it to the air to cool it down to the surrounding environmental temperature.

[0047] (G) Maximum principal strain distribution acquisition process This step is a step of calculating strain based on the acquired digital images using a digital image correlation method, and obtaining a distribution of maximum principal strain based on the strain. The acquired digital images are digital images of the concrete specimen 5 before and after treatment, and the maximum principal strain after deformation is calculated using the digital image correlation method. The digital image correlation method is a method of calculating the amount of movement on the concrete based on the distribution of brightness values ​​of digital images acquired before and after treatment, and converting it into maximum principal strain.

[0048] Specifically, the strain is calculated through the following calculation process. (i) In the pre-treatment digital image, the distribution of brightness values ​​within a subset centered on an arbitrary position is determined. (ii) A subset of the pre-treatment digital image having a luminance value distribution that is most highly correlated with the luminance value distribution of the post-treatment digital image is searched for, its center point is taken as the position after the displacement of the point of interest, the amount of displacement from the point of interest to the center point is calculated, and the amount of displacement is converted into the maximum principal strain. The correlation between the subsets before and after the treatment is expressed using the correlation coefficient R in the following formula (1).

[0049]

number

[0050] However, in reality, the subset may not be rectangular because the digital image after treatment itself is deformed compared to the subset before treatment, which is set to a rectangle. In this case, to correct this, we assume that the displacement gradient is constant within the subset, and calculate the coordinates (x, y) before and after treatment and (x * ,y * ) is expressed by the following formula (2).

number

[0051] In the formula (2), u and v are the displacement components at the center of the subset image, and Δx and Δy are the distances from the center of the subset to the point (x, y). The above calculations can be performed using commercially available image analysis software (e.g., Digital: Correlated Solutions).

[0052] Next, the criteria for detecting the causes of concrete deterioration from the strain distribution image acquired above will be described below. (a) In the strain distribution image, the area with a tortoiseshell pattern is detected as an alkali silica reaction (ASR). The lines of the pattern show a larger positive (expansion) strain, and the matrix (area other than the pattern) also shows a positive (expansion) strain overall. (b) In the strain distribution image, if a uniform pattern appears overall, it is detected as delayed ettringite formation (DEF). Also, the part where the aggregate is located on the surface layer shows a low strain value, but the other paste or mortar parts show a positive (expansion) strain overall. (c) If a spotted pattern appears in the strain distribution image, it is detected as freezing and thawing. The spotted areas indicate large positive (expansion) strain. Areas other than the spots have positive (expansion) or negative (contraction) strain depending on the concrete mix conditions and installation conditions, so they cannot be used to detect deterioration. (d) In the strain distribution image, if a linear pattern appears in an area where there is no reinforcing bar, or if a linear pattern appears diagonally to the columns, beams, or other members of the structure, it is detected as drying shrinkage. Note that areas in a structure where there is no reinforcing bar can be confirmed in advance using existing methods such as drawings or radio radar. Furthermore, diagonal patterns to members such as columns or beams do not limit the angle to each member. Also, the lines in the pattern indicate positive (expansion) strain, while the substrate generally indicates negative (shrinkage) strain. (e) If a linear pattern appears directly above the rebar (the part of the rebar that is covered), it is detected as corrosion of the rebar. The position of the rebar can be confirmed in advance using existing methods such as drawings of the structure and radio radar. The lines in the pattern indicate positive (expansion) strain, while the strain in the other parts will be positive (expansion) or negative (contraction) depending on the concrete mix conditions and installation conditions.

[0053] In this way, by overlaying the strain distribution on the original image, the positions of the coarse aggregate and mortar and the areas where strain is concentrated can be grasped, and the causes of deterioration can be estimated. Furthermore, when detecting the causes of various types of deterioration, taking into consideration the form of strain distribution and the focal points that serve as criteria for judgment, as shown in Table 1, deterioration phenomena can be detected more efficiently, and the overall causes of deterioration can be estimated. Furthermore, by having the system learn (including deep learning) the characteristics of strain distribution for each type of deterioration, as well as data on the number of years in service and the environment in which it is used, it becomes possible to use AI to estimate the causes of deterioration.

[0054] [Table 1]

[0055] As described above, the method for early detection of concrete deterioration can detect various causes of concrete deterioration at an early stage, allowing measures to be taken against deterioration at an early stage, thereby contributing to the maintenance and extension of the lifespan of concrete.

[0056] [Example] The fixing jig of this embodiment was used to perform early detection of deterioration of a concrete specimen in the following procedure. (1) Preparation of concrete specimens A φ100mm core sample was taken from the concrete structure to be measured. The ends of the core sample were cut off to prepare a concrete specimen with a shape of φ100mm and thickness of 20mm. (2) Installation on the fixture The prepared concrete specimen was placed on a fixture, and the fixture on which the concrete specimen was placed was then placed on a line sensor scanner. (3) Acquire images before treatment A digital image of the target surface of the concrete specimen was obtained (image acquisition process before strain elicitation procedure). (4) Distortion manifestation treatment The fixture was removed from the line sensor scanner, and the concrete specimen was left in place on the fixture and the measurement surface of the concrete specimen was heated. In this embodiment, the rubber heater 39 was used to continue the heating treatment for 10 minutes from the point when the heated surface reached 60°C (strain manifestation treatment step). (5) Post-treatment image acquisition After the strain elicitation procedure, the rubber heater 39 was removed from the fixing jig, and the fixing jig with the concrete specimen installed was placed back on the line sensor scanner, and a digital image of the target surface of the concrete specimen was obtained (image acquisition process after strain elicitation procedure). (6) Estimation of strain distribution and deterioration factors The images before and after the strain elicitation treatment were compared, and the strain distribution was obtained by the image correlation method. From the characteristics of the obtained strain distribution, the cause of deterioration was estimated. Figure 5 shows the strain distribution obtained in this example. In this example, as shown in Figure 5, the strain distribution indicated a tortoiseshell-shaped expansion, so it was estimated to be an alkali-aggregate reaction.

[0057] As described above, the present invention makes it possible to detect deterioration of a concrete structure at an early stage by using a core sample obtained from the concrete structure, without the need to install a line sensor scanner directly on the concrete structure to be measured. In addition, a flat and wide installation space was required for the line sensor scanner on the concrete structure to be measured, but by using the fixing jig of the present invention, it becomes possible to measure the concrete structure to be measured no matter where the concrete structure to be measured is located as long as a core sample can be obtained. Furthermore, since the strain elicitation treatment, which is any one of drying, heating, and cooling treatments, and the image acquisition treatment of the measurement surface of the concrete specimen performed before and after the treatment are all performed with the concrete specimen fixed to the fixing jig, it becomes possible to install the line sensor scanner at the same reading position and in the same direction and capture the image, and it becomes possible to more accurately acquire the change before and after the strain elicitation treatment. [Explanation of symbols]

[0058] 1 Fixture 3 Line Sensor Scanner 5. Concrete specimen 11 Plate-shaped member 13 Through hole 15 Hollow columnar member 17 Fixed part 19 Support part 21 Locking hole 23 Fixing member 29 Handle 31 Light-shielding cover 39 Rubber Heater

Claims

1. A fixture that fixes a concrete specimen to be read at a fixed position on a reading surface of a line sensor scanner, A plate-like member having one or more through holes; A hollow columnar member surrounding one open end of the through hole and having a hollow portion for accommodating the concrete specimen; A fixing portion is provided in the hollow columnar member and fixes the contained concrete specimen, A fixing jig, wherein an inner diameter of the through hole is smaller than an inner diameter of the hollow columnar member.

2. 2. The fixture according to claim 1, wherein the plate-like member and the hollow columnar member are made of a heat-resistant material.

3. 3. The fixing jig according to claim 1, wherein the fixing portion is composed of two or more locking holes formed in a side surface of the hollow columnar member and a fixing member that fits into the locking holes.

4. 3. The fixture according to claim 1, wherein the fixing portion is formed of two or more locking claws formed on the inner surface of the hollow columnar member.

5. 3. The fixture according to claim 1, wherein the fixing portion is composed of a pair of gripping portions and a biasing means for biasing the fixing portion to a closed state so as to grip the contained concrete specimen.

6. 3. The fixture according to claim 1, wherein the fixing portion is an elastic body formed on an inner surface of the hollow columnar member.

7. 7. The fixture according to claim 1, further comprising a support portion on the other surface side of the plate-like member of the through hole.

8. A method for early detection of deterioration of concrete using the fixing jig according to any one of claims 1 to 7, placing and fixing the concrete specimen in a fixture; A step of placing the fixture on which the concrete specimen is placed on a line sensor scanner and acquiring a digital image of an image acquisition target surface of the concrete specimen; A step of removing the fixture on which the concrete specimen is placed from the line sensor scanner, and performing any one of drying, heating, and cooling of the concrete specimen while the concrete specimen is placed on the fixture; A step of placing the concrete specimen that has been subjected to any one of the drying, heating, and cooling processes on a line sensor scanner while the concrete specimen is placed on a fixing jig, and acquiring a digital image of the target surface of the concrete specimen; Calculating strain based on the two acquired digital images using a digital image correlation method, and obtaining a distribution of changes in maximum principal strain based on the strain; A method for early detection of concrete deterioration comprising at least a step of estimating a cause of concrete deterioration based on the acquired distribution of positive and negative strain.

Images