JP7079055B2 - Installation method of optical fiber sensor to detect deterioration of concrete due to frost damage and deterioration detection method of concrete structure - Google Patents

Description

The present invention relates to an installation method of an optical fiber sensor for detecting deterioration of concrete due to frost damage and a method for detecting deterioration of a concrete structure.

A typical deterioration of concrete structures in cold regions is frost damage. Freezing damage is a phenomenon in which the water content in concrete is affected by the outside air temperature and sunlight, causing cracks and scaling from the concrete surface due to the freeze-thaw action that repeats freezing and thawing, resulting in deterioration of the concrete. It often interferes with durability and is regarded as one of the important problems in the maintenance of concrete structures.

Since neutralization, salt damage, and alkali-aggregate reaction, which are typical deterioration of concrete, are accompanied by chemical changes due to deterioration, it is possible to quantitatively grasp the cause and degree of deterioration. On the other hand, deterioration due to frost damage causes volume expansion when the water in the concrete freezes, and at that time, if there is no gap inside the concrete to absorb the volume expansion, the expansion pressure causes cracks in the concrete. Causes scaling etc. That is, since deterioration due to frost damage is physical deterioration due to expansion of water in concrete, deterioration is often judged as circumstantial evidence such as surface cracking and scaling.

Conventionally, as a method for evaluating the frost damage resistance of concrete, in laboratory experiments, the degree of deterioration due to frost damage of concrete is diagnosed using the relative dynamic elastic modulus obtained from the change in the primary resonance frequency of the test piece as a deterioration index. In general, the evaluation of a concrete structure is carried out by collecting the core of the concrete structure and examining the distribution of the ultrasonic propagation velocity to evaluate the frost damage deterioration depth and the degree of deterioration.

On the other hand, core removal is a destructive test and damages the structure, so studies are being conducted to evaluate frost damage deterioration in a non-destructive test. A method of evaluating the degree of deterioration from the concrete surface by the ultrasonic method has been reported, but a method of evaluating the concrete surface and the inside of the concrete of the actual structure has not been established.

In Patent Document 1 and Patent Document 2, the frost damage deterioration curve at the prediction point reflecting the characteristic value based on the concrete structure data is predicted based on the frost damage deterioration curve of concrete based on the exposure test at the reference point in the natural environment. The technology is disclosed.

Japanese Unexamined Patent Publication No. 2005-156547 Japanese Unexamined Patent Publication No. 2008-249733

In concrete structures, deterioration due to frost damage gradually progresses from the surface, and it is important to understand the deterioration depth. However, in the method for evaluating the frost damage resistance of concrete, when evaluating a concrete structure, generally, the core of the concrete structure is sampled and the distribution of the ultrasonic propagation velocity is examined to determine the depth of frost damage deterioration and the degree of deterioration. Evaluation is done. As described above, since different evaluation methods are used between the laboratory experiment and the actual structure, it is difficult to compare the laboratory experiment and the actual structure for evaluation. In addition, since the frequency of freezing and thawing in the concrete structure differs between the shade and the sun, the degree of deterioration of the concrete also differs. In such a case, it is preferable to grasp the deterioration depth and the degree of deterioration of the concrete structure at a plurality of places, but it is difficult to remove the core at the plurality of places of the concrete structure.

Further, Patent Document 1 and Patent Document 2 are techniques for predicting a frost damage deterioration curve at a prediction point reflecting a characteristic value based on concrete structure data, based on a frost damage deterioration curve of concrete based on an exposure test. It does not show the deterioration of the concrete structure itself.

In addition, although a method of detecting strain using an optical fiber sensor has been proposed, it is possible to detect the deterioration status of a concrete structure due to frost damage with high accuracy and efficiency by embedding the optical fiber sensor in a concrete structure. Such a method of installing an optical fiber sensor and a method of detecting deterioration of a concrete structure have not been established.

The present invention has been made in view of such circumstances, and provides a method for installing an optical fiber sensor and a method for detecting deterioration of a concrete structure in an early and accurate manner. The purpose.

(1) In order to achieve the above object, the present invention has taken the following measures. That is, the installation method of the present invention is an installation method of an optical fiber sensor that detects deterioration of concrete due to frost damage, and is a characteristic of changes in light waves propagating before or during concrete placement. A step of installing a first optical fiber sensor that detects strain based on the above, a step of installing a temperature sensor in the vicinity of the strain detection unit of the first optical fiber sensor, and the concrete. It is characterized by including, at least, a step of burying a first optical fiber sensor and a temperature sensor installed in a structure with concrete.

In this way, a first optical fiber sensor that detects strain based on the characteristics of changes in propagating light waves is installed inside the concrete structure before or during concrete placement. A temperature sensor is installed near the strain detection unit of the first optical fiber sensor, and the first optical fiber sensor and the temperature sensor installed in the concrete structure are embedded in concrete, so that the measurement is performed by the optical fiber sensor. From the strain, it is possible to detect the deterioration status inside the structure due to frost damage and accurately grasp the range that needs repair. Further, since the temperature sensor is installed near the strain detection unit, it is possible to calculate the strain of concrete in consideration of the strain due to the temperature change. In addition, since the temperature history of concrete is clarified, it can be easily determined that deterioration due to frost damage has occurred without performing detailed analysis.

(2) Further, in the installation method of the present invention, the first optical fiber sensor is embedded in parallel with the surface of the concrete structure, and the temperature sensor is the strain of the first optical fiber sensor. It is characterized in that it is buried at substantially the same depth as the detection unit.

In this way, the first optical fiber sensor is embedded parallel to the surface of the concrete structure, and the temperature sensor is embedded at substantially the same depth as the strain detection unit of the first optical fiber sensor. Therefore, it is possible to monitor the strain over a wide range of the structure while considering the change in strain due to the temperature change. As a result, even if there are places in the same structure where the deterioration status is different, the deteriorated location and the deterioration status can be specified, and the range requiring repair can be accurately grasped.

(3) Further, in the installation method of the present invention, the first optical fiber sensor is embedded perpendicular to the surface of the concrete structure, and the temperature sensor is the strain of the first optical fiber sensor. It is characterized in that it is buried at substantially the same depth as the detection unit.

In this way, the first optical fiber sensor is embedded perpendicular to the surface of the concrete structure, and the temperature sensor is embedded at substantially the same depth as the strain detection portion of the first optical fiber sensor. Therefore, it is possible to grasp the deterioration depth of the concrete structure and accurately grasp the range requiring repair while considering the change in strain due to the temperature change.

(4) Further, in the installation method of the present invention, the first optical fiber sensor is embedded so as to be inclined in the depth direction from the surface of the concrete structure, and the temperature sensor is embedded in the first optical fiber. It is characterized in that it is embedded at substantially the same depth as the strain detection unit of the fiber sensor.

As described above, the first optical fiber sensor is embedded so as to be inclined in the depth direction from the surface of the concrete structure, and the temperature sensor is substantially the same as the strain detection unit of the first optical fiber sensor. Since it is buried at a depth, it is possible to shorten the interval between the buried depths of the strain detection unit while ensuring adhesion to the concrete, and it is possible to monitor the inside of the concrete structure with higher accuracy.

(5) Further, in the installation method of the present invention, the first optical fiber sensor is embedded spirally from the surface of the concrete structure in the depth direction, and the temperature sensor is the first light. It is characterized in that it is embedded at substantially the same depth as the strain detection unit of the fiber sensor.

In this way, the first optical fiber sensor is embedded spirally from the surface of the concrete structure in the depth direction, and the temperature sensor is substantially the same as the strain detection unit of the first optical fiber sensor. Since it is buried at a depth, it is possible to shorten the interval between the buried depths of the strain detection unit while ensuring adhesion to the concrete, and it is possible to monitor the inside of the concrete structure with higher accuracy.

(6) Further, in the installation method of the present invention, the temperature sensor has a second optical fiber sensor that detects the temperature based on the characteristics of the change of the propagating light wave, and the outer periphery of the second optical fiber sensor. It is composed of a covering portion to be covered, and one or more of the temperature sensors are embedded in the concrete of the concrete structure along the first optical fiber sensor.

As described above, the temperature sensor is composed of a second optical fiber sensor that detects the temperature based on the characteristics of the change of the propagating light wave, and a covering portion that covers the outer periphery of the second optical fiber sensor. Since one or more temperature sensors are embedded along the first optical fiber sensor inside the concrete of the structure to be measured, the strain with respect to the temperature at the time of measurement is grasped in advance in the concrete structure to be measured. It is possible to measure the strain due to more accurate temperature change in real time. As a result, it is possible to calculate the residual strain more accurately, and it is possible to grasp the deterioration state.

(7) Further, the deterioration detection method of the present invention is a deterioration detection method for detecting deterioration of concrete due to frost damage, and is a first optical fiber sensor before or during concrete placement. A step of installing a temperature sensor in the concrete structure, a step of installing a temperature sensor in the vicinity of the strain detection unit of the first optical fiber sensor, and a first optical fiber sensor and temperature installed in the concrete structure. The step of burying the sensor in concrete, the step of measuring the strain of the concrete based on the characteristic change of the light wave propagating in the first optical fiber sensor, and the characteristic of the time-dependent change of the measured strain are detected. A deterioration detection method comprising at least a step of detecting deterioration of concrete due to frost damage based on the characteristics of the detected change in strain with time.

In this way, a first optical fiber sensor that detects strain based on the characteristics of changes in propagating light waves is installed inside the concrete structure before or during the placement of concrete. A temperature sensor is installed in the vicinity of the strain detection unit of the first optical fiber sensor, the first optical fiber sensor and the temperature sensor installed in the concrete structure are embedded in concrete, and the inside of the first optical fiber sensor. The strain of concrete is measured based on the characteristic change of the light wave propagating in the Since it is detected, it is possible to embed an optical fiber sensor in an actual structure and measure the strain. As a result, it is no longer necessary to sample the core of the concrete structure in order to investigate the distribution of ultrasonic propagation velocities as has been done so far. Further, the measurement of the relative dynamic elastic modulus cannot be applied to an actual structure, but in the deterioration detection method according to the present invention, the optical fiber sensor can be easily and constantly measured by embedding it in concrete. It is possible to detect the state of deterioration in concrete early and accurately. In addition, since the temperature history of concrete is clarified, it can be easily determined that deterioration due to frost damage has occurred without performing detailed analysis.

(8) Further, the deterioration detection method of the present invention is further characterized by further including a step of removing the strain due to a temperature change measured by using the temperature sensor from the detected strain of concrete.

In this way, since the strain due to the temperature change measured by using the temperature sensor is removed from the detected strain of the concrete, it is not necessary to measure the strain at a specific temperature in advance, and the versatility is increased.

According to the present invention, it is possible to accurately and efficiently detect the deterioration state of a concrete structure due to frost damage. As a result, it is possible to grasp the deteriorated part and the deteriorated state of the concrete structure and accurately identify the range requiring repair.

It is a figure which shows the test piece used for verifying whether the optical fiber sensor detects strain by deterioration of concrete by frost damage. It is a figure which shows the strain measurement result of the optical fiber sensor in each cycle, and the value of the relative dynamic elastic modulus in each cycle. It is a figure (deterioration state) which shows the measurement result of the optical fiber sensor and the relative dynamic elastic modulus in the verification example 2. It is a figure (deterioration state) which shows the mass change rate in the verification example 2. It is a figure (healthy state) which shows the measurement result of the optical fiber sensor and the relative dynamic elastic modulus in the verification example 2. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 1. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 1. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 1. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 2. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 2. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 3. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 3. It is a figure which shows the outline of the installation example of the optical fiber sensor in Example 4.

The present inventors have focused on a situation in which deterioration due to frost damage to a concrete structure in a cold region is judged by deterioration based on situational evidence such as cracking and scaling of the concrete surface, and an optical fiber sensor is applied to the concrete structure. We have found a method for installing an optical fiber sensor that is buried and detects the deterioration status of a concrete structure due to frost damage with high accuracy and efficiency, and have arrived at the present invention. Hereinafter, embodiments of the present invention will be described.

First, the mechanism of frost damage will be described. Freezing damage is a deterioration phenomenon caused by expansion of water in concrete when it freezes. Water causes a volume expansion of 9% when frozen. In addition, concrete generally shrinks or expands in response to changes in temperature. Within the normal temperature range, the coefficient of linear expansion is about 10 × 10 ^-6 / ° C. When the temperature drops, the water in the concrete freezes and an expansion pressure is generated. Moisture in the concrete repeats freezing and thawing, and the concrete expanded by the expansion pressure of water during freezing does not shrink during thawing and remains as residual strain. This residual strain causes cracks and scaling from the concrete surface, deteriorating the concrete.

The deterioration detection method according to the present embodiment calculates the residual strain caused by frost damage by embedding an optical fiber sensor in a concrete structure, and detects deterioration due to frost damage. The residual strain appears as the strain of the fiber optic sensor when it is melted in the concrete. Since the strain of the optical fiber sensor includes the strain caused by the influence of temperature, the strain obtained by removing the strain caused by the influence of temperature from the strain of the optical fiber sensor becomes the residual strain at the time of melting.

In this way, by measuring the strain of the optical fiber sensor during the melting period, it is possible to determine the degree of deterioration of the concrete due to frost damage. In addition, since an optical fiber sensor can be installed with a plurality of sensors on one thin cable, when used in a concrete structure, it is necessary to measure a plurality of parts with one extremely thin optical fiber sensor. Can be done. Further, by embedding the optical fiber sensor in the depth direction, the deterioration depth of the concrete structure can be monitored. If it is an optical fiber sensor, extend the cable connected to the optical fiber sensor to a place where measurement is possible even in a place where it is difficult to perform core removal or ultrasonic method work in a concrete structure. Therefore, the measurement can be easily performed.

Further, as a method for evaluating frost damage, when an optical fiber sensor is embedded in a concrete structure, even one optical fiber sensor (hereinafter, also referred to as an FGB unit or a strain detection unit) may be embedded. Multiple pieces may be used. Further, one FBG unit may be provided for one optical fiber sensor, or a plurality of FBG units may be provided. In an actual structure in which deterioration gradually progresses from the surface, the deterioration status can be grasped in more detail by installing optical fiber sensors at intervals as short as possible in the depth direction from the surface layer portion. By embedding the optical fiber sensor at a depth of 1 to 4 cm from the edge or surface of the concrete, or at a depth in the middle of the concrete, it is possible to grasp the deterioration state of the concrete in more detail.

[Detection method]
An optical fiber sensor equipped with an FBG unit is embedded in concrete and connected to an optical fiber measuring instrument. The optical fiber sensor is distorted due to temperature changes. The thermometer may use a thermocouple, and is not limited to the thermocouple as long as it can measure the temperature inside the concrete. In the strain of the optical fiber sensor excluding the influence (strain) due to the temperature change, the value of the strain when the concrete is subjected to the melting action is measured. When the strain measured at a specific temperature is used, it is not necessary to correct the strain due to the temperature change because the strain received by the optical fiber sensor at that temperature is constant.

[Verification example 1]
FIG. 1 is a diagram showing a test piece used for verifying whether an optical fiber sensor detects strain due to deterioration of concrete due to frost damage. The materials used in Verification Example 1 are as shown in Table 1. The composition of the materials used in Verification Example 1 is as shown in Table 2. Concrete 17 obtained by kneading the materials shown in Table 1 with the formulations shown in Table 2 is poured into two steel formwork, one of which is an optical fiber sensor 11 and the other of which is a thermometer 21. It is buried in the state of hanging in the center of 15. After the optical fiber sensor 11 is embedded, the concrete 17 and the FBG portion 13 of the optical fiber sensor 11 need to be integrally contracted or expanded. Therefore, when the optical fiber sensor 11 is embedded, the concrete 17 is optical. It is embedded so as to adhere to the FBG portion 13 of the fiber sensor 11. Further, the optical fiber sensor 11 may be embedded in the concrete 17 in a state where tension is applied (a state in which tension is generated). Further, in the verification example 1, the FBG sensor is used as the optical fiber sensor, but the present invention is not limited to this.

As shown in FIG. 1, the optical fiber sensor 11 is installed in advance on the steel formwork 15 so that the FBG portion 13 is located at the center of the test piece (cylindrical), and concrete is poured and molded. Further, a test body in which a thermometer 21 such as a thermocouple is embedded is also generated in the same manner, and the temperature inside the concrete 17 is measured. The FBG unit 13 and the thermometer 21 of the optical fiber sensor 11 have a cover in the vertical direction of 100 mm in the measuring unit 23.

Then, underwater curing was carried out for 28 days, and a freeze-thaw test was carried out in a constant temperature and humidity chamber. The conditions for freezing and thawing were one cycle (11 hours), and the core temperature (environmental temperature) of the concrete was changed from 5 ° C. to −20 ° C. to 5 ° C.

FIG. 2 is a diagram showing the strain measurement results of the optical fiber sensor in each cycle and the values of the relative dynamic elastic modulus in each cycle. The strain of the optical fiber sensor shown in FIG. 2 is a value obtained by subtracting the strain generated by the change in the environmental temperature, and shows the maximum value at the time of melting after removing the influence of the change in the environmental temperature. The strain of the fiber optic sensor increases as the cycle progresses.

This indicates the residual strain in which the concrete deteriorated due to freezing and thawing. Compared with the value of the relative dynamic elastic modulus shown in Fig. 2, both values change significantly around 38 cycles, so it is possible to measure the residual strain of concrete with an optical fiber sensor and judge deterioration due to frost damage. Is. It was also confirmed that the strain can be measured even in the range of less than 80% of the relative elastic modulus, which is shown to be effective in frost damage resistance by JIS A 1148.

Therefore, using this test piece, it is possible to evaluate the resistance of concrete to the freeze-thaw action. In addition, before using concrete for a structure, it is possible to evaluate freeze-thaw resistance and develop or select concrete having high freeze-thaw resistance. In the present invention, freeze-thaw resistance is also referred to as freeze-thaw resistance, and resistance to a phenomenon (freezing damage) in which the water present inside the cement composition repeatedly freezes and thaw, which causes the composition to deteriorate and collapse. Gender and tolerance.

[Verification example 2]
Furthermore, using a freeze-thaw tank, the effectiveness of determining deterioration due to frost damage due to residual strain of concrete measured by an optical fiber sensor was verified. In Verification Example 2, Test Body A, which has the same materials, formulations, and test body shape as in Verification Example 1, and Test Body B, which differs only in the amount of air from Verification Example 1 (air amount: 4.8%), were used. .. The freeze-thaw test was carried out in accordance with JIS A 1148 (1 cycle, 4 hours) using a freeze-thaw test device. When the freeze-thaw test device is used, the temperature can be known without installing the thermometer 21.

FIG. 3 is a diagram showing the measurement results of the optical fiber sensor and the relative dynamic elastic modulus of the deteriorated test piece A in the verification example 2. FIG. 4 is a diagram showing the mass change rate of the test body A in which deterioration has occurred in Verification Example 2. FIG. 5 is a diagram showing the measurement results of the optical fiber sensor and the relative dynamic elastic modulus of the sound test piece B in the verification example 2 in which deterioration has not occurred.

As shown in FIG. 3, it is considered that the test piece A can measure the residual strain due to freezing and thawing because the value of the relative dynamic elastic modulus increases as the strain of the optical fiber sensor increases. Further, the strain of the optical fiber sensor of the test piece A has increased from around 20 cycles, whereas the relative dynamic elastic modulus has not decreased. That is, it is possible to detect even minute deterioration that does not appear in the relative dynamic elastic modulus by the optical fiber sensor.

Further, as shown in FIG. 4, the concrete of the test piece A has an increased mass and is wet and expanded due to water absorption. That is, the residual strain shown in FIG. 3 includes the strain due to wet expansion.

On the other hand, as shown in FIG. 5, in the sound test piece B in which residual strain due to freezing and thawing is unlikely to occur, the relative dynamic elastic modulus is not decreased, but the strain due to the optical fiber is slightly increased. Since the strain shown in FIG. 5 is the strain due to wet expansion, the strain due to wet expansion of concrete is obtained by subtracting the strain value of test piece B shown in FIG. 5 from the strain value of test piece A shown in FIG. Can be canceled. As a result, the accurate residual strain of the test piece A can be calculated.

A healthy test piece B without deterioration for measuring the wet expansion of concrete can be produced by increasing the amount of air by 0.5 to 4% as compared with the test piece A to be tested. If the amount of increase in the amount of air is less than 0.5%, the deterioration of the healthy test piece B without deterioration cannot be delayed from that of the test piece A to be tested, or due to freezing and thawing due to frost damage. It may contain residual strain. Further, if the increase in the amount of air exceeds 4%, the tendency of wet expansion may deviate from the test piece A. In addition, a more accurate residual strain may be calculated by preparing a test piece that is exactly the same as the measurement target and curing it in water to measure and cancel the strain due to wet expansion.

[Installation method]
Next, the installation method will be described. First, concrete is poured up to the position where the optical fiber sensor (first optical fiber sensor, second optical fiber sensor) is installed. After that, an optical fiber sensor is installed, and concrete is further placed. The optical fiber sensor may be installed inside the concrete structure before the concrete is placed, or may be installed inside the concrete structure during the concrete placement.

The first optical fiber sensor 101 includes one or more FBG units 105, and is an optical fiber sensor that measures strain in a concrete structure. When burying the first optical fiber sensor 101, the concrete 107 is buried so as to adhere to the FBG portion 105 of the first optical fiber sensor 101. Further, the FBG portion 105 is installed so as to be located at the measurement point in the concrete structure. Further, since it is necessary that the FBG portion 105 of the optical fiber sensor 101 and the optical fiber sensor 101 are integrally contracted or expanded after the optical fiber sensor 101 is embedded, in order to sufficiently secure the adhesion between the optical fiber sensor 101 and the concrete 107. , The FBG portion 105 is preferably arranged at a distance of 50 mm or more on the left and right. Further, it is preferable that the depth at which the FBG portion 105 is embedded is arranged at a depth of 20 mm or more, which is the maximum diameter of the aggregate used for the concrete 107.

The second optical fiber sensor 102 is an optical fiber sensor that measures strain due to a temperature change in a concrete structure, and includes one FBG unit 105. Since the second optical fiber sensor 102 is an optical fiber sensor that measures strain due to a temperature change in the concrete structure, it is separated from the concrete 107 by a protective tube 109 or the like and buried without restraint. Further, the depth at which the second optical fiber sensor 102 is embedded is in the vicinity of the first optical fiber sensor 101, and is the same depth. The second optical fiber sensor is for measuring the strain caused by the temperature change, and it is sufficient if the temperature in the concrete structure can be measured and the strain caused by the temperature change can be measured from the measured temperature. Therefore, the thermometer may use a thermocouple and is not limited to the optical fiber sensor. When using a thermocouple, grasp the strain of the optical fiber sensor with respect to temperature. The value of the strain when the concrete is melted is measured from the strain of the optical fiber sensor excluding the influence (strain) due to the temperature change. When measuring the strain at a specific temperature, it is not necessary to correct the strain due to the temperature change because the strain received by the optical fiber sensor at that temperature is constant.

Next, an example of installing an optical fiber sensor in a concrete structure will be described.
[Example 1]
6A to 6C are diagrams showing an outline of an installation example of the optical fiber sensor in the first embodiment. The optical fiber sensor (first optical fiber sensor) 101 shown in FIG. 6A is embedded parallel to the frozen surface of the concrete structure. The optical fiber sensor (second optical fiber sensor) 102 shown in FIG. 6B is an optical fiber sensor that measures strain due to a temperature change in the concrete structure, and is parallel to the frozen surface of the concrete structure. Buried. Further, when the temperature inside the concrete differs greatly depending on each measurement point in FIG. 6A, as shown in FIG. 6C, the second optical fiber sensor 102 is embedded in the vicinity of each FBG portion of the first optical fiber sensor. However, it is preferable to measure the strain due to the temperature change at each measurement point.

By embedding the optical fiber sensor in the concrete structure in this way, it is possible to simultaneously perform a wide range of monitoring with one thin cable. For example, by embedding an optical fiber sensor in a place where the antifreeze agent is sprayed and a place where the antifreeze agent is not sprayed on a deck or the like, it is possible to judge the effect such as the presence or absence of the effect of the antifreeze agent. .. In addition, even if the deterioration status is different due to the influence of outside air temperature and sunlight on the same concrete structure, the deterioration points can be identified and repaired by measuring the strain at multiple points on the same concrete structure. Can accurately grasp the required range.

[Example 2]
7A and 7B are diagrams showing an outline of an installation example of an optical fiber sensor in the second embodiment. The optical fiber sensor (first optical fiber sensor) 101 shown in FIG. 7A is embedded perpendicular to the frozen surface of the concrete structure. The optical fiber sensor (second optical fiber sensor) 102 shown in FIG. 7B is an optical fiber sensor that measures strain due to a temperature change in a concrete structure, and is embedded perpendicular to the frozen surface of the concrete structure. .. When repairing concrete structures due to frost damage deterioration, it is important to understand the deterioration depth. Therefore, when evaluating the degree of deterioration of a concrete structure due to frost damage, it is preferable to install an optical fiber sensor as shown in FIGS. 7A and 7B.

In this way, by installing an optical fiber sensor in the depth direction of the concrete structure and monitoring the strain, it is possible to determine the deterioration depth and accurately grasp the range requiring repair. When the temperature inside the concrete changes greatly depending on the depth, the second optical fiber sensor 102 is embedded in the vicinity of each FBG portion of the first optical fiber sensor as in the first embodiment, and the second optical fiber sensor 102 is embedded at each measurement point. It is preferable to measure the strain due to temperature change.

[Example 3]
8 and 9 are diagrams showing an outline of an installation example of the optical fiber sensor in the third embodiment. In a concrete structure, deterioration due to frost damage progresses from the surface, so it is preferable to be able to monitor the deterioration depth in detail. As shown in FIG. 8, the optical fiber sensors 101 and 102 may be embedded by inclining the surface of the concrete structure. Further, as shown in FIG. 9, the optical fiber sensors 101 and 102 may be embedded in a spiral shape in the depth direction of the concrete structure. By embedding the optical fiber sensor in this way, it is possible to shorten the interval of the embedding depth of the FGB portion while ensuring the adhesion to the concrete. In this way, by shortening the interval between the FGB units 105, more detailed monitoring can be performed.

[Example 4]
FIG. 10 is a diagram showing an outline of an installation example of the optical fiber sensor in the fourth embodiment. As shown in FIG. 10, by embedding an optical fiber sensor in the deck overhanging portion 121 and the abutment end portion 123 and extending the cable 111 to a place where measurement can be performed, the deterioration status of the concrete structure can be easily grasped. can do.

By combining the installation examples described above, a plurality of first optical fiber sensors can be embedded in the same concrete structure, and as a result, the deterioration state in the concrete structure can be detected more accurately. For example, by embedding an optical fiber sensor in a place where the antifreeze agent is sprayed and a place where the antifreeze agent is not sprayed on a deck or the like, it is possible to judge the effect such as the presence or absence of the effect of the antifreeze agent. .. In addition, even if the deterioration status is different due to the influence of outside air temperature and sunlight on the same concrete structure, the deterioration points can be identified and repaired by measuring the strain at multiple points on the same concrete structure. Can accurately grasp the required range.

As described above, by embedding an optical fiber sensor in a concrete structure and using an installation method of the optical fiber sensor that enables accurate and efficient detection of deterioration of the concrete structure due to frost damage. , It is possible to grasp the deteriorated part and deterioration status of the concrete structure and accurately identify the range that needs repair.

11 Optical fiber sensor 13 FBG part 15 Steel mold 17 Concrete 21 Thermometer 23 Measuring part 101 First optical fiber sensor 102 Second optical fiber sensor 105 FBG part 107 Concrete 109 Protective tube 111 Cable 121 Floor slab overhanging part 123 Hashidai end

Claims (4)

It is an installation method of an optical fiber sensor that detects deterioration of concrete due to frost damage.
Before or during concrete placement, a first optical fiber sensor that detects strain based on the characteristics of changes in propagating light waves is installed inside the concrete structure on the frozen surface of the concrete structure. The process of installing in parallel or perpendicular to the concrete structure, tilting it in the depth direction from the frozen surface of the concrete structure, or spirally installing it in the depth direction from the frozen surface of the concrete structure .
The process of installing the temperature sensor at the same depth as the strain detection unit of the first optical fiber sensor, and
At least including a step of burying a first optical fiber sensor and a temperature sensor installed in the concrete structure with concrete.
By burying the concrete so as to adhere to the FBG portion of the first optical fiber sensor, the concrete and the FBG portion of the first optical fiber sensor are integrally shrunk or expanded , resulting in strain due to frost damage. An installation method characterized by detecting . The temperature sensor includes a second optical fiber sensor that detects the temperature based on the characteristics of the change of the propagating light wave.
It is composed of a covering portion that covers the outer periphery of the second optical fiber sensor, and is composed of a covering portion.
The installation method according to claim 1, wherein one or more temperature sensors are embedded in the concrete of the concrete structure along the first optical fiber sensor. It is a deterioration detection method that detects the deterioration of concrete due to frost damage.
Before or during concrete placement, a first optical fiber sensor that detects strain based on the characteristics of changes in propagating light waves is installed inside the concrete structure on the frozen surface of the concrete structure. The process of installing in parallel or perpendicular to the concrete structure, tilting it in the depth direction from the frozen surface of the concrete structure, or spirally installing it in the depth direction from the frozen surface of the concrete structure .
The process of installing the temperature sensor at the same depth as the strain detection unit of the first optical fiber sensor, and
The process of burying the first optical fiber sensor and temperature sensor installed in the concrete structure with concrete, and
A step of measuring the strain of the concrete based on the characteristic change of the light wave propagating in the first optical fiber sensor, and
At least including the step of detecting the characteristics of the measured change of strain with time.
By embedding the concrete so as to adhere to the FBG portion of the first optical fiber sensor, the concrete and the FBG portion of the first optical fiber sensor are integrally shrunk or expanded.
A deterioration detection method characterized by detecting deterioration of concrete due to frost damage based on the characteristics of the detected change over time of strain. The deterioration detection method according to claim 3 , further comprising a step of removing the strain due to a temperature change measured by using the temperature sensor from the detected strain of concrete.

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