JP7174479B2 - Concrete Deterioration Detection Method Due to Freezing Damage, Freeze-Thaw Resistance Evaluation Method, and Concrete Specimen - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for detecting deterioration of concrete due to frost damage, a method for evaluating freeze-thaw resistance, and a concrete test specimen.

Frost damage is a typical deterioration of concrete structures in cold regions. Freezing damage is a phenomenon in which cracks and scaling occur on the surface of concrete due to the repeated freezing and thawing of water content in concrete due to the effects of outside air temperature and solar radiation, resulting in deterioration of concrete. Durability is often hindered, and it is regarded as one of the important problems in the maintenance and management of structures.

Neutralization, salt damage, and alkali-aggregate reaction, which are typical deteriorations of concrete, are accompanied by chemical changes due to deterioration, so it is possible to quantitatively grasp the cause and progress of deterioration. On the other hand, deterioration due to frost damage causes volumetric expansion when the water in the concrete freezes, and at that time, if there are no gaps inside the concrete to absorb the volumetric expansion, the expansion pressure will cause the concrete to crack or crack. causes scaling, etc. In other words, since deterioration due to frost damage is physical deterioration due to the expansion of water in concrete, deterioration is often judged based on circumstantial evidence such as surface cracks and scaling.

Conventionally, as a method for evaluating the resistance to frost damage of concrete, in laboratory experiments, the relative dynamic elastic modulus obtained from the change in the primary resonance frequency of the specimen is used as a deterioration index to judge the degree of deterioration due to frost damage. In the evaluation of actual structures, the depth of frost damage and the degree of deterioration are generally evaluated by extracting cores from concrete structures and examining the distribution of ultrasonic wave propagation speed.

In Patent Documents 1 and 2, based on the freezing damage deterioration curve of concrete based on the exposure test at the reference point in the natural environment, the freezing damage deterioration curve at the prediction point reflecting the characteristic value based on the concrete structural data is predicted. Techniques are disclosed.

JP-A-2005-156547 JP 2008-249733 A

However, in the method of evaluating the frost damage resistance of concrete, when evaluating an actual structure, the depth of frost damage and the degree of deterioration are generally determined by sampling the core of the concrete structure and examining the distribution of the ultrasonic wave propagation velocity. An evaluation is made. Since different evaluation methods are used for laboratory experiments and actual structures, it is difficult to compare laboratory experiments and actual structures for evaluation. In addition, the physical significance of the relative dynamic modulus of elasticity indicating frost damage deterioration is not clear, and it is commonly recognized as one of the permissible limits of deterioration. Therefore, there is no method for physically evaluating the degree of deterioration that occurs inside concrete due to frost damage.

Further, in Patent Documents 1 and 2, a technique for predicting a frost damage deterioration curve at a prediction point reflecting characteristic values based on concrete structure data based on a concrete frost damage deterioration curve based on an exposure test, It does not show the state of deterioration of the actual structure itself.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for quickly and accurately detecting the state of deterioration in concrete using an optical fiber sensor.

(1) In order to achieve the above objects, the present invention takes the following measures. That is, the deterioration detection method of the present invention is a deterioration detection method for detecting deterioration of concrete due to frost damage, and includes a step of embedding an optical fiber sensor in the concrete, and a change in characteristics of a light wave propagating in the optical fiber sensor. Based on, at least the step of measuring the strain of the concrete and the step of detecting the characteristics of the measured strain over time, and based on the detected characteristics of the strain over time, the concrete due to frost damage It is characterized by detecting the deterioration of

In this way, the optical fiber sensor is embedded in the concrete, the strain of the concrete is measured based on the characteristic change of the light wave propagating in the optical fiber sensor, and the characteristics of the measured strain change over time are detected and detected. Since deterioration of concrete due to frost damage is detected based on the characteristics of changes in strain over time, it is possible to embed optical fiber sensors in actual structures and measure strain. As a result, it is no longer necessary to take cores of concrete structures in order to examine the distribution of ultrasonic wave propagation velocities, as has been done up to now. In addition, the measurement of the relative dynamic elastic modulus cannot be applied to the actual structure, but in the deterioration detection method according to the present invention, by embedding the optical fiber sensor in the concrete, the measurement can be performed easily and at all times. This makes it possible to detect the state of deterioration in concrete early and accurately.

(2) Further, the deterioration detection method of the present invention is characterized by further including the steps of embedding a thermometer in the concrete and removing strain due to temperature change from the detected strain of the concrete.

In this manner, the thermometer is embedded in the concrete, and strain due to temperature change is removed from the detected strain of the concrete, eliminating the need to measure the strain at a specific temperature in advance, increasing versatility. In addition, since the temperature history of concrete is clarified, it can be easily determined that deterioration due to frost damage has occurred without detailed analysis.

(3) In addition, the evaluation method of the present invention is a method for evaluating the freeze-thaw resistance of concrete, wherein the above-mentioned first A step of measuring the strain of the concrete of No. 1, a step of subjecting the first concrete to a predetermined freeze-thaw cycle by changing the environmental temperature, and characteristics of temporal change of the measured strain due to the freeze-thaw cycle , a step of calculating a residual strain from the characteristics of the time-dependent change in the detected strain, and using the calculated residual strain to evaluate the freeze-thaw resistance of concrete.

In this way, the strain information is acquired from the optical fiber sensor embedded in the concrete, the strain under the specific environmental temperature separately acquired from the acquired strain information is removed, the characteristics of the change over time are detected, and the detected time Since the residual strain is calculated from the characteristics of the change in temperature and the deterioration of the concrete due to frost damage is evaluated based on the calculated residual strain, it is possible to quickly and accurately grasp the deterioration in the concrete. In addition, measuring the relative dynamic modulus of elasticity requires a lot of labor and time to take out and measure the specimen in the test room. Measurement can be performed easily and at all times while the device is still in the machine.

(4) In addition, the evaluation method of the present invention measures strain from a thermometer embedded in a second concrete having a larger air content than the first concrete under the environmental temperature, and measures the strain from the first concrete. removing the strain measured in the second concrete from the strain measured in 1, and calculating the residual strain in the first concrete.

In this way, in addition to the concrete to be measured, the strain due to wet expansion is also measured by increasing the amount of air in concrete with the same composition and excellent frost damage resistance. It is possible to calculate a more accurate residual strain due to frost damage by removing the strain due to

(5) In addition, the evaluation method of the present invention is a method for evaluating the freeze-thaw resistance of concrete, wherein the above-mentioned first any of the steps of: measuring the strain of a piece of concrete; subjecting the first concrete to a predetermined freeze-thaw cycle by changing the environmental temperature; and the freeze-thaw cycle of the measured strain. The method is characterized by detecting a strain hysteresis characteristic represented by temperature and strain magnitude in a freeze-thaw cycle, and evaluating the freeze-thaw resistance of concrete from the detected strain hysteresis characteristic.

In this way, the strain information is acquired from the optical fiber sensor embedded in the concrete, the strain under the separately acquired environmental temperature is removed from the acquired strain information, and the freeze-thaw cycle is , The strain history characteristic (hysteresis loop) represented by the temperature and strain magnitude is detected, and the deterioration of concrete due to frost damage is evaluated based on the detected strain history characteristic. It becomes possible to estimate the degree of deterioration in the concrete. In addition, measuring the relative dynamic modulus of elasticity requires a lot of labor and time to take out and measure the specimen in the test room. Measurement can be performed easily and at all times while the device is still in the machine.

(6) In addition, the evaluation method of the present invention is characterized in that the freeze-thaw resistance of concrete is evaluated using the temporal change in the maximum strain represented by the strain hysteresis characteristic.

In this way, since the freeze-thaw resistance of concrete is evaluated using the temporal change in maximum strain represented by the strain hysteresis, it is possible to accurately and easily estimate the degree of deterioration in concrete. .

(7) In addition, the evaluation method of the present invention evaluates the freeze-thaw resistance of concrete using the temporal change in the amount of strain change from the start point to the end point of the freezing process represented by the strain hysteresis characteristic. Characterized by

In this way, since the freeze-thaw resistance of concrete is evaluated using the temporal change in the amount of strain change from the start to the end of the freezing process, which is represented by the strain hysteresis, the degree of deterioration in concrete can be accurately determined. And it becomes possible to estimate easily.

(8) In addition, the evaluation method of the present invention is characterized in that the freeze-thaw resistance of concrete is evaluated using the temporal change in the amount of change in expansion strain that occurs during the freezing process, which is represented by the strain hysteresis characteristic. .

In this way, since the freeze-thaw resistance of concrete is evaluated using the temporal change in the amount of expansion strain change that occurs during the freezing process, which is represented by the strain hysteresis characteristic, the degree of deterioration in concrete can be accurately and easily determined. It is possible to estimate

(9) Further, the concrete test body of the present invention is a concrete test body applied to the freeze-thaw resistance evaluation method according to any one of (3) to (8), wherein the strain detection of the optical fiber sensor It is characterized in that it consists of a first concrete test piece in which a part is installed in the center and a second concrete test piece in which a thermometer is installed.

In this way, since it is composed of the first concrete test piece in which the strain detection part of the optical fiber sensor is installed in the center and the second concrete test piece in which the thermometer is installed, It becomes possible to grasp deterioration early and accurately. In addition, measuring the relative dynamic elastic modulus requires a lot of labor and time to take out the specimen and measure it in the test room. Measurement can be performed easily and at all times while it is in the case.

According to the present invention, deterioration of concrete due to frost damage can be detected early and accurately by embedding an optical fiber sensor in an actual structure and measuring strain. As a result, it is no longer necessary to take cores of concrete structures in order to examine the distribution of ultrasonic wave propagation velocities, as has been done up to now.

FIG. 4 is a diagram showing a test specimen used for verifying whether an optical fiber sensor detects strain due to deterioration of concrete due to 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. FIG. 10 is a diagram (degraded state) showing the measurement results of the optical fiber sensor and the relative dynamic elastic modulus in Verification Example 2; FIG. 11 is a diagram (degraded state) showing a mass change rate in Verification Example 2; FIG. 10 is a diagram (healthy state) showing the measurement results of the optical fiber sensor and the relative dynamic elastic modulus in Verification Example 2; FIG. 10 is a diagram showing a hysteresis loop in a range where the relative dynamic elastic modulus is 90% or more; FIG. 10 is a diagram showing a hysteresis loop with a relative dynamic elastic modulus in the range of about 80 to 60%; FIG. 4 is a diagram showing a hysteresis loop in a range where the relative dynamic elastic modulus is about 60%; FIG. 4 is a diagram showing a hysteresis loop in the range of relative dynamic elastic modulus of 60% or less; FIG. 7 shows the maximum strain (δ _max ) of the hysteresis loop of FIG. 6; FIG. 8 shows the maximum strain (δ _max ) of the hysteresis loop of FIG. 7; FIG. 9 shows the maximum strain (δ _max ) of the hysteresis loop of FIG. 8; FIG. 10 shows the maximum strain (δ _max ) of the hysteresis loop of FIG. 9; FIG. 7 is a diagram showing a strain change amount (δ) that occurs in the freezing process of the hysteresis loop of FIG. 6; FIG. 8 is a diagram showing a strain change amount (δ) that occurs in the freezing process of the hysteresis loop of FIG. 7; FIG. 9 is a diagram showing a strain change amount (δ) that occurs in the freezing process of the hysteresis loop of FIG. 8; FIG. 10 is a diagram showing a strain change amount (δ) that occurs in the freezing process of the hysteresis loop of FIG. 9; FIG. 7 is a diagram showing an expansion strain change amount (δ′) that occurs in the freezing process of the hysteresis loop of FIG. 6 ; FIG. 8 is a diagram showing an expansion strain change amount (δ′) occurring in the freezing process of the hysteresis loop of FIG. 7; FIG. 9 is a diagram showing the amount of expansion strain change (δ′) that occurs in the freezing process of the hysteresis loop of FIG. 8 ; FIG. 10 is a diagram showing an expansion strain change amount (δ′) occurring in the freezing process of the hysteresis loop of FIG. 9; FIG. 4 is a diagram showing changes over time in maximum strain (δ _max );

The present inventors focused on the fact that deterioration due to freezing damage to concrete structures in cold regions is judged by circumstantial evidence such as cracks and scaling on the concrete surface, and embedded an optical fiber sensor in the concrete. By measuring the strain, it was possible to detect the deterioration of concrete. Embodiments of the present invention will be described below.

First, the mechanism of frost damage will be explained. Frost damage is a deterioration phenomenon caused by expansion of water in concrete when it freezes. Water undergoes a 9% volume expansion when frozen. Concrete also generally shrinks or expands in response to temperature changes. Within a normal temperature range, the coefficient of linear expansion is about 10×10 ^-6 /°C. When the temperature drops, the water in the concrete freezes, creating expansion pressure. The water in the concrete repeatedly freezes and melts, and the concrete that expands due to the expansion pressure of the water when frozen does not shrink when melted and remains as residual strain.

In this embodiment, by embedding an optical fiber sensor in concrete, residual strain caused by frost damage is measured to detect deterioration due to frost damage. Residual strain appears as strain in the fiber optic sensor when subjected to melting action in concrete. Since the strain of the optical fiber sensor includes the strain caused by the temperature effect, the strain obtained by removing the strain caused by the temperature effect from the strain of the optical fiber sensor becomes the residual strain at the time of melting. Thus, by measuring the strain of the optical fiber sensor during the melting period, it is possible to judge the degree of deterioration of the concrete due to frost damage. In addition, since multiple sensors can be installed on a single thin cable, optical fiber sensors can be used to measure multiple locations with a single optical fiber sensor when used on an actual structure. Become.

Moreover, when embedding an optical fiber sensor in concrete as a method of evaluating frost damage, the number of optical fiber sensors to be embedded may be one (one FBG portion) or a plurality of them. At this time, it is preferable that the embedded location of the optical fiber sensor is positioned at least near the center of the concrete. Furthermore, if the optical fiber sensor is embedded in a depth of 1 to 4 cm from the edge or surface of the concrete, or in the middle of the concrete, the progress of deterioration can be grasped in more detail.

[Detection method]
An optical fiber sensor is embedded in concrete and connected to an optical fiber measuring instrument. Fiber optic sensors distort due to temperature changes. Therefore, a thermometer is embedded in the concrete to measure the temperature change inside the concrete. In this embodiment, a thermocouple is used as a thermometer, but it is not limited to a thermocouple as long as the temperature inside the concrete can be measured. The strain of the optical fiber sensor, excluding the influence (strain) due to temperature change, is measured when the concrete is melted. When measuring strain at a specific temperature, since the strain received by the optical fiber sensor at that temperature is constant, it is sufficient to measure the strain at that temperature in advance, and there is no need to correct the strain due to temperature changes. .

[Verification example 1]
FIG. 1 is a diagram showing a test specimen used for verifying whether an optical fiber sensor detects strain due to deterioration of concrete due to frost damage. Materials used in Verification Example 1 are as shown in Table 1. The formulation is as shown in Table 2. Concrete 17 prepared by kneading the materials shown in Table 1 with the formulation shown in Table 2 is poured into two steel molds 15 . It is buried in a hanging state in the center of the When burying the optical fiber sensor 11, the concrete 17 and the FBG portion 13 of the optical fiber sensor 11 are buried so that the concrete 17 adheres to the FBG portion 13 of the optical fiber sensor 11 so that they shrink or expand together. do. Also, the optical fiber sensor 11 may be embedded in the concrete 17 in a tensioned state (a state in which tension is generated). Although the FBG sensor is used as the optical fiber sensor in Verification Example 1, it is not limited to this.

As shown in FIG. 1, the optical fiber sensor 11 is installed in advance in the steel mold 15 so that the FBG portion 13 is positioned at the center of the specimen (columnar), and concrete 17 is poured and molded. In addition, a test body in which a thermometer 21 such as a thermocouple is embedded is similarly produced, and the temperature inside the concrete is measured. The FBG portion 13 of the optical fiber sensor 11 and the measuring portion 23 of the thermometer 21 have a vertical fogging of 100 mm.

After that, it was cured in water for 28 days, and then subjected to a freeze-thaw test in a constant temperature and humidity chamber. The freezing and thawing conditions consisted of one cycle (11 hours), and the central temperature of the concrete (environmental temperature) was changed from 5°C to -20°C to 5°C.

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

This indicates the residual strain that the concrete deteriorated due to freezing and thawing. Compared to the values of the relative dynamic elastic modulus shown in Fig. 2, both values change greatly around 38 cycles. is. It was also confirmed that the strain can be measured even when the relative dynamic modulus of elasticity is below 80%, which is indicated by JIS A 1148 as effective frost damage resistance.

Therefore, by using this test specimen, it is possible to evaluate the resistance of concrete to freeze-thaw action. In addition, it becomes possible to evaluate the freeze-thaw resistance and to develop or select concrete with high freeze-thaw resistance before using the concrete for a structure. In the present invention, freeze-thaw resistance is also referred to as frost damage resistance, and is resistance to a phenomenon (freeze damage) that causes the composition to deteriorate and collapse due to repeated freezing and thawing of the water present inside the cement composition. , refers to tolerance.

[Verification example 2]
Furthermore, using a freeze-thaw tank, we verified the effectiveness of judging the deterioration due to frost damage due to the residual strain of concrete measured by an optical fiber sensor. In Verification Example 2, Test Body A, which has the same materials, composition, and test body shape as in Verification Example 1, and Test Body B, which differs from Verification Example 1 only in the air content (air content: 4.8%), were used. . The freeze-thaw test was conducted in accordance with JIS A 1148 (4 hours per cycle) using a freeze-thaw test apparatus. Note that when a freeze-thaw test apparatus 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 specimen A that has deteriorated in Verification Example 2. As shown in FIG. FIG. 4 is a diagram showing the mass change rate of the specimen A that deteriorated in Verification Example 2. As shown in FIG. FIG. 5 is a diagram showing measurement results of the optical fiber sensor and the relative dynamic elastic modulus of the healthy specimen B in which deterioration has not occurred in Verification Example 2. FIG.

As shown in FIG. 3, as the strain of the optical fiber sensor increases, the value of the relative dynamic elastic modulus of the test sample A increases. In addition, the strain of the optical fiber sensor of test sample A increased from around 20 cycles, but the relative dynamic elastic modulus did not decrease. In other words, the optical fiber sensor can detect even minute deterioration that does not appear in the relative dynamic elastic modulus.

Moreover, as shown in FIG. 4, the mass of the concrete of the specimen A has increased, and it has wet-expanded due to water absorption. That is, the residual strain shown in FIG. 3 is a value including the strain due to wet expansion.

On the other hand, as shown in FIG. 5, the sound test specimen B, in which residual strain due to freezing and thawing is less likely to occur, has no decrease in the relative dynamic elastic modulus, but the strain caused by the optical fiber is slightly increased. Since the strain shown in FIG. 5 is the strain due to wet expansion, by subtracting the strain value of the test piece B shown in FIG. 5 from the strain value of the test piece A shown in FIG. can be canceled. As a result, the accurate residual strain of the specimen A can be calculated.

A healthy test specimen B without deterioration for measuring the wet expansion of concrete can be prepared by increasing the air content from the test specimen A by 0.5 to 4%. If the increase in the amount of air is less than 0.5%, the deterioration of the sound specimen B, which is not deteriorated, cannot be delayed more than the specimen A to be tested, or the deterioration due to freezing and thawing due to freezing damage It may contain residual strain. Moreover, if the increase in the amount of air exceeds 4%, the tendency of wet swelling may deviate from that of the specimen A. In addition, a test body that is exactly the same as the object to be measured may be prepared and cured in water to measure and cancel the strain due to wet expansion, thereby calculating a more accurate residual strain.

[Verification example 3]
In Verification Examples 1 and 2, the relationship between residual strain and progress of frost damage deterioration was verified. Next, the relationship between the behavior of the hysteresis loop (strain hysteresis characteristic) in the freeze-thaw cycle and the progress of frost damage deterioration will be verified. A method for evaluating the freeze-thaw resistance of concrete by evaluating the degree of change in the hysteresis loop of the strain generated in concrete due to freeze-thaw will be described below.

In Verification Example 3, Test Specimen C, which differs from Verification Example 1 only in air content (air content: 3.0%), was used. The freeze-thaw test conformed to the JIS A 1148 method, and was an accelerated test using a freeze-thaw test chamber.

First, using the specimen C, the relationship between the value of the relative dynamic elastic modulus and the expansion and contraction of the strain was verified. 6 to 9 are diagrams showing the relationship between the value of each relative dynamic elastic modulus and the expansion and contraction of strain. FIG. 6 is a diagram showing a hysteresis loop in a range (5 cycles) in which the relative dynamic modulus of elasticity is 90% or more. As shown in FIG. 6, in the hysteresis loop in which the relative dynamic elastic modulus is in the range of 90% or more (5 cycles), contraction strain occurs during freezing and expansion strain occurs during melting. It can be seen that the expansion and contraction of concrete due to temperature change is dominant.

FIG. 7 is a diagram showing a hysteresis loop when the relative dynamic elastic modulus is in the range of about 80 to 60% (529 cycles). As shown in FIG. 7, in the hysteresis loop in which the relative dynamic elastic modulus is in the range of about 80 to 60% (529 cycles), expansion strain occurs during the freezing action. This shows that as the deterioration progresses, in addition to internal damage, the amount of water that can be frozen increases, and the expansion pressure that exceeds the shrinkage due to the temperature change of concrete is generated.

FIG. 8 is a diagram showing a hysteresis loop in a range (550 cycles) where the relative dynamic elastic modulus is about 60%. As shown in FIG. 8, in the hysteresis loop in which the relative dynamic elastic modulus is in the range of about 60% (550 cycles), the expansion pressure further increases and becomes comparable to the shrinkage of concrete due to freezing action.

FIG. 9 is a diagram showing a hysteresis loop in a range (839 cycles) where the relative dynamic modulus of elasticity is 60% or less. As shown in FIG. 9, in the hysteresis loop in which the relative dynamic elastic modulus is in the range of 60% or less (839 cycles), expansion strain occurs during freezing and contraction strain occurs during melting. This is because the expansion and contraction due to the freezeable water in the concrete is dominant, and it can be seen that the initial hysteresis loop as shown in FIG. 6 is reversed.

In this way, in a healthy state (Fig. 6), strain due to temperature change in concrete is dominant, but as concrete deteriorates, strain due to temperature change in water in concrete is dominant. can be determined from the measured strain. That is, as shown in FIG. 7, it can be determined that deterioration has started when expansion strain occurs during the freezing action.

Next, a description will be given of a method of evaluating deterioration based on the time-dependent change in the hysteresis loop value of each cycle described above.

(i) Evaluation Method Using Maximum Strain (δ _max ) FIGS. 10A to 10D are diagrams showing the maximum strain (δ _max ) of the hysteresis loop in each freeze-thaw cycle of FIGS. 6 to 9. FIG. As shown in FIGS. 10A to 10D, deterioration is evaluated from the change in maximum strain (δ _max ) of each hysteresis loop over time.

(ii) Evaluation method using strain change amount (δ) FIGS. 11A to 11D are diagrams showing the strain change amount (δ) that occurs during the freezing process of the hysteresis loop in each freeze-thaw cycle of FIGS. 6 to 9. . As shown in FIGS. 11A to 11D, deterioration is evaluated from changes over time in the amount of strain change (δ) that occurs during the freezing process of each hysteresis loop. The strain change amount (δ) is calculated by Equation (1).
Strain change (δ) during freezing process
= (strain at the start of the freezing process - strain at the end of the freezing process) (1)

(iii) Evaluation method using expansion strain change amount (δ′) FIGS. FIG. 4 is a diagram showing; As shown in FIGS. 12A to 12D, deterioration is evaluated from the change over time in the amount of change in expansion strain (δ′) that occurs during the freezing process of each hysteresis loop. The expansion strain change amount is calculated by Equation (2).
Amount of change in expansion strain (δ) that occurs during the freezing process
= (maximum strain in the freezing process - strain at the start of the freezing process) (2)

FIG. 13 is a diagram showing temporal changes in the maximum strain (δ _max ) of (i). Similar to the residual strain, the maximum strain (δ _max ) increased as the relative dynamic elastic modulus decreased, indicating that deterioration due to freezing and thawing can be evaluated. (ii) strain change amount (δ) and (iii) expansion strain change amount (δ′) can also be similarly evaluated.

As described above, according to this embodiment, it is possible to embed an optical fiber sensor in an actual structure and measure strain. As a result, it is no longer necessary to take cores of concrete structures in order to examine the distribution of ultrasonic wave propagation velocities, as has been done up to now. In addition, by embedding the optical fiber sensor in concrete, strain during the freezing and thawing process in concrete can be measured. Since there is a correlation with the elastic modulus, it becomes possible to evaluate frost damage deterioration, and to detect the state of deterioration in concrete early and accurately. In addition, the behavior of the hysteresis loop during freeze-thaw cycles makes it possible to estimate the degree of degradation.

11 Optical fiber sensor 13 FBG section 15 Steel formwork
17 Concrete 21 Thermometer 23 Measuring part

Claims (8)

A deterioration detection method for detecting deterioration of concrete due to frost damage,
embedding an optical fiber sensor in the concrete;
embedding a thermometer in the concrete;
measuring strain in the concrete based on changes in properties of light waves propagating in the optical fiber sensor;
detecting a characteristic of the measured strain over time;
and removing strain due to temperature change from the detected strain of concrete,
A deterioration detection method, comprising detecting deterioration of concrete due to frost damage based on the characteristics of the detected strain change over time. A method for evaluating the freeze-thaw resistance of concrete,
measuring the strain of the first concrete based on changes in the characteristics of light waves propagating in an optical fiber sensor embedded in the first concrete;
subjecting the first concrete to a predetermined freeze-thaw cycle by varying the environmental temperature;
detecting the characteristics of the measured strain over time due to the freeze-thaw cycle;
at least a step of calculating a residual strain from the characteristics of the detected strain change over time,
A freeze-thaw resistance evaluation method, wherein the freeze-thaw resistance of concrete is evaluated using the calculated residual strain. measuring strain from a thermometer embedded in a second concrete having a higher air content than the first concrete at the ambient temperature;
3. The method of claim 2 , further comprising: removing the strain measured in the second concrete from the strain measured in the first concrete, and calculating the residual strain in the first concrete. Freeze-thaw resistance evaluation method. A method for evaluating the freeze-thaw resistance of concrete,
measuring the strain of the first concrete based on changes in the characteristics of light waves propagating in an optical fiber sensor embedded in the first concrete;
subjecting the first concrete to a predetermined freeze-thaw cycle by varying the environmental temperature;
detecting a strain hysteresis characteristic expressed by temperature and strain magnitude in any given freeze-thaw cycle of the measured strain among the freeze-thaw cycles;
A freeze-thaw resistance evaluation method, wherein the freeze-thaw resistance of concrete is evaluated from the detected strain hysteresis characteristics. 5. A method for evaluating freeze-thaw resistance according to claim 4 , wherein the freeze-thaw resistance of concrete is evaluated using the temporal change in the maximum strain represented by the strain hysteresis. 5. The freeze-thaw resistance according to claim 4 , wherein the freeze-thaw resistance of concrete is evaluated using the change over time in the amount of strain change from the start point to the end point of the freezing process represented by the strain hysteresis characteristic. evaluation method. 5. A method for evaluating freeze-thaw resistance according to claim 4 , wherein the freeze-thaw resistance of concrete is evaluated using the time-dependent change in the amount of change in expansion strain occurring during the freezing process represented by the strain hysteresis characteristic. . A concrete specimen applied to the freeze-thaw resistance evaluation method according to any one of claims 2 to 7 ,
A first concrete test piece in which the strain detection part of the optical fiber sensor is installed at the center;
and a second concrete test body in which a thermometer is installed.

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