JP2018040671A - Method of estimating cavity volume in concrete structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of estimating cavity volume in a concrete structure capable of accurately estimating the volume of a cavity under a condition of large air leakage from the cavity in the concrete structure.SOLUTION: The method of estimating cavity volume in a concrete structure is a method for estimating the volume of a cavity X in a concrete structure (101) in a state of air leakage communicating with outside air, includes the steps of: setting the cavity X and a vacuum vessel 3 of a known volume to communicate with each other via an openable/closable valve 9; obtaining plural pieces of measurement data by measuring the pressure in the vacuum vessel 3 and the pressure of the air which flows through the cavity X for a predetermined period of time before and after opening the openable/closable valve 9; selecting a piece of measurement data which is used for approximation by using a determination coefficient Rfrom the plural pieces of measurement data of the pressure of a mixture gas which is measured after the openable/closable valve 9 is opened; determining a pressure Pof the mixture gas based on a function approximated from the selected measurement data; and calculating the volume of the cavity X by substituting the pressure Pof the mixture gas in a formula (8) which is derived from a state equation of an ideal gas.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for estimating a void amount in a concrete structure. More specifically, the present invention relates to a method for estimating a void amount in a PC grout unfilled portion existing in a sheath pipe of a PC structure that is a concrete structure. The present invention relates to a method for estimating a cavity amount in a filling portion.

  Post-tension type PC structures in which prestress is applied to concrete with PC steel or other tendon material, PC grout is filled in the sheath tube for the purpose of protecting the PC steel from corrosion and integrating it with the structure. . However, it is known that some old structures are not fully filled with PC grout because of the material performance and construction techniques at the time of construction. There is a concern that the PC steel material may be corroded or broken at such insufficiently filled portions of the PC grout, and there is a concern that the load resistance performance of the PC structure may be reduced due to the corrosion. In order to recover the function of such a PC structure, it is considered effective to reinject the PC grout into the insufficiently filled portion. PC structures are prestressed concrete by placing high-strength steel materials (PC tendons) with tension on concrete structures such as bridges (PC girders, PC floor slabs, segments) and building beams. By giving (compressive force), it refers to a structure that has improved properties of concrete that is weak against tensile force and easily cracked.

  To reinject PC grout into the PC structure, drill the concrete part of the PC structure from the surface of the structure to the sheath tube, and inject the PC grout by connecting a grout hose to the drilled hole. . When reinjecting grout into a PC structure, it is necessary to check how much refilling of the voids in the sheath tube is possible, and whether the grout has leaked from the end or bridge surface. From the aspect of safety management, it is important to know in advance the amount of PC grout to be injected. That is, it is necessary to grasp in advance the amount of cavities in the PC grout unfilled portion existing in the PC structure.

  As a method for estimating the amount of voids in a concrete structure, for example, in Patent Document 1, a concrete structure (PC structure 100) is drilled, and a predetermined amount of gas is supplied from the hole (inspection hole 130) at a predetermined pressure. A method for inspecting a cavity of a concrete structure is described in which the capacity of the cavity 120 communicating with the hole (inspection hole 130) is measured by time variation of the pressure ratio obtained by flowing in or out and dividing the measured pressure by the predetermined pressure ( (See claim 1 of patent document 1, paragraphs [0013] to [0019] of the specification, FIGS. 1 to 4 of the drawings, etc.).

  In Patent Document 2, a concrete structure (PC structure 100) is perforated, and a gas adjusted to a constant pressure and flow rate flows into or out of the cavity 120 communicating with the hole from the hole (inspection hole 130). The cavity of a concrete structure is obtained by measuring the pressure fluctuation together with time information, and obtaining the capacity of the cavity 120 by the time to reach a predetermined reference pressure in the time range before the measured pressure starts to increase and converge to a constant value after the start of inflow An inspection method is described (refer to claims 1 and 4 in claims of Patent Document 2, paragraphs [0020] to [0025] of the specification, and FIGS. 5 to 8 of the drawings).

  However, the method for inspecting a cavity of a concrete structure described in Patent Documents 1 and 2 is based on a calibration curve obtained from a laboratory experiment result, and therefore, when applied to an actual concrete structure with various measurement conditions, there is an error. There is a problem that it may become large and is not practical.

  This is because in the laboratory experiment of the concrete structure cavity inspection method described in Patent Documents 1 and 2, the gas passage (cross-sectional shape) is constant, whereas the actual structure is partially filled with grout. This is because there may be a narrow section, and in this case, since the gas flow velocity during measurement decreases, the time variation of pressure is greatly affected by this, and the estimation error becomes large.

  Also, if the atmospheric pressure changes, the time variation of the measured pressure ratio will also differ, so if this is not taken into account, an estimation error will occur, and an estimation error will be generated due to the effect of the temperature difference between the outside air and the structure. there is a possibility. Moreover, it is difficult to ensure the airtightness of the seal portion 30 in a short time, and there is a problem in workability. For this reason, it is difficult to maintain airtightness, causing an error. In other words, in the cavity inspection method for a concrete structure that relies on the calibration curve described in Patent Documents 1 and 2, the time variation of pressure is greatly affected by the site and the environment of the structure. May become excessive, and there is a problem that stable good accuracy cannot be satisfied.

  In an actual concrete structure, cracks and holes are present in cavities such as sheath tubes, and the airtightness of the cavities is often not ensured, and the discovery is not easy. Therefore, even if the cavities in the concrete structure are in a state of leakage that communicates with the outside air and the leakage is large (a large amount of leakage per hour), the amount of cavities can be estimated accurately. There is a great need for a method for estimating the void volume of concrete structures.

JP 2009-150734 A Japanese Patent No. 5286427

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to provide a site where the leakage from the cavity of the concrete structure is large, such as changes in atmospheric pressure and temperature. It is an object of the present invention to provide a method for estimating the amount of cavities in a concrete structure that can accurately estimate the volume of the cavities regardless of weather conditions and the shape of the cavities.

The method for estimating a void amount of a concrete structure according to claim 1, wherein the void volume of the concrete structure is calculated by estimating the volume of the cavity existing inside the concrete structure in a leaked state where the cavity communicates with the outside air. In the estimation method, the cavity and a decompression container having a known volume that has been decompressed to a predetermined pressure are communicated with each other via an openable / closable open / close valve, and the pressure in the decompression container is communicated with the interior of the cavity. The air pressure is measured for a predetermined time before and after the opening of the on-off valve to obtain a plurality of measurement data, and the determination coefficient R is determined from among the plurality of measurement data of the pressure of the mixed gas measured after the opening of the on-off valve. comprising the step of selecting the measurement data used to approximated using ^2, to determine the pressure P ₃ of the gas mixture based on the function approximated from the selected measurement data, the pressure P ₃ of the gas mixture ideal It is substituted into the following equation derived from the equation of state of the body and calculating the volume of the cavity.

Where P _{1 is the} pressure of the gas in the decompression vessel, V _{1 is} the volume of the gas in the decompression vessel, P _{2 is} the pressure of the gas in the cavity, V _{2 is} the volume of the gas in the cavity, and P _{3 is the} mixed gas. Pressure.

The method for estimating the void amount of a concrete structure according to claim 2 is the method for estimating the void amount of a concrete structure according to claim 1, wherein the determination coefficient R ² is 0.99 or more in the step of selecting the measurement data. The measurement data is selected so that the number of measurement data is 10 or more.

  The method for estimating the void amount of a concrete structure according to claim 3 is the method for estimating the void amount of a concrete structure according to claim 1 or 2, wherein the approximated function is a linear function with time as a variable. It is characterized by.

  According to the first to third aspects of the invention, in a condition where the amount of air leakage per hour is large in the cavity, the concrete is not affected by the on-site weather conditions such as changes in atmospheric pressure or temperature and the cavity shape in the structure. The amount of cavities in the structure can be estimated with high accuracy.

  In particular, according to the invention described in claim 2, since the data of the section affected by the atmospheric pressure can be excluded, it is possible to estimate the cavity amount of the concrete structure with higher accuracy.

  In particular, according to the invention described in claim 3, since the section with a high degree of vacuum is considered to change linearly without being affected by the change in the leak rate near the atmospheric pressure, by approximating the linear function linearly, It is optimal as a regression model under conditions where air leakage from the cavity of the concrete structure is large, and the amount of cavity of the concrete structure can be estimated more accurately.

It is composition explanatory drawing which showed typically the structure of the cavity amount estimation system used for the cavity amount estimation method of the concrete structure which concerns on embodiment of this invention. It is explanatory drawing explaining the data processing procedure in the case of carrying out a straight line approximation by the least squares method in the cavity amount estimation method of a concrete structure. Explanatory drawing of the data processing procedure which shows the process of reducing a data use range based on the value of the determination coefficient of the step which selects the measurement data used for the approximation in the cavity amount estimation method of the concrete structure which concerns on embodiment of this invention It is. It is explanatory drawing of the data processing procedure which shows the process of drawing an approximate line based on the value of the determination coefficient of the step which selects measurement data same as the above.

  Hereinafter, an embodiment for carrying out a method for estimating a void amount of a concrete structure according to the present invention will be described in detail with reference to the drawings.

[Cavity estimation system]
First, the cavity amount estimation system used in the method for estimating a cavity amount of a concrete structure according to an embodiment of the present invention will be described with reference to FIG. A cavity amount estimation system 1 according to this embodiment includes a vacuum pump 2 that reduces pressure to a predetermined vacuum pressure, a known pressure reducing container 3 having a volume (about 10 L in this embodiment) that communicates with the vacuum pump 2 through a pipe, and the like. A pressure sensor 4 that measures the pressure in the decompression vessel 3, a temperature sensor 5 that measures the temperature in the decompression vessel 3, and a data logger 6 that records measurement values measured by the pressure sensor 4 and the temperature sensor 5. And a personal computer 7 that is electrically connected to the data logger 6 and performs calculation by executing a cavity amount estimation method described later by a predetermined program.

  This cavity amount estimation system 1 includes an opening / closing valve in which a decompression container 3 is formed in a hole forming portion 103 which is a hole communicating with a sheath tube 102 embedded in concrete of a PC structure 101 exemplified as a concrete structure. In order to measure the pressure and temperature in the connection pipe 104, a pressure sensor 4 ′ and a temperature sensor 5 ′ having the same configuration as the pressure sensor 4 and the temperature sensor 5 are installed. These pressure sensor 4 ′ and temperature sensor 5 ′ are connected to the data logger 6.

  Then, the opening / closing valve 8 is opened, the inside of the decompression vessel 3 is depressurized to a predetermined degree of vacuum by the vacuum pump 2, the opening / closing valve 8 is closed, the opening / closing valve 9 is opened, and the two pressure sensors 4, 4 ′ Measurement values measured by the two temperature sensors 5 and 5 ′ are taken into the personal computer 7 via the data logger 6, and the personal computer 7 estimates the amount of the cavity X that is an unfilled portion of the grout existing in the sheath tube 102. Calculated. A specific estimation method will be described in detail later.

[Estimation principle]
Next, the estimation principle of the method for estimating the void amount of the concrete structure of the present invention will be described with reference to FIG. As the estimation principle of the void amount estimation method of the concrete structure of the present invention, the unknown state of the concrete structure is determined by using the ideal gas equation of state (formula combining Boyle-Charles' law and Avogadro's law: PV = nRT). The cavity volume, which is the cavity volume, is estimated and calculated.

  However, air is used as the gas to be measured such as pressure. Of course, air is an actual mixed gas composed of nitrogen, oxygen, water vapor, carbon dioxide, and other trace gases, and is not an ideal gas. Since the equation of state of the ideal gas ignores the influence of the size of the molecule itself and the intermolecular force, when the ideal gas equation of state is applied to a real gas, the error increases as the pressure condition increases. However, even if it is not an ideal gas but a real gas, it exhibits behavior close to that of an ideal gas under low pressure conditions. Therefore, in the method for estimating the amount of cavities in a concrete structure according to the present invention, the measurement target air is measured in a reduced pressure environment. Therefore, the equation of state of ideal gas can be applied without error. In a reduced pressure environment, even if it is a mixed gas, the state equation of an ideal gas can be applied as a single gas if there is no change in the amount of substance (change in state such as chemical reaction or condensation).

Based on this concept, it is assumed that the formula (1) is established for the gas in the decompression vessel 3. Where P _{1 is the} pressure of the gas in the decompression container, V _{1 is} the volume of the gas in the decompression container, n _{1 is the} number of moles of the gas in the decompression container, R is the gas constant, and T ₁ is the gas in the decompression container. Temperature.

It is assumed that equation (2) holds for the gas in the cavity X that is the volume estimation target. Where P _{2 is} the pressure of the gas in the cavity, V _{2 is} the volume of the gas in the cavity, n _{2 is the} number of moles of the gas in the cavity, R is the gas constant, and T ₂ is the temperature of the gas in the cavity. .

It is assumed that equation (3) holds for the mixed gas after the gas in the decompression vessel 3 and the gas in the cavity X are mixed by opening the opening / closing valve 9. Here, P _{3 is} the pressure of the mixed gas, V _{3 is} the volume of the mixed gas, n _{3 is the} number of moles of the mixed gas, R is the gas constant, and T ₃ is the temperature of the mixed gas.

  Further, if the deformation of the container due to the pressure change is negligible, the equation (4) is established.

  If it is assumed that there is no change in the amount of substance after gas mixing, the equation (5) is established.

  When formulas (1), (2), and (3) are arranged in terms of the number of moles n and substituted into formula (5), formula (6) is obtained.

Eliminating V ₃ using the equations (6) to (4) and rearranging V ₂ , equation (7), which is an estimation equation for the amount of cavity X, is obtained. Here, since V ₁ is known, by measuring P ₁ , P ₂ , P ₃ , T ₁ , T ₂ , T ₃ , it is possible to calculate V ₂ that is the volume (cavity amount) of an unknown number of cavities X become.

In addition, when the temperature change before and after gas mixing is slight, even if this is ignored, there is almost no influence on the estimated value. Therefore, a simple estimation formula ignoring the temperature is shown below. Since V ₁ is already known, an unknown number of V ₂ can be calculated by measuring P ₁ , P ₂ , and P ₃ on-site using this equation (8).

  It should be noted that Equation (7) and Equation (8) were derived on the assumption that there was no change in the amount of material. However, in actual concrete structures, the airtightness of the cavity X is often not ensured, causing leakage. The amount of substances may increase. In addition, when water is immersed in the cavity, the amount of gas after mixing increases because water after being decompressed vaporizes as water vapor. However, the influence of the change in the amount of these substances can be eliminated by introducing the correction method based on the selection of the measurement data to be used, which will be described later, and the approximation of the pressure of the mixed gas from the data.

  Next, with reference to FIG. 1, a concrete structure cavity amount estimation method according to an embodiment of the present invention will be described in detail.

(Drilling of concrete structures)
First, using a drilling machine or the like, a concrete portion of the PC structure 101 exemplified as a concrete structure is drilled, and a drilling portion 103 that is a hole reaching the sheath tube 102 from the outer surface of the PC structure 101 is formed. Perforated and provided.

(Sheath tube excavation)
Next, a portion of the sheath tube 102 that comes into contact with the hole 103 is cut and opened while taking care not to damage a tension material such as a PC steel material (not shown) inserted into the sheath tube 102.

(Cavity confirmation)
Next, an endoscope or the like is inserted into the drilled hole 103, and the presence or absence of the cavity X is confirmed by visual inspection of the inside of the sheath tube 102. When the cavity X is confirmed, the amount of the cavity is estimated.

(Installation of connecting pipe)
Next, the connecting pipe 104 for connecting to the hole 103 is connected to a hose that communicates with the decompression vessel 3, and the decompression vessel 3 and the cavity X are communicated with each other through the hole 103 and the connection pipe 104. However, when a suction cup type pad is attached to the tip of the hose and directly connected to the surface of the PC structure 101, the connection pipe 104 is unnecessary.

(Decompression in the decompression vessel)
Next, the opening / closing valve 8 is opened, and the inside of the decompression vessel 3 is decompressed to a predetermined degree of vacuum by the vacuum pump 2. In this embodiment, the pressure is reduced to 95%, that is, −95 [kPa], and the on-off valve 8 is closed. Of course, the predetermined degree of vacuum is appropriately determined according to the exhaust capacity of the vacuum pump 2, the scale of the PC structure 101, and the situation of the cavity, and it goes without saying that the degree of vacuum is not limited to 95%. Absent.

(Measurement of pressure and temperature change)
Next, interval measurement (in this embodiment, 0.2 second interval measurement) is started at predetermined control times by the two pressure sensors 4, 4 ′ and the two temperature sensors 5, 5 ′. In this measurement, the opening / closing valve 9 as an intermediate valve is opened and released, the air in the decompression vessel 3 and the air in the cavity X are mixed, and the pressure, temperature, and cavity of the air in the decompression vessel 3 along with the time information. The pressure and temperature on the side of the hole forming portion 103 outside the on-off valve 9 corresponding to the pressure and temperature of the air in X are measured. Each pressure and temperature is measured by the pressure sensors 4 and 4 ′ and the temperature sensors 5 and 5, and the measurement data is recorded by the data logger 6. The measurement data is taken into the personal computer 7 through the data logger 6 and used for the cavity amount calculation.

  After opening the on-off valve 9, the air pressure at each location changes instantaneously, but the measurement by the pressure sensors 4, 4 'and the temperature sensors 5, 5 continues for about 10 seconds thereafter. For several seconds (1.5 seconds) immediately after opening the on-off valve 9, it can be considered that the influence of pressure vibration is large, and, as will be described later, a section that changes linearly without being affected by leakage. This is because the measurement data is used after sorting.

(Calculation of void volume)
Next, the cavity amount which is the volume of the cavity X is calculated by the personal computer 7 using the acquired measurement data. As a calculation formula, the volume (cavity amount) V ₂ of the cavity X is calculated using the above-described formula (8). Thereby, the measurement by the temperature sensors 5 and 5 becomes unnecessary, and it becomes unnecessary to install the temperature sensors 5 and 5.

In the void amount estimation method for the concrete structure according to the present embodiment, when calculating the void amount, the pressure measurement data measured by the pressure sensors 4 and 4 ′ are not directly substituted into the equation (8), The measurement data is linearly approximated to a linear function, the pressure P ₃ of the gas mixture is determined using the approximate value, and is substituted into equation (8) to calculate the volume (cavity volume) V ₂ of the cavity X To do. Eliminates the effects of gas mass changes due to air leakage from the cavity X, water accumulated in the cavity X, and the measurement error of the pressure sensors 4, 4 'due to pressure vibration immediately after the opening of the on-off valve 9 Because it can be done.

(Step of selecting measurement data used for approximation)
Next, the step of selecting measurement data used for approximation in the method for estimating the amount of cavities in a concrete structure according to the present embodiment will be described.

As shown in FIG. 2, as a method of determining the pressure P _{3 of the} mixed gas using the above-mentioned linear approximation, 1.5 seconds immediately after opening of the opening / closing valve considered to be greatly affected by pressure vibration. Then, the data for 10 seconds before and after (50 data) are linearly approximated by the least square method. However, this method is useful when the leak from the cavity of the concrete structure is small, but when the leak increases, the degree of vacuum is released to atmospheric pressure in a short time, and the pressure difference between the inside and outside is close to atmospheric pressure. There is a possibility that a large error will be generated in the estimated value due to the influence of the decrease in the air leakage rate due to the decrease in the value.

  However, if the total cross-sectional area of the air leakage path from the cavity of the concrete structure, such as the size of the air leakage hole, does not change over time, in a section where sufficient negative pressure is maintained with respect to atmospheric pressure It is considered that the decrease in the degree of vacuum due to air leakage is proportional to time. Therefore, when the linear approximation is performed using the measurement data of the section, when the correlation of the straight line derived by the regression analysis is evaluated, the straight line should show a strong correlation. In the method for estimating the void amount of the concrete structure according to the present embodiment, paying attention to this point, the function of the approximate line is determined using regression analysis only with the data of the section having a strong correlation.

Accordingly, the cavity estimation method of concrete structures according to the present embodiment, the measurement data to be used for approximation by using the determined coefficient R ² from the plurality of measurement data of the pressure of the mixed gas was measured after opening of the closing valve The pressure P _{3 of the} mixed gas is determined based on a linear function approximated from the selected measurement data.

There are a plurality of definitions of the determination coefficient R ² , but as a general definition, it represents a ratio that can be explained by a regression equation among fluctuations, and is based on the following equation. It is also called a contribution rate, and when the determination coefficient R ² is close to 1, it can be evaluated as a good regression model with small residual fluctuation.

Here, (x _i , y _i ) is the measured pressure data, x _i is the elapsed time (seconds), y _i is the pressure [kPa] measured by the pressure sensor, μ _Y is the average of y _i , f (x _i ) is a regression model that is linearly approximated.

  The measurement data selection method in the method for estimating the cavity amount of the concrete structure according to the present embodiment uses only the data of the straight section for the data after opening the on-off valve, so that the measurement used to delete from the data having a long elapsed time. Select data. This is because the section with a high degree of vacuum changes linearly without being affected by the change in the leak rate near the atmospheric pressure. Specifically, as shown in FIG. 3, the data use range is narrowed while looking at the value of the determination coefficient so as not to use the data of the section affected by the atmospheric pressure. If the data usage range is narrowed more than necessary, the approximate line is affected not only by the influence of air leakage but also by the noise of the measuring instrument. Therefore, the number of data should be as large as possible.

  For this reason, in the method for estimating the amount of cavities in the concrete structure according to the present embodiment, as shown in FIG. 4, the data to be used is in principle a section below a predetermined pressure near −20 kPa, and the data usage range is 10 data ( 2 seconds) or more. From the past measurement results, this is greatly affected by the pressure difference from the atmospheric pressure in the section where the degree of vacuum is lower than −20 kPa, and if the data use range is less than 10 data, the measurement data is greatly affected by the noise of the measuring instrument. This is to cause an error in the measurement result. However, when changing the measurement system, it is necessary to appropriately determine the data usage range from the accuracy of the measuring instrument used, the influence of noise, the data acquisition interval, and the like.

Specifically, as shown in FIG. 4, measurement data in a continuous section where the determination coefficient R ² is 0.99 or more, and a range showing the strongest correlation in which the number of measurement data is 10 or more. Select the data.

  In addition, the application range of the step which selects the measurement data used for approximation in the cavity amount estimation method of the concrete structure according to the present embodiment is limited to when there is an influence due to air leakage. This is because in a space where the cavity of the concrete structure is completely sealed, the graph of pressure fluctuation after opening of the on-off valve becomes flat, and the noise of the measuring instrument is dominant in the data change. Then, since the data fluctuates due to noise in a section where the degree of vacuum is essentially constant, the correlation of the graph becomes very weak and data showing a strong correlation cannot be obtained.

And in the cavity amount estimation method of the concrete structure which concerns on this embodiment, it uses the measurement data selected at the step which selects the measurement data demonstrated above, it linearly approximates to a linear function, and it is mixed gas from the approximated value. The volume P of the cavity X (cavity amount) V ₂ is calculated by substituting the pressure P ₃ in the formula (8).

  According to the method for estimating the cavity amount of the concrete structure according to the embodiment of the present invention described above, the cavity amount is estimated by linear approximation from the selected measurement data without using the data of the section affected by the atmospheric pressure. To do. For this reason, even under conditions where there is a large amount of air leakage per hour in the cavity, the cavity volume of the concrete structure is extremely accurate, regardless of the on-site weather conditions such as changes in atmospheric pressure and temperature and the cavity shape in the structure. Can be estimated and calculated.

  In addition, although the cavity amount estimation method for a concrete structure according to the embodiment of the present invention has been described in detail, the above-described or illustrated embodiments all show one embodiment embodied in carrying out the present invention. However, the technical scope of the present invention should not be construed in a limited manner. In particular, when determining the pressure of a mixed gas, a linear approximation to a linear function has been described as an example, but the approximation function is not limited to a linear function, and other polynomial functions, exponential functions, logarithmic functions, trigonometric functions, etc. A regression model combining a curve such as a function or a curve and a straight line may be used.

  Moreover, although the PC structure was illustrated and demonstrated as a concrete structure, the other concrete structure which does not add prestress etc. may be sufficient. In addition, the grout unfilled portion in the sheath tube was illustrated as an example of the cavity of the concrete structure. However, if the cavity formed in the concrete structure such as a junker and the decompression vessel can be communicated with each other by any method, this cavity amount estimation It is possible to apply the method.

  Furthermore, although the case where the hole 103 is provided by drilling in the cavity and the decompression vessel 3 and the cavity X communicate with each other has been described as an example, the interior of the concrete structure such as a crack is communicated with the surface from the beginning. Obviously, if there are holes or the like, there is no need to drill holes to provide holes.

1: Cavity estimation system 2: Vacuum pump 3: Depressurized container 4, 4 ′: Pressure sensor 5, 5 ′: Temperature sensor 6: Data logger 7: Personal computer 8, 9: Open / close valve 101: PC structure 102: Sheath tube 103: Drilling part 104: Connection pipe X: Cavity

Claims (3)

A method for estimating the amount of cavities in a concrete structure, wherein the volume of the cavities existing inside the concrete structure is estimated and calculated in a leaked state where the cavities communicate with outside air,
The cavity and a decompression container with a known volume that has been decompressed to a predetermined pressure are communicated via an open / close valve that can be freely opened and closed, and the pressure in the decompression container and the pressure of the air that communicates with the interior of the cavity are While measuring for a predetermined time before and after opening the on-off valve, obtain multiple measurement data,
Comprising the step of selecting the measurement data to be used for approximation by using the determined coefficient R ² from the plurality of measurement data of the pressure of the mixed gas was measured after opening of the closing valve,
Determine the pressure P ₃ of the gas mixture based on the function approximated from the selected measurement data, and calculate the volume of the cavity by substituting the pressure P ₃ of the gas mixture into the following equation derived from the equation of state of the ideal gas A method for estimating the amount of cavities in a concrete structure characterized by the above.
Where P ₁ : gas pressure in the decompression vessel (kPa), V ₁ : gas volume in the decompression vessel (ml), P ₂ : gas pressure in the cavity (kPa), V ₂ : in the cavity Gas volume (ml), P ₃ : Pressure of mixed gas (kPa). In the step of selecting the measurement data, selection is made so that the measurement data is a continuous section in which the determination coefficient R ² is 0.99 or more and the number of measurement data is 10 or more. Item 2. A method for estimating a void amount in a concrete structure according to item 1. The method of estimating a void amount in a concrete structure according to claim 1 or 2, wherein the approximated function is a linear function having time as a variable.