Non-destructive testing method and apparatus for detecting internal deformation of concrete.

Abstract

This invention provides a method for measuring the propagation speed of elastic waves passing through concrete, a non-destructive testing method for determining the presence or absence of deformation inside concrete, and apparatus for these, which enable non-destructive and accurate testing of deformation inside concrete. [Solution] The method for measuring the propagation speed of elastic waves calculates the propagation speed of elastic waves as they pass through the concrete 5, based on the transmission time of the elastic waves generated by the impact on the concrete 5 and the round-trip time of the elastic waves within the concrete 5.

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the propagation speed of elastic waves transmitted through concrete, a non-destructive testing method for determining whether or not there is deformation inside concrete, a device for measuring the propagation speed of elastic waves transmitted through concrete, and a non-destructive testing device for determining whether or not there is deformation inside concrete. [Background technology]

[0002] Concrete structures can deteriorate over time with prolonged use. For example, highway bridges experience significant deformation due to aging, fatigue from heavy vehicle traffic, and salt damage, among other harsh environmental factors. Furthermore, concrete structures can develop internal defects such as voids and pitting during construction.

[0003] Given this situation, non-destructive testing, which directly tests structures without damaging them, is an effective means of checking the occurrence of internal deformations in concrete during construction and conducting periodic inspections. In particular, non-destructive testing methods that have fewer constraints for application and can be carried out efficiently in a short time are effective.

[0004] While there are various non-destructive testing methods, the impact elastic wave method is known as a non-destructive testing method that receives elastic waves generated by striking a concrete surface (see, for example, Non-Patent Document 1). Annex A of Non-Patent Document 1 describes a method for measuring elastic wave propagation speed using propagation time differences, and Annex B describes a method for measuring elastic wave propagation speed using the frequency characteristics of multiple reflections, and both methods are standardized. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Japanese Society for Nondestructive Inspection Standard: Nondestructive Testing of Concrete - Elastic Wave Method - Part 2: Impact Elastic Wave, NDIS 2426-2:2014, Japanese Society for Nondestructive Inspection [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in order to confirm the occurrence of deformation inside concrete using the method specified in Annex A of Non-Patent Literature 1 mentioned above, there were the following problems: (1) it is necessary to accurately determine the distance between the point where elastic waves are input and the point where they are received (the distance between the point on the concrete surface struck with a hammer and the point on the opposite surface of the concrete surface where the acceleration sensor is installed), and (2) concrete has the property that the elastic wave propagation speed changes even without the presence or absence of internal deformation. Furthermore, in order to confirm the occurrence of deformation inside concrete using the method specified in Annex B of Non-Patent Literature 1 mentioned above, there were the following problems: (1) it is difficult to inspect deformations with small cross-sectional areas inside the concrete, and (2) if the distance from the concrete surface to the opposite surface of the concrete surface at each measurement point is uneven, it becomes difficult to determine the presence or absence of deformation (voids, weak areas) inside the concrete. Due to these problems, conventional techniques have been a source of errors in testing the presence or absence of deformation (voids, weak areas) inside concrete and the extent of the deformation.

[0007] The present invention has been made in view of these points, and aims to provide a method for measuring the propagation speed of elastic waves that penetrate the inside of concrete, a non-destructive testing method for determining the presence or absence of deformation inside concrete, and apparatus thereof, which enable non-destructive and accurate testing of deformation inside concrete. [Means for solving the problem]

[0008] A method for measuring the propagation speed of elastic waves passing through concrete according to an aspect of the present invention calculates the propagation speed of the elastic waves passing through the concrete based on the transmission time of the elastic waves generated by impact on the concrete being measured and the round-trip time of the elastic waves within the concrete. [Effect of the Invention]

[0009] According to the present invention, it is possible to accurately test the deformation inside the concrete nondestructively. [Brief Description of the Drawings]

[0010] [Figure 1] Part of a method for measuring the propagation speed of elastic waves passing through the inside of concrete and a nondestructive test method for the presence or absence of deformation inside concrete using a device for measuring the propagation speed of elastic waves passing through the inside of concrete and a nondestructive test device for the presence or absence of deformation inside concrete according to an embodiment of the present invention are schematically shown. (a) is a cross-sectional view and (b) is a plan view. [Figure 2] Another part of the method for measuring the propagation speed of elastic waves passing through the inside of the same concrete and the nondestructive test method for the presence or absence of deformation inside concrete are schematically shown. (a) is a cross-sectional view and (b) is a plan view. [Figure 3] (a) is a graph showing an example of an acceleration waveform received by the receiving means of the propagation speed measuring device on the impact surface side of the concrete, and (b) is a graph showing an example of an acceleration waveform received by the receiving means on the opposite surface side of the concrete. [Embodiments for Carrying Out the Invention]

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] [[ID=3l]] In FIGS. 1 and 2, reference numeral 1 denotes a propagation speed measuring device (hereinafter simply referred to as the measuring device 1). The measuring device 1 includes a striking means 2, a receiving means 3, and a calculating means 4. This measuring device 1 measures the propagation speed of elastic waves inside the concrete 5 of an existing concrete structure or the like, and is used in a nondestructive test device 6 (hereinafter simply referred to as the test device 6) for nondestructively testing the concrete 5.

[0013] The striking means 2 applies an impact to the concrete 5 by striking, causing an elastic wave to propagate within the concrete 5. In the present embodiment, as the striking means 2, one striking means 2a and another striking means 2b are used.

[0014] One striking means 2a is for measuring the transmission time (one-way transmission time) of the elastic wave inside the concrete 5. As one striking means 2a, for example, a hammer or a steel ball is used. In the illustrated example, a hammer is used as one striking means 2a.

[0015] Another striking means 2b is for measuring the round-trip time of the elastic wave inside the concrete 5. As another striking means 2b, for example, a hammer or a steel ball is used. Preferably, as another striking means 2b, steel balls with different masses according to the thickness of the concrete 5 are used. That is, it is preferable to prepare in advance a plurality of types of steel balls with different diameters, that is, different masses, as another striking means 2b, and appropriately select according to the thickness of the concrete 5 to be measured.

[0016] Note that the one striking means 2a and the other striking means 2b do not necessarily have to be separate and different, and they may be the same.

[0017] The receiving means 3 is an accelerometer (acceleration sensor) for measuring the above-mentioned transmission time and round-trip time by receiving the elastic wave applied to the concrete 5 by the striking means 2. In the present embodiment, among the elastic waves generated by striking the concrete 5 by the striking means 2, the P wave is used. In the present embodiment, as the receiving means 3, one receiving means 3a, 3b and another receiving means 3c are used.

[0018] The receiving means 3a and 3b are used as a pair and receive acceleration to measure the transmission time. The receiving means 3a measures the impact input to the impact surface (input surface) 5a of the concrete 5 by the impact means 2a. Preferably, the receiving means 3a is built into the impact means 2a. By being built into the impact means 2a, the measuring device 1 and the testing device 6 can be made compact and the positional deviation between the impact point and the measurement point can be reduced. However, the receiving means 3a may be installed near the input point of the impact of the impact means 2a on the impact surface 5a of the concrete 5. The receiving means 3b is installed on the opposing surface 5b of the concrete 5 that faces the impact surface 5a.

[0019] The other receiving means 3c receives acceleration in order to measure the round-trip time. The other receiving means 3c is installed on the striking surface 5a of the concrete 5 near the input point of the impact of the other striking means 2b.

[0020] Furthermore, either one of the receiving means 3a or 3b may be used as the other receiving means 3c.

[0021] Calculation means 4 analyzes the signal output from receiving means 3 and calculates the transmission time and round-trip time. Receiving means 3 and calculation means 4 are connected by wire or wireless, and the signal output from receiving means 3 is input to calculation means 4. For example, when calculating the transmission time, as shown in the examples in Figures 3(a) and 3(b), the difference Δt between the time t1 when the amplitude of the acceleration waveform (horizontal axis: time, vertical axis: amplitude) received by one receiving means 3a becomes large and the time t2 when the amplitude of the acceleration waveform received by one receiving means 3b becomes large is calculated as the transmission time. When calculating the round-trip time, the acceleration waveform received by the other receiving means 3c shown in Figures 2(a) and 2(b) is frequency-analyzed using a known analysis method such as Fourier transform, the frequency (fundamental frequency) that appears due to the reflected waves (multiple reflections) of the elastic wave is measured, and the reciprocal of that frequency is calculated as the round-trip time. Then, calculation means 4 calculates the propagation speed of the elastic wave based on the calculated transmission time and round-trip time. The specific method for calculating the propagation speed will be described later. As calculation method 4, for example, a computer with pre-installed analysis software can be used. This computer may be a dedicated or general-purpose computer.

[0022] Furthermore, the test apparatus 6 includes a determination means 7 for determining the presence and extent of deformation (voids, weak areas) inside the concrete 5. The determination means 7 determines the presence or absence of deformation inside the concrete 5 by analyzing the propagation velocity calculated at multiple different measurement points on the concrete 5 to be measured by the measuring device 1. This analysis and determination will also be described later. As the determination means 7, for example, a computer with determination software pre-installed is used. In this embodiment, the determination means 7 is the same computer as the calculation means 4, but this is not limited to this, and the calculation means 4 and the determination means 7 may be separate. Also, the determination software may be configured as one software with the analysis software of the calculation means 4, or it may be separate from the analysis software.

[0023] Next, we will explain the method for measuring the propagation speed of elastic waves using measuring device 1 and the method for non-destructive testing of concrete 5 using testing device 6.

[0024] First, as shown in Figures 1(a) and 1(b), the measurer presses one receiving means 3b against the opposing surface 5b of the concrete 5 to be measured, and strikes the striking surface 5a with one striking means 2a, which contains one receiving means 3a. When the elastic waves generated inside the concrete 5 by this strike are received by the one receiving means 3b, the calculation means 4 calculates the difference Δt (Figures 3(a) and 3(b)) between the time t1 when the amplitude of the acceleration waveform measured by the one receiving means 3a becomes large and the time t2 when the amplitude of the acceleration waveform measured by the one receiving means 3b becomes large as the transmission time.

[0025] Next, as shown in Figures 2(a) and 2(b), the measurer presses the other receiving means 3c against the striking surface 5a of the concrete 5 to be measured, and strikes the vicinity of it with the other striking means 2b. When the elastic waves generated inside the concrete 5 by this striking are reflected by the opposing surface 5b and received by the other receiving means 3c, the calculation means 4 performs frequency analysis on the acceleration waveform measured by the other receiving means 3c to calculate the fundamental frequency, and calculates its reciprocal as the round-trip time.

[0026] The estimated distance D between the point of impact by one striking means 2a or between one receiving means 3a and one receiving means 3b at the time of impact. T The round trip time is T R Based on this, any speed V S Using this, it can be expressed by the following formula.

[0027]

number

[0028] Therefore, the propagation speed V of the elastic wave that passed through the interior of the concrete 5 TM is the transmission time T M and round-trip time T R Using this, it can be calculated as follows.

[0029] [Number]

[0030] Therefore, from this equation, the propagation velocity V of the elastic wave transmitted through the inside of the concrete 5 TM is the distance D between the point where the elastic wave is input and the point where it is received T [[ID=1 (14)]](the distance between a point on the striking surface 5a of the concrete 5 struck by one striking means 2a and a point on the opposing surface 5b of the concrete 5 where one receiving means 3b is installed) is unknown, but can be measured from the transmission time T M and the round-trip time T R and.

[0031] Here, assuming that there is no deformation inside the concrete 5 at each point, the following equation holds.

[0032] [Number]

[0033] [Number]

[0034] In these equations, D R is the actual distance between the point on the striking surface 5a of the concrete 5 struck by one striking means 2a and the point on the opposing surface 5b of the concrete 5 where one receiving means 3b is installed, V RR is the velocity of the elastic wave actually traveling back and forth inside the concrete 5, V TR represents the velocity of the elastic wave actually transmitted through the inside of the concrete 5.

[0035] When the above equation is transformed, it becomes the following equation.

[0036] [Number]

[0037] Therefore, from this equation, if there is no deformation inside the concrete 5, the propagation speed V of the elastic wave that has passed through the concrete 5 is TM This is the velocity V of the elastic wave actually traveling back and forth inside the concrete 5. RR And the velocity V of elastic waves actually passing through the inside of concrete 5 TR Determined from (V TR / V RR (proportional to) the distance D from each measurement point on the striking surface 5a of the concrete 5 to the installation point of one of the receiving means 3b on the opposing surface 5b of the concrete 5. T It does not depend on the presence or absence of internal deformation in concrete 5, and even if there are conditions that cause the propagation speed of elastic waves to change other than the presence or absence of internal deformation in concrete 5, the velocity V TR and velocity V RR Since they change at a similar rate, the quotient of the two (V TR / V RR ) remains unchanged, and the propagation speed V TM It will not affect that.

[0038] Based on the above, the measurer uses measuring device 1 to determine the propagation speed V TM The measurement is taken at multiple different measurement points. The determination means 7 compares these measurement results and determines the propagation speed V of elastic waves that have passed through the concrete 5 as measured by the measuring device 1. TM If the propagation velocity V is an abnormal value, it can be determined that there is a deformation inside the concrete 5 at that measurement point, and the extent of the deformation can be estimated from the distribution of measurement points. TM Whether or not a value is an outlier can be determined using any statistical method. For example, one could calculate the average value and standard deviation σ of all propagation velocities and determine that propagation velocities that are more than 3σ away from the average value are outliers, or that propagation velocities that fall outside the range of measurement error confirmed in previous experience are outliers.

[0039] Thus, according to the elastic wave propagation speed measurement method of one embodiment, even if the distance between the point where the elastic wave is input and the point where it is received (the distance between the point on the striking surface 5a of the concrete 5 struck by one striking means 2a and the point on the opposing surface 5b of the concrete 5 where one receiving means 3b is installed) is unknown, or if this distance is different, a constant measurement value can be obtained as long as there is no deformation inside the concrete 5. Therefore, the work of confirming this distance is unnecessary. Furthermore, if deformation exists inside the concrete 5, even if it is a deformation with a small cross-sectional area, the above formula will not hold, and the measurement value will be an abnormal value. By utilizing these properties, the elastic wave propagation speed inside the concrete 5 can be measured with high accuracy.

[0040] Furthermore, by performing the above propagation velocity measurement method at multiple measurement points on the concrete 5 to be measured, the presence or absence of abnormal values ​​in the measured propagation velocity and the distribution of measurement points where abnormal values ​​were found can be non-destructively and accurately tested for the presence or absence of deformation inside the concrete 5 and the extent of such deformation.

[0041] Moreover, the above-mentioned propagation speed measurement method and non-destructive testing method can be easily implemented on-site using general means, without the need for special parts or specialized equipment. [Explanation of Symbols]

[0042] 1. Propagation speed measuring device 2. Strike means 3. Receiving means 4. Calculation method 5. Concrete 5a Striking surface 5b Opposite surface 6. Non-destructive testing equipment 7 Judgment means

Claims

1. Based on the transmission time of the elastic wave generated by the impact on the concrete being measured, and the round-trip time of the elastic wave within the concrete, the propagation velocity of the elastic wave as it passes through the concrete is calculated. A method for measuring the propagation speed of elastic waves that penetrate the interior of concrete, characterized by the following:

2. The propagation velocity measurement method described in claim 1 is performed on the concrete to be measured at multiple measurement points, and the presence or absence of deformation inside the concrete is determined based on the presence or absence of abnormal values ​​in the propagation velocity measured at those measurement points. A non-destructive testing method for determining the presence or absence of internal deformation in concrete, characterized by the following features.

3. A striking means for striking the concrete to be measured, A receiving means for receiving elastic waves generated by the impact by the aforementioned impact means, A calculation means for calculating the propagation speed of the elastic wave as it passes through the concrete, based on the transmission time of the elastic wave through the concrete, which is determined by reception by the receiving means on a surface opposite to the striking surface of the concrete, and the round-trip time of the elastic wave through the concrete, which is determined by reception by the receiving means on the striking surface. A device for measuring the propagation speed of elastic waves that penetrate the interior of concrete, characterized by comprising the following:

4. A propagation speed measuring device according to claim 3, This propagation velocity measuring device includes a determination means that determines whether or not there is any deformation inside the concrete based on the presence or absence of abnormal values ​​in the propagation velocity calculated at multiple measurement points on the concrete being measured, A non-destructive testing device for detecting the presence or absence of internal deformation in concrete, characterized by comprising the following features.

Images