Method for measuring concrete crack by inclination of ground penetrating radar based on mixed medium

Abstract

According to the method for measuring the concrete crack through the inclination of the ground penetrating radar based on the mixed medium, the right-angle triangular concrete cushion block filled with the mixed medium is adopted, antenna inclination measurement is supported, and the detection accuracy is improved. And the dielectric constant of the constructed triangular pyramid is variable and is close to the dielectric constant of the concrete structure to be measured, so that the influence caused by refraction and wave velocity change when electromagnetic waves pass through layered media can be reduced. And through a layered medium backward projection imaging algorithm, the adaptability of dielectric constants of the concrete structure and the right-angle triangular concrete cushion block is improved, and the detection effect is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete detection, and in particular to a method for measuring concrete cracks by tilting a ground penetrating radar based on a mixed medium. Background Art

[0002] my country's transportation system is characterized by high passenger density, long mileage, and large-scale construction. Cement concrete and reinforced concrete, with their excellent rigidity, strength, and waterproof properties, are widely used in highway and railway subgrade construction, bridge decks, tunnel linings, and airport runways. However, concrete undergoes physical, chemical, and biological changes over time and under environmental influences, gradually deteriorating its mechanical properties and microstructure. Many highway bridges have experienced varying degrees of damage and aging, with concrete structures experiencing cracks, corrosion, deformation, and breakage. Cracks account for over 60% of these defects, often occurring within the structure and difficult to detect. Acidic substances in the environment can easily penetrate into the subgrade through these cracks, compromising structural stability and durability. Detecting cracks within concrete structures can promptly identify affected areas, ensuring transportation safety and extending the service life of highway bridges.

[0003] Cement concrete and reinforced concrete used in current road surfaces are often plagued by cracks. These cracks occur not only on the concrete surface but also within the concrete, extending in all directions. For cracks extending in a direction close to the radar measurement direction, the reflected echo from below is often obscured by the scattered echo from strong scattering points above. Therefore, when directly using ground-penetrating radar to measure cracks in concrete structures, interpreting the raw echo image of the radar is difficult. The target echo within the medium exhibits hyperbolic characteristics. Furthermore, when detecting vertical cracks, strong scattering points at the crack top can obscure the echo from the underlying cracks, resulting in weak radar echo energy from the structural features below the longitudinal crack, making accurate detection difficult. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a method for inclined measurement of concrete cracks using a ground-penetrating radar based on a mixed medium, so as to solve the technical problem in the prior art that in the detection of vertical cracks, the strong scattering point at the top of the crack will cover the echo of the underlying crack, resulting in weak radar echo energy of the structural form below the longitudinally extending crack, making it difficult to accurately detect.

[0005] The present invention provides a method for measuring concrete cracks by tilting a ground penetrating radar based on a mixed medium, comprising:

[0006] S1. Discretely grid the imaging area of ​​the concrete structure to be measured, measure the relative dielectric constant of the concrete structure to be measured, and construct a right-angled triangular concrete pad of mixed medium;

[0007] S2. Placing a radar antenna at the hypotenuse of the right-angled triangular concrete pad, moving the right-angled triangular concrete pad so that the radar antenna moves horizontally to start measuring grid points in the imaging area, and obtaining scattered echo data of the crack;

[0008] S3. Constructing the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point of the measurement interface between the concrete structure and the right-angled triangular concrete pad;

[0009] S4. The coordinates of the refraction point are solved by combining the refraction position relationship with the approximate solution formula of the refraction point;

[0010] S5. Measure the coordinates of the refraction point K times until all grid points are traversed, obtain K scattered echo data and their two-way delays between the measurement target point and the radar antenna, and coherently superimpose all scattered echo data to image the measurement target point.

[0011] Optionally, the right-angled triangular concrete pad for constructing the mixed medium includes:

[0012] The relative dielectric constant of the right-angled triangular concrete pad is expressed as:

[0013] ε c =V1ε1+V2ε2+…+V n ε n

[0014] Among them, ε1, ε2, …, ε n is the dielectric constant of the material that makes up the right-angled triangular concrete pad, V1, V2, ..., V n Indicates the volume percentage of the material, and V1+V2+…+V n =1.

[0015] Optionally, the step of constructing the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point at the measurement interface between the concrete structure and the right-angled triangular concrete pad includes:

[0016] The refraction position relationship is expressed as:

[0017]

[0018] Among them, (x k ,h r )、(x k ,0)、(x p ,z p ) are the positions of the radar antenna, the refraction point of the interface, and the measurement target point, respectively. i and θ rare the incident and exit angles of refraction, ε r is the ratio of the relative dielectric constants between the concrete structure and the right-angled triangular concrete pad, expressed as:

[0019]

[0020] Among them, ε a Represents the relative dielectric constant of the concrete structure.

[0021] Optionally, the refraction position relationship is combined with an approximate solution formula for the refraction point to solve the refraction point coordinates, including:

[0022] The coordinates of the refraction point are expressed as:

[0023]

[0024] Optionally, the K times of measuring the scattered echo data between the target point and the radar antenna and the round-trip delay thereof includes:

[0025] The scattered echo data of the target point and the radar antenna measured K times is expressed as y k (t), the round-trip delay is expressed as:

[0026]

[0027] Among them, v1 and v2 are the propagation speeds of electromagnetic waves in the right-angled triangular concrete pad and concrete structure, respectively.

[0028] Optionally, the coherently superimposing all scattered echo data to image the measurement target point includes:

[0029] The scattering intensity of the scattered echo data of the measurement target point at the Kth measurement is expressed as:

[0030] e p,k =y k (t=τ p,k )

[0031] All scattered echo data are coherently superimposed to image the measurement target point:

[0032] E p,k =∑y k (t=τ p,k ).

[0033] Compared with the prior art, the present invention:

[0034] 1. A right-angled triangular concrete pad filled with a mixed medium is used to support the antenna tilt measurement to increase detection accuracy. The dielectric constant of the triangular pyramid is variable, making it close to the dielectric constant of the concrete structure being measured, which can reduce the effects of refraction and wave velocity changes when electromagnetic waves pass through layered media.

[0035] 3. Through the layered medium back-projection imaging algorithm, the dielectric constant adaptability of the measured concrete structure and the right-angled triangular concrete pad is improved, thereby enhancing the detection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0038] Figure 1 Schematic diagram of the method flow of the present invention;

[0039] Figure 2 A schematic diagram of a concrete crack reflection echo according to an embodiment of the present invention;

[0040] Figure 3 A schematic diagram of tilt measurement according to an embodiment of the present invention;

[0041] Figure 4 A schematic diagram of a refraction point according to an embodiment of the present invention;

[0042] Figure 5 A schematic diagram of a simulation scenario in another embodiment of the present invention;

[0043] Figure 6 FIG. 4 is a schematic diagram of imaging results according to another embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The functional units with the same labels in the examples of the present invention have the same and similar structures and functions.

[0045] See also Figure 1 The present invention provides a method for measuring concrete cracks using a ground penetrating radar tilt method based on a mixed medium, comprising:

[0046] S1. Discretely grid the imaging area of ​​the concrete structure to be measured, measure the relative dielectric constant of the concrete structure to be measured, and construct a right-angled triangular concrete pad of mixed medium;

[0047] S2. Placing a radar antenna at the hypotenuse of the right-angled triangular concrete pad, moving the right-angled triangular concrete pad so that the radar antenna moves horizontally to start measuring grid points in the imaging area, and obtaining scattered echo data of the crack;

[0048] S3. Constructing the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point of the measurement interface between the concrete structure and the right-angled triangular concrete pad;

[0049] S4. The coordinates of the refraction point are solved by combining the refraction position relationship with the approximate solution formula of the refraction point;

[0050] S5. Measure the coordinates of the refraction point K times until all grid points are traversed, obtain K scattered echo data and their two-way delays between the measurement target point and the radar antenna, and coherently superimpose all scattered echo data to image the measurement target point.

[0051] In this embodiment, S1 , the imaging area of ​​the concrete structure to be measured is discretely gridded, the relative dielectric constant of the concrete structure to be measured is measured, and a right-angled triangular concrete pad of a mixed medium is constructed.

[0052] First, the imaging area of ​​the concrete structure to be measured is discretized and meshed. Second, considering that crack damage not only occurs on the surface of the concrete but also extends into the interior of the structure, the cracks also have different directions. When performing ground-penetrating radar measurements, a group of antennas are usually used to transmit and receive signals. These antennas are placed together and move along a horizontal survey line at a certain step length for measurement. When ground-penetrating radar measures transverse cracks, that is, the direction of the survey line is consistent with the direction of the crack extension, there are many strong signal scattering points along the crack path, and the radar can detect the shape and location of the crack. However, when detecting vertical cracks, the echo energy of the scattering point at the top of the crack is too strong, making it difficult to observe the scattering point below in the radar image.

[0053] like Figure 2 As shown in the figure, we first built a right-angled triangle-shaped concrete pad and set up the detection radar antenna at a certain angle for tilt measurement. When the vertical crack is at a certain angle to the electromagnetic wave emitted by the antenna, the SNR of the crack target is greatly increased.

[0054] Furthermore, to minimize the mismatch between the target imaging area of ​​the concrete structure under test and the medium of the concrete pad, which would cause changes in the velocity and direction of the electromagnetic wave during propagation, leading to errors in the final imaging, the relative dielectric constant of the concrete structure under test was measured, and a right-angled triangular concrete pad with mixed medium was constructed.

[0055] Considering that soil is a mixture of solid mineral particles, water, and air, we control the dielectric constant by controlling the ratio of the three. The solid mineral particles can be composed of a variety of solid particles with different dielectric constants, such as dry fine sand, loam, etc. The ratio of water and air in concrete is represented by compaction and water content as indicators. A decrease in porosity and an increase in compaction will increase the dielectric constant. By mixing solid particle media with multiple dielectric constants, a solid mixture with an initial dielectric constant value is obtained. Subsequently, the water content and compaction are controlled to further adjust the dielectric constant of the mixed medium to adapt to the relative dielectric constant of the concrete to be tested.

[0056] After determining the relative dielectric constants of each component, the composite dielectric constant of the mixed medium can be calculated using the dielectric constant model. The dielectric constant model is expressed as:

[0057] ε c =V1ε1+V2ε2+…+V n ε n

[0058] Among them, ε1, ε2, …, ε n is the dielectric constant of the material that makes up the right-angled triangular concrete pad, V1, V2, ..., V n Indicates the volume percentage of the material, and V1+V2+…+V n =1. The dielectric constants of common substances are shown in Table 1:

[0059] Material Relative dielectric constant Air 1 water 81 Old concrete 8 New concrete 10-20 asphalt concrete >8 Dry fine sand 2-6 dry loam 4-10 Dry limestone 4-8 Salt 5-6 quartz 4.2-5 marble 8.2-9

[0060] Using the above method, a mixed medium is used to fill a right-angled triangular concrete pad. The dielectric constant of the mixed medium can be made close to the dielectric constant of the concrete structure to be tested by mixing materials in different proportions and controlling the water content and compaction degree, so as to reduce the influence of wave velocity changes and electromagnetic wave refraction.

[0061] S2. Place the radar antenna at the hypotenuse of the right-angled triangular concrete pad, move the right-angled triangular concrete pad, and move the radar antenna in the horizontal direction to start measuring the grid points in the imaging area to obtain scattered echo data of the crack.

[0062] See also Figure 3The radar antenna is placed at the hypotenuse of the right-angled triangular concrete pad. The ground-penetrating radar antenna detects along the survey line in the form of a common offset. The scattered echo data of the crack is in a hyperbolic shape, and the crack morphology cannot be observed from the original data.

[0063] S3. Construct the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point of the measurement interface between the concrete structure and the right-angled triangular concrete pad.

[0064] Using layered media backprojection imaging technology, the target echo energy can be shifted to its true physical location, further increasing detection accuracy. The relative dielectric constant of the right-angled triangular concrete pad is difficult to approximate to the relative dielectric constant of concrete. When the dielectric constant between the media changes, electromagnetic waves will produce refraction effects and changes in electromagnetic wave velocity at the interface.

[0065] See also Figure 4 In order to solve the above problem, the ratio of the relative dielectric constant between the concrete structure and the right-angled triangular concrete pad is calculated and expressed as:

[0066]

[0067] Among them, ε c is the relative dielectric constant of the right-angled triangular concrete pad, ε a represents the relative dielectric constant of the concrete structure. Both are isotropic, uniform, and lossless dielectrics. The antenna is located at the hypotenuse of a right-angled triangular concrete pad, at a distance h from the concrete surface. The geometric position relationship is as follows: Figure 4 As shown, the path of electromagnetic wave transmission becomes a broken line, following Snell's law, and the refraction point (x l ,0) also changes before and after the wave velocity, the following relationship holds:

[0068]

[0069] When the radar antenna moves horizontally for measurement, the refraction position relationship among the radar antenna, the measurement target point of the concrete structure, and the refraction point at the measurement interface between the concrete structure and the right-angled triangular concrete pad is expressed as follows:

[0070]

[0071] Among them, (x k ,h r )、(x k ,0)、(x p ,z p ) are the positions of the radar antenna, the refraction point of the interface, and the measurement target point, respectively. i and θr are the incident and exit angles of refraction.

[0072] S4. The coordinates of the refraction point are solved by combining the refraction position relationship with the approximate solution formula of the refraction point.

[0073] Considering that the core of the backprojection imaging algorithm is to calculate the two-way time delay of a spatial point, it is necessary to solve a quartic equation to obtain the two-way time delay of the double-layer medium. However, due to the large number of grid points in the imaging area, solving the quartic equation one by one is computationally complex. Therefore, an approximate solution formula for the refraction point is introduced to replace the solution of the quartic equation to quickly calculate the refraction point position. The complex equation-solving process is simplified to a single algebraic operation, and the equation for solving the refraction point coordinates is expressed as:

[0074]

[0075] S5. Measure the coordinates of the refraction point K times until all grid points are traversed, obtain K scattered echo data and their two-way delays between the measurement target point and the radar antenna, and coherently superimpose all scattered echo data to image the measurement target point.

[0076] Based on step S4, until the Kth measurement, the target point (x p ,z p ) and the round-trip delay between the antenna:

[0077]

[0078] Where v1 and v2 are the propagation speeds of electromagnetic waves in the mixed medium and concrete respectively, and the kth echo data is represented by y k (t), the scattering intensity of the target point p on the kth echo data is expressed as:

[0079] e p,k =yk(t=τ p, k)

[0080] All echo data are coherently superimposed to image point p:

[0081] E p,k =∑y k (t=τ p,k )

[0082] Imaging of concrete cracks can be achieved through the complete steps S5 described above. The present invention not only utilizes a right-angled triangular concrete pad filled with a mixed medium to support antenna tilt measurement, thereby increasing detection accuracy. Furthermore, the dielectric constant of the constructed triangular pyramid is variable, making it close to the dielectric constant of the concrete structure to be measured, thereby reducing the effects of refraction and wave velocity changes when electromagnetic waves pass through layered media. Furthermore, through a layered medium back-projection imaging algorithm, the dielectric constant compatibility between the measured concrete structure and the right-angled triangular concrete pad is improved, thereby enhancing detection effectiveness.

[0083] In another embodiment, a concrete crack simulation experiment with tilt measurement was performed, and simulation data was generated using electromagnetic simulation software GPRMAX based on the finite-difference time-domain method (FDTD). The simulation used a Ricker wavelet with a center frequency of 3.0 GHz. The tilted pad was a right-angled triangular pyramid with two right-angled sides of 3 cm and 10 cm, respectively, and the angle between the hypotenuse and the horizontal direction was 16.7°. The transceiver radar antenna was located at the hypotenuse of the pad, with a vertical distance of 1.5 cm from the concrete structure below. In each measurement, the pad and the transceiver antenna were moved step by step along the measurement line by a distance of 1 cm. The sampling window was 20 ns, and the spatial-temporal two-dimensional data B-scan was collected, which contained 81 radar echo data.

[0084] See also Figure 5 As shown, the relative dielectric constants of the upper inclined pad and the lower concrete are 3.5 and 5.0 respectively. The upper end of the crack is 5 cm away from the upper surface of the concrete, and its length and width are 3 cm and 0.4 cm. The layered back-projection imaging based on the refraction point approximation in the present invention is used to image the echo data, and the imaging results are as follows: Figure 6 As shown in the figure, it can be seen that the beginning and end of the crack are offset to the correct position, and there are several strong reflection echoes at the two end points, which can clearly reflect the shape and direction of the crack.

[0085] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0086] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for measuring concrete cracks by tilting a ground penetrating radar based on a mixed medium, characterized in that: include: S1. Discretely grid the imaging area of ​​the concrete structure to be measured, measure the relative dielectric constant of the concrete structure to be measured, and construct a right-angled triangular concrete pad of mixed medium; S2. Placing a radar antenna at the hypotenuse of the right-angled triangular concrete pad, moving the right-angled triangular concrete pad so that the radar antenna moves horizontally to start measuring grid points in the imaging area, and obtaining scattered echo data of the crack; S3. Constructing the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point of the measurement interface between the concrete structure and the right-angled triangular concrete pad; S4. The coordinates of the refraction point are solved by combining the refraction position relationship with the approximate solution formula of the refraction point; S5. Measure the coordinates of the refraction point K times until all grid points are traversed, obtain K scattered echo data and their two-way delays between the measurement target point and the radar antenna, and coherently superimpose all scattered echo data to image the measurement target point.

2. The method for measuring concrete cracks by tilting using a ground penetrating radar based on a mixed medium according to claim 1, wherein: The right-angled triangular concrete pad for constructing the mixed medium includes: The relative dielectric constant of the right-angled triangular concrete pad is expressed as: e c =V1ε1+V2ε2+…+V n e n Among them, ε1, ε2, …, ε n is the dielectric constant of the material that makes up the right-angled triangular concrete pad, V1, V2, ..., V n Indicates the volume percentage of the material, and V1+V2+…+V n =1.

3. The method for measuring concrete cracks by tilting using a ground penetrating radar based on a mixed medium according to claim 2, wherein: The method of constructing the refraction position relationship between the radar antenna, the measurement target point of the concrete structure, and the refraction point of the measurement interface between the concrete structure and the right-angled triangular concrete pad includes: The refraction position relationship is expressed as: Among them, (x k ,h r )、(x k ,0)、(x p ,z p ) are the positions of the radar antenna, the refraction point of the interface, and the measurement target point, respectively. i and θ r are the incident and exit angles of refraction, ε r is the ratio of the relative dielectric constants between the concrete structure and the right-angled triangular concrete pad, expressed as: Among them, ε a Represents the relative dielectric constant of the concrete structure.

4. The method for measuring concrete cracks by tilting using a ground penetrating radar based on a mixed medium as claimed in claim 3, wherein: The coordinates of the refraction point are solved by combining the refraction position relationship with an approximate solution formula of the refraction point, including: The coordinates of the refraction point are expressed as:

5. The method for measuring concrete cracks by tilting using a ground penetrating radar based on mixed media according to claim 4, wherein: The K times of measuring the scattered echo data between the target point and the radar antenna and the round-trip delay thereof include: The scattered echo data of the target point and the radar antenna measured K times is expressed as y k (t), the round-trip delay is expressed as: Among them, v1 and v2 are the propagation speeds of electromagnetic waves in the right-angled triangular concrete pad and concrete structure, respectively.

6. The method for measuring concrete cracks by tilting using a ground penetrating radar based on mixed media according to claim 5, characterized in that: The coherent superposition of all scattered echo data to image the measurement target point includes: The scattering intensity of the scattered echo data of the measurement target point at the Kth measurement is expressed as: e p,k =y k (t=τ p,k ) All scattered echo data are coherently superimposed to image the measurement target point: E p,k =∑y k (t=τ p,k )。

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