Porosity electromagnetic nondestructive testing method, medium and system capable of eliminating moisture influence

Abstract

The invention belongs to the technical field of concrete detection, and particularly relates to a porosity electromagnetic nondestructive testing method, medium and system capable of eliminating moisture influence, and the method comprises the following steps: preparing test pieces with different moisture contents by adopting a to-be-tested medium, and obtaining the porosity of each test piece; obtaining the dielectric constant and the conductivity of each test piece through a ground penetrating radar, and constructing a data set containing the dielectric constant, the conductivity and the porosity; deriving a dielectric model under a water-containing condition and a conductivity model under an unsaturated state, and simultaneously eliminating water content parameters in the models to obtain a porosity detection model containing unknown parameters; the data set is substituted into the porosity detection model for fitting, and the porosity detection model which is not affected by moisture is obtained. Compared with the prior art, the method has the advantages that the problem that in the prior art, the GPR testing of the concrete porosity is easily interfered by moisture is solved, and the influence of moisture on calculation in electromagnetic nondestructive testing is eliminated.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete detection, and in particular relates to a porosity electromagnetic nondestructive detection method, medium and system for eliminating the influence of moisture. Background Art

[0002] As a key parameter for measuring the performance and durability of concrete structures, porosity profoundly affects the strength, permeability and service life of concrete. Therefore, the development of high-precision non-destructive testing technology to evaluate and control the pore structure of concrete is of great significance for improving the long-term reliability and durability of engineering structures.

[0003] Non-destructive testing (NDT) is a method of testing and evaluating materials or structures by physical, chemical or mechanical means without destroying the target object. Its significant advantage is that the testing process will not damage the structure, which is particularly suitable for engineering applications that require high reliability and long-term use. The current mainstream non-destructive testing methods include acoustic wave, elastic wave and electromagnetic wave technology, among which electromagnetic testing has attracted widespread attention for its high efficiency, portability and reliability. Electromagnetic testing technology represented by ground penetrating radar (GPR) inverts dielectric parameters by analyzing the attenuation of electromagnetic waves by the medium to evaluate the porosity of the material. However, moisture has a significant impact on dielectric properties and can easily interfere with test results. Therefore, how to effectively reduce moisture interference has become a key issue that needs to be urgently solved in the current electromagnetic non-destructive testing technology for concrete porosity. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the above problems and provide a porosity electromagnetic nondestructive testing method, medium and system that eliminate the influence of moisture, so as to solve the problem that the GPR test of concrete porosity in the prior art is easily disturbed by moisture. This scheme eliminates the influence of moisture on the calculation in electromagnetic nondestructive testing.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The first aspect of the present invention discloses a porosity electromagnetic nondestructive testing method for eliminating the influence of moisture, comprising the following steps:

[0007] T1: Prepare specimens with different water contents using the medium to be tested, and obtain the porosity of each specimen;

[0008] T2: The dielectric constant and conductivity of each specimen are obtained through ground penetrating radar, and a data set containing dielectric constant, conductivity and porosity is constructed;

[0009] T3: Take water as one of the components of the medium to be tested to derive the dielectric model under water-containing conditions and the conductivity model under unsaturated conditions. Combine the dielectric model and the conductivity model to eliminate the water content parameter in the model and obtain a porosity detection model containing unknown parameters.

[0010] T4: Substituting the data set obtained in step T2 into the porosity detection model obtained in step T3 to fit the unknown parameters, thereby obtaining a porosity detection model that is not affected by moisture;

[0011] T5: The dielectric constant and conductivity of the medium to be tested are obtained by ground penetrating radar, and the porosity of the medium to be tested is calculated by substituting the porosity detection model obtained in step T4.

[0012] Preferably, the method is used for electromagnetic nondestructive testing of concrete porosity.

[0013] Preferably, in step T1, the porosity of each specimen is obtained by a water absorption method.

[0014] Preferably, in step T2,

[0015] According to the time domain signal of the reflected wave collected by the ground penetrating radar, the dielectric constant of the specimen is obtained by calculating the propagation speed of the wave in the specimen;

[0016] The attenuation coefficient is estimated based on the amplitude attenuation of the reflected wave signal, and the conductivity of the specimen is obtained in combination with the dielectric constant.

[0017] Preferably, in step T3, the dielectric model under water-containing conditions is:

[0018]

[0019] Where: ε t represents the dielectric constant of concrete, ε w represents the dielectric constant of water, ε j It represents the dielectric constant of the solid part in the medium to be measured, ξ represents the water content, and φ represents the porosity.

[0020] Preferably, in step T3, the conductivity model is:

[0021]

[0022] Where: t represents the electrical conductivity of concrete, σ p represents the conductivity of the pore solution, ξ c represents the critical moisture content, m represents the Archie index, and η represents an unknown parameter.

[0023] Preferably, in step T4, the porosity detection model not affected by moisture is:

[0024] φ=Aσ t B +Cε t ′+D;

[0025] Where:

[0026]

[0027] in, ε t represents the dielectric constant of concrete, ε w represents the dielectric constant of water, ε j represents the dielectric constant of the solid part of the medium to be measured, φ represents the porosity, σ t represents the electrical conductivity of concrete, σ p represents the conductivity of the pore solution, ξ c represents the critical moisture content, m represents the Archie index, and η represents an unknown parameter.

[0028] Preferably, the method further comprises:

[0029] T4-1: Use the least squares method to optimize the unknown parameters of the porosity detection model fitting obtained in step T4.

[0030] Preferably, in step T2, the acquired data set is divided into sample set A and sample set B in a ratio of 4:1, wherein sample set A is used to perform steps T3 and T4 to fit unknown parameters, and sample set B is used to perform step T4-1 to optimize unknown parameters.

[0031] Preferably, step T4-1 includes the following steps:

[0032] T4-1-1: Define the loss function as the sum of squared errors;

[0033] T4-1-2: Solve the partial derivative of the loss function with respect to the parameters and update the parameters Where α is the learning rate;

[0034] T4-1-3: Iterate and optimize until convergence using the gradient descent method.

[0035] A second aspect of the present invention discloses a computer-readable storage medium, wherein the computer-readable storage medium includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute any of the above methods.

[0036] The third aspect of the present invention discloses a porosity electromagnetic nondestructive testing system, comprising: one or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and are configured to be executed by the one or more processors, and the one or more programs are used to execute any of the methods described above.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention uses machine learning combined with ground penetrating radar detection technology to measure the porosity of concrete through dielectric constant and conductivity parameters, which not only effectively eliminates the influence of moisture on electromagnetic data, but also can quickly and conveniently perform non-destructive testing of the porosity of existing concrete structures, achieving good results in detection accuracy, fast detection speed and high accuracy. In actual application, the test results can be quickly obtained, and once an abnormal situation is found, it can be quickly located and remedied, greatly improving the efficiency of concrete porosity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the process of electromagnetic nondestructive testing method for porosity;

[0040] Figure 2 Schematic diagram of the process flow for least squares optimization. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In the following description, if there are any matters not covered, they can be implemented using the existing technology or conventional methods in the field.

[0043] The dielectric property of concrete is one of the electromagnetic properties that characterize concrete materials, generally expressed as the dielectric constant ε Φ Or relative dielectric constant ε r The smaller the relative dielectric constant, the easier it is for microwaves to penetrate the material. The dielectric properties of non-metallic materials are usually expressed by dielectric constant and dielectric loss (or loss tangent). The dielectric constant is a measure of the material's ability to store electromagnetic energy. The larger the dielectric constant, the stronger the material's ability to store electromagnetic energy; while the dielectric loss (or loss tangent) is a measure of the material's loss of electromagnetic energy. Both are functions of the frequency of the electromagnetic wave. Mathematically, the two are written in complex form as the complex dielectric constant, that is:

[0044] ε Φ=ε0(ε′-jε″);

[0045] The relative dielectric constant is taken as:

[0046] εr=εΦ / ε0=ε′-jε″=ε′(1-j×tanδ);

[0047] Where:

[0048] ε Φ represents the dielectric constant of the propagation medium;

[0049] ε0 represents the dielectric constant of free space;

[0050] ε′ represents the potential energy stored in the material in the form of electromagnetic field;

[0051] j represents the imaginary unit;

[0052] ε″ represents the energy lost in the material in the form of heat;

[0053] Tanδ represents the loss tangent, which is the proportion of electromagnetic wave energy lost in the material as heat energy.

[0054] The imaginary part of the complex dielectric constant can be correlated with the conductivity of the material, reflecting the loss characteristics of the material, and is used to evaluate the conductivity, polarization loss and other properties of the material. The relationship between the imaginary part of the complex dielectric constant ε″ and the material conductivity σ can be expressed by the following formula:

[0055] σ=ωε0ε″;

[0056] Where:

[0057] ω is the angular frequency, ω=2πf, where f is the frequency of the signal.

[0058] In the process of nondestructive testing of geological radar, the electromagnetic waves emitted by the radar instrument are sent into the medium in the form of broadband pulses, reflected by the medium and returned to the surface, and then the echo signal is received by the radar's receiving antenna. When electromagnetic waves propagate in the medium, their path, electromagnetic field strength and waveform vary with the dielectric properties and geometric dimensions of the medium they pass through. Therefore, studying the dielectric properties of the target body is of great significance to the results of radar detection. To accurately describe the internal structure of the medium, it is necessary to analyze the information contained in the echo signal received by the radar, so the dielectric properties of the medium are an important factor affecting the results of radar detection.

[0059] The composite dielectric model is a theoretical model used to describe the dielectric properties of multi-component composite materials. It predicts the equivalent dielectric response of the material by integrating the dielectric properties of each component and its distribution, structure and proportion. The model can relate the microscopic composition of the material (such as the proportion of solid, liquid and gas phases) to the macroscopic electromagnetic response, and is used to detect information such as the moisture content, porosity and internal defects of the material.

[0060] According to the composite dielectric model theory, concrete can be considered as a three-phase composite medium composed of solid, liquid and gas. However, the traditional concrete composite dielectric model can only describe the solid-gas two-phase composite structure, and water is a polar molecule, which has a great influence on the dielectric constant.

[0061] Nondestructive testing of concrete can monitor its quality and provide a basis for subsequent maintenance. The dielectric constant and electromagnetic properties are inferred by analyzing the propagation speed, reflection intensity and attenuation characteristics of the radar waveform, and the porosity is calculated using a composite dielectric model. However, moisture affects the detection accuracy, so it is particularly important to develop an electromagnetic nondestructive testing method for porosity that is not affected by moisture.

[0062] Based on the above principles, the present invention provides an electromagnetic nondestructive testing method for concrete porosity that is not affected by moisture, such as Figure 1 As shown, the method comprises the following steps:

[0063] S1: Prepare concrete specimens and collect electromagnetic signal data sets of concrete specimens;

[0064] S101: Preparation of concrete specimens:

[0065] According to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete", standard size specimens were made. During the specimen making process, the controlled variable method was used to obtain concrete specimens with different porosities. By controlling the determined water-cement ratio, aggregate and curing conditions:

[0066] The concrete is mixed to form concrete specimens, and then cured to obtain concrete specimens with different porosities. Each specimen is numbered and grouped into three specimens to facilitate the subsequent concrete porosity test and the corresponding data during the ground penetrating radar non-destructive test.

[0067] S102: Testing Ground Penetrating Radar:

[0068] The cured specimens were immersed in water until the weight no longer changed, and the water in the specimens was controlled to evaporate in an oven to obtain concrete specimens with different moisture contents;

[0069] Concrete specimens with different moisture contents were taken out, and a 900MHz antenna was selected to perform ground penetrating radar nondestructive testing on them using the profile method. The echo information was recorded corresponding to the concrete specimen number to obtain an electromagnetic signal data set.

[0070] S2: collect concrete porosity data sets of concrete specimens;

[0071] Ground penetrating radar was used to detect concrete specimens with different moisture contents, and the porosity test was carried out using the water absorption method. The porosity information was recorded corresponding to the concrete specimen numbers to obtain the concrete porosity dataset.

[0072] S3: Processing electromagnetic signal dataset and concrete porosity dataset;

[0073] S301: Based on the reflected wave time domain signal collected by the ground penetrating radar, the dielectric constant of the measured medium is derived by calculating the wave propagation speed in the medium; the amplitude attenuation of the reflected wave signal is further analyzed to estimate the attenuation coefficient, and the conductivity of the medium is calculated in combination with the known dielectric constant, and finally the dielectric constant and conductivity data set of the concrete medium is obtained;

[0074] S302: Divide the dielectric constant and conductivity data sets obtained in S301 into two groups at a ratio of 4:1, one of which is marked as sample set A and the other is marked as sample set B;

[0075] S303: Mark the sample set A and the sample set B respectively, so that each set of dielectric constant and conductivity corresponds to the concrete strength obtained from the actual test.

[0076] S4: Derive concrete porosity detection model and training parameters that are not affected by moisture;

[0077] S401: Taking water as one of the components of concrete medium, the dielectric model of concrete under water-containing conditions is derived, namely:

[0078]

[0079] Where:

[0080] ε t represents the dielectric constant of concrete;

[0081] ε w Represents the dielectric constant of water, generally taken as 78;

[0082] ε j Indicates the dielectric constant of the solid part of the medium to be measured;

[0083] ξ represents the moisture content;

[0084] φ represents the porosity;

[0085] make

[0086] S402: Based on Archie's law, the conductivity model of concrete under unsaturated state is derived, namely:

[0087] σ t =ησ p ·(ξ-ξ c ) (m-1) ;

[0088] Where: t Indicates the electrical conductivity of concrete;

[0089] σ p represents the conductivity of the pore solution;

[0090] ξ c represents the critical moisture content;

[0091] m represents the Archie index;

[0092] η represents an unknown parameter (empirical parameter).

[0093] S403: The dielectric constant model formula is combined with the conductivity model formula, the moisture content parameter ξ is eliminated, and the model is simplified to obtain a concrete porosity detection model, which includes an unknown parameter η, that is:

[0094] φ=Aσ t B +Cε t ′+D;

[0095] Where:

[0096]

[0097] S404: Using the sample set A obtained in S302 as model training data, inputting the sample set A, fitting unknown parameters, and obtaining a concrete porosity detection model that is not affected by moisture.

[0098] S5: Validate and tune the model;

[0099] S501: using the sample set B obtained in S302 as an input parameter and inputting it into the concrete porosity nondestructive testing model not affected by the moisture content obtained in S403;

[0100] S502: comparing the output result of the concrete porosity nondestructive testing model with the corresponding porosity data in sample set B;

[0101] S503: Based on the comparison results, the least square method is used to optimize the fitting parameters in the concrete porosity nondestructive testing model, such as Figure 2 As shown, the specific steps include:

[0102] S50301: Define the loss function as the sum of squared errors;

[0103] S50302: Solve the partial derivative of the loss function with respect to the parameter, and update the parameter θ←θ-α▽L(θ), where α is the learning rate;

[0104] S50303: Optimize parameters continuously through gradient descent iteration until convergence or error is small (less than a set threshold).

[0105] The sample set A of the training data is input into the concrete porosity nondestructive testing model to fit the unknown parameters of the model, and the fit of the concrete porosity nondestructive testing model is verified using the sample set B of the test data. The sum of squares of the model errors is calculated as the loss function for the subsequent optimization of the model parameters using the least squares method.

[0106] The least squares method is used to optimize the model parameters, and the loss function is defined as the sum of squared errors. The partial derivatives of the loss function with respect to the parameters are solved to find the direction and size of the parameter adjustment. Through the gradient descent iterative algorithm, the parameters are continuously adjusted to minimize the loss function and improve the accuracy of the model.

[0107] S6: Application model;

[0108] A detection path is planned in advance on the surface of the water-containing concrete structure, and a ground penetrating radar with a 900MHz antenna is used to detect the structure along the planned path to obtain echo information, which is processed according to S301. The processed data is input into the non-destructive detection model of the porosity of concrete not containing water to obtain the porosity of the concrete.

[0109] In summary, the present invention uses machine learning combined with ground penetrating radar detection technology to measure the porosity of concrete through dielectric constant and conductivity parameters, which not only effectively eliminates the influence of moisture on electromagnetic data, but also can quickly and conveniently perform non-destructive testing of the porosity of existing concrete structures, achieving good results in detection accuracy, fast detection speed and high accuracy. When applied, once an abnormal situation is found, it can be quickly located and remedied, greatly improving the efficiency of concrete porosity detection.

[0110] In other embodiments, the porosity electromagnetic nondestructive testing method can also be used for other multi-component composite media. When conducting test processing, a test piece made of the corresponding medium is used, and when performing calculations, the parameters of the corresponding medium are used.

[0111] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A porosity electromagnetic nondestructive testing method for eliminating the influence of moisture, characterized in that: The steps include: T1: Prepare specimens with different water contents using the medium to be tested, and obtain the porosity of each specimen; T2: Obtain the dielectric constant and conductivity of each specimen through ground penetrating radar, and construct a data set containing dielectric constant, conductivity and porosity; T3: Take water as one of the components of the medium to be tested to derive the dielectric model under water-containing conditions and the conductivity model under unsaturated conditions. Combine the dielectric model and the conductivity model to eliminate the water content parameter in the model and obtain a porosity detection model containing unknown parameters. T4: Substituting the data set obtained in step T2 into the porosity detection model obtained in step T3 to fit the unknown parameters, thereby obtaining a porosity detection model that is not affected by moisture; T5: The dielectric constant and conductivity of the medium to be tested are obtained by ground penetrating radar, and the porosity of the medium to be tested is calculated by substituting the porosity detection model obtained in step T4.

2. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 1, characterized in that: In step T2, According to the time domain signal of the reflected wave collected by the ground penetrating radar, the dielectric constant of the specimen is obtained by calculating the propagation speed of the wave in the specimen; The attenuation coefficient is estimated based on the amplitude attenuation of the reflected wave signal, and the conductivity of the specimen is obtained in combination with the dielectric constant.

3. The porosity electromagnetic nondestructive testing method for eliminating the influence of moisture according to claim 1 is characterized in that: In step T3, the dielectric model under water conditions is: Where: ε t represents the dielectric constant of concrete, ε w represents the dielectric constant of water, ε j It represents the dielectric constant of the solid part in the medium to be measured, ξ represents the water content, and φ represents the porosity.

4. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 1, characterized in that: In step T3, the conductivity model is: s t =is p ·(x-x c ) (m-1) ; Where: t represents the electrical conductivity of concrete, σ p represents the conductivity of the pore solution, ξ c represents the critical moisture content, m represents the Archie index, and η represents an unknown parameter.

5. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 1, characterized in that: In step T4, the porosity detection model not affected by moisture is: φ=Aσ t B +Ce t ′+D; Where: in, ε t represents the dielectric constant of concrete, ε w represents the dielectric constant of water, ε j represents the dielectric constant of the solid part of the medium to be measured, φ represents the porosity, σ t represents the electrical conductivity of concrete, σ p represents the conductivity of the pore solution, ξ c represents the critical moisture content, m represents the Archie index, and η represents an unknown parameter.

6. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 1, characterized in that: The method further comprises: T4-1: Use the least squares method to optimize the unknown parameters of the porosity detection model fitting obtained in step T4.

7. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 6, characterized in that: In step T2, the acquired data set is divided into sample set A and sample set B in a ratio of 4:1, wherein sample set A is used to perform steps T3 and T4 to fit unknown parameters, and sample set B is used to perform step T4-1 to optimize unknown parameters.

8. The electromagnetic nondestructive testing method for porosity to eliminate the influence of moisture according to claim 6, characterized in that: Step T4-1 includes the following steps: T4-1-1: Define the loss function as the sum of squared errors; T4-1-2: Solve the partial derivative of the loss function with respect to the parameters and update the parameters Where α is the learning rate; T4-1-3: Iterate and optimize until convergence using the gradient descent method.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein when the program is executed, the device where the computer-readable storage medium is located is controlled to execute the method according to any one of claims 1 to 8.

10. A porosity electromagnetic nondestructive testing system, characterized in that: include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs are used to execute the method according to any one of claims 1 to 8.

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