Reinforced concrete structure corrosion electrochemical nondestructive testing device and state recognition method

Abstract

The invention provides an electrochemical nondestructive testing device for corrosion of a reinforced concrete structure and a state recognition method, and belongs to the technical field of civil engineering. The device comprises an indirect impedance measuring instrument and an external four-electrode array sensor, wherein the external four-electrode array sensor is connected with the indirect impedance measuring instrument through an electrode lead; wherein the indirect impedance measuring instrument comprises an indirect impedance measuring module, a main control module, a relay module, a communication module, a voltage stabilizing circuit and a direct current power supply; the external four-electrode array sensor comprises an RE1 potential measuring electrode, a CE1 current injection electrode, a CE2 current injection electrode and an RE2 potential measuring electrode. The problem that drilling or sensor pre-embedding is needed in traditional electrochemical detection is avoided, and the defects that in a traditional method, the detection efficiency is low, the area is limited, and a sensor cannot be moved and replaced are overcome; the state identification method provided by the invention has the same accuracy for identifying the corrosion state of the reinforced concrete test piece as that of an embedded sensor.

Description

Technical Field

[0001] The invention relates to an electrochemical nondestructive detection device for corrosion of reinforced concrete structures and a state identification method, belonging to the technical field of civil engineering. Background Art

[0002] Corrosion damage to steel bars is one of the main factors leading to the degradation of the durability of steel-concrete structures, seriously threatening the safety and service life of engineering structures. Worldwide, the problem of corrosion damage causes huge economic losses every year, involving high costs such as repair, reinforcement and even reconstruction. Even more serious is that accidents of local damage or overall collapse of structures caused by severe corrosion of steel bars have occurred repeatedly, posing a major threat to people's lives and safety. Steel bar corrosion detection technology is the key to ensuring the safe service of steel-concrete structures, and directly affects durability assessment and repair decisions. Accurate and timely corrosion detection can optimize maintenance strategies, prevent structural failures, and significantly extend service life. Therefore, the development of efficient detection technology is of great significance to infrastructure maintenance.

[0003] Current corrosion detection technologies for reinforced concrete structures can be categorized into destructive testing and nondestructive testing. Traditional destructive testing methods require removing the concrete cover to expose the rebar. While this method allows for a visual assessment of corrosion conditions, it suffers from inherent drawbacks such as low detection efficiency and a tendency to cause secondary damage. Nondestructive testing technologies for rebar corrosion primarily include fiber Bragg grating (FBG), acoustic emission, radiographic imaging, and electrochemical detection. Because rebar corrosion is inherently an electrochemical process, electrochemical detection methods can directly monitor key parameters of the corrosion reaction, enabling early warning during the corrosion initiation phase. In contrast, other detection methods rely on physical damage characterization, such as corrosion product accumulation, rebar cross-sectional loss, or concrete cracking, making it difficult to effectively identify and warn of corrosion in its early stages. Electrochemical detection methods employ either embedded or external sensor placement. Embedded sensors typically utilize a small steel electrode made of the same material as the structural rebar as the working electrode for measurement. However, the corrosion state of the rebar dynamically evolves with the concrete's environmental parameters. This necessitates that embedded sensors be placed simultaneously with concrete pouring to ensure long-term electrochemical similarity with the rebar. This makes it impossible to replace embedded sensors, and reinforced concrete structures usually have a design life of more than 50 years, which places extremely high demands on the durability of the sensors and greatly limits the applicability of embedded sensors in existing structures. In addition, embedded sensors can only detect the corrosion of steel bars at the installation location. Since the development of corrosion in steel-concrete structures has obvious spatial differences, a comprehensive assessment of the corrosion status of the structure requires the dense deployment of a large number of sensors, which will significantly increase costs. Currently, external electrochemical detection mainly uses auxiliary electrodes and reference electrodes attached to the surface of concrete to evaluate the corrosion status by exciting current and measuring the potential of the steel bars. However, this method has two major technical bottlenecks: First, the current diffusion effect makes it difficult to accurately define the polarization area of ​​the steel bars, affecting the accuracy of data analysis. Second, it is necessary to drill holes locally in the concrete protective layer to connect the structural steel bar conductors, which limits the detection efficiency and the inspectable area.

[0004] Therefore, the invention of a removable external electrochemical detection technology that does not require an electrical connection to the structural reinforcement has significant engineering value. First, it avoids the damage to the protective layer caused by traditional methods, achieving true nondestructive testing. Second, the external design allows for the replacement of sensors at any time, effectively resolving the problem of the mismatch between the service life of embedded sensors and the design life of the structure. Most importantly, the free movement of the technology allows for integration with intelligent inspection robot systems, providing a new technical approach for automated and intelligent corrosion inspection of concrete structures. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and further provide an electrochemical nondestructive detection device for corrosion of reinforced concrete structures and a state identification method.

[0006] First, the present invention provides a new type of external electrochemical detection sensor that is attached to the concrete surface to measure indirect impedance, thereby evaluating the corrosion status of steel bars, breaking through the technical limitation of the traditional method that requires drilling holes to connect steel bars; second, based on the working principle of the sensor, a dedicated indirect impedance measurement circuit is innovatively designed; finally, an advanced indirect impedance analysis algorithm is established, which successfully realizes the decoupling analysis of geometric factors, concrete resistivity and steel-concrete interface impedance, thereby obtaining the steel-concrete interface impedance to accurately determine the corrosion status of steel bars.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A device for electrochemical nondestructive testing of corrosion of reinforced concrete structures, comprising: an indirect impedance measuring instrument and an external four-electrode array sensor, wherein the external four-electrode array sensor is connected to the indirect impedance measuring instrument via electrode wires; wherein:

[0009] The indirect impedance measuring instrument includes: an indirect impedance measurement module, a main control module, a relay module, a communication module, a voltage stabilizing circuit and a DC power supply; the DC power supply is connected to the voltage stabilizing circuit, and the voltage stabilizing circuit is electrically connected to the main control module, the communication module, the indirect impedance measurement module and the relay module respectively to supply power to the four modules; the signal input end of the main control module is connected to the signal output end of the indirect impedance measurement module and the communication module respectively; the signal output end of the main control module is connected to the signal input end of the indirect impedance measurement module, the communication module and the relay module respectively; the indirect impedance measurement module is connected to the external four-electrode array sensor through the relay module;

[0010] The external four-electrode array sensor includes: RE1 potential measurement electrode, CE1 current injection electrode, CE2 current injection electrode and RE2 potential measurement electrode; the RE1 potential measurement electrode, CE1 current injection electrode, CE2 current injection electrode and RE2 potential measurement electrode are respectively connected to the relay module of the indirect impedance meter through electrode wires.

[0011] An indirect impedance measurement module is used to excite and measure an external four-electrode array sensor; using the potential difference between the RE1 potential measurement electrode and the RE2 potential measurement electrode of the external four-electrode array sensor as a feedback control signal, the module automatically adjusts the current applied between the CE1 current injection electrode and the CE2 current injection electrode so that the potential difference signal between the RE1 potential measurement electrode and the RE2 potential measurement electrode is a sinusoidal signal of a set frequency and amplitude, and simultaneously converts the potential difference signal between the RE1 potential measurement electrode and the RE2 potential measurement electrode and the current signal between the CE1 current injection electrode and the CE2 current injection electrode into the measurement range of the main control module;

[0012] The main control module is used to run the indirect impedance measurement program, obtain the measurement instructions of the host computer through the communication module, input the excitation signal for setting the potential difference signal between the RE1 potential measurement electrode and the RE2 potential measurement electrode into the indirect impedance measurement module according to the instruction, and collect the potential difference signal between the RE1 potential measurement electrode and the RE2 potential measurement electrode and the current signal between the CE1 current injection electrode and the CE2 current injection electrode output by the indirect impedance measurement module, and transmit the data back to the host computer through the communication module;

[0013] A relay module, used to control the connection and disconnection of the electrodes of the external four-electrode array sensor and the indirect impedance measurement module;

[0014] Communication module, used for the indirect impedance measuring instrument to receive measurement instructions from the host computer and upload measurement data;

[0015] A voltage stabilizing circuit, used to convert the voltage of the DC power supply input into the digital power supply and analog power supply required by each circuit module of the indirect impedance measuring instrument;

[0016] DC power supply for powering the indirect impedance meter.

[0017] Preferably, the external four-electrode array sensor further comprises an electrode fixing bracket, and the RE1 potential measuring electrode, CE1 current injection electrode, CE2 current injection electrode and RE2 potential measuring electrode are detachably fixedly mounted on the electrode fixing bracket.

[0018] Preferably, the indirect impedance measurement module includes a low-pass filtering circuit, a potential measurement circuit, a potential signal conditioning circuit, a current measurement circuit, a current signal conditioning circuit and a feedback control circuit;

[0019] The input end of the low-pass filter circuit is connected to the output end of the main control module, the output end of the low-pass filter circuit is connected to the input end of the feedback control circuit, the output end of the potential measurement circuit is connected to the input end of the feedback control circuit and the potential signal conditioning circuit, the input end of the current measurement circuit is respectively connected to the output end of the feedback control circuit and the CE1 current injection electrode, and the output end of the current measurement circuit is connected to the input end of the current signal conditioning circuit; the output ends of the potential signal conditioning circuit and the current signal conditioning circuit are respectively connected to the analog-to-digital converter input end of the main control module.

[0020] The low-pass filter circuit is used to filter out the high-frequency components of the sinusoidal excitation signal input by the main control module at the interface Set, and then input the excitation signal into the non-inverting input terminal of the operational amplifier OP2 of the feedback control circuit;

[0021] A potential measurement circuit is used to measure the potentials of the RE1 potential measurement electrode and the RE2 potential measurement electrode, and convert the differential potential into a single-ended signal, which is input into the inverting input terminal of the operational amplifier OP2 of the feedback control circuit and the potential signal conditioning circuit respectively;

[0022] A potential signal conditioning circuit, used for converting a single-ended potential signal inputted by the potential measurement circuit into a measurement range within the analog-to-digital converter;

[0023] A current measurement circuit is configured to connect the output of the operational amplifier OP2 of the feedback control circuit and the CE1 current injection electrode, wherein the CE2 current injection electrode is connected to the ground line AGND of the indirect impedance measurement module; the current measurement circuit converts the current between the CE1 current injection electrode and the CE2 current injection electrode into a single-ended voltage signal and inputs the signal into the current signal conditioning circuit;

[0024] A current signal conditioning circuit, used for converting the signal input from the current measurement circuit into a measurement range within the analog-to-digital converter;

[0025] The feedback control circuit is used to automatically adjust the current applied between the CE1 current injection electrode and the CE2 current injection electrode so that the single-ended voltage signal input by the potential measurement circuit, which represents the potential difference between the RE1 potential measurement electrode and the RE2 potential measurement electrode, is consistent with the excitation signal input by the low-pass filter circuit.

[0026] Preferably, the main control module includes a single-chip microcomputer, a digital-to-analog converter and an analog-to-digital converter; the single-chip microcomputer controls the digital-to-analog converter to generate an excitation signal for indirect impedance measurement, and obtains the voltage measurement signal and current measurement signal of the external four-electrode array sensor through the analog-to-digital converter.

[0027] A state identification method based on an electrochemical nondestructive testing device for corrosion of reinforced concrete structures, the steps of the state identification method are as follows:

[0028] First, an external four-electrode array sensor was placed on the concrete surface of the steel-concrete structure, and the indirect impedance spectrum Z was measured by an indirect impedance meter. IDT ;

[0029] Then, an equivalent circuit model capable of calculating the indirect impedance spectrum is generated based on the geometric parameters of the steel-concrete structure and the external four-electrode array sensor. The equivalent circuit model calculates the indirect impedance spectrum Z according to the corrosion state parameter P of the steel-concrete structure. IDEC ;

[0030] Finally, the corrosion state parameter P is fitted nonlinearly until the measured indirect impedance spectrum Z IDT and the indirect impedance spectrum Z calculated by the equivalent circuit model IDEC The error E between them meets the set requirements; the calculation method of the error E is:

[0031]

[0032] in, Representative frequency Indirect impedance measurement under Represents the frequency of the equivalent circuit model when the corrosion state parameter P is input The calculated indirect impedance value under is the frequency number, N is the total number of frequencies, Re(·) is the operator for finding the real part of impedance, and Im(·) is the operator for finding the imaginary part of impedance.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The electrochemical nondestructive testing device and state identification method for reinforced concrete structure corrosion provided by the present invention avoid the problem of drilling or pre-embedded sensors required for traditional electrochemical testing, and address the shortcomings of traditional methods such as low detection efficiency, limited area, and non-removable and replaceable sensors. The measurement frequency range of the indirect impedance meter in the nondestructive testing device is 0.001Hz to 63Hz. Within the measurement range of 100~10000Ω, the relative error between the measured amplitude and the theoretical value of 95.63% of the data points is less than 5%, and the relative error between the measured phase angle and the theoretical value of 91.84% of the data points is less than 5% or the absolute error is less than 1°. The error of the equivalent circuit model for calculating the indirect impedance spectrum of the electrochemical state identification method is less than 3Ω, and the error of identifying the charge transfer resistance Rct of uniformly corroded steel-concrete is less than 6%. The proposed nondestructive testing device and state identification method have an accuracy of identifying the corrosion state of steel-concrete specimens comparable to that of embedded sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to the present invention.

[0036] Figure 2 This is a circuit block diagram of the indirect impedance measuring instrument of the present invention.

[0037] Figure 3 This is a circuit diagram of the indirect impedance measurement module of the present invention.

[0038] Figure 4 This is a flow chart of the corrosion electrochemical state identification method of the present invention.

[0039] Figure 5 Schematic diagram of the steel-concrete interface impedance model of the present invention.

[0040] Figure 6 Schematic diagram of the equivalent circuit model for calculating the indirect impedance of the steel-concrete structure according to the present invention.

[0041] Figure 7 Schematic diagram of the steel-concrete structure finite element model of the present invention; wherein:

[0042] Figure 7 (a) is a schematic side view of the finite element model of the steel-concrete structure of the present invention;

[0043] Figure 7 (b) is a schematic front view of the finite element model of the steel-concrete structure of the present invention.

[0044] Figure 8 Flowchart for calculating indirect impedance spectrum for the equivalent circuit model of the present invention.

[0045] Figure 9 This is a diagram of the experimental device for testing the performance of the indirect impedance measuring instrument of the present invention.

[0046] Figure 10 Schematic diagram of the performance test results of the indirect impedance measuring instrument of the present invention; wherein:

[0047] Figure 10 (a) is the amplitude-frequency characteristic curve of the indirect impedance measurement instrument performance test results;

[0048] Figure 10 (b) is the phase-frequency characteristic curve of the indirect impedance meter performance test results.

[0049] Figure 11 The equivalent circuit model of the present invention is shown in Figure 2. ct Indirect impedance spectrum calculated when ; where:

[0050] Figure 11 (a) Equivalent circuit model at different R ct Nyquist curve diagram when ;

[0051] Figure 11 (b) Equivalent circuit model at different R ct Amplitude-frequency characteristic curve when ;

[0052] Figure 11 (c) Equivalent circuit model at different R ct Phase-frequency characteristic curve when .

[0053] Figure 12 The equivalent circuit model of the present invention is in different Y 0Q Indirect impedance spectrum calculated when ; where:

[0054] Figure 12 (a) is the equivalent circuit model at different Y 0Q Nyquist curve diagram when ;

[0055] Figure 12(b) Equivalent circuit model at different Y 0Q Amplitude-frequency characteristic curve when ;

[0056] Figure 12 (c) Equivalent circuit model at different Y 0Q Phase-frequency characteristic curve when .

[0057] Figure 13 It is the indirect impedance spectrum calculated by the equivalent circuit model of the present invention at different β; wherein:

[0058] Figure 13 (a) Nyquist curve of the equivalent circuit model at different β;

[0059] Figure 13 (b) is the amplitude-frequency characteristic curve of the equivalent circuit model at different β;

[0060] Figure 13 (c) is the phase-frequency characteristic curve of the equivalent circuit model at different β.

[0061] Figure 14 The equivalent circuit model of the present invention is in different Y 0W Indirect impedance spectrum calculated when ; where:

[0062] Figure 14 (a) is the equivalent circuit model at different Y 0W Nyquist curve diagram when ;

[0063] Figure 14 (b) Equivalent circuit model at different Y 0W Amplitude-frequency characteristic curve when ;

[0064] Figure 14 (c) Equivalent circuit model at different Y 0W Phase-frequency characteristic curve when .

[0065] Figure 15 It is the indirect impedance spectrum calculated by the equivalent circuit model of the present invention at different ρ; wherein:

[0066] Figure 15 (a) Nyquist curve of the equivalent circuit model at different ρ;

[0067] Figure 15 (b) is the amplitude-frequency characteristic curve of the equivalent circuit model at different ρ;

[0068] Figure 15 (c) is the phase-frequency characteristic curve of the equivalent circuit model at different ρ.

[0069] Figure 16Schematic diagram of the non-uniform corrosion condition calculated by the equivalent circuit model of the present invention.

[0070] Figure 17 This is an indirect impedance spectrum calculated by the equivalent circuit model of the present invention under non-uniform corrosion conditions; wherein:

[0071] Figure 17 (a) Nyquist curve of the equivalent circuit model under non-uniform corrosion conditions;

[0072] Figure 17 (b) Amplitude-frequency characteristic curve of the equivalent circuit model under non-uniform corrosion conditions;

[0073] Figure 17 (c) is the phase-frequency characteristic curve of the equivalent circuit model under non-uniform corrosion conditions.

[0074] Figure 18 Schematic diagram of the Rct identification results of the non-uniform corrosion condition 1 of the present invention; wherein:

[0075] Figure 18 (a) is R of non-uniform corrosion condition 1 ct distribution map;

[0076] Figure 18 (b) is the indirect impedance spectrum of non-uniform corrosion condition 1.

[0077] Figure 19 Schematic diagram of the Rct identification results of the non-uniform corrosion condition 2 of the present invention; wherein:

[0078] Figure 19 (a) is R under non-uniform corrosion condition 2 ct distribution map;

[0079] Figure 19 (b) is the indirect impedance spectrum of non-uniform corrosion condition 2.

[0080] Figure 20 Schematic diagram of the Rct identification results of the non-uniform corrosion condition 3 of the present invention; wherein:

[0081] Figure 20 (a) is R under non-uniform corrosion condition 3 ct distribution map;

[0082] Figure 20 (b) is the indirect impedance spectrum of non-uniform corrosion condition 3.

[0083] Figure 21 Schematic diagram of the Rct identification results of the non-uniform corrosion condition 4 of the present invention; wherein:

[0084] Figure 21(a) is R of non-uniform corrosion condition 4 ct distribution map;

[0085] Figure 21 (b) is the indirect impedance spectrum of non-uniform corrosion condition 4.

[0086] Figure 22 This is a schematic diagram of using the nondestructive testing device of the present invention to perform indirect impedance measurement of steel-concrete structures.

[0087] Figure 23 The figure is a schematic diagram of measuring the potential gradient on the concrete surface of a steel-concrete structure using the corrosion nondestructive testing device of the present invention.

[0088] Figure 24 This is a schematic diagram of the electrochemical impedance spectroscopy measurement of the steel-concrete structure embedded sensor of the present invention.

[0089] Figure 25 The indirect impedance spectrum of the steel-concrete specimen measured by the corrosion nondestructive testing device of the present invention is shown in FIG.

[0090] Figure 25 (a) Nyquist plot of the steel-concrete specimen measured using a corrosion nondestructive testing device;

[0091] Figure 25 (b) is the amplitude-frequency characteristic curve of the steel-concrete specimen measured using the corrosion non-destructive testing device;

[0092] Figure 25 (c) is the phase-frequency characteristic curve of the steel-concrete specimen measured using the corrosion non-destructive testing device.

[0093] Figure 26 This is a three-electrode electrochemical impedance spectroscopy diagram measured by the embedded sensor of the steel-concrete specimen of the present invention; wherein:

[0094] Figure 26 (a) Three-electrode electrochemical impedance spectroscopy of RC-U0%;

[0095] Figure 26 (b) Three-electrode electrochemical impedance spectroscopy of RC-U0.5%;

[0096] Figure 26 (c) Three-electrode electrochemical impedance spectroscopy of RC-U3%;

[0097] Figure 26 (d) is the three-electrode electrochemical impedance spectroscopy of RC-Nonuniform.

[0098] Figure 27 This is the surface potential gradient diagram of the steel-concrete specimen concrete of the present invention.

[0099] Figure 28 The present invention is used to detect the non-uniform corrosion of steel-concrete specimen R by using the corrosion non-destructive testing method and embedded sensor. ct Spatial distribution map.

[0100] In the figure, 01 is an indirect impedance meter, 011 is an indirect impedance measurement module, 0111 is a low-pass filter circuit, 0112 is a potential measurement circuit, 0113 is a potential signal conditioning circuit, 0114 is a current measurement circuit, 0115 is a current signal conditioning circuit, 0116 is a feedback control circuit, 012 is a main control module, 0121 is a single-chip microcomputer, 0122 is a digital-to-analog converter, 0123 is an analog-to-digital converter, 013 is a relay module, 014 is a communication module, 015 is a voltage stabilizing circuit, and 016 is a DC power supply; 02 is an external four-electrode array sensor, 021 is a RE1 potential measurement electrode, 022 is a CE1 current injection electrode, 023 is a CE2 current injection electrode, 024 is a RE2 potential measurement electrode, 025 is an electrode fixing bracket, and 026 is an electrode wire; 03 is a reinforced concrete structure, 031 is concrete, and 032 is steel bars; 04 is an equivalent circuit model, and 05 is a standard test circuit. DETAILED DESCRIPTION

[0101] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method is given, but the protection scope of the present invention is not limited to the following embodiments.

[0102] like Figures 1 to 28 As shown, the electrochemical nondestructive detection device and state identification method for reinforced concrete structure corrosion involved in this embodiment include:

[0103] The present invention provides an electrochemical nondestructive testing device for corrosion of reinforced concrete structures. Figure 1As shown; the nondestructive testing device includes an indirect impedance measuring instrument 01 and an external four-electrode array sensor 02; the four-electrode array sensor 02 includes a RE1 potential measuring electrode 021 (hereinafter referred to as RE1 electrode), a CE1 current injection electrode 022 (hereinafter referred to as CE1 electrode), a CE2 current injection electrode 023 (hereinafter referred to as CE2 electrode), a RE2 potential measuring electrode 024 (hereinafter referred to as RE2 electrode), an electrode fixing bracket 025, and an electrode wire 026; the four-electrode array sensor 02 is attached to the concrete of the reinforced concrete structure 03. The surface of concrete 031 is measured; the four-electrode array sensor 02 is connected to the indirect impedance meter 01 via the electrode wire 026; the indirect impedance meter 01 first measures the open-circuit potential difference between the RE1 electrode 021 and the RE2 electrode 024, and then uses the potential signal between the RE1 electrode 021 and the RE2 electrode 024 as feedback control to automatically adjust the current between the CE1 electrode 022 and the CE2 electrode 023, so that the potential signal between the RE1 electrode 021 and the RE2 electrode 024 is the open-circuit potential difference superimposed on a sinusoidal perturbation excitation signal with a frequency of f:

[0104]

[0105] in, is the potential signal between RE1 electrode 021 and RE2 electrode 024, is the complex voltage amplitude containing voltage amplitude and phase information, j is the imaginary sign, ω is the angular frequency, t is time, and Re{·} is the operator for calculating the real part of the complex number;

[0106] Simultaneously measure the sinusoidal current signal between CE1 electrode 022 and CE2 electrode 023:

[0107]

[0108] in, is the current signal between CE1 electrode 022 and CE2 electrode 023, is the current complex amplitude containing current amplitude and phase information;

[0109] Thus calculating the frequency The indirect impedance of the steel-concrete structure 03 is as follows:

[0110]

[0111] The indirect impedance spectrum of the steel-concrete structure 03 was obtained by measuring the indirect impedance at different frequencies;

[0112] The circuit block diagram of the indirect impedance measuring instrument 01 is as follows Figure 2As shown; the indirect impedance measuring instrument 01 includes an indirect impedance measuring module 011, a main control module 012, a relay module 013, a communication module 014, a voltage stabilizing circuit 015, and a DC power supply 016; the DC power supply 016 supplies power to the indirect impedance measuring instrument 01; the voltage stabilizing circuit 015 converts the voltage input by the DC power supply 016 into the digital power supply and analog power supply required by each circuit module of the indirect impedance measuring instrument 01; the communication module 014 is used for the indirect impedance measuring instrument 01 to receive measurement instructions from the host computer and upload measurement data; the main control module 012 includes a single-chip microcomputer 0121, a digital-to-analog converter 0122 and an analog-to-digital converter 0123; the single-chip microcomputer 0121 controls the digital-to-analog converter 0122 to generate an excitation signal for indirect impedance measurement, and obtains the voltage measurement signal and current measurement signal of the external four-electrode array sensor 02 through the analog-to-digital converter 0123; the relay module 013 is used to control the connection and disconnection of the electrodes of the external four-electrode array sensor 02 and the indirect impedance measuring module 011;

[0113] The circuit schematic diagram of the indirect impedance measurement module 011 is as follows: Figure 3As shown; the indirect impedance measurement module 011 includes a low-pass filter circuit 0111, a potential measurement circuit 0112, a potential signal conditioning circuit 0113, a current measurement circuit 0114, a current signal conditioning circuit 0115, and a feedback control circuit 0116; the low-pass filter circuit 0111 filters out the high-frequency components of the sinusoidal excitation signal input by the main control module 012 at the interface Set, and then inputs the excitation signal into the non-inverting input terminal of the operational amplifier OP2 of the feedback control circuit 0112; the potential measurement circuit 0112 measures the potential of the RE1 electrode 021 and the RE2 electrode 024 of the external four-electrode array sensor 02, and converts the differential potential into a single-ended signal, which is input into the inverting input terminal of the operational amplifier OP2 of the feedback control circuit 0116 and the potential signal conditioning circuit 0113 respectively; the potential signal conditioning circuit 0113 converts the single-ended potential signal input by the potential measurement circuit 0112 into the inverting input terminal of the analog-to-digital converter 0123 within the measurement range; the current measurement circuit 0114 is connected to the output end of the operational amplifier OP2 of the feedback control circuit 0112 and the CE1 electrode 022 of the external four-electrode array sensor 02, and the CE2 electrode 023 is connected to the ground wire AGND of the indirect impedance measurement module 011; the current measurement circuit 0114 converts the current between the CE1 electrode 022 and the CE2 electrode 023 into a single-ended voltage signal and inputs it to the current signal conditioning circuit 0115; the current signal conditioning circuit 0115 converts the signal input by the current measurement circuit 0114 into the measurement range of the analog-to-digital converter 0123; the feedback control circuit 0116 automatically adjusts the current applied between the CE1 electrode 022 and the CE2 electrode 023, so that the single-ended voltage signal representing the potential difference between the RE1 electrode 021 and the RE2 electrode 024 input by the potential measurement circuit 0112 is consistent with the excitation signal input by the low-pass filter circuit 0111;

[0114] The present invention provides a method for identifying the electrochemical state of corrosion of reinforced concrete structures. Figure 4 As shown; First, the external four-electrode array sensor 02 is placed on the surface of the concrete 031 of the steel-concrete structure 03 to be measured, and the indirect impedance spectrum measurement Z is performed by the indirect impedance measuring instrument 01 IDT Then, an equivalent circuit model 04 for calculating the indirect impedance spectrum is generated based on the geometric parameters of the steel-concrete structure 03 and the external four-electrode array sensor 02; Then, the equivalent circuit model 04 calculates the indirect impedance spectrum Z of the steel-concrete structure 03 based on the corrosion state parameter P of the steel-concrete structure 03 IDEC Finally, a nonlinear fitting is performed on the parameter P until the measured indirect impedance spectrum Z IDT and the indirect impedance spectrum Z calculated by the equivalent circuit model 04 IDEC The difference E between them is less than the set error requirement E m , then the corrosion state parameter P of the steel-concrete structure 03 is obtained; the ZIDT and Z IDEC The difference E between them is calculated as:

[0115]

[0116] Where, Representative frequency Indirect impedance measurement under Represents the frequency of equivalent circuit model 04 when the corrosion state parameter P is input The indirect impedance calculation value under ; i is the frequency index, N is the total number of frequencies, Re(·) is the operator for the real part of the impedance, and Im(·) is the operator for the imaginary part of the impedance.

[0117] The corrosion state parameter P of the steel structure 03 includes the concrete resistivity and steel-concrete interface impedance model parameters; the steel-concrete interface impedance model is as follows Figure 5 As shown, the charge transfer resistance R ct (Ω·cm 2 ) is used to calculate the corrosion current density i of the steel bar using the Stern-Geary formula corr :

[0118]

[0119] Where B is the Stern-Geary constant; the constant phase angle element CPE is used to describe the non-ideal capacitance characteristics of the steel-concrete interface, and the impedance Z of the constant phase angle element is CPE for:

[0120]

[0121] Among them, Y 0Q (Ω -1 cm -2 ·s β ) is the basic admittance of CPE, β is a parameter that characterizes the non-ideal degree of steel-concrete interface capacitance, and ω (rad / s) is the angular frequency; Warburg impedance is used to characterize the influence of dissolved oxygen in concrete 031 on the diffusion process to steel 032. Warburg impedance Z W for:

[0122]

[0123] Among them, Y 0W (Ω -1 cm -2 ·s 0.5) is the basic admittance of the Warburg impedance; therefore, the steel-concrete interface impedance is calculated as:

[0124]

[0125] The equivalent circuit model 04 for calculating the indirect impedance spectrum is as follows Figure 6 As shown in the figure, the equivalent circuit model 04 discretizes the steel bar surface into h segments. The interface impedance, interface current and surface concrete potential of the steel bar segment x are expressed as Z x , I x and ; The internal potential of all steel sections is the same, denoted as The surface concrete potential of RE2 electrode 024 is the zero reference point, and the surface concrete potential of RE1 electrode 021 is denoted as V. The current that flows only in the concrete and does not enter the steel bars is denoted as J, and the direction from CE1 electrode 022 to CE2 electrode 023 is defined as positive. The steel bars are divided into two major regions: the interface current of the steel bars in Area A (segment 1 to g) flows into the concrete or originates from CE1 electrode 022, and the interface current of the steel bars in Area B (segment g+1 to h) flows into the concrete or originates from CE2 electrode 023. Assuming that the concrete has uniform resistivity within the measurement area of ​​the external four-electrode array sensor 02 and that the capacitive reactance effect of the concrete can be ignored within the measurement frequency range, the concrete is a linear system. According to the superposition principle of linear systems, we know that:

[0126]

[0127] Where I represents the reinforcement interface current matrix with dimension h×1, and its element I x represents the interface current of the steel bar segment x, whose positive direction is defined as flowing from the CE1 electrode 022 to the steel bar or from the steel bar to the CE2 electrode 023 in the concrete; J represents the current with dimension 1×1 that only transmits in the concrete and does not enter the steel bar; is the concrete potential matrix on the steel bar surface with dimension h×1, represents the surface concrete potential of the steel bar segment x, and V represents the surface concrete potential of RE1 electrode 021. The concrete impedance matrices K (h×h dimensions), M (h×1 dimensions), N (1×h dimensions), and L (1×1 dimensions) are composed of the geometric configuration, concrete resistivity, and the impedance distribution of the steel-concrete interface, K xy Reflects the unit current I y right Contribution of M x Reflects the unit current J Contribution, N y Reflects the unit current Iy The contribution of J to V, L represents the contribution of unit current J to V. Since concrete is a linear system, we can get:

[0128]

[0129] in, 、 、 and is the concrete impedance matrix under unit concrete resistivity, which is obtained by Figure 7 The steel-concrete structure finite element model shown is calculated. Figure 7 The steel-concrete interface is defined as insulation. A voltage is applied between CE1 electrode 022 and CE2 electrode 023. The finite element calculation results are extracted to calculate :

[0130]

[0131] Simultaneous calculation :

[0132]

[0133] in, is a matrix The element in row x, Φ RE1 and Φ RE2 are the mean surface concrete potentials of RE1 electrode 021 and RE2 electrode 024 in the calculation results; Φ x is the mean concrete potential on the surface of the reinforced section x; J is the current integral on the surface of CE1 electrode 022; is the concrete resistivity set by the finite element model; and It is only related to the geometric parameters. and Respectively expressed as:

[0134]

[0135]

[0136] Among them, A and B are h×h dimensional matrices, and C and D are 1×h dimensional matrices. These matrices depend only on the geometric parameters, but the parameter g is related to the uniformity of the steel-concrete interface impedance. The matrix is ​​formed by concatenating columns 1 to g of matrix A and columns g+1 to h of matrix B. The matrix is ​​formed by concatenating columns 1 to g of matrix C and columns g+1 to h of matrix D. xy Reflects the potential of the concrete surface in the x section when the unit current flows from the CE1 electrode 022 to the steel bar y section Contribution of B xy Reflects the effect of unit current flowing from the steel bar y section to the CE2 electrode 023 Contribution of C y Reflects the contribution of the unit current flowing from CE1 electrode 022 to the steel bar y segment to the concrete potential V on the surface of RE1 electrode 021, D y Reflects the contribution of unit current to V when it flows from the steel bar y section to the CE2 electrode 023. When calculating matrices A and C, Figure 7 The surface of electrode 023 in CE2 is set to insulation, the surface of segment y of the rebar is activated (the remaining segments are set to insulation), and a voltage is applied between electrode 022 in CE1 and the rebar. The finite element calculation results are extracted and the matrices A and C are calculated as follows:

[0137]

[0138]

[0139] Among them, A xy is the element in the xth row and yth column of matrix A, C y is the element in the yth column of matrix C; i y represents the current between CE1 electrode 022 and steel bar y segment. When calculating matrices B and D, Figure 7 The surface of electrode 022 in CE1 is set to insulation, the surface of segment y of the rebar is activated (the rest of the segments are set to insulation), and a voltage is applied between electrode 023 in CE2 and the rebar. The finite element calculation results are extracted and the matrices B and D are calculated as follows:

[0140]

[0141]

[0142] Among them, B xy represents the element in the xth row and yth column of matrix B, D y is the element in the yth column of matrix D; i y represents the current between CE2 electrode 023 and steel bar segment y. The steel bar interface current matrix I and the steel bar surface concrete potential matrix in Equation (9) are Respectively expressed as:

[0143]

[0144]

[0145] Among them, I A and They are the current and potential matrices of the steel bars in area A, with dimensions g×1; I B and are the current and potential matrices representing the steel bars in zone B, respectively, with dimensions p×1, where p=hg; Equation (9) can be transformed into:

[0146]

[0147] Among them, K AA is a submatrix of K with rows 1 to g and columns 1 to g, and dimensions g×g; K AB is a submatrix of K with dimensions g×p, from row 1 to row g, from column g+1 to column h; K BA is a submatrix of the matrix K with the g+1th row to the hth row and the 1st column to the gth column, and the dimension is p×g; K BB is the submatrix of matrix K from row g+1 to row h, column g+1 to column h, with dimension p×p; M A is a submatrix of M with dimensions g×1 from the 1st row to the gth row; M B It is the submatrix p=hg of the matrix M with dimensions of p×1 from the g+1th row to the hth row; N A is a submatrix of the matrix N with dimensions of 1×g from the 1st column to the gth column; N B It is a submatrix of the matrix N with dimensions of 1×p from the g+1th column to the hth column, where p=hg;

[0148] The steel-concrete interface impedance matrix is ​​represented by a diagonal matrix Z of dimension h×h:

[0149]

[0150] Among them, the steel-concrete interface impedance matrix Z is a diagonal matrix, Z A and Z B are the diagonal matrices representing the interface impedances of the steel bars in area A and area B, is the submatrix of matrix Z with dimensions g×g, from row 1 to row g and from column 1 to column g; is the submatrix of matrix Z with dimensions p×p, from row g+1 to row h, and from column g+1 to column h; It is a matrix of dimension g×p, with all elements set to 0; It is a matrix of dimension p×g, with all elements set to 0;

[0151] Z xx Denotes the interfacial impedance of the reinforcement segment x:

[0152]

[0153] in, is the complex frequency, , is the imaginary number symbol, is pi, is the frequency, is the reinforcement section number;

[0154] Based on the relationship between the steel bar interface current and the overpotential, it can be obtained that:

[0155]

[0156] in, is the potential of the electronic conductor phase inside the steel bar, is a matrix of dimension h×1, with all elements being 1;

[0157] During the indirect impedance spectrum measurement, the net current of the steel bar is 0, so:

[0158]

[0159] in, is a matrix of dimension 1×g, with all elements being 1; is a matrix of dimension 1×p, with all elements being 1;

[0160] According to equations (21), (24) and (25), we can calculate:

[0161]

[0162] Among them, I A and I B are the interface current matrices of the steel bars in area A and area B, with dimensions of g×1 and p×1, respectively, where p=hg; K AA is a submatrix of K with rows 1 to g and columns 1 to g, and dimensions g×g; K AB is a submatrix of K with dimensions g×p, from row 1 to row g, from column g+1 to column h; K BA is a submatrix of the matrix K with the g+1th row to the hth row and the 1st column to the gth column, and the dimension is p×g; K BB is the submatrix of matrix K with dimensions p×p, from row g+1 to row h, and from column g+1 to column h; is a matrix of dimension g×1, with all elements being 1; is a matrix of dimension p×1, with all elements being 1; is a matrix of dimension 1×g, with all elements being 1; is a matrix of dimension 1×p, with all elements being 1; is a matrix of dimension (h+1)×1, with all elements being 0; J is the value of the concrete current that does not enter the steel bars; φ is the potential of the electronic conductor phase inside the steel bars;

[0163] Furthermore, the current response under potential excitation V can be calculated:

[0164]

[0165] in, is a function of the undetermined parameter g, representing the total current between the CE1 current injection electrode 022 and the CE2 current injection electrode 023. The value of g, i.e., the boundary between the steel bars in area A and the steel bars in area B, is related to the uniformity of the steel-concrete interface impedance and is difficult to solve directly. Substituting all possible g values ​​into Equation (27) for calculation, the maximum value obtained is the correct value:

[0166]

[0167] Among them, I m and θ are the current response The magnitude and phase angle of is the imaginary number sign. Then, the indirect impedance can be calculated:

[0168]

[0169] In summary, the process of calculating the indirect impedance spectrum of the equivalent circuit model 04 is as follows: Figure 8 As shown; First, according to the geometric shape of the external four-electrode array sensor 02 and the steel-concrete structure 03, the matrices A, B, C, D are calculated using the finite element model and formulas (11) to (18). and ; Then, calculate each measurement frequency according to equations (22) and (23) The impedance matrix Z of the steel-concrete structure under the condition of g is calculated according to equations (10), (13) and (14); the matrix Q under each value of g is calculated according to equations (26) and (27). , and according to formula (28) we can get The maximum value is the true value; finally, each measurement frequency is calculated according to formula (29) Indirect impedance , that is, the indirect impedance spectrum is obtained.

[0170] Example 1

[0171] In this embodiment, calibrated resistors and capacitors are used to construct a series of standard test circuits 05 for verifying the function and measurement accuracy of the indirect impedance meter 01, such as Figure 9 As shown in Figure 1, resistors R1, R2, R5, R6, and R7 simulate the concrete resistance, R3 and R4 simulate the interfacial charge transfer resistance of the steel bars, and capacitors C1 and C2 simulate the interfacial capacitance of the steel-concrete interface. The resistance and capacitance values ​​of all components are calibrated using an LCR meter. Table 1 summarizes the parameters of standard test circuits A to G. The theoretical indirect impedance of standard test circuit 05 can be calculated using the following formula:

[0172]

[0173]

[0174] Table 1 Standard test circuit parameters

[0175]

[0176] The test results of indirect impedance meter 01 are as follows Figure 10 As shown, for all standard test circuits 05, the theoretical values ​​and the measured values ​​using the indirect impedance meter 01 show a high degree of agreement. The measurement frequency range of the indirect impedance meter 01 is 0.001 Hz to 63 Hz. Within the measurement range of 100 to 10,000 Ω, the relative error between the measured amplitude and the theoretical value was less than 5% for 95.63% of the data points, and the relative error between the measured phase angle and the theoretical value was less than 5% or the absolute error was less than 1 degree for 91.84% of the data points.

[0177] Example 2

[0178] In this embodiment, the equivalent circuit model 04 calculates the following Figure 7 The indirect impedance spectrum of the steel-concrete structure with the geometric shape shown in the figure under uniform corrosion conditions is compared with the indirect impedance spectrum calculated by the finite element method to verify the accuracy of the equivalent circuit model 04; the finite element model for calculating the indirect impedance spectrum is as follows Figure 7As shown, the concrete measures 10 × 10 × 60 cm and contains longitudinal reinforcement with a diameter of 1.2 cm. The surfaces of electrodes 022 (CE1) and 023 (CE2) are circles with a diameter of 2 cm, while the surfaces of electrodes 021 (RE1) and 024 (RE2) are circles with a diameter of 1 cm. The finite element mesh consists of free tetrahedral elements, with a maximum element size of 1 mm on the electrode surfaces, 2 mm on the reinforcement surfaces, and 8 mm in the concrete matrix. The potential distribution in the concrete is described by the Laplace equation:

[0179]

[0180] in, is the gradient operator, is the concrete potential;

[0181] Under external AC excitation with a frequency of ω, the AC disturbance of the concrete potential is:

[0182]

[0183] in, It is a complex phase quantity representing the amplitude and phase of the concrete potential disturbance, which is a function of frequency and position. The potential disturbance of the electronic conductor phase inside the steel bar is:

[0184]

[0185] in, It is a complex phasor representing the amplitude and phase of the potential disturbance inside the steel bar. It is only related to the frequency and has nothing to do with the position. This is because the electronic conductor phase inside the steel bar can be regarded as an equipotential body. The current disturbance at the steel-concrete interface is:

[0186]

[0187] in, Represents the concrete potential on the steel bar surface. Z represents the steel-concrete interface impedance, which is defined as a function of frequency and position according to formula (8). In the finite element model, the current between CE1 electrode 022 and CE2 electrode 023 is defined as I, and the concrete potential on the surface of RE1 electrode 021 in the calculation results is extracted. and RE2 electrode 024 surface concrete potential , and then calculate the indirect impedance of the steel-concrete structure at each frequency:

[0188]

[0189] Equivalent circuit model 04 and finite element model calculation Figure 7 The indirect impedance of the steel-concrete structure with the geometry shown in the figure under uniform corrosion conditions is as follows: Figures 11 to 15 In the equivalent circuit model 04, the steel bar surface is discretized into a semi-cylindrical element with a length of 1 cm and a parameter h = 120. Figure 11 Shown in Y 0Q = 2×10 -5 Ω -1 cm -2 ·s β , β = 1, Y 0W =+∞, ρ= 120 Ω·m when different R ct Indirect impedance spectroscopy under ; Figure 12 Shown in R ct = 2×10 4 Ω·cm 2 , β =1, Y 0W = +∞, ρ= 120 Ω·m Different Y 0Q Indirect impedance spectroscopy under ; Figure 13 Shown in Y 0Q = 2×10 -5 Ω -1 cm -2 ·s β , Y 0W = +∞, R ct =1×10 5 Ω·cm 2 , indirect impedance spectra under different β when ρ=120 Ω·m; Figure 14 Shown in Y 0Q = 2×10 -4 Ω -1 cm -2 ·s β , β = 1, R ct =1×10 3 Ω·cm 2 , different Y when ρ=120 Ω·m 0W Indirect impedance spectroscopy under ; Figure 15 Shown in Y 0Q = 1 × 10 -4 Ω -1 cm -2 ·s β , β = 1, Y 0W = +∞, R ct = 2×10 4 Ω·cm 2 Indirect impedance spectra under different ρ. Figures 11 to 15On the one hand, it shows that the indirect impedance is sensitive to the corrosion state parameter P of the steel-concrete structure, and it is feasible to solve the corrosion state by fitting the indirect impedance spectrum; on the other hand, it shows that the calculation accuracy of the equivalent circuit model 04 is comparable to that of the finite element model, and the impedance error is less than 3Ω. The calculation speed of the equivalent circuit model 04 is much higher than that of the finite element model, and it is more suitable for Figure 4 Iteratively solve the corrosion state parameter P of steel-concrete structure.

[0190] Example 3

[0191] In this embodiment, the equivalent circuit model 04 calculates the indirect impedance spectrum of the steel-concrete structure under non-uniform corrosion conditions and compares it with the indirect impedance spectrum calculated by the finite element model. Figure 16 As shown in the figure, the anode area is 5 cm long and is located 16 cm from one end of the steel-concrete structure model, and the rest is the cathode area. Figure 17 Shows the cathode region R ct =10 6 Ω·cm 2 When the anode area is different R ct The indirect impedance spectrum under the condition of ρ=120 Ω·m, Y 0Q = 2×10 -5 Ω -1 cm -2 ·s β , β = 1, Y 0W = +∞. The results show that the equivalent circuit model 04 is suitable for the calculation of indirect impedance spectrum under non-uniform corrosion conditions.

[0192] Example 4

[0193] This example shows Figure 4 The state identification method shown in the figure identifies the corrosion state parameter P of the steel-concrete structure under uniform corrosion. The corrosion state parameter P includes the concrete resistivity and steel-concrete interface impedance parameter R ct 、Y 0Q ,β,Y 0W The indirect impedance spectrum of the steel-concrete structure is calculated using the finite element model in Example 2. Figure 4 and Figure 8 The equivalent circuit model 04 shown in the figure iteratively fits and identifies the corrosion state parameter P set by the finite element model. The comparison results of the set and identified corrosion state parameter P are shown in Table 2. Cases 1 to 7 represent passive and low-speed corrosion states and are not affected by the diffusion process (Warburg impedance can be ignored). The remaining cases correspond to active corrosion states with different corrosion rates, and their electrochemical processes are all affected by the diffusion process. In all cases, Figure 4The state identification methods shown above all achieve high-precision identification of the corrosion state parameter P. ct In terms of the number of samples, the largest recognition error occurs in Example 5, with a relative error of 6%.

[0194] Table 2 Identification of corrosion state parameter P under uniform corrosion conditions

[0195]

[0196] Example 5

[0197] This example shows Figure 4 The state recognition method shown in the figure is effective in identifying the corrosion state of the steel-concrete structure with non-uniform corrosion. This embodiment assumes that there is only one anode area in the detection area. ct The interface impedance parameters of the outer anode region and the cathode region are consistent. The finite element model is used to obtain the R near a single anode region. ct The distribution law is used as a priori knowledge for the identification procedure. In the finite element model, the Butler-Volmer equation is used to describe the polarization curve parameters of the steel bar:

[0198]

[0199]

[0200] Where η represents the overpotential of the steel bar; E represents the potential of the steel bar; E corr represents the open circuit potential of the steel bar; i represents the interface current of the steel bar; β a and β c represent the anodic Tafel slope and the cathodic Tafel slope, respectively; is the corrosion exchange current density. Discretize the steel bar surface, define the Butler-Volmer equations for the anode region and cathode region according to Equations (37) and (38), respectively, and solve the potential E of each discrete steel bar unit through finite element method, and then solve the charge transfer resistance R of each discrete steel bar unit. ct :

[0201]

[0202] in, The net current density at the steel-concrete interface; then, according to R ct The spatial distribution of and other corrosion state parameters are used to calculate the indirect impedance spectrum of the steel-concrete structure using the finite element model in Example 2. Figure 4 The method described above uses the equivalent circuit model 04 to fit the indirect impedance spectrum generated by the finite element model to identify the R ctAssuming that the R of the steel-concrete structure steel bars in the detection area is ct The spatial distribution is:

[0203]

[0204] Where x represents the position of the discrete steel bar unit, with the center of the anode area as the origin; x1 is the position of the edge of the anode area; x2 is the farthest point of the detection area from the center of the anode area; and Represents R at positions x1 and x2 respectively ct ; The dimensionless parameters k and n characterize the R between positions x1 and x2 ct The shape of the transition zone curve. In the case of non-uniform corrosion in this embodiment, Figure 4 The corrosion state parameter P identified by the state identification method is a uniformly distributed Y 0Q and β, and describes R ct Spatial distribution parameters 、 The origin position of the anode area and x1 and x2 are prior knowledge and can be obtained from the concrete surface potential gradient map in engineering practice. Figures 18 to 21 Demonstrates the ability to identify non-uniform corrosion ct Spatial distribution example. Figure 18 The polarization curve parameters of the anode region are A3 in Table 3, and the parameters of the cathode region are A4. Figure 18 The dot diagram in (a) is the R calculated by formula (39) ct Spatially distributed set values. Figure 18 The dot diagram in (b) is set to R ct Indirect impedance spectrum generated by the finite element model described in Example 2 under spatial distribution. Figures 18 to 21 , parameter Y 0Q and β are uniformly set to Y 0Q = 2×10 -5 Ω -1 cm -2 ·s β and β = 0.9. Figure 18 (b) The midline diagram is based on Figure 4 The state identification method uses the indirect impedance spectrum obtained by fitting the equivalent circuit model 04. Figure 18 The line graph in (a) is Figure 4 The method identifies R ct Spatial distribution. Similarly, Figure 19 The polarization curve parameters of the anode region are A3 in Table 3, and the parameters of the cathode region are A4, but the anode position is different from Figure 18 different. Figure 20The polarization curve parameters of the anode region are A2 in Table 3, and the parameters of the cathode region are A4. Figure 21 The polarization curve parameters of the anode region are A1 in Table 3, and the parameters of the cathode region are A4.

[0205] Table 3 Polarization curve parameters of steel bars

[0206]

[0207] Example 6

[0208] In this example, indirect impedance spectrum measurement is performed on reinforced concrete specimens to evaluate the corrosion state, and its accuracy is verified by embedded sensors. Figure 22 As shown. The CE1 electrode 022 and CE2 electrode 023 of the external four-electrode array sensor 02 are graphite disc electrodes with a diameter of 2 cm. The RE1 electrode 021 and RE2 electrode 024 are MnO2 reference electrodes with a diameter of 1 cm. The MnO2 reference electrode uses graphite coated with a MnO2 functional layer as an electrode, alkaline slurry as an electrolyte, and hardened cement slurry as an encapsulation layer. Each electrode of the external four-electrode array sensor 02 is wrapped with fabric. Before measurement, the fabric is fully soaked with 0.1M KCl solution to ensure that the electrode establishes good contact with the concrete surface. This embodiment prepares four geometric dimensions and Figure 7 The same reinforced concrete specimens were used, with the longitudinal reinforcement being HRB400 steel bars with a diameter of 1.2 cm. To verify the effectiveness of indirect impedance in evaluating the corrosion state, three embedded sensors were buried at 10 cm, 30 cm, and 50 cm along the length of each specimen. The embedded sensors consisted of a working area of ​​7.5 cm. 2 The test specimens consist of a small-sized steel bar electrode and a reference electrode, and the auxiliary electrode is external. The four steel-concrete specimens are numbered RC-U0%, RC-U0.5%, RC-U3% and RC-Nonuniform, respectively. RC-U0%, RC-U0.5% and RC-U3% are cast with concrete containing 0%, 0.5% and 3% of NaCl by weight of cement, respectively, while the RC-Nonuniform specimens are cast in sections. The section from 6cm to 14cm of the specimen is cast with concrete containing 3% of NaCl by weight of cement, and the remaining concrete does not contain NaCl. All specimens were demoulded 48 hours after casting and cured in a 60℃ steam environment for 3 days. After the curing was completed, 0.1 mA / cm 2Accelerated corrosion was conducted for 3 hours at an anodic current density of 100 nm. During the accelerated corrosion process, the working electrode of the embedded sensor was short-circuited to the steel bar. The potential gradient on the concrete surface provides prior information on the anode position in the non-uniform corrosion process, which is used as the equivalent circuit model for fitting the indirect impedance spectrum. The potential gradient on the concrete surface is measured using two external reference electrodes, such as Figure 23 As shown in the figure, one reference electrode is fixed in position and the other electrode moves on the concrete surface. The measurement points in the anode area of ​​the RC-Nonuniform specimen are encrypted. To verify the effect of indirect impedance on the corrosion state evaluation, electrochemical impedance spectroscopy measurements were performed on the embedded sensors in the steel-concrete specimen, as shown in the figure. Figure 24 The external CE electrode is a graphite plate electrode, and a wet fabric is used to establish good contact with the concrete surface.

[0209] The indirect impedance spectrum measurement results of steel-concrete structure are as follows Figure 25 As shown in the figure, the dot graph is the measurement result, and the line graph is the fitting result of the equivalent circuit model 04. The potential gradient on the concrete surface is as follows: Figure 27 As shown, the surface potentials of RC-U0%, RC-U0.5%, and RC-U3% are approximately uniformly distributed, and are fitted according to the uniform corrosion assumption shown in Example 4. The potential of the anode area of ​​RC-Nonuniform is significantly lower than that of the cathode area, with a potential difference of nearly 120mV, and is fitted according to the non-uniform corrosion assumption shown in Example 5. The electrochemical impedance spectrum of the embedded sensor is shown in Figure 26 The dot graph is the measurement result and the line graph is the fitting result. The corrosion state parameters identified by the external sensor and the embedded sensor are shown in Table 4. The three embedded sensors buried in the specimen RC-U0% all confirmed that the working electrode was in a passivation state. ct More than 7×10 6 Ω·cm 2 Although the R ct 6.7×10 5 Ω·cm 2 , but according to the classification standard in Table 5, it is still in the passivation range and the corrosion rate can be ignored. ctThe value is highly consistent with that of embedded sensor 2, but higher than that of embedded sensors 1 and 3. Since the chloride concentration threshold for steel corrosion in concrete is in the range of 0.2%-0.8% of cement mass, there is a large discreteness. The chloride ion content of the RC-U0.5% specimen is within this range, and the initial state of the steel surface roughness, oxide layer, etc. also has a large discreteness. Although the NaCl distribution in the RC-U0.5% specimen is uniform, due to the above reasons, its corrosion state distribution still shows smaller-scale non-uniformity. This leads to the relative difference in the measurement results of the external sensor and the embedded sensor. In the RC-U3% specimen, the R ct The values ​​are highly consistent, indicating that the steel bar is in a high corrosion rate state. ct Spatial distribution Figure 28 As shown, good consistency is shown.

[0210] Table 4 Corrosion status identification parameters of steel-concrete structures

[0211]

[0212] Table 5 Corrosion state classification

[0213]

[0214] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An electrochemical nondestructive testing device for corrosion of reinforced concrete structures, characterized in that: The nondestructive testing device comprises: an indirect impedance measuring instrument (01) and an external four-electrode array sensor (02), wherein the external four-electrode array sensor (02) is connected to the indirect impedance measuring instrument (01) via an electrode wire (026); wherein: The indirect impedance measuring instrument (01) comprises: an indirect impedance measuring module (011), a main control module (012), a relay module (013), a communication module (014), a voltage stabilizing circuit (015) and a direct current power supply (016); the direct current power supply (016) is connected to the voltage stabilizing circuit (015), the voltage stabilizing circuit (015) is electrically connected to the main control module (012), the communication module (014), the indirect impedance measuring module (011) and the relay module (013) respectively, and supplies power to the four modules; the signal input end of the main control module (012) is connected to the signal output end of the indirect impedance measuring module (011) and the communication module (014) respectively; the signal output end of the main control module (012) is connected to the signal input end of the indirect impedance measuring module (011), the communication module (014) and the relay module (013) respectively; the indirect impedance measuring module (011) is connected to the external four-electrode array sensor (02) via the relay module (013); The external four-electrode array sensor (02) comprises: an RE1 potential measurement electrode (021), a CE1 current injection electrode (022), a CE2 current injection electrode (023), and an RE2 potential measurement electrode (024); the RE1 potential measurement electrode (021), the CE1 current injection electrode (022), the CE2 current injection electrode (023), and the RE2 potential measurement electrode (024) are respectively connected to the relay module (013) of the indirect impedance measurement instrument (01) via electrode wires (026).

2. The electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to claim 1, characterized in that: An indirect impedance measurement module (011) is used for exciting and measuring an external four-electrode array sensor (02); using the potential difference between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) of the external four-electrode array sensor (02) as a feedback control signal, automatically adjusting the current applied between the CE1 current injection electrode (022) and the CE2 current injection electrode (023), so that the potential difference signal between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) is a sinusoidal signal of set frequency and amplitude, and simultaneously converting the potential difference signal between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) and the current signal between the CE1 current injection electrode (022) and the CE2 current injection electrode (023) into a measurement range of the main control module (012); A main control module (012) is used to run an indirect impedance measurement program, obtain a measurement instruction from a host computer through a communication module (014), input an excitation signal for setting a potential difference signal between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) to the indirect impedance measurement module (011) according to the instruction, collect the potential difference signal between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) and the current signal between the CE1 current injection electrode (022) and the CE2 current injection electrode (023) output by the indirect impedance measurement module (011), and transmit the data back to the host computer through the communication module (014); A relay module (013) for controlling the connection and disconnection between the electrodes of the external four-electrode array sensor (02) and the indirect impedance measurement module (011); A communication module (014) is used for the indirect impedance measuring instrument (01) to receive measurement instructions from a host computer and upload measurement data; A voltage stabilizing circuit (015) is used to convert the voltage input by the DC power supply (016) into a digital power supply and an analog power supply required by each circuit module of the indirect impedance measuring instrument (01); A DC power supply (016) is used to power the indirect impedance measuring instrument (01).

3. The electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to claim 1, characterized in that: The external four-electrode array sensor (02) further comprises an electrode fixing bracket (025), on which the RE1 potential measuring electrode (021), the CE1 current injection electrode (022), the CE2 current injection electrode (023), and the RE2 potential measuring electrode (024) are detachably fixed.

4. The electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to claim 2, characterized in that: The indirect impedance measurement module (011) comprises a low-pass filter circuit (0111), a potential measurement circuit (0112), a potential signal conditioning circuit (0113), a current measurement circuit (0114), a current signal conditioning circuit (0115), and a feedback control circuit (0116); The input end of the low-pass filter circuit (0111) is connected to the output end of the main control module (012), the output end of the low-pass filter circuit (0111) is connected to the input end of the feedback control circuit (0116), the output end of the potential measurement circuit (0112) is connected to the input end of the feedback control circuit (0116) and the potential signal conditioning circuit (0113), the input end of the current measurement circuit (0114) is respectively connected to the output end of the feedback control circuit (0116) and the CE1 current injection electrode (022), the output end of the current measurement circuit (0114) is connected to the input end of the current signal conditioning circuit (0115); and the output ends of the potential signal conditioning circuit (0113) and the current signal conditioning circuit (0115) are respectively connected to the input end of the analog-to-digital converter (0123) of the main control module (012).

5. The electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to claim 4, characterized in that: A low-pass filter circuit (0111) is used to filter out high-frequency components from a sinusoidal excitation signal inputted from a main control module (012) at an interface Set, and then input the excitation signal into a non-inverting input terminal of an operational amplifier OP2 of a feedback control circuit (0116); A potential measurement circuit (0112) is used to measure the potentials of the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024), and convert the differential potential into a single-ended signal, which is input to the inverting input terminal of the operational amplifier OP2 of the feedback control circuit (0116) and the potential signal conditioning circuit (0113). A potential signal conditioning circuit (0113) is used to convert a single-ended potential signal inputted by the potential measuring circuit (0112) into a measurement range of an analog-to-digital converter (0123); The current measurement circuit (0114) is used to connect the output end of the operational amplifier OP2 of the feedback control circuit (0116) and the CE1 current injection electrode (022), and the CE2 current injection electrode (023) is connected to the ground wire AGND of the indirect impedance measurement module (011); the current measurement circuit (0114) converts the current between the CE1 current injection electrode (022) and the CE2 current injection electrode (023) into a single-ended voltage signal and inputs the signal into the current signal conditioning circuit (0115); A current signal conditioning circuit (0115) is used to convert the signal input by the current measuring circuit (0114) into a measurement range of the analog-to-digital converter (0123); The feedback control circuit (0116) is used to automatically adjust the current applied between the CE1 current injection electrode (022) and the CE2 current injection electrode (023) so that the single-ended voltage signal input by the potential measurement circuit (0112) representing the potential difference between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) is consistent with the excitation signal input by the low-pass filter circuit (0111).

6. The electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to claim 2, characterized in that: The main control module (012) comprises a single-chip microcomputer (0121), a digital-to-analog converter (0122), and an analog-to-digital converter (0123); the single-chip microcomputer (0121) controls the digital-to-analog converter (0122) to generate an excitation signal for indirect impedance measurement, and obtains a voltage measurement signal and a current measurement signal of an external four-electrode array sensor (02) through the analog-to-digital converter (0123).

7. A method for identifying the state of the electrochemical nondestructive testing device for corrosion of reinforced concrete structures according to any one of claims 1 to 6, characterized in that: The steps of the state recognition method are as follows: First, the external four-electrode array sensor (02) is placed on the concrete surface of the steel-concrete structure, and the indirect impedance spectrum Z is measured by the indirect impedance meter (01). IDT ; Then, an equivalent circuit model capable of calculating the indirect impedance spectrum is generated based on the geometric parameters of the steel-concrete structure and the external four-electrode array sensor (02), and the equivalent circuit model calculates the indirect impedance spectrum Z based on the corrosion state parameter P of the steel-concrete structure. IDEC ; Finally, the corrosion state parameter P is fitted nonlinearly until the measured indirect impedance spectrum Z IDT and the indirect impedance spectrum Z calculated by the equivalent circuit model IDEC The error E between them meets the set requirements; the calculation method of the error E is: in, Representative frequency Indirect impedance measurement under Represents the frequency of the equivalent circuit model when the corrosion state parameter P is input The calculated indirect impedance value under is the frequency number, N is the total number of frequencies, Re(·) is the operator for finding the real part of impedance, and Im(·) is the operator for finding the imaginary part of impedance.

8. The state recognition method according to claim 7, characterized in that: The equivalent circuit model is established as follows: (1) According to the geometric parameters of the steel-concrete structure and the external four-electrode sensor, the steel bar surface is discretized into h segments under the condition of uniform resistivity, and the concrete impedance matrix A, B, C, D, 、 ,The effects of geometric parameters on the concrete impedance matrix are obtained through the finite element model; When calculating matrices A and C, the interface of the CE2 current injection electrode (023) in the finite element model is set to insulation, the steel bar segment y is activated, and the remaining segments are set to insulation. A unit voltage is applied between the CE1 current injection electrode (022) and the steel bar, and the voltage and current calculation results in the finite element model are extracted. The matrices A and C are calculated as follows: Among them, A is a matrix of dimension h×h, C is a matrix of dimension 1×h, A xy is the element in the xth row and yth column of matrix A, C y is the element in the yth column of matrix C; i y represents the current value between the CE1 current injection electrode (022) and the steel bar section y, Φ RE1 and Φ RE2 are the extracted mean concrete potentials on the surface of RE1 potential measurement electrode (021) and RE2 potential measurement electrode (024), Φ x is the average potential of concrete on the steel bar surface extracted from section x, is the concrete resistivity set by the finite element model; When calculating matrices B and D, the interface of the CE1 current injection electrode (022) in the finite element model is set to insulation, the steel bar segment y is activated, and the remaining segments are set to insulation; a unit voltage is applied between the CE2 current injection electrode (023) and the steel bar, and the voltage and current calculation results in the finite element model are extracted. Matrices B and D are calculated according to the following formula: Among them, B is a matrix of dimension h×h, D is a matrix of dimension 1×h, B xy represents the element in the xth row and yth column of matrix B, is the element in the y-th column of matrix D; represents the current value between the CE2 current injection electrode (023) and the steel bar section y, Φ RE1 and Φ RE2 are the extracted mean concrete potentials on the surface of RE1 potential measurement electrode (021) and RE2 potential measurement electrode (024), Φ x is the average potential of concrete on the steel bar surface extracted from section x, is the concrete resistivity set by the finite element model; Calculate the matrix and When all the steel segment interfaces in the finite element model are set to be insulated, a unit voltage is applied between the CE1 current injection electrode (022) and the CE2 current injection electrode (023), and the voltage and current calculation results in the finite element model are extracted. The matrix is ​​calculated as follows: and : in, is a matrix of dimension h×1, is a matrix of dimension 1×1, is a matrix The element of row x, J is the current value extracted between the CE1 current injection electrode (022) and the CE2 current injection electrode (023), Φ RE1 and Φ RE2 are the extracted mean concrete potentials on the surface of RE1 potential measurement electrode (021) and RE2 potential measurement electrode (024), Φ x is the average potential of concrete on the steel bar surface extracted from section x, is the concrete resistivity set by the finite element model; (2) The discrete steel bar segments are divided into two categories: segments 1 to g are steel bars in zone A, and segments g+1 to h are steel bars in zone B. The interface current of the steel bars in zone A flows into the concrete or comes from the CE1 current injection electrode (022), and the interface current of the steel bars in zone B flows into the concrete or comes from the CE1 current injection electrode (022). The current flowing into or coming from CE2 in the concrete is injected into the electrode (023), g is the unknown number to be solved, and the matrix is ​​calculated based on g and : in, The matrix is ​​formed by concatenating columns 1 to g of matrix A and columns g+1 to h of matrix B. The matrix is ​​formed by concatenating columns 1 to g of matrix C and columns g+1 to h of matrix D to calculate the concrete impedance matrix K, M, N, and L: Among them, the concrete resistivity is one of the corrosion state parameters P to be identified; (3) Calculate the steel-concrete interface impedance matrix based on the corrosion state parameter P: Among them, the steel-concrete interface impedance matrix Z is a diagonal matrix, Z A and Z B are the diagonal matrices representing the interface impedances of the steel bars in area A and area B, is a matrix of dimension p×g, all elements are 0; It is a matrix of dimension g×p, with all elements being 0; the steel-concrete interface impedance matrix Z is determined by the corrosion state parameter P, which is to be identified; (4) When the potential between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024) is V, calculate the current between the CE1 current injection electrode (022) and the CE2 current injection electrode (023): Among them, I A and I B are the interface current matrices of the steel bars in area A and area B, with dimensions of g×1 and p×1, respectively, where p=hg; K AA is a submatrix of K with rows 1 to g and columns 1 to g, and dimensions g×g; K AB is a submatrix of K with dimensions g×p, from row 1 to row g, from column g+1 to column h; K BA is a submatrix of the matrix K with the g+1th row to the hth row and the 1st column to the gth column, and the dimension is p×g; K BB is the submatrix of matrix K with dimensions p×p, from row g+1 to row h, and from column g+1 to column h; is a matrix of dimension g×1, with all elements being 1; is a matrix of dimension p×1, with all elements being 1; is a matrix of dimension 1×g, with all elements being 1; is a matrix of dimension 1×p, with all elements being 1; It is a matrix of dimension (h+1)×1, with all elements being 0; J is the value of the concrete current that does not enter the steel bars; is the potential of the electronic conductor phase inside the steel bar; is a function of the unknown parameter g, representing the total current between the CE1 current injection electrode (022) and the CE2 current injection electrode (023); the total current is calculated by exhaustive method for all g values. , its maximum value is the correct solution, yes The amplitude of is the imaginary number symbol, yes The phase angle of Finally, calculate the indirect impedance obtained from the equivalent circuit model: in, is the indirect impedance obtained from the equivalent circuit model, for The maximum value of .

9. The state recognition method according to claim 8, characterized in that: The corrosion state parameter P is the concrete resistivity under uniform corrosion state. , steel-concrete interface charge transfer resistance R ct 、Warburg impedance basic admittance Y 0W , basic admittance Y of non-ideal capacitance at steel-concrete interface 0Q , non-ideal capacitance coefficient β; the corrosion state parameter is the concrete resistivity under the non-uniform corrosion state , basic admittance Y of non-ideal capacitance at steel-concrete interface 0Q , non-ideal capacitance coefficient β and the description of R ct Spatial distribution parameters 、 , k, n; the R ct The spatial distribution function of is: Where x represents the position of the discrete steel bar segment, with the center of the anode area as the origin; x1 is the position of the edge of the anode area; x2 is the farthest point of the detection area from the center of the anode area; and Represents R at positions x1 and x2 respectively ct ; The dimensionless parameters k and n characterize the R between positions x1 and x2 ct Transition zone curve shape.

10. The state recognition method according to claim 9, characterized in that: The calculation method of the steel-concrete interface impedance matrix is: Among them, the steel-concrete interface impedance matrix Z is a diagonal matrix of dimension h×h, Z xx R represents the interface impedance of the steel bars in section x, ct (x), Y 0W (x), Y 0Q (x) and β(x) represent the charge transfer resistance of the steel-concrete interface, the basic admittance of Warburg impedance, the basic admittance of non-ideal capacitance of the steel-concrete interface, and the non-ideal capacitance coefficient of the steel bar in section x, respectively. is the complex frequency, , is the imaginary number symbol, is pi, It's the frequency.

Images