Electrochemical Non-destructive Testing Device and Condition Identification Method for Corrosion of Reinforced Concrete Structures

Abstract

This invention provides an electrochemical non-destructive testing device and condition identification method for corrosion of reinforced concrete structures, belonging to the field of civil engineering technology. The invention includes: an indirect impedance measuring instrument and an external four-electrode array sensor. The external four-electrode array sensor is connected to the indirect impedance measuring instrument via electrode wires. The indirect impedance measuring instrument includes: an indirect impedance measurement module, a main control module, a relay module, a communication module, a voltage regulator circuit, and a DC power supply. The external four-electrode array sensor includes: a RE1 potential measuring electrode, a CE1 current injection electrode, a CE2 current injection electrode, and a RE2 potential measuring electrode. This invention avoids the problem of drilling or pre-embedding sensors required in traditional electrochemical detection, and solves the defects of traditional methods such as low detection efficiency, limited area, and non-replaceable sensors. The condition identification method proposed in this invention has an accuracy comparable to embedded sensors in identifying the corrosion condition of reinforced concrete specimens.

Description

Technical Field

[0001] This invention relates to an electrochemical non-destructive testing device and condition identification method for corrosion of reinforced concrete structures, belonging to the field of civil engineering technology. Background Technology

[0002] Corrosion damage to reinforcing steel bars is one of the leading causes of durability degradation in reinforced concrete structures, seriously threatening the safety and service life of engineering structures. Globally, corrosion damage results in enormous economic losses annually, involving high costs for repair, reinforcement, and even reconstruction. More seriously, accidents caused by severe steel bar corrosion leading to localized damage or complete structural collapse occur frequently, posing a significant threat to public safety. Steel bar corrosion detection technology is crucial for ensuring the safe service life of reinforced concrete structures, directly impacting durability assessment and repair decisions. Accurate and timely corrosion detection can optimize maintenance strategies, prevent structural failure, and significantly extend service life. Therefore, developing efficient detection technologies is of great significance for infrastructure maintenance.

[0003] Currently, corrosion detection technologies for reinforced concrete structures can be divided into destructive testing and non-destructive testing methods. Traditional destructive testing methods require removing the concrete cover to expose the reinforcing steel. While this provides a direct assessment of corrosion, it suffers from inherent drawbacks such as low detection efficiency and the potential for secondary damage. Non-destructive testing technologies for steel corrosion mainly include fiber optic grating methods, acoustic emission technology, X-ray imaging technology, and electrochemical detection methods. Since steel corrosion is essentially an electrochemical process, electrochemical detection methods can directly monitor key parameters of the corrosion reaction, enabling early warning even in the initiation stage of corrosion. In contrast, other detection methods rely on the characterization of physical damage such as corrosion product accumulation, steel section loss, or concrete cracking, making effective identification and early warning difficult in the early stages of corrosion. Electrochemical detection methods can employ embedded and external sensor placement. Embedded sensors typically use small steel electrodes made of the same material as the structural steel reinforcement as the working electrode for measurement. However, the corrosion state of the steel reinforcement dynamically evolves with the concrete environment parameters, requiring the embedded sensor to be implanted simultaneously during concrete pouring to ensure its long-term electrochemical similarity to the structural steel reinforcement. This makes embedded sensors unreplaceable, while reinforced concrete structures typically have a design life of over 50 years, placing extremely high demands on sensor durability and significantly limiting the applicability of embedded sensors in existing structures. Furthermore, embedded sensors can only detect corrosion at the installation location. Due to the significant spatial variability in corrosion development in reinforced concrete structures, a comprehensive assessment of the corrosion state requires a dense deployment of numerous sensors, which significantly increases costs. Currently, external electrochemical detection primarily uses auxiliary and reference electrodes attached to the concrete surface, assessing corrosion status by excitation current and measuring the potential of the reinforcing steel. However, this method suffers from two main technical bottlenecks: first, the current diffusion effect makes it difficult to accurately define the polarization region of the reinforcing steel, affecting data analysis accuracy; second, it requires drilling holes in the concrete cover to connect structural reinforcing steel wires, limiting detection efficiency and the detectable area.

[0004] Therefore, inventing a portable external electrochemical detection technology that does not require electrical connection to the structural steel reinforcement has significant engineering value. Firstly, it avoids the damage to the protective layer caused by traditional methods, achieving truly non-destructive testing. Secondly, the external design allows for easy sensor replacement, effectively solving the problem of mismatch between the lifespan of embedded sensors and the structural design lifespan. Most importantly, its free mobility 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 this invention is to solve the problems existing in the prior art, and to provide an electrochemical non-destructive testing device and a condition identification method for corrosion of reinforced concrete structures.

[0006] First, this invention provides a novel external electrochemical detection sensor that is attached to the concrete surface to measure indirect impedance, thereby assessing the corrosion status of reinforcing steel, breaking through the technical limitation of traditional methods that require drilling holes to connect the reinforcing steel. Second, based on the working principle of this sensor, a dedicated indirect impedance measurement circuit is innovatively designed. Finally, an advanced indirect impedance analysis algorithm is established, successfully achieving 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 reinforcing steel.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] An electrochemical non-destructive testing device for corrosion of reinforced concrete structures, the non-destructive testing device 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 measuring module, a main control module, a relay module, a communication module, a voltage regulator circuit, and a DC power supply; the DC power supply is connected to the voltage regulator circuit, which is electrically connected to the main control module, the communication module, the indirect impedance measuring module, and the relay module to supply power to these four modules; the signal input terminal of the main control module is connected to the signal output terminal of the indirect impedance measuring module and the communication module, and the signal output terminal of the main control module is connected to the signal input terminal of the indirect impedance measuring module, the communication module, and the relay module; the indirect impedance measuring module is connected to an 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 measuring instrument through electrode wires.

[0011] The indirect impedance measurement module is used for excitation and measurement of the external four-electrode array sensor. Using the potential difference between the RE1 and RE2 potential measurement electrodes of the external four-electrode array sensor as the feedback control signal, it automatically adjusts the current applied between the CE1 and CE2 current injection electrodes, so that the potential difference signal between the RE1 and RE2 potential measurement electrodes is a sinusoidal signal with a set frequency and amplitude. At the same time, it converts the potential difference signal between the RE1 and RE2 potential measurement electrodes and the current signal between the CE1 and CE2 current injection electrodes into the measurement range of the main control module.

[0012] The main control module is used to run the indirect impedance measurement program. It obtains the measurement instructions from the host computer through the communication module, and inputs the excitation signal to the indirect impedance measurement module to set the potential difference signal between the RE1 potential measurement electrode and the RE2 potential measurement electrode according to the instructions. It also collects 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 transmits the data back to the host computer through the communication module.

[0013] The relay module is used to control the connection and disconnection between the electrodes of the external four-electrode array sensor and the indirect impedance measurement module.

[0014] The communication module is used for the indirect impedance meter to receive measurement commands from the host computer and upload measurement data;

[0015] A voltage regulator circuit is used to convert the voltage input from a DC power supply into digital and analog power supplies required by the various circuit modules of the indirect impedance measuring instrument.

[0016] A DC power supply is used to power the indirect impedance measuring instrument.

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

[0018] Preferably, the indirect impedance measurement module includes a low-pass filter 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 terminal of the low-pass filter circuit is connected to the output terminal of the main control module, the output terminal of the low-pass filter circuit is connected to the input terminal of the feedback control circuit, the output terminal of the potential measurement circuit is connected to the input terminals of the feedback control circuit and the potential signal conditioning circuit, the input terminal of the current measurement circuit is connected to the output terminal of the feedback control circuit and the CE1 current injection electrode, and the output terminal of the current measurement circuit is connected to the input terminal of the current signal conditioning circuit; the output terminals of the potential signal conditioning circuit and the current signal conditioning circuit are connected to the input terminal of the analog-to-digital converter of the main control module.

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

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

[0022] A potential signal conditioning circuit is used to convert the single-ended potential signal input from the potential measurement circuit into the measurement range of the analog-to-digital converter;

[0023] The current measurement circuit is used to connect the output of the operational amplifier OP2 of the feedback control circuit and the CE1 current injection electrode. 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 it to the current signal conditioning circuit.

[0024] A current signal conditioning circuit is used to convert the signal input from the current measurement circuit to the measurement range of 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 to the potential measurement circuit, which represents the potential difference between the RE1 and RE2 potential measurement electrodes, is consistent with the excitation signal input to the low-pass filter circuit.

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

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

[0028] First, an external four-electrode array sensor is placed on the concrete surface of a reinforced concrete structure, and the indirect impedance spectrum Z is measured using 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 reinforced concrete structure and the external four-electrode array sensor. This equivalent circuit model calculates the indirect impedance spectrum Z based on the corrosion state parameter P of the reinforced concrete structure. IDEC ;

[0030] Finally, a nonlinear fitting was performed on the corrosion state parameter P until the measured indirect impedance spectrum Z was obtained. IDT Indirect impedance spectrum Z calculated from the equivalent circuit model IDEC The error E between them meets the set requirements; the method for calculating the error E is as follows:

[0031]

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

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The electrochemical nondestructive testing device and state identification method for corrosion of reinforced concrete structures provided by this invention avoid the problems of drilling or pre-embedded sensors required by traditional electrochemical testing, and solve the defects of traditional methods such as low detection efficiency, limited area, and non-replaceable sensors. The indirect impedance measuring instrument in the nondestructive testing device has a measurement frequency range of 0.001Hz to 63Hz. Within the measurement range of 100~10000Ω, the relative error between the measured amplitude and the theoretical value is less than 5% for 95.63% of the data points, and the relative error between the measured phase angle and the theoretical value is less than 5% or the absolute error is less than 1° for 91.84% of the data points. The equivalent circuit model calculation of the indirect impedance spectrum of the electrochemical state identification method has an error of less than 3Ω, and the error in identifying the charge transport resistance Rct of uniformly corroded reinforced concrete is less than 6%. The accuracy of the proposed nondestructive testing device and state identification method in identifying the corrosion state of reinforced concrete specimens is comparable to that of embedded sensors. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the electrochemical non-destructive 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 flowchart of the corrosion electrochemical state identification method of the present invention.

[0039] Figure 5 This is a schematic diagram of the steel-concrete interface impedance model of the present invention.

[0040] Figure 6 This is a schematic diagram of the equivalent circuit model for calculating the indirect impedance of a reinforced concrete structure according to the present invention.

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

[0042] Figure 7 (a) is a side view schematic diagram 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 This is a flowchart for calculating the indirect impedance spectrum using the equivalent circuit model of the present invention.

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

[0046] Figure 10 This is a schematic diagram showing the performance test results of the indirect impedance measuring instrument of the present invention; wherein:

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

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

[0049] Figure 11 The equivalent circuit model of the present invention is shown in different R... ct The indirect impedance spectrum calculated at time; where:

[0050] Figure 11 (a) is the equivalent circuit model in different R... ct Nyquist curve at time;

[0051] Figure 11 (b) For the equivalent circuit model in different R... ct Amplitude-frequency response curve at time;

[0052] Figure 11 (c) is the equivalent circuit model in different R... ct The phase frequency response curve at that time.

[0053] Figure 12 The equivalent circuit model of the present invention is shown in different Y... 0Q The indirect impedance spectrum calculated at time; where:

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

[0055] Figure 12(b) is the equivalent circuit model in different Y... 0Q Amplitude-frequency response curve at time;

[0056] Figure 12 (c) is the equivalent circuit model in different Y... 0Q The phase frequency response curve at that time.

[0057] Figure 13 The indirect impedance spectra calculated for the equivalent circuit model of the present invention at different β values ​​are shown below; where:

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

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

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

[0061] Figure 14 The equivalent circuit model of the present invention is shown in different Y... 0W The indirect impedance spectrum calculated at time; where:

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

[0063] Figure 14 (b) is the equivalent circuit model in different Y... 0W Amplitude-frequency response curve at time;

[0064] Figure 14 (c) is the equivalent circuit model in different Y... 0W The phase frequency response curve at that time.

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

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

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

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

[0069] Figure 16This is a schematic diagram of the non-uniform corrosion condition calculated using the equivalent circuit model of the present invention.

[0070] Figure 17 The indirect impedance spectrum calculated under non-uniform corrosion conditions for the equivalent circuit model of this invention; wherein:

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

[0072] Figure 17 (b) is the amplitude-frequency response 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 This is a schematic diagram of the Rct identification results under the non-uniform corrosion condition 1 of the present invention; wherein:

[0075] Figure 18 (a) R is under 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 This is a schematic diagram of the Rct identification results under the non-uniform corrosion condition 2 of the present invention; wherein:

[0078] Figure 19 (a) 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 This is a schematic diagram of the Rct identification results for non-uniform corrosion condition 3 of the present invention; wherein:

[0081] Figure 20 (a) 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 This is a schematic diagram of the Rct identification results for non-uniform corrosion condition 4 of the present invention; wherein:

[0084] Figure 21(a) R under 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 indirect impedance measurement of a reinforced concrete structure using the non-destructive testing device of the present invention.

[0087] Figure 23 This is a schematic diagram illustrating the use of the corrosion non-destructive testing device of the present invention to measure the potential gradient on the concrete surface of a reinforced concrete structure.

[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 a steel-concrete composite specimen measured using the corrosion nondestructive testing device of the present invention; wherein:

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

[0091] Figure 25 (b) A graph showing the amplitude-frequency response of a steel-concrete composite specimen measured using a corrosion nondestructive testing device;

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

[0093] Figure 26 The three-electrode electrochemical impedance spectroscopy of the steel-concrete specimen of the present invention was measured by an embedded sensor; wherein:

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

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

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

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

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

[0099] Figure 28 To utilize the corrosion non-destructive testing method and embedded sensor of this invention to identify non-uniformly corroded steel-concrete specimens R ct Spatial distribution map.

[0100] In the attached diagram, the following labels represent different components: 01 is the indirect impedance measuring instrument; 011 is the indirect impedance measuring module; 0111 is the low-pass filter circuit; 0112 is the potential measuring circuit; 0113 is the potential signal conditioning circuit; 0114 is the current measuring circuit; 0115 is the current signal conditioning circuit; 0116 is the feedback control circuit; 012 is the main control module; 0121 is the microcontroller; 0122 is the digital-to-analog converter; 0123 is the analog-to-digital converter; 013 is the relay module; 014 is the communication module; 015 is the voltage regulator circuit; and 016 is the DC power supply. 02 is an external four-electrode array sensor; 021 is the RE1 potential measuring electrode; 022 is the CE1 current injection electrode; 023 is the CE2 current injection electrode; 024 is the RE2 potential measuring electrode; 025 is the electrode mounting bracket; and 026 is the electrode wire. 03 represents a reinforced concrete structure; 031 represents concrete; and 032 represents reinforcing steel. 04 is the equivalent circuit model; and 05 is the standard test circuit. Detailed Implementation

[0101] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are 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 testing device and condition identification method for corrosion of reinforced concrete structures involved in this embodiment include:

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

[0104]

[0105] in, It is the potential signal between electrode 021 of RE1 and electrode 024 of RE2. It is the complex voltage amplitude containing voltage magnitude and phase information, j is the imaginary number 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, It is the current signal between electrode 022 of CE1 and electrode 023 of CE2. It is the complex amplitude of the current, which includes information about the current amplitude and phase.

[0109] Therefore, the frequency is calculated. Indirect impedance of the reinforced concrete structure 03 below:

[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 regulator circuit 015, and a DC power supply 016; the DC power supply 016 supplies power to the indirect impedance measuring instrument 01; the voltage regulator circuit 015 converts the voltage input from the DC power supply 016 into digital and analog power supplies required by the various circuit modules of the indirect impedance measuring instrument 01; the communication module 014 is used for the indirect impedance measuring instrument 01 to receive measurement commands from the host computer and upload measurement data; the main control module 012 includes a microcontroller 0121, a digital-to-analog converter 0122, and an analog-to-digital converter 0123; the microcontroller 0121 controls the digital-to-analog converter 0122 to generate excitation signals for indirect impedance measurement, and obtains voltage and current measurement signals from 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 with the indirect impedance measuring module 011;

[0113] The circuit 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 high-frequency components from the sinusoidal excitation signal input to the main control module 012 at interface Set, and then inputs the excitation signal to the non-inverting input of the operational amplifier OP2 of the feedback control circuit 0112. The potential measurement circuit 0112 measures the potentials of electrodes RE1 021 and RE2 024 of the external four-electrode array sensor 02, and converts the differential potentials into single-ended signals, which are respectively input to the inverting input of the operational amplifier OP2 of the feedback control circuit 0116 and the potential signal conditioning circuit 0113. The potential signal conditioning circuit 0113 converts the single-ended potential signal input from the potential measurement circuit 0112 to the analog-to-digital converter 0123. Within the measurement range; the current measurement circuit 0114 is connected to the output of the operational amplifier OP2 of the feedback control circuit 0112 and the CE1 electrode 022 and CE2 electrode 023 of the external four-electrode array sensor 02, which are 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 input by the potential measurement circuit 0112, which represents the potential difference between the RE1 electrode 021 and the RE2 electrode 024, is consistent with the excitation signal input by the low-pass filter circuit 0111;

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

[0115]

[0116] In the formula, Representing frequency The indirect impedance measurement value below, The frequency of the equivalent circuit model 04 under the input condition of corrosion state parameter P The indirect impedance is calculated as follows: i is the frequency index, N is the total number of frequencies, Re(·) is the operator for finding the real part of the impedance, and Im(·) is the operator for finding the imaginary part of the impedance.

[0117] The corrosion state parameter P of the steel reinforcement structure 03 includes the concrete resistivity. and the parameters of the steel-concrete interface impedance model; the steel-concrete interface impedance model is as follows Figure 5 As shown, the charge transfer resistance R ct (Ω·cm 2 This is used to calculate the corrosion current density i of reinforcing steel 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... CPE for:

[0120]

[0121] Among them, Y 0Q (Ω -1 ·cm -2 ·s β ) is the fundamental admittance of CPE, β is a parameter characterizing the non-ideal degree of the interfacial capacitance between steel and concrete, and ω (rad / s) is the angular frequency; the Warburg impedance is used to characterize the effect of dissolved oxygen diffusion from concrete 031 to steel reinforcement 032, and the Warburg impedance Z W for:

[0122]

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

[0124]

[0125] The equivalent circuit model for calculating the indirect impedance spectrum is shown in Figure 04. Figure 6 As shown; the equivalent circuit model 04 discretizes the steel reinforcement surface into segments h. The interface impedance, interface current, and surface concrete potential of the steel reinforcement segment x are respectively represented by Z. x I x and The internal potential of all steel reinforcement sections is the same, denoted as . The surface concrete potential of electrode RE2 024 is taken as the zero reference point, and the surface concrete potential of electrode RE1 021 is denoted as V. The current that only flows through the concrete and does not enter the reinforcing steel is denoted as J, and the direction from electrode CE1 022 to electrode CE2 023 is defined as positive. The reinforcing steel is divided into two large regions: the interface current of the reinforcing steel in region A (section 1~g) flows into or originates from electrode CE1 022 in the concrete, and the interface current of the reinforcing steel in region B (section g+1~h) flows into or originates from electrode CE2 023 in the concrete. Assuming that the concrete has a 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, then the concrete is a linear system. According to the superposition principle of linear systems, we know that:

[0126]

[0127] Where I represents the steel reinforcement interface current matrix of dimension h×1, and its element I x The interface current represents the section x of the reinforcing steel, and its positive direction is defined as flowing from the CE1 electrode 022 to the reinforcing steel or from the reinforcing steel to the CE2 electrode 023 in the concrete; J represents the current of dimension 1×1 that only travels in the concrete and does not enter the reinforcing steel. Let h×1 be the potential matrix of the reinforced concrete surface. Let represent the surface concrete potential of the reinforced section x, and V represent the surface concrete potential of the RE1 electrode 021. The concrete impedance matrices K (h×h dimension), M (h×1 dimension), N (1×h dimension), and L (1×1 dimension) are determined by the geometric configuration and concrete resistivity. K is determined by the impedance distribution at the steel-concrete interface. xy Reflecting unit current I y right M's contribution x Reflecting unit current J to N's contribution y Reflecting unit current Iy The contribution of current J to V is given by L, which characterizes the contribution of a unit current J to V. Since concrete is a linear system, we can obtain:

[0128]

[0129] in, , , and It is the concrete impedance matrix under unit concrete resistivity, through, as... Figure 7 The finite element model of the reinforced concrete structure shown is calculated. Figure 7 The steel-concrete interface is defined as insulation. A voltage is applied between electrode 022 (CE1) and electrode 023 (CE2). The finite element analysis results are extracted, and the calculation is performed. :

[0130]

[0131] Simultaneous calculation :

[0132]

[0133] in, It is a matrix The element in the x-th row, Φ RE1 and Φ RE2 These are the average surface concrete potentials of electrodes RE1 (021) and RE2 (024) in the calculation results; Φ x is the average concrete potential on the surface of the reinforcing steel section x; J is the current integral on the surface of electrode 022 of CE1. It is the concrete resistivity set by the finite element model; and It depends only on geometric parameters. and They are represented as follows:

[0134]

[0135]

[0136] Where A and B are h×h dimensional matrices, and C and D are 1×h dimensional matrices, these matrices depend only on geometric parameters, but 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. A xy This reflects the surface concrete potential of section x when a unit current flows from electrode 022 of CE1 to section y of the reinforcing bar. B's contribution xy Reflects the effect of unit current flowing from the Y section of the reinforcing bar to the CE2 electrode 023. C's contribution; y D reflects the contribution of a unit current flowing from electrode 022 of CE1 to the concrete potential V on the surface of electrode 021 of RE1. y This reflects the contribution of a unit current flowing from the y-section of the reinforcing bar to the CE2 electrode 023 to V. When calculating matrices A and C, [the following will be included]. Figure 7 The surface of electrode 023 (CE2) is set to insulated, and the surface of section y of the reinforcing bar is activated (all other sections are set to insulated). A voltage is applied between electrode 022 (CE1) and the reinforcing bar. The finite element analysis results are extracted, and matrices A and C are calculated using the following formula:

[0137]

[0138]

[0139] Among them, A xy C is the element in the x-th row and y-th column of matrix A. y i is the element in the y-th column of matrix C; y This represents the current between electrode 022 of CE1 and the y-section of the reinforcing bar. When calculating matrices B and D, [the following is used]. Figure 7 The surface of electrode 022 (CE1) is set to insulated, and the surface of section y of the reinforcing bar is activated (all other sections are set to insulated). A voltage is applied between electrode 023 (CE2) and the reinforcing bar. The finite element analysis results are extracted, and matrices B and D are calculated using the following formula:

[0140]

[0141]

[0142] Among them, B xy Let D represent the element in the x-th row and y-th column of matrix B. y It is the element in the y-th column of matrix D; i y This represents the current between electrode 023 of CE2 and the y-section of the reinforcing bar. The reinforcing bar interface current matrix I and the concrete potential matrix on the reinforcing bar surface in equation (9) are used to represent this current. They are represented as follows:

[0143]

[0144]

[0145] Among them, I A and These represent the current and potential matrices of the reinforcing bars in area A, with a dimension of g×1; I B and These represent the current and potential matrices of the reinforcing bars in zone B, with dimensions p×1, where p=hg; Equation (9) can be transformed into:

[0146]

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

[0148] Let the impedance matrix of the steel-concrete interface be represented by a diagonal matrix Z of dimension h×h:

[0149]

[0150] Among them, the impedance matrix Z of the steel-concrete interface is a diagonal matrix, Z A and Z B These are diagonal matrices representing the interfacial impedance of the reinforcing bars in area A and area B, respectively. It is a submatrix of matrix Z, consisting of rows 1 to g and columns 1 to g, with dimensions g×g; It is a submatrix of matrix Z with dimensions p×p, consisting of rows g+1 to h and columns g+1 to h. It is a matrix of dimension g×p with all elements being 0; It is a matrix of dimension p×g with all elements being 0;

[0151] Z xx The interfacial impedance of the reinforcing steel section x is:

[0152]

[0153] in, It is a complex frequency. , It is the symbol for an imaginary number. It is pi. It's frequency. It is the rebar section number;

[0154] Based on the relationship between the interfacial current and overpotential of the reinforcing steel, we can obtain:

[0155]

[0156] in, It is the electrical potential of the electronically conductive phase inside the steel reinforcement. It is a matrix of dimension h×1, with all elements being 1;

[0157] During indirect impedance spectroscopy measurement, the net current in the reinforcing steel is 0, therefore:

[0158]

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

[0160] According to equations (21), (24), and (25), the following can be calculated:

[0161]

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

[0163] Furthermore, it is possible to calculate the current response under potential excitation V:

[0164]

[0165] in, It 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 is related to the boundary between the reinforcement in area A and area B and the uniformity of the steel-concrete interface impedance, which is difficult to solve directly; by substituting all possible g values ​​into equation (27), the maximum value obtained is the correct value:

[0166]

[0167] Among them, I m θ and θ are the current responses, respectively. The amplitude and phase angle, It is an imaginary number. Therefore, indirect impedance can be calculated:

[0168]

[0169] In summary, the process for calculating the indirect impedance spectrum of the equivalent circuit model 04 is as follows: Figure 8 As shown; firstly, based on the geometry of the external four-electrode array sensor 02 and the steel-concrete structure 03, matrices A, B, C, and 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 is calculated; then the matrix Q for each value of g is calculated according to equations (10), (13) and (14); then the matrix Q for each value of potential excitation V is calculated according to equations (26) and (27). And calculate according to equation (28) The maximum value is the true value; finally, each measurement frequency is calculated according to formula (29). indirect impedance Thus, the indirect impedance spectrum was obtained.

[0170] Example 1

[0171] In this embodiment, calibrated resistors and capacitors are used to construct a series of standard test circuits 05 to verify the function and measurement accuracy of the indirect impedance measuring instrument 01, such as... Figure 9 As shown. Resistors R1, R2, R5, R6, and R7 simulate the resistance of concrete; R3 and R4 simulate the interface charge transfer resistance of the reinforcing steel; and capacitors C1 and C2 simulate the interface capacitance of the steel-concrete system. The resistance and capacitance values ​​of all components were calibrated using an LCR meter. Table 1 summarizes the parameters of standard test circuits A through 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 the indirect impedance measuring instrument 01 are as follows: Figure 10 As shown, in all standard test circuits 05, the theoretical values ​​and the measured values ​​of the indirect impedance measuring instrument 01 show a high degree of agreement. The measurement frequency range of the indirect impedance measuring instrument 01 is 0.001Hz to 63Hz. Within the measurement range of 100~10000Ω, the relative error between the measured amplitude and the theoretical value is less than 5% for 95.63% of the data points, and the relative error between the measured phase angle and the theoretical value is less than 5% or the absolute error is less than 1 degree for 91.84% of the data points.

[0177] Example 2

[0178] In this embodiment, the equivalent circuit model 04 calculated as follows: Figure 7 The indirect impedance spectrum of the steel-concrete structure with the shown geometry under uniform corrosion conditions is obtained and 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 dimensions are 10 × 10 × 60 cm, with embedded longitudinal reinforcing bars of 1.2 cm diameter. The surfaces of electrodes CE1 022 and CE2 023 are circles with a diameter of 2 cm, while the surfaces of electrodes RE1 021 and RE2 024 are circles with a diameter of 1 cm. The finite element mesh consists of free tetrahedral elements, with the maximum element size set to 1 mm on the electrode surfaces, 2 mm on the reinforcing bar surfaces, and 8 mm in the concrete matrix. The potential distribution in the concrete is described by the Laplace equation:

[0179]

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

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

[0182]

[0183] in, It is a complex phasor representing the amplitude and phase of the potential disturbance in concrete, and is a function of frequency and position. The potential disturbance of the electronically conducting phase inside the reinforcing steel is:

[0184]

[0185] in, This is a complex phasor representing the amplitude and phase of the potential disturbance within the reinforcing steel bar, and it depends only on the frequency, not the location. This is because the electronically conducting phase inside the reinforcing steel bar can be considered an equipotential body. The current disturbance at the steel-concrete interface is:

[0186]

[0187] in, Z represents the concrete potential on the surface of the steel reinforcement. Z represents the interfacial impedance of the steel-concrete interface, defined by equation (8), which is a function of frequency and position. In the finite element model, the current between electrode 022 of CE1 and electrode 023 of CE2 is defined as I, and the concrete potential on the surface of electrode 021 of RE1 is extracted from the calculation results. and the surface concrete potential of RE2 electrode 024 Then, the indirect impedance of the reinforced concrete structure at each frequency is calculated:

[0188]

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

[0190] Example 3

[0191] In this embodiment, equivalent circuit model 04 calculates the indirect impedance spectrum of the reinforced concrete structure under non-uniform corrosion conditions and compares it with the indirect impedance spectrum calculated by the finite element model. The non-uniform corrosion condition of the reinforced concrete structure is as follows: Figure 16 As shown, the anode region is 5 cm long and is located 16 cm from one end of the reinforced concrete structure model, while the remaining part is the cathode region. Figure 17 The cathode region R was shown. ct =10 6 Ω·cm 2 At that time, different R values ​​in the anode region ct The indirect impedance spectrum was set below, and other corrosion state parameters were set to 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 calculating the indirect impedance spectrum under non-uniform corrosion conditions.

[0192] Example 4

[0193] This embodiment demonstrates Figure 4 The illustrated state identification method identifies the corrosion state parameter P of a reinforced concrete structure under uniform corrosion conditions. The corrosion state parameter P includes the concrete resistivity. The interfacial impedance parameter R of steel-concrete composite ct Y 0Q ,β,Y 0W The indirect impedance spectrum of the reinforced concrete structure was calculated using the finite element model in Example 2. Figure 4 and Figure 8 The equivalent circuit model 04 shown is used for iterative fitting to identify the corrosion state parameter P set in the finite element model. The comparison results of the set and identified corrosion state parameter P are shown in Table 2. Examples 1-7 represent passivation and low-rate corrosion states, unaffected by the diffusion process (Warburg impedance can be ignored). The remaining examples correspond to active corrosion states with different corrosion rates, whose electrochemical processes are all affected by the diffusion process. In all examples, Figure 4The state identification methods shown all achieve high-precision identification of the corrosion state parameter P. For R... ct The largest recognition error occurred 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 embodiment demonstrates Figure 4 The illustrated state identification method demonstrates its effectiveness in identifying the corrosion state of non-uniformly corroded steel-concrete structures. This embodiment assumes that only one anodic region exists within the detection area, except for R... ct The interface impedance parameters of the outer anode region and the cathode region are the same. The finite element model is used to obtain Ra near a single anode region. ct Distribution patterns serve as prior knowledge for the identification process. In the finite element model, the Butler-Volmer equations are used to describe the polarization curve parameters of the reinforcing bars:

[0198]

[0199]

[0200] Where η represents the overpotential of the reinforcing bar; E represents the potential of the reinforcing bar; E corr β represents the open-circuit potential of the reinforcing bar; i represents the interface current of the reinforcing bar; β a and β c These represent the anode Tafel slope and the cathode Tafel slope, respectively; This is the corrosion exchange current density. The surface of the reinforcing bar is discretized, and the Butler-Volmer equations for the anodic and cathodic regions are defined according to equations (37) and (38), respectively. The potential E of each discrete reinforcing bar element is solved using the finite element method, and then the charge transfer resistance R of each discrete reinforcing bar element is solved. ct :

[0201]

[0202] in, Net current density at the steel-concrete interface; then, according to R ct The spatial distribution and other corrosion state parameters of the steel-concrete structure were calculated using the finite element model in Example 2 to determine the indirect impedance spectrum. Finally, the spatial distribution and other corrosion state parameters were used... Figure 4 The method described above uses an equivalent circuit model 04 to fit the indirect impedance spectrum generated by the finite element model to identify the R of the reinforced concrete structure. ctSpatial distribution. Assume the R of the steel reinforcement in the reinforced concrete structure within the detection area. ct The spatial distribution is as follows:

[0203]

[0204] Where x represents the position of the discrete rebar element, with the center of the anode region as the origin; x1 is the position of the edge of the anode region; and x2 is the point in the detection area that is farthest from the center of the anode region. and R represents positions x1 and x2 respectively. ct ; Dimensionless parameters k and n characterize the R-value 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 recognition method is a uniformly distributed Y 0Q and β, and the description of R ct Spatial distribution parameters , k, n. The origin of the anode region and x1 and x2 are prior knowledge, which can be obtained through the potential gradient diagram of the concrete surface in engineering practice. Figures 18 to 21 R demonstrates the ability to identify non-uniform corrosion. ct Spatial distribution examples. Figure 18 The polarization curve parameters for the anode region are A3 in Table 3, and the parameters for the cathode region are A4. Figure 18 The point graph in (a) is the R calculated by equation (39). ct Spatial distribution settings. Figure 18 The dot plot in (b) is set to R. ct The indirect impedance spectrum generated according to the finite element model described in Example 2 under spatial distribution. Figures 18 to 21 Parameter Y 0Q And β are both set to Y 0Q = 2×10 -5 Ω -1 ·cm -2 ·s β And β = 0.9. Figure 18 (b) The centerline diagram is based on... Figure 4 The aforementioned state recognition 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 for the anode region are A3 in Table 3, and the parameters for the cathode region are A4, but the anode position is different from... Figure 18 different. Figure 20The polarization curve parameters for the anode region are A2 in Table 3, and the parameters for the cathode region are A4. Figure 21 The polarization curve parameters for the anode region are A1 in Table 3, and the parameters for the cathode region are A4.

[0205] Table 3 Parameters of Reinforcing Steel Polarization Curve

[0206]

[0207] Example 6

[0208] This embodiment uses indirect impedance spectroscopy to assess corrosion status in reinforced concrete specimens and verifies its accuracy using an embedded sensor. The indirect impedance measurement experiment of the reinforced concrete structure is as follows: Figure 22 As shown. The CE1 electrode 022 and CE2 electrode 023 of the external four-electrode array sensor 02 are 2cm diameter graphite disk electrodes. The RE1 electrode 021 and RE2 electrode 024 are 1cm diameter MnO2 reference electrodes. The MnO2 reference electrodes use graphite with a surface coated with a MnO2 functional layer as the electrode, an alkaline slurry as the electrolyte, and hardened cement slurry as the encapsulation layer. Each electrode of the external four-electrode array sensor 02 is wrapped with fabric. Before measurement, the fabric is thoroughly wetted with 0.1M KCl solution to ensure good contact between the electrodes and the concrete surface. This embodiment fabricates four electrodes with geometric dimensions... Figure 7 Identical reinforced concrete specimens were used, with longitudinal reinforcement consisting of 1.2 cm diameter HRB400 steel bars. To verify the effectiveness of indirect impedance in assessing corrosion status, three embedded sensors were installed along the length of each specimen at 10 cm, 30 cm, and 50 cm, respectively. Each embedded sensor had a working area of ​​7.5 cm². 2 The test specimens consisted of small-sized steel rebar electrodes and a reference electrode, with external auxiliary electrodes. Four reinforced concrete specimens were numbered RC-U0%, RC-U0.5%, RC-U3%, and RC-Nonuniform. The RC-U0%, RC-U0.5%, and RC-U3% specimens were cast using concrete containing 0%, 0.5%, and 3% NaCl by weight of cement, respectively. The RC-Nonuniform specimen was cast in sections; the 6cm to 14cm section contained concrete containing 3% NaCl by weight of cement, while the remaining sections contained no NaCl. All specimens were demolded 48 hours after casting and cured in a 60℃ steam environment for 3 days. After curing, the RC-U0.5% and RC-U3% specimens were subjected to a 0.1 mA / cm² pressure. 2The anolyte current density was used for 3 hours of accelerated corrosion, during which the working electrode of the embedded sensor was short-circuited to the reinforcing steel. The concrete surface potential gradient provides prior information for fitting the indirect impedance spectrum of the anolyte location in non-uniform corrosion as an equivalent circuit model 04. The concrete surface potential gradient was measured using two external reference electrodes, such as... Figure 23 As shown, one reference electrode is fixed in position, while the other electrode moves on the concrete surface. Measurement points are densely packed in the anodic region of the RC-Nonuniform specimen. To verify the effectiveness of indirect impedance in assessing corrosion status, electrochemical impedance spectroscopy measurements were performed on the embedded sensor in the reinforced concrete specimen, as shown... Figure 24 As shown. The external CE electrode is a graphite plate electrode, which establishes good contact with the concrete surface using a damp fabric.

[0209] The indirect impedance spectrum measurement results of the reinforced concrete structure are as follows: Figure 25 As shown, the dot plot represents the measurement results, and the line plot represents the fitting results of the equivalent circuit model 04. The potential gradient of 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 fitted according to the uniform corrosion assumption shown in Example 4. The anodic potential of RC-Nonuniform is significantly lower than that of the cathode region, with a potential difference of nearly 120 mV, and fitted according to the non-uniform corrosion assumption shown in Example 5. The electrochemical impedance spectroscopy of the embedded sensor is as follows: Figure 26 As shown in the figure, the scatter plot represents the measurement results, and the line plot represents the fitting results. The corrosion state parameters identified by the external and embedded sensors are shown in Table 4. All three embedded sensors embedded in the RC-U0% specimen confirmed that the working electrode was in a passivated state. ct More than 7×10 6 Ω·cm 2 Although the external sensor measured R ct It is 6.7×10 5 Ω·cm 2 However, according to the classification criteria in Table 5, it still falls within the passivation range, and the corrosion rate is negligible. The R value measured by the external sensor in the RC-U0.5% specimen... ctThe value is highly consistent with embedded sensor 2, but higher than the values ​​measured by embedded sensors 1 and 3. This is because the chloride concentration threshold for steel corrosion in concrete ranges from 0.2% to 0.8% of the cement mass, exhibiting significant dispersion. The chloride ion content of the RC-U 0.5% specimen falls within this range, and the initial state of the steel reinforcement, such as surface roughness and oxide layer, also shows considerable dispersion. Although NaCl is uniformly distributed in the RC-U 0.5% specimen, due to the above reasons, its corrosion state distribution still exhibits smaller-scale non-uniformity. This leads to the relative difference between the measurement results of the external and embedded sensors. In the RC-U 3% specimen, the R values ​​measured by the external and embedded sensors... ct The values ​​are highly consistent, indicating that the reinforcing steel is in a state of high corrosion rate. In the RC-Nonuniform specimen, the R values ​​measured by the external sensor and the embedded sensor are highly consistent. ct Spatial distribution such as Figure 28 As shown, it exhibits good consistency.

[0210] Table 4 Corrosion Status Identification Parameters for Reinforced Concrete Structures

[0211]

[0212] Table 5 Corrosion State Classification

[0213]

[0214] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology 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 determined by the scope of the claims.

Claims

1. A method for identifying the non-destructive electrochemical state of corrosion in reinforced concrete structures, characterized in that, The steps of the state recognition method are as follows: First, an external four-electrode array sensor (02) is placed on the concrete surface of a reinforced concrete structure, and the indirect impedance spectrum Z is measured by an indirect impedance measuring instrument (01). IDT ; Then, an equivalent circuit model capable of calculating the indirect impedance spectrum is generated based on the geometric parameters of the reinforced concrete structure and the external four-electrode array sensor (02). The equivalent circuit model is based on the corrosion state parameters of the reinforced concrete structure. Calculate the indirect impedance spectrum Z IDEC The specific steps are as follows: (1) Based on the geometric parameters of the reinforced concrete structure and the external four-electrode sensor, under uniform resistivity conditions, the surface of the reinforcing steel is discretized into... For each section, establish concrete impedance matrices A, B, C, and D. , The influence of the concrete impedance matrix was obtained through a finite element model. (2) Divide the discrete steel reinforcement sections into two categories: sections 1 to g are section A steel reinforcement, and sections g+1 to g+2 are section A steel reinforcement. Section B is the reinforcing steel. The interface current of the reinforcing steel in section A flows into the concrete or comes from the CE1 current injection electrode (022). The interface current of the reinforcing steel in section B is... The current flowing into or from the CE2 current is injected into the electrode (023) in the concrete. g is the unknown to be solved. The matrix is ​​calculated based on g. and ; (3) Based on corrosion state parameters Calculate the impedance matrix of the steel-concrete interface; (4) When the potential between the RE1 potential measuring electrode (021) and the RE2 potential measuring electrode (024) is V, calculate the current between the CE1 current injection electrode (022) and the CE2 current injection electrode (023); (5) Calculate the indirect impedance obtained from the equivalent circuit model; Finally, the corrosion state parameters Perform nonlinear fitting until the measured indirect impedance spectrum Z is obtained. IDT Indirect impedance spectrum Z calculated from the equivalent circuit model IDEC The error E between them meets the set requirements; the method for calculating the error E is as follows: in, Representing frequency The indirect impedance measurement value below, The equivalent circuit model in the corrosion state parameters Frequency of input The calculated value of indirect impedance is as follows. is the frequency index, N is the total number of frequencies, Re(·) is the operator for finding the real part of the impedance, and Im(·) is the operator for finding the imaginary part of the impedance.

2. The state recognition method according to claim 1, characterized in that, The method for establishing the equivalent circuit model is as follows: (1) When calculating matrices A and C, the interface of the CE2 current injection electrode (023) in the finite element model is set to insulation, and the reinforcing steel is... Section 1 is activated, and the remaining sections are set to insulation. A unit voltage is applied between the CE1 current injection electrode (022) and the reinforcing bar. The voltage and current calculation results in the finite element model are extracted, and matrices A and C are calculated according to the following formula: Where A is dimension The matrix, where C is the dimension. The matrix, It is the first matrix A. Line number Column elements, It is the matrix C of the first generation. Column elements; This indicates the CE1 current injection electrode (022) and the reinforcing bar. The current value between sections, Φ RE1 and Φ RE2 The values ​​are the average concrete potentials extracted from the surfaces of the RE1 potential measuring electrode (021) and the RE2 potential measuring electrode (024), respectively. For extraction Average surface potential of concrete on the reinforcing steel in section [number] It 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, and the reinforcing steel is... Section 023 is activated, and the remaining sections are set to insulation; a unit voltage is applied between the CE2 current injection electrode (023) and the reinforcing 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: Where B is the dimension. The matrix, where D is the dimension. The matrix, Represents the matrix B of the first generation. Line number Column elements, It is the matrix D of the first generation. Column elements; This indicates the CE2 current injection electrode (023) and the reinforcing bar. The current value between sections, Φ RE1 and Φ RE2 The values ​​are the average concrete potentials extracted from the surfaces of the RE1 potential measuring electrode (021) and the RE2 potential measuring electrode (024), respectively. For extraction Average surface potential of concrete on the reinforcing steel in section [number] It is the concrete resistivity set by the finite element model; Calculate matrix and At that time, all steel reinforcement sections in the finite element model were set to be insulated. A unit voltage was applied between the CE1 current injection electrode (022) and the CE2 current injection electrode (023). The voltage and current calculation results in the finite element model were extracted, and the matrix was calculated according to the following formula. and : in, It is a dimension The matrix, It is a 1×1 matrix. It is a matrix No. Row elements, It is the extracted current value between the CE1 current injection electrode (022) and the CE2 current injection electrode (023), Φ RE1 and Φ RE2 The values ​​are the average concrete potentials extracted from the surfaces of the RE1 potential measuring electrode (021) and the RE2 potential measuring electrode (024), respectively. For extraction Average surface potential of concrete on the reinforcing steel in section [number] It is the concrete resistivity set by the finite element model; (2) in, The matrix consists of columns 1 to g of matrix A and columns g+1 to g of matrix B. It is composed of columns. The matrix consists of columns 1 to g of matrix C and columns g+1 to g of matrix D. The columns are pieced together to calculate the concrete impedance matrix K, M, N, L: Among them, concrete resistivity These are the corrosion state parameters to be identified. one; (3) Among them, the impedance matrix Z at the steel-concrete interface is a diagonal matrix, Z A and Z B These are diagonal matrices representing the interfacial impedance of the reinforcing bars in area A and area B, respectively. It is a dimension A matrix whose elements are all 0; It is a dimension The matrix has all elements as 0; the steel-concrete interface impedance matrix Z is composed of corrosion state parameters. Decide, It is to be identified; (4) in, and These are the interface current matrices for the reinforcing bars in areas A and B, with dimensions respectively. and , ;K AA It is a submatrix of matrix K, consisting of rows 1 to g and columns 1 to g, with dimensions g × g; K AB It is a submatrix of matrix K, consisting of rows 1 to g and columns g+1 to h, with dimension g×p; K BA It is a submatrix of matrix K, consisting of rows g+1 to h and columns 1 to g, with dimension p×g; K BB It is a submatrix of matrix K, from row g+1 to row h and from column g+1 to column h, with dimension p×p; It is a matrix of dimension g×1, with all elements being 1; It is a dimension A matrix whose elements are all 1; It is a 1×g matrix with all elements being 1; It is a dimension A matrix whose elements are all 1; It is a matrix of dimension (h+1)×1, with all elements being 0; It is the current value in the concrete that does not enter the reinforcing steel. It is the electrical potential of the electronically conductive phase inside the steel reinforcement; It 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 values ​​of g are calculated using an exhaustive method. Its maximum value is the correct solution. yes amplitude, It is the symbol for an imaginary number. yes The phase angle; in, The indirect impedance is obtained from the equivalent circuit model. for The maximum value.

3. The state recognition method according to claim 2, characterized in that, The corrosion state parameters Under uniform corrosion conditions, the resistivity of concrete is... Steel-concrete interface charge transport resistance Warburg impedance fundamental admittance Basic admittance of non-ideal capacitance at the steel-concrete interface Non-ideal capacitance coefficient The corrosion state parameter is the concrete resistivity under non-uniform corrosion conditions. Basic admittance of non-ideal capacitance at the steel-concrete interface Non-ideal capacitance coefficient β and description Spatial distribution parameters , , k, n; the aforementioned The spatial distribution function is: in, This represents the location of the discrete reinforcement section, with the center of the anode region as the origin. It is the location of the edge of the anode region; It is the point farthest from the center of the anode area in the detection area; and Representing positions respectively and place Dimensionless parameters k and n characterize position. and Between The shape of the transition zone curve.

4. The state recognition method according to claim 3, characterized in that, The method for calculating the impedance matrix of the steel-concrete interface is as follows: Wherein, the impedance matrix Z of the steel-concrete interface is a dimension diagonal matrix, express Interfacial impedance of the reinforcing bars in section [number] They represent Charge transport resistance, Warburg impedance fundamental admittance, fundamental admittance and non-ideal capacitance coefficient of the steel-concrete interface of the reinforcing bars in section No. It is a complex frequency. , It is the symbol for an imaginary number. It is pi. It refers to frequency.

5. A detection device based on the electrochemical non-destructive testing method for identifying the corrosion state of reinforced concrete structures according to any one of claims 1-4, characterized in that, The detection device includes: 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 electrode wires (026); wherein: 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 regulator circuit (015), and a DC power supply (016); the DC power supply (016) is connected to the voltage regulator circuit (015), and the voltage regulator 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) to supply power to these four modules; the signal input terminal of the main control module (012) is connected to the signal output terminal of the indirect impedance measuring module (011) and the communication module (014), and the signal output terminal of the main control module (012) is connected to the signal input terminal of the indirect impedance measuring module (011), the communication module (014), and the relay module (013); the indirect impedance measuring module (011) is connected to the external four-electrode array sensor (02) through the relay module (013); The external four-electrode array sensor (02) includes: RE1 potential measuring electrode (021), CE1 current injection electrode (022), CE2 current injection electrode (023) and RE2 potential measuring electrode (024); the RE1 potential measuring electrode (021), CE1 current injection electrode (022), CE2 current injection electrode (023) and RE2 potential measuring electrode (024) are respectively connected to the relay module (013) of the indirect impedance measuring instrument (01) through electrode wires (026).

6. The detection device according to claim 5, characterized in that, The indirect impedance measurement module (011) is used for excitation and measurement of the external four-electrode array sensor (02); 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) is used as a feedback control signal to automatically adjust 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 with a set frequency and amplitude, and at the same time, 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) are converted into the measurement range of the main control module (012); The main control module (012) is used to run the indirect impedance measurement program, obtain the measurement instructions from the host computer through the communication module (014), input the excitation signal of setting the 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 instructions, and 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); The relay module (013) is used to control the connection and disconnection between the electrodes of the external four-electrode array sensor (02) and the indirect impedance measurement module (011); 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 voltage regulator circuit (015) is used to convert the voltage input from the DC power supply (016) into the digital and analog power supplies required by the various circuit modules of the indirect impedance measuring instrument (01); A DC power supply (016) is used to power the indirect impedance measuring instrument (01).

7. The detection device according to claim 5, characterized in that, The external four-electrode array sensor (02) also includes an electrode fixing bracket (025), and the RE1 potential measuring electrode (021), CE1 current injection electrode (022), CE2 current injection electrode (023) and RE2 potential measuring electrode (024) are detachably fixed on the electrode fixing bracket (025).

8. The detection device according to claim 6, characterized in that, 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 input terminal of the low-pass filter circuit (0111) is connected to the output terminal of the main control module (012). The output terminal of the low-pass filter circuit (0111) is connected to the input terminal of the feedback control circuit (0116). The output terminal of the potential measurement circuit (0112) is connected to the input terminals of the feedback control circuit (0116) and the potential signal conditioning circuit (0113). The input terminal of the current measurement circuit (0114) is connected to the output terminal of the feedback control circuit (0116) and the CE1 current injection electrode (022) respectively. The output terminal of the current measurement circuit (0114) is connected to the input terminal of the current signal conditioning circuit (0115). The output terminals of the potential signal conditioning circuit (0113) and the current signal conditioning circuit (0115) are connected to the input terminal of the analog-to-digital converter (0123) of the main control module (012).

9. The detection device according to claim 8, characterized in that, The low-pass filter circuit (0111) is used to filter out the high-frequency components of the sinusoidal excitation signal input by the main control module (012) at the interface Set, and then input the excitation signal to the non-inverting input terminal of the operational amplifier OP2 of the feedback control circuit (0116); The potential measurement circuit (0112) is used to measure the potential of the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024), and convert the differential potential into a single-ended signal and input it to the inverting input terminal of the operational amplifier OP2 of the feedback control circuit (0116) and the potential signal conditioning circuit (0113). The potential signal conditioning circuit (0113) is used to convert the single-ended potential signal input from the potential measurement circuit (0112) into the measurement range of the analog-to-digital converter (0123); The current measurement circuit (0114) is used to connect the output terminal of the operational amplifier OP2 of the feedback control circuit (0116) and the CE1 current injection electrode (022). 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 it to the current signal conditioning circuit (0115). The current signal conditioning circuit (0115) is used to convert the signal input from the current measurement circuit (0114) into the 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 to the potential measurement circuit (0112), which represents the potential difference between the RE1 potential measurement electrode (021) and the RE2 potential measurement electrode (024), is consistent with the excitation signal input to the low-pass filter circuit (0111).

10. The detection device according to claim 6, characterized in that, The main control module (012) includes a microcontroller (0121), a digital-to-analog converter (0122), and an analog-to-digital converter (0123); the microcontroller (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).

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