Method for monitoring and discriminating the corrosion process of steel bars in concrete

Abstract

This invention provides a method for monitoring and identifying the corrosion process of reinforcing steel bars in concrete. A zero-resistance galvanometer is used to measure the steel bars embedded in the concrete. The galvanometer measurement results are processed using spectral analysis to characterize the corrosion status of the steel bar surface. Noise signal processing analysis is employed to determine changes in the concrete state and the aging process by analyzing white noise and other signal variations. Advantages of this invention include: low detection cost and no damage to the overall building structure. It is suitable for on-site installation and testing. It provides a comprehensive assessment of reinforced concrete structures. The collected signals are processed to evaluate the localized and uniform corrosion of the reinforcing steel bars, and the failure and aging status of the concrete is assessed based on the signal processing results.

Description

Technical Field

[0001] This invention relates to the field of methods for monitoring and identifying the corrosion process of steel bars in concrete, which can monitor the pitting corrosion process of steel bars in concrete and the expansion of the rust layer on the surface of the steel bars. Background Technology

[0002] Reinforced concrete structures are the most common building materials. The high alkalinity (pH 12-13) of the microporous aqueous solution in concrete usually provides protection for the reinforcing steel, i.e., the high alkalinity can passivate the steel. Due to the high resistivity of concrete, it can reduce the penetration of some corrosive factors (such as chlorides, carbon dioxide, and water) to the surface of the reinforcing steel; it also reduces the corrosion current flowing from the anodic region to the cathodic region, thus lowering its corrosion rate. However, in actual use, steel corrosion has become a major cause of structural performance degradation in many reinforced concrete structures.

[0003] Generally, there are two main factors that lead to steel corrosion: carbonation and the presence of chloride ions, which may originate during concrete formation or infiltrate the concrete during service. When corrosion begins, the corrosion products, namely iron oxides and hydroxides, accumulate to several times their original size. The expansion of these corrosion products generates internal stress, which can cause the concrete cover of the steel reinforcement to crack along the reinforcement and even peel off.

[0004] Corrosion of steel reinforcement in concrete is a slow, gradual process that occurs and develops within the concrete, making it difficult to detect and monitor. Once failure occurs, it is instantaneous, resulting in significant losses. Therefore, on-site testing methods for reinforced concrete structures in marine or other special environments are receiving increasing attention. Currently, several testing methods are available, including non-destructive testing on actual structures, physical, chemical, and petrographic analysis of samples taken from the structure, and load-bearing capacity tests. Among these, electrochemical methods are one of the most suitable non-destructive testing methods for detecting corrosion in reinforced concrete structures. Based on practical applications, the half-cell potential method, concrete resistivity testing, and DC linear polarized resistance method are mainly used. However, current methods for monitoring steel corrosion in concrete in marine environments all employ electrochemical polarization or impedance measurement, applying a potential to the steel surface, which has a destructive effect on the surface condition. Furthermore, due to the high internal resistance of concrete itself, the test results are subject to significant errors. Summary of the Invention

[0005] The purpose of this invention is to provide a method for monitoring and identifying the corrosion process of reinforcing steel in concrete. This method uses a zero-resistance galvanometer to measure the steel reinforcement embedded in the concrete, and processes the galvanometer measurement results using spectral analysis to characterize the corrosion status of the steel reinforcement surface. Furthermore, a noise signal processing analysis method is employed to determine changes in the concrete state and the aging process by analyzing variations in white noise and other signals.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for monitoring and identifying the corrosion process of reinforcing steel bars in concrete is disclosed, employing a zero-resistance current module and accompanying software to monitor the corrosion process of reinforced concrete. During measurement, two identical reinforcing steel electrodes are used as the working electrode and counter electrode, with a solid Ag / AgCl electrode selected as the reference electrode. The working and counter electrodes are made of reinforcing steel bars with a diameter of 10-50 mm and a length of 10-200 mm, while the reference electrode has a diameter of 1-10 mm. During installation, the reinforcing steel bars and reference electrode are encapsulated within the concrete to be tested. The conductors are made of anti-interference single-core copper mesh shielded PVC insulated copper core wire to avoid signal interference. After the conductors are led out, one reinforcing steel electrode is grounded and simultaneously connected to the other reinforcing steel electrode via a zero-resistance galvanometer to detect the current signal between the reinforcing steel bars. The Ag / AgCl reference electrode is connected to a current-compensated potential measurement component, and after amplification, the potential signal between the ungrounded reinforcing steel electrode and the reference electrode is detected. The acquired current and potential signals are amplified, converted, stored, and further analyzed to obtain the corrosion assessment results. The sampling period is between 5 s and 60 s, with the specific time set according to the situation.

[0008] The acquired potential and current signals are labeled as E. n =E1, E2, E3, E4...E n； I n =I1, I2, I3, I4...I n..

[0009] Concrete has a high resistivity, and various monitoring noises significantly interfere with the data analysis results. Therefore, the following processing method is adopted: Accumulate 1024 sets of current and potential data for processing, and select the data as a data cluster for analysis. Alternatively, select 1024 sets of data for analysis based on data fluctuations.

[0010] I. Assessment of Uniform Corrosion of Reinforcing Steel Electrodes

[0011]

[0012] σ is the standard deviation of potential or current noise, n is the data sample size, and x i Given a data sample sequence, x represents the average value. The noise resistance R is then calculated. nR n This is the ratio of the standard deviation of potential noise to the standard deviation of current noise, corresponding to the corrosion rate of the reinforcing steel.

[0013] R n The value of Rn is inversely proportional to the corrosion rate of the corrosion system: the larger the value of Rn, the smaller the corrosion rate and the milder the corrosion; R n The smaller the value, the greater the corrosion rate and the more severe the corrosion.

[0014]

[0015] II. Assessment of Localized Corrosion of Reinforcing Steel Electrodes

[0016] After organizing the potential or current signal into a time-sorted data cluster of 1024 data units, the data is processed using Fourier Transform (FFT) to transform the time-domain signal into a frequency-domain signal.

[0017]

[0018] Where x(t) is a time-domain function of potential or current, T is the measurement period, and ω is the angular frequency. For a time series, its power spectral density is:

[0019]

[0020] Where N is the number of data records in the noise record, and Δt is the sampling time interval.

[0021] Based on the frequency domain data obtained from the Fourier transform, the PSD (Power Distribution Spectrum) data of the data signal is processed to determine localized corrosion. The PSD data shows the variation of the data signal with frequency, presented as a sloping curve. The slope of the curve is used to determine the probability of localized corrosion. A larger slope value indicates that the corrosion is mainly localized, while a smaller slope value indicates uniform corrosion or complete passivation.

[0022] III. Assessment of Changes in Concrete Structures

[0023] Based on the measured current and potential signals, an exponential envelope Gaussian white noise modulation signal data processing method was used to identify changes in the external environment and alterations in the concrete structure. The signal changes caused by changes in the external environment mainly consisted of clearly shaped peak signals and periodic pulse signals; while the signal changes caused by alterations in the concrete structure mainly consisted of continuous signal fluctuations at a single frequency.

[0024] The specific data processing methods are as follows:

[0025]

[0026] Where ε(t) is Gaussian white noise with a mean of 0 and a variance of 1. After processing the data, the corresponding waveform curve of the white noise is obtained.

[0027] Furthermore, the working electrodes are two identical steel bars, 1-10 mm in diameter and 10-200 mm in length. The reference electrode is a solid Ag / AgCl electrode.

[0028] Furthermore, during installation, two steel bars serve as working electrodes. The distance between the steel bars is 5-30cm. One steel bar (working electrode 2) is led out with a wire and splits into two, one end connected to the grounding terminal and the other end connected to the detection equipment. One steel bar (working electrode 2) is connected to the other steel bar (working electrode 2) through the zero-resistance galvanometer module in the detection equipment.

[0029] Furthermore, the conductor uses anti-interference single-core copper mesh shielded PVC insulated copper core wire to avoid interference with the acquired signal.

[0030] Furthermore, the Ag / AgCl reference electrode is connected to a current-compensated potential measurement component, and the potential signal between the ungrounded rebar electrode and the reference electrode is detected after amplification. The acquired current and potential signals are then amplified, converted, stored, and further analyzed to obtain corrosion assessment results.

[0031] Furthermore, signal processing methods are employed to process and analyze the detection signals. The results of localized and uniform corrosion of the reinforcing steel in the concrete are then obtained. Based on the signal processing results, the aging and failure status of the concrete is assessed.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. Low detection cost and no damage to the overall building structure. The probe structure required for this concrete corrosion behavior assessment method is simple and inexpensive, and can be installed using existing steel reinforcement without damaging or interfering with the planned solidification of the concrete.

[0034] 2. Suitable for on-site installation and testing. This invention employs an external signal acquisition and processing method to process and analyze the acquired electrochemical signals. The probe is pre-embedded; it only needs to be connected to the testing equipment during measurement; when not measuring, the data cable port is protected to ensure its integrity.

[0035] 3. Conduct a comprehensive assessment of the reinforced concrete structure. The collected signals are processed to evaluate the localized and uniform corrosion of the reinforcing steel. Based on the signal processing results, the failure and aging of the concrete are assessed. Attached Figure Description

[0036] Figure 1 Schematic diagram of a method for monitoring the corrosion and failure behavior of steel bars in concrete;

[0037] In the diagram, 1 is a concrete block; 2 is a working electrode; 3 is a solid electrode, i.e., a silver / silver chloride electrode; 4 is a protective copper core wire; 5 is a grounding terminal; and 6 is a zero-resistance galvanometer and data processing and analysis device.

[0038] Figure 2 A schematic diagram of the electrochemical testing module completed in the embodiment;

[0039] Figure 3 Schematic diagram of the detected potential and current signals;

[0040] Figure 4 Schematic diagram of uniform corrosion data processing results;

[0041] Figure 5 Schematic diagram of localized corrosion data processing results;

[0042] Figure 6 A schematic diagram showing the comparison results of changes in concrete condition. Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments, but is not limited thereto.

[0044] Example

[0045] Sample preparation:

[0046] (1) The electrode fabrication process for monitoring the corrosion behavior of steel bars in concrete is as follows: Electrodes are pre-fabricated on a single steel bar... Two 20cm long steel bar segments were cut from the reinforcing bars to ensure that the steel materials and properties were identical. A wire was welded to one side of each steel bar segment to serve as the working electrode. After welding, the weld joint was ground smooth to ensure that the two working electrodes were in the same condition. A solid Ag / AgCl electrode was selected as the reference electrode. The electrode is a silver rod with a uniform silver chloride layer on its surface, which has a relatively stable potential and fluctuates little with the external environment.

[0047] (2) Two steel bars and a reference electrode are encapsulated within the concrete to be tested, with a distance of approximately 10 cm between the steel bars. The reference electrode is installed near the steel bar serving as the working electrode, approximately 10 cm away from one of the steel bars (working electrode 2). The other steel bar (working electrode 2) is led out with a wire and split into two, one end connected to the grounding terminal and the other end connected to the testing equipment. The wires are made of anti-interference single-core copper mesh shielded PVC insulated copper core wire to avoid interference with the acquired signal. One steel bar (working electrode 2) is connected to the other steel bar (working electrode 2) through the zero-resistance galvanometer module in the testing equipment, and the steel bar (working electrode 2) is also connected to the grounding terminal. Then, concrete is poured to encapsulate all three electrodes within the concrete, leaving the wires exposed on the outside.

[0048] (3) During installation, the Ag / AgCl reference electrode is connected to the current compensation potential measurement component. After amplification, the potential signal between the ungrounded steel bar electrode and the reference electrode is detected. The collected current and potential signals are then converted and stored by a signal amplifier, and further analyzed to obtain the corrosion assessment results.

[0049] After the concrete has been cured for about 28 days, the testing electrodes and equipment can be used to carry out measurement work.

[0050] Test method:

[0051] With attachment Figure 2 Taking a laboratory-encapsulated electrochemical test block as an example, the corrosion behavior of concrete was evaluated. To accelerate concrete corrosion, the encapsulated test block was immersed in simulated seawater. Two working electrodes and a reference electrode were connected to the detection equipment, and the measurement interval was set to 10 seconds.

[0052] The testing equipment contains a zero-resistance galvanometer module and a data acquisition and analysis device. Based on the acquired current and potential signals, it determines whether the steel reinforcement is uniformly corroded or locally corroded. Through signal processing, it obtains signals of changes in the concrete structure and determines the degree of concrete deterioration.

[0053] Data Analysis:

[0054] The measurement and analysis results are attached. Figure 3 , 4 As shown in Figures 5 and 6. The results indicate that the acquired current and voltage signals fluctuate significantly over time, as shown in the attached figures. Figure 3 As shown in the attached figure. The uniform corrosion measurement results were obtained after signal processing. Figure 4 As shown, the corrosion rate of the reinforcing steel fluctuates over time. Initially, the corrosion rate is low; then it gradually increases and remains within a relatively stable range, which is consistent with the passivation process of the reinforcing steel in concrete. (See attached image) Figure 5 PSD graphs at different time points were used to determine the probability of localized corrosion of the reinforcing steel. The comparison revealed that the slope of the PSD curve in the early stage was significantly lower than that in the later stage, indicating that after passivation of the reinforcing steel occurred, localized corrosion became the dominant phenomenon, manifested as the damage and regeneration of the passivation film on the steel surface. The white noise signal processing results are attached. Figure 6 As shown, when there are interfering signals, such as vibration or friction signals, the test results show obvious data fluctuation peaks; when the concrete ages or fails, and during the process of external corrosive ions penetrating, obvious large-area fluctuation peaks appear, and the overall data shows regular changes. Based on this, the overall corrosion state of reinforced concrete can be judged.

Claims

1. A method for monitoring and identifying the corrosion process of reinforcing steel in concrete, characterized in that: The corrosion process of reinforced concrete is monitored using a zero-resistance current module and supporting software. During measurement, two identical steel bars are used as the working electrode and the counter electrode, and a solid Ag / AgCl electrode is selected as the reference electrode. The working electrode and the counter electrode are steel bars with a diameter of 10-50mm and a length of 10-200mm, and the reference electrode has a diameter of 1-10mm. During installation, the steel bars and the reference electrode are encapsulated in the concrete to be tested. The conductors are anti-interference single-core copper mesh shielded PVC insulated copper core wires to avoid interference with the acquired signal. After the wires are led out, one of the steel bar electrode wires is grounded and connected to the other steel bar electrode through a zero-resistance galvanometer to detect the current signal between the steel bars; the Ag / AgCl reference electrode is connected to the current compensation potential measurement component, and after amplification, the potential signal between the ungrounded steel bar electrode and the reference electrode is detected; the collected current and potential signals are amplified, converted, stored, and further analyzed to obtain the corrosion assessment results, with a sampling period of 5-60 seconds; The acquired potential and current signals are labeled as E. n =E1, E2, E3, E4...E n ;I n =I1, I2, I3, I4...I n ; Accumulate 1024 sets of current and potential data for data processing, select the data as a data cluster for analysis, or select 1024 sets of data for analysis based on data fluctuations; I. Assessment of Uniform Corrosion of Reinforcing Steel Electrodes σ is the standard deviation of potential or current noise, n is the data sample size, and x i Given a data sample sequence, x represents the average value; the noise resistance R is calculated from this sequence. n ;R n This is the ratio of the standard deviation of potential noise to the standard deviation of current noise, which corresponds to the corrosion rate of the reinforcing steel. R n The value of Rn is inversely proportional to the corrosion rate of the corrosion system: the larger the value of Rn, the smaller the corrosion rate and the milder the corrosion; R n The smaller the value, the greater the corrosion rate and the more severe the corrosion. II. Assessment of Localized Corrosion of Reinforcing Steel Electrodes After organizing the potential or current signal into a time-sorted data cluster according to 1024 data units, the data is processed by Fast Fourier Transform to transform the time-domain signal into a frequency-domain signal. Where x(t) is a time-domain function of potential or current, T is the measurement period, and ω is the angular frequency; for a time series, its power spectral density is: Where N is the number of noise records and Δt is the sampling time interval; Based on the frequency domain data obtained from the Fourier transform, after processing, PSD spectrum data for identifying localized corrosion is obtained. The PSD spectrum data shows the pattern of data signal variation with frequency, which is in the form of a sloping curve. The probability of localized corrosion is determined based on the slope of the curve. The larger the slope value, the more localized the corrosion, while the smaller the slope value, the more uniform the corrosion or the overall passivation. III. Assessment of Changes in Concrete Structures Based on the measured current and potential signals, the exponential envelope Gaussian white noise modulation signal data processing method is used to identify changes in the external environment and changes in the concrete structure. The signal changes caused by changes in the external environment are mainly peak signals with obvious shapes and periodic pulse signals; while the signal changes caused by changes in the concrete structure are mainly continuous signal fluctuations at a single frequency. The specific data processing methods are as follows: Where ε(t) is Gaussian white noise with a mean of 0 and a variance of 1; the corresponding waveform curve of the white noise is obtained after processing the data.

2. The method for monitoring and identifying the corrosion process of reinforcing steel in concrete according to claim 1, characterized in that: The working electrodes are two identical steel bars, 1-10mm in diameter and 10-200mm in length; the reference electrode is a solid Ag / AgCl electrode; during installation, the two steel bars serve as the working electrodes; the distance between the steel bars is 5-30cm; after a wire is led out from one steel bar, it splits into two, one end of which is connected to the grounding terminal and the other end is connected to the detection equipment; one steel bar is connected to the other steel bar through the zero-resistance galvanometer module in the detection equipment.

3. The method for monitoring and identifying the corrosion process of reinforcing steel in concrete according to claim 1, characterized in that: The conductor uses a single-core copper mesh shielded PVC insulated copper core wire.

4. The method for monitoring and identifying the corrosion process of reinforcing steel in concrete according to claim 1, characterized in that: The Ag / AgCl reference electrode is connected to the current compensation potential measurement component. After amplification, the potential signal between the ungrounded steel bar electrode and the reference electrode is detected. The acquired current and potential signals are converted and stored by the signal amplifier, and then further analyzed to obtain the corrosion assessment results.

5. The method for monitoring and identifying the corrosion process of reinforcing steel in concrete according to claim 1, characterized in that: Signal processing methods are used to process and analyze the detection signals, and finally the results of local and uniform corrosion of steel bars in concrete are obtained. Based on the signal processing results, the failure and aging of concrete are evaluated.

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