Method for monitoring and judging corrosion process of steel bars in concrete

Abstract

The invention provides a method for monitoring and judging the corrosion process of steel bars in concrete, which adopts a zero-resistance galvanometer to measure the steel bars pre-buried in the concrete, and processes the measurement result of the zero-resistance galvanometer through a spectral analysis method to represent the corrosion condition of the surfaces of the steel bars. A noise signal processing analysis method is adopted, concrete state changes are judged according to white noise and other signal changes, and the concrete aging process is determined. The method has the advantages of low detection cost and no damage to the overall structure of the building. The method is suitable for field installation and detection. And overall evaluation is carried out on the reinforced concrete structure. Local corrosion and uniform corrosion results of the reinforcing steel bars are evaluated by processing the collected signals, and concrete failure aging conditions are evaluated according to signal processing results.

Description

Technical Field

[0001] The invention relates to the field of monitoring and distinguishing methods for steel bar corrosion process in concrete, and can monitor the process of steel bar pitting in concrete and the expansion of rust layer on the surface of the steel bar. Background Art

[0002] Reinforced concrete structures are the most common building materials. The high alkalinity (pH 12-13) of the microporous aqueous solution of concrete can usually provide protection for the steel bars, that is, high alkalinity can make the steel bars passivated. Due to the high resistivity of concrete, it can reduce the penetration of some corrosive factors (such as chlorides, carbon dioxide and water) into the surface of the steel bars; it also reduces the corrosion current flowing from the anode area to the cathode and reduces its corrosion rate. However, in actual use, the corrosion of steel bars in many reinforced concrete structures has become the main reason for the degradation of structural performance.

[0003] Generally, there are two main factors that can cause steel corrosion: one is carbonation; the other is the presence of chloride ions, which may come from the formation of concrete or penetrate into the concrete during service. When the corrosion process begins, the corrosion products, namely iron oxides and hydroxides, will accumulate several times the original iron, and the expansion of the rust products will generate internal stress, which will cause the concrete protective layer of the steel bar to crack along the reinforcement or even peel off.

[0004] The corrosion of steel bars in concrete is a slow and gradual process. It occurs and develops in concrete, which is difficult to detect and monitor. Once failure occurs, it is an instantaneous process. Therefore, the loss caused by the failure of steel bars in concrete is huge. The on-site detection method of reinforced concrete structures in marine environment or other special environments is increasingly gaining widespread attention. At present, there are some optional detection methods, including non-destructive experiments on actual structures, physical, chemical and petrographic analysis methods and bearing capacity tests for samples taken from the structure. Among them, the electrochemical method is one of the most suitable non-destructive detection methods for detecting the corrosion of reinforced concrete structures. According to the actual application situation on site, the half-cell potential method, concrete resistivity detection method and DC linear polarization resistance method are mainly used. However, the existing monitoring of steel corrosion in concrete under marine environment adopts electrochemical polarization or impedance measurement methods. The potential is applied to the surface of the steel bar, which has a certain destructive effect on the surface state of the steel bar. Moreover, due to the large internal resistance of concrete itself, there is a large error in the detection results. Summary of the invention

[0005] The purpose of the present invention is to provide a method for monitoring and distinguishing the steel bar corrosion process in concrete, using a zero-resistance ammeter to measure the steel bars embedded in concrete, and processing the measurement results of the zero-resistance ammeter by spectrum analysis to characterize the corrosion of the steel bar surface. Using a noise signal processing and analysis method, the concrete state change is determined by the white noise and other signal changes to determine the concrete aging process.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for monitoring and distinguishing the corrosion process of steel bars in concrete uses a zero-resistance current module and supporting software to monitor the corrosion process of reinforced concrete. Two identical steel bar electrodes are used as working electrodes and counter electrodes during measurement, and a solid Ag / AgCl electrode is selected as the reference electrode. The working electrode and the counter electrode are selected from steel bars with a diameter of 10-50 mm and a length of 10-200 mm, and the reference electrode has a diameter of 1-10 mm. During installation, the steel bar and the reference electrode are encapsulated in the concrete to be detected, and the wire uses an anti-interference single-core copper mesh shielded polyvinyl chloride insulated copper core wire to avoid interference with the collected signal. After the wire is led out, one of the steel bar electrode wires is grounded and connected to the other steel bar electrode through a zero-resistance ammeter to detect the current signal between the steel bars. The Ag / AgCl reference electrode is connected to a current compensation potential measurement component, and the potential signal between the ungrounded steel bar electrode and the reference electrode is detected after amplification. After the collected current and potential signals are converted and stored through the signal amplifier, they are further analyzed and processed to obtain the corrosion assessment result. The sampling period is between 5s and 60s, and the specific time is set according to the situation.

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

[0009] The resistance value in concrete is relatively high, and various monitoring noises interfere significantly with the data analysis results. Therefore, the following processing method is used for processing. 1024 sets of current and potential data are accumulated for data processing, and the selected data are analyzed as data clusters. Or 1024 sets of data are selected for analysis according to data fluctuations.

[0010] 1. Evaluation of Uniform Corrosion of Steel Bar Electrodes

[0011]

[0012] σ is the standard deviation of potential or current noise, n is the data sample size, x i is the data sample sequence, and x is the average value. The noise resistance R is calculated from this n. R n It 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 steel bar.

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

[0014]

[0015] 2. Assessment of local corrosion of steel bar electrodes

[0016] After the potential or current signal is organized into a time-ordered data cluster according to 1024 data units, the data is processed using Fourier transform (FFT) to convert the time domain signal into a frequency domain signal.

[0017]

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

[0019]

[0020] Where N is the number of noise recorded data and Δt is the sampling time interval.

[0021] According to the frequency domain data obtained by Fourier transform, after sorting, the PSD spectrum data of the data signal for judging local corrosion is obtained. The PSD spectrum data is the law of the data signal changing with frequency, which is in the shape of an inclined curve. The probability of local corrosion is judged according to the slope of the curve. The larger the slope value, the more local corrosion is dominant, while the smaller the slope value, the more uniform corrosion or overall passivation is predicted.

[0022] 3. Assessment of concrete structure changes

[0023] According to the measured current and potential signals, the exponential envelope Gaussian white noise modulation signal data processing method is used to distinguish the changes in the external environment and the changes in the concrete structure. The signal changes caused by the changes in the external environment are mainly peak signals with obvious shapes and periodic pulse signals; while the signal changes caused by the changes in the concrete structure are mainly single-frequency continuous signal fluctuations.

[0024] The specific data processing method is as follows:

[0025]

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

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

[0028] Furthermore, during installation, two steel bars are used as working electrodes. The distance between the steel bars is 5-30 cm. A steel bar (working electrode 2) is divided into two after the lead wire is drawn out, one end is connected to the ground terminal, and the other end is connected to the detection device. One steel bar (working electrode 2) is connected to another steel bar (working electrode 2) through a zero-resistance ammeter module in the detection device.

[0029] Furthermore, the conductor adopts an anti-interference single-core copper mesh shielded polyvinyl chloride insulated copper core wire to avoid interference with the collected signals.

[0030] Furthermore, the Ag / AgCl reference electrode is connected to the flow compensation potential measurement component, and the potential signal between the ungrounded steel bar electrode and the reference electrode is detected after amplification. The collected current and potential signals are converted and stored after passing through the signal amplifier, and then further analyzed and processed to obtain the corrosion assessment results.

[0031] Furthermore, the signal processing method is used to process and analyze the detection signal. Finally, the local corrosion and uniform corrosion results of the steel bars in the concrete are obtained. And based on the signal processing results, the concrete failure aging condition is evaluated.

[0032] The beneficial effects of the present invention are:

[0033] 1. Low detection cost and no damage to the overall structure of the building. The probe required for the concrete corrosion behavior assessment method is simple in structure and low in cost. It can be installed using existing steel bars and will not damage or interfere with the planned solidification of concrete.

[0034] 2. Suitable for on-site installation and testing. The present invention adopts an external signal acquisition and processing method to process and analyze the collected electrochemical signals. The probe is pre-buried and can be connected to the detection equipment when measuring; when not measuring, the data line port is protected intact.

[0035] 3. Make an overall assessment of the reinforced concrete structure. The collected signals are processed to evaluate the local corrosion and uniform corrosion of the steel bars. And based on the signal processing results, the concrete failure and aging are evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0037] In the figure, 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 ground terminal; 6 is a zero-resistance ammeter and a data processing and analysis device;

[0038] Figure 2 Schematic diagram of the electrochemical test 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 local corrosion data processing results;

[0042] Figure 6 Schematic diagram of comparison results of concrete state changes. DETAILED DESCRIPTION

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

[0044] Example

[0045] Sample preparation:

[0046] (1) The electrode processing process for monitoring the corrosion behavior of steel bars in concrete is as follows: Cut two 20cm long steel bars from the steel bars to ensure that the steel bars have the same material and performance. Weld a wire on one side of the steel bar segment as the working electrode. After welding, polish the weld point to make it smooth and flat so that the two working electrodes are in the same state. The reference electrode is a solid Ag / AgCl 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) Encapsulate two steel bars and a reference electrode in the concrete to be tested, with a distance of about 10 cm between the steel bars. The reference electrode can be installed near the steel bar used as the working electrode, about 10 cm away from one of the steel bars (working electrode 2). The other steel bar (working electrode 2) is divided into two wires after the lead wire is drawn out, one end is connected to the ground terminal, and the other end is connected to the detection equipment. The wire uses an anti-interference single-core copper mesh shielded polyvinyl chloride insulated copper core wire to avoid interference with the collected signal. One steel bar (working electrode 2) is connected to another steel bar (working electrode 2) through the zero-resistance ammeter module in the detection equipment, and the steel bar (working electrode 2) is also connected to the ground terminal. Then pour the concrete, encapsulate all three electrodes in the concrete, and reserve wires outside.

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

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

[0050] Test method:

[0051] Attach Figure 2 The laboratory encapsulated electrochemical test block was used as an example to evaluate the corrosion behavior of concrete. To accelerate the corrosion of concrete, the encapsulated test block was immersed in simulated seawater. The two working electrodes and the reference electrode were connected to the detection equipment respectively, and the measurement interval was set to 10s.

[0052] The detection equipment contains a zero-resistance ammeter module and a data acquisition and analysis device. Based on the collected current and potential signals, it can judge the uniform corrosion and local corrosion of the steel bars respectively. Through signal processing, it can obtain the signal of concrete structure change and judge the deterioration of the concrete.

[0053] Data Analysis:

[0054] The measurement and analysis results are as attached. Figure 3 , 4 , 5, and 6. The results show that the collected current and voltage signals fluctuate greatly over time. Figure 3 After signal processing, the uniform corrosion measurement results are obtained, as shown in the attached Figure 4 As shown in Figure 2, the corrosion rate of steel bars fluctuates over time. At the beginning, the corrosion rate is low; then it gradually increases and remains in a relatively stable range, which is consistent with the passivation process of steel bars in concrete. Figure 5 The PSD graphs at different times are used to determine the probability of local corrosion of the steel bar. By comparison, it is found that the slope of the early PSD curve is significantly lower than that of the later PSD curve, indicating that after the steel bar is passivated, local corrosion begins to dominate, which is manifested as the damage and regeneration of the passive film on the steel bar surface. The white noise signal processing results of the detection are shown in the attached figure. Figure 6 As shown in the figure, when there are interference signals, such as vibration and friction signals, the test results show obvious data fluctuation peaks; when the concrete is aged or failed, and when external corrosive ions penetrate, obvious large-area fluctuation peaks appear, and the overall data changes regularly. Based on this, the overall corrosion state of reinforced concrete can be judged.

Claims

1. A method for monitoring and distinguishing the corrosion process of steel bars in concrete, characterized in that: The zero-resistance current module and supporting software are used to monitor the corrosion process of reinforced concrete. Two identical steel bar electrodes are used as working electrodes and counter electrodes during measurement, and a solid Ag / AgCl electrode is selected as the reference electrode. The working electrode and counter electrode are selected from 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 bar and the reference electrode are encapsulated in the concrete to be tested, and the wire uses an anti-interference single-core copper mesh shielded PVC insulated copper core wire to avoid interference with the collected 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 ammeter to detect the current signal between the steel bars; the Ag / AgCl reference electrode is connected to the flow compensation potential measurement component, and the potential signal between the ungrounded steel bar electrode and the reference electrode is detected after amplification; the collected current and potential signals are converted and stored after passing through the signal amplifier, and then further analyzed and processed to obtain the corrosion assessment results. The sampling period is between 5-60s; The collected potential and current signals are marked as E n =E1, E2, E3, E4;;E n； I n =I1, I2, I3, I4; n.. Accumulate 1024 sets of current and potential data for data processing, and analyze the selected data as a data cluster, or select 1024 sets of data for analysis based on data fluctuations; 1. Evaluation of Uniform Corrosion of Steel Bar Electrodes σ is the standard deviation of potential or current noise, n is the data sample size, x i is the data sample sequence, x is the average value; the noise resistance R is calculated from this n ; R n is the ratio of the standard deviation of potential noise to the standard deviation of current noise, corresponding to the corrosion rate of steel bars; R n The value is inversely proportional to the corrosion rate of the corrosion system: the larger the Rn, the smaller the corrosion rate and the milder the corrosion; n The smaller it is, the greater the corrosion rate and the more serious the corrosion; 2. Assessment of local corrosion of steel bar electrodes After the potential or current signal is organized into a time-ordered data cluster according to 1024 data units, the data is processed using Fourier transform (FFT) to transform the time domain signal into a frequency domain signal; Where x(t) is the 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 recorded data, and Δt is the sampling time interval; The frequency domain data obtained by Fourier transform is sorted to obtain the PSD spectrum data of the data signal for judging local corrosion; the PSD spectrum data is the law of the data signal changing with frequency, in the shape of an inclined curve; the probability of local corrosion is judged according to the slope of the curve; the larger the slope value, the more local corrosion is dominant, while the smaller the slope value, the more uniform corrosion or overall passivation is predicted; 3. Assessment of concrete structure changes 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 concrete structure. The signal changes caused by the external environment changes are mainly peak signals with obvious shapes and periodic pulse signals; while the signal changes caused by the concrete structure changes are mainly single-frequency continuous signal fluctuations. The specific data processing method is as follows: Where ε(t) is a 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.

2. The method for monitoring and distinguishing steel bar corrosion process in concrete according to claim 1, characterized in that: The working electrodes are two steel bars of the same state, with a diameter of 1-10 mm and a length of 10-200 mm; the reference electrode is a solid Ag / AgCl electrode; during installation, the two steel bars are used as working electrodes; the distance between the steel bars is 5-30 cm; a steel bar is divided into two after the lead wire is led out, one end is connected to the ground terminal, and the other end is connected to the detection equipment, and one steel bar is connected to the other steel bar through the zero-resistance ammeter module in the detection equipment.

3. The method for monitoring and distinguishing steel bar corrosion process in concrete according to claim 1, characterized in that: The conductor adopts single-core copper mesh shielding and PVC insulation to protect the copper core wire.

4. The method for monitoring and distinguishing steel bar corrosion process in concrete according to claim 1, characterized in that: The Ag / AgCl reference electrode is connected to the flow compensation potential measurement component, and the potential signal between the ungrounded steel bar electrode and the reference electrode is detected after amplification; the collected current and potential signals are converted and stored through the signal amplifier, and then further analyzed and processed to obtain the corrosion assessment results.

5. The method for monitoring and distinguishing steel bar corrosion process in concrete according to claim 1, characterized in that: The signal processing method is used to process and analyze the detection signal, and finally the local corrosion and uniform corrosion results of the steel bars in the concrete are obtained. According to the signal processing results, the failure and aging of the concrete are evaluated.

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