Monitoring instrument and monitoring method for longitudinal non-uniform corrosion of reinforcing steel bar based on magnetic field

Abstract

The invention provides a monitoring instrument and a monitoring method for longitudinal non-uniform corrosion of a reinforcing steel bar based on a magnetic field, a monitoring sensor is fixed at the periphery of the monitoring reinforcing steel bar, the monitoring sensor comprises two Hall elements, and the two Hall elements in the longitudinal direction of the reinforcing steel bar monitor the change of the magnetic field intensity around the reinforcing steel bar in situ; the data collector converts voltage signals output by the monitoring sensor into numerical signals and transmits the numerical signals to the data processing system; and the data processing system receives and records the voltage signal data in real time. The corrosion condition of the reinforcing steel bar in the reinforced concrete can be monitored in real time in a lossless and quantitative mode, and the method has the advantages of being easy to operate and high in precision.

Description

Technical Field

[0001] The invention provides a monitoring instrument and a monitoring method for longitudinal non-uniform corrosion of steel bars based on a magnetic field, and relates to the technical field of steel bar corrosion rate monitoring in the engineering field. Background Art

[0002] Reinforced concrete structures are widely used in civil engineering due to their many advantages. However, after chloride attack or concrete carbonization, the passive film is destroyed and the steel begins to corrode. At present, corrosion of steel bars in structures caused by chloride ion attack is relatively common, especially in coastal areas or areas in the north where deicing salt is frequently used. However, there is no absolute way to prevent corrosion; or some protective measures are expensive and cannot be applied to all projects, so regular inspections of building structures are necessary.

[0003] At present, there are many methods for detecting steel corrosion, all of which can be clearly divided into destructive detection and non-destructive detection. Since non-destructive detection methods do not cause additional damage to concrete structures, they are widely used in the study of reinforced concrete corrosion. There are two main types of sensors used for monitoring the durability of reinforced concrete in actual engineering projects: one is based on the principle of macroscopic batteries, such as the anode ladder sensor developed by the Institute of Civil Engineering of Aachen University of Technology in Germany and the CorroWatch sensor developed by FORCE in Denmark; the other is based on the principle of linear polarization, such as the ECI-2 durability monitoring sensor developed by VTI in the United States. In addition, there are many other sensors under development, such as fiber optic sensors, piezoelectric sensors, ultrasonic detection sensors, and new ground penetrating radars. The above sensors can basically determine qualitatively whether the steel bars are corroded. However, due to the complexity of the on-site environment, it is impossible to accurately and quantitatively analyze the deterioration of the durability of the steel bars. Therefore, it is impossible to obtain a comprehensive picture of the corrosion of reinforced concrete structures. There is still a lot of room for development in the durability monitoring of actual projects.

[0004] Based on magnetic medium and magnetic field theory, a magnetic field-based non-destructive dynamic monitoring instrument (MCD) for steel bars has been developed. The MCD instrument can non-destructively and quantitatively monitor the corrosion of steel bars in reinforced concrete in real time, and is also easy to operate and highly accurate. Before pouring concrete, the steel bars are placed in the test area of ​​the MCD sensor. The steel bars are in the magnetic circuit path of the MCD, so they have a positive effect on the magnetic field of the MCD. When reinforced concrete is in use, the steel bars are corroded by substances such as water and chloride ions. Due to the huge difference in magnetic conductivity between the steel bars and the rust products, the magnetic field around the steel bars also changes. The change in the magnetic signal will be captured by the Hall element, and the change in the magnetic signal will be converted into the steel bar corrosion rate through the instrument's own calibration curve. Therefore, MCD has great development potential in engineering applications.

[0005] Since MCD is limited by the diameter of the steel bar in the test area, it is only applicable to plain round steel bars of a certain diameter. After more tests, it was found that the magnetic induction intensity measured by MCD does not indicate the corrosion rate of the entire steel bar, but indicates the corrosion condition of the side of the steel bar close to the measuring point, so MCD can only be applied to the situation where the steel bar is uniformly corroded. In order to obtain a more comprehensive understanding of the corrosion condition of the steel bar, the present invention provides a monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, such as the limitation of the diameter of the steel bar and the fact that the corrosion of only one position of the steel bar can be tested. The present invention provides a magnetic field-based longitudinal non-uniform steel bar corrosion monitoring instrument and a testing method thereof.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] A monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field, comprising a monitoring sensor, a data collector and a data processing system;

[0009] The monitoring sensor is fixed to the periphery of the monitoring steel bar, and the monitoring sensor includes two Hall elements. The two Hall elements in the longitudinal direction of the steel bar monitor the change of the magnetic field intensity around the steel bar in situ;

[0010] The data collector converts the output voltage signal of the monitoring sensor into a numerical signal and transmits it to the data processing system;

[0011] The data processing system receives voltage signal data and records it in real time.

[0012] The monitoring sensor specifically includes:

[0013] Silicon steel frame, used to form a magnetic field loop;

[0014] The silicon steel frame is U-shaped, with a permanent magnet installed in the middle recess to generate a steady-state magnetic field;

[0015] Both ends of the silicon steel frame are provided with Hall element slots for installing Hall elements;

[0016] The installed Hall element is SS495A Hall sensor, which outputs the magnetic field change caused by steel bar corrosion as voltage change based on the Hall effect;

[0017] It also includes a data acquisition board, which is an ADS1256IDB data acquisition board for collecting and transmitting the voltage signal of the Hall element;

[0018] The four-core cable connects the monitoring sensor to the data collector.

[0019] The data collector specifically includes:

[0020] The circuit board of the ADS1256 signal acquisition main chip converts the sensor output voltage signal into a numerical signal through four processes: sampling, holding, quantization and encoding;

[0021] RS232 USB to serial port chip realizes USB to serial port conversion, thereby connecting the data logger to the computer USB interface.

[0022] The data processing system specifically includes: a monitoring instrument module, which automatically stores, automatically processes, and records in real time the voltage signal output by the sensor and displays it as a specific voltage value.

[0023] A method for monitoring longitudinal non-uniform corrosion of steel bars based on a magnetic field, using the aforementioned monitoring instrument for longitudinal non-uniform corrosion of steel bars based on a magnetic field; comprising the following steps:

[0024] Step 1: Measure the voltage value of a type of steel bar when it is not corroded;

[0025] Step 2: corrode the steel bar, measure the voltage value of the steel bar after corrosion, and measure the corrosion rate of the steel bar at the same time;

[0026] Step 3: Repeat step 2 to establish the relationship between the steel bar corrosion rate and the measured voltage;

[0027] Step 4: embed the sensor in the reinforced concrete component, measure the voltage value, and obtain the steel corrosion rate based on the relationship established in step 3.

[0028] Working principle:

[0029] The monitoring sensor for longitudinal non-uniform corrosion of steel bars based on magnetic field comprises a permanent magnet and a silicon steel frame. The permanent magnet itself can generate a fixed magnetic field. When combined with the silicon steel frame in the monitoring sensor, the magnetic flux will generate a magnetic circuit along the silicon steel frame and the air. When the steel bar is located at the test position of the monitoring sensor, that is, the air position on the magnetic circuit path, since the steel bar is a magnetic conductor and the air is a non-magnetic conductor, the presence of the steel bar interferes with the magnetic circuit of the monitoring sensor. The change of the magnetic circuit is detected by the Hall element in the monitoring sensor and output as a voltage signal, which is displayed as a certain magnetic induction intensity value on the computer terminal after being processed by the data acquisition device. As the steel bar corrodes, the interference to the magnetic circuit changes, resulting in a change in the magnetic induction intensity value finally output. In this way, a correlation between the steel bar corrosion rate and the magnetic induction intensity value is established, so as to achieve the purpose of quantitatively judging the steel bar corrosion rate by monitoring the magnetic induction intensity value.

[0030] Based on magnetic medium and magnetic field theory, the present invention can non-destructively and quantitatively monitor the corrosion of steel bars in reinforced concrete in real time, and has the characteristics of easy operation and high precision. Therefore, it has great development potential in engineering applications.

[0031] Compared with the prior art, the beneficial effects of the present invention are mainly manifested in:

[0032] 1. The sensor has a small structure, is easy to install and simple to operate.

[0033] 2. There is no restriction on the diameter of steel bars in the sensor test area, so it can be applied to steel bars of different diameters.

[0034] 3. The sensor has two measuring points in the longitudinal direction of the steel bar. The test results show that the sensor can respectively indicate the magnetic induction intensity values ​​at two longitudinal positions of the steel bar under different corrosion conditions. That is, when the steel bar is non-uniformly corroded in the longitudinal direction, the corrosion conditions at the two positions can be obtained and converted into the steel bar corrosion rate.

[0035] 4. Before the sensor is embedded in reinforced concrete, the relationship between the amount of steel corrosion and the magnetic induction intensity value has been established. When applied in subsequent projects, the monitoring sensor embedded in reinforced concrete can quantitatively determine the corrosion of the steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the appearance of the monitoring sensor;

[0037] Figure 2 To monitor the internal structure of the sensor;

[0038] Figure 3 To monitor the internal structure of the sensor;

[0039] Figure 4 Schematic diagram of the semi-immersion impressed current accelerated corrosion test. DETAILED DESCRIPTION

[0040] like Figures 1 to 4 As shown, a monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field includes a monitoring sensor 1, a data collector 2 and a data processing system 4;

[0041] The monitoring sensor 1 is fixed to the periphery of the monitoring steel bar 5. The monitoring sensor 1 includes two Hall elements 14. The two Hall elements 14 in the longitudinal direction of the steel bar 5 monitor the change of the magnetic field intensity around the steel bar 5 in situ.

[0042] The data collector 2 converts the output voltage signal of the monitoring sensor 1 into a numerical signal and transmits it to the data processing system 4;

[0043] The data processing system 4 receives the voltage signal data and records it in real time.

[0044] The monitoring sensor 1 specifically comprises:

[0045] Silicon steel frame 12, used to form a magnetic field loop;

[0046] The silicon steel frame 12 is U-shaped, and a permanent magnet 11 is installed in the middle concave portion for generating a steady-state magnetic field;

[0047] Both ends of the silicon steel frame 12 are provided with Hall element slots 13 for installing Hall elements 14;

[0048] The installed Hall element 14 is a SS495A Hall sensor, which outputs the magnetic field change caused by the corrosion of the steel bar 5 as a voltage change according to the Hall effect;

[0049] It also includes a data acquisition board 15, which is an ADS1256IDB data acquisition board, used to collect and transmit the voltage signal of the Hall element 14;

[0050] The four-core cable 8 connects the monitoring sensor 1 to the data collector 2 .

[0051] The data collector 2 specifically includes:

[0052] The circuit board of the ADS1256 signal acquisition main chip converts the sensor output voltage signal into a numerical signal through four processes: sampling, holding, quantization and encoding;

[0053] RS232 USB to serial port chip realizes USB to serial port conversion, thereby connecting the data collector 2 to the computer USB interface.

[0054] The data processing system 4 specifically includes: a monitoring instrument module that automatically stores, automatically processes, and records in real time the voltage signal output by the sensor and displays it as a specific voltage value.

[0055] A method for monitoring longitudinal non-uniform corrosion of steel bars based on a magnetic field, using the aforementioned monitoring instrument for longitudinal non-uniform corrosion of steel bars based on a magnetic field; comprising the following steps:

[0056] Step 1: Measure the voltage value of a type of steel bar when it is not corroded;

[0057] Step 2: corrode the steel bar, measure the voltage value of the steel bar after corrosion, and measure the corrosion rate of the steel bar at the same time;

[0058] Step 3: Repeat step 2 to establish the relationship between the steel bar corrosion rate and the measured voltage;

[0059] Step 4: embed the sensor in the reinforced concrete component, measure the voltage value, and obtain the steel corrosion rate based on the relationship established in step 3.

[0060] The implementation method of the present invention is specifically described below using 16mmHPB300 plain round steel bars as an example.

[0061] 1. Prepare 2 steel bars with a length of 15 cm, measure the mass with an electronic scale, and calculate the mass of the middle 5 cm as m;

[0062] 2. Weld the wire on one side of the steel bar, then apply epoxy resin 5cm from both ends, and wrap it with waterproof tape after solidification, so that only the middle 5cm will be corroded. (The corrosion rate of the two ends of the steel bar corroded by electricity is quite different from that of the middle steel bar, so only the middle part is measured);

[0063] 3. The mass of the entire sample after measurement and processing is M0;

[0064] 4. Mark two points at the center of each steel bar and measure the initial voltage value V0 with a sensor;

[0065] 5. As Figure 4 , the data collector 2 is connected to the power supply 3 and the data processing system 4 of the data collector, the steel bar 1 is placed in a 5% NaCl solution, and an auxiliary electrode 6 is also placed. The steel bar 5 and the auxiliary electrode 6 are respectively connected to the two poles of the power supply 7. The steel bar is placed in a 5% NaCl solution, and the current density is 20A / m 2 , after every 24 hours, take out the rusted steel bars, use the monitoring sensor 1 to measure the post-rust voltage V11, V21 (the voltage of two measuring points), then use the steel bar rust remover to remove the external rust layer, and after drying, use an electronic scale to measure the post-rust mass M1;

[0066] 6. Repeat step 5, record the post-rust voltage V12, V22, V13, V23...; post-rust mass M2, M3... When the steel bar corrosion rate is close to 20%, the measurement ends.

[0067] 7. Use the formula (V0-Vi j ) / V0 is used to calculate the voltage change rate of the i measuring point in the jth cycle; (M0-Mi) / m is used to calculate the corrosion rate of the middle 5cm steel bars, and this value is used as the corrosion rate of the two calibration points of each steel bar.

[0068] 8. With the mass loss rate as the horizontal coordinate and the voltage change rate as the vertical coordinate, the voltage change rate and the corresponding mass loss rate of all points and all cycles are substituted to obtain the correlation between the voltage change rate and the mass loss rate of this type of steel bar. The obtained relationship is a nonlinear relationship: Among them, ΔU is the voltage change rate, Δm is the mass loss rate, and a, b, and c are nonlinear coefficients.

[0069] 9. When pouring reinforced concrete components, bury the sensor at the key point of the component (such as the mid-span of the bending beam), measure the voltage V0 of the monitoring point before corrosion, and measure the voltage Vi of the monitoring point again after the component has corroded for a certain period of timej , calculate the voltage reduction rate, substitute it into the formula obtained in step 8, and get the corrosion rate of the two measuring points in the longitudinal direction of the steel bar, which respectively represent the corrosion conditions of the two longitudinal positions of the steel bar, and then get the actual corrosion rate of the steel bar in the two longitudinal positions.

[0070] 10. Use the measured steel corrosion rate to evaluate the concrete structure. When the steel corrosion rate is less than 5%, appropriate measures can be taken to prevent further corrosion of the steel. When the steel corrosion rate is greater than 5% and less than 10%, it is necessary to evaluate the components to see whether local maintenance is required. When the steel corrosion rate is greater than 10%, the components need to be maintained or replaced.

Claims

1. A monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field, characterized by: It comprises a monitoring sensor (1), a data collector (2) and a data processing system (4); The monitoring sensor (1) is fixed to the periphery of the monitoring steel bar (5), and the monitoring sensor (1) comprises two Hall elements (14). The two Hall elements (14) in the longitudinal direction of the steel bar (5) monitor the change of the magnetic field intensity around the steel bar (5) in situ; The data collector (2) converts the output voltage signal of the monitoring sensor (1) into a numerical signal and transmits it to the data processing system (4); The data processing system (4) receives voltage signal data and records it in real time.

2. The monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field according to claim 1, characterized in that: The monitoring sensor (1) specifically comprises: A silicon steel frame (12) for forming a magnetic field loop; The silicon steel frame (12) is U-shaped, and a permanent magnet (11) is installed in the middle concave portion for generating a steady-state magnetic field; Both ends of the silicon steel frame (12) are provided with Hall element slots (13) for installing Hall elements (14); The Hall element (14) is a SS495A Hall sensor, which outputs the magnetic field change caused by the corrosion of the steel bar (5) as a voltage change according to the Hall effect; It also includes a data acquisition board (15), which is an ADS1256IDB data acquisition board, used for collecting and transmitting the voltage signal of the Hall element (14); A four-core cable (8) connects the monitoring sensor (1) and the data collector (2).

3. The monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field according to claim 1, characterized in that: The data collector (2) specifically comprises: The circuit board of the ADS1256 signal acquisition main chip converts the sensor output voltage signal into a numerical signal through four processes: sampling, holding, quantization and encoding; The RS232 USB to serial port chip realizes USB to serial port conversion, thereby connecting the data collector (2) to the computer USB interface.

4. The monitoring instrument for longitudinal non-uniform corrosion of steel bars based on magnetic field according to claim 1, characterized in that: The data processing system (4) specifically comprises: The monitoring instrument module automatically stores, processes and records the voltage signal output by the sensor in real time and displays it as a specific voltage value.

5. A method for monitoring longitudinal non-uniform corrosion of steel bars based on magnetic field, characterized in that: A monitoring instrument for longitudinal non-uniform corrosion of steel bars based on a magnetic field as claimed in any one of claims 1 to 4 is adopted; the monitoring instrument comprises the following steps: Step 1: Measure the voltage value of a type of steel bar when it is not corroded; Step 2: corrode the steel bar, measure the voltage value of the steel bar after corrosion, and measure the corrosion rate of the steel bar at the same time; Step 3: Repeat step 2 to establish the relationship between the steel bar corrosion rate and the measured voltage; Step 4: embed the sensor in the reinforced concrete component, measure the voltage value, and obtain the steel corrosion rate based on the relationship established in step 3.

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