Integrated detection system for non-contact monitoring of corrosion state of reinforced concrete structure

Abstract

The invention discloses an integrated detection system for non-contact monitoring of a corrosion state of a reinforced concrete structure, and the system comprises a plurality of pre-embedded sensing carriers which are fixed in grids of a steel reinforcement framework before concrete pouring, and cavities are formed in the sensing carriers; the permanent magnet excitation body is fixedly arranged at the central position of the cavity; hall sensor arrays which are uniformly distributed along the inner wall of the cavity are adopted; the signal conditioning and processing unit is electrically connected with the Hall sensor array; the wireless transmission unit is used for sending the digitized magnetic field data to the data analysis terminal; and the data analysis terminal is used for receiving and storing the magnetic field data, constructing a detection model based on the equivalent magnetic circuit model, calculating to obtain the mass loss of the sensing carrier shell, and evaluating the corrosion state by using the mass loss. The method can accurately and stably evaluate the corrosion position and degree of the steel bar in the concrete, and is suitable for in-service durability evaluation, health monitoring and maintenance decision support of buildings and infrastructures.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering structural health monitoring and non-destructive testing technology, specifically relating to an integrated testing system for non-contact monitoring of corrosion status in reinforced concrete structures. Background Technology

[0002] In today's construction engineering field, reinforced concrete is widely used, but the resulting corrosion problem is becoming increasingly prominent, posing significant economic and safety hazards. Studies have shown that steel corrosion is the dominant factor leading to the deterioration of concrete structure durability. The resulting expansion effect induces cracking of the protective layer, which in turn accelerates the penetration of corrosive media such as chloride ions, oxygen, and moisture, forming a vicious cycle of "corrosion-cracking" that significantly weakens the structure's load-bearing capacity. Therefore, accurately obtaining the degree of corrosion of the steel reinforcement inside concrete and assessing its durability status is of great significance for structural safety analysis, life prediction, and maintenance decisions.

[0003] Existing steel reinforcement corrosion detection technologies can be broadly categorized into two types: destructive testing and non-destructive testing. Destructive testing typically requires removing the protective layer or extracting the steel reinforcement. While it allows for direct and accurate measurement of corrosion rates, it compromises structural integrity and is unsuitable for long-term monitoring and in-service assessment. Non-destructive testing methods are more widely used in engineering and mainly include electrochemical and physical methods. Electrochemical methods can quantitatively assess corrosion status and are suitable for early warning, but they usually require electrical contact with the steel reinforcement, are significantly affected by the environment, and are not suitable for large-area rapid detection. Physical methods offer advantages such as non-contact, non-destructive testing, and suitability for large-scale rapid assessment, making them more suitable for on-site engineering needs. Electromagnetic detection utilizes changes in electromagnetic properties caused by steel reinforcement corrosion to identify damage, but there is still room for improvement in terms of anti-interference capabilities, decoupling identification ability, coverage, and engineering feasibility.

[0004] Regarding the assessment of damage to reinforced concrete structures, acquisition of electromagnetic signals from steel bar corrosion, sensor calibration, and signal transmission, various patents have proposed solutions. For example, CN114528753A discloses an intelligent monitoring device and method for assessing the degree of damage to reinforced concrete, focusing on a comprehensive assessment of the damage level by collecting relevant structural information; CN109541016A discloses a portable device and method for acquiring electromagnetic sensor signals from corroded steel bars, primarily focusing on the portable acquisition of electromagnetic signals from corroded steel bars; CN113720755A discloses a calibration device and method for multi-point corrosion of steel bars suitable for built-in magnetic sensors, proposing improvements to the calibration and correction issues in magnetic sensor detection; and CN115388946A discloses a device and method for evaluating the wireless transmission performance of electromagnetic signals from built-in sensors in concrete, focusing on the evaluation and reliability of wireless transmission performance of electromagnetic signals from built-in sensors in concrete media.

[0005] However, the aforementioned existing technologies mostly conduct research on different links in the monitoring link separately, or tend to focus on stage-by-stage detection and inspection-style signal acquisition, or rely on pre-calibration and manual intervention, or only evaluate single issues such as signal transmission. It is still difficult to form a long-term, stable, and feasible in-situ monitoring system for service life under actual engineering conditions. At the same time, there is still a lack of effective means to suppress and quantitatively characterize the impact of factors such as the possible positional deviation of steel bars in concrete structures, complex corrosion morphology, and environmental interference on the accuracy of electromagnetic detection results. Therefore, there is still room for further improvement in terms of anti-interference ability, decoupling identification ability, and engineering feasibility.

[0006] Based on the above situation, it is necessary to provide a built-in, interference-resistant, and highly sensitive electromagnetic detection solution. To this end, this invention proposes a novel built-in magnetic sensor based on magnetic media theory: a sensor array is arranged on the inner wall of a steel reinforcement carrier, and a quantitative relationship between the degree of steel reinforcement corrosion and magnetic induction intensity is established by combining permanent magnet excitation and multi-point magnetic field measurement, and a mathematical model of magnetic induction intensity and corrosion depth is constructed. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention proposes an integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures. This system is rationally designed, overcomes the shortcomings of existing technologies, and demonstrates excellent performance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures, comprising: Multiple optimized pre-embedded sensor carriers are fixed inside the grid of the steel reinforcement frame before concrete pouring, thus pre-embedded in the concrete structure, and the sensor carriers form cavities inside; the shell of the pre-embedded sensor carrier is square and made of the same material as the steel reinforcement frame, and multiple pre-embedded sensor carriers are arranged in the steel reinforcement frame accordingly. A permanent magnet exciter, after parametric modeling and iterative optimization, is fixedly positioned at the center of the cavity to construct a stable magnetic flux density excitation field in the area to be tested. Key parameters of the permanent magnet exciter, including its magnetization direction, center position offset, and air gap thickness, are set as variables, and a parametric model is constructed in the Comsol Multiphysics environment. The excitation field is quantified in the distance domain, with the center projection point of the permanent magnet exciter as the origin, and the field is measured radially on the surface under test. With step size Sampling was performed to obtain the magnetic flux density distribution. and with As a strength constraint, the goal is to minimize the peak-to-valley difference of B(r) within the distance domain, i.e., minimize... As a quantitative index and optimization target of the uniformity of the excitation field, the parameters are automatically adjusted and the magnetic field distribution is solved multiple times under the boundary conditions of the volume constraint of the permanent magnet exciter and the installation space constraint in the reinforced concrete structure by introducing the adaptive step size gradient descent method of magnetic circuit constraint, and finally the optimal parameter combination that meets the design requirements is obtained. A Hall sensor array uniformly arranged along the inner wall of the cavity is used to collect the magnetic flux density response signal caused by the change in the corrosion state of the tested steel bar; multiple Hall sensors in the Hall sensor array are arranged at the center of the six inner wall surfaces and the eight inner corner positions of the cavity to form a multi-point magnetic field measurement in three-dimensional space. The data analysis terminal is used to receive and store magnetic field data, and to build a detection model based on the equivalent magnetic circuit model. The equivalent magnetic circuit model converts the magnetic field path into parallel inner and outer branches. The mass loss of the sensor carrier shell is calculated according to the detection model, and the corrosion state is assessed by using the mass loss. Magnetic induction intensity during uniform corrosion With the loss of steel reinforcement quality Detection model between: ; Magnetic induction intensity during non-uniform corrosion With the loss of steel reinforcement quality The detection model between them is .

[0009] in, and These are the equivalent magnetomotive force and equivalent magnetic reluctance of the permanent magnet exciter, respectively. The effective air gap area of ​​the cavity. and The permeability of the inner branches under uniform corrosion and non-uniform corrosion are respectively. and The thicknesses of the rust layer are respectively for uniform corrosion and non-uniform corrosion. For the magnetic permeability of the external branch.

[0010] Furthermore, multiple pre-embedded sensor carriers are correspondingly arranged in the easily corroded or critical stress sections of the steel reinforcement frame.

[0011] Furthermore, the volume constraint of the permanent magnet exciter is that its length, width, and height must be smaller than the inner dimensions of the cavity in the corresponding direction; the installation space constraint is determined based on the grid size of the steel reinforcement skeleton and the design thickness of the concrete protective layer in the target reinforced concrete structure, in order to limit the effective size of the cavity, the installable position and offset range of the permanent magnet exciter in the cavity, and the upper and lower limits of the allowable air gap thickness.

[0012] Furthermore, it also includes a signal conditioning and processing unit, which is electrically connected to the Hall sensor array, and is used to filter, amplify and convert the acquired magnetic field signal into digital data. The signal conditioning and processing unit includes low-noise amplification, filtering, and a data acquisition circuit based on STM32F303RE, which uses its on-chip high-speed and high-precision ADC to efficiently and with low noise acquire and process the magnetic field signal of the Hall sensor.

[0013] Furthermore, a data transmission line is provided between the Hall sensor and the signal conditioning and processing unit. The data transmission line is a shielded twisted pair cable or a coaxial cable, and is led out through a waterproof connector and a sealed conduit to reduce electromagnetic interference and adapt to the construction environment.

[0014] Furthermore, it also includes a wireless transmission unit for sending digitized magnetic field data to a data analysis terminal; the wireless transmission unit is cellular communication, Wi-Fi or Bluetooth, and supports local storage and cloud synchronization.

[0015] Furthermore, a replaceable anti-wear insulating layer is provided on the side of the Hall sensor that contacts the inner wall of the cavity to ensure measurement stability and electrical insulation safety.

[0016] Furthermore, the corrosion of steel bars is divided into two states: uniform corrosion and non-uniform corrosion. Analyzing the multi-point data of the Hall sensor array, if the standard deviation of the rate of change of each point's data relative to the initial value is less than a preset threshold, it is determined to be uniform corrosion, and a uniform corrosion detection model is selected for calculation. If the standard deviation of the rate of change is greater than the preset threshold, or if the sensor data change in a specific direction is significantly higher than in other directions, it is determined to be non-uniform corrosion, and a non-uniform corrosion detection model is selected for calculation.

[0017] Furthermore, the equivalent magnetic circuit model equates the magnetic field path to parallel inner and outer branches; wherein, the inner branch is the path formed by the magnetic flux passing through the air gap inside the shell, the inner wall of the shell, and the uncorroded shell wall before returning to the permanent magnet exciter; the outer branch is the path formed by the magnetic flux sequentially passing through the inner wall of the shell, the uncorroded shell wall, the rust layer on the outer surface of the shell, and the concrete and air medium before returning to the permanent magnet exciter.

[0018] The beneficial technical effects of this invention are as follows: Non-contact and integrated: The sensor array is arranged inside the rebar and pre-embedded in the protective layer, enabling non-conductive contact detection of the rebar itself, avoiding structural damage and achieving long-term in-situ monitoring. Compared with traditional electrochemical detection, structural integrity is improved by approximately 30%, and the monitoring life can exceed 20 years.

[0019] Highly sensitive multi-point magnetic measurement: The combination of permanent magnet steady-state excitation and three-dimensional multi-point Hall array improves the system's response sensitivity to slight changes in magnetic permeability caused by corrosion by about 1–2 orders of magnitude.

[0020] Low-noise, high-fidelity acquisition: The signal acquisition path based on the STM32F303RE+OPA architecture achieves low-noise, high dynamic range signal acquisition, significantly improving signal stability and enhancing anti-interference performance.

[0021] By constructing a magnetic circuit analysis model, factors such as cross-sectional loss and magnetic permeability changes caused by steel corrosion are incorporated into the calculation, establishing a quantitative correlation between corrosion degree and magnetic induction intensity, and realizing the inversion of corrosion indicators from measured magnetic signals. This method reduces dependence on empirical thresholds, improves the accuracy, repeatability, and anti-interference ability of detection results, facilitates rapid and non-destructive on-site assessment, and provides a basis for maintenance decisions.

[0022] Highly adaptable and scalable: The system supports both scanning and long-term monitoring modes, is compatible with wired and wireless communication, and its modular design facilitates batch embedding and long-term maintenance, making it particularly suitable for health monitoring of large concrete structures.

[0023] In summary, the built-in non-contact electromagnetic detection system proposed in this invention has synergistic advantages in terms of layout, signal link, anti-interference design, core acquisition devices and multi-source fusion. It can accurately and stably assess the location and extent of corrosion of steel bars in concrete and is suitable for in-service durability assessment, health monitoring and maintenance decision support of buildings and infrastructure. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the pre-embedded sensing carrier structure in this invention; Among them, 1-corrosion layer; 2-shell; 3-permanent magnet exciter; 4-cavity; 5-Hall sensor array; Figure 2 This is a magnetic field distribution diagram of the pre-embedded sensing carrier in this invention; Figure 3 This is a predicted response curve of the equivalent magnetic circuit model in this invention; (a) shows the relationship between corrosion thickness and magnetic induction intensity; (b) shows the relationship between mass loss and magnetic induction intensity. Figure 4 The simulation results of magnetic field distribution for three steel reinforcement models with different shell and cavity shapes in this invention are shown. Among them, (a) is the simulation result of the magnetic field distribution of Model 1; (b) is the simulation result of the magnetic field distribution of Model 2; and (c) is the simulation result of the magnetic field distribution of Model 3. Figure 5 The graph shows the relationship between the magnetic induction enhancement at the detection points and the corrosion radius of the steel bars for three different steel bar models. Among them, (a) is the relationship between the magnetic induction enhancement at the detection point and the corrosion radius of the steel bar in Model 1; (b) is the relationship between the magnetic induction enhancement at the detection point and the corrosion radius of the steel bar in Model 2; and (c) is the relationship between the magnetic induction enhancement at the detection point and the corrosion radius of the steel bar in Model 3. Figure 6 The figure shows the simulation results of magnetic flux density as a function of corrosion radius under uniform and non-uniform corrosion conditions. Figure 7 This is a graph showing the relationship between voltage change and time. Figure 8 The relationship between the mass loss due to steel corrosion and the change in magnetic induction intensity based on a Hall effect sensor; Among them, (a) is the relationship diagram under uniform corrosion; (b) is the relationship diagram under non-uniform corrosion. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to specific examples: An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures, such as Figure 1 As shown, it includes: Multiple optimized pre-embedded sensor carriers are fixed inside the grid of the steel reinforcement skeleton before concrete pouring, thus pre-embedded in the concrete structure, and a cavity is formed inside the sensor carrier 4. Specifically, the top surface of the sensing carrier is basically level with the height of the rebar detection point to maintain the integrity of non-contact detection. The shell 2 of the pre-embedded sensing carrier is square and made of the same material as the rebar skeleton. Multiple pre-embedded sensing carriers are arranged in the easily corroded or critical stress sections of the rebar skeleton.

[0026] A permanent magnet exciter 3, after parametric modeling and iterative optimization, is fixedly positioned at the center of the cavity to construct a stable magnetic flux density excitation field in the area to be tested. Key parameters of the permanent magnet exciter, including the magnetization direction, center position offset, and air gap thickness, are set as variables, and a parametric model is constructed in the Comsol Multiphysics environment. The excitation field is quantified in the distance domain, with the center projection point of the permanent magnet exciter as the origin, and the field is measured radially on the surface under test. With step size Sampling was performed to obtain the magnetic flux density distribution. and with As a strength constraint, minimizing the peak-to-valley difference of B(r) within the distance domain, i.e., minimizing maxB(r)−minB(r), serves as the quantitative index and optimization objective for the uniformity of the excitation field; by introducing magnetic circuit constraints (i.e. An adaptive step-size gradient descent method (for strength constraints) is used to automatically adjust parameters and solve the magnetic field distribution multiple times under the boundary conditions of volume constraints of the permanent magnet exciter and installation space constraints within the reinforced concrete structure, ultimately obtaining the optimal parameter combination that meets the design requirements. The volume constraint of the permanent magnet exciter is that its length, width, and height must be smaller than the inner dimensions of the cavity in the corresponding direction. The installation space constraint is determined based on the grid size of the steel reinforcement skeleton in the target reinforced concrete structure and the design thickness of the concrete protective layer, in order to limit the effective size of the cavity, the installable position and offset range of the permanent magnet exciter in the cavity, and the upper and lower limits of the allowable air gap thickness.

[0027] In this embodiment, the distance between the outer surface of the pre-embedded sensing carrier and the adjacent reinforcing bar is ≥25mm, and the distance from the concrete protective layer surface is ≥20mm; the effective size of the cavity must meet the following requirements: permanent magnet size + 2 * minimum allowable wall thickness ≤ cavity size ≤ carrier outline size - 2 * minimum allowable wall thickness, where the minimum allowable wall thickness is 10mm; the minimum distance between the outer surface of the permanent magnet and the inner wall of the cavity in any direction must be ≥2mm, and the offset of the permanent magnet center relative to the geometric center of the cavity must not exceed ±3mm to prevent excessive magnetic field skewness from causing uneven signal in the detection area; the allowable range of air gap thickness is: g∈[1.0mm, 6.0mm]; The permanent magnet exciter is made of neodymium iron boron material, and the magnetic circuit is designed so that the surface magnetic flux density at the measured surface does not exceed 0.3T during the attachment operation; The position and polarity of the permanent magnet exciter are optimized according to the spatial arrangement of the test area to ensure that the magnetic flux lines are uniformly distributed inside the target steel reinforcement. The magnetic field excitation intensity can be adjusted according to the steel reinforcement diameter and the thickness of the concrete cover to ensure that the Hall array can detect a stable and distinguishable magnetic flux density signal.

[0028] Hall sensor array 5, comprising multiple Hall sensors, is distributed along the inner wall of the cavity of the pre-embedded sensing carrier and is used to collect magnetic flux density response signals caused by changes in the corrosion state of the tested steel bars. Specifically, multiple Hall sensors in the Hall sensor array are arranged at the center of the six inner walls and eight inner corners of the cavity to form a multi-point magnetic field measurement in three-dimensional space.

[0029] The signal conditioning and processing unit is electrically connected to the Hall sensor array and is used to filter, amplify and convert the acquired magnetic field signal into digital data. Specifically, a data transmission line is provided between the Hall sensor and the signal conditioning and processing unit. The data transmission line is a shielded twisted pair cable or coaxial cable, and is led out through a waterproof connector and a sealed conduit to reduce electromagnetic interference and adapt to the construction environment, ensuring long-term stable operation in concrete environments.

[0030] The signal conditioning and processing unit includes low-noise amplification, filtering, and a data acquisition circuit based on the STM32F303RE. It utilizes its on-chip high-speed, high-precision ADC to efficiently and with low noise acquire and process the magnetic field signals of the Hall sensor. It features high sampling rate and high resolution, enabling real-time acquisition and synchronous processing of multi-channel magnetic field signals.

[0031] The amplified and filtered signal is input to the microcontroller for digital conversion and preprocessing to obtain stable magnetic flux density data. This unit also features online zero-point calibration and sensitivity temperature compensation, maintaining measurement accuracy and system stability under conditions of ambient temperature changes or external interference.

[0032] A wireless transmission unit is used to send digitized magnetic field data to a data analysis terminal. Specifically, the wireless transmission unit supports cellular communication, Wi-Fi, or Bluetooth, and local storage and cloud synchronization. In environments with high electromagnetic interference, wired shielded twisted-pair cable or coaxial cable can be used for transmission. The data analysis terminal is used to receive and store magnetic field data, construct a detection model based on an equivalent magnetic circuit model, calculate the mass loss of the sensor carrier shell, and use the mass loss to assess the corrosion state.

[0033] Specifically, in order to study the functional relationship between the output voltage of the Hall element and the degree of steel corrosion, such as Figure 2 As shown, this invention establishes an equivalent magnetic circuit model, which equates the magnetic field path to parallel inner and outer branches. The inner branch is the path formed by the magnetic flux passing through the air gap inside the shell, the inner wall of the shell, and the uncorroded shell wall before returning to the permanent magnet exciter. The outer branch is the path formed by the magnetic flux passing through the inner wall of the shell, the uncorroded shell wall, the rust layer 1 on the outer surface of the shell, and the concrete and air medium before returning to the permanent magnet exciter. The corrosion of steel bars is divided into two states: uniform corrosion and non-uniform corrosion. Analyzing the multi-point data of the Hall sensor array, if the standard deviation of the rate of change of each point data relative to the initial value is less than a preset threshold, it is determined to be uniform corrosion, and a uniform corrosion detection model is selected for calculation. If the standard deviation of the rate of change is greater than the preset threshold, or if the sensor data change in a specific direction is significantly higher than in other directions, it is determined to be non-uniform corrosion, and a non-uniform corrosion detection model is selected for calculation. Assume the outer wall side length of the shell in the uncorroded state is... The side length of the cavity is When corrosion is uniform, the thickness of the rust layer is The thickness of the rust layer during non-uniform corrosion is The magnetic source uses equivalent magnetomotive force. With equivalent magnetic reluctance Characterization was performed; material parameters included vacuum permeability. Relative permeability with the sensor carrier housing Length of the air gap in the cavity , This is the correction factor for the effective area of ​​the air gap. This is the equivalent length coefficient for the internal path; The reference steel yoke thickness, i.e., the wall thickness of the sensor housing when it is not corroded, is: (1) To establish the series reluctance model of the inner branch (composed of the air gaps at both ends of the inner cavity and the steel yoke section connected in series), the effective air gap area of ​​the inner cavity is first given. air gap magnetoresistance The expression is: (2) (3) During uniform corrosion: The thickness of the steel yoke after corrosion is: (4) For the steel yoke segment carrying the main magnetic flux, its reluctance expression can be obtained by approximating it with equivalent length and equivalent cross-section, where... This indicates the equivalent magnetic circuit length of the steel yoke. Represents the equivalent cross-sectional area of ​​the steel yoke: (5) The magnetic reluctance of the steel yoke is: (6) To facilitate subsequent derivation and dimensional verification, a constant is introduced. Based on the storage materials and geometric parameters: (7) get: (8) The total magnetic reluctance of the inner branch is Its permeability (i.e., the equivalent conductance of the parallel branches) is : (9) The outer branch's permeability is formed by the corrosion layer outside the reinforcing steel, concrete, and air, creating an additional magnetic flux channel. This channel has low permeability and a long path, resulting in a much weaker overall permeability than the inner branch. Furthermore, its geometric changes are mainly concentrated in the extremely thin corrosion layer region, having a relatively small impact on the total magnetic reluctance. Therefore, to simplify the magnetic circuit model, the outer branch is considered to have a constant permeability independent of corrosion depth. (10) The total permeability is formed by connecting the inner and outer magnetic flux paths in parallel: (11) Then connect the parallel system with the equivalent magnetic reluctance of the permanent magnet. By connecting them in series, we obtain the equivalent magnetic reluctance: (12) Therefore, the total magnetic flux is: (13) The magnetic flux allocated to the inner branch is: (14) The magnetic induction intensity of the air gap in the inner wall is: (15) To reconcile the experimentally measurable mass loss with the equivalent corrosion thickness in the model, corrosion layer thickness was established for both types of operating conditions. With quality loss Relationship: (16) (17) (18) In summary, the detection model for the relationship between magnetic induction intensity and steel reinforcement mass loss under uniform corrosion is obtained as follows: (19) During non-uniform corrosion, The expression for the variation of the thickness of the corroded steel yoke with the corrosion depth is as follows: (20) The magnetic circuit of the steel yoke surrounding the cavity is divided into four segments according to the top, bottom, left, and right sides. An equivalent magnetic circuit length correction factor is assumed. If the magnetic reluctance is evenly distributed across the four segments, then the magnetic reluctance of the corroded segment is: ;(twenty one) Total magnetic reluctance of steel yoke : ;(twenty two) Uncorroded section magnetic reluctance : ;(twenty three) Internal branch through magnetic permeability : ;(twenty four) Inner wall air gap magnetic induction intensity: (25) Corrosion layer thickness With quality loss Relationship: (26) (27) (28) In summary, the detection model for the relationship between magnetic induction intensity and steel reinforcement mass loss under non-uniform corrosion is obtained as follows: (29).

[0034] The steel corrosion detection model proposed in this invention includes, for example... Figure 2 As shown, a permanent magnet exciter is embedded inside the reinforcing bar as a stable magnetic source. Uniform or non-uniform corrosion occurs on the outside of the reinforcing bar, and the corroded area is considered as a low-permeability material. The progression of corrosion will change the distribution path of the magnetic flux, thereby affecting the magnetic induction intensity of the Hall element on or near the surface of the reinforcing bar, and thus altering the Hall voltage output.

[0035] and The functional relationship between them is as follows: Figure 3 As shown in (a), the simultaneous equations and The expression yields the magnetic flux density. Directly related to quality loss Relationships, such as Figure 3 As shown in (b); This invention utilizes the COMSOL finite element simulation platform to construct a steel reinforcement corrosion detection model and magnetic field distribution. The simulation parameters are as follows: the relative permeability of each medium is consistent with the data in Table 1; the residual magnetic flux density of the permanent magnet exciter is set to 6T; and three steel reinforcement model sizes are constructed, with model one being... Figure 4 In model (a), the diameter of the cylindrical steel bar is 6mm, and the side length of the square cavity is 4mm; Model 2 is... Figure 4 In model (b), the side length of the square steel bar is 6mm and the diameter of the spherical cavity is 4mm; Model 3 is... Figure 4 In (c), the diameter of the square steel bar is 6mm, and the side length of the square cavity is 4mm. The permanent magnet exciters are all cubes with a side length of 2mm. Assuming the volume expansion coefficient of the steel bar is 2, the expansion of the steel bar during corrosion has no effect on the volume expansion ratio. To systematically analyze the key influencing factors of steel bar corrosion monitoring from multiple perspectives, firstly, in terms of geometric structure, a comparative study was conducted on different steel bar models. From the perspective of magnetic field distribution characteristics, different "steel bar-cavity" combination structures showed significant differences in corrosion sensitivity, such as... Figure 5As shown, comparing the response characteristics of magnetic induction intensity with corrosion radius in the three structures reveals that, under the same corrosion radius conditions, the amplitude and gradient of magnetic induction intensity change at each measuring point in Model 3 are more significant. With increasing corrosion radius, structure c exhibits a more pronounced magnetic flux redistribution characteristic, and the differences in magnetic response are more easily distinguishable, indicating that it is more sensitive to changes in corrosion size and has better detection and resolution capabilities than the first two structures.

[0036] Table 1 Magnetic permeability of medium in concrete ; To further investigate the influence of corrosion morphology on magnetic field distribution, a non-uniform corrosion model was introduced based on the aforementioned uniform corrosion analysis. Non-uniform corrosion primarily simulates the actual situation of localized intensified corrosion on the surface of the reinforcing steel, where the corrosion depth and radius are no longer uniformly distributed along the axial direction of the steel. By monitoring the changes in magnetic flux density at measuring points 1–4 arranged on the inner wall of Model 3, the differences in magnetic signals under different corrosion forms can be systematically analyzed, such as… Figure 6 As shown.

[0037] The simulation model was based on a mm-sized geometric model, while the experimental samples were enlarged tenfold while maintaining the same proportions to facilitate processing and measurement. Since the model maintained a consistent geometric scale, the scaling did not affect the qualitative characteristics of the results. The feasibility of this method in practical engineering was verified through accelerated corrosion testing.

[0038] The concrete specimens were 120×120×120mm³ in size, the steel bars used were HRB400, the embedded sensor carrier was 60×60×60mm³, and the concrete cover thickness was 30mm.

[0039] Before pouring, the reinforcing bars were derusted, and after pouring, standard curing was performed. Exposed parts of the reinforcing bars were protected with an anti-corrosion coating to prevent corrosion in non-test areas. The cement used was PO 42.5 ordinary Portland cement, the fine aggregate was medium sand from Qingdao with a modulus of 2.6, and the coarse aggregate particle size was 5–20 mm. A water-reducing agent (30% water-cement ratio) was added to improve workability.

[0040] The SS49E Hall sensor used in this study has advantages such as low cost, high sensitivity, and good linear response, and is suitable for non-contact measurement of AC and DC magnetic fields.

[0041] This invention conducted a 100-hour accelerated corrosion experiment and recorded voltage changes as follows: Figure 7As shown in the figure, around 10 hours, each curve exhibits a clear initial inflection point, corresponding to the destruction of the passivation film on the rebar surface and the initiation of corrosion. As the experiment progresses, pitting corrosion expands and rust products accumulate, further increasing the voltage change ratio measured by the sensor, showing a rapid growth rate between 40 and 80 hours. The inserted photographs of the corrosion samples correspond to the key nodes of the curves, visually reflecting the evolution of the corrosion morphology on the rebar surface at different stages. Finally, around 100 hours, all measuring points reach a high voltage change ratio and tend towards a stable state, indicating that the rebar corrosion is quite severe. Overall, the results verify that the Hall sensor has good sensitivity and tracking capability for the rebar corrosion process.

[0042] As mentioned earlier, this device is developed based on the extremely different magnetic permeability between the corrosion layer and the reinforcing steel. The corrosion layer causes a change in the magnetic flux density around the reinforcing steel, which can be detected by a Hall effect sensor and characterized by an output voltage signal. By calibrating and equivalently converting the Hall sensor output signal, the voltage increment can be converted into the corresponding change in magnetic flux density. Based on this, the calibration process aims to establish a quantitative correspondence between the mass loss of the corroded reinforcing steel and the change in magnetic flux density, such as... Figure 8 As shown in (a) and (b), its calibration expression is as follows: under uniform corrosion conditions Under non-uniform corrosion conditions . in ; , and These represent the magnetic flux density and mass of the uncorroded steel bars, respectively.

[0043] Under uniform corrosion conditions, the change in magnetic induction intensity obtained by this invention exhibits a good linear relationship with the mass loss of the reinforcing steel, with a sensitivity coefficient of 0.66621, significantly higher than the results reported in References 1 (An innovative corrosion evaluation technique for reinforced concrete structures using magnetic sensors) and 2 (Experimental and numerical study of an electromagnetic sensor for non-destructive evaluation of steel corrosion in concrete) (see Table 2). Although the aforementioned references all achieved high goodness of fit (R²>0.99), their sensitivity coefficients were relatively small, indicating that the change in magnetic response was limited under the same mass loss conditions. In contrast, the Hall sensor proposed in this invention is more sensitive to the overall cross-sectional loss of the reinforcing steel and can effectively amplify the change in magnetic response caused by corrosion.

[0044] Under nonuniform corrosion conditions, the irregularity of the corrosion morphology leads to a more complex magnetic field distribution, resulting in variations in sensitivity coefficients across different studies. The linear coefficient obtained in this invention under nonuniform corrosion conditions is 0.57117, which is on the same order of magnitude as the results in Reference 3 (Evaluation of nonuniform corrosion of steel in concrete based on two-yoke magnetic sensor) and Reference 4 (Coupled application of innovative electromagnetic sensors and digital image correlation technique to monitor corrosion process of reinforced bars in concrete), and still maintains a high goodness of fit. This indicates that although nonuniform corrosion weakens the linear consistency between magnetic response and mass loss, the proposed sensing method still possesses good stability and applicability.

[0045] Table 2. Comparison of sensitivity between the novel built-in sensor and the electromagnetic sensor in the literature for the same type of reinforcing steel. ; It should be noted that the differences in sensitivity coefficients among different studies are related to the experimental environment and working conditions, in addition to the sensor type and detection principle. However, overall, the built-in sensor proposed in this invention shows high sensitivity and reliable linearity under both uniform and non-uniform corrosion conditions, verifying its feasibility and advantages in the quantitative assessment of steel corrosion.

[0046] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures, characterized in that, include: Multiple optimized pre-embedded sensor carriers are fixed inside the grid of the steel reinforcement frame before concrete pouring, thus pre-embedded in the concrete structure, and the sensor carriers form cavities inside; the shell of the pre-embedded sensor carrier is square and made of the same material as the steel reinforcement frame, and multiple pre-embedded sensor carriers are arranged in the steel reinforcement frame accordingly. A permanent magnet exciter, after parametric modeling and iterative optimization, is fixedly positioned at the center of the cavity to construct a stable magnetic flux density excitation field in the area to be tested. Key parameters of the permanent magnet exciter, including its magnetization direction, center position offset, and air gap thickness, are set as variables, and a parametric model is constructed in the Comsol Multiphysics environment. The excitation field is quantified in the distance domain, with the center projection point of the permanent magnet exciter as the origin, and the field is measured radially on the surface under test. With step size Sampling was performed to obtain the magnetic flux density distribution. and with As a strength constraint, the goal is to minimize the peak-to-valley difference of B(r) within the distance domain, i.e., minimize... As a quantitative index and optimization target of the uniformity of the excitation field, the parameters are automatically adjusted and the magnetic field distribution is solved multiple times under the boundary conditions of the volume constraint of the permanent magnet exciter and the installation space constraint in the reinforced concrete structure by introducing the adaptive step size gradient descent method of magnetic circuit constraint, and finally the optimal parameter combination that meets the design requirements is obtained. A Hall sensor array uniformly arranged along the inner wall of the cavity is used to collect the magnetic flux density response signal caused by the change in the corrosion state of the tested steel bar; multiple Hall sensors in the Hall sensor array are arranged at the center of the six inner wall surfaces and the eight inner corner positions of the cavity to form a multi-point magnetic field measurement in three-dimensional space. The data analysis terminal is used to receive and store magnetic field data, and to build a detection model based on the equivalent magnetic circuit model. The equivalent magnetic circuit model converts the magnetic field path into parallel inner and outer branches. The mass loss of the sensor carrier shell is calculated according to the detection model, and the corrosion state is assessed by using the mass loss. Magnetic induction intensity during uniform corrosion With the loss of steel reinforcement quality Detection model between: ； Magnetic induction intensity during non-uniform corrosion With the loss of steel reinforcement quality The detection model between them is ； in, and These are the equivalent magnetomotive force and equivalent magnetic reluctance of the permanent magnet exciter, respectively. The effective air gap area of ​​the cavity. and The permeability of the inner branches under uniform corrosion and non-uniform corrosion are respectively. and The thicknesses of the rust layer are respectively for uniform corrosion and non-uniform corrosion. For the magnetic permeability of the external branch.

2. The integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, Multiple pre-embedded sensor carriers are arranged in the easily corroded or critical stress sections of the steel reinforcement frame.

3. The integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, The volume constraint of the permanent magnet exciter is that its length, width, and height must be smaller than the inner dimensions of the cavity in the corresponding direction. The installation space constraint is determined based on the grid size of the steel reinforcement skeleton and the design thickness of the concrete protective layer in the target reinforced concrete structure, in order to limit the effective size of the cavity, the installable position and offset range of the permanent magnet exciter in the cavity, and the upper and lower limits of the allowable air gap thickness.

4. The integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, It also includes a signal conditioning and processing unit, which is electrically connected to the Hall sensor array and is used to filter, amplify and convert the acquired magnetic field signal into digital magnetic field data. The signal conditioning and processing unit includes low-noise amplification, filtering, and a data acquisition circuit based on STM32F303RE, which uses its on-chip high-speed and high-precision ADC to efficiently and with low noise acquire and process the magnetic field signal of the Hall sensor.

5. An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, A data transmission line is provided between the Hall sensor and the signal conditioning and processing unit. The data transmission line is a shielded twisted pair cable or a coaxial cable, and is led out through a waterproof connector and a sealed conduit to reduce electromagnetic interference and adapt to the construction environment.

6. The integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, It also includes a wireless transmission unit for sending digitized magnetic field data to a data analysis terminal; the wireless transmission unit is cellular communication, Wi-Fi or Bluetooth, and supports local storage and cloud synchronization.

7. An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, The side of the Hall sensor that contacts the inner wall of the cavity is provided with a replaceable anti-wear insulating layer to ensure measurement stability and electrical insulation safety.

8. An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, The criteria for determining uniform corrosion and non-uniform corrosion are as follows: Analyze the multi-point data of the Hall sensor array. If the standard deviation of the rate of change of each point's data relative to the initial value is less than a preset threshold, it is determined to be uniform corrosion, and a uniform corrosion detection model is selected for calculation. If the standard deviation of the rate of change is greater than the preset threshold, it is determined to be non-uniform corrosion, and a non-uniform corrosion detection model is selected for calculation.

9. An integrated detection system for non-contact monitoring of corrosion status in reinforced concrete structures according to claim 1, characterized in that, The equivalent magnetic circuit model equates the magnetic field path to parallel inner and outer branches; wherein, the inner branch is the path formed by the magnetic flux passing through the air gap inside the shell, the inner wall of the shell, and the uncorroded shell wall before returning to the permanent magnet exciter; the outer branch is the path formed by the magnetic flux passing through the inner wall of the shell, the uncorroded shell wall, the rust layer on the outer surface of the shell, and the concrete and air medium before returning to the permanent magnet exciter.

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