A method for detecting and reinforcing corrosion of existing reinforced concrete structures

Abstract

The application discloses a kind of reinforced concrete structure corrosion detection and reinforcing method, belong to the technical field of corroded reinforced concrete.It includes: collecting magnetic flux leakage field signal, acoustic emission signal and surface stress data on the surface of concrete structure, after stress compensation of magnetic flux leakage field is weighted and fused with acoustic emission parameter, calculate corrosion damage comprehensive evaluation index I, according to this, the detection area is divided into mild, moderate and severe corrosion area;According to the corrosion grade and I value of each area, respectively calculate cathodic protection current density, electrochemical deposition voltage and deposition time, the grid spacing of CFRP-SMA composite bar net and the prestress value of SMA bar in moderate and severe corrosion area are also calculated;According to the calculated parameters, reinforce by partition construction;After reinforcement is completed, periodically retest I value of each area, when I value rises more than threshold value, increase cathodic protection current density, when I value exceeds alarm threshold value, send alarm.The application realizes the integration closed loop processing of corrosion reinforced concrete structure detection, reinforcement and long-term monitoring.

Description

Technical Field

[0001] This invention belongs to the field of corrosion-resistant reinforced concrete technology, specifically relating to a method for detecting and reinforcing corrosion in existing reinforced concrete structures. Background Technology

[0002] Reinforced concrete structures are widely used in bridge, building, and port engineering due to their excellent mechanical properties and durability. However, with increasing service life, the corrosion of steel reinforcement in concrete has become an increasingly prominent problem. Steel corrosion not only reduces the bond strength between the steel and concrete, but the volume expansion of corrosion products also generates rust expansion force, leading to cracking or even spalling of the concrete cover, seriously threatening the safety and durability of the structure. Therefore, accurate detection, assessment, and effective reinforcement and repair of corroded reinforced concrete structures have become crucial issues urgently needing to be addressed in the field of civil engineering.

[0003] Currently, the detection methods for steel reinforcement corrosion in concrete structures mainly fall into two categories: physical methods and electrochemical methods. Physical methods assess the degree of corrosion by measuring changes in physical properties related to steel reinforcement corrosion, such as the resistance rod method, eddy current detection method, X-ray method, and acoustic emission detection method. These methods are convenient to operate and easy to conduct on-site testing, but they are easily affected by other damaging factors in the concrete, making it difficult to establish an accurate correlation between physical measurement indicators and the amount of steel reinforcement corrosion. Electrochemical methods, such as the linear polarization method and AC impedance spectroscopy, have high sensitivity, but the testing process is complex and significantly affected by environmental factors such as concrete humidity and temperature.

[0004] In recent years, magnetic field leakage (MFL) detection technology has attracted attention in the corrosion detection of reinforced concrete structures due to its sensitivity to ferromagnetic materials. However, existing MFL detection methods mainly focus on localized corrosion and have the following shortcomings: First, concrete structures are subjected to varying degrees of load stress during actual service. Stress changes can alter the magnetic domain structure of the reinforcing steel, generating additional magnetic signals. Existing methods have failed to effectively eliminate the interference of stress on the MFL signal. Second, a single detection method cannot comprehensively reflect the corrosion damage state. MFL signals are sensitive to corrosion products but not to the initiation of microcracks, while acoustic emission signals can capture micro-fracture activity during the corrosion process. However, existing methods lack an evaluation system that effectively integrates multi-source detection information. Third, different corrosion morphologies (such as pitting and uniform corrosion) have different mechanisms of influence on structural mechanical properties. Existing detection methods fail to differentiate corrosion types during the evaluation stage, resulting in insufficient specificity and accuracy of the evaluation results.

[0005] In terms of reinforcement and repair, traditional methods include increasing the cross-section, bonding steel plates, and wrapping with fiber-reinforced polymer (FRP) composite materials. However, these methods are passive reinforcements, only improving the structural load-bearing capacity and failing to inhibit the continued corrosion of the reinforcing steel. Electrochemical repair technologies (such as cathodic protection and electrochemical deposition) can inhibit further corrosion of the reinforcing steel and are a rapidly developing type of active protection method in recent years. However, existing electrochemical repair technologies have the following problems: First, the construction parameters (current density, voltage, deposition time, etc.) for cathodic protection and electrochemical deposition are usually determined based on experience, lacking a method for determining parameters that quantitatively correlate with the degree of corrosion damage, resulting in varying reinforcement effects depending on the individual and the project. Second, electrochemical repair technologies carry the risk of hydrogen embrittlement of the reinforcing steel, limiting their application in load-bearing components. Third, if the same electrochemical parameters are used to reinforce areas with different degrees of corrosion, it can lead to overprotection in lightly corroded areas and underprotection in severely corroded areas, and stray current interference may occur between different areas due to potential differences.

[0006] Furthermore, existing research has explored dual-repair methods combining cathodic protection and structural reinforcement technologies, as well as attempts to use shape memory alloys (SMA) and CFRP composites for structural reinforcement. However, most of these technical solutions separate detection and evaluation, parameter calculation, and reinforcement construction into relatively independent processes, lacking a closed-loop technical system covering the entire process from "detection and evaluation—parameter calculation—zonal reinforcement—effect monitoring," making it difficult to achieve dynamic adjustment of reinforcement schemes and long-term effect tracking.

[0007] In summary, the existing technology lacks a systematic method that can simultaneously solve the problems of insufficient detection accuracy, lack of quantitative basis for reinforcement parameters, lack of differentiated treatment for different rusted areas, and lack of dynamic monitoring of reinforcement effect. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide a method for detecting and reinforcing corrosion in existing reinforced concrete structures.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for detecting and reinforcing corrosion in existing reinforced concrete structures includes the following steps: S1. Collect leakage magnetic field signal, acoustic emission signal and surface stress distribution data on the surface of the concrete structure to be tested, and eliminate stress interference in the leakage magnetic field signal; weight and fuse the stress-compensated leakage magnetic field signal with the acoustic emission characteristic parameters to calculate the comprehensive corrosion damage assessment index I of each test location, and divide the test area into light corrosion area, moderate corrosion area and severe corrosion area according to the I value. S2. Calculate the reinforcement parameters for each region based on its corrosion level and I value. The reinforcement parameters for all regions include: cathodic protection current density, electrochemical deposition voltage, and electrochemical deposition time. For moderate and severe corrosion areas, the reinforcement parameters also include: the grid spacing of the CFRP-SMA composite reinforcement mesh and the prestress value of the SMA reinforcement. S3. Perform reinforcement construction on each area according to the reinforcement parameters calculated in S2; S4. After reinforcement is completed, repeat the detection of S1 at a preset time interval and monitor the I value of each area separately. When the current I value of any area increases by more than a preset threshold compared to the I value of the area in the last detection, the cathodic protection current density of the area is increased by a preset amount. When the current I value of any area exceeds the preset alarm threshold, an alarm signal is issued.

[0010] As a further preferred embodiment of the present invention, S1 specifically includes the following steps: S11. Set up test points on the surface of the concrete structure to be tested in a grid pattern with a grid spacing of 10 cm. At each test point, use a magnetometer to collect leakage magnetic field signals and use an acoustic emission detector to collect acoustic emission signals. At the same time, use a bonded strain gauge or a surface fiber optic strain gauge to measure the surface stress value. S12. Perform stress compensation on the leakage magnetic field signal at each test point: Before testing, measure the leakage magnetic field signal under different stress levels on a non-corroded area of ​​the structure or a non-corroded test block under the same conditions, and establish a reference table or linear relationship between the stress value and the corresponding additional magnetic signal value; During the formal test, based on the measured stress value at the test point, subtract the stress-added magnetic signal value determined by the reference table or linear relationship from the measured total leakage magnetic field signal to obtain the leakage magnetic field signal caused only by corrosion; S13. Divide the peak value of the leakage magnetic field after stress compensation at each test point by the background leakage magnetic field value when there is no corrosion at the test point to obtain the leakage magnetic field ratio; divide the measured acoustic emission energy count at the test point by the background noise energy value to obtain the acoustic emission ratio; according to the leakage magnetic field weight and acoustic emission weight determined in advance through on-site sample calibration, add the leakage magnetic field ratio and acoustic emission ratio together to calculate the comprehensive corrosion damage assessment index I of the test point; S14. Divide the areas according to the I value of each detection point: the area with an I value not exceeding 0.3 is the light corrosion area, the area with an I value greater than 0.3 but not exceeding 0.7 is the moderate corrosion area, and the area with an I value greater than 0.7 is the severe corrosion area.

[0011] As a further preferred embodiment of the present invention, S2 specifically includes the following steps: S21. Based on the corrosion level of each area, determine the range of cathodic protection current density, the range of electrochemical deposition voltage, and the target deposition thickness for that area. Then, based on the comprehensive corrosion damage assessment index I value for that area, linearly interpolate to determine the cathodic protection current density within the current density range. Linearly interpolate to determine the reference value of the electrochemical deposition voltage within the voltage range, and adjust this reference value by adding or subtracting it according to the thickness of the concrete protective layer for that area based on a preset voltage correction per unit thickness, to obtain the final electrochemical deposition voltage. Determine the electrochemical deposition time based on the target deposition thickness, the final electrochemical deposition voltage, and the I value, and the electrochemical deposition time is negatively correlated with the final electrochemical deposition voltage and the I value. S22. If the area is moderately or severely corroded, then proceed with the following sub-steps: S221. Based on the corrosion level and I value of the area, determine the grid spacing of the CFRP-SMA composite mesh according to the preset grading rules, where the larger the I value, the smaller the corresponding grid spacing. S222. Determine the corresponding SMA reinforcement prestress reference value according to the corrosion level of the area, and then determine the prestress value according to the I value by the preset magnification factor, and the prestress value shall not exceed the ultimate recovery stress of the SMA reinforcement.

[0012] As a further preferred embodiment of the present invention, S3 specifically includes the following steps: S31. Clean the surface of each area to remove loose concrete, loose rust and contaminants, and expose the base surface; S32. In the lightly corroded, moderately corroded, and severely corroded areas, anodes and cathodes are arranged respectively, and cathodic protection power supplies are connected. Current is applied according to the cathodic protection current density calculated in S2 for each area. At the same time, electrochemical deposition electrodes are arranged in each area, and electrochemical deposition repair is carried out according to the electrochemical deposition voltage and electrochemical deposition time calculated in S2 for each area. S33. For moderately and severely corroded areas, after completing S32, lay the composite reinforcement mesh according to the mesh spacing of the CFRP-SMA composite reinforcement mesh calculated in S2, and anchor both ends of the SMA reinforcement. Excite the SMA reinforcement to produce shape memory effect by electric heating or infrared heating, apply the prestress value calculated in S2 to it, and then allow the SMA reinforcement to cool naturally or by forced cooling to lock the prestress. S34. Apply an anti-corrosion sealing coating to all areas by spraying or brushing, and cure for the specified time.

[0013] As a further preferred embodiment of the present invention, S4 specifically includes the following steps: S41. After all reinforcement work is completed, set a monitoring time interval T; S42. At each monitoring time point, according to the detection method in S1, leakage magnetic field signal, acoustic emission signal and surface stress distribution data are collected for each area. After stress compensation and weighted fusion, the comprehensive evaluation index I of corrosion damage for each area is recalculated. S43. Compare the current I value of each region with the I value of the last detection of that region: S431. If the current I value of any region increases by more than a preset threshold compared to the I value detected in the previous test of that region, and the preset threshold ranges from 0.05 to 0.1, then the cathodic protection current density of that region is increased by a preset amount, which is 5% to 15% of the original current density. S432. If the current I value of any area exceeds the preset alarm threshold, the preset alarm threshold ranges from 0.75 to 0.85, then an alarm signal is issued, indicating that the rust damage in the area exceeds the safety limit and further reinforcement or repair measures need to be taken. S44. Record the I value for each monitoring session and update the previous monitoring value for that area for comparative analysis in the next monitoring session.

[0014] As a further preferred embodiment of the present invention, in S1, before calculating the comprehensive evaluation index I of corrosion damage, the corrosion type of the leakage magnetic field signal is first identified: when the half-width at half-maximum (WHM) of the leakage magnetic field signal is less than 1.5 times the diameter of the reinforcing bar, it is determined to be pitting corrosion; when the WHM of the leakage magnetic field signal is greater than 2 times the diameter of the reinforcing bar, it is determined to be uniform corrosion; when the WHM of the leakage magnetic field signal is greater than or equal to 1.5 times the diameter of the reinforcing bar and less than or equal to 2 times the diameter of the reinforcing bar, it is determined to be mixed corrosion; different weighted fusion weights are selected according to the corrosion type: for pitting corrosion, the acoustic emission weight is greater than the leakage magnetic field weight; for uniform corrosion, the leakage magnetic field weight is greater than the acoustic emission weight; for mixed corrosion, the leakage magnetic field weight and the acoustic emission weight are equal, both taking 0.5.

[0015] As a further preferred embodiment of the present invention, in S2, for moderately and severely corroded areas, when calculating the grid spacing of the CFRP-SMA composite reinforcement mesh, the remaining cross-sectional area loss rate of the reinforcement is also considered: the actual remaining diameter of the corroded reinforcement in the area is determined by local damage or electromagnetic induction method, and the bearing capacity reduction coefficient is determined according to the ratio of the remaining diameter to the original diameter. The grid spacing is inversely proportional to this reduction coefficient. Simultaneously, the prestress value of the SMA reinforcement is amplified according to the remaining cross-sectional area loss rate, with a magnification factor of [missing value]. And less than or equal to the ultimate recovery stress of the SMA reinforcement.

[0016] As a further preferred embodiment of the present invention, in S4, during the monitoring process, when the current I value of any region increases by more than a preset threshold compared to the I value detected previously, in addition to increasing the cathodic protection current density, the electrochemical deposition voltage of that region is simultaneously reduced and the electrochemical deposition time is shortened, so that the total electrochemical effect intensity of that region is kept in dynamic balance, so as to prevent excessively high cathodic current density from causing hydrogen embrittlement or alkaline aggregate reaction; the total electrochemical effect intensity is defined as the weighted sum of cathodic protection current density, electrochemical deposition voltage and electrochemical deposition time, and the weighting coefficients of the three are 0.5, 0.3 and 0.2, respectively.

[0017] As a further preferred embodiment of the present invention, in step S3, before applying the cathodic protection current and performing electrochemical deposition, a layer of hygroscopic water-retaining material is laid on the concrete surface of the area to be treated, and its moisture content is maintained at 60%-80%; the electrode is arranged on the water-retaining material, and the moisture in the water-retaining material is used as a conductive medium; after the reinforcement is completed, the water-retaining material is recovered, and the iron ion content therein is detected. Based on the iron ion content, it is determined whether the corrosion activity of the area has been effectively inhibited, and the reinforcement parameters are adjusted accordingly; if the iron ion content exceeds the preset threshold, the electrochemical deposition time is extended by 24-48 hours or the cathodic protection current density is increased by 5%-10%.

[0018] The beneficial effects of this invention are as follows: (1) This invention effectively eliminates the interference of structural service stress on the detection of leakage magnetic field by simultaneously collecting leakage magnetic field signal, acoustic emission signal and surface stress distribution data during the detection stage and performing stress compensation on leakage magnetic field signal; at the same time, it identifies three types of corrosion, namely pitting corrosion, uniform corrosion and mixed corrosion, based on the spatial distribution pattern of leakage magnetic field signal, and dynamically adjusts the fusion weight of leakage magnetic field and acoustic emission accordingly, solving the problems of incomplete information of single detection method and large differences in detection sensitivity under different corrosion patterns, and significantly improving the accuracy of corrosion assessment.

[0019] (2) This invention quantitatively links the reinforcement parameters with the degree of corrosion damage: the cathodic protection current density and electrochemical deposition voltage are determined by linear interpolation based on the I value, and the electrochemical deposition time is calculated in conjunction with the voltage and the I value; for moderate and severe corrosion areas, the grid spacing of the CFRP-SMA composite reinforcement mesh is also related to the loss rate of the remaining cross-sectional area of ​​the reinforcement, and the prestress value of the SMA reinforcement is amplified in conjunction with the loss rate of the remaining cross-sectional area, thus realizing differentiated quantitative parameter allocation under different corrosion areas and different residual bearing capacity conditions of the reinforcement, overcoming the defects of traditional methods that rely on empirical values.

[0020] (3) In the monitoring stage, the present invention adopts an electrochemical parameter linkage adjustment strategy. When the I value rises, the electrochemical deposition voltage is reduced and the deposition time is shortened at the same time as the cathodic protection current density is increased, so that the total electrochemical effect intensity is kept in dynamic balance, effectively preventing the risk of hydrogen embrittlement of steel bars and alkaline aggregate reaction that may be caused by simply increasing the cathodic current.

[0021] (4) In the electrochemical repair construction, the present invention uses hygroscopic water-retaining material as a conductive medium between the electrode and the concrete, which solves the practical problem of high contact resistance in the dry outdoor environment. After the construction is completed, the material is recycled and the content of iron ions adsorbed is detected. Based on this, it is determined whether the corrosion activity has been effectively inhibited and the reinforcement parameters are further adjusted. The water-retaining material has the dual functions of conductive medium and effect evaluation, and the reinforcement effect can be quickly evaluated on site without adding extra testing procedures.

[0022] (5) The present invention establishes a long-term monitoring and adaptive maintenance mechanism after reinforcement through step S4. The I value of each area is regularly re-measured and compared with historical values. When corrosion accelerates, the cathodic protection current is automatically increased for dynamic compensation. When the safety limit is exceeded, an alarm is triggered in time, forming a closed-loop process of "detection-reinforcement-monitoring-compensation". This overcomes the defects of existing methods where detection, evaluation and reinforcement are separated and lack feedback mechanism. Attached Figure Description

[0023] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a flowchart of the corrosion type identification and dynamic weight adjustment method of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1-2 As shown, the present invention provides a method for detecting and reinforcing corrosion of existing reinforced concrete structures, comprising four steps: detection and evaluation stage (S1), parameter calculation stage (S2), reinforcement construction stage (S3), and long-term monitoring stage (S4).

[0026] I. Specific Implementation Methods of the Testing and Evaluation Phase (S1) This embodiment uses a reinforced concrete bridge pier that has been in service for 15 years as an example. The cross-sectional dimensions of the pier are 1.2m × 1.2m, and the area of ​​the inspection area is 2.4m × 2.4m.

[0027] Step S11 – Data Acquisition: Test points were set up on the surface of the concrete structure to be tested using a grid layout with a grid spacing of 10 cm. For a test area of ​​2.4m × 2.4m, a total of 25 × 25 = 625 test points were arranged.

[0028] At each testing point, a high-precision magnetometer was used to collect the leakage magnetic field signal. The testing probe was placed close to the concrete surface, and the acquisition time for each testing point was 3 seconds. The average value was taken as the measured value of the leakage magnetic field at that point.

[0029] Acoustic emission signals were collected using an acoustic emission detector. The center frequency of the acoustic emission sensor was 150kHz, the preamplifier gain was 40dB, the sampling frequency was 1MHz, and the acquisition time for each measurement point was 60 seconds. The number of acoustic emission events and the energy count were recorded.

[0030] Meanwhile, surface stress values ​​were measured using bonded strain gauges with a resistance of 120Ω and a sensitivity coefficient of 2.08. A 1 / 4 bridge connection was used, and strain values ​​were read through a static strain gauge and converted into stress values ​​based on the elastic modulus of concrete.

[0031] Step S12 – Stress compensation for leakage magnetic field signal: Before formal testing, seven different stress levels (0 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, and 30 MPa) were applied to the rust-free area of ​​the structure (or a rust-free test block under the same conditions), and the corresponding leakage magnetic field signals were measured. A correlation was established by plotting the stress value on the x-axis and the additional magnetic signal value on the y-axis. In this embodiment, the calibration results show that for every 10 MPa increase in stress, the additional magnetic signal increases by approximately 3.8 nT.

[0032] In formal testing, based on the measured stress values ​​at each measuring point, the additional magnetic signal value corresponding to that stress is subtracted from the measured total leakage magnetic field signal to obtain the leakage magnetic field signal caused only by corrosion: in, This is the corrosion leakage magnetic field signal after removing stress interference. To measure the total leakage magnetic field signal, This is the additional magnetic signal value at this stress level, determined according to the calibration relationship.

[0033] Taking a certain measuring point as an example: the measured total leakage magnetic field is 1250nT, the measured stress is 12MPa, and the additional magnetic signal under this stress is about 5nT according to the calibration table. Therefore, the corrosion leakage magnetic field after deduction is 1245nT.

[0034] The interference of structural service stress on leakage magnetic field detection is eliminated, so that the test results only reflect the true extent of corrosion damage.

[0035] Step S13 – Calculation of the Comprehensive Corrosion Damage Assessment Index I: The peak value of the leakage magnetic field at each detection point after stress compensation. Divide by the background leakage magnetic field value when there is no corrosion at the location of the test point. (In this embodiment) nT), to obtain the leakage magnetic field ratio : The measured acoustic emission energy count at this detection point Divide by background noise energy value (In this embodiment) ), to obtain the acoustic emission ratio : According to the leakage magnetic field weight determined in advance through on-site sample calibration. Harmony emission weight The two values ​​are weighted and added together to calculate the comprehensive corrosion damage assessment index I for the detection point: Assuming the calibration in this embodiment is obtained , Taking a certain measuring point as an example: the ratio of leakage magnetic field acoustic emission ratio ,but: Repeat the above calculations to obtain the I values ​​for all 625 measuring points.

[0036] It combines the advantages of two detection methods: leakage magnetic field (sensitive to corrosion products) and acoustic emission (sensitive to microcracks), resulting in more comprehensive and accurate evaluation results.

[0037] Step S14 – Region Division: Based on the I value of each detection point, the detection area is divided into three levels according to the following criteria: Areas with an I value not exceeding 0.3: areas of light corrosion. Areas with an I value greater than 0.3 but not exceeding 0.7: Moderately corroded areas. Areas with an I value greater than 0.7: Severely corroded areas. Among the 625 measuring points in this embodiment, 49.9% of the measuring points have I ≤ 0.3, 36.2% have 0.3 < I ≤ 0.7, and 13.9% have I > 0.7. Spatial clustering is carried out according to the positions of the measuring points, and the continuous similar measuring points are merged into one area, and finally divided into: 3 slightly rusted areas, 2 moderately rusted areas, and 1 severely rusted area.

[0038] Subsequent to this, different reinforcement parameters and reinforcement schemes are adopted for areas with different degrees of rust, avoiding the traditional one-size-fits-all approach.

[0039] II. Specific implementation manner of the parameter calculation stage (S2) Step S21 - Electrochemical parameter calculation: According to the rust grades of each area, determine the cathodic protection current density within the following ranges : Then linearly interpolate within the above range according to the I value of the area to determine the specific value. Taking a certain area (I = 0.52) in the moderately rusted area of this embodiment as an example: The determination method of the electrochemically deposited voltage is similar. Still taking the above moderately rusted area (I = 0.52) as an example: This area belongs to moderate rust, and the reference voltage range is 1.6 - 3.0V. Linearly interpolate according to the I value within the range of 0.3 - 0.7 to calculate the reference voltage as follows: Then correct it according to the concrete cover thickness of this area. For every 1 cm increase in the cover, the voltage increases by 0.15V; taking the reference cover thickness of 4 cm as the reference. The actually measured cover thickness of this area is 3.5 cm, which is 0.5 cm thinner than the reference value, so the voltage is reduced by 0.5 × 0.15 = 0.075V: The target deposition thickness is determined according to the rust grade: 50 - 100μm for slight rust, 100 - 200μm for moderate rust, and 200 - 400μm for severe rust, and interpolate the value according to the I value. The deposition time is determined comprehensively according to the target deposition thickness, electrochemically deposited voltage and I value. The basic rule is that the higher the voltage and the larger the I value, the shorter the time required to reach the target deposition thickness. The target deposition thickness in the moderate area of this embodiment is 150μm, and the voltage is 2.30V. The calculated deposition time is about 27 hours.

[0040] Quantitatively associating the electrochemically reinforced parameters with the I value realizes the scientific calculation of parameters rather than empirical estimation, ensuring the consistency and reliability of the reinforcement effect.

[0041] Step S22 – Calculation of CFRP-SMA composite reinforcing mesh parameters in moderately and severely corroded areas: For moderately and severely corroded areas, it is necessary to additionally calculate the mesh spacing of the CFRP-SMA composite reinforcement mesh and the prestress value of the SMA reinforcement.

[0042] The grid spacing is determined according to the corrosion grade and I value as follows: Taking the medium zone (I=0.52) in this embodiment as an example, the grid spacing is 150mm.

[0043] The prestress value of SMA reinforcement is determined according to the following formula: in, The prestress benchmark values ​​are determined based on the corrosion level (150 MPa for moderate corrosion and 250 MPa for severe corrosion), with 1.2 being a magnification factor. Taking the moderate zone (I=0.52) in this embodiment as an example: This value is less than the ultimate recovery stress of the selected SMA reinforcement, which is 480 MPa, and meets the requirements. If the calculated value exceeds 480 MPa, then 480 MPa should be used.

[0044] A differentiated design of structural reinforcement schemes was achieved. The larger the I value, the denser the rib mesh and the greater the prestress, which is precisely matched with the degree of corrosion damage.

[0045] III. Specific Implementation Methods of Reinforcement Construction Stage (S3) Step S31 – Surface Cleaning: The surfaces of each area were cleaned using high-pressure water jets to remove loose concrete, rust, and contaminants, exposing a solid base. For cracked areas, a 5cm radius around each side of the crack was thoroughly cleaned. After cleaning, compressed air was used to blow away surface dust.

[0046] S32 Step – Electrochemical Strengthening Construction: Anodes and cathodes are arranged separately in each area. The anodes are titanium-based mixed metal oxide mesh anodes (MMO anodes), with a mesh size of 500mm × 1000mm and a spacing of 15~20mm between the anode mesh and the concrete surface. The cathodes utilize the internal steel reinforcement of the structure, and electrical connections are achieved by welding wires to the steel reinforcement.

[0047] Connect the cathodic protection power supply and apply the current calculated in step S2 for each area. In this embodiment, approximately 10 mA / m², 26 mA / m², and 45 mA / m² are applied to the three areas with different corrosion levels, respectively.

[0048] Simultaneously, electrochemical deposition electrodes (stainless steel plates, material 316L) were arranged in each area, and electrochemical deposition repair was performed according to the voltage and time calculated in step S2. Taking the medium area in this embodiment as an example: a voltage of 2.30V was applied, and the deposition time was 27 hours.

[0049] Step S33 – Laying and Applying Prestressing of CFRP-SMA Composite Reinforcement Mesh: For moderately and severely corroded areas, CFRP-SMA composite reinforcing mesh is laid after S32 is completed. The mesh is woven from longitudinal and transverse SMA reinforcing bars (8mm in diameter), and the mesh intersections are tied and fixed with stainless steel wire. CFRP sheets (carbon fiber cloth, 300g / m²) are pasted at the joints.

[0050] According to the calculated grid spacing, the SMA reinforcement is positioned on the concrete surface by marking lines. After laying the reinforcement mesh, the two ends of the SMA reinforcement are anchored to pre-embedded chemical anchors. Prestressing is applied by electric heating: a high-current, low-voltage power supply (output voltage 5~10V, current 50~200A) is connected to both ends of the SMA reinforcement. The SMA reinforcement heats up to its phase transition temperature range (approximately 85~95℃) using its own resistance, and is maintained at this temperature for 10 minutes. The SMA reinforcement generates a shape memory effect, applying prestress to the structure. The prestress value is monitored by strain gauges attached to the SMA reinforcement. When the calculated value is reached, the power is cut off, and the reinforcement is locked in by natural cooling.

[0051] Step S34 – Surface Sealing and Curing: Apply an epoxy resin-based anti-corrosion sealing coating to all areas by spraying or brushing, applying two coats. Each coat should have a dry film thickness of not less than 80 μm, and the total thickness of both coats should not be less than 160 μm. Allow to cure for 48 hours, avoiding rain and mechanical disturbance.

[0052] Electrochemical strengthening (cathodic protection + electrochemical deposition) and structural strengthening (CFRP-SMA prestressed mesh) work synergistically, with the former inhibiting further corrosion and the latter restoring the structural load-bearing capacity, resulting in a better effect than a single method.

[0053] IV. Specific Implementation Methods for the Long-Term Monitoring Phase (S4) Step S41 – Setting the monitoring time interval: After the reinforcement work is completed, the monitoring interval is set to T=3 months. For important structures or severely corroded areas, the interval can be shortened to 1-2 months.

[0054] S42 Steps – Periodic Retesting: At each monitoring time point, data were re-collected and the comprehensive assessment index of corrosion damage for each area was calculated according to the method in step S1. .

[0055] Step S43 – I-value Comparison and Adaptive Adjustment: Current status of each region Value compared to the previous test The values ​​are compared.

[0056] S431—Dynamic upward adjustment of cathodic protection current density: If the current I value in any region increases by more than 0.05 to 0.1 (0.08 in this embodiment) compared to the previous detection value, then the cathodic protection current density in that region will be increased by 5% to 15% (10% in this embodiment). Taking the moderate zone in this embodiment as an example: if the retest shows that the I value increases from 0.52 to 0.62 (an increase of 0.10, exceeding 0.08), then: By periodically retesting the I value to determine the corrosion activity status, the cathodic protection is actively enhanced when corrosion accelerates, thereby achieving dynamic adaptive adjustment of the reinforcement scheme.

[0057] S432 – Alarm and Emergency Response: If the current I value in any area exceeds 0.75~0.85 (0.80 in this embodiment), an alarm signal will be issued, indicating that the corrosion damage in that area exceeds the safety limit. The on-site engineer should conduct a manual re-inspection within 24 hours, including partially chiseling open the steel bars to check the actual corrosion status, measuring the diameter of the remaining steel bars, and assessing whether further measures such as adding additional prestressing or partially replacing concrete are needed.

[0058] Step S44 – Data Update: Record the I value of each monitoring session to the electronic structural archive and update the previous monitoring value for that area. This will be used for the next comparative analysis.

[0059] A closed-loop mechanism of "detection-reinforcement-monitoring-compensation" has been established, realizing the transformation from "one-time reinforcement" to "full life cycle maintenance".

[0060] V. Specific Implementation Methods for Rust Type Identification and Dynamic Weight Adjustment This embodiment further defines the weighted fusion process in step S1.

[0061] Before calculating the I value, the corrosion type of the leakage magnetic field signal is identified. The full width at half maximum (FWHM) of the leakage magnetic field peak value is measured at each detection point. (That is, the spatial width corresponding to when the leakage magnetic field value drops from the peak value to half of the peak value), let the diameter of the reinforcing bar corresponding to this measuring point be... (Obtained through design drawings or rebar detectors), determined according to the following rules: when At that time, it was determined to be pitting corrosion. when At that time, it was determined to be uniform corrosion type. when At that time, it was determined to be a mixed type of corrosion. Different weights are selected based on the type of corrosion: Then follow the formula Calculate the I value.

[0062] Taking a measuring point in a severely corroded area as an example: the rebar diameter is 25mm, and the half-height width is 32mm. Since 32 / 25 = 1.28 < 1.5, it is determined to be pitting corrosion. , If the measuring point , ,but .

[0063] Pitting corrosion is characterized by localized stress concentration and microcrack propagation, with acoustic emission signals being more sensitive to microcracks. Uniform corrosion is characterized by overall cross-sectional loss, with leakage magnetic field signals being more sensitive to volumetric loss. By dynamically assigning weights after identifying the corrosion type, the assessment results become more targeted.

[0064] VI. Specific Implementation Methods for Correcting the Residual Cross-sectional Area Loss Rate of Reinforcing Steel For moderately and severely corroded areas, the remaining cross-sectional area loss rate of the reinforcing bars is further considered when calculating the parameters of the CFRP-SMA composite reinforcement mesh.

[0065] The actual remaining diameter of the corroded steel bars in this area was determined by either a localized destructive testing method (drilling a 50mm diameter concrete core sample from a non-critical load-bearing area) or an electromagnetic induction method. Taking a severely corroded area as an example: the designed diameter mm, measured remaining diameter mm, then the remaining cross-sectional area loss rate for: Bearing capacity reduction factor Grid spacing according to Correction: The original spacing was 120mm, and the corrected spacing is 120 / 0.74≈162mm, but it does not exceed the upper limit of 150mm for this grade, so we take 150mm.

[0066] SMA reinforcement prestress value based on loss rate enlarge: The above-mentioned serious areas ( MPa , For example: The stress exceeds the limit recovery stress of 480 MPa, so we take 480 MPa.

[0067] The reinforcement scheme is precisely matched with the actual degradation state of the steel bars. The greater the loss of the remaining section, the stronger the reinforcement, thus avoiding over- or under-reinforcement.

[0068] VII. Specific Implementation Methods for Dynamic Equilibrium of Total Electrochemical Effect Intensity When monitoring detects that the I value rises above the threshold, the cathodic protection current density is increased while the electrochemical deposition voltage is simultaneously decreased and the deposition time is shortened. Total electrochemical intensity. Defined as the weighted sum of the three: Taking a moderately affected area as an example: Original mA / m², V. h, then .

[0069] When the I value rises and triggers regulation, the current is first increased by 10% to 28.6 mA / m². Then, the voltage and time are gradually decreased (the voltage is decreased by 0.02V each time, and the time is decreased by 0.3h each time). After each decrease, the E value is recalculated so that the E value gradually approaches the target value (the target value is approximately the current E value multiplied by 0.95~0.98).

[0070] The final adjustment result of this embodiment is: mA / m², V. h, at this time The value is slightly lower than the original E value of 19.09, achieving a dynamic balance of total electrochemical intensity.

[0071] While increasing the cathodic protection current to enhance protection, the voltage is reduced and the time is shortened to avoid excessive total electrochemical action, effectively preventing the risks of hydrogen embrittlement of steel bars and alkaline aggregate reaction.

[0072] VIII. Specific Implementation Methods for the Application of Hygroscopic and Water-Retaining Materials Before applying cathodic protection current and performing electrochemical deposition, a layer of hygroscopic and water-retaining material is laid on the concrete surface of the area to be treated. In this embodiment, waste cotton fiber pressed felt is used, with a unit area mass of 400g / m², a thickness of 7mm, and a water absorption rate of approximately 5 times its own weight.

[0073] Soak the felt cloth in clean water until saturated and allow it to drain naturally until it no longer drips (moisture content approximately 70%). Apply it to the concrete surface and secure it with plastic anchors (30cm spacing, 20cm spacing for vertical or top structures). The overlap of the felt cloth should be no less than 5cm. Electrodes are placed on top of the felt cloth, utilizing the moisture in the cloth as a conductive medium. This embodiment shows a measured reduction in contact resistance of approximately 60%.

[0074] During construction, water should be added every 4 to 6 hours using a sprayer. In high temperature (>35℃) or strong wind (>3 level) weather, a plastic film (0.03mm thick) should be covered on the outside of the felt to ensure that the moisture content is maintained at 60% to 80%.

[0075] After reinforcement, the felt cloth was removed, dried, cut into pieces, and soaked in deionized water. After shaking for 30 minutes, it was filtered, and the iron ion concentration in the soaking solution was measured to estimate the total amount of iron ions deposited. In this example, the total amount of iron ions deposited in a severely affected area was approximately 1062 mg, higher than the threshold of 650 mg calibrated for a rust-free test block under the same conditions. This indicates that the corrosion activity in this area was not effectively suppressed. Therefore, the electrochemical deposition time was extended by 36 hours, and the cathodic protection current density was increased by 8%. If the amount of iron ions deposited is less than half the threshold (i.e., <325 mg), the reinforcement effect is good, and the original plan can be followed. The felt cloth can be reused after repeated rinsing and drying with clean water, up to a maximum of 3 times.

[0076] The water-retaining material not only solves the problem of poor contact between electrodes and concrete in dry outdoor environments, but also allows for evaluation of the reinforcement effect by testing the iron ion content after recycling. It serves two purposes without adding any extra testing procedures.

[0077] In summary, this invention provides a method for detecting and reinforcing corrosion in existing reinforced concrete structures. Through a complete technical chain—"multi-source fusion detection → corrosion type identification → differentiated quantitative parameter matching → electrochemical + structural synergistic reinforcement → long-term dynamic monitoring → adaptive parameter compensation"—it solves the systemic problems of insufficient detection accuracy, lack of quantitative basis for reinforcement parameters, lack of differentiated treatment for different corrosion areas, and lack of dynamic monitoring of reinforcement effects in existing technologies. This method has been verified in laboratory and field tests and can be widely applied to the detection, evaluation, reinforcement, and repair of corroded reinforced concrete structures in engineering fields such as bridges, buildings, and ports.

[0078] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for detecting and reinforcing corrosion in existing reinforced concrete structures, characterized in that, Includes the following steps: S1. Collect leakage magnetic field signal, acoustic emission signal and surface stress distribution data on the surface of the concrete structure to be tested, and eliminate stress interference in the leakage magnetic field signal; weight and fuse the stress-compensated leakage magnetic field signal with the acoustic emission characteristic parameters to calculate the comprehensive corrosion damage assessment index I of each test location, and divide the test area into light corrosion area, moderate corrosion area and severe corrosion area according to the I value. S2. Calculate the reinforcement parameters for each area based on its corrosion level and I value; The reinforcement parameters for all areas include: cathodic protection current density, electrochemical deposition voltage, and electrochemical deposition time; for moderate and severe corrosion areas, the reinforcement parameters also include: the grid spacing of the CFRP-SMA composite reinforcement mesh and the prestress value of the SMA reinforcement. S3. Perform reinforcement construction on each area according to the reinforcement parameters calculated in S2; S4. After reinforcement is completed, repeat the detection of S1 at a preset time interval and monitor the I value of each area separately. When the current I value of any area increases by more than a preset threshold compared to the I value of the area in the last detection, the cathodic protection current density of the area is increased by a preset amount. When the current I value of any area exceeds the preset alarm threshold, an alarm signal is issued.

2. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: S1 specifically includes the following steps: S11. Set up test points on the surface of the concrete structure to be tested in a grid pattern with a grid spacing of 10 cm. At each test point, use a magnetometer to collect leakage magnetic field signals and use an acoustic emission detector to collect acoustic emission signals. At the same time, use a bonded strain gauge or a surface fiber optic strain gauge to measure the surface stress value. S12. Perform stress compensation on the leakage magnetic field signal at each test point: Before testing, measure the leakage magnetic field signal under different stress levels on a non-corroded area of ​​the structure or a non-corroded test block under the same conditions, and establish a reference table or linear relationship between the stress value and the corresponding additional magnetic signal value; During the formal test, based on the measured stress value at the test point, subtract the stress-added magnetic signal value determined by the reference table or linear relationship from the measured total leakage magnetic field signal to obtain the leakage magnetic field signal caused only by corrosion; S13. Divide the peak value of the leakage magnetic field after stress compensation at each test point by the background leakage magnetic field value when there is no corrosion at the test point to obtain the leakage magnetic field ratio; divide the measured acoustic emission energy count at the test point by the background noise energy value to obtain the acoustic emission ratio; according to the leakage magnetic field weight and acoustic emission weight determined in advance through on-site sample calibration, add the leakage magnetic field ratio and acoustic emission ratio together to calculate the comprehensive corrosion damage assessment index I of the test point; S14. Divide the areas according to the I value of each detection point: the area with an I value not exceeding 0.3 is the light corrosion area, the area with an I value greater than 0.3 but not exceeding 0.7 is the moderate corrosion area, and the area with an I value greater than 0.7 is the severe corrosion area.

3. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: S2 specifically includes the following steps: S21. Based on the corrosion level of each area, determine the range of cathodic protection current density, the range of electrochemical deposition voltage, and the target deposition thickness for that area. Then, based on the comprehensive corrosion damage assessment index I value for that area, linearly interpolate to determine the cathodic protection current density within the current density range. Linearly interpolate to determine the reference value of the electrochemical deposition voltage within the voltage range, and adjust this reference value by adding or subtracting it according to the thickness of the concrete protective layer for that area based on a preset voltage correction per unit thickness, to obtain the final electrochemical deposition voltage. Determine the electrochemical deposition time based on the target deposition thickness, the final electrochemical deposition voltage, and the I value, and the electrochemical deposition time is negatively correlated with the final electrochemical deposition voltage and the I value. S22. If the area is moderately or severely corroded, then proceed with the following sub-steps: S221. Based on the corrosion level and I value of the area, determine the grid spacing of the CFRP-SMA composite mesh according to the preset grading rules, where the larger the I value, the smaller the corresponding grid spacing. S222. Determine the corresponding SMA reinforcement prestress reference value according to the corrosion level of the area, and then determine the prestress value according to the I value by the preset magnification factor, and the prestress value shall not exceed the ultimate recovery stress of the SMA reinforcement.

4. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: S3 specifically includes the following steps: S31. Clean the surface of each area to remove loose concrete, loose rust and contaminants, and expose the base surface; S32. In the lightly corroded, moderately corroded, and severely corroded areas, anodes and cathodes are arranged respectively, and cathodic protection power supplies are connected. Current is applied according to the cathodic protection current density calculated in S2 for each area. At the same time, electrochemical deposition electrodes are arranged in each area, and electrochemical deposition repair is carried out according to the electrochemical deposition voltage and electrochemical deposition time calculated in S2 for each area. S33. For moderately and severely corroded areas, after completing S32, lay the composite reinforcement mesh according to the mesh spacing of the CFRP-SMA composite reinforcement mesh calculated in S2, and anchor both ends of the SMA reinforcement. Excite the SMA reinforcement to produce shape memory effect by electric heating or infrared heating, apply the prestress value calculated in S2 to it, and then allow the SMA reinforcement to cool naturally or by forced cooling to lock the prestress. S34. Apply an anti-corrosion sealing coating to all areas by spraying or brushing, and cure for the specified time.

5. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: S4 specifically includes the following steps: S41. After all reinforcement work is completed, set a monitoring time interval T; S42. At each monitoring time point, according to the detection method in S1, leakage magnetic field signal, acoustic emission signal and surface stress distribution data are collected for each area. After stress compensation and weighted fusion, the comprehensive evaluation index I of corrosion damage for each area is recalculated. S43. Compare the current I value of each region with the I value of the last detection of that region: S431. If the current I value of any region increases by more than a preset threshold compared to the I value detected in the previous test of that region, and the preset threshold ranges from 0.05 to 0.1, then the cathodic protection current density of that region is increased by a preset amount, which is 5% to 15% of the original current density. S432. If the current I value of any area exceeds the preset alarm threshold, the preset alarm threshold ranges from 0.75 to 0.85, then an alarm signal is issued, indicating that the rust damage in the area exceeds the safety limit and further reinforcement or repair measures need to be taken. S44. Record the I value for each monitoring session and update the previous monitoring value for that area for comparative analysis in the next monitoring session.

6. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: In S1, before calculating the comprehensive corrosion damage assessment index I, the corrosion type is first identified by the leakage magnetic field signal: when the half-width at half-maximum (WHM) of the leakage magnetic field signal is less than 1.5 times the diameter of the reinforcing bar, it is determined to be pitting corrosion; when the WHM of the leakage magnetic field signal is greater than twice the diameter of the reinforcing bar, it is determined to be uniform corrosion; when the WHM of the leakage magnetic field signal is greater than or equal to 1.5 times the diameter of the reinforcing bar and less than or equal to twice the diameter of the reinforcing bar, it is determined to be mixed corrosion. Different weighted fusion weights are selected according to the corrosion type: for pitting corrosion, the acoustic emission weight is greater than the leakage magnetic field weight; for uniform corrosion, the leakage magnetic field weight is greater than the acoustic emission weight; for mixed corrosion, the leakage magnetic field weight and the acoustic emission weight are equal, both taking 0.

5.

7. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: In S2, for moderately and severely corroded areas, when calculating the grid spacing of the CFRP-SMA composite reinforcement mesh, the remaining cross-sectional area loss rate of the reinforcement is also considered: the actual remaining diameter of the corroded reinforcement in the area is determined by local damage or electromagnetic induction method, and the bearing capacity reduction coefficient is determined according to the ratio of the remaining diameter to the original diameter. The grid spacing is inversely proportional to this reduction coefficient. At the same time, the prestress value of the SMA reinforcement is amplified according to the remaining cross-sectional area loss rate.

8. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: In S4, during the monitoring process, when the current I value of any region increases by more than the preset threshold compared to the previous I value, in addition to increasing the cathodic protection current density, the electrochemical deposition voltage and the electrochemical deposition time of that region are simultaneously reduced to maintain a dynamic balance of the total electrochemical effect intensity in that region, so as to prevent excessively high cathodic current density from causing hydrogen embrittlement or alkaline aggregate reaction. The total electrochemical effect intensity is defined as the weighted sum of the cathodic protection current density, the electrochemical deposition voltage, and the electrochemical deposition time, with weighting coefficients of 0.5, 0.3, and 0.2, respectively.

9. The method for detecting and reinforcing corrosion of existing reinforced concrete structures according to claim 1, characterized in that: In S3, before applying the cathodic protection current and performing electrochemical deposition, a layer of hygroscopic water-retaining material is laid on the concrete surface of the area to be treated, and its moisture content is kept at 60%-80%; the electrode is arranged on the water-retaining material, and the moisture in the water-retaining material is used as a conductive medium. After the reinforcement is completed, the water-retaining material is recycled, and the iron ion content is tested. The iron ion content is used to determine whether the corrosion activity in the area has been effectively inhibited, and the reinforcement parameters are adjusted accordingly. If the iron ion content exceeds the preset threshold, the electrochemical deposition time is extended by 24-48 hours or the cathodic protection current density is increased by 5%-10%.

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