A device and method for detecting the resistivity of a concrete structure using ring electrodes

Abstract

The application discloses a kind of annular electrode resistivity detection device and detection method of concrete structure, including current source, annular electrode probe, voltage acquisition multimeter, the annular electrode probe includes probe mould, central electrode, two layers of pressure ring electrode, outermost layer reflow ring electrode, and central electrode, two layers of pressure ring electrode, outermost layer reflow ring electrode are coaxial concentric annular arrangement.This application forms axisymmetric radial diffusion current field by annular coaxial electrode, eliminates the direction sensitivity caused by the unidirectional current of traditional linear electrode, naturally reduces the disturbance of component boundary, internal reinforcement to current field, and the basic measurement error is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for concrete structures, specifically to a ring electrode resistivity testing device and method for concrete structures. Background Technology

[0002] Under the combined effects of chloride ion corrosion, carbonization, and external loads, in-service concrete structures are prone to durability degradation problems such as steel bar depassivation corrosion and protective layer cracking, which directly threaten structural safety and design service life. Therefore, high-precision and stable non-destructive testing methods for concrete are urgently needed to evaluate the risk of steel bar corrosion.

[0003] Concrete is a porous medium, and its resistivity is highly correlated with its internal pore structure, pore fluid saturation, and ion migration rate. In engineering, concrete resistivity is widely used as a core non-destructive testing indicator for determining the risk of steel corrosion and assessing structural durability. The current mainstream testing method in the industry is the Winner four-electrode method. This method uses four linearly equidistant metal electrodes to pass current through the concrete surface and collect the potential difference. Based on the assumption of a semi-infinite homogeneous medium, an analytical resistivity model is established. It has the advantages of simple operation, non-destructive nature, and low cost, and is widely used in laboratory tests and on-site physical testing.

[0004] However, the Winner four-electrode method has inherent drawbacks:

[0005] (i) Significant boundary size effect: When the thickness of the component under test is small and the measuring point is close to the component boundary, the current diffusion path is constrained and the measured resistivity deviates from the true value.

[0006] (ii) Severe interference from reinforcing steel: The conductivity of reinforcing steel is far superior to that of concrete, which will change the local current field distribution and disturb the potential gradient, causing detection errors;

[0007] (III) High directional sensitivity: The linear electrode arrangement causes the current to diffuse in one direction, resulting in large fluctuations in the measured values ​​in non-uniform concrete areas and poor repeatability.

[0008] Existing improvement schemes are all based on the optimization of the Winner linear four-electrode configuration, relying solely on finite element simulation fitting correction coefficients, adjusting electrode spacing, and multi-point retesting to compensate for errors, without optimizing the electrode structure from the perspective of current field distribution mechanism. The relevant correction models rely on empirical parameters, lack unified physical analytical formula support, and the applicable range of correction coefficients is narrow. In scenarios with complex reinforcement and small components, the detection accuracy and stability cannot be guaranteed. Summary of the Invention

[0009] To address the problems mentioned in the background art, the present invention aims to provide a ring electrode resistivity detection device and method for concrete structures. By forming an axisymmetric radially uniform diffused current field through the ring electrode, the boundary size effect and reinforcement current disturbance are weakened from the root. A unified analytical calculation model with clear physical meaning is established, and a dual-dimensional correction system for size and reinforcement is provided, which greatly improves the accuracy and stability of concrete resistivity detection under complex working conditions.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a ring electrode resistivity detection device for concrete structures, comprising a current source, a ring electrode probe, and a voltage acquisition multimeter. The ring electrode probe includes a probe mold, a central electrode, two layers of pressure-measuring ring electrodes, and an outermost return ring electrode, wherein the central electrode, the two layers of pressure-measuring ring electrodes, and the outermost return ring electrode are arranged coaxially and concentrically in a ring. The output terminal of the current source is electrically connected to the central electrode and the outermost return ring electrode, respectively, for introducing a constant current into the concrete. The voltage acquisition multimeter is electrically connected to two layers of voltage-sensing ring electrodes at both ends to acquire the potential difference between the two layers of voltage-sensing rings. After the ring electrode probe is attached to the concrete surface, the current diffuses radially outward from the central electrode to the outermost return ring electrode, forming an axisymmetric radially uniform current field inside the concrete.

[0011] Define electrode geometry parameters: The center radius of the two layers of pressure measuring ring electrodes. It is the center radius of the outermost return ring electrode.

[0012] As a preferred embodiment of the present invention, the following steps are included:

[0013] Step 1: Concrete surface assessment and reinforcement distribution detection; Select smooth, defect-free concrete inspection areas and clean the surface; use a reinforcement scanner to obtain the planar side lengths of the component. Component thickness , diameter of reinforcing bars Thickness of concrete cover for reinforcing bars Spacing of steel mesh ;

[0014] Step 2: Preparation for ring electrode resistivity testing; Place the ring electrode probe against the concrete surface and apply a constant current through the current source. A multimeter is used to collect the potential difference between the two voltage measuring rings. ;

[0015] Step 3: Resistivity calculation method;

[0016] 3.1 Calculation of the geometric coefficients of the ring probe :

[0017]

[0018] In the formula , This is a complete elliptic integral of the first kind;

[0019] 3.2 Calculation of apparent resistivity of concrete :

[0020]

[0021] Step 4: Calculation of adjustments for influencing factors;

[0022] 4.1 Size effect correction: maximum outer diameter of the probe ,like and Size correction factor If the condition is not met, retrieve the result from the table. ,calculate ;

[0023] 4.2 Reinforcement interference correction: no reinforcement, protective layer exceeding probe detection depth, reinforcement mesh spacing When, reinforcement correction factor When the reinforcing bar is within the probe's sensitive area, the table should be consulted to obtain the information. Calculate the intrinsic resistivity of concrete Unified correction formula: .

[0024] As a preferred embodiment of the present invention, the size correction factor Reinforcement correction factor All parameters were calibrated through finite element numerical simulation, and a standardized coefficient lookup table was generated. Different component sizes and different reinforcement parameters can be directly retrieved from the table.

[0025] As a preferred embodiment of the present invention, under the finite element simulation verification conditions, the relative error between the calculation result of the annular electrode analytical model and the simulation true value is less than 3%.

[0026] As a preferred embodiment of the present invention, the center electrode, the pressure measuring ring electrode, and the outermost return ring electrode are all metal conductive rings, which are integrated into the insulating probe mold to ensure that the electrodes are arranged coaxially and concentrically.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Optimized current field distribution, weakening boundary and reinforcement interference: The ring coaxial electrode forms an axisymmetric radially diffused current field, eliminating the directional sensitivity caused by the unidirectional current of the traditional linear electrode, naturally reducing the disturbance of the current field by the component boundary and internal reinforcement, and significantly reducing the foundation measurement error;

[0029] 2. Possesses a complete physical analytical model with strong versatility: Based on the Laplace equation and the integral derivation of the ring current source, a standardized geometric coefficient calculation formula is obtained, which is different from the existing purely empirical fitting model. The physical mechanism is clear, and it can be directly applied to ring probes of different sizes.

[0030] 3. Graded correction system, adaptable to all working conditions: Two-level judgment criteria are set for size effect and reinforcement interference. When the threshold conditions are met, correction can be omitted. When not met, correction can be quickly made through the coefficient table of finite element calibration. Small thin components and densely reinforced thick protective layer components can be accurately measured.

[0031] 4. High detection stability and controllable error: Under ideal semi-infinite medium conditions, the relative error between the analytical model and the finite element simulation results is less than 3%; under the same component and reinforcement conditions, the measured value dispersion is much smaller than that of the Wenner four-electrode method.

[0032] 5. High engineering practicality: The device has a simple, non-destructive, and portable structure, and the testing process is standardized. It can be used for laboratory concrete durability testing, health monitoring of various existing concrete structures such as bridges, tunnels, and civil buildings. Attached Figure Description

[0033] Figure 1 This is a flowchart of the concrete annular electrode resistivity detection method of the present invention;

[0034] Figure 2 This is a schematic diagram of the overall structure of the annular electrode resistivity detection device of the present invention;

[0035] Figure 3 This is a schematic diagram of the finite element simulation modeling of the present invention, which includes a theoretical verification model, a size correction model, and a reinforcement correction model.

[0036] Figure 4 This is a graph showing the influence of the concrete component size boundary on the resistivity test results.

[0037] Figure 5 This is a graph showing the influence of steel bar parameters on resistivity detection results under different protective layer thicknesses according to the present invention. Detailed Implementation

[0038] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example

[0040] 1. Device parameter settings

[0041] A ring electrode probe is selected. Electrode geometry: inner radius of the pressure measuring ring. outer radius of the pressure measuring ring The outermost return ring electrode radius Maximum outer diameter of the probe The current source outputs a constant current. Intrinsic resistivity of concrete .

[0042] 2. Step 1: Concrete Surface Assessment and Reinforcement Distribution Detection

[0043] The concrete component to be tested is a square thin slab with a side length of [missing information]. Component thickness The rebar scanner detected the following: rebar diameter. Reinforcing bar protective layer thickness Rebar mesh spacing .

[0044] Parameter determination: , The dimensions do not meet the requirements for no correction. The reinforcing bars are located in the sensitive area of ​​the probe, and both dimensional and reinforcing bar corrections are required simultaneously.

[0045] 3. Step 2: Preparation for Ring Electrode Detection

[0046] Clean the surface of the concrete measuring point of laitance and dust, and fully attach the ring electrode probe to the measuring point; connect the current source to the center electrode and the outermost return loop, and connect the multimeter to the two pressure measuring loops; then apply current. Constant current, collecting potential difference .

[0047] 4. Apparent resistivity in step 3 calculate

[0048] 4.1 Calculation :

[0049]

[0050]

[0051] 4.2 Substitute the geometric coefficients Calculation formula:

[0052]

[0053] Substitute into elliptic integral Solving for the given information ;

[0054] 4.3 Calculation of apparent resistivity:

[0055]

[0056] 5. Step 4: Adjustment Calculation of Influencing Factors

[0057] 5.1 Size Effect Correction

[0058] Consult the size correction factor table in the instruction manual to obtain... ;

[0059] Resistivity after size correction:

[0060]

[0061] 5.2 Reinforcement Interference Correction

[0062] protective layer Rebar diameter , Query protection layer 40 The table of reinforcement correction factors is obtained. ;

[0063] Ultimate intrinsic resistivity of concrete:

[0064]

[0065] 6. Simulation Verification and Comparison

[0066] Establish a finite element model with identical dimensions and reinforcement parameters, and the true values ​​of the infinite element boundary theory are... The corrected detection value of this invention The relative error is less than 3%; under the same working conditions, the detection error of the traditional Wenner four-electrode method exceeds 12%, proving that the detection accuracy of the present invention is significantly improved.

[0067] 7. On-site engineering expansion

[0068] The device and calculation method described in this embodiment can be directly applied to the testing of solid structures such as bridge box girders, underground utility tunnels, and civil floor slabs; when components , And when the spacing between the reinforcing bars is greater than 1.1 times the outer diameter of the probe, No need to look up tables for correction, directly use apparent resistivity As the true resistivity of concrete, it greatly simplifies the on-site testing and calculation process.

[0069] Table 1 Comparison of theoretical and simulated values ​​of the geometric coefficient k under different toroidal electrode parameters

[0070] Table 2 Size Correction Factors

[0071] Table 3 Reinforcement Correction Factors (Protective Cover cc = 20 mm)

[0072] Table 4 Reinforcement Correction Factors (Protective Cover cc = 40 mm) Table 5 Reinforcement Correction Factors (Protective Cover cc=60 mm)

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for detecting the resistivity of a ring electrode in a concrete structure, comprising a current source, a ring electrode probe, and a voltage acquisition multimeter, characterized in that: The ring electrode probe includes a probe mold, a central electrode, two layers of pressure-measuring ring electrodes, and an outermost return ring electrode. The central electrode, the two layers of pressure-measuring ring electrodes, and the outermost return ring electrode are arranged coaxially and concentrically in a ring. The output terminal of the current source is electrically connected to the central electrode and the outermost return ring electrode, respectively, for introducing a constant current into the concrete. The voltage acquisition multimeter is electrically connected to two layers of voltage-sensing ring electrodes at both ends to acquire the potential difference between the two layers of voltage-sensing rings. After the ring electrode probe is attached to the concrete surface, the current diffuses radially outward from the central electrode to the outermost return ring electrode, forming an axisymmetric radially uniform current field inside the concrete. Define electrode geometry parameters: The center radius of the two layers of pressure measuring ring electrodes. It is the center radius of the outermost return ring electrode.

2. The detection method of the annular electrode resistivity detection device for concrete structures according to claim 1, comprising the following steps: Step 1: Concrete surface assessment and reinforcement distribution detection; Select smooth, defect-free concrete inspection areas and clean the surface; use a reinforcement scanner to obtain the planar side lengths of the component. Component thickness , diameter of reinforcing bars Thickness of concrete cover for reinforcing bars Spacing of steel mesh ; Step 2: Preparation for ring electrode resistivity testing; Place the ring electrode probe against the concrete surface and apply a constant current through the current source. A multimeter is used to collect the potential difference between the two voltage measuring rings. ; Step 3: Resistivity calculation method; Calculate the geometric coefficients of the ring probe : In the formula , This is a complete elliptic integral of the first kind; Calculate the apparent resistivity of concrete : Step 4: Calculation of adjustments for influencing factors; Size effect correction: maximum outer diameter of the probe ,like and Size correction factor If the condition is not met, retrieve the result from the table. ,calculate ; Reinforcement interference correction: no reinforcement, protective layer exceeding probe detection depth, reinforcement mesh spacing When, reinforcement correction factor When the reinforcing bar is within the probe's sensitive area, the table should be consulted to obtain the information. Calculate the intrinsic resistivity of concrete ; Unified correction formula: .

3. The detection method of the annular electrode resistivity detection device for concrete structures according to claim 2, characterized in that: Size correction factor Reinforcement correction factor All parameters were calibrated through finite element numerical simulation, and a standardized coefficient lookup table was generated. Different component sizes and different reinforcement parameters can be directly retrieved from the table.

4. The detection method of the annular electrode resistivity detection device for concrete structures according to claim 2, characterized in that: Under the finite element simulation verification conditions, the relative error between the calculation results of the annular electrode analytical model and the simulation true value is less than 3%.

5. The annular electrode resistivity detection device for concrete structures according to claim 1, characterized in that: The center electrode, pressure measuring ring electrode, and outermost return ring electrode are all metal conductive rings, which are integrated into the insulating probe mold to ensure that the electrodes are arranged coaxially and concentrically.

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