Concrete resistivity measuring device and measuring method

Abstract

A concrete resistivity measuring device disclosed by the present invention comprises a concrete test piece, two sleeves, a plate electrode and a ring electrode, the two sleeves are of a semicircular structure, the two sleeves can form a cylinder, the cylinder is used for hooping the concrete test piece, and the sleeves are made of an insulating material; the two plate electrodes are of circular structures, the two plate electrodes are arranged at the upper end and the lower end of a concrete test piece respectively, and the multiple ring electrodes are evenly arranged in the axial direction of the concrete test piece at intervals; the plurality of test leads are arranged on the sleeve in a penetrating manner and are respectively and correspondingly connected with one ring electrode; the invention further provides a concrete resistivity measuring method. According to the invention, the resistivity of the concrete test piece can be rapidly measured, the resistance of different height differences can be tested, the uniformity of the concrete test piece can be verified, the real resistivity distribution in the concrete structure can be measured losslessly, accurately and conveniently, and the method has important engineering application value.

Description

Technical Field

[0001] This invention relates to the field of concrete testing technology, and in particular to a concrete resistivity measuring device and method. Background Technology

[0002] Concrete resistivity is a key parameter for evaluating the durability and service performance of reinforced concrete structures. It directly reflects the conductivity of the pore solution within the concrete and is strongly correlated with chloride ion diffusion coefficient and steel corrosion rate. Accurate measurement of concrete resistivity is crucial for the durability design, life prediction, and maintenance decisions of infrastructure. Specifically, the main functions of concrete resistivity testing include:

[0003] 1. Assessing the risk and rate of steel corrosion: Resistivity is the decisive factor in controlling the ion migration rate during the electrochemical corrosion of steel. Low resistivity usually means higher corrosion current and faster corrosion rate. By monitoring resistivity, the instantaneous risk of steel corrosion can be assessed indirectly and non-destructively.

[0004] 2. Reflecting the internal condition of concrete: Resistivity is highly sensitive to the moisture content, pore structure, ion content (such as chloride ions and alkaline ions), and crack development of concrete. Therefore, it can serve as a comprehensive indicator reflecting the density, impermeability, and internal damage of concrete.

[0005] 3. Guiding Durability Design and Quality Control: During the design and construction phases, resistivity is used as an auxiliary indicator to evaluate concrete mix design optimization, the effect of mineral admixtures, and curing quality, in order to ensure that concrete has long-term resistance to erosion.

[0006] Currently, the mainstream methods for measuring concrete resistivity in the field and laboratory mainly include the four-electrode method (Wenner array method), the two-electrode method, and the embedded sensor method, but these methods all have certain limitations:

[0007] 1. Limitations of the traditional four-electrode method (surface measurement):

[0008] Insufficient measurement depth and representativeness: This method uses four electrodes arranged at equal intervals on the surface for measurement, and its effective detection depth is usually limited to the depth of the electrode spacing. For concrete structures with a protective layer and uneven internal humidity / salt distribution, surface measurement results are difficult to accurately characterize the true resistivity of key areas on the steel reinforcement surface, leading to misjudgment of corrosion risk.

[0009] Highly dependent on surface condition: Measurement results are easily affected by the moisture content of the concrete surface, carbonation layer, laitance, or surface coating. Fine surface treatment and wetting are required, which is cumbersome and may introduce human error.

[0010] Limited spatial resolution: It is difficult to achieve precise measurement of the resistivity gradient inside the structure, and it is impossible to accurately locate defects or intrusion fronts.

[0011] 2. Limitations of the two-electrode method (core drilling or counter-measurement method):

[0012] High requirements for destructive or contact applications: These applications typically require drilling holes in concrete to install electrodes or measuring on both sides of a component, causing localized damage to the structure, or require the component to have two contactable opposing surfaces, thus limiting the application scenarios.

[0013] Contact resistance has a significant impact: the contact resistance between the electrode and the concrete can seriously affect the measurement accuracy, especially in dry or high-impedance conditions, where the error may far exceed the resistance being measured itself.

[0014] 3. Limitations of embedded sensors:

[0015] Pre-embedding requirements and long-term stability issues: The sensor must be pre-embedded before concrete pouring and cannot be used for detecting existing structures. Furthermore, the sensor's durability, packaging reliability, and electrode polarization issues during long-term operation in the highly alkaline environment of concrete may lead to data drift or failure.

[0016] Locality and high cost: Sensors can only provide local information at fixed points. To obtain the overall state of the structure, they need to be densely deployed, which is costly and impractical.

[0017] In summary, existing concrete resistivity measurement technologies have significant shortcomings in terms of measurement depth representativeness, adaptability to structural conditions, reliability of long-term monitoring, and ease of operation. In particular, there is a lack of a non-destructive, accurate, and convenient method for measuring the true resistivity distribution within concrete structures, especially in the reinforcing steel cover and deeper areas. Summary of the Invention

[0018] The purpose of this invention is to provide a concrete resistivity measuring device and method to solve the problems mentioned in the background art.

[0019] To achieve the above objectives, the present invention provides the following technical solution: a concrete resistivity measuring device, comprising:

[0020] A concrete specimen, wherein the concrete specimen is a cylindrical structure and is the test body used for concrete resistivity testing;

[0021] The sleeve is semi-circular in structure and there are two sleeves. The two sleeves can form a cylinder and the cylinder is used to hold the concrete specimen. The sleeve is made of insulating material.

[0022] The plate electrode is circular and there are two of them. The two plate electrodes are respectively disposed at the upper and lower ends of the concrete specimen, and the plate electrode is connected to a power source.

[0023] Ring electrodes, wherein there are several ring electrodes and they are evenly spaced along the axial direction of the concrete specimen;

[0024] The test leads are of several kinds, and the number of test leads is the same as the number of ring electrodes. Each of the test leads is passed through a sleeve and is connected to a ring electrode. A voltmeter is connected to each test lead.

[0025] Further optimization involves connecting the sleeve to an adjustable inner diameter circular fastener, which is used to clamp the cylinder formed by the two sleeves.

[0026] Further optimization involves providing several mounting slots evenly spaced vertically along the circumference of the inner wall of the sleeve. The number and position of the mounting slots are adapted to the ring electrode. Several test leads are respectively connected to a mounting slot and can be connected to the ring electrode.

[0027] Further optimization involves providing a base below one of the two plate electrodes and a top cover above the other of the two plate electrodes.

[0028] Further optimization involves adjusting the diameter of the plate electrode to adjust its surface area, or by providing a through-hole in the center of the plate electrode.

[0029] Further optimization involves providing a wet sponge contact layer between both plate electrodes and the concrete specimen.

[0030] Further optimization involves adding five ring electrodes and five mounting slots.

[0031] Further optimization involves using a stainless steel plate electrode and a conductive sponge ring electrode.

[0032] The present invention also provides a method for measuring the resistivity of concrete, including the concrete resistivity measuring device described in the above claims, the steps of which are as follows:

[0033] Step S1: Prepare a cylindrical concrete specimen. Place five ring electrodes on the circumference of the concrete specimen and position them corresponding to the mounting grooves of the sleeves. Then, clamp two sleeves onto the concrete specimen and fix the ring fasteners. Next, place a plate electrode at each of the upper and lower ends of the concrete specimen and place them together on the base. Then, place the top cover on the plate electrode located above. Place a wet sponge sheet with a surface area not less than that of the plate electrode on both plate electrodes and the concrete specimen.

[0034] Step S2: Inject low-frequency alternating current into the two plate electrodes via a power supply. Then, the potential difference between each pair of adjacent ring electrodes, between the top and bottom ring electrodes, and between the two plate electrodes was measured using a voltmeter, resulting in six sets of voltage data. , , , , , And according to Ohm's law, resistance Calculation formula Calculate the resistance at each height difference. ;

[0035] Step S3: Using COMSOL software, establish a numerical model with the same geometry, dimensions, and electrode configuration as the actual concrete specimen and measuring device. Specify the resistivity of the concrete in the numerical model as... The potential difference between the corresponding ring electrode models and the plate electrode models in the numerical model was measured. , , , , , According to the formula Calculate the resistance for each corresponding height difference. Then according to the formula Calculate the geometric factors of the same model. ;

[0036] Step S4, according to the formula The resistivity of actual concrete specimens at different heights was calculated. Size, depending on different heights Numerical values ​​were used to verify the uniformity of the concrete specimens.

[0037] Further optimization involves applying conductive gel to the contact surface between the ring electrode and the concrete specimen in step S1.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] By setting up sleeves, plate electrodes, ring electrodes, and test leads, the resistivity of concrete specimens can be measured rapidly, and the resistance at different height differences can be tested. Combined with numerical modeling correction, the resistivity of concrete specimens at different heights can be measured. Based on the resistivity values ​​at different heights, the uniformity of concrete specimens can be verified. This enables non-destructive, accurate, and convenient measurement of the true resistivity distribution inside concrete structures, which has significant engineering application value and is urgently needed to improve the accuracy and efficiency of durability assessment of reinforced concrete structures.

[0040] The insulating sleeve effectively blocks lateral leakage current, ensuring accurate resistivity measurement of the concrete specimen. Multiple ring electrodes are used to measure potential differences at different heights. The ring electrodes are made of conductive sponge, which can adapt to the micro-unevenness of the concrete specimen surface, increasing the effective contact area, reducing contact resistance, dispersing current density, suppressing electrode polarization, and avoiding changes in humidity conditions near the measurement potential. The stainless steel plate electrode setup has good conductivity, stable chemical properties, strong corrosion resistance, high mechanical strength, and controllable contact pressure, ensuring the stability of the contact area between the plate electrode and the concrete specimen.

[0041] The circular fasteners enable the two sleeves to be quickly locked together after forming a cylinder, and have high compatibility; the wet sponge contact layer between the plate electrode and the concrete specimen reduces the contact resistance and electrode polarization.

[0042] The measuring device has a simple structure, is easy to manufacture and use, and is easy to maintain and replace, with low cost and simple operation. The measurement method is based on the measuring device, is easy to operate, and can achieve rapid and accurate measurement of the resistivity of concrete specimens. It combines numerical modeling to correct geometric factors to achieve accurate internal resistivity distribution of concrete, overcoming the limitations of existing technologies such as insufficient measurement depth, strong surface dependence, and high destructiveness. It achieves non-destructive, accurate, and convenient resistivity measurement, and is particularly suitable for evaluating the uniformity and internal defects of concrete. Furthermore, by changing the contact area between the plate electrode and the concrete specimen, it can be used to study the influence of the injected electrode size on resistivity measurement. Attached Figure Description

[0043] Figure 1 This is a structural schematic diagram illustrating the principle of Ohm's law disclosed in this invention;

[0044] Figure 2 This is a schematic diagram of the structure of the concrete resistivity measuring device disclosed in this invention;

[0045] Figure 3 This is a diagram showing the distribution of electrode measurement positions as disclosed in this invention.

[0046] Figure 4 This is a schematic diagram of the structure disclosed in this invention, which involves setting a circular hole on a plate electrode.

[0047] Reference numerals: 1-sleeve, 11-mounting groove, 2-plate electrode, 21-round hole, 3-ring electrode, 4-test lead, 5-ring fastener, 6-base, 7-top cover, 8-concrete specimen. Detailed Implementation

[0048] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0049] like Figure 2 As shown, a concrete resistivity measuring device includes:

[0050] Concrete specimen 8 is a cylindrical structure and is used as the test body for concrete resistivity testing.

[0051] Sleeve 1, sleeve 1 is semi-circular and there are two sleeves 1. The two sleeves 1 can form a cylinder and the cylinder is used to clamp the concrete specimen 8. Sleeve 1 is made of insulating material.

[0052] Plate electrode 2, which is circular and there are two of them. The two plate electrodes 2 are respectively located at the upper and lower ends of the concrete specimen 8, and the plate electrodes 2 are connected to a power source.

[0053] Ring electrode 3, there are several ring electrodes 3 and they are evenly spaced along the axial direction of the concrete specimen 8.

[0054] Test leads 4, there are several test leads 4, and the number of test leads 4 is the same as the number of ring electrodes 3. The test leads 4 are all passed through the sleeve 1 and are respectively connected to a ring electrode 3. A voltmeter is connected to the test leads 4.

[0055] In this application, the measuring device is used to measure the resistivity of the side edges of the concrete specimen 8 at different heights, and to verify the uniformity of the concrete specimen 8 based on the resistivity at different heights, which can improve the accuracy and efficiency of the durability assessment of reinforced concrete structures.

[0056] The measuring device includes a sleeve 1, plate electrodes 2, ring electrodes 3, test leads 4, and a concrete specimen 8 for testing. The sleeve 1 has a semi-circular structure; two sleeves 1 can clamp the concrete specimen 8, fixing it and facilitating measurement. Simultaneously, the insulating sleeve 1 effectively blocks lateral leakage current, ensuring that current flows only along the axial direction of the concrete specimen 8, thus ensuring accurate resistivity measurement. The plate electrodes 2 are located at both ends of the concrete specimen 8 for connecting to a power source, injecting current into the specimen. The plate electrodes 2 have a circular structure to accommodate the cylindrical shape of the concrete specimen 8. The ring electrodes 3 are fitted onto the concrete specimen 8, with multiple ring electrodes 3 evenly spaced along the axial direction of the specimen 8, i.e., evenly distributed along the height of the test unit—the concrete specimen 8—to achieve potential difference measurement at different heights. Test lead 4 is mounted on sleeve 1, passing through sleeve 1 and connecting to ring electrode 3, thus facilitating the connection of the voltmeter to ring electrode 3 for potential difference measurement. This simple measuring device enables rapid measurement of the resistivity of concrete specimen 8.

[0057] Reference Figure 2 As shown, in one embodiment of this application, the sleeve 1 is connected to an adjustable inner diameter ring fastener 5, which is used to clamp the cylinder formed by the two sleeves 1.

[0058] In this embodiment, the circular fastener 5 enables rapid fixing of the cylinder composed of the two sleeves 1, allowing the sleeves 1 to be placed around the concrete specimen 8. Furthermore, the movable inner diameter of the circular fastener 5 is adjustable, facilitating its placement on the cylinder composed of the two sleeves 1, ensuring secure locking of the sleeves 1, and adapting to locking of sleeves 1 with different diameters.

[0059] In this embodiment, the circular fastener 5 is a clamp structure, which not only facilitates the adjustment of the movable inner diameter (i.e., the inner diameter adjustment of the clamp), but also ensures convenient adjustment and secure locking. Furthermore, the clamp structure is simple, easy to manufacture, and low in cost.

[0060] Continue to refer to Figure 2 As shown, in another embodiment of this application, the inner wall of the sleeve 1 is provided with a plurality of mounting grooves 11 evenly spaced vertically along its circumference. The number and position of the mounting grooves 11 are adapted to the ring electrode 3. A plurality of test leads 4 are respectively connected to a mounting groove 11 and can be connected to the ring electrode 3.

[0061] In this embodiment, by providing an installation groove 11 on the sleeve 1, the installation of the ring electrode 3 is facilitated without damaging it. The ring electrode 3 is also positioned quickly, eliminating the need to separately measure the concrete specimen 8 with a ruler and then measure the distance between adjacent ring electrodes 3 to adjust their position relative to the concrete specimen 8. This reduces the process steps and measurement CT (total contact area) required for the measuring device, achieving high-efficiency measurement. Furthermore, the precise positioning of the ring electrode 3 via the installation groove 11 ensures accurate measurement of the concrete resistivity. The test lead 4 is connected to the corresponding installation groove 11, protecting the connector of the test lead 4 and ensuring precise connection between the ring electrode 3 and the test lead 4.

[0062] Continue to refer to Figure 2 As shown, in another embodiment of this application, a base 6 is provided below one of the two plate electrodes 2, and a top cover 7 is provided above the other of the two plate electrodes 2.

[0063] In this embodiment, the base 6 supports the bottom plate electrode 2 and the concrete specimen 8, ensuring the stability and levelness of the plate electrode 2 and ensuring effective contact between the bottom plate electrode 2 and the concrete specimen 8. The top cover 7 presses down on the top plate electrode 2 of the concrete specimen 8, preventing the top plate electrode 2 from moving during measurement and ensuring effective contact between the top plate electrode 2 and the concrete specimen 8.

[0064] In this embodiment, both the base 6 and the top cover 7 are made of insulating PVC material, which provides electrical insulation and prevents leakage and conduction, thus ensuring the accuracy of resistivity measurement of the concrete specimen 8.

[0065] like Figure 3 As shown, in another embodiment of this application, the diameter of the plate electrode 2 can be adjusted to achieve adjustment of its surface area, or the surface area can be adjusted by providing a through circular hole 21 in the center of the plate electrode 2.

[0066] In this embodiment, by changing the surface area of ​​the plate electrode 2, the contact area between the plate electrode 2 and the concrete specimen 8 can be changed, thereby optimizing the current injection effect, controlling the electric field distribution, reducing measurement errors, and ensuring the accuracy of resistivity measurement. There are two ways to change the surface area of ​​the plate electrode 2: one is to directly change the diameter of the plate electrode 2, which can be done by shielding the plate electrode 2 with an insulating ring, or by directly replacing the plate electrode 2 with one of a different diameter; another is to provide a circular hole 21 on the plate electrode 2, thereby removing the middle portion of the plate electrode 2 to change its surface area, and thus changing the contact area with the concrete specimen 8.

[0067] In another embodiment of this application, a wet sponge contact layer is provided between each of the two plate electrodes 2 and the concrete specimen 8. This wet sponge contact layer reduces contact resistance and the influence of electrode polarization. Specifically, it addresses the impact of additional resistance on measurements caused by factors such as microscopic unevenness of the concrete surface, potential media present in the contact cross-section, and insufficient pressure exerted by the plate electrodes 2 on the concrete specimen 8. The wet sponge contact layer increases the effective contact area between the plate electrodes 2 and the concrete specimen 8, reduces the current density, and slows down the electrochemical reaction rate on the surface of the plate electrodes 2. Furthermore, the conductive liquid in the wet sponge contact layer acts as an ion buffer, sharing some of the polarization reaction, thus reducing the aforementioned problems and preventing irreversible electrochemical reactions on the surface of the plate electrodes 2 that could lead to charge accumulation and generate additional electromotive force, interfering with the measurement of the true potential difference. Simultaneously, using low-frequency alternating current can reduce the influence of polarization.

[0068] Furthermore, based on the above implementation method, there are five ring electrodes 3 and five mounting slots 11. Five ring electrodes 3 are installed through the five mounting slots 11, and the potential difference at multiple different heights of the concrete specimen 8 is measured through the five ring electrodes 3.

[0069] In another embodiment of this application, the plate electrode 2 is a stainless steel plate electrode, which has good conductivity, providing a stable current path for the concrete specimen 8 and ensuring that the electric field distribution conforms to the theoretical model; it also has stable chemical properties, strong corrosion resistance, high mechanical strength, and controllable contact pressure, ensuring a stable contact area. The ring electrode 3 is a conductive sponge ring electrode, which, while ensuring conductivity, adapts to the micro-undulations on the surface of the concrete specimen 8 through the porous structure and elasticity of the sponge, increasing the effective contact area, reducing contact resistance, dispersing current density, suppressing electrode polarization, and avoiding changes in humidity conditions near the measurement potential.

[0070] like Figure 4 As shown, the present invention also provides a method for measuring the resistivity of concrete, based on a concrete resistivity measuring device, the steps of which are as follows:

[0071] Step S1: Prepare a cylindrical concrete specimen 8 with a diameter of 75mm and a height of 75mm. Place five ring electrodes 3 on the circumference of the concrete specimen 8 and position them corresponding to the mounting groove 11 of the sleeve 1. Then, clamp two sleeves 1 onto the concrete specimen 8 and fix the ring fasteners 5. Next, place a plate electrode 2 at the top and bottom of the concrete specimen 8 and place them together on the base 6. Then, place the top cover on the plate electrode 2 located above. Place a wet sponge sheet with a surface area not less than that of the plate electrode 2 on both plate electrodes 2 and the concrete specimen 8.

[0072] Step S2: Inject low-frequency alternating current into the two plate electrodes 2 via a power supply. The frequency of low-frequency alternating current is 50Hz, and the current is... The voltage was 0.5A. Then, the potential difference between each pair of adjacent ring electrodes 3, between the uppermost and lowermost ring electrodes 3, and between the two plate electrodes 2 was measured using a voltmeter, resulting in 6 sets of voltage data. , , , , , And according to Ohm's law, resistance Calculation formula Calculate the resistance at each height difference. ;

[0073] Step S3: Using COMSOL software, establish a numerical model with the same geometry, dimensions, and electrode configuration as the actual concrete specimen 8 and measuring device. Specify the resistivity of the concrete in the numerical model as... The potential difference between the corresponding ring electrode models and the plate electrode models in the numerical model was measured. , , , , , According to the formula Calculate the resistance for each corresponding height difference. Then according to the formula Calculate the geometric factors of the same model. ;

[0074] Step S4, according to the formula The resistivity of the actual concrete specimen 8 at different heights was calculated. Size, depending on different heights The numerical values ​​were used to verify the uniformity of concrete specimen 8.

[0075] In this invention, the measurement method adopts the four-electrode measurement method. By injecting alternating current into the plate electrode 2, the potential difference between the ring electrodes 3 is measured. Combined with numerical modeling to correct the geometric factor, the resistivity distribution inside the concrete can be accurately calculated.

[0076] In step S1, conductive gel is applied to the contact surface between the ring electrode 3 and the concrete specimen 8 to ensure good contact between the ring electrode 3 and the concrete specimen 8 without hindering the conductivity of the ring electrode 3.

[0077] In step S2, the current is an alternating current with a frequency of 50Hz and a magnitude of 0.5A, which can reduce the polarization effect. Its core principle is to use the characteristic of the periodic reversal of the direction of alternating current to break the continuous accumulation of charge on the electrode surface under direct current, thereby suppressing the generation of electrochemical polarization.

[0078] In step S3, the resistivity measurement directly applies Ohm's law, such as... Figure 1 As shown, because the geometry of the tested concrete specimen 8 is very simple, the resistivity of concrete specimen 8 is... With cross-sectional area Proportional to length They are inversely proportional, as shown in the following equation:

[0079]

[0080] Where ρ is resistivity and the geometric factor G is the cross-sectional area A (m²). 2 The ratio of the length L (m) to the resistance R is the potential drop ΔV (v) obtained by applying a current I to A and measuring the resistance R.

[0081] Based on the concrete resistivity measurement method of the present invention, by changing the contact area between the plate electrode 2 and the concrete specimen 8, the influence of the injected electrode size on resistivity measurement can be studied. Changing the contact area between the plate electrode 2 and the concrete specimen 8 can be achieved by changing the diameter of the plate electrode 2, insulating and shielding the plate electrode 2, or drilling circular holes 21 of different sizes on the plate electrode 2; all of these methods can achieve the purpose of changing the surface area of ​​the plate electrode 2.

[0082] As shown in the table below, the geometric factor G was obtained by modeling and simulating using five different diameter plate electrodes 2, with diameters of 4mm, 10mm, 20mm, 30mm and 75mm respectively.

[0083]

[0084] The table above shows that the effect of changing the injected electrode diameter on various modeling geometric factors varies significantly: most factors decrease with increasing diameter, only... Reverse growth; at the same time, and , and The two sets of factors exhibit synchronous changes due to geometric and physical symmetry, resulting in a numerically bound relationship. These patterns provide crucial information for subsequent optimization of the resistivity measurement model based on electrode size.

[0085] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A concrete resistivity measuring device, characterized in that, include: Concrete specimen (8), the concrete specimen (8) is a cylindrical structure and is the test body used for concrete resistivity testing; The sleeve (1) has a semi-circular structure and there are two of them. The two sleeves (1) can form a cylinder and the cylinder is used to hold the concrete specimen (8). The sleeve (1) is made of insulating material. Plate electrode (2), the plate electrode (2) is a circular structure and there are two of them. The two plate electrodes (2) are respectively located at the upper and lower ends of the concrete specimen (8). The plate electrode (2) is connected to a power source. Ring electrode (3), there are several ring electrodes (3) and they are evenly spaced along the axial direction of the concrete specimen (8); Test leads (4), there are several test leads (4) and the number of test leads (4) is the same as the number of ring electrodes (3). Several test leads (4) are all passed through the sleeve (1) and are respectively connected to a ring electrode (3). A voltmeter is connected to the test leads (4).

2. The concrete resistivity measuring device according to claim 1, characterized in that, The sleeve (1) is connected to an adjustable inner diameter ring fastener (5), which is used to clamp the cylinder formed by the two sleeves (1).

3. The concrete resistivity measuring device according to claim 1, characterized in that, The inner wall of the sleeve (1) is provided with a number of mounting grooves (11) evenly spaced up and down along its circumference. The number and position of the mounting grooves (11) are adapted to the ring electrode (3). A number of test leads (4) are respectively connected to a mounting groove (11) and can be connected to the ring electrode (3).

4. The concrete resistivity measuring device according to claim 1, characterized in that, A base (6) is provided below the lower one of the two plate electrodes (2), and a top cover (7) is provided above the other one of the two plate electrodes (2).

5. The concrete resistivity measuring device according to claim 1, characterized in that, The diameter of the plate electrode (2) can be adjusted to adjust its surface area, or the surface area can be adjusted by providing a through hole (21) in the center of the plate electrode (2).

6. The concrete resistivity measuring device according to claim 1, characterized in that, A wet sponge contact layer is provided between the two plate electrodes (2) and the concrete specimen (8).

7. A concrete resistivity measuring device according to claim 3, characterized in that, The number of ring electrodes (3) and mounting slots (11) are both five.

8. The concrete resistivity measuring device according to claim 1, characterized in that, The plate electrode (2) is a stainless steel plate electrode, and the ring electrode (3) is a conductive sponge ring electrode.

9. A method for measuring the resistivity of concrete, characterized in that, The concrete resistivity measuring device according to any one of claims 1 to 8 comprises the following steps: Step S1: Prepare a cylindrical concrete specimen (8), and set five ring electrodes (3) on the circumference of the concrete specimen (8) and the position corresponding to the mounting groove (11) of the sleeve (1). Then, clamp the two sleeves (1) onto the concrete specimen (8) and fix the ring fastener (5). Next, place a plate electrode (2) on the upper and lower ends of the concrete specimen (8) and place them together on the base (6). Then, place the top cover on the plate electrode (2) located above. Place a wet sponge with a surface area not less than that of the plate electrode (2) on both plate electrodes (2) and the concrete specimen (8). Step S2: Inject low-frequency alternating current into the two plate electrodes (2) through the power supply. Then, the potential difference between each pair of adjacent ring electrodes (3), between the uppermost ring electrode (3) and the lowermost ring electrode (3), and between the two plate electrodes (2) was measured using a voltmeter, and six sets of voltage data were obtained respectively. , , , , , And according to Ohm's law, resistance Calculation formula Calculate the resistance at each height difference. ; Step S3: Using COMSOL software, establish a numerical model with the same geometry, dimensions, and electrode configuration as the actual concrete specimen (8) and measuring device. Specify the resistivity of the concrete in the numerical model as... The potential difference between the corresponding ring electrode models and the plate electrode models in the numerical model was measured. , , , , , According to the formula Calculate the resistance for each corresponding height difference. Then according to the formula Calculate the geometric factors of the same model. ; Step S4, according to the formula The resistivity of the actual concrete specimen (8) at different heights was calculated. Size, depending on different heights The numerical values ​​were used to verify the uniformity of the concrete specimen (8).

10. A method for measuring the resistivity of concrete according to claim 9, characterized in that, In step S1, conductive gel is applied to the contact surface between the ring electrode (3) and the concrete specimen (8).

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