Method for detecting the state of corrosion of reinforcing steel in concrete based on electrodeless resistivity

Abstract

The present application relates to a kind of based on electrodeless resistivity Reinforced concrete corrosion state detection method, comprising the following steps: the prepared reinforced concrete sample vacuum drying treatment is placed in test device, with electrolyte solution composition series circuit, electrodeless resistivity meter is tested to obtain system total resistance, again test obtains electrolyte solution resistance, the resistance of steel in concrete is obtained by calculation.By the change of steel in concrete in different curing age, the corrosion rate of steel in concrete is calculated, compared with relevant standard, the corrosion state of steel in concrete is obtained.The present application adopts electrodeless non-contact method, eliminates the influence of contact resistance and contact capacitance between electrode and concrete on measurement, will not produce electrode polarization and other problems, it is convenient and fast, the result is expressed in the form of steel corrosion depth rate, the result is more intuitive, consistent with the result of weight loss rate of steel corrosion in the current national standard, the same state of steel is distinguished.

Description

Technical Field

[0001] This invention relates to the field of building material testing, and more specifically, to a method for detecting the corrosion status of reinforcing steel bars in concrete based on electrode-free resistivity. Background Technology

[0002] The economic losses caused by steel reinforcement corrosion in concrete are enormous. Many concrete structures exhibit insufficient durability and steel reinforcement corrosion relatively early after being put into use. This significantly increases the risk of cracking, spalling, and even failure of the concrete structure during its service life. Solving the problem of steel reinforcement corrosion in concrete structures requires a substantial investment of manpower, material resources, and financial resources for inspection, evaluation, repair, and reinforcement. This not only results in economic losses and resource waste but may also lead to issues with structural reliability and safety.

[0003] The most direct method for detecting steel reinforcement corrosion in concrete is to split the concrete and directly measure the weight loss rate of the steel reinforcement due to corrosion, as described in the national standard "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082). However, this method is not only cumbersome but also damages the reinforced concrete. Therefore, electrochemical technology is now widely used to characterize steel reinforcement corrosion. Existing electrochemical detection methods for steel reinforcement corrosion in concrete include the half-potential method, linear polarization method, AC impedance method, and resistivity method. These methods characterize the corrosion rate of steel reinforcement in concrete based on different electrochemical characteristic parameters, thereby determining the degree of corrosion. These methods vary considerably in terms of detection speed, measurement parameters, interference levels, and applicable conditions. Chinese patent CN102706933A, "An Electrochemical Detection Method for the Degree of Steel Reinforcement Corrosion in Concrete," uses a three-electrode testing system. It measures the instantaneous polarization current value by performing polarization scanning near the natural potential and calculates the steel reinforcement corrosion current density based on empirical formulas, thereby determining the degree of steel reinforcement corrosion. Although this method selects a weakly polarized region for polarization scanning to minimize the adverse effects of polarization, it still causes irreversible disturbances to the reinforcing steel due to its polarization principle. Furthermore, the spontaneous potential is significantly affected by factors such as concrete humidity and pore structure, and using spontaneous potential as the starting point for polarization scanning can lead to substantial errors. Chinese patent CN109374519A, "A Detection Method for Characterizing the Corrosion Rate of Reinforcing Steel in Concrete Based on AC Impedance Spectroscopy," uses AC impedance spectroscopy to obtain the Nyquist curve and then uses software to fit electrical parameters to obtain the charge transfer resistance value of the reinforcing steel in the concrete, judging the corrosion rate based on the magnitude of the charge transfer resistance value. However, this method uses linear polarization to obtain the polarization resistance, still suffering from the problem of irreversible disturbances to the reinforcing steel caused by polarization. Moreover, the testing process is cumbersome, the reinforced concrete sample cannot be tested again after the initial test, and a set of concrete components needs to be formed for each test age. Representing the corrosion rate of reinforcing steel with charge transfer resistance value is not intuitive or clear enough.

[0004] Therefore, there is a need for a steel reinforcement testing method that is easy to operate, provides intuitive results, and has minimal impact on reinforced concrete. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for detecting the corrosion status of steel bars in concrete based on electrodeless resistivity, which is simple to operate, provides intuitive results, and has little impact on reinforced concrete.

[0006] The technical solution adopted by this invention to solve its technical problem is: to construct a method for detecting the corrosion state of steel bars in concrete based on electrode-free resistivity, comprising the following steps:

[0007] (1) Prepare reinforced concrete samples in molds of specified dimensions and harden them before demolding.

[0008] (2) Vacuum drying treatment of reinforced concrete samples;

[0009] (3) After cleaning the surface of the pretreated reinforced concrete sample, place it in the ring mold device and apply Vaseline to the bottom, inner and outer surfaces of the sample to make the sample fit tightly with the device. Pour the electrolyte solution into the rest of the device so that the liquid level is lower than the upper surface of the reinforced concrete sample.

[0010] (4) Start the electrodeless resistivity meter and begin the test. After a period of time, allow the data to stabilize and obtain the total resistance R0 of the system. After the test is completed, remove the reinforced concrete sample and electrolyte solution and clean the device.

[0011] (5) Add a certain amount of electrolyte solution, the same as in step (3), into the device. The liquid level is the same as in step (3). Start the electrodeless resistivity meter and begin testing. After a period of time, allow the data to stabilize and obtain the electrolyte solution resistance R2.

[0012] (6) Calculate the initial resistance R1 of the steel reinforcement in the concrete;

[0013] (7) After curing in a specific test environment for t hours, conduct tests according to steps (2) to (5), and obtain the steel resistance R in the concrete after t hours according to the formula in step (6). t The corrosion rate V of steel bars in concrete is calculated, and the corrosion state of steel bars in concrete is obtained according to the discrimination criteria.

[0014] Further, in step (1), the mold of the specified specifications is an annular mold adapted to the electrodeless resistivity meter, the specified size is 1 / 8 of the ring length of the mold, the steel bars in the concrete are arranged along the ring length and are flush with both ends of the concrete sample, the steel bar radius is d mm, and the concrete is covered and sealed for curing for 24 to 48 hours after molding.

[0015] Furthermore, in step (3), the electrolyte solution is either sodium chloride or sodium sulfate, with a mass fraction of 5%.

[0016] Furthermore, in step (4), the test time is 5 to 15 minutes.

[0017] Furthermore, in step (5), the test time is 1 to 3 minutes.

[0018] Furthermore, in step (6), the calculation of the resistance R1 of the steel reinforcement in the concrete is given by formula 1:

[0019] R1=R0-0.875R2 Formula 1

[0020] When reinforced concrete and electrolyte solution are present in the annular mold, the resistance R1 of the reinforcing steel can be considered as the resistance R of the concrete. 砼 After being connected in parallel and then in series with the electrolyte resistor R2', we have Formula 3:

[0021]

[0022] Because the resistance of the steel reinforcement R1 is much smaller than the resistance of the concrete R 砼 Formula 3 can be simplified to Formula 4:

[0023] R1+R′2=R0 Formula 4

[0024] When the ring mold contains only the electrolyte solution, the total resistance measured is the electrolyte solution resistance R2. Since the electrolyte solution occupies 7 / 8 of the ring length when tested together with the reinforced concrete, formula 5 applies:

[0025] R′2=0.875R2 Formula 5

[0026] Therefore, we obtain formula 1 for calculating the resistance R1 of the reinforcing steel:

[0027] R1=R0-0.875R2 Formula 1

[0028] Furthermore, in step (7), the calculation of the steel reinforcement corrosion rate V is given by formula 2:

[0029]

[0030] When steel bars in concrete corrode, the resistivity of the bars themselves does not change, but the resistance increases due to the decrease in cross-sectional area. After the reinforced concrete hardens and the formwork is removed, the resistance R1 of the steel bars is shown in Formula 6:

[0031]

[0032] In the formula, ρ is the resistivity of the steel bar, L is the length of the steel bar, and S is the cross-sectional area of ​​the steel bar; after t hours, the resistance R of the steel bar at this time is... t See Formula 7:

[0033]

[0034] Dividing and transforming the two equations above, we obtain formula 8:

[0035]

[0036] The initial radius of the reinforcing bar is d mm. Assuming the corrosion depth of the reinforcing bar is X mm after t hours, let d and X represent S1 and S in the above formula. t The corrosion depth X is given by formula 9:

[0037]

[0038] Therefore, after t hours, the corrosion rate V (mm / a) of the reinforcing steel can be expressed by Formula 2:

[0039]

[0040] The criteria are as follows: when V value < 0.0023 mm / a, the steel bar is not corroded and is in a passivated state; when V value is between 0.0023 and 0.0059 mm / a, the steel bar corrosion rate is low; when V value is between 0.0059 and 0.0117 mm / a, the steel bar corrosion rate is moderate; when V value is between 0.0117 and 0.1173 mm / a, the steel bar corrosion rate is high; when V value > 0.1173 mm / a, the steel bar corrosion rate is extremely high.

[0041] Therefore, this invention uses an electrodeless resistivity meter to characterize the change in the resistance of steel bars in concrete, thereby obtaining the rate of steel bar corrosion, and using this as a basis to determine the state of steel bar corrosion in concrete.

[0042] The principle of this invention is as follows:

[0043] This invention provides a method for detecting the corrosion state of steel bars in concrete based on electrodeless resistivity. The method uses an electrodeless resistivity meter to test the resistance of the system and obtain the resistance value of the steel bars in the concrete. By measuring the change in the resistance value of the steel bars in the environment, the corrosion rate of the steel bars is calculated. The results are displayed in millimeters per year (mm / a).

[0044] The electrodeless resistivity meter consists of a signal generator, amplifier, signal sensing device, sample mold, and data acquisition system. The signal generator and amplifier produce an alternating voltage signal on the primary coil of the signal sensing device. This alternating voltage signal is then induced by the iron core to form an alternating magnetic field. A secondary coil, composed of a toroidal cement sample, generates a corresponding induction. The ring voltage U induced in the secondary coil (i.e., the toroidal mold) is measured, and the corresponding current I is measured by the data acquisition device. The resistance value of the sample can then be determined according to Ohm's law. Because it uses an electrodeless, non-contact method, the influence of contact resistance and capacitance between the electrode and the concrete on the measurement is eliminated, and problems such as electrode polarization are avoided.

[0045] The method for detecting the corrosion state of reinforcing steel in concrete based on electrode-free resistivity, as described in this invention, has the following beneficial effects:

[0046] (1) The resistance of steel reinforcement in concrete is characterized by an electrodeless resistivity meter. Due to its non-contact and electrodeless nature, the influence of contact resistance and contact capacitance between the electrode and the concrete on the measurement is eliminated, and problems such as electrode polarization are avoided, resulting in accurate results. At the same time, this invention not only maintains the structural integrity of the reinforced concrete sample, but also avoids irreversible disturbances to the steel reinforcement caused by polarization reactions. The same sample can be studied at different ages, and the results are more reliable and accurate.

[0047] (2) Pretreatment of reinforced concrete samples before testing eliminates the potential impact of differences in concrete sample humidity on the results. The entire testing process takes only 5 to 20 minutes and is convenient and quick to operate.

[0048] (3) Compared with the electrochemical parameters used to represent the corrosion status of steel bars, the results of the steel bar corrosion status detection method in concrete of the present invention are expressed by the steel bar corrosion depth rate, which is more intuitive and clear. It is consistent with the steel bar corrosion weight loss rate obtained by directly splitting the concrete in the national standard, and the steel bar status is the same. However, the detection method of the present invention does not require splitting the concrete to destroy it, and the results are consistent with the splitting method in a non-destructive testing manner. Attached Figure Description

[0049] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0050] Figure 1 This is a schematic diagram of the structure of an electrodeless resistivity meter;

[0051] Figure 2 This is a picture of an electrodeless resistivity meter. Detailed Implementation

[0052] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0053] Example 1

[0054] A method for detecting the corrosion state of steel reinforcement in concrete based on electrode-free resistivity includes the following steps:

[0055] (1) Prepare reinforced concrete samples in molds of specified dimensions and harden them before demolding.

[0056] (2) Vacuum dry the reinforced concrete sample for 2 hours;

[0057] (3) After cleaning the surface of the pretreated reinforced concrete sample, place it in the ring mold device 2, and apply Vaseline to the bottom, inner and outer surfaces of the sample to make the sample fit tightly with the device. Pour the electrolyte solution into the rest of the device so that the liquid level is 5 mm lower than the upper surface of the reinforced concrete sample.

[0058] (4) Start the electrodeless resistivity meter 1 and begin the test. After a period of time, allow the data to stabilize and obtain the total resistance R0 of the system. After the test is completed, remove the reinforced concrete sample and electrolyte solution and clean the device.

[0059] (5) Add a certain amount of electrolyte solution, the same as in step (3), into the device. The liquid level is the same as in step (3). Start the electrodeless resistivity meter 1 and begin testing. After a period of time, allow the data to stabilize and obtain the electrolyte solution resistance R2.

[0060] (6) Calculate the initial resistance R1 of the steel reinforcement in the concrete according to the formula;

[0061] (7) After curing in a sodium chloride salt spray dry-wet cycle environment for 2400 hours, conduct tests according to steps (2) to (5), and obtain the steel resistance R in the concrete after 2400 hours according to the formula in step (6). t The corrosion rate V of steel bars in concrete is calculated using a formula and compared with relevant standards to determine the corrosion status of steel bars in concrete.

[0062] In step (1), the mold of the specified specifications is an annular mold adapted to the electrodeless resistivity meter 1, and the specified size is 1 / 8 of the ring length of the mold. The steel bars in the concrete are arranged along the ring length and are flush at both ends of the concrete sample. The steel bar radius is 3 mm. After the concrete is formed, it is covered and sealed for 24 hours.

[0063] In step (3), the electrolyte solution is sodium chloride with a mass fraction of 5%.

[0064] In step (4), the test time is 5 to 15 minutes;

[0065] In step (5), the test time is 1 to 3 minutes;

[0066] In step (6), the formula for calculating the resistance R1 of the steel reinforcement in the concrete is:

[0067] R1 = R0 - 0.875R2

[0068] In step (7), the formula for calculating the steel corrosion rate V is:

[0069]

[0070] The criteria are as follows: when V value < 0.0023 mm / a, the steel bar is not corroded and is in a passivated state; when V value is between 0.0023 and 0.0059 mm / a, the steel bar corrosion rate is low; when V value is between 0.0059 and 0.0117 mm / a, the steel bar corrosion rate is moderate; when V value is between 0.0117 and 0.1173 mm / a, the steel bar corrosion rate is high; when V value > 0.1173 mm / a, the steel bar corrosion rate is extremely high.

[0071] The test results of the steel corrosion rate in concrete in this embodiment are shown in Table 1.

[0072] Example 2

[0073] A method for detecting the corrosion state of steel reinforcement in concrete based on electrode-free resistivity includes the following steps:

[0074] (1) Prepare reinforced concrete samples in molds of specified dimensions and harden them before demolding.

[0075] (2) Vacuum dry the reinforced concrete sample for 2 hours;

[0076] (3) After cleaning the surface of the pretreated reinforced concrete sample, place it in the ring mold device 2, and apply Vaseline to the bottom, inner and outer surfaces of the sample to make the sample fit tightly with the device. Pour the electrolyte solution into the rest of the device so that the liquid level is 5 mm lower than the upper surface of the reinforced concrete sample.

[0077] (4) Start the electrodeless resistivity meter 1 and begin the test. After a period of time, allow the data to stabilize and obtain the total resistance R0 of the system. After the test is completed, remove the reinforced concrete sample and electrolyte solution and clean the device.

[0078] (5) Add a certain amount of electrolyte solution, the same as in step (3), into the device. The liquid level is the same as in step (3). Start the electrodeless resistivity meter 1 and begin testing. After a period of time, allow the data to stabilize and obtain the electrolyte solution resistance R2.

[0079] (6) Calculate the initial resistance R1 of the steel reinforcement in the concrete according to the formula;

[0080] (7) After curing in an environment of 50℃, 100% carbon dioxide concentration, and 0.4MPa for 24 hours, and then curing in an outdoor atmospheric environment for 720 hours, the test was carried out according to steps (2) to (5). The steel resistance R in the concrete after 744 hours was obtained according to the formula in step (6). t The corrosion rate V of steel bars in concrete is calculated using a formula and compared with relevant standards to determine the corrosion status of steel bars in concrete.

[0081] In step (1), the mold of the specified specifications is an annular mold adapted to the electrodeless resistivity meter 1, and the specified size is 1 / 8 of the ring length of the mold. The steel bars in the concrete are arranged along the ring length and are flush at both ends of the concrete sample. The steel bar radius is 6 mm. After the concrete is formed, it is covered and sealed for curing for 48 hours.

[0082] In step (3), the electrolyte solution is sodium sulfate with a mass fraction of 5%.

[0083] In step (4), the test time is 5 to 15 minutes;

[0084] In step (5), the test time is 1 to 3 minutes;

[0085] In step (6), the formula for calculating the resistance R1 of the steel reinforcement in the concrete is:

[0086] R1 = R0 - 0.875R2

[0087] In step (7), the formula for calculating the steel corrosion rate V is:

[0088]

[0089] The criteria are as follows: when V value < 0.0023 mm / a, the steel bar is not corroded and is in a passivated state; when V value is between 0.0023 and 0.0059 mm / a, the steel bar corrosion rate is low; when V value is between 0.0059 and 0.0117 mm / a, the steel bar corrosion rate is moderate; when V value is between 0.0117 and 0.1173 mm / a, the steel bar corrosion rate is high; when V value > 0.1173 mm / a, the steel bar corrosion rate is extremely high.

[0090] The test results of the steel corrosion rate in concrete in this embodiment are shown in Table 1.

[0091] Comparative Example 1

[0092] This comparative example uses the same raw materials and mix proportions as Example 1 to form reinforced concrete, and is cured for 2400 hours under the same test environment. The steel corrosion weight loss rate is tested using the steel corrosion test in the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082), and the steel corrosion weight loss rate is converted into steel corrosion rate.

[0093] The test results of the steel corrosion rate in this comparative example are shown in Table 1.

[0094] Comparative Example 2

[0095] This comparative example uses the same raw materials and mix proportions as Example 2 to form reinforced concrete, and is cured for 744 hours under the same test environment. The steel corrosion weight loss rate is tested using the steel corrosion test in the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082), and the steel corrosion weight loss rate is converted into steel corrosion rate.

[0096] The test results of the steel corrosion rate in this comparative example are shown in Table 1.

[0097] Table 1. Performance test results of Examples 1-2 and Comparative Examples 1-2

[0098]

[0099] As can be seen from the above performance test results, the steel corrosion rate obtained by Examples 1-2 of the present invention is close to that of Comparative Examples 1-2, which directly split the steel bars to measure the weight loss due to corrosion. The results of the two methods differ by only about 5%, and the steel corrosion state is consistent according to the standard.

[0100] In summary, the method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity of this invention yields results consistent with the steel corrosion weight loss rate method in the national standard "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082), which identifies the same corrosion state of reinforcing steel in concrete, but without requiring the concrete to be split and destroyed. Due to its non-contact and electrodeless nature, this invention eliminates the influence of contact resistance and contact capacitance between the electrode and the concrete on the measurement, and avoids problems such as electrode polarization, resulting in accurate results. Furthermore, this invention not only maintains the structural integrity of the reinforced concrete sample but also avoids irreversible disturbances to the reinforcing steel caused by polarization reactions, allowing for the study of the same sample at different ages, and is simple and quick to operate.

[0101] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity, characterized in that, Includes the following steps: (1) Prepare reinforced concrete samples in molds of specified dimensions and harden them before demolding; (2) Vacuum drying treatment of reinforced concrete samples; (3) After cleaning the surface of the pretreated reinforced concrete sample, place it in the ring mold device and apply Vaseline to the bottom, inner and outer surfaces of the sample to make the sample fit tightly with the device. Pour the electrolyte solution into the rest of the device so that the liquid level is lower than the upper surface of the reinforced concrete sample. (4) Start the electrodeless resistivity meter and begin the test. After a period of time, allow the data to stabilize and obtain the total resistance R0 of the system. After the test is completed, remove the reinforced concrete sample and electrolyte solution and clean the device. (5) Add a certain amount of electrolyte solution, the same as in step (3), into the device. The liquid level is the same as in step (3). Start the electrodeless resistivity meter and begin testing. After a period of time, allow the data to stabilize and obtain the electrolyte solution resistance R2. (6) Calculate the initial resistance R1 of the steel reinforcement in the concrete; (7) After curing for t hours, conduct tests according to steps (2) to (5), and obtain the steel resistance R in the concrete after t hours according to the formula in step (6). t The corrosion rate V of steel bars in concrete is calculated, and the corrosion state of steel bars in concrete is obtained according to the discrimination criteria. In step (6), the formula for calculating the resistance R1 of the steel reinforcement in the concrete is: ； In step (7), the formula for calculating the steel corrosion rate V is: The criteria are as follows: when the V value is <0.0023 mm / a, the steel bar is not corroded and is in a passivated state; when the V value is between 0.0023 and 0.0059 mm / a, the steel bar corrosion rate is low; when the V value is between 0.0059 and 0.0117 mm / a, the steel bar corrosion rate is moderate; when the V value is between 0.0117 and 0.1173 mm / a, the steel bar corrosion rate is high; and when the V value is >0.1173 mm / a, the steel bar corrosion rate is extremely high.

2. The method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity according to claim 1, characterized in that, In step (1), the mold of the specified specifications is an annular mold adapted to the electrodeless resistivity meter, and the specified size is 1 / 8 of the ring length of the mold. The steel bars in the concrete are arranged along the ring length and are flush with both ends of the concrete sample. The radius of the steel bars is d mm. After the concrete is formed, it is covered and sealed for curing for 24~48 hours.

3. The method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity according to claim 1, characterized in that, In step (3), the electrolyte solution is sodium chloride or sodium sulfate with a mass fraction of 5%.

4. The method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity according to claim 1, characterized in that, In step (4), the test time is 5 to 15 minutes.

5. The method for detecting the corrosion state of reinforcing steel in concrete based on electrodeless resistivity according to claim 1, characterized in that, In step (5), the test time is 1 to 3 minutes.

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