Evaluation method for natural passivation effect of steel bars with different surface states

Abstract

The application discloses a kind of different surface state's steel natural passivation effect evaluation method, belong to reinforced concrete protection technical field, and the different surface state's steel natural passivation effect evaluation method of this application includes step one, preparation different surface state's steel test sample;Step two, soak steel test sample and carry out open circuit potential test;Step three, electrochemical impedance spectroscopy test is carried out to steel test sample;Step four, the open circuit potential and electrochemical impedance spectroscopy of steel test sample are continuously tested;Step five, to steel test sample, dynamic potential polarization curve test is carried out;Step six, to steel test sample, Mott-Schottky curve test is carried out;Step seven, to steel test sample, x ray photoelectron spectroscopy characterization is carried out;Step eight, comprehensive analysis.This evaluation method is used to comprehensively evaluate the natural passivation effect of different surface state's steel, and provides reference and suggestion for the natural passivation effect evaluation of different surface state's steel during concrete maintenance.

Description

Technical Field

[0001] This invention relates to the field of reinforced concrete protection technology, and in particular to a method for evaluating the natural passivation effect of steel bars with different surface conditions. Background Technology

[0002] During the curing process of concrete, the hydration of cement produces pore fluid containing calcium hydroxide, creating a highly alkaline environment. Under the long-term action of the alkaline solution, a passivation film will spontaneously form on the surface of the reinforcing steel. The presence of this passivation film can, to some extent, inhibit the anodic dissolution reaction of the reinforcing steel and reduce its corrosion rate.

[0003] In actual engineering projects, since a large number of steel bars are exposed to the air for a long time, the surface conditions of the steel bars are different. If the passivation effect of steel bars with different surface conditions cannot be evaluated, it is difficult to accurately consider the impact of steel bars with different surface conditions on the structure, resulting in the inability to assess the service life of the steel bars, which leads to design risks in the durability of reinforced concrete structures. Summary of the Invention

[0004] The purpose of this invention is to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for evaluating the natural passivation effect of steel bars with different surface conditions, which can evaluate the natural passivation effect of steel bars with different surface conditions during concrete curing and reduce the risk of structural design.

[0005] The method for evaluating the natural passivation effect of reinforcing bars under different surface conditions according to embodiments of the present invention includes:

[0006] Step 1: Prepare steel bar samples with different surface conditions;

[0007] Step 2: Immerse the steel bar sample in concrete pore simulation liquid, perform open circuit potential test on the steel bar sample, and record the change of open circuit potential over time.

[0008] Step 3: Perform electrochemical impedance spectroscopy on the steel bar sample, plot the collected impedance information into an electrochemical impedance spectrum, and perform reasonable equivalent circuit fitting analysis on the data.

[0009] Step 4: Continuously test the open circuit potential and electrochemical impedance spectroscopy of the steel bar samples, with each test interval of 24 hours.

[0010] Step 5: Perform potentiodynamic polarization curve tests on the steel bar samples at the initial and final stages of immersion, scanning from the cathode to the anode, and perform fitting analysis on the test data;

[0011] Step 6: Perform Mott-Schottky curve tests on the steel bar samples at the initial and final stages of immersion to obtain the steel bar Mott-Schottky curves. Fit the linear region to obtain the slope of the fitted curve, thereby obtaining the point defect density.

[0012] Step 7: X-ray photoelectron spectroscopy characterization was performed on the steel bar sample at the beginning and end of the soaking period to obtain the fine spectrum of Fe, and the obtained results were corrected for binding energy and peak fitting was performed.

[0013] Step 8: Comprehensively analyze the changes in open circuit potential and polarization impedance of the steel reinforcement specimens with immersion time, and analyze the self-corrosion current density and point defect density of the steel reinforcement specimens after passivation, as well as the Fe content before and after passivation. 3+ and Fe 2+ The ratio change.

[0014] The method for evaluating the natural passivation effect of reinforcing bars under different surface conditions according to embodiments of the present invention has at least the following beneficial effects: by comprehensively analyzing polarization impedance, self-corrosion current density, point defect density, and Fe... 3+ and Fe 2+ The changes in the ratio of the natural passivation effect of steel bars with different surface conditions at multiple angles and levels have the advantages of being comprehensive, accurate, and integrated. Furthermore, by combining the results of electrochemical testing and component characterization, a passivation effect evaluation index is introduced to evaluate the passivation effect of steel bars with different surface conditions. This method is suitable for comprehensively evaluating the natural passivation effect of steel bars with different surface conditions and provides a reference and suggestions for assessing the natural passivation effect of steel bars with different surface conditions during concrete curing.

[0015] According to some embodiments of the present invention, in step one, steel bars with different surface conditions are cut into 30mm long steel bar samples, the steel bar samples are cleaned and degreased with ethanol, rinsed with deionized water and dried, then wires are welded to one end of the steel bar sample, and both ends of the steel bar sample are sealed, using the ribbed curved surface of the steel bar sample as the working surface to ensure that the end face of the steel bar sample is not exposed.

[0016] According to some embodiments of the present invention, in step two, the open circuit potential test time is not less than 200s, so as to obtain a relatively stable open circuit potential value in a short time.

[0017] According to some embodiments of the present invention, in step three, the perturbation potential amplitude selected for the electrochemical impedance spectroscopy test is ±10mV, and the sinusoidal signal frequency range is 10. 5 Up to 10 -2 The impedance data was measured at Hz, and a reasonable equivalent circuit fitting analysis was performed on the collected impedance data.

[0018] According to some embodiments of the present invention, in step four, the soaked steel bar sample is continuously tested for 10 days.

[0019] According to some embodiments of the present invention, in step five, the voltage range is set to -0.3 to 1.2V, and the scan rate is 3mV / s.

[0020] According to some embodiments of the present invention, in step six, the voltage range of the Mott-Schottky curve test is -0.3 to 0.6V, the disturbance signal is 10mV, the frequency is 1kHz, the scan rate is 50mV / s, and the delay time is 2s.

[0021] According to some embodiments of the present invention, in step seven, the obtained result is corrected for binding energy using C1s = 284.80 eV.

[0022] According to some embodiments of the present invention, in step eight, when the open-circuit potential of the reinforcing bar sample shifts to the positive direction and tends to stabilize, it indicates that the corrosion tendency of the reinforcing bar surface decreases and it gradually becomes passivated; when the polarization impedance of the reinforcing bar is higher, the self-corrosion current density and the point defect density are smaller, and the Fe... 3+ and Fe 2+ The larger the ratio, the better the natural passivation effect of the steel bars.

[0023] According to some embodiments of the present invention, in step eight, passivation evaluation indicators are defined. Where Z is the ratio of the polarization resistance of the passivated steel bar to that of the initial surface state steel bar, and C is the ratio of the Fe of the passivated steel bar to that of the initial surface state steel bar. 3+ and Fe 2+ If the passivation effect evaluation index P < 1, it indicates that the passivation effect is poor, meaning that different surface conditions will affect the passivation of the steel bars. The smaller the value, the greater the influence of the surface condition on the passivation of the steel bars. If the passivation effect evaluation index P ≥ 1, it indicates that the passivation of the steel bars is excellent, and the surface condition has no effect on the passivation effect of the steel bars.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0026] Figure 1 This is a flowchart of the method for evaluating the natural passivation effect of steel bars under different surface conditions according to an embodiment of the present invention;

[0027] Figure 2 These are the open circuit potential variation curves with immersion time during the passivation process of two types of steel bar samples in this embodiment of the invention.

[0028] Figure 3This is a graph showing the change of electrochemical impedance spectroscopy of two types of steel bar samples during the passivation process in this embodiment of the invention as a function of immersion time.

[0029] Figure 4 This is the equivalent circuit diagram used for electrochemical impedance spectroscopy fitting in the embodiments of the present invention;

[0030] Figure 5 This is a graph showing the change of polarization impedance of two types of steel bar samples with immersion time in an embodiment of the present invention;

[0031] Figure 6 These are the electrodynamic polarization curves of two types of steel bars after passivation in this embodiment of the invention;

[0032] Figure 7 These are two Mott-Schottky curves after steel bar passivation in embodiments of the present invention;

[0033] Figure 8 This is a graph showing the change in Fe content in different valence states before and after passivation of two types of steel bars in an embodiment of the present invention. Detailed Implementation

[0034] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0035] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0036] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0037] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0038] refer to Figures 1 to 8A method for evaluating the natural passivation effect of reinforcing bars under different surface conditions according to embodiments of the present invention is described.

[0039] like Figures 1 to 8 As shown, the method for evaluating the natural passivation effect of reinforcing bars under different surface conditions according to an embodiment of the present invention includes:

[0040] Step 1: Cut the steel bars with different surface conditions into 30mm long steel bar samples using a wire cutting machine. Clean the steel bar samples with ethanol to remove oil, and rinse and dry them with deionized water. Then, weld copper wires to one end of the steel bar sample and seal both ends of the steel bar sample, using the ribbed curved surface of the steel bar sample as the working surface, while ensuring that there is no external exposure on the end face of the steel bar sample.

[0041] Step 2: Immerse the steel bar sample in concrete pore simulation liquid, perform open circuit potential test on the steel bar sample, and record the change of open circuit potential over time. Specifically, the open circuit potential test time should not be less than 200s in order to obtain a relatively stable open circuit potential value in a short time.

[0042] Step 3: Perform electrochemical impedance spectroscopy (EIS) on the steel reinforcement samples. The perturbation potential amplitude selected for the EIS is ±10mV to avoid damage to the steel reinforcement samples from high voltage. Furthermore, to obtain experimental results more quickly, the sinusoidal signal frequency range for the EIS is 10... 5 Up to 10 -2 The impedance information was collected and plotted as an electrochemical impedance spectrum. Then, ZSimp Win was used to perform a reasonable equivalent circuit fitting analysis on the data in order to analyze the electrochemical mechanism inside the system more clearly. It should be noted that the sum of the charge transfer resistance and the gap resistance obtained by fitting is defined as the polarization impedance.

[0043] Step 4: Continuously test the open circuit potential and electrochemical impedance spectroscopy of the steel bar sample, with each test interval of 24 hours, for 10 consecutive days, to ensure that the steel bar sample can be completely passivated.

[0044] Step 5: Perform potentiodynamic polarization curve tests on the steel bar samples during the initial and final stages of immersion. To avoid the influence of polarization, the scan should be performed from the cathode to the anode. Then, the test data should be fitted and analyzed. Specifically, in order to obtain the typical passivation range of the steel bar samples, the voltage range is set to -0.3 to 1.2V and the scan rate is 3mV / s.

[0045] Step 6: Perform Mott-Schottky curve tests on the steel bar samples at the initial and final stages of immersion to obtain the Mott-Schottky curves. Fit the linear region to obtain the slope of the fitted curve, thereby obtaining the point defect density. Specifically, the voltage range for the Mott-Schottky curve test is -0.3 to 0.6V, the perturbation signal is 10mV, the frequency is 1kHz, the scan rate is 50mV / s, and the delay time is 2s.

[0046] Step 7: X-ray photoelectron spectroscopy characterization was performed on the steel bar sample at the beginning and end of the soaking period to obtain the fine spectrum of Fe, and the obtained results were corrected for binding energy and peak fitting was performed.

[0047] In step seven, the obtained results were corrected for binding energy using C1s = 284.80 eV, and peak fitting was performed using Avantage software.

[0048] Step 8: Comprehensively analyze the changes in open circuit potential and polarization impedance of the steel reinforcement specimens with immersion time, and analyze the self-corrosion current density and point defect density of the steel reinforcement specimens after passivation, as well as the Fe content before and after passivation. 3+ and Fe 2+ The change in the ratio, specifically, when the open-circuit potential of the steel bar sample shifts to the positive direction and tends to stabilize, indicates that the corrosion tendency of the steel bar surface decreases and it gradually becomes passivated; when the polarization impedance of the steel bar is higher, the self-corrosion current density and the point defect density are smaller, the Fe... 3+ and Fe 2+ The larger the ratio, the better the natural passivation effect of the steel bars;

[0049] Furthermore, define passivation evaluation indicators. Where Z is the ratio of the polarization resistance of the passivated steel bar to that of the initial surface state steel bar, and C is the ratio of the Fe of the passivated steel bar to that of the initial surface state steel bar. 3+ and Fe 2+ If the passivation effect evaluation index P < 1, it indicates that the passivation effect is poor, meaning that different surface conditions will affect the passivation of the steel bars. The smaller the value, the greater the influence of the surface condition on the passivation of the steel bars. If the passivation effect evaluation index P ≥ 1, it indicates that the passivation of the steel bars is excellent, and the surface condition has no effect on the passivation effect of the steel bars.

[0050] It should be noted that in electrochemical impedance spectroscopy (EIS) evaluation, EIS tests can obtain Nyquist and Bode plots. In the Nyquist plot, the horizontal axis represents the real part of the impedance, and the vertical axis represents the imaginary part. A larger capacitive arc indicates greater resistance to anodic dissolution of the metal on the rebar surface, i.e., a better passivation effect. The Bode plot has two branches, with the common logarithm of frequency as the horizontal axis and the common logarithm of the impedance modulus and phase angle as the vertical axis. A larger impedance modulus at low frequencies, a wider phase angle peak, and a shift of the maximum phase angle towards lower frequencies indicate a better passivation effect on the rebar. Using ZSimp Win software to perform equivalent circuit fitting on the EIS spectrum, the pore resistance and charge transfer resistance of the system can be obtained. The sum of these two is defined as the polarization impedance, which reflects the ease with which corrosion occurs in the system. A larger polarization impedance indicates a better passivation effect on the rebar.

[0051] It should be noted that in the evaluation of potentiodynamic polarization curves, these curves provide important information about the electrochemical reaction kinetics. The shape and slope of the curve can reveal different reaction steps, reaction rates, and the performance of the reinforcing steel in the electrochemical system. Generally, the horizontal axis represents the logarithm of the absolute value of the current, and the vertical axis represents the voltage. The potentiodynamic polarization curve is divided into two parts: the anodic reaction on the steel surface is mainly the dissolution of iron, and the cathodic reaction is mainly the oxygen absorption reaction. By analyzing the potentiodynamic polarization curve of the steel, typical passivation regions, Wienton current densities, corrosion current densities, corrosion potentials, and breakdown potentials can be obtained. Generally, to judge whether a steel is passivable, one can observe whether it has a typical passivation region. Within this region, the applied potential gradually increases while the current density remains basically constant, and the rate of the electrochemical reaction slows down significantly. The current corresponding to this is the Wienton current density, and the potential at which the current changes abruptly is the breakdown potential. Furthermore, by performing a conventional Tafel fit on the Tafel region of the potentiodynamic polarization curve, the corrosion potential and corrosion current density of the system can be obtained. The lower the passivation current density and corrosion current density, the better the passivation effect of the steel reinforcement.

[0052] It should be noted that in the evaluation of point defect density, the passivation film on the surface of the steel bar exhibits semiconductor characteristics, but unlike intrinsic semiconductors, the passivation film typically displays heavily doped, highly degenerate semiconductor properties. According to electronic band theory, when the number of electrons in the conduction band of an oxide is greater than the number of holes in the valence band, the oxide behaves as an n-type semiconductor; otherwise, it behaves as a p-type semiconductor. The semiconductor characteristics of the passivation film can be described by the Mott-Schottky relation. According to the point defect model, the passivation film on the surface of the steel bar contains various high concentrations of point defects. The main point defect in p-type semiconductors is the cation vacancy, which acts as an electron acceptor and exhibits metal hole transport characteristics; the main point defect in n-type semiconductors is the oxygen vacancy / cation interstic, which acts as an electron donor and exhibits electron transport characteristics. The lower the concentration of donors or acceptors on the surface of the steel bar, the higher the Cl...- The more corrosive ions are adsorbed into surface vacancies, the more difficult the anodic reaction becomes, and the better the passivation effect.

[0053] It should be noted that Fe 3+ and Fe 2+ In the ratio evaluation, the passivation process of steel bars during concrete curing is essentially a transformation of ferrous oxides into ferric compounds. According to the Poubaix diagram, in the alkaline system of concrete, ferric compounds are more stable than ferrous oxides. 3+ and Fe 2+ The ratio of [value] to [value] is an important indicator for judging passivation performance. Generally, the higher the ratio, the better the passivation effect of the steel bars.

[0054] Furthermore, since steel bars with different surface conditions may reach the passivation state at different times during concrete curing, if the soaking time is too short, the steel bars will not reach the passivation state, and thus their true natural passivation effect cannot be evaluated. Therefore, to accurately evaluate the natural passivation effect of steel bars, it is recommended that the soaking time be more than 5 days.

[0055] Furthermore, due to the complexity of steel reinforcement surfaces with different surface conditions, using a single method to evaluate the natural passivation effect of the steel reinforcement is prone to misjudgment. Therefore, combining electrochemical impedance spectroscopy, potentiodynamic polarization curve testing, Mott-Schottky curve testing, and X-ray photoelectron spectroscopy characterization yields polarization impedance, passivation current density, corrosion current density, point defect density, and Fe... 3+ and Fe 2+ The ratios are analyzed comprehensively to evaluate the natural passivation effect of steel bars under different surface conditions.

[0056] The following is a specific construction example to illustrate the evaluation method for the natural passivation effect of steel bars under different surface conditions:

[0057] To obtain steel rebar samples with different surface conditions, a batch of rebars was naturally exposed to an outdoor industrial atmosphere for three months. The rebar surfaces developed a pale yellow rust product, while the unexposed rebars showed a bluish-brown color. Both types of rebar samples were cut into 30mm lengths using a wire cutter, cleaned with ethanol to remove oil, rinsed with deionized water, and dried to eliminate interference from residual corrosive ions. A copper wire was welded to one end of each rebar sample, and both ends were sealed with 704 silicone rubber to ensure no external exposure of the rebar end faces. The ribbed curved surface of the rebar was used as the working surface, with an exposed area of ​​9.42 cm². 2 A saturated calcium hydroxide solution with a pH of approximately 12.5 was used as the pore saturation fluid for concrete, and it was replaced every 7 days.

[0058] Two types of steel bar samples were immersed in a solution and isolated from carbon dioxide in the air using an acrylic sheet to simulate the natural passivation behavior of steel bars during concrete curing.

[0059] The steel bar sample, counter electrode, and reference electrode were connected to the electrochemical workstation, which was then connected to a computer. The CS Studio 6 electrochemical testing software was opened. First, the open-circuit potential of the two types of steel bars was measured for 200 seconds, followed by electrochemical impedance spectroscopy (EIS) testing. The selected sinusoidal signal frequency range for the EIS testing was 10 Hz. 5 Up to 10 -2 With a perturbation voltage amplitude of ±10mV, a reasonable equivalent circuit fitting analysis was performed using ZSimp Win software to obtain the polarization impedance that reflects the passivation effect of the reinforcing steel. Open-circuit potential and electrochemical impedance spectroscopy were tested at 10-day intervals, with each interval lasting 24 hours.

[0060] Two types of passivated steel bars were subjected to potentiodynamic polarization (PVP) and Mott-Schottky curve tests. X-ray photoelectron spectroscopy (XPS) characterization was performed on both types of steel bars at the initial and final stages of immersion. The PVP test voltage range was -0.3 to 1.2 V (relative to open circuit potential), with scanning from cathode to anode at a scan rate of 3 mV / s. The test data were analyzed using CVIEW software, and the obtained Witton current density and corrosion current density were used to evaluate the passivation effect of the steel bars. The Mott-Schottky curve test voltage range was -0.3 to 0.6 V (relative to reference electrode potential), with a perturbation signal of 10 mV, a frequency of 1 kHz, a scan rate of 50 mV / s, and a delay time of 2 s. The linear region was fitted using Origin software, and the obtained point defect density was used to evaluate the passivation effect of the steel bars.

[0061] The results obtained from X-ray photoelectron spectroscopy characterization were corrected for binding energy at C1s = 284.80 eV, and the fine spectrum of Fe was fitted using Avantage software to obtain the Fe... 3+ and Fe 2+ The ratio is used to evaluate the passivation effect of the steel bars.

[0062] like Figure 2 As shown, Figure 2The curves showing the change of open circuit potential (OPP) of two types of steel reinforcement samples in simulated concrete pore liquid with immersion time reveal that the OPPP of both types of steel reinforcement increases continuously with increasing immersion time. Within 0 to 1 day, the OPPP of the rusted steel reinforcement increases rapidly, then increases slowly, reaching -153 mV after 10 days of immersion. In contrast, the OPPP of the normal steel reinforcement increases rapidly within 0 to 3 days, then stabilizes, reaching -105 mV after 10 days of immersion. It should be noted that OPPP is an important indicator reflecting the thermodynamic characteristics of the steel reinforcement surface. The more positive the OPPP, the lower the corrosion tendency of the metal. Therefore, the experimental results of OPPP indicate that with prolonged immersion time, the corrosion tendency of both types of steel reinforcement in simulated concrete pore liquid decreases, and both reach a stable state after 5 days of immersion. After 10 days, both types of steel reinforcement are in a passivated state.

[0063] like Figure 3 As shown, Figure 3 The graphs show the changes in electrochemical impedance spectroscopy (EIS) of two types of steel bar samples during the passivation process as a function of immersion time. The first horizontal row shows the data for rusted steel bar samples, and the second horizontal row shows the data for normal steel bar samples. The leftmost graph in each row is a Nyquist plot, and the middle and rightmost graphs are Bode plots.

[0064] As shown in the Nyquist plot, the capacitive arc radius of both types of steel bars gradually increases with prolonged immersion time. The Bode plot shows that the low-frequency impedance modulus and phase angle peak width of both types of steel bars significantly increase with immersion time, and the maximum phase angle also shifts towards lower frequencies. Both types of steel bars exhibit similar impedance behavior and variation patterns in the simulated concrete pore solution. All electrochemical impedance parameters increase rapidly in the initial immersion period (0-3 days) and tend to stabilize in the later immersion period (5-10 days). Electrochemical impedance spectroscopy reflects the surface characteristics of steel bars and the kinetic parameters of electrochemical reactions. The impedance modulus at low frequencies represents the solution resistance and polarization impedance of the electrochemical system; the larger the modulus, the better the corrosion resistance of the steel bar surface. Electrochemical test results show that the corrosion resistance of both types of steel bars immersed in the simulated concrete pore solution continuously improves. After 10 days of immersion, the corrosion resistance of normal steel bars is slightly higher than that of rusted steel bars. The electrochemical impedance spectra of the two types of steel bars show an asymmetry in the phase angle within the low-frequency range, indicating the existence of two overlapping time constants.

[0065] Due to the non-uniformity of the steel reinforcement surface, a constant phase angle element CPE (denoted by Q) is used instead of the ideal capacitor C. Based on the results and analysis of electrochemical impedance spectroscopy, and considering the redox reactions on the steel reinforcement surface, a... Figure 4 The equivalent circuit fits the data. Where R... s R is the resistance of the solution. ox Q is the pore resistance. oxFor pore capacitance, R ct For charge transfer resistance, Q dl It is a double-layer capacitor. R ox With R ct The sum is defined as the total resistance R. t This reflects the passivation effect of the reinforcing steel. The R values ​​of the two types of reinforcing steel... t The value changes with soaking time as follows Figure 5 As shown, the Rt value of both types of reinforcing bars increases continuously with the extension of soaking time. After soaking for 10 days, the Rt value of the rusted reinforcing bar is 0.89 MΩ·cm. 2 The Rt value of normal reinforcing steel is 2.58 MΩ·cm. 2 This indicates that after immersing in the concrete pore simulation solution for 10 days, the corrosion resistance of both types of steel bars was enhanced, with the passivation effect of normal steel bars being better than that of rusted steel bars.

[0066] like Figure 6 As shown, Figure 6 The electrodynamic polarization curves of the two types of reinforcing bars after passivation show that both types exhibit typical passivation regions, indicating that both types of reinforcing bars are passivable in the simulated concrete pore solution. Analysis of the curves reveals that after immersion in the simulated concrete pore solution for 10 days, the self-corrosion potential (Ecorr) of the rusted reinforcing bar is -0.25V, lower than the -0.18V of the normal reinforcing bar, while the self-corrosion current density (Icorr) of the rusted reinforcing bar is 0.87 μA·cm. -2 It is 0.43 μA·cm higher than that of normal steel reinforcement. -2 In the typical passivation zone of reinforcing steel, the passivation current density Ip and breakdown potential E of the rusted reinforcing steel are... p The values ​​ranged from 1.54 to 2.85 μA·cm. -2 The Ip and Ep of normal reinforcing steel are 0.37V, while those of normal reinforcing steel range from 0.79 to 2.12 μA·cm. -2 And 0.40V. The potentiodynamic polarization curve is a characteristic index reflecting the dynamic information of steel bars. For passivable systems, I p and E p It can be used to measure the corrosion resistance of steel bars, E p The higher, I p The smaller the value, the better the corrosion resistance of the steel reinforcement. Therefore, the results of the potentiodynamic polarization curve test show that both types of steel reinforcement can be passivated in the simulated pore liquid of concrete, and the passivation effect of normal steel reinforcement is better than that of rusted steel reinforcement.

[0067] like Figure 7 As shown, Figure 7 These are the Mott-Schott curves of two types of steel bars after passivation in a simulated concrete pore liquid for 10 days. It can be seen that both types of steel bars exhibit similar semiconductor behavior; when the applied potential is in the range of -0.3 to 0.4 V, the C0.05 on the surface of both types of steel bars... -2The -E relationship exhibits a clear Mott-Schottky curve relationship, with a positive slope, indicating n-type semiconductor properties. Figure 6 It was found that both types of steel rebar electrodes exhibit passivability in the simulated concrete pore liquid, with a passivation potential range of -0.3 to 0.4 V. Within this potential range, the steel rebar undergoes continuous passivation, generating a large amount of trivalent Fe compounds, and the electrode process exhibits electron transport characteristics. When the applied potential is between 0.4 and 0.6 V, the slope of the Mott-Schottky curve is negative, indicating that the steel rebar exhibits p-type semiconductor behavior. At this point, the electrode process of the steel rebar exhibits metal-hole transport characteristics of divalent Fe oxides. Fitting the Mott-Schottky curves of the two types of steel rebar yielded a donor concentration of 1.08 × 10⁻⁶ for the rusted steel rebar. 22 cm -3 The donor concentration for normal reinforcing steel is 1.05 × 10⁻⁶. 21 cm -3 The Mott-Schottky curve test results show that the electrode process in the passivation range for both types of steel bars is electron transport. The rusted steel bars have a higher surface defect density and a worse passivation effect than the normal steel bars.

[0068] Based on the fine-spectral peak fitting results of Fe before and after passivation of the two types of steel bars, the fine spectral lines of Fe2p3 / 2 on the surface of the two types of steel bars were fitted as elemental Fe (709.4 eV), ferrous oxide FeO (710.2 eV), ferric oxide Fe2O3 (710.9 eV), and ferric hydroxide FeOOH (713.2 eV). To more intuitively understand the changes in surface composition of the two types of steel bars before and after passivation in the concrete pore slurry, the relative content changes of the four iron products were plotted on [the graph]. Figure 8 The results show that before immersing the rusted steel bars in the simulated concrete pore liquid, the main surface components were Fe2O3 (50.12%), FeO (40.63%), FeOOH (6.71%), and Fe (2.54%). After 10 days of immersion, the content of ferrous oxides significantly decreased to 22.21%, while the contents of ferric oxides and hydroxyl oxides significantly increased to 53.43% and 22.45%, respectively, and the content of elemental Fe was 1.91%. Before immersion in the simulated concrete pore liquid, the main surface components of normal steel bars were Fe2O3 (40.44%), FeO (35.71%), FeOOH (19.64%), and Fe (4.21%). After immersion for 10 days, the content of ferrous oxides significantly decreased to 7.42%, while the contents of ferric oxides and hydroxyl oxides significantly increased to 61.81% and 29.58%, respectively, and the content of elemental Fe was 1.19%. 3+ and Fe 2+ The ratio of Fe to Fe is an important indicator for judging passivation performance. Generally, the higher the ratio, the better the passivation effect of the steel reinforcement. The difference between Fe and Fe after passivation of rusted steel reinforcement and normal steel reinforcement is also significant. 3+ and Fe2+ The ratios were 3.5 and 12.3, respectively. X-ray photoelectron spectroscopy (XPS) results showed that the main components of the two types of steel bars remained unchanged before and after immersion, but their contents changed significantly, primarily manifested in a marked decrease in divalent iron oxides and a significant increase in trivalent iron oxides and hydroxyl oxides. The passivation process in the simulated concrete pore liquid showed an inverse relationship between Fe(II) oxides and Fe(III) compounds; the passivation process was essentially a conversion of Fe(II) oxides to Fe(III) compounds. According to the Poubaix diagram, in an alkaline system, Fe(III) compounds were more stable than Fe(II) oxides, which is consistent with the electrochemical test results showing a continuous improvement in the corrosion resistance of the two types of steel bars after immersion in the simulated concrete pore liquid. Furthermore, the higher the content of Fe(III) compounds, the more stable the steel bar surface and the better the corrosion resistance, which is the main reason why normal steel bars had a better passivation effect than rusted steel bars. Therefore, XPS characterization shows that the passivation effect of normal steel bars is better than that of rusted steel bars.

[0069] Therefore, the evaluation index for the passivation effect of rusted steel bars is:

[0070]

[0071] That is, the passivation effect of rusted steel bars after three months of natural exposure is not good, and the rust state has a certain impact on the passivation of steel bars.

[0072] Therefore, through comprehensive analysis of polarization impedance, self-corrosion current density, point defect density, and Fe... 3+ and Fe 2+ The changes in the ratio of the natural passivation effect of steel bars with different surface conditions at multiple angles and levels have the advantages of being comprehensive, accurate, and integrated. Furthermore, by combining the results of electrochemical testing and component characterization, a passivation effect evaluation index is introduced to evaluate the passivation effect of steel bars with different surface conditions. This method is suitable for comprehensively evaluating the natural passivation effect of steel bars with different surface conditions and provides a reference and suggestions for assessing the natural passivation effect of steel bars with different surface conditions during concrete curing.

[0073] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for evaluating the natural passivation effect of reinforcing bars under different surface conditions, characterized in that, include: Step 1: Prepare steel bar samples with different surface conditions; Step 2: Immerse the steel bar sample in concrete pore simulation liquid, perform open circuit potential test on the steel bar sample, and record the change of open circuit potential over time. Step 3: Perform electrochemical impedance spectroscopy on the steel bar sample, plot the collected impedance information into an electrochemical impedance spectrum, and perform equivalent circuit fitting analysis on the data. The sum of the charge transfer resistance and the gap resistance obtained by the fitting is defined as the polarization impedance. Step 4: Continuously test the open circuit potential and electrochemical impedance spectroscopy of the steel bar samples, with each test interval of 24 hours. Step 5: Perform potentiodynamic polarization curve tests on the steel bar samples at the initial and final stages of immersion, scanning from the cathode to the anode, and perform fitting analysis on the test data; Step 6: Perform Mott-Schottky curve tests on the steel bar samples at the initial and final stages of immersion to obtain the steel bar Mott-Schottky curves. Fit the linear region to obtain the slope of the fitted curve, thereby obtaining the point defect density. Step 7: X-ray photoelectron spectroscopy characterization was performed on the steel bar sample at the beginning and end of the soaking period to obtain the fine spectrum of Fe, and the obtained results were corrected for binding energy and peak fitting was performed. Step 8: Comprehensively analyze the changes in open circuit potential and polarization impedance of the steel reinforcement specimens with immersion time, and analyze the self-corrosion current density and point defect density of the steel reinforcement specimens after passivation, as well as the Fe content before and after passivation. 3+ and Fe 2+ The change in the ratio; In step eight, when the open-circuit potential of the steel bar sample shifts to the positive direction and tends to stabilize, it indicates that the corrosion tendency of the steel bar surface decreases and it gradually becomes passivated; the higher the polarization impedance of the steel bar, the lower the self-corrosion current density and point defect density, and the lower the Fe... 3+ and Fe 2+ The larger the ratio, the better the natural passivation effect of the steel bars; In step eight, the passivation effect evaluation index P is defined. Where Z is the ratio of the polarization resistance of the passivated steel bar to that of the initial surface state steel bar, and C is the ratio of the Fe of the passivated steel bar to that of the initial surface state steel bar. 3+ and Fe 2+ If the passivation effect evaluation index P < 1, it indicates that the passivation effect is poor, meaning that different surface conditions will affect the passivation of the steel bars. The smaller the value, the greater the influence of the surface condition on the passivation of the steel bars. If the passivation effect evaluation index P ≥ 1, it indicates that the passivation of the steel bars is excellent, and the surface condition has no effect on the passivation effect of the steel bars.

2. The method for evaluating the natural passivation effect of reinforcing bars with different surface conditions according to claim 1, characterized in that, Reinforcing bars with different surface conditions were cut into 30mm long samples. The samples were cleaned with ethanol to remove oil, rinsed with deionized water and dried. A wire was then welded to one end of the sample, and both ends were sealed. The ribbed curved surface of the sample was used as the working surface to ensure that there was no external exposure at the end face of the sample.

3. The method for evaluating the natural passivation effect of reinforcing bars with different surface conditions according to claim 1, characterized in that, In step two, the open circuit potential test time shall not be less than 200 seconds, so as to obtain a relatively stable open circuit potential value in a short time.

4. The method for evaluating the natural passivation effect of reinforcing bars with different surface conditions according to claim 1, characterized in that, In step three, the perturbation potential amplitude selected for the electrochemical impedance spectroscopy test is ±10 mV, and the sinusoidal signal frequency range is 10. 5 Up to 10 -2 The impedance data was measured at Hz, and the collected impedance data was subjected to equivalent circuit fitting analysis.

5. The method for evaluating the natural passivation effect of reinforcing bars with different surface conditions according to claim 1, characterized in that, In step four, the soaked steel bar samples are tested continuously for 10 days.

6. The method for evaluating the natural passivation effect of reinforcing bars with different surface states according to claim 1, characterized in that, In step five, the voltage range is set to -0.3 to 1.2 V, and the scan rate is 3 mV / s.

7. The method for evaluating the natural passivation effect of reinforcing bars with different surface conditions according to claim 1, characterized in that, In step six, the voltage range of the Mott-Schottky curve test is -0.3 to 0.6 V, the disturbance signal is 10 mV, the frequency is 1 kHz, the scan rate is 50 mV / s, and the delay time is 2 s.

8. The method for evaluating the natural passivation effect of reinforcing bars with different surface states according to claim 1, characterized in that, In step seven, the obtained result is corrected for binding energy using C 1s = 284.80 eV.

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