Method for predicting chloride ion resistance of cement-based material based on electrochemical impedance spectroscopy

Abstract

The invention discloses a method for predicting chloride ion resistance of a cement-based material based on electrochemical impedance spectroscopy. The method comprises the following steps: firstly, carrying out electrochemical impedance spectroscopy test on the cement-based material, carrying out fitting analysis on an obtained electrochemical impedance spectroscopy curve by adopting an equivalent circuit model to obtain Rccp, establishing a stable and reliable quantitative relationship by utilizing the Rccp and a chloride ion migration coefficient measured by a classical RCM method, and ensuring that the fitting variance is greater than 0.86. According to the method, the chloride ion resistance of the cement-based material is predicted by adopting a rapid and lossless electrochemical impedance spectroscopy method, the method is suitable for rapidly evaluating the performance of an auxiliary cementing material on a large scale, early-stage lossless diagnosis of the chloride ion invasion resistance of concrete is realized, and a monitoring means is provided for guaranteeing long-life safe operation of major infrastructures.

Description

Technical Field

[0001] This invention belongs to the field of building materials and relates to a method for predicting the chloride ion resistance of cement-based materials based on electrochemical impedance spectroscopy. Background Technology

[0002] Chloride-induced steel corrosion is one of the major threats to reinforced concrete, severely hindering the design service life of reinforced concrete structures in coastal areas. Driven by concentration or humidity gradients, chlorides from seawater, de-icing salts, etc., accumulate on the surface of steel reinforcement. These chlorides penetrate through pores, causing corrosion. Over time, this leads to deterioration in structural stiffness and durability, resulting in significant economic losses for repair or reconstruction. Furthermore, the substantial consumption of natural resources and CO2 emissions from concrete production have a lasting environmental impact. Currently, the service life requirements for reinforced concrete exposed to chlorides have significantly increased. Developing and testing new, durable cement-based materials is an effective approach, with chloride ion penetration resistance serving as a simplified qualitative and quantitative indicator.

[0003] The most commonly used method for chloride resistance testing is the rapid chloride migration coefficient method (RCM). The RCM method is a key experimental method for evaluating the ability of concrete to resist chloride ion penetration. It accelerates the migration process of chloride ions in concrete specimens by applying an external electric field, and measures the charge passing through the sample for 6 hours under a fixed voltage, and uses it as an indicator of chloride penetration resistance. The depth of chloride ion penetration is measured by a colorimetric reagent, and the unsteady chloride ion migration coefficient is calculated. This coefficient can quickly and quantitatively reflect the density and impermeability of concrete, thus providing an important basis for durability design and evaluation. However, its test results are affected by a number of factors: (1) The strong electric field applied during the experiment will cause the temperature of the specimen to rise, causing the measured chloride ion migration coefficient to deviate from the true value; (2) The test cycle is long, and the timeliness of early concrete performance evaluation is insufficient, and it is impossible to quickly provide feedback on the direction of material optimization; (3) The specimen needs to be split after the test, and it cannot be reused, which increases the workload and wastes materials.

[0004] Electrochemical impedance spectroscopy (EIS) offers advantages such as high sensitivity, low cost, and ease of operation. As a non-destructive and continuous testing method, EIS has been used to study the physicochemical transformations occurring in cement under different environmental conditions. Hydration refers to the physical and chemical processes involving ion transport and gel material formation; therefore, this process can significantly influence the electrochemical behavior of cement systems (e.g., resistance to ion transfer and diffusion). As the hydration process proceeds, EIS can rapidly and automatically obtain the electrochemical characteristics of cement hydration. Summary of the Invention

[0005] The purpose of this invention is to provide a method for predicting the chloride ion resistance of cement-based materials based on electrochemical impedance spectroscopy (EIS). This method utilizes the EIS measurement results... ccp Establishing a stable and reliable quantitative relationship with the classical RCM diffusion coefficient, thereby enabling rapid and non-destructive electrochemical impedance spectroscopy to quantitatively predict the chloride ion migration coefficient, is of great significance for increasing the structural safety and lifespan of marine areas.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] A method for predicting the chloride ion resistance of cement-based materials based on electrochemical impedance spectroscopy includes the following steps:

[0008] Step 1: Inject cement-based material into the mold, shake to remove air bubbles, then cure the cement specimen. After that, demold the specimen and place it in the curing chamber for additional curing.

[0009] Step 2: After the specimens have been cured to the set age, they are removed and subjected to electrochemical impedance spectroscopy (EIS) testing to obtain the EIS curve. An equivalent circuit model is used to fit and analyze the EIS curve to obtain the pore solution resistance R. s and charge transfer resistance R ct1 According to formula R ccp = R s + R ct1 The resistance (R) of the continuously connected micropores in the specimen was calculated. ccp The equivalent circuit model is defined by the function R. s (Q1R ct1 )(Q2(R ct2 W2)), where R s Q1 represents the resistance of the pore solution within the cementitious material, and R represents the double-layer capacitance at the solid-liquid interface in the composite cementitious material. ct1 Q1 represents the resistance related to ion transfer within the cementitious material, Q2 represents the double-layer capacitance between the cementitious material and the electrode, and R represents the capacitance related to ion transfer within the cementitious material. ct2 W1 represents the resistance of the electrode surface related to charge transfer, and W2 represents the resistance of the electrode surface related to electron diffusion.

[0010] Step 3: Test the specimens according to the standard RCM method to obtain the chloride ion migration coefficient (D) for each specimen. RCM );

[0011] Step 4, R ccp and D RCM Perform mathematical regression analysis to obtain R. ccp and D RCM The linear relationship D RCM =a*R ccp +b;

[0012] Step 5: Perform electrochemical impedance spectroscopy (EIS) on the test specimen with the same cement-based material composition as in Step 1 to obtain the EIS curve. Use an equivalent circuit model to fit and analyze the EIS curve to obtain the pore solution resistance R of the test specimen. s and charge transfer resistance R ct1 According to formula R ccp = R s +R ct1 The R of the test piece is calculated. ccp ;

[0013] Step 6, R of the test piece ccp Substitute R from step 4 ccp and D RCM The linear relationship D RCM =a*R ccp In +b, the D of the test piece is calculated. RCM .

[0014] Furthermore, in step 1, the cement-based materials include, but are not limited to, metakaolin-limestone powder-cement systems, ball milled coal gangue-limestone powder-cement systems, and calcined clay-limestone powder-cement systems.

[0015] Furthermore, in step 1, the curing time for the cement specimens is 1 day.

[0016] Furthermore, in step 1, the age period is set to 28 days or 90 days.

[0017] Furthermore, in step 1, the curing conditions in the curing room are: temperature 20±2 ℃, relative humidity >95%.

[0018] Furthermore, in step 2 or 5, an electrochemical impedance spectroscopy test is performed using a CS2350H electrochemical workstation with the following parameters: test frequency range of 0.1 Hz to 1 MHz, and open circuit potential maintained at 20 mV.

[0019] Further, the specific method of step 3 is as follows: after soaking the specimen in a saturated Ca(OH)2 solution for 24 hours, place it in a rubber bucket between the positive and negative electrodes, then inject 300 ml of 0.3 mol / L NaOH solution into the anode, and at the same time inject 12 L of 10% NaCl solution into the cathode test cell. The test operation method follows the standard GB / T50082-2009.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) Compared with the traditional RCM method, the method of the present invention significantly shortens the testing time, can quickly obtain the chloride ion migration coefficient of cement-based materials, and significantly improves the efficiency of material research and development and quality control. At the same time, the sample will not be damaged during the entire testing process. After the test is completed, the sample can continue to be used for other research or long-term observation.

[0022] (2) The results obtained by the prediction method of the present invention are highly consistent with the test results of the current authoritative RCM method. The fitting variance of the chloride ion migration coefficient exceeds 0.86, and the fitting variance is as high as 0.96 in several typical systems (such as calcined clay-limestone powder-cement). The prediction is accurate and reliable.

[0023] (3) The method of this invention provides key technical support for the large-scale and rapid evaluation of the performance of auxiliary cementitious materials (such as coal gangue, calcined clay, etc.). These materials can largely replace cement, thereby significantly reducing carbon emissions and energy consumption in the cement production process. The non-destructive and rapid nature of the method of this invention enables efficient screening of optimal mix proportions during the material research and development stage, accelerating the process of industrial solid waste resource utilization and directly contributing to the green and low-carbon transformation of the building materials industry. Attached Figure Description

[0024] Figure 1 For R s (Q1R ct1 )(Q2(R ct2 A schematic diagram of the equivalent circuit model of W2);

[0025] Figure 2 The relationship between chloride ion migration coefficient and Rs value in the metakaolin-limestone powder-cement system;

[0026] Figure 3 For the ball mill coal gangue-limestone powder-cement system, the R value at 28 days ccp and chloride ion migration coefficient;

[0027] Figure 4 The chloride ion migration coefficient and R of ball milled coal gangue-limestone powder-cement system ccp The relationship between values;

[0028] Figure 5 For the calcined clay-limestone powder-cement system at 90d R ccp and chloride ion migration coefficient;

[0029] Figure 6 The chloride ion migration coefficient and R of the calcined clay-limestone powder-cement system ccp The relationship between values;

[0030] Figure 7 For the metakaolin-limestone powder-cement system, R in 28 daysccp and chloride ion migration coefficient;

[0031] Figure 8 The chloride ion migration coefficient and R of the metakaolin-limestone powder-cement system ccp The relationship between values. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0033] The electrochemical parameters of the microstructure of concrete include: the electrical resistance (Rt) of the continuously connected micropores in the concrete. ccp The study investigated the resistance to discontinuous micropores (RCP) and the capacitance to discontinuous micropores (QDP) in concrete blocked by cement paste layers. Both cement paste and concrete are porous materials; cement paste is a smaller material with a similar pore structure compared to concrete. In the current study, R... s (Q1R1) can also be used to characterize cement paste. The resistance of continuously connected micropores in cement paste is directly related to the evolution of its microstructure, and R is calculated based on the equivalent circuit. ccp The value can serve as a valuable parameter for studying the hydration process in a composite system.

[0034] The equivalent circuit model used in this invention is defined by the function R. s (Q1R ct1 )(Q2(R ct2 W2)), such as Figure 1 As shown. The components of this equivalent circuit include: R s Q1 represents the resistance of the pore solution within the cementitious material, and R represents the double-layer capacitance at the solid-liquid interface in the composite cementitious material. ct1 Q1 represents the resistance related to ion transfer within the cementitious material, Q2 represents the double-layer capacitance between the cementitious material and the electrode, and R represents the capacitance related to ion transfer within the cementitious material. ct2 W1 represents the resistance of the electrode surface related to charge transfer, and W2 represents the resistance related to electron diffusion on the electrode surface.

[0035] In the following examples, an electrochemical impedance spectroscopy test was performed using a CS2350H electrochemical workstation. The test parameters were: a test frequency range of 0.1 Hz to 1 MHz, and an open circuit potential maintained at approximately 20 mV.

[0036] Example 1

[0037] 1. Preparation of mortar specimens for ball milled coal gangue-limestone powder-cement system with different mineral admixtures: Seven groups were prepared by replacing silicate cement (OPC) with 0%, 10%, 15%, and 20% ball milled coal gangue, and then replacing the ball milled coal gangue with limestone powder at a replacement rate of one-third. The specimens were cylindrical blocks with a diameter of 110 mm and a height of 230 mm. First, cement, mineral admixtures, standard sand, and tap water were mixed and stirred evenly, then poured into cylindrical molds. The mixture was then vibrated for 30-60 seconds to remove air bubbles. After curing for one day, the specimens were demolded and placed in a curing chamber for additional curing at a temperature of 20±2℃ and a relative humidity >95%.

[0038] 2. After the test blocks have reached an age of 28 days, remove them and perform electrochemical impedance spectroscopy (EIS) on each block to obtain the EIS curve. Use Zsimpwin software to select the equivalent circuit model R. s (Q1R ct1 )(Q2(R ct2 W2)) The electrochemical impedance spectroscopy curve was fitted and analyzed to obtain the pore solution resistance R. s and charge transfer resistance R ct1 According to formula R ccp = R s + R ct1 The R of the test block was calculated. ccp The value was recorded, and the R value for each specimen was also recorded. ccp value.

[0039] 3. For the same batch of specimens, tests were conducted according to the standard RCM method. Mortar blocks cured for 28 days were used for rapid chloride ion migration testing. The specimens were immersed in a saturated Ca(OH)₂ solution for 24 hours and then placed in a rubber container between the positive and negative electrodes. Then, 300 ml of a 0.3 mol / L NaOH solution was injected into the anode, and simultaneously 12 L of a 10% NaCl solution was injected into the cathode test cell. The accurate chloride ion migration coefficient D for each specimen was obtained. RCM .

[0040] The obtained data set (R) ccp D RCM Mathematical regression analysis was performed to obtain the mathematical relationship between the two.

[0041] Example 2

[0042] 1. Preparation of mortar specimens for calcined clay-limestone powder-cement systems with different mineral admixtures: Calcined clay was used to replace OPC at proportions of 0%, 10%, 30%, and 40%, while limestone powder replaced calcined clay at one-third of the proportion. The remaining two groups used limestone powder to replace OPC at proportions of 20% and 40%, for a total of six groups. The specimens were cylindrical blocks with a diameter of 110 mm and a height of 230 mm. First, cement, mineral admixtures, standard sand, and tap water were mixed and stirred evenly, then poured into cylindrical molds. The mixture was then vibrated for 30-60 seconds to remove air bubbles. After curing for one day, the specimens were demolded and placed in a curing chamber for additional curing at a temperature of 20±2℃ and a relative humidity >95%.

[0043] 2. After the test blocks have reached an age of 28 days, remove them and perform electrochemical impedance spectroscopy (EIS) on each block to obtain the EIS curve. Use Zsimpwin software to select the equivalent circuit model R. s (Q1R ct1 )(Q2(R ct2 W2)) The electrochemical impedance spectroscopy curve was fitted and analyzed to obtain the pore solution resistance R. s and charge transfer resistance R ct1 According to formula R ccp = R s + R ct1 The R of the test block was calculated. ccp The value was recorded, and the R value for each specimen was also recorded. ccp value.

[0044] 3. For the same batch of specimens, tests were conducted according to the standard RCM method. Mortar blocks cured for 28 days were used for rapid chloride ion migration testing. After immersing the samples in a saturated Ca(OH)₂ solution for 24 hours, they were placed in a rubber container between the positive and negative electrodes. Then, 300 ml of a 0.3 mol / L NaOH solution was injected into the anode, while 12 L of a 10% NaCl solution was injected into the cathode test cell. The accurate chloride ion migration coefficient D for each specimen was obtained. RCM .

[0045] The obtained data set (Rccp, D) RCM Mathematical regression analysis was performed to obtain the mathematical relationship between the two.

[0046] Example 3

[0047] 1. Preparation of mortar specimens for a metakaolin-limestone powder-cement system with different mineral admixtures: Seven groups were prepared, replacing OPC with metakaolin at proportions of 0%, 20%, 30%, 60%, and 100%. The specimens were cylindrical blocks with a diameter of 110 mm and a height of 230 mm. First, cement, mineral admixtures, standard sand, and tap water were mixed and stirred thoroughly, then poured into cylindrical molds. The mixture was then vibrated for 30-60 seconds to remove air bubbles. After curing for one day, the specimens were demolded and placed in a curing chamber for additional curing at a temperature of 20±2℃ and a relative humidity >95%.

[0048] 2. After the test blocks have reached an age of 28 days, remove them and perform electrochemical impedance spectroscopy (EIS) on each block to obtain the EIS curve. Use Zsimpwin software to select the equivalent circuit model R. s (Q1R ct1 )(Q2(R ct2 W2)) The electrochemical impedance spectroscopy curve was fitted and analyzed to obtain the pore solution resistance R. s and charge transfer resistance R ct1 According to formula R ccp = R s + R ct1 The R of the test block was calculated. ccp The value was recorded, and the R value for each specimen was also recorded. ccp value.

[0049] 3. For the same batch of specimens, tests were conducted according to the standard RCM method. Mortar blocks cured for 28 days were used for rapid chloride ion migration testing. After immersing the samples in a saturated Ca(OH)₂ solution for 24 hours, they were placed in a rubber container between the positive and negative electrodes. Then, 300 ml of a 0.3 mol / L NaOH solution was injected into the anode, while 12 L of a 10% NaCl solution was injected into the cathode test cell. The accurate chloride ion migration coefficient D for each specimen was obtained. RCM .

[0050] The obtained data set (Rccp, D) RCM Mathematical regression analysis was performed to obtain the mathematical relationship between the two.

[0051] The R obtained from the above three embodiments ccp Value and D RCM Fitting the data separately, both equations showed a clear linear relationship with variances ≥ 0.86. Specifically, the mathematical relationship for Example 1 was y = -0.006x + 50.2 with a variance of 0.89; for Example 2, it was y = -0.003x + 20.1 with a variance of 0.96; and for Example 3, it was y = 0.02x + 72.6 with a variance of 0.86, where x represents R0.ccp Value, y represents R ccp Value. See the results of the three test groups. Figure 3-8 .

[0052] Figure 2 The relationship between the chloride ion migration coefficient and the Rs value in the metakaolin-limestone powder-cement system can be seen. s Value and D RCM No significant correlation. Figure 3-8 It can be seen that R ccp Value and D RCM The changes in R are correlated, indicating that R ccp With D RCM There is a highly significant linear negative correlation, i.e., D RCM Value varies with R ccp The value decreases linearly as it increases; the linear model has been tested, and the correlation coefficient R0 is [value missing]. 2 A value greater than 0.86 confirms the reliability and accuracy of the method of the present invention.

[0053] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical nature of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for predicting the chloride ion resistance of cement-based materials based on electrochemical impedance spectroscopy, characterized in that, Includes the following steps: Step 1: Inject cement-based material into the mold, shake to remove air bubbles, then cure the cement specimen. After that, demold the specimen and place it in the curing chamber for additional curing. Step 2: After the specimens have been cured to the set age, they are removed and subjected to electrochemical impedance spectroscopy (EIS) testing to obtain the EIS curve. An equivalent circuit model is used to fit and analyze the EIS curve to obtain the pore solution resistance R. s and charge transfer resistance R ct1 According to formula R ccp = R s + R ct1 The resistance R of the continuously connected micropores in the specimen was calculated. ccp ; The equivalent circuit model is defined by the function R. s (Q1R ct1 )(Q2(R ct2 W2)), where R s Q1 represents the resistance of the pore solution within the cementitious material, and R represents the double-layer capacitance at the solid-liquid interface in the composite cementitious material. ct1 Q1 represents the resistance related to ion transfer within the cementitious material, Q2 represents the double-layer capacitance between the cementitious material and the electrode, and R represents the capacitance related to ion transfer within the cementitious material. ct2 W1 represents the resistance of the electrode surface related to charge transfer, and W2 represents the resistance of the electrode surface related to electron diffusion. Step 3: Test the specimens according to the standard RCM method to obtain the chloride ion migration coefficient D for each specimen. RCM ; Step 4, R ccp and D RCM Perform mathematical regression analysis to obtain R. ccp and D RCM The linear relationship D RCM =a*R ccp +b; Step 5: Perform electrochemical impedance spectroscopy (EIS) on the test specimen with the same cement-based material composition as in Step 1 to obtain the EIS curve. Use an equivalent circuit model to fit and analyze the EIS curve to obtain the pore solution resistance R of the test specimen. s and charge transfer resistance R ct1 According to formula R ccp = R s +R ct1 The R of the test piece is calculated. ccp ; Step 6, R of the test piece ccp Substitute R from step 4 ccp and D RCM The linear relationship D RCM =a*R ccp In +b, the D of the test piece is calculated. RCM .

2. The method according to claim 1, characterized in that, In step 1, the cement-based material is a metakaolin-limestone powder-cement system, a ball milled coal gangue-limestone powder-cement system, or a calcined clay-limestone powder-cement system.

3. The method according to claim 1, characterized in that, In step 1, the cement specimens are cured for 1 day.

4. The method according to claim 1, characterized in that, In step 2, the age period is set to 28 days or 90 days.

5. The method according to claim 1, characterized in that, In step 1, the curing conditions in the curing room are: temperature 20±2℃, relative humidity >95%.

6. The method according to claim 1, characterized in that, In step 2 or 5, an electrochemical impedance spectroscopy test is performed using a CS2350H electrochemical workstation. The test parameters are: test frequency range of 0.1 Hz to 1 MHz, and open circuit potential maintained at 20 mV.

7. The method according to claim 1, characterized in that, The specific method for step 3 is as follows: After soaking the specimen in a saturated Ca(OH)2 solution for 24 hours, place it in a rubber bucket between the positive and negative electrodes, then inject 300 ml of 0.3 mol / L NaOH solution into the anode, and at the same time inject 12 L of 10% NaCl solution into the cathode test cell. The test operation method follows the standard GB / T50082-2009.

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