Method for testing chloride ion concentration in reinforced concrete based on micron-sized X-CT and comsol finite element technology

Abstract

The invention discloses a method for testing the concentration of chloride ions in reinforced concrete based on micron-sized X-CT and comsol finite element technologies. The method comprises the following steps: S1, preparing the reinforced concrete: treating reinforcing steel bars: selecting Q235 carbon round steel with the length of 20-30mm and the diameter of 5-8mm; and placing the reinforcing steel bar on a polishing machine, and polishing for 5-8 minutes by using SiC abrasive paper. According to the method, the micron-sized X-CT technology and the comsol finite element technology are combined, the limitation of a traditional testing method is overcome, the micron-sized X-CT technology provides a real image of the internal microstructure of the concrete, accurate basic data are provided for simulation analysis of comsol software, the testing result is closer to the actual situation, and the accuracy of chloride ion concentration testing is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of reinforced concrete corrosion detection, and more particularly to a method for testing chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology. Background Art

[0002] Reinforced concrete, a primary material for building infrastructure, is subject to corrosion, a common cause of structural degradation. In chloride-exposed environments, corrosion of the rebar can cause debonding from the concrete, leading to concrete cracking. Therefore, effective testing and evaluation of chloride ion concentrations in reinforced concrete is crucial.

[0003] Currently, traditional testing methods include the splitting test method and the COMSO numerical simulation method. For example, Reference 1 uses the traditional method to break open reinforced concrete and then use a rapid chloride ion content analyzer to measure chloride ion content at different locations. Reference 2 uses the COMSO numerical simulation method combined with MATLAB software to simulate internal conditions and measure chloride ion content. However, the traditional splitting test method damages the internal structure of the specimen, making the test results potentially inaccurate. While the COMSO numerical simulation method can simulate the internal structure, it still deviates from the actual situation.

[0004] Micron-scale X-ray CT technology offers the advantages of non-destructive characterization and analysis, as well as the ability to reveal internal microstructures, making it possible to study reinforced concrete materials at the microscopic level. Against this backdrop, this invention aims to provide a method that combines micron-scale X-ray CT with COMSO finite element analysis to more accurately measure chloride ion concentrations in reinforced concrete.

[0005] Document 1: Brenna A, Bolzoni F, Pedeferri MP, Ormellese M. Corrosioninhibitors for reinforced concrete structures: a study of binary mixtures[J]. Int. J. Corros. Scale Inhib., 2021, 1: 59–69. Document 2: Zhao Y, Dong J, Ding H, Jin W. Cracking effects on chloride diffusion and corrosion initiation in RC structures via finite element simulation [J]. Scientia Iranica, 2020, 27: 2301–2315。 Summary of the Invention

[0006] To overcome the above defects of the prior art, an embodiment of the present invention provides a method for testing chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for testing chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology, comprising the following steps: S1. Preparation of reinforced concrete: Reinforcement treatment: Select Q235 carbon round steel with a length of 20-30 mm and a diameter of 5-8 mm; Place the reinforcement on a polishing machine and polish it with SiC sandpaper for 5-8 minutes; Place the reinforcement in alcohol for cleaning for 20-30 minutes, and then place it in alcohol for standby; S2. Preparation of concrete: It is composed of 20-30 parts of fine sand, 20-30 parts of crushed stone, 15-20 parts of H2O and 40-45 parts of cement by mass; Mix the above components in a ball mill at a high speed for 3-5 min; Inject the obtained slurry into the mold and vibrate it sufficiently, and implant the reinforcement in the slurry; After the sample preparation is completed, place it in a standard curing room for curing for 15-20 h (temperature 15-20 °C, humidity 80-85%), and place it in a curing box for curing for 20-22 d (temperature and humidity are the same as those in the curing room) after demolding; Preparation of test solution: It is composed of 80-85 parts of H2O and 10-15 parts of NaCl by mass; S3. Chloride ion concentration test: Place the reinforced concrete specimen in the test solution; Use micron-level X-CT technology to obtain the two-dimensional microscopic morphology image of the specimen; The two-dimensional image was imported into the COMSO software to obtain the distribution of chloride ions inside the reinforced concrete specimen, and the chloride ion concentration was calculated based on it.

[0008] In a preferred embodiment, in the steel bar processing step, the length of the Q235 carbon round steel is 20 mm, 25 mm or 30 mm, and the diameter is 5 mm, 6 mm, 7 mm or 8 mm.

[0009] In a preferred embodiment, in the steel bar processing step, the grinding time is 5 minutes, 6 minutes, 7 minutes or 8 minutes.

[0010] In a preferred embodiment, in the steel bar processing step, the cleaning time in alcohol is 20 minutes, 25 minutes or 30 minutes.

[0011] In a preferred embodiment, in the concrete preparation step, the mass fraction of the fine sand is 20 parts, 25 parts or 30 parts, the mass fraction of the crushed stone is 20 parts, 25 parts or 30 parts, the mass fraction of H2O is 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, and the mass fraction of the cement is 40 parts, 41 parts, 42 parts, 43 parts, 44 parts or 45 parts.

[0012] In a preferred embodiment, in the concrete preparation step, the low-speed dry stirring time is 2 minutes or 3 minutes, and in the concrete preparation step, the mixing and stirring time in the ball mill is 3 minutes, 4 minutes or 5 minutes.

[0013] In a preferred embodiment, in the test solution preparation step, the mass fraction of H2O is 80 parts, 81 parts, 82 parts, 83 parts, 84 parts or 85 parts, and the mass fraction of NaCl is 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This method combines micron-scale X-CT technology with COMSOL finite element analysis to overcome the limitations of traditional testing methods. Micron-scale X-CT technology provides a true image of the concrete's internal microstructure, providing accurate basic data for COMSOL software simulation analysis, making test results more realistic and improving the accuracy of chloride ion concentration testing.

[0015] This method is a non-destructive test that avoids the damage to the sample structure caused by traditional dissection testing methods. It can perform multiple tests and long-term monitoring without affecting the integrity of reinforced concrete samples. It helps to deeply study the changing patterns of reinforced concrete during chloride ion corrosion, and provide a scientific basis for evaluating the durability of building structures and formulating maintenance strategies.

[0016] By precisely controlling the preparation process of reinforced concrete and the test conditions, it has strong repeatability, can provide stable and reliable test results for different research and engineering applications, is conducive to popularization and application in the engineering field, and ensures the safety and service life of building structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart of the method for quantitatively evaluating the internal chloride ion concentration of reinforced concrete based on micron-level X-CT and Comsol finite element technology provided by the present invention; Figure 2 It is a two-dimensional phase diagram of reinforced concrete obtained by the micron-level X-CT technology provided by the present invention; Figure 3 It is a distribution map of the internal chloride ion concentration of reinforced concrete obtained by the Comsol finite element technology provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Steel bar preparation Select Q235 carbon round steel with a length of 20 - 30 mm and a diameter of 5 - 8 mm according to the standard (China National Standard GB / T3274 - 2017). For example, steel bars with a length of 20 mm, 25 mm or 30 mm and a diameter of 5 mm, 6 mm, 7 mm or 8 mm can be selected to meet different test requirements and research purposes.

[0020] Place the selected steel bars on a polishing machine, use appropriate SiC sandpaper, and perform the polishing operation with uniform force and speed. The polishing time is controlled within 5 - 8 minutes. For example, when the surface of the steel bar is severely rusted, a longer polishing time, such as 7 - 8 minutes, can be selected to ensure that the surface rust layer is completely removed; if the surface of the steel bar is relatively smooth, the polishing time can be appropriately shortened to 5 - 6 minutes.

[0021] After polishing, immediately immerse the steel bars in alcohol for soaking and cleaning. The cleaning time is 20 - 30 minutes. During this period, the alcohol can be appropriately stirred to enhance the cleaning effect and ensure the removal of all oil stains, debris and residual polishing particles on the surface of the steel bars. After cleaning, completely immerse the steel bars in alcohol to prevent the steel bars from contacting the air and undergoing oxidation reaction, and wait for the next operation.

[0022] Concrete preparation and molding Accurately weigh 20 - 30 parts by mass of fine sand (ISO679:1989), 20 - 30 parts of crushed stone (diameter 10 - 15 mm), 15 - 20 parts of H2O, and 40 - 45 parts of cement (P・II42.5R). For example, a combination of 20 parts of fine sand, 25 parts of crushed stone, 15 parts of water, and 40 parts of cement can be used, or the proportions of each component can be adjusted according to specific research needs, such as increasing the amount of fine sand and crushed stone to study the effect of aggregates on chloride ion diffusion, etc.

[0023] Put the weighed fine sand, crushed stone, and cement into a ball mill, start the ball mill, and mix and stir at a relatively high speed. The stirring time is set to 3 - 5 min. During the stirring process, closely observe the mixing situation of the materials to ensure that each component is evenly mixed to form a concrete slurry with a delicate texture and no obvious agglomeration.

[0024] Slowly pour the stirred slurry into a pre - prepared mold. During the pouring process, at the same time, use a vibrating rod to fully vibrate the slurry in the mold. When vibrating, the vibrating rod should be vertically inserted into the slurry, and the vibrating operation should be carried out in a certain order and spacing to fully discharge the air bubbles in the slurry and ensure the density of the concrete structure. After vibration, carefully implant the pre - treated steel bars into the slurry, so that the steel bars are located at the center of the mold or at a specific position determined according to the test requirements, and ensure that the steel bars are closely combined with the concrete without obvious gaps.

[0025] After the steel bars are implanted, place the sample in a standard curing room for curing. The temperature of the curing room should be strictly controlled between 15 - 20 °C, and the humidity should be maintained at 80 - 85%. The curing time is 15 - 20 h. During this period, the concrete will gradually harden and its strength will continuously increase. After 15 - 20 h of curing, take the specimen out of the mold, and note that the demolding process should be carefully operated to avoid damaging the specimen. The demolded specimen is transferred to a curing box for continued curing for 20 - 22 d. The temperature and humidity conditions of the curing box should be the same as those of the curing room, so that the concrete further completes the hydration reaction and reaches stable physical properties, providing a reliable specimen for subsequent chloride ion concentration testing.

[0026] Preparation of test solution and immersion of specimen Accurately prepare the test solution by mass fraction, taking 80 - 85 parts of H2O and 10 - 15 parts of NaCl. For example, a solution of 80 parts of water and 10 parts of NaCl can be prepared, or according to the need to simulate different chloride ion concentration environments, adjust the content of NaCl, such as a high - concentration chloride ion solution of 85 parts of water and 15 parts of NaCl. Stir the prepared solution evenly to ensure that NaCl is completely dissolved in water to form a stable test solution.

[0027] Carefully place the cured reinforced concrete specimens in Example 1 into the prepared test solution, ensuring that the specimens are completely immersed in the solution and in full contact with the solution, to simulate the state of reinforced concrete in a chloride corrosion environment in actual engineering. The soaking time can be determined according to the test purpose and research requirements, generally for a certain period, such as 7 days, 14 days, or 28 days, etc., to observe the diffusion and concentration changes of chloride ions in the concrete.

[0028] Image acquisition and analysis Use micron-level X-CT technology to scan the specimens immersed in the test solution. Before scanning, adjust the scanning parameters according to the size and shape of the specimens, such as scanning resolution, scanning range, etc., to obtain clear and accurate two-dimensional microscopic morphology images. During the scanning process, ensure the stable position of the specimens to avoid image blurring or distortion caused by specimen movement.

[0029] Export the obtained two-dimensional images in a suitable format (such as common image formats.tif,.jpg, etc.) and import them into Comsol software.

[0030] In Comsol software, set appropriate boundary conditions, initial conditions, and solution parameters, etc., according to the physical properties of the reinforced concrete material, test conditions, and relevant mathematical models. Through the numerical calculation and simulation functions of the software, analyze and process the image data to obtain the distribution of chloride ions inside the reinforced concrete specimens. The analysis results can be presented in two-dimensional or three-dimensional forms, such as using a color cloud map to represent the chloride ion concentration distribution, with different colors representing different concentration ranges, visually showing the diffusion path, concentration gradient of chloride ions in the concrete, and the aggregation situation on the steel surface, etc.

[0031] According to the analysis results, further calculate the specific values of the chloride ion concentration, such as the average concentration, local maximum concentration, etc., so as to achieve quantitative testing of the corrosion chloride ion concentration in the reinforced concrete.

[0032] Only some exemplary embodiments of the present invention are described above by way of illustration. Undoubtedly, for those of ordinary skill in the art, without departing from the spirit and scope of the present invention, the described embodiments can be modified in various different ways. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the protection scope of the claims of the present invention.

Claims

1. A method for testing the chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology, characterized in that: The following steps are involved: S1. Reinforced concrete preparation: Rebar processing: Choose Q235 carbon round steel with a length of 20-30 mm and a diameter of 5-8 mm; Place the steel bar on a polishing machine and polish it with SiC sandpaper for 5-8 minutes; Place the steel bars in alcohol to clean for 20-30 minutes, then place them in alcohol for later use; S2. Concrete preparation: By mass, it is composed of 20-30 parts of fine sand, 20-30 parts of crushed stone, 15-20 parts of H2O and 40-45 parts of cement; The above components were mixed and stirred in a ball mill at high speed for 3-5 minutes; The obtained slurry is poured into a mold and vibrated thoroughly, and steel bars are embedded in the slurry; After the sample is prepared, place it in a standard curing room for 15-20 hours (temperature 15-20°C, humidity 80-85%). After demoulding, place it in a curing box for 20-22 days (temperature and humidity are the same as those in the curing room). Test solution preparation: By mass, it is composed of 80-85 parts of H2O and 10-15 parts of NaCl; S3. Chloride ion concentration test: Place the reinforced concrete specimen in the test solution; Micron-level X-CT technology is used to obtain two-dimensional microscopic morphological images of the sample; The two-dimensional image was imported into the COMSO software to obtain the distribution of chloride ions inside the reinforced concrete specimen, and the chloride ion concentration was calculated based on it.

2. The method for testing the chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology according to claim 1, wherein: In the steel bar processing step, the length of the Q235 carbon round steel is 20 mm, 25 mm or 30 mm, and the diameter is 5 mm, 6 mm, 7 mm or 8 mm.

3. The method for testing the chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology according to claim 1, characterized in that: In the steel bar processing step, the grinding time is 5 minutes, 6 minutes, 7 minutes or 8 minutes.

4. A method for testing the chloride ion concentration in reinforced concrete based on micron-scale X-CT and Comsol finite element technology according to claim 1, characterized in that: In the steel bar processing step, the cleaning time in alcohol is 20 minutes, 25 minutes or 30 minutes.

5. The method for testing the chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology according to claim 1, wherein: In the concrete preparation step, the mass fraction of the fine sand is 20 parts, 25 parts or 30 parts, the mass fraction of the crushed stone is 20 parts, 25 parts or 30 parts, the mass fraction of H2O is 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, and the mass fraction of the cement is 40 parts, 41 parts, 42 parts, 43 parts, 44 parts or 45 parts.

6. The chloride ion concentration testing method in reinforced concrete based on micron-level X-CT and Comsol finite element technology according to claim 1, wherein: In the concrete preparation step, the mixing and stirring time in the ball mill is 3 minutes, 4 minutes or 5 minutes.

7. A method for testing the chloride ion concentration in reinforced concrete based on micron-level X-CT and Comsol finite element technology according to claim 1, characterized in that: In the test solution preparation step, the mass fraction of the H2O is 80 parts, 81 parts, 82 parts, 83 parts, 84 parts or 85 parts, and the mass fraction of the NaCl is 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts.

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