A method for establishing a prediction model for the chloride ion corrosion life of existing concrete

Abstract

The present invention relates to the field of nuclear power plant concrete structure assessment, and in particular to a method for establishing a chloride ion corrosion life prediction model for existing concrete. Most of the existing concrete indoor durability test parameters adopt the test parameters commonly used in the industry. This type of test is suitable for measuring the durability of different concrete materials when selecting concrete materials in the engineering design stage. For the existing concrete structures of nuclear power plants, their material parameters have been determined. Currently, there is no method for predicting the expected life of existing concrete structures based on the current status of the concrete structures. The present invention includes step one: condition investigation; step two: designing the experimental environment; step three: conducting experiments; and step four: conducting verification. The present invention proposes a method for conducting a chloride ion accelerated corrosion test on concrete samples based on similarity theory, and predicting the expected life of existing structures based on the test results.

Description

Technical Field

[0001] The invention relates to the field of nuclear power plant concrete structure assessment, in particular to a method for establishing a chloride ion corrosion life prediction model for existing concrete. Background Art

[0002] Reinforced concrete structure is the most widely used structure in nuclear power plants. my country's nuclear power plants are all located in coastal areas. The marine corrosive environment in coastal areas will cause the reinforced concrete of nuclear power plant structures to prematurely suffer from chloride corrosion, sulfate corrosion, and atmospheric carbonization, which will lead to aging problems such as concrete cracking and spalling, steel bar corrosion and expansion, and coating hollowing and shedding, which will bring serious threats to the durability (support capacity and containment capacity) of the structure and even threaten the safe operation of nuclear power plants. In recent years, with the increasing attention paid by domestic nuclear power plants to the monitoring and inspection of important safety structures and the increase in the operating life of structures, similar experience feedback reports of reinforced concrete structural failure in corrosive marine environments have also appeared in safety-critical structures such as containment and marine structures. With the increasing number of newly built nuclear power units in my country and the longer operating time of operating units, the durability of important safety structures of nuclear power plants in corrosive marine environments will become increasingly prominent. Therefore, it is of great value and significance to deeply study the diffusion law and protection measures of chloride ions in the specific environment of power plants.

[0003] Under the action of seawater, chloride ions mainly penetrate into concrete by diffusion in the concrete structure in the marine environment. However, in the area of ​​alternating dry and wet seawater, such as the tidal range and splash zone in the marine environment, the corrosion mechanism of chloride ions on the surface of concrete is relatively complex, mainly including capillary adsorption, penetration, diffusion, etc. on the surface of concrete, while diffusion is still the main effect in the deep layer. Indoor accelerated tests and field tests have been used for the durability research of concrete structures for a long time, but how to link the results of indoor accelerated tests with the results of field tests to establish a set of concrete durability life prediction models suitable for specific environments is still a key issue in the current research on the durability of concrete structures. Most of the existing concrete indoor durability test parameters adopt the test parameters commonly used in the industry. This type of test is suitable for measuring the durability performance of different concrete materials when selecting concrete materials in the engineering design stage. For the existing concrete structures of nuclear power plants, their material parameters have been determined. How to apply more "harsh" test parameters to the existing concrete materials in the laboratory than the real environment, so as to obtain the life of the existing structure in the real environment is the core of this technology. The similarity theory is proposed to establish the connection between the simulation experiment and the real environment, and to constrain the selection of experimental parameters through the internal relationship of the similarity ratio, so as to achieve the behavior law of the "simulated" research object in the real environment. Summary of the invention

[0004] Purpose

[0005] In order to overcome the problem that there is currently no method to predict the expected life of existing concrete structures based on the current status of the concrete structures, the present invention proposes a method based on similarity theory, which conducts chloride ion accelerated corrosion tests on concrete samples and predicts the expected life of existing structures based on the test results.

[0006] Technical Solution

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A method for establishing a chloride ion corrosion life prediction model for existing concrete includes: step one: condition investigation; step two: designing an experimental environment; step three: conducting experiments; and step four: conducting verification.

[0009] The step 1: condition investigation specifically includes: natural environment investigation and concrete design parameter investigation. The natural environment investigation includes: historical monthly average temperature and average humidity since the concrete structure was built; seawater tidal cycle, seawater chloride ion content parameters. The concrete design parameter investigation includes: investigating and collecting concrete mix ratio, design strength, and steel bar protective layer thickness h.

[0010] The second step is to design the experimental environment, which specifically includes: (1) dividing the environment into three categories: atmospheric zone concrete, dry-wet alternating zone concrete, and underwater zone concrete; and (2) designing three indoor chloride ion accelerated corrosion tests in the underwater zone, dry-wet alternating zone, and atmospheric zone, respectively.

[0011] The underwater zone selects the chloride ion concentration and the temperature of the soaking solution as control parameters; the dry-wet alternating zone selects the chloride ion concentration, the temperature of the soaking solution, and the dry-wet cycle time ratio as control parameters; the atmospheric zone selects the chloride ion concentration in the salt spray and the salt spray test temperature as control parameters.

[0012] The environment where the existing concrete structure is located is divided into three categories: atmospheric zone concrete, dry-wet alternating zone concrete, and underwater zone concrete; the concrete in the atmospheric zone is mainly in contact with salt in the air and has no direct contact with seawater; the concrete in the dry-wet alternating zone is in contact with seawater only part of the time; and the underwater zone is located below the horizontal plane and is immersed in seawater all year round.

[0013] The step three: conducting an experiment, specifically comprising:

[0014] (1) The underwater simulation test box is filled with an immersion solution with a chloride ion concentration of c, ranging from 8220 to 35000 mg / L, and a liquid temperature of T, which is 20 to 60°C. Then 24 concrete specimens with a height of H, H greater than 2h, are placed in the immersion test box for a test;

[0015] (2) Place 24 concrete specimens with a height of H greater than 2h in the dry-wet alternating zone simulation test chamber. The chloride ion concentration of the solution set in the dry-wet alternating zone simulation test is c, the solution temperature is T, and the time ratio of the test drying stage and the immersion stage is 2:1;

[0016] (3) Place 24 concrete specimens with a height of H greater than 2h in the atmospheric zone test chamber. The chloride ion concentration of the atmospheric zone salt spray is c and the salt spray test temperature is T.

[0017] During the test, three samples were taken out from three test boxes every month for testing. The testing method was to grind the powder layer by layer every 5 mm along the depth of the concrete, and measure the chloride ion content of the powder as c0, c1, c2, c3, and c4. The chloride ion diffusion coefficient Dm at the current time is obtained by fitting.

[0018] The fourth step is to verify, specifically including: determining whether the chloride ion concentration at a distance h from the upper surface of the sample reaches the chloride ion concentration limit of 1.4%. If the chloride ion concentration at a distance h from the upper surface of the sample reaches 1.4%, the test time at this time is recorded as time t m , the steel bars began to rust and the concrete structure was damaged.

[0019] The calculation formula for the expected life span (t) of the existing concrete structure is:

[0020] The unit is unified as month

[0021] Where D m (m 2 / s) is the chloride ion diffusion coefficient under indoor simulation test;

[0022] D(m 2 / s) is the chloride ion diffusion coefficient under the actual on-site environment, which is obtained by the coulometric method or on-site sampling method;

[0023] t m It is the time when the chloride ion concentration at a distance h from the upper surface of the specimen reaches 1.4% in the indoor simulation test. By substituting the above parameters into the concrete structure, the expected life t of the concrete structure in the real environment can be obtained.

[0024] Effect

[0025] The significant effect of the present invention is that the method uses the similarity principle to establish a quantitative relationship between the chloride ion corrosion process in an indoor simulated accelerated environment and the actual chloride ion corrosion process of the on-site structure. Using this quantitative relationship, combined with the diffusion coefficient Dm obtained from the chloride ion simulation test under three conditions, the life of the concrete structure under the real environment can be predicted.

[0026] 1. Establishing a quantitative relationship

[0027] 2. Applicable to life prediction of existing concrete structures BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is an overall schematic diagram of the life prediction method of the present invention;

[0029] Figure 2 Flowchart for calculation of life expectancy. DETAILED DESCRIPTION

[0030] The present invention converts real environment data into simulated accelerated test parameters according to the similarity principle, and obtains the quantitative relationship between the sample life of the simulated accelerated test and the real life of the concrete structure in the real environment, thereby realizing the service life prediction of the existing concrete structure. The specific implementation methods of the present invention are as follows:

[0031] The environment and structural material parameters of existing concrete structures were investigated to obtain the actual service environment data and concrete material information of the structure. The survey of natural environment data includes: historical monthly average temperature and average humidity since the construction of the concrete structure; seawater tidal cycle and seawater chloride ion content parameters. Concrete material information includes concrete mix ratio, design strength, and steel bar protective layer thickness (50mm).

[0032] The environment where the existing concrete structures are located is divided into three categories: atmospheric zone concrete, dry-wet alternating zone concrete, and underwater zone concrete. The concrete in the atmospheric zone is mainly exposed to salt in the air and is not in direct contact with seawater; the concrete in the dry-wet alternating zone is only in contact with seawater part of the time; and the concrete in the underwater zone is located below the water level and is immersed in seawater all year round.

[0033] Three kinds of indoor chloride ion accelerated corrosion tests were designed, namely, underwater area, dry-wet alternating area and atmospheric area. In the underwater area, the chloride ion concentration of the immersion solution and the temperature of the immersion solution were selected as control parameters; in the dry-wet alternating area, the chloride ion concentration of the immersion solution, the temperature of the immersion solution and the dry-wet cycle time ratio were selected as control parameters; in the atmospheric area, the chloride ion concentration in the salt spray and the salt spray test temperature were selected as control parameters.

[0034] The underwater simulation test box is filled with an immersion solution with a chloride ion concentration of 14436 mg / L and a liquid temperature of 52.2°C, and then 24 concrete specimens with a height of 150 mm are placed in it for an immersion experiment.

[0035] 24 concrete specimens with a height of 150 mm were placed in the dry-wet alternating zone simulation test box. The chloride ion concentration of the solution set in the dry-wet alternating zone simulation experiment was 14436 mg / L, the solution temperature was 52.2 °C, and the time ratio of the test drying stage and the immersion stage was 2:1.

[0036] 24 concrete specimens with a height of 150 mm were placed in the atmospheric zone test chamber. The chloride ion concentration of salt spray in the atmospheric zone was 14436 mg / L, and the salt spray test temperature was 52.2°C.

[0037] During the test, three samples were taken out from three test boxes every month for testing. The test method was to grind the samples into powder layer by layer every 5 mm along the depth of the concrete, and measure the chloride ion content (c0, c1, c2, c3, c4) of the powder. The chloride ion diffusion coefficient D at the current time is obtained by fitting m =4.74×10 -1 1m 2 / s.

[0038] At the same time, determine whether the chloride ion concentration at a distance h from the upper surface of the sample reaches the chloride ion concentration limit of 1.4% specified in the Durability Design Code.

[0039] If the chloride ion concentration at a distance of 50 mm from the upper surface of the specimen reaches 1.4%, the test time at this time is recorded as 8 months, the steel bars begin to rust and the concrete structure is damaged.

[0040] The calculation formula for the expected life (t) of existing concrete structures is:

[0041] (Unit is month)

[0042] Where D m (m 2 / s) is the chloride ion diffusion coefficient under indoor simulation test;

[0043] D(m 2 / s) is the chloride ion diffusion coefficient under the actual on-site environment. According to the Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete GB / T 50082-2009, D=1.31×10 -13 m 2 / s;

[0044] The calculated life expectancy is t = 2894.6 (months).

Claims

1. A method for establishing a prediction model for the chloride ion corrosion life of existing concrete, characterized in that: Step 1: Condition investigation; Step 2: Design the experimental environment; Step 3: Conduct the experiment; Step 4: Verify; The step 1: condition investigation, specifically includes: natural environment investigation and concrete design parameter investigation; The natural environment survey includes: historical monthly average temperature and average humidity since the concrete structure was built; seawater tidal cycle and seawater chloride ion content parameters; the concrete design parameter survey includes: investigating and collecting concrete mix ratio, design strength, and steel bar protective layer thickness h; The second step is to design the experimental environment, specifically including: (1) dividing the environment into three categories: atmospheric zone concrete, dry-wet alternating zone concrete, and underwater zone concrete; (2) respectively designing three indoor chloride ion accelerated corrosion tests in the underwater zone, dry-wet alternating zone, and atmospheric zone; The underwater zone selects the chloride ion concentration of the soaking solution and the temperature of the soaking solution as control parameters; the dry-wet alternating zone selects the chloride ion concentration of the soaking solution, the temperature of the soaking solution, and the dry-wet cycle time ratio as control parameters; the atmospheric zone selects the chloride ion concentration in the salt spray and the salt spray test temperature as control parameters; The step three is to conduct an experiment, specifically comprising: (1) filling an underwater zone simulation test box with a chloride ion concentration of c, ranging from 8220 to 35000 mg / L, a liquid temperature of T, and T being 20 to 60° C., and then placing 24 concrete specimens with a height of H, H being greater than 2h, and conducting an immersion experiment; (2) placing 24 concrete specimens with a height of H, H being greater than 2h in a dry-wet alternating zone simulation test box, the solution chloride ion concentration of c, the solution temperature of T in the dry-wet alternating zone simulation experiment, and the time ratio of the test drying stage and the immersion stage being 2:1; (3) placing 24 concrete specimens with a height of H, H being greater than 2h in an atmospheric zone test box, the atmospheric zone salt spray chloride ion concentration of c, and the salt spray test temperature of T; During the test, three samples were taken out from three test boxes every month for testing. The testing method was to grind the powder layer by layer every 5 mm along the depth of the concrete, and measure the chloride ion content of the powder as c0, c1, c2, c3, and c4. The chloride ion diffusion coefficient Dm at the current time is obtained by fitting; The fourth step is to verify, specifically including: determining whether the chloride ion concentration at a distance h from the upper surface of the sample reaches the chloride ion concentration limit of 1.4%. If the chloride ion concentration at a distance h from the upper surface of the sample reaches 1.4%, the test time at this time is recorded as time t m , the steel bars began to rust and the concrete structure was damaged; The calculation formula for the expected life t of existing concrete structures is: The unit is unified as month Where Dm is the chloride ion diffusion coefficient under indoor simulation test, unit is m2 / s; D is the chloride ion diffusion coefficient under the actual on-site environment, in m2 / s, obtained by the coulometric method or on-site sampling method; t m It is the time when the chloride ion concentration at a distance h from the upper surface of the specimen reaches 1.4% in the indoor simulation test. By substituting the above parameters into the expected life t of the concrete structure in the real environment; The environment in which existing concrete structures are located is divided into three categories: concrete in the atmospheric zone, concrete in the wet-dry alternating zone, and concrete in the underwater zone. The concrete in the atmospheric zone is exposed to salt in the air but not in direct contact with seawater. The concrete in the wet-dry alternating zone is in contact with seawater only part of the time. The underwater zone is located below the horizontal plane and is submerged in seawater all year round.

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