A method for constructing a model of chloride ion diffusion coefficient in concrete

Abstract

This invention provides a method for constructing a chloride ion diffusion coefficient model for concrete, comprising the following steps: S1, obtaining the concrete mix proportion and the chloride ion diffusion coefficient of the concrete mortar made from the mix proportion; S2, based on the mix proportion, constructing a two-dimensional three-phase geometric model of the concrete using finite element software; S3, establishing a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model. This invention considers the influence of large aggregate distribution, enabling more accurate simulation of concrete erosion and providing reliable technical support for the durability of large-size aggregate concrete projects.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and in particular relates to a method for constructing a model of the chloride ion diffusion coefficient in concrete. Background Technology

[0002] With the rapid development of the social economy, the construction speed of port buildings has accelerated. Meanwhile, the durability of concrete, the most important material for coastal structures, has become increasingly prominent. To ensure that large-volume concrete does not crack during construction, a common practice is to increase the aggregate size and reduce the amount of cementitious materials. Therefore, the aggregate used in concrete has evolved from two-dimensional to three-dimensional and even four-dimensional gradations. As the aggregate gradation increases, the aggregate size also increases. The maximum aggregate size in two-dimensional concrete reaches 40mm, in three-dimensional concrete it reaches 80mm, and in four-dimensional concrete it reaches 120mm. With the increase in aggregate size, some testing methods are no longer suitable. This is because, when molding specimens, the maximum aggregate size of the concrete mixture should not exceed 1 / 3 of the minimum side length of the mold. A common practice is to use a wet sieving method to remove large-diameter aggregates before testing their relevant properties. This point is mentioned in the "Test Procedures for Hydraulic Concrete" (DL / T 5150-2017).

[0003] Although the standard mentions that wet-sieved two-stage aggregate concrete can be used to prepare chloride ion diffusion coefficient specimens of fully graded concrete, wet-sieved two-stage aggregate concrete removes large-diameter aggregates from fully graded concrete, leaving only small-diameter aggregates. This practice changes the paste-aggregate ratio in the concrete, resulting in more paste in the molded specimens compared to fully graded concrete, and a reduced interfacial transition zone (ITZ). This practice seriously affects the chloride ion diffusion coefficient of the concrete, and the measured chloride ion diffusion coefficient is lower than that of fully graded concrete.

[0004] Existing rapid chloride ion migration determination methods, such as the RCM method and the electrical flux method, require aggregate particle size not to exceed 25 mm. Therefore, if these two methods are used to test the chloride ion diffusion coefficient of fully graded concrete, only wet-sieved two-stage aggregate concrete can be used. This approach yields an overestimation of the chloride ion diffusion coefficient, often requiring increased cement or admixture dosage to meet design specifications, which contradicts the original design intent of fully graded concrete. To address the drawbacks of wet-sieved two-stage aggregate concrete, existing methods also use modeling to obtain the chloride ion diffusion coefficient of three-stage equal-proportion concrete. However, existing models do not consider the influence of large aggregates. Therefore, accurately and quickly establishing a chloride ion diffusion coefficient model for large-size aggregate concrete is a major challenge currently faced by engineering technicians. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing a model of the chloride ion diffusion coefficient in concrete, which takes into account the influence of the distribution of large aggregates, and can more accurately simulate concrete erosion, providing reliable technical support for the durability of concrete projects with large aggregate size.

[0006] This invention is achieved through the following technical solution:

[0007] A method for constructing a model of chloride ion diffusion coefficient in concrete includes the following steps:

[0008] S1. Obtain the concrete mix proportion and the chloride ion diffusion coefficient of the concrete mortar made from the mix proportion;

[0009] S2. Based on the mix proportion, a two-dimensional three-phase geometric model of concrete is constructed using finite element software;

[0010] S3. Based on the constructed two-dimensional three-phase geometric model, establish the chloride ion diffusion coefficient model. The specific steps are as follows:

[0011] S31. Determine the creation of the simulation environment;

[0012] S32. Import the two-dimensional three-phase geometric model into the simulation environment, establish the three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and construct it into a complex. Use Boolean algorithm to remove the aggregate part.

[0013] S33. Based on the obtained chloride ion diffusion coefficient of concrete mortar, set the basic parameters that need to be defined in the model establishment. The basic parameters include the initial chloride ion concentration in concrete, the initial chloride ion diffusion coefficient of mortar, the initial chloride ion diffusion coefficient of the interface transition zone, and the decay coefficient of mortar chloride ion diffusion coefficient with age.

[0014] S34. Set up a time-varying model for mortar diffusion coefficient and a time-varying model for chloride ion concentration on concrete surface;

[0015] S35. Set the zero flux boundary and chloride ion inflow boundary for the two-dimensional three-phase geometric model. The zero flux boundary is the boundary that does not allow chloride ions to pass through or enter, and the chloride ion inflow boundary is the boundary that allows chloride ions to pass through or enter.

[0016] S36. Define the transfer properties of each component phase in the two-dimensional three-phase geometric model;

[0017] S37. The process of establishing the chloride ion diffusion coefficient model is completed by using ultra-fine mesh for mesh generation.

[0018] Furthermore, based on the mix proportions, the steps for constructing a two-dimensional three-phase geometric model of concrete using finite element software include:

[0019] S21. Based on the mix proportion, determine the model region of the two-dimensional three-phase geometric model, set the geometry of polygonal aggregates with different particle sizes, and use the Walraven formula to obtain the area fraction of polygonal aggregates with different particle sizes, and use the obtained area fraction as the target area fraction.

[0020] S22. Randomly place polygonal aggregates within the model area and determine whether there is any overlap between the placed polygonal aggregates and the existing polygonal aggregates within the model area.

[0021] S23. If so, delete the newly placed polygonal aggregate and randomly place polygonal aggregates again within the model area.

[0022] S24. Generate a thin film around the polygonal aggregate that corresponds to the shape of the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix.

[0023] S25. Repeat steps 22 to S24 until the area fraction of polygonal aggregates with different particle sizes in the model area reaches the target area fraction, thus completing the construction of the two-dimensional three-phase geometric model of concrete.

[0024] Furthermore, in the step of obtaining the area fraction of polygonal aggregates with different particle sizes using the Walraven formula, the specific formula is as follows:

[0025] (1);

[0026] In the formula, For any point on a two-dimensional cross-section, the aggregate diameter is... The probability of the inscribed circle appearing. This represents the percentage of coarse aggregate in the total volume of concrete. The diameter of the sieve aperture is 1. This represents the maximum aggregate particle size.

[0027] Furthermore, the step of generating a thin film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix includes:

[0028] S241. Set the thickness of the interface transition area and calculate the coordinates of each vertex of the interface transition area. The specific calculation formula is as follows:

[0029] (2);

[0030] In the formula, The first of the interface transition area The coordinates of the vertices, The first polygonal aggregate represents the first... The coordinates of the vertices, It refers to the thickness of the interface transition area. It is the first polygonal aggregate The polar angle of each vertex relative to the center of the polygon aggregate;

[0031] S242. Connect all vertices of the interface transition area.

[0032] Furthermore, the steps for setting the thickness of the interface transition area include:

[0033] S2411. Obtain the chloride ion diffusion coefficient of the concrete slab prepared by the mix proportion;

[0034] S2412. Randomly select a thickness within a preset thickness range as the target thickness;

[0035] S2413. Set the thickness of the interface transition zone to the target thickness, and under the condition that the thickness of the interface transition zone is the target thickness, construct a two-dimensional three-phase geometric model, and establish a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model.

[0036] S2414. The chloride ion diffusion coefficient of concrete is obtained by numerical simulation through the established chloride ion diffusion coefficient model.

[0037] S2415. Determine whether the error between the chloride ion diffusion coefficient of the simulated concrete and the chloride ion diffusion coefficient of the concrete slab is within the preset error range. If not, proceed to steps S2416 to S2417. If yes, proceed to step S2418.

[0038] S2416. Determine whether the chloride ion diffusion coefficient of the simulated concrete is greater than the chloride ion diffusion coefficient of the concrete slab. If it is greater, reduce the target thickness to obtain a new target thickness. If it is less, increase the target thickness to obtain a new target thickness.

[0039] S2417. Repeat steps S2413 to S2415;

[0040] S2418. Set the thickness of the interface transition area to the target thickness.

[0041] Furthermore, the steps for obtaining the chloride ion diffusion coefficient of the concrete slab prepared from the mix proportions include:

[0042] Concrete slabs are prepared according to the concrete mix design.

[0043] Multiple sets of concrete test blocks were taken from the concrete slab;

[0044] The chloride ion diffusion coefficient of each group of concrete test blocks was obtained by RCM or natural soaking grinding method;

[0045] The average chloride ion diffusion coefficient of multiple concrete test blocks was calculated, and the average value was used as the chloride ion diffusion coefficient of the concrete slab.

[0046] Furthermore, in the steps of setting up the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on concrete surface, the time-varying model of mortar diffusion coefficient is as follows:

[0047] (3);

[0048] (4);

[0049] In the formula, The chloride ion diffusion coefficient of the mortar at different erosion times. This represents the decay coefficient of the chloride ion diffusion coefficient of the mortar with age. For the erosion of time, This refers to the curing age of the concrete.

[0050] Furthermore, in the steps of setting up the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on concrete surface, the time-varying model of chloride ion concentration on concrete surface is as follows:

[0051] (5);

[0052] In the formula, The chloride ion concentration on the concrete surface. For erosion time.

[0053] Compared with existing technologies, the beneficial effects of this invention are as follows: a two-dimensional three-phase geometric model of concrete is established based on the mix proportion, which fully considers the influence coefficient of large aggregates, improves the accuracy of the chloride ion resistance design value of large aggregate concrete, and can obtain a more accurate chloride ion diffusion coefficient through the established chloride ion diffusion coefficient model, providing technical support for the durability design of large aggregate concrete, ensuring the quality of the project, making up for the shortcomings of existing testing methods in the determination of chloride ion diffusion coefficient of large aggregate concrete, and the method is simple, feasible and accurate. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating the steps of constructing the concrete chloride ion diffusion coefficient model according to the present invention.

[0055] Figure 2 This is a schematic diagram of the two-dimensional three-phase geometric model constructed in the method for constructing the chloride ion diffusion coefficient model of concrete in this invention;

[0056] Figure 3 This is a schematic diagram of the boundary condition setting in the method for constructing the concrete chloride ion diffusion coefficient model of the present invention;

[0057] Figure 4 This is a schematic diagram of the model mesh generation;

[0058] Figure 5 This is a diagram showing the chloride ion concentration distribution in the chloride ion erosion model.

[0059] Figure 6 This is a schematic diagram showing the distribution of the chloride ion diffusion coefficient in concrete as a function of the number of simulations. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0061] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0062] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0063] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0064] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. 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.

[0065] Please see Figure 1 , Figure 1 This is a flowchart illustrating the steps of constructing the concrete chloride ion diffusion coefficient model according to the present invention. A method for constructing a concrete chloride ion diffusion coefficient model includes the following steps:

[0066] S1. Obtain the concrete mix proportion and the chloride ion diffusion coefficient of the concrete mortar made from the mix proportion;

[0067] S2. Based on the mix proportion, a two-dimensional three-phase geometric model of concrete is constructed using finite element software;

[0068] S3. Based on the constructed two-dimensional three-phase geometric model, establish the chloride ion diffusion coefficient model. The specific steps are as follows:

[0069] S31. Determine the creation of the simulation environment;

[0070] S32. Import the two-dimensional three-phase geometric model into the simulation environment, establish the three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and construct it into a complex. Use Boolean algorithm to remove the aggregate part.

[0071] S33. Based on the obtained chloride ion diffusion coefficient of concrete mortar, set the basic parameters that need to be defined in the model establishment. The basic parameters include the initial chloride ion concentration in concrete, the initial chloride ion diffusion coefficient of mortar, the initial chloride ion diffusion coefficient of the interface transition zone, and the decay coefficient of mortar chloride ion diffusion coefficient with age.

[0072] S34. Set up a time-varying model for mortar diffusion coefficient and a time-varying model for chloride ion concentration on concrete surface;

[0073] S35. Set the zero flux boundary and chloride ion inflow boundary for the two-dimensional three-phase geometric model. The zero flux boundary is the boundary that does not allow chloride ions to pass through or enter, and the chloride ion inflow boundary is the boundary that allows chloride ions to pass through or enter.

[0074] S36. Define the transfer properties of each component phase in the two-dimensional three-phase geometric model;

[0075] S37. The process of establishing the chloride ion diffusion coefficient model is completed by using ultra-fine mesh for mesh generation.

[0076] In step S1 above, the mix proportion of the engineering concrete is first confirmed, and then, based on the confirmed concrete mix proportion, concrete mortar with that mix proportion is prepared. Specifically, it is molded indoors. A 100mm×50mm cylindrical concrete mortar was cured for 28 days according to standard. The chloride ion diffusion coefficient of the concrete mortar was determined by RCM or natural soaking grinding method.

[0077] In step S2 above, the finite element software can be one of MATLAB, COMSOL, ANSYS, etc. Based on the principle of random aggregate addition, a two-dimensional three-phase geometric model of concrete with the concrete mix proportion confirmed in step S1 is constructed in the finite element software. The two-dimensional three-phase geometric model usually refers to a model that describes the distribution and interaction of three different phases in two-dimensional space.

[0078] Further, in step S2, the step of constructing a two-dimensional three-phase geometric model of concrete using finite element software based on the mix proportion includes:

[0079] S21. Based on the mix proportion, determine the model region of the two-dimensional three-phase geometric model, set the geometry of polygonal aggregates with different particle sizes, and use the Walraven formula to obtain the area fraction of polygonal aggregates with different particle sizes, and use the obtained area fraction as the target area fraction.

[0080] S22. Randomly place polygonal aggregates within the model area and determine whether there is any overlap between the placed polygonal aggregates and the existing polygonal aggregates within the model area.

[0081] S23. If so, delete the newly placed polygonal aggregate and randomly place polygonal aggregates again within the model area.

[0082] S24. Generate a thin film around the polygonal aggregate that corresponds to the shape of the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix.

[0083] S25. Repeat steps 22 to S24 until the area fraction of polygonal aggregates with different particle sizes in the model area reaches the target area fraction, thus completing the construction of the two-dimensional three-phase geometric model of concrete.

[0084] In step S21 above, the model region of the two-dimensional three-phase geometric model is first determined. The model region is a rectangular region with a length of [missing information]. , width is The geometry of polygonal aggregates can be described by defining the range of the number of sides and the range of particle size. The number of sides of the polygonal aggregate can be randomly selected from a preset range, and all polygonal aggregates are then constructed according to this randomly selected number of sides. The particle size range is determined by the aggregate range in the mix design. For example, if the mix design is a three-gradation mix containing three types of aggregates, the particle size range of each polygonal aggregate is set based on the particle size range of the three types of aggregates. The defined polygonal aggregates are assumed to have coordinate systems of... The coordinates of each vertex of the polygon aggregate can be calculated using the following formula:

[0085] (6);

[0086] In the formula, It is the first The distance from each vertex to the center It is the first The polar angle of each vertex;

[0087] In a two-dimensional model, the three-dimensional aggregate proportions cannot be directly used. Therefore, the volume fraction of the three-dimensional aggregate is converted into an area fraction on a two-dimensional plane using the Walraven formula, resulting in the area fractions of polygonal aggregates of different particle sizes. The specific formula is as follows:

[0088] (1);

[0089] In the formula, For any point on a two-dimensional cross-section, the aggregate diameter is... The probability of the inscribed circle appearing. This represents the percentage of coarse aggregate in the total volume of concrete. The diameter of the sieve aperture is 1. This represents the maximum aggregate particle size.

[0090] In step S22 above, the entire polygonal aggregate placed within the model area must be within the model area; that is, all vertices of the polygonal aggregate must satisfy the following condition: and Therefore, during the random placement of polygonal aggregates within the model area, they can be placed in ascending order of particle size, descending order of particle size, or simultaneously placed from one polygonal aggregate within each particle size range. During placement, the center coordinates of the polygonal aggregates are first randomly generated. The center point of the polygonal aggregate can be randomly generated using the following formula:

[0091] (7);

[0092] (8);

[0093] In the formula, Representing an interval Uniformly random numbers;

[0094] Determine if all vertices of the generated polygonal aggregate are within the model area. If not, regenerate the center coordinates of the polygonal aggregate. If they are within the model area, perform collision detection to determine if the deployed polygonal aggregate overlaps with existing polygonal aggregates within the model area. The collision detection formula is:

[0095] (9);

[0096] In the formula, These are the coordinates of the center point of the currently deployed polygonal aggregate. It is the existing first The coordinates of the center point of the polygonal aggregate This indicates the distance between the center of the currently generated polygonal aggregate and the center of the already deployed polygonal aggregate;

[0097] like If the polygonal aggregate overlaps with an existing polygonal aggregate within the model area, then a collision has occurred. Otherwise, the polygonal aggregate does not overlap with an existing polygonal aggregate within the model area.

[0098] In step S23 above, if the polygonal aggregate being placed overlaps with an existing polygonal aggregate within the model area, the generated polygonal aggregate is deleted, and then a new polygonal aggregate is regenerated and placed according to step S22 until there is no overlap.

[0099] In step S24 above, the step of generating a thin film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the substrate includes:

[0100] S241. Set the thickness of the interface transition area and calculate the coordinates of each vertex of the interface transition area. The specific calculation formula is as follows:

[0101] (2);

[0102] In the formula, The first of the interface transition area The coordinates of the vertices, The first polygonal aggregate represents the first... The coordinates of the vertices, It refers to the thickness of the interface transition area. It is the first polygonal aggregate The polar angle of each vertex relative to the center of the polygon aggregate;

[0103] S242. Connect all vertices of the interface transition area.

[0104] In steps S241 and S242 above, the thickness of the interface transition zone can be set according to experimental data or relevant standards. For each polygonal aggregate, the boundary vertex coordinates of the interface transition zone can be calculated by expanding the vertices of the original polygonal aggregate outward, and then connecting the vertices of the interface transition zone will yield the interface transition zone on the polygonal aggregate.

[0105] Further, in step S241, the step of setting the thickness of the interface transition zone includes:

[0106] S2411. Obtain the chloride ion diffusion coefficient of the concrete slab prepared by the mix proportion;

[0107] S2412. Randomly select a thickness within a preset thickness range as the target thickness;

[0108] S2413. Set the thickness of the interface transition zone to the target thickness, and under the condition that the thickness of the interface transition zone is the target thickness, construct a two-dimensional three-phase geometric model, and establish a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model.

[0109] S2414. The chloride ion diffusion coefficient of concrete is obtained by numerical simulation through the established chloride ion diffusion coefficient model.

[0110] S2415. Determine whether the error between the chloride ion diffusion coefficient of the simulated concrete and the chloride ion diffusion coefficient of the concrete slab is within the preset error range. If not, proceed to steps S2416 to S2417. If yes, proceed to step S2418.

[0111] S2416. Determine whether the chloride ion diffusion coefficient of the simulated concrete is greater than the chloride ion diffusion coefficient of the concrete slab. If it is greater, reduce the target thickness to obtain a new target thickness. If it is less, increase the target thickness to obtain a new target thickness.

[0112] S2417. Repeat steps S2413 to S2415;

[0113] S2418. Set the thickness of the interface transition area to the target thickness.

[0114] In step S2411 above, the step of obtaining the chloride ion diffusion coefficient of the concrete slab prepared by the mix proportion includes:

[0115] S24111. Prepare concrete slabs according to the concrete mix proportions;

[0116] S24112. Take multiple sets of concrete test blocks from the concrete slab;

[0117] S24113. The chloride ion diffusion coefficient of each group of concrete test blocks was obtained by RCM or natural soaking grinding method.

[0118] S24114. Calculate the average value of the chloride ion diffusion coefficient of multiple concrete test blocks, and use the calculated average value as the chloride ion diffusion coefficient of the concrete slab.

[0119] In steps S24111 to S24114 above, according to the concrete mix proportion, a 500mm×400mm×300mm concrete slab is formed indoors. After standard curing for 28 days, multiple sets of concrete test blocks are obtained from the concrete slab using a uniform core sampling method. The specific number can be selected according to the actual situation. In this embodiment, 12 cylindrical concrete test blocks of 100mm×50mm are uniformly extracted from the concrete slab. Then, the chloride ion diffusion coefficient of the extracted multiple sets of concrete test blocks is determined using the RCM or natural immersion grinding method to obtain the chloride ion diffusion coefficient of each set of concrete test blocks. Finally, based on the chloride ion diffusion coefficient of each set of concrete test blocks, the average value of the chloride ion diffusion coefficient of the multiple sets of concrete test blocks is calculated, and the calculated average value is used as the chloride ion diffusion coefficient of the concrete slab.

[0120] In step S2412 above, the thickness of the interface transition zone of ordinary concrete is generally 10-100 mm. Therefore, the preset thickness range can be set to 10-100. Then, randomly select a thickness within the preset thickness range as the target thickness.

[0121] In step S2413 above, the thickness of the interface transition zone is set as the target thickness. Under the condition that the thickness of the interface transition zone is the target thickness, a two-dimensional three-phase geometric model is constructed according to step S2, and a chloride ion diffusion coefficient model is established according to step S3.

[0122] In step S2414 above, after establishing the chloride ion diffusion coefficient model, transient calculation is selected, the calculation step size is set, and the calculation is performed to obtain the result of the change of chloride ion concentration in concrete with depth. Based on the result of the change of chloride ion concentration in concrete with depth, the chloride ion diffusion coefficient of concrete is inverted using Fick's second law.

[0123] In step S2415 above, the chloride ion diffusion coefficient of concrete is compared with the chloride ion diffusion coefficient obtained by core sampling of concrete slab to determine whether the error between the two is within the preset error range. The error range can be set to within 3%. This is to indirectly verify whether the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness by using the chloride ion diffusion coefficient obtained by core sampling of concrete slab.

[0124] In step S2416 above, if the error between the chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient obtained from the core sample of the concrete slab is outside the preset error range, it indicates that the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is not very accurate, that is, the thickness setting of the interface transition zone is inaccurate and needs to be adjusted. Therefore, a fixed value for reducing or increasing the interface transition zone is preset. In this embodiment, the fixed value is set to 10. Then, it is determined whether the chloride ion diffusion coefficient of the simulated concrete is greater than that of the concrete slab. If it is greater, the thickness of the interface transition zone needs to be reduced, that is, the target thickness needs to be reduced by 10. The new target thickness is obtained. If it is less than the target thickness, the thickness of the interface transition zone needs to be increased, that is, the target thickness is increased by 10. This yields a new target thickness.

[0125] S2417 After obtaining the new target thickness, the thickness of the interface transition zone is reset to the new target thickness. Steps S2413 to S2415 are repeated to continue to determine whether the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is accurate.

[0126] In step S2418 above, if the error between the chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient obtained from the core sample of the concrete slab is within the preset error range, it indicates that the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is accurate. That is, the thickness of the interface transition zone is set accurately and does not need to be adjusted. Therefore, the thickness of the interface transition zone is set as the target thickness. Furthermore, the set thickness of the interface transition zone can be used to establish chloride ion diffusion coefficient models for other mix proportions.

[0127] In step S25 above, repeat steps 22 to S24 to place polygonal aggregates in the model area until the area fractions of polygonal aggregates with different particle sizes in the model area all reach the target area fraction, thus completing the construction of the two-dimensional three-phase geometric model of concrete. The constructed two-dimensional three-phase geometric model is then saved to a .dxf format file for easy access later.

[0128] In step S3 above, based on the previously established two-dimensional three-phase geometric model in the finite element software, chloride salt erosion is introduced to establish a chloride ion diffusion coefficient model that considers large aggregates.

[0129] In steps S31 to S32 above, a simulation environment is created in COMSOL software. The .dxf file containing the two-dimensional three-phase geometric model information is imported into the simulation environment to establish the two-dimensional three-phase geometric model of the concrete slab. The two-dimensional three-phase geometric model is divided into three different domains: aggregate, interface transition zone and mortar, and constructed into a complex. Since aggregate is a path through which chloride ions do not pass, it needs to be set to zero flux. Therefore, the aggregate part is deducted using Boolean algorithm to complete the creation of the geometric model.

[0130] In step S33 above, the basic parameters and their values ​​that need to be defined in the numerical simulation are set, including the initial chloride ion concentration in the concrete. Set to 0%, the initial chloride ion diffusion coefficient of the mortar. This refers to the chloride ion diffusion coefficient of the concrete mortar obtained in step S1. The initial chloride ion diffusion coefficient of the interface transition zone is a multiple of the chloride ion diffusion coefficient of the concrete mortar. In this embodiment, the initial chloride ion diffusion coefficient of the interface transition zone is set to 12 times the chloride ion diffusion coefficient of the concrete mortar. The decay coefficient of the mortar chloride ion diffusion coefficient with age is... Set to 0.55, referring to the "Standard for Quality Control of High-Performance Concrete in Harbor Engineering" (JTS 257-2-2012).

[0131] In step S34 above, the time-varying model of the mortar diffusion coefficient is as follows:

[0132] (3);

[0133] (4);

[0134] In the formula, The chloride ion diffusion coefficient of the mortar at different erosion times. This represents the decay coefficient of the chloride ion diffusion coefficient of the mortar with age. For the erosion of time, This refers to the curing age of concrete.

[0135] The time-varying model of chloride ion concentration on concrete surface is obtained by fitting the change of chloride ion concentration on the surface of three-grade concrete with erosion time, as shown in the following formula:

[0136] (5);

[0137] In the formula, The chloride ion concentration on the concrete surface. For erosion time.

[0138] In steps S35 to S37 above, the zero flux boundary and chloride ion inflow boundary of the chloride ion diffusion model are set, including three zero flux boundaries and one chloride ion inflow boundary, such as... Figure 3 As shown. Then, the transport properties of each constituent phase in the chloride ion diffusion model were set, and an ultra-fine mesh was used for mesh generation. The mesh generation result is shown in the figure. Figure 4 As shown, after mesh generation, the chloride ion diffusion coefficient model is established. This model enables engineering applications. For different mix proportions, simply input the measured chloride ion diffusion coefficient of the concrete mortar and the established two-dimensional three-phase geometric model of the concrete with that mix proportion into the model. This will yield a chloride ion diffusion coefficient model for concrete considering large-diameter aggregates, providing data support for engineering durability design.

[0139] The following example illustrates the method for constructing the chloride ion diffusion coefficient model for concrete according to the present invention:

[0140] The concrete mix design for a certain ship lock project is shown in Table 1 below.

[0141] Table 1 Concrete mix proportions for a ship lock project

[0142]

[0143] According to the concrete mix proportions in Table 1, concrete slabs measuring 500mm × 400mm × 300mm were formed indoors. Twelve 100mm × 50mm cylindrical concrete mortar specimens were uniformly extracted from a concrete slab after 28 days of standard curing. The chloride ion diffusion coefficients of the concrete mortar and the extracted concrete specimens were then determined using the RCM or natural immersion grinding method. The chloride ion diffusion coefficients of the concrete mortar and concrete slab prepared based on the mix proportions in Table 1 were determined to be 8.0 × 10⁻⁶. -12 m 2 / s, 4.5×10 -12 m 2 / s.

[0144] Based on the concrete mix proportions for the lock project in Table 1, the proportions of aggregates in each particle size range within the two-dimensional geometry of the three-graded concrete were calculated using the Walraven formula. The calculated proportions of aggregates with sizes of 5-20mm, 20-40mm, and 40-80mm were 20.13%, 28.35%, and 51.52%, respectively. Furthermore, the total area ratio of all aggregates (the proportion of the total aggregate area to the cube) was calculated to be 55.3% based on the mix proportions. Using a random placement principle, a two-dimensional, three-phase geometric model of the three-graded concrete (240mm × 240mm × 240mm, with a side length three times the maximum aggregate particle size) in .dxf format was constructed using MATLAB, as shown below. Figure 2 As shown.

[0145] The concrete geometry model was imported into COMSOL and divided into three distinct domains: aggregate, interface transition zone, and mortar, which were then constructed as a union. The aggregate portion was removed using a Boolean algorithm, completing the creation of the geometry model.

[0146] The basic parameters for setting the chloride ion diffusion coefficient model are the initial chloride ion concentration in the concrete. Set to 0%, the initial chloride ion diffusion coefficient of the mortar. Set to 8.0×10 -12 m 2 / s, initial chloride ion diffusion coefficient of the interface transition region Set to 1.2×10 -10 m 2 / s (12 times the chloride ion diffusion coefficient of mortar), the decay coefficient of chloride ion diffusion coefficient of mortar with age Set it to 0.55.

[0147] The time-varying models for mortar diffusion coefficient and concrete surface chloride ion concentration are set as follows:

[0148] (3);

[0149] (4);

[0150] A time-varying model for chloride ion concentration on the concrete surface is established, as shown in the following formula:

[0151] (5);

[0152] The boundary conditions for the chloride ion diffusion model are set, including three zero-flux boundaries and one chloride ion inflow boundary, as shown in the schematic diagram. Figure 3 As shown; the transport properties of each constituent phase in the chloride ion diffusion model are defined; an ultra-fine mesh is used for mesh generation, and the mesh generation result is shown in the figure. Figure 4 As shown, the chloride ion diffusion coefficient model has been established.

[0153] After completing the chloride ion diffusion coefficient model, select transient calculation, set the calculation step size to 30 days, and perform the calculation. After the calculation is completed, export the chloride ion concentration cloud map of the concrete, as shown below. Figure 5 As shown, the variation of chloride ion concentration in concrete with depth is obtained, and the chloride ion diffusion coefficient of concrete is inverted using Fick's second law. Finally, the distribution law of the chloride ion diffusion coefficient of concrete with the number of simulations is obtained, as shown below. Figure 6 As shown, by Figure 6 It can be seen that the chloride ion diffusion coefficient simulated by the concrete chloride ion diffusion coefficient model is consistent with the chloride ion diffusion coefficient of 4.5 × 10⁻⁶ obtained from core sampling of the concrete slab. -12 m 2 The relative error of / s is within 3%, which indirectly verifies the accuracy of the concrete chloride ion diffusion model established by the construction method of the present invention, and facilitates its engineering application. Therefore, the construction method of the concrete chloride ion diffusion coefficient model of the present invention can produce a concrete chloride ion diffusion model with a relative error of less than 3% compared with the chloride ion diffusion coefficient obtained from concrete core sampling. This avoids the drawbacks of using the chloride ion diffusion coefficient of wet-sieved two-grade concrete to evaluate three-grade concrete, and improves the accuracy of durability assessment of large-size aggregate concrete.

[0154] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for constructing a model of the chloride ion diffusion coefficient in concrete, characterized in that, Includes the following steps: S1. Obtain the concrete mix proportion and the chloride ion diffusion coefficient of the concrete mortar made from the mix proportion; S2. Based on the mix proportion, a two-dimensional three-phase geometric model of concrete is constructed using finite element software. The specific steps are as follows: S21. Based on the mix proportion, determine the model region of the two-dimensional three-phase geometric model, set the geometry of polygonal aggregates with different particle sizes, and use the Walraven formula to obtain the area fraction of polygonal aggregates with different particle sizes. Use the obtained area fraction as the target area fraction, where the specific formula is: （1）； In the formula, For any point on a two-dimensional cross-section, the aggregate diameter is... The probability of the inscribed circle appearing. This represents the percentage of coarse aggregate in the total volume of concrete. The diameter of the sieve aperture is 1. Maximum aggregate particle size; S22. Randomly place polygonal aggregates within the model area and determine whether the placed polygonal aggregates overlap with existing polygonal aggregates within the model area. S23. If so, delete the newly placed polygonal aggregate and randomly place polygonal aggregates again within the model area. S24. Generate a thin film around the polygonal aggregate that corresponds to the shape of the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix. S25. Repeat steps 22 to S24 until the area fraction of the polygonal aggregates with different particle sizes in the model area reaches the target area fraction, thus completing the construction of the two-dimensional three-phase geometric model of concrete. S3. Based on the constructed two-dimensional three-phase geometric model, establish a chloride ion diffusion coefficient model. The specific steps are as follows: S31. Determine the creation of the simulation environment; S32. Import the two-dimensional three-phase geometric model into the simulation environment, establish the three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and construct it into a complex. Use Boolean algorithm to remove the aggregate part. S33. Based on the obtained chloride ion diffusion coefficient of the concrete mortar, set the basic parameters that need to be defined in the model establishment. The basic parameters include the initial chloride ion concentration in the concrete, the initial chloride ion diffusion coefficient of the mortar, the initial chloride ion diffusion coefficient of the interface transition zone, and the decay coefficient of the chloride ion diffusion coefficient of the mortar with age. S34. Set up a time-varying model for mortar diffusion coefficient and a time-varying model for chloride ion concentration on concrete surface; S35. Set the zero flux boundary and chloride ion inflow boundary of the two-dimensional three-phase geometric model. The zero flux boundary is the boundary that does not allow chloride ions to pass through or enter, and the chloride ion inflow boundary is the boundary that allows chloride ions to pass through or enter. S36. Set the transfer properties of each component phase in the two-dimensional three-phase geometric model; S37. The process of establishing the chloride ion diffusion coefficient model is completed by using ultra-fine mesh for mesh generation.

2. The method for constructing the concrete chloride ion diffusion coefficient model according to claim 1, characterized in that, The step of generating a thin film around the polygonal aggregate corresponding to the shape of the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix includes: S241. Set the thickness of the interface transition area and calculate the coordinates of each vertex of the interface transition area. The specific calculation formula is as follows: （2）； In the formula, The first of the interface transition area The coordinates of the vertices, The first polygonal aggregate represents the first... The coordinates of the vertices, It refers to the thickness of the interface transition area. It is the first polygonal aggregate The polar angle of each vertex relative to the center of the polygon aggregate; S242. Connect the vertices of the interface transition area.

3. The method for constructing the concrete chloride ion diffusion coefficient model according to claim 2, characterized in that, The step of setting the thickness of the interface transition zone includes: S2411. Obtain the chloride ion diffusion coefficient of the concrete slab made from the said mix proportion; S2412. Randomly select a thickness within a preset thickness range as the target thickness; S2413. Set the thickness of the interface transition zone to the target thickness, and under the condition that the thickness of the interface transition zone is the target thickness, construct the two-dimensional three-phase geometric model, and establish a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model. S2414. The chloride ion diffusion coefficient of concrete is obtained by numerical simulation through the established chloride ion diffusion coefficient model. S2415. Determine whether the error between the chloride ion diffusion coefficient of the simulated concrete and the chloride ion diffusion coefficient of the concrete slab is within the preset error range. If not, proceed to steps S2416 to S2417. If yes, proceed to step S2418. S2416. Determine whether the chloride ion diffusion coefficient of the simulated concrete is greater than the chloride ion diffusion coefficient of the concrete slab. If it is greater, reduce the target thickness to obtain a new target thickness. If it is less, increase the target thickness to obtain a new target thickness. S2417. Repeat steps S2413 to S2415; S2418. Set the thickness of the interface transition area to the target thickness.

4. The method for constructing the concrete chloride ion diffusion coefficient model according to claim 3, characterized in that, The step of obtaining the chloride ion diffusion coefficient of the concrete slab made from the said mix proportion includes: Concrete slabs are prepared according to the concrete mix design. Multiple sets of concrete test blocks were taken from the concrete slab; The chloride ion diffusion coefficient of each group of concrete test blocks was obtained by RCM or natural soaking grinding method; The average chloride ion diffusion coefficient of multiple concrete test blocks was calculated, and the average value was used as the chloride ion diffusion coefficient of the concrete slab.

5. The method for constructing the concrete chloride ion diffusion coefficient model according to claim 1, characterized in that, In the steps of setting the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on concrete surface, the time-varying model of mortar diffusion coefficient is as follows: （3）； （4）； In the formula, The chloride ion diffusion coefficient of the mortar at different erosion times. This represents the decay coefficient of the chloride ion diffusion coefficient of the mortar with age. For the erosion of time, This refers to the curing age of the concrete.

6. The method for constructing the concrete chloride ion diffusion coefficient model according to claim 1, characterized in that, In the steps of setting the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on concrete surface, the time-varying model of chloride ion concentration on concrete surface is as follows: （5）； In the formula, The chloride ion concentration on the concrete surface. For erosion time.

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