Concrete multi-ion coupling erosion numerical simulation method based on random aggregate model

Abstract

The invention belongs to the technical field of civil engineering materials, and provides a concrete multi-ion coupling erosion numerical simulation method based on a random aggregate model, which comprises the following steps: S1, mesoscopic geometric modeling; s2, establishing a multi-physical field model; and S3, model solving and post-processing. According to the scheme, transmission and reaction rules of multiple ions in the concrete microstructure can be effectively simulated under the sulfur-chlorine-calcium coupling effect, and theoretical support is provided for durability design and service life prediction of the concrete structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of civil engineering materials, and particularly relates to a concrete multi-ion coupling erosion numerical simulation method based on a random aggregate model. BACKGROUND

[0002] As the most widely used building material, the long-term durability of concrete is a key factor determining the safety and service life of structures. In coastal, saline soil and other environments, the erosion process of concrete structures is extremely complex, often being the result of the synergistic effect of chloride ion penetration, sulfate erosion and matrix calcium dissolution. These processes interact with each other, and the coupling effect of concrete structure deterioration caused by these processes is different from the simple superposition of a single factor.

[0003] Currently, the main technical means to study the durability of concrete include physical tests and numerical simulations. Physical tests, such as indoor accelerated erosion tests and outdoor long-term exposure tests, can partially simulate real erosion environments and are the traditional means to obtain the deterioration law of concrete materials. However, physical tests have limitations such as long test period (especially exposure tests) and high cost. In addition, in environments where multiple chemical substances coexist, physical tests are difficult to effectively separate and quantify the independent contribution and coupling effect of different ions.

[0004] To make up for the shortcomings of physical tests, efficient and low-cost numerical simulation methods have emerged and have become an indispensable research tool in the field of concrete durability. However, a high-fidelity numerical simulation method must also make breakthroughs in two aspects: one is the authenticity of the geometric model, that is, accurately reproducing the heterogeneous microstructure of concrete; the other is the completeness of the physical and chemical model, that is, accurately describing the complex coupling mechanism of multi-species ion erosion.

[0005] Existing multi-ion coupling erosion numerical simulation methods have significant shortcomings in both key aspects. In the geometric model aspect, existing multi-ion coupling erosion simulation mostly uses macro-homogeneous models, which regard concrete as a whole and ignore the multi-phase structure of aggregates, mortar, interfaces and other internal structures of concrete, which may lead to distortion of the simulation of ion transport paths, and thus affect the accuracy of the design and evaluation of concrete structure durability. In the physical and chemical model aspect, the description of the multi-ion coupling mechanism in existing research is severely insufficient. Current models describe the erosion process of two ions (such as chloride-sulfate). For the complex system of chloride-sulfate-calcium ion coupling, existing research is extremely limited. SUMMARY

[0006] In order to overcome the above-mentioned defects of the prior art, the purpose of the present application is to provide a concrete multi-ion coupling erosion numerical simulation method based on a random aggregate model, which can efficiently generate a random aggregate geometric model and stably and accurately solve the complex process of multi-ion synergistic erosion on the high-fidelity structure, and has great theoretical and engineering value for improving the accuracy of concrete structure durability evaluation and life prediction.

[0007] The technical scheme adopted by the present application to solve its technical problems is:

[0008] A concrete multi-ion coupling erosion numerical simulation method based on a random aggregate model, comprising the following steps:

[0009] S1: Meso-geometric modeling: based on preset concrete mix proportion parameters, a two-dimensional or three-dimensional concrete random aggregate geometric model of random size and random spatial distribution is generated in a predetermined calculation domain using Python;

[0010] S2: Multi-physical field model establishment: the random aggregate geometric model generated in the foregoing S1 is imported into COMSOL simulation software to identify three regions: cement mortar, aggregate and interface transition zone, and a set of equations for controlling the entire erosion process is defined;

[0011] S3: Model solving and post-processing: initial conditions and environmental boundary conditions are set for the model, a transient solver of the simulation software is used to numerically solve the set of equations, the distribution of ion concentrations and chemical reaction products in the concrete meso-structure at different erosion times is obtained, and the results are visually analyzed.

[0012] Preferably, in the step S1, the preset concrete mix proportion parameters are determined according to the actual mix proportion of the concrete to be simulated, the volume fraction of the aggregate, the maximum and minimum particle size of the aggregate, and the aggregate grading curve.

[0013] Preferably, in the step S1, the step of generating a two-dimensional or three-dimensional concrete random aggregate geometric model of random size and random spatial distribution is as follows:

[0014] S11, a series of aggregate particle sizes satisfying the size distribution requirements are randomly generated according to the grading curve;

[0015] S12, an irregular polygon or a circle or an ellipse geometric shape is randomly generated for each particle size of the aggregate;

[0016] S13, the generated aggregates are randomly placed one by one in the calculation domain, and overlap judgment is performed to ensure that the aggregates do not overlap, until the volume fraction of the aggregates in the calculation domain reaches the preset value;

[0017] S14. After all the aggregate positions are fixed, perform an outward offset operation of a fixed thickness for each placed aggregate geometry to achieve and form the interface transition zone;

[0018] S15. Export the final generated geometry model into a data format recognizable by COMSOL simulation software.

[0019] Preferably, in the step S2, the equation group controlling the entire erosion process includes ion coupling transport equation, transport-reaction equation;

[0020] In the ion coupling transport equation:

[0021] The transport process of ions in concrete satisfies Fick's second law, as shown in formula (1), wherein C i , B i are the concentrations of free ions and solidified ions respectively, D i is the diffusion coefficient of ions, i represents sulfate ions, chloride ions, calcium ions, and t is the erosion time;

[0022] The relationship between the solidified chloride ions and the free chloride ions can be represented by formula (2), wherein α and β are solidification constants, and w e is the water content per unit mass of mortar;

[0023] The reaction kinetics equation of the solidified chloride ions is shown in formula (3), wherein k b is the solidification reaction rate of chloride ions;

[0024] The relationship between the solid phase calcium ions C s-Ca and the free calcium ions C f-Ca is shown in formula (4) and (5), wherein C CHO is the initial solid phase calcium hydroxide concentration, C CSH0 is the initial hydrated calcium silicate gel concentration, x3 is the saturated calcium ion concentration in the pore solution when no dissolution occurs, x2 and x1 are the calcium ion concentrations when CH is completely dissolved and C-S-H begins to rapidly dissolve, respectively, a, b, and c are polynomial coefficients, calculated according to formula (5), and q is the stoichiometric number

[0025] Considering the dissolution effect, the relationship between the solidified chloride ions and the free chloride ions can be further modified to formula (6), wherein C s-Ca0 represents the initial solid phase calcium concentration during the reaction process;

[0026] Formulas (1) to (6) are as follows:

[0027]

[0028] In the transport-reaction equation:

[0029] In the transport process, ions will react with each other, and when establishing the model, a reaction source term should be added to the transport equation, as shown in formula (7), wherein S i is the reaction source term, C i is the concentration of free chlorine ions, D i is the diffusion coefficient of ions, i represents different ions such as sulfate ions, chlorine ions, calcium ions, and the products of calcium aluminate phase CA, gypsum gyp, Friedel salt, and t is the erosion time;

[0030] The reaction source terms of calcium ions, sulfate ions, and chlorine ions are shown in formula (8), wherein C f-Ca , C s-Ca are the concentrations of free calcium ions and solid-phase calcium ions in the concrete, is the concentration of sulfate ions, C CA is the concentration of calcium aluminate phase, C Fs is the concentration of Friedel salt, and k i is the chemical reaction rate constant;

[0031] During the chemical reaction process, the concentrations of calcium aluminate phase, gypsum (gyp) (C gyp ), and Friedel salt (C Fs ) change as shown in formula (9), wherein q and δ are measurement constants;

[0032]

[0033]

[0034] Preferably, in the step S3:

[0035] The initial concentration of erosion ions inside the concrete is zero; on the boundary exposed to the erosion environment, a fixed first-type boundary condition is set, that is, the ion concentration is equal to the concentration of the external environment; the other boundaries are set as the second-type boundary condition of no flux;

[0036] The transient solver of COMSOL is configured, the total simulation time and the time step are set, and the calculation is started;

[0037] After the calculation is completed, the post-processing function of COMSOL is used to generate two-dimensional or three-dimensional cloud maps of free chlorine ions, total chlorine ions, sulfate ions, calcium ions, and ettringite in the mesostructure of the concrete at different erosion times.

[0038] Preferably, in the step S3:

[0039] Set initial and boundary conditions: set all the concentrations of eroded ions in the model at initial time t=0 to be 0; the initial concentrations of solid phase products C-S-H, CH and CA are set to be 4593 mol / m3, 4314 mol / m3 and 337 mol / m3 respectively; the top boundary of the geometric model is set as the eroded exposure surface, and the first type of boundary condition is adopted, and the concentrations of sulfate and chloride ions are set to be 104 mol / m 3 , 536 mol / m 3 .

[0040] Configuration and execution of the transient solver of the simulation software: in the COMSOL simulation software, the transient research step is selected, and the time-dependent solver is configured; the calculation domain is meshed, the mesh is encrypted in the interface transition zone and the near boundary area, the total simulation time is set to be 180 days, the time step of the solver is set to be 2 days, and then the solving is executed.

[0041] Result analysis and discussion: after the calculation is completed, the results are analyzed by using the post-processing function of the COMSOL simulation software, and the concentration distribution cloud diagrams of total chloride ions, sulfate ions, free calcium ions, Friedel salt, aluminum phase and gypsum in the concrete at the erosion time of 180 days are generated.

[0042] Preferably, in the step S1: the pre-set concrete is C 30 concrete, the calculation domain is set to be a two-dimensional square area with a size of 100mm*100mm; the volume fraction of the aggregate is set to be 33.3%; and the particle size range of the aggregate is 5mm-40mm.

[0043] Compared with the prior art, the beneficial effects of the present application include:

[0044] The present scheme can effectively simulate the transmission and reaction rules of multiple ions in the concrete mesostructure under the sulfur-chlorine-calcium coupling effect, and provide theoretical support for the durability design and life prediction of the concrete structure. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0046] Fig. 1 The flowchart of the present application.

[0047] Fig. 2 The geometric figure of the interface transition zone of the present application;

[0048] Fig. 3A concentration distribution cloud chart of total chloride ions, sulfate ions, free calcium ions, Friedel salt, aluminum phase, and gypsum of the concrete of the embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to enable a more clearly understanding of the above-mentioned objects, features and advantages of the present application, the present application will be described in detail below with the accompanying drawings and specific embodiments. It should be noted that the embodiments and the features in the embodiments of the present application can be combined with each other without conflict. In the following description, a lot of specific details are described in order to facilitate a full understanding of the present application, and the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing the specific embodiments and is not intended to limit the present application.

[0051] Embodiment:

[0052] As shown in Figs. 1-3 the present embodiment provides a concrete multi-ion coupling erosion numerical simulation method based on a random aggregate model, comprising the following steps:

[0053] S1: Meso geometric modeling: based on the preset concrete mix ratio parameters, a two-dimensional or three-dimensional concrete random aggregate geometric model with random size and random spatial distribution is generated in the predetermined calculation domain by using Python;

[0054] The core of the above steps is to generate a geometric model that can truly reflect the mesostructure of concrete, which specifically includes:

[0055] S11, according to the grading curve, a series of aggregate particle sizes meeting the size distribution requirements are randomly generated: specifically, in the present embodiment, first, according to the actual mix ratio of the C 30 concrete to be simulated, the core parameters required for modeling are determined. In the present embodiment, the calculation domain is set as a two-dimensional square region of 100mm×100mm; the volume fraction of the aggregate is set to 33.3%; the particle size range of the aggregate is 5mm~40mm, and the aggregate grading meets the Fuller grading curve.

[0056] S12, randomly generate an irregular polygon or a circle or an ellipse geometry for each size of aggregate: specifically, in this embodiment, using Python, a series of 5mm-20mm aggregate sizes are randomly generated according to the gradation curve, and a circular geometry is randomly generated for each size of aggregate.

[0057] S13, randomly place the generated aggregate one by one into the calculation domain, and perform overlap judgment to ensure that there is no overlap between the aggregates, until the volume fraction of the aggregate in the calculation domain reaches the preset value, specifically until the area fraction of the aggregate in the calculation domain reaches 33.3%.

[0058] S14, after fixing the positions of all aggregates, perform an outward offset operation of a fixed thickness for each placed aggregate geometry to realize and form the interface transition zone, specifically, after fixing the positions of all aggregates, perform an outward offset operation of 50 microns thickness for each aggregate polygon to generate the ITZ (interface transition zone) region, the geometry of the generated region is shown in Fig. 2 .

[0059] S15, export the finally generated geometry model to a data format that can be recognized by COMSOL simulation software, which is a.dxf format.

[0060] S2: Multi-physical field model establishment: import the random aggregate geometry model generated in the foregoing S1 into COMSOL simulation software, identify three regions according to the layer information retained during import: cement mortar, aggregate and interface transition zone, define the equation set that controls the entire erosion process, specifically:

[0061] The equation set that controls the entire erosion process includes ion coupling transport equation, transport-reaction equation;

[0062] In the ion coupling transport equation:

[0063] The transport process of ions in concrete satisfies Fick's second law, as shown in formula (1), where C i , B i are the concentrations of free ions and solidified ions respectively, D i is the diffusion coefficient of ions, i represents sulfate ions, chloride ions, calcium ions, and t is the erosion time;

[0064] The relationship between solidified chloride ions and free chloride ions can be represented by formula (2), where a and β are solidification constants, and w e is the water content per unit mass of mortar;

[0065] The reaction kinetics equation of solidified chloride ions is shown in formula (3), where kb the solidification reaction rate of chloride ions;

[0066] solid phase calcium ions C s-Ca and free calcium ions C f-Ca The relationship between and is shown in equations (4) and (5), wherein C CHO is the initial solid phase calcium hydroxide concentration, C CSH0 is the initial hydrated calcium silicate gel concentration, x3 is the saturation calcium ion concentration in the pore solution when no dissolution occurs, x2 and x1 are the calcium ion concentrations when CH is completely dissolved and C-S-H begins to dissolve rapidly, respectively, a, b, and c are polynomial coefficients calculated according to equation (5), and q is the stoichiometric number

[0067] Considering the dissolution effect, the relationship between the solidified chloride ions and the free chloride ions can be further modified to equation (6), wherein C s-Ca0 represents the initial solid phase calcium concentration during the reaction process;

[0068] Equations (1) to (6) are as follows:

[0069]

[0070]

[0071] In the transport-reaction equation:

[0072] During the transport of ions, chemical reactions occur between them, and when establishing the model, a reaction source term should be added to the transport equation, as shown in equation (7), wherein S i is the reaction source term, C i is the concentration of free chloride ions, D i is the diffusion coefficient of ions, i represents different ions such as sulfate ions, chloride ions, calcium ions, and products of calcium aluminate phase CA, gypsum gyp, and Friedel salt, and t is the corrosion time;

[0073] The reaction source terms of calcium ions, sulfate ions, and chloride ions are shown in equation (8), wherein C f-Ca , C s-Ca are the concentrations of free calcium ions and solid phase calcium ions in the concrete, is the concentration of sulfate ions, C CA is the concentration of calcium aluminate phase, C Fs is the concentration of Friedel salt, and k i is the chemical reaction rate constant;

[0074] During the chemical reaction process, the calcium aluminate phase, gypsum (gyp) (C gyp ), and Friedel salt (C Fs) The concentration change is shown in equation (9), wherein q, δ are measurement constants;

[0075]

[0076] S3: Model solving and post-processing: Set initial conditions and environmental boundary conditions for the model, use the transient solver of the simulation software to numerically solve the above equation set, obtain the distribution of ion concentration and chemical reaction products in the concrete mesostructure at different erosion times, and perform visual analysis on the results. Specifically:

[0077] The initial erosion ion concentration inside the concrete is zero; on the boundary exposed to the erosion environment, set it as a fixed first type boundary condition, i.e. the ion concentration is equal to the external environment concentration; other boundaries are set as second type boundary conditions with no flux;

[0078] Configure the transient solver of COMSOL, set the total simulation time and time step, and start the calculation;

[0079] After the calculation is completed, use the post-processing function of COMSOL to generate two-dimensional or three-dimensional cloud maps of free chloride ions, total chloride ions, sulfate ions, calcium ions, and ettringite in the concrete mesostructure at different erosion times.

[0080] More specifically:

[0081] Set initial and boundary conditions: Set the concentration of all erosion ions inside the model to be 0 at the initial time t=0; the initial concentrations of solid products C-S-H, CH, and CA are set to 4593 mol / m3, 4314 mol / m3, and 337 mol / m3, respectively; the top boundary of the geometric model is set as the erosion exposure surface, and the first type boundary condition is adopted, with the concentrations of sulfate and chloride ions set to 104 mol / m 3 and 536 mol / m 3 , respectively.

[0082] Configuration and execution of the transient solver of the simulation software: In the COMSOL simulation software, select the "transient" research step, configure the time-dependent solver, perform grid subdivision on the calculation domain, perform grid densification in the interface transition zone and near the boundary area, set the total simulation time to 180 days, set the time step of the solver to 2 days, and then perform the calculation.

[0083] Result analysis and discussion: After the calculation is completed, use the post-processing function of the COMSOL simulation software to analyze the results and generate concentration distribution cloud maps of total chloride ions, sulfate ions, free calcium ions, Friedel salt, aluminum phase, and gypsum in the concrete at 180 days of erosion time, as shown in Fig. 3 .

[0084] In summary, the beneficial effects of the present application are:

[0085] 1. High model authenticity: By generating random aggregate models using Python, the irregular shape, size gradation, and random distribution of aggregates in real concrete can be highly restored, overcoming the limitations of traditional idealized models and significantly improving the accuracy of simulation results.

[0086] 2. Strong multi-field coupling capability: Using the PDE general module of COMSOL, the coupling between ion transport, chemical reaction kinetics, and other multi-fields can be directly and flexibly defined and implemented, accurately representing the complex interactions between factors.

[0087] 3. High research efficiency: Compared to physical tests, this method greatly shortens the research period and reduces costs. At the same time, parameterized research can be easily conducted to systematically explore the effects of aggregate gradation, external ion concentration, and other factors on concrete durability.

[0088] 4. In-depth mechanism revelation: This method can provide detailed information on ion concentration and product distribution at any position and time within the concrete, enabling visualization of the erosion process and providing a powerful tool for in-depth revelation of the degradation mechanism of concrete under complex environments.

[0089] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Any modification, equivalent change, and modification of the above embodiment that does not deviate from the technical solution content of the present application, in accordance with the technical essence of the present application, is still within the scope of the present application.

Claims

1. A method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model, characterized in that, The method comprises the following steps: S1: microscopic geometric modeling: based on the preset concrete mix ratio parameters, Python is used to generate a two-dimensional or three-dimensional concrete random aggregate geometric model with random size and random spatial distribution in a predetermined calculation domain; S2: multi-physical field model establishment: the random aggregate geometric model generated in the foregoing S1 is imported into the COMSOL simulation software to identify three regions: cement mortar, aggregate and interface transition zone, and a set of equations for controlling the entire erosion process is defined; S3: model solving and post-processing: initial conditions and environmental boundary conditions are set for the model, the transient solver of the simulation software is used to numerically solve the above set of equations, the distribution of ion concentrations and chemical reaction products in the concrete mesostructure at different erosion times is obtained, and the results are visualized and analyzed.

2. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 1, characterized in that, In the step S1, the preset concrete mix ratio parameters are determined according to the actual mix ratio of the concrete to be simulated, the volume fraction of the aggregate, the maximum and minimum particle size of the aggregate, and the aggregate grading curve.

3. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 2, characterized in that, In the step S1, the steps of generating a two-dimensional or three-dimensional concrete random aggregate geometric model with random size and random spatial distribution are as follows: S11, a series of aggregate particle sizes meeting the size distribution requirements are randomly generated according to the grading curve; S12, an irregular polygon or a circle or an ellipse geometric shape is randomly generated for each particle size of the aggregate; S13, the generated aggregate is randomly placed one by one in the calculation domain, and overlap judgment is performed to ensure that the aggregates do not overlap, until the volume fraction of the aggregates in the calculation domain reaches the preset value; S14, after the positions of all aggregates are fixed, a fixed-thickness outward offset operation is performed for each placed aggregate geometric body to realize and form the interface transition zone; S15, the finally generated geometric model is exported in a data format recognizable by the COMSOL simulation software.

4. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 3, characterized in that, In the step S2, the set of equations for controlling the entire erosion process includes ion coupling transport equations and transport-reaction equations; In the ion coupling transport equations: The transport process of ions in concrete satisfies Fick's second law, as shown in equation (1), where C i , B i are the concentrations of free ions and solidified ions, respectively, D i is the diffusion coefficient of ions, i represents sulfate ions, chloride ions, calcium ions, and t is the erosion time. Relationship between solidified chloride ions and free chloride ions may be expressed by equation (2), where a, β are solidification constants, w e is the water content per unit mass of the mortar; The reaction kinetics equation of solidified chloride ions is shown in equation (3), where k b is the solidification reaction rate of chloride ions; solid phase calcium ions C s-Ca and free calcium ions C f-Ca The relationship between the solid phase calcium ions C CHO and the free calcium ions C CSH0 is shown in equations (4) and (5), where C CHO is the initial solid phase calcium hydroxide concentration, C CSH0 is the initial hydrated calcium silicate gel concentration, x3 is the saturation calcium ion concentration in the pore solution when no dissolution has occurred, x2, xi are the calcium ion concentrations when CH has completely dissolved and C-S-H begins to dissolve rapidly, respectively, a, b, c are polynomial coefficients calculated according to equation (5), and q is the stoichiometric number Considering the dissolution effect, the relationship between the solidified chloride ion and the free chloride ion can be further modified as equation (6), where C s-Ca0 represents the initial solid phase calcium concentration during the reaction process; Formulas (1) to (6) are as follows: In the transport-reaction equations: During the transport process, the ions will react with each other. When the model is established, a reaction source term should be added on the basis of the transport equation, as shown in formula (7), wherein S i is the reaction source term, C i is the concentration of free chlorine ions, D i is the diffusion coefficient of ions, i represents different ions such as sulfate ions, chlorine ions, calcium ions, and the products of calcium aluminate phase CA, gypsum gyp, and Friedel salt, and t is the corrosion time. The reaction source terms of calcium ion, sulfate radical and chloride ion are shown in equation (8), wherein C f-Ca , C s-Ca is the concentration of free calcium ion in the concrete, is the concentration of sulfate radical ion, C CA is the concentration of calcium aluminate phase, Fs is the concentration of Friedel salt, k i is the chemical reaction rate constant; During the chemical reaction process, the concentration of calcium aluminate phase, gypsum (C gyp ), Friedel salt (C Fs ) changes as shown in equation (9), where q and δ are measurement constants.

5. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 4, characterized in that, In the step S3: The initial concentration of the erosion ions in the concrete is zero; on the boundary exposed to the erosion environment, a fixed first-type boundary condition is set, that is, the ion concentration is equal to the external environment concentration; other boundaries are set as second-type boundary conditions without flux; The transient solver of COMSOL is configured, the total simulation time and the time step are set, and the calculation is started; After the calculation is completed, the COMSOL post-processing function is used to generate two-dimensional or three-dimensional cloud charts of free chloride ions, total chloride ions, sulfate ions, calcium ions, ettringite and other substances in the concrete mesostructure at different erosion times.

6. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 5, characterized in that, In the step S3: Setting initial and boundary conditions: setting the concentration of all eroded ions inside the model to be 0 at the initial time t = 0; the initial concentrations of solid phase products C-S-H, CH and CA are set to be 4593 mol / m3, 4314 mol / m3 and 337 mol / m3 respectively; the top boundary of the geometric model is set as the eroded exposure surface, and the first type of boundary condition is adopted, and the concentrations of sulfate and chloride ions are set to be 104 mol / m 3 and 536 mol / m 3 respectively. Configuration and execution of the transient solver of the simulation software: in the COMSOL simulation software, the "transient” research step is selected, the time-dependent solver is configured, the calculation domain is meshed, the mesh in the interface transition zone and the near-boundary region is densified, the total simulation time is set to 180 days, the time step of the solver is set to 2 days, and then the solving is performed. Result analysis and discussion: after the calculation, the results are analyzed by using the post-processing function of COMSOL simulation software, and the concentration distribution nephogram of total chloride ion, sulfate ion, free calcium ion, Friedel salt, aluminum phase and gypsum of concrete at the erosion time of 180 days is generated.

7. The method for numerical simulation of multi-ion coupling erosion of concrete based on random aggregate model according to claim 3, characterized in that, In the step S1: the preset concrete is C 30 concrete, the calculation domain is set as a two-dimensional square area of 100mm*100mm; the volume fraction of the aggregate is set as 33.3%; and the particle size range of the aggregate is 5mm-40mm.

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