1. A theoretical model for development and evolution of a saturated steel-concrete structure phase field and a particle field in a stray electric field is characterized by comprising the following thermodynamic processes, transmission equations and coupling relations:

the thermodynamic process is as follows: the determination and interaction of the initial values of the saturated concrete pore liquid particles and the hydration products are realized through thermodynamic calculation;

the transmission equation: (1) describing the transport of particles in the water-saturated concrete pore liquid under the action of a stray electric field by utilizing a Nernst-Planck equation, wherein the transport comprises concentration diffusion of the particles and an electromigration process of ions; (2) calculating the diffusion process of oxygen in concrete by adopting Fick's second law; (3) the nonlinear polarization of the steel-concrete interface under the action of the stray electric field is characterized by a Tafel equation; (4) the consumption of oxygen at the steel-concrete interface under the action of the stray electric field is calculated by a Faraday equation;

coupling relation: (1) the particle concentration in the concrete pore liquid is taken as an intermediate variable, and coupled calculation is realized through an operator splitting algorithm with a Nernst-Planck equation; (2) the oxygen diffusion and consumption process is coupled with the cathode electrode reaction process described by the Tafel equation, and the electric field formed by the total electric field density at the interface and the driving force for the ion electromigration process in the Nernst-Planck equation at the interface are obtained.

2. The stray electric field lower water-saturated steel-concrete structure phase field and particle field development evolution theoretical model as claimed in claim 1, characterized in that the determination of the initial values of the water-saturated concrete pore liquid particles and hydration products is obtained based on the chemical analysis result of cement and thermodynamic calculation based on the minimization of the Gibbs free energy of the system.

3. The theoretical model for the evolution of the phase field and the particle field of the water-saturated steel-concrete structure under the stray electric field according to claim 2, wherein the implementation of the minimization of Gibbs free energy of the system comprises the following three aspects: (1) an activity model describing non-ideal behavior of the pore fluid particles; (2) determining a cement hydration thermodynamic database of each reaction Gibbs free energy in the system; (3) and obtaining a hydration kinetic formula of the hydration degree of the cement clinker in a given time.

4. The stray electric field lower water-saturated steel-concrete structure phase field and particle field development evolution theoretical model as claimed in claim 1, characterized in that the interaction of the water-saturated concrete pore liquid particles and hydration products comprises a pure-phase dissolution deposition equilibrium model, a solid solution model and an electric double layer complex reaction equilibrium model.

5. The stray electric field lower water-saturated steel-concrete structure phase field and particle field development evolution theoretical model as claimed in claim 1, wherein at the steel-concrete interface, the electrochemical reaction kinetics process of the steel bar is described by Tafel empirical formula, and comprises iron oxidation process, oxygen reduction process and hydrogen evolution process, wherein: the coupling between the kinetics of oxygen reduction and the diffusion process described by Fick's second law is achieved by modifying the exchange current density.

6. The stray electric field lower water-saturated steel-concrete structure phase field and particle field development evolution theoretical model as claimed in claim 1, wherein the element types of the pore liquid particles comprise: H. o, Al, Ca, Cl, Fe, K, Mg, Na, S and Si.

Background

In recent years, the electrified rail transit is rapidly developed in China and even in the world, not only is the traffic pressure relieved, but also the requirements of the sustainable development strategy are met, and the electrified rail transit becomes one of the most important traffic ways for people to go out daily. Corresponding rail transit infrastructures are in a large-scale construction period, and the infrastructures mainly based on reinforced concrete structures are the premise and guarantee of rail transit safe operation. However, the stray electric field formed by the rail transit power supply system has a great influence on the durability of the reinforced concrete structure, and a potential threat is generated on the service safety of the rail transit infrastructure.

The influence of the stray electric field on the durability of the reinforced concrete structure is mainly reflected in the following two points: firstly, the influence on the electrochemical corrosion behavior of the steel bar is mainly shown as the reduction of the cross section area of the steel bar, the accumulation of corrosion products, the reduction of the adhesive force of a steel-concrete interface and the like; secondly, the influence on the distribution of the pore liquid particles in the concrete porous material is mainly shown in the diffusion and migration of the pore liquid particles under an electric field formed by stray current, on one hand, the concentration of aggressive ions (such as chloride ions) or alkali metal ions (such as sodium ions and potassium ions) in a local area can be too high, and further corrosion of reinforcing steel bars or alkali aggregate reaction can be caused, on the other hand, the original thermodynamic balance of the ions can be broken in the electromigration process, and a new balance tends to be established, so that the dissolution or deposition of hydration product phases can be caused, even new phases are formed, and meanwhile, the phase change process can also influence the transportation process of the particles in the concrete. Therefore, determining the development and evolution law of the steel-concrete structure phase field and the pore liquid particle field caused by the stray electric field is important for evaluating the durability, service safety and performance-based design of the rail transit infrastructure.

Disclosure of Invention

The invention aims to provide a phase field and particle field development and evolution theoretical model of a water-saturated steel-concrete structure under a stray electric field, which is compared with a traditional isothermal adsorption empirical model and takes thermodynamics as a theoretical basis, firstly, initial values and interaction of a cement matrix system lower phase and pore liquid particles are obtained through a Gibbs free energy minimization system and three thermodynamic models based on a pure phase dissolution deposition equilibrium model, a solid solution model (an ideal solid solution and a non-ideal binary solid solution) and a double electric layer complex reaction equilibrium model; and secondly, realizing the coupling of the thermodynamic model and the finite element model by an operator splitting method, and further realizing the calculation of the phase field and the particle field. Therefore, the method provides scientific basis and theoretical model for accurately calculating the pore liquid particle field and the phase field in the concrete under the action of the stray electric field.

The purpose of the invention is realized by the following technical scheme:

a theoretical model for development and evolution of a saturated steel-concrete structure phase field and a particle field in a stray electric field comprises the following thermodynamic processes, transmission equations and coupling relations:

the thermodynamic process is as follows: the determination and interaction of the initial values of the saturated concrete pore liquid particles and the hydration products are realized through thermodynamic calculation;

the transmission equation: (1) describing the transport of particles in the water-saturated concrete pore liquid under the action of a stray electric field by utilizing a Nernst-Planck equation, wherein the transport comprises concentration diffusion of the particles and an electromigration process of ions; (2) calculating the diffusion process of oxygen in concrete by adopting Fick's second law; (3) the nonlinear polarization of the steel-concrete interface under the action of the stray electric field is characterized by a Tafel equation; (4) the consumption of oxygen at the steel-concrete interface under the action of the stray electric field is calculated by a Faraday equation;

coupling relation: (1) the particle concentration in the concrete pore liquid is taken as an intermediate variable, and coupled calculation is realized with a Nernst-Planck equation through an operator splitting algorithm (a sequential non-iterative method); (2) the oxygen diffusion and consumption process is coupled with the cathode electrode reaction process (reduction of oxygen) described by Tafel equation, and an electric field formed by the total electric field density (cathode and anode reaction current density) at the interface and a driving force for the ion electromigration process in the Nernst-Planck equation are obtained.

In the invention, the determination of the initial values of the saturated concrete pore liquid particles and hydration products is obtained based on the thermodynamic calculation of the minimization of the Gibbs free energy of the system according to the chemical analysis result of cement, and the realization of the minimization of the Gibbs free energy of the system comprises the following three aspects: (1) an activity model describing non-ideal behavior of the pore fluid particles; (2) determining a cement hydration thermodynamic database of each reaction Gibbs free energy in the system; (3) and obtaining a hydration kinetic formula of the hydration degree of the cement clinker in a given time.

In the invention, the interaction between the saturated concrete pore liquid particles and hydration products comprises a pure-phase dissolution deposition equilibrium model, a solid solution model (an ideal solid solution model and a non-ideal binary solid solution model) and an electric double layer complex reaction equilibrium model, wherein:

the pure phase type considered by the pure phase dissolution and deposition equilibrium model depends on the type of the adopted cement, and for the portland cement, the pure phase type mainly comprises Friedel salt, Kuzels salt, Portland salt, Hydrotalcite, Monosulpate (four different crystal waters) with different numbers of crystal waters and the like, and can be obtained by thermodynamic calculation;

solid solutions and components thereof considered by the solid solution model depend on the type of adopted cement, for portland cement, the ideal solid solutions mainly comprise AFt ideal solid solutions, C3(AF) S0.84H ideal solid solutions, CSHQ ideal solid solutions, Straeling ideal solid solutions and the like, the non-ideal binary solid solutions mainly comprise AFm non-ideal binary solid solutions and the like, and can be obtained by thermodynamic calculation;

the electric double layer complex reaction equilibrium model is mainly expressed as the adsorption reaction (complex reaction) of the surface sites of the hydrated calcium silicate gel to chloride ions.

In the present invention, the elemental species of the pore liquid particles include: H. o, Al, Ca, Cl, Fe, K, Mg, Na, S and Si.

In the invention, Nernst-Planck equation describing the transport of particles in the water-saturated concrete pore liquid under the action of a stray electric field takes the influence of the connectivity, the tortuosity and the porosity of concrete pores on the ion transport process into consideration.

In the invention, the nonlinear polarization process of the steel bar is formed by three electrode reactions of an iron oxidation process, an oxygen reduction process and a hydrogen evolution process, and the dynamic processes of the three electrode reactions are represented by a Tafel empirical formula, wherein: the coupling between the kinetics of oxygen reduction and the diffusion process described by Fick's second law is achieved by modifying the exchange current density.

In the invention, the adsorption effect of the C-S-H gel on the chloride ions is realized by a double electric layer complex reaction equilibrium model.

Compared with the prior art, the invention has the following advantages:

1. the invention provides a theoretical model which is based on a thermodynamic process and a transmission equation and can reveal the development and evolution essence of an internal phase field and a pore liquid particle field in a steel-concrete structure under the action of a stray electric field, aiming at the space-time distribution of the phase components and the pore liquid particle concentration of concrete under the action of the stray electric field.

2. Compared with the traditional isothermal adsorption empirical model, the method takes thermodynamics as a theoretical basis to consider the interaction between the phase components of the hydration products and the pore liquid ions, and has higher accuracy and wider adaptability for calculating the phase change of the reinforced concrete structure and the transportation of the pore liquid particles which bear stray electric fields under different proportions and different service environments.

3. For the main hydration product of cement, namely calcium silicate hydrate gel (C-S-H), the invention considers the C-S-H of four different calcium-silicon ratios (0.6667, 1.25, 1.33 and 2.25) by introducing a CSHQ ideal solid solution model, and is closer to the real situation compared with a pure phase dissolution deposition equilibrium model adopting a single calcium-silicon ratio.

4. On one hand, the invention considers the adsorption of cement hydration products (CSHQ ideal solid solution, AFt ideal solid solution and AFm non-ideal binary solid solution) to free ions in pore liquid through a solid solution model, and mainly comprises the following steps: k⁺、Na⁺、Ca²⁺、SO₄ ^2-、OH^-Plasma; on the other hand, the calculation of the C-S-H gel on the chloride ion adsorption is realized through an electric double layer complexation reaction equilibrium model.

5. The theoretical model can be used for predicting key information such as the phase change of concrete, the concentration of aggressive ions (such as chloride ions), the concentration of alkali metal ions (such as sodium ions, potassium ions and the like), the dissolution deposition of pH and solid phase components, the generation of new phases and the change trend of the new phases along with time and the like in pore liquid on the surface of the steel bar under the action of a stray electric field, and provides scientific basis for the formulation of a corrosion protection strategy of a reinforced concrete structure bearing the stray electric field of rail transit, performance-based design, later-stage maintenance and reinforcement and the like.

Drawings

FIG. 1 is a schematic view of a reinforced concrete structure subjected to stray electric fields;

FIG. 2 is a mesh subdivision of numerical calculations;

FIG. 3 shows the distribution (60d) of chloride ions in concrete under the action of stray electric fields;

FIG. 4 is the change rule of the average value of the chloride ions of the cathode area and the anode area along with the time;

FIG. 5 is the variation of the average values of potassium ions in the cathode region and the anode region with time;

FIG. 6 shows the time dependence of the average values of the resulting Friedel's salt and Kuzels salt in concrete.

Detailed Description

The technical solution of the present invention is further described below with reference to the accompanying drawings, but not limited thereto, and any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be covered by the protection scope of the present invention.

The invention provides a theoretical model for development and evolution of a saturated steel-concrete structure phase field and a pore liquid particle field under the action of a stray electric field, which comprises the following thermodynamic processes, transport equations and coupling relations:

first, thermodynamic process

The determination and interaction of the initial values of the saturated concrete pore liquid particles and the hydration product phase are realized by a thermodynamic process, wherein: the determination of the initial value is obtained based on thermodynamic calculation of the minimization of Gibbs free energy of the system, and mainly comprises the following three aspects: (1) an activity model describing non-ideal behavior of the pore fluid particles; (2) determining a cement hydration thermodynamic database of each reaction Gibbs free energy in the system; (3) and obtaining a hydration kinetic formula of the hydration degree of the cement clinker in a given time. The interaction includes: a pure-phase dissolution deposition equilibrium model, a solid solution model (ideal solid solution and non-ideal binary solid solution), and an electric double layer complexation reaction equilibrium model.

Two, transport equation

Nernst-Planck equation is used to describe the transport of particles in a water-saturated concrete pore liquid under the action of a stray electric field, and includes concentration diffusion of the particles and an ionic electromigration process.

Three, coupling relation

The thermodynamic process and the Nernst-Planck equation adopt the concentration of pore fluid particles as a coupling variable, and an operator splitting method (a sequential non-iterative method) is adopted to realize coupling calculation. The diffusion and electromigration processes of the pore fluid particles under the action of stray electric fields are simultaneously influenced by the diffusion of oxygen in the concrete and the nonlinear polarization of the steel reinforcement, which are described by the Nernst-Planck equation, wherein: the nonlinear polarization of the reinforcing steel bars is characterized by a Tafel empirical formula; the concentration difference diffusion process of oxygen in concrete is calculated by Fick's second law; the oxygen consumed by the steel bar during the nonlinear polarization process is obtained by the Faraday's law. There is a coupling relationship between the three processes (non-linear polarization of the rebar, diffusion and consumption of oxygen): the rate of consumption of oxygen, described by the Faraday's law, is directly proportional to the cathodic reaction (reduction of oxygen) current density in the nonlinear polarization of the steel reinforcement, while the concentration gradient formed by the consumption of oxygen is the driving force for oxygen diffusion, described by Fick's second law, while the steel reinforcement nonlinear polarization cathodic exchange current density is corrected by the oxygen concentration at the steel-concrete interface.

Specifically, the embodiment is as follows:

according to the provided analysis result of the chemical components of the cement, calculating the components of cement hydration products and pore fluid particles by adopting a Gibbs free energy minimization method of a system shown as a formula 1:

wherein P and C respectively represent that the reaction system consists of P phases and C components, and n_i ^kIs the molar number of component i in the k-th phase of the system, mu_i ^kIs the chemical potential of component i in the kth phase of the system; furthermore, Gibbs free energy is constrained by component mole non-negativity and mass/mole conservation, which can be described by conservation of chemical elements in the reaction system:

wherein, a_ei ^kDenotes the gram atom number of the element e in component i, A_eRepresents the total gram atom number of the element e in the system, N_eIs the number of elements in the system.

The activity formula describing the interaction between concrete pore liquid particles adopts a 'WATEQ' DEBYE-HUKEL formula:

wherein, a_iAnd b_iIs an ion-specific parameter (the magnitude of the value depends on the radius of the ion), the parameters A and B are 0.51 and 0.33 at 25 ℃, z_iIs the number of charges carried by the ion, and I is the ionic strength.

For incompletely hydrated concrete, the hydration kinetics formula (Parrot and Killoh) can be coupled in the above model:

wherein alpha is_i(t) represents the hydration level of the cement at time t; s and S₀Actual specific surface area and reference specific surface area of cement, respectively; r_1,i、R_2,iAnd R_3,iRespectively represents the hydration rates of three stages of nucleation, diffusion and shell formation, and is determined by the hydration degree alpha_i(t) and a series of kinetic empirical parameters; f (w/c) is a correction to the water-cement ratio; beta is a_HIs a correction of humidity; the exponential term is the temperature correction term, T, described by the Arrhenius equation₀Taking 293.15K as a reference temperature; t is the actual temperature in K; r is an ideal gas constant; e_iIs the apparent activation free energy.

The phase composition of the cement hydration product and the concentration of the pore liquid particles obtained in the thermodynamic process are used as initial values for calculating the development and evolution of the concrete phase field and the pore liquid particle field.

Based on the initial values, thermodynamic equilibrium between a pure-phase dissolution deposition equilibrium model, a solid solution model (an ideal solid solution and a non-ideal binary solid solution) and a double electric layer complex reaction equilibrium model and pore liquid is comprehensively considered, and thermodynamic equilibrium between the cement hydration product and the pore liquid particle concentration is calculated again. Wherein, the calculation of the equilibrium of dissolution and deposition of pure phase is based on the equilibrium constant of reaction, and the relationship with the Gibbs free energy is as follows:

wherein Δ_rG₀Is the reaction Gibbs free energy, Δ_fG₀Is the standard for generating Gibbs free energy, v_iIs the stoichiometric coefficient and K is the equilibrium constant of the reaction.

The type of pure phase considered depends on the type of cement chosen, resulting from the thermodynamic calculations described above. For ordinary portland cement, it mainly consists of: friedel's salts, Kuzels salts, Portlandite, Hydrotalcite, Monosulnote (with crystal water in band 4), etc., and the equilibrium constants of the phase dissolution sedimentation reactions are derived from the CEMDATA18 cement hydration thermodynamic database.

Unlike pure phase, the concept of activity is introduced for solid solutions in the system, and the activity of the solid solution component is defined by the following formula:

wherein the content of the first and second substances,which represents the activity of the solid solution component,is the molar fraction of component p in solid solution,the activity coefficient is 1 for an ideal solid solution, and the calculation formula for the activity coefficient of a non-ideal binary solid solution is as follows:

wherein λ is₁And λ₂Is the activity coefficient of component 1 and component 2, respectively, and for non-ideal binary solid solutions the sum of the mole fractions of component 1 and component 2 is 1, i.e. x₁+x₂＝1；a₀And a₁Is a dimensionless constant that depends on the magnitude of the excess gibbs free energy of the solid solution component.

Likewise, the type of solid solution and of the components of the system considered also depends on the type of cement used, and for portland cements mainly comprises: CSHQ ideal solid solutions, AFt ideal solid solutions, C3(AF) S0.84H solid solutions, Straelingite solid solutions, and AFm non-ideal binary solid solutions, among others. The equilibrium constants for the components of the solid solution were taken from the CEMDATA18 database.

A double-electric-layer surface complexation equilibrium model is used for describing the adsorption effect (complexation reaction) of the surface sites of the C-S-H gel on the chloride ions, wherein the double-electric-layer model adopts a Gouy-Chapman model.

The transportation process of the particles in the water-saturated concrete pore liquid is calculated by a Nernst-Planck equation:

wherein, c_iDenotes the concentration of ion i in the pore liquid, t is time, J_iRepresents the diffusion flux of ion i, including both diffusion and electromigration:

wherein D is_iRepresents the diffusion coefficient of ion i; z is a radical of_iIs the charge number of ion i; f is the Faraday constant equal to 96485C/mol; phi is a_lIs the electrolyte potential.

Furthermore, the ions in the pore liquid satisfy the principle of electrical neutrality:

D_ithe influence of the porosity of the concrete and the tortuosity tau and the penetration gamma of the pores is shown as the formula (12):

D_i＝D_{i_free}·f(ρ)·τ·γ (12)；

wherein D is_{i_free}The diffusion coefficient of ions in water can be obtained from a PHREEQC.data database, the connectivity and the tortuosity tau gamma of pores are obtained by a rapid chloride ion mobility coefficient method (RCM), and the correction formula of the porosity is as follows:

where ρ isPorosity of the concrete; rho₀Represents the initial porosity of the concrete; the porosity is obtained by the volumes of hydration products and pore liquid obtained by the above thermodynamic calculations and the volumes of cement, aggregate and water initially:

wherein, V_cement,tRepresents the volume of cement at time t; v_solution,tRepresents the volume of the solution at time t; v_hydrates,tRepresents the volume of the muddy water gasification product at the time t; v_{coarseaggregate}And V_{fineaggregate}The volumes of coarse aggregate and fine aggregate are indicated, respectively.

In the formula (10), phi_lRepresenting the electrolyte potential, is the driving force of electromigration of the particles of the pore liquid under the action of a stray electric field, and the directional movement of the particles in the pore liquid forms the electrolyte current density i_lIts relationship to diffusion flux:

for electrode current density i_sObeying ohm's law and the current conservation equation:

wherein σ_sRepresents the electrode conductivity, phi_sRepresenting the electrode potential.

At the steel-concrete interface, the electrochemical reaction kinetics process of the steel bar is described by Tafel empirical formula, and comprises an iron oxidation process, an oxygen reduction process and a hydrogen evolution process:

wherein i_a/cIs the anodic/cathodic reaction current density i_0,a/cIs the anode/cathode exchange current density, eta is the overpotential, A_a/cIs the Tafel slope; the exchange current density for the cathodic oxygen reduction reaction was corrected by the oxygen concentration at the electrode interface:

wherein, c_interfaceRepresents the concentration of oxygen at the interface; c. C_bulkIndicating the concentration of oxygen in the bulk solution.

The electrode and electrolyte current densities are related to the current densities determined by the cathode and anode reaction kinetics equation at the steel-concrete interface as follows:

n·i_l＝i_a+i_c (20)；

n·i_s＝-(i_a+i_c) (21)；

where n is a normal vector.

The distribution of oxygen in concrete depends on the consumption rate and diffusion rate of oxygen, wherein the mass of consumption of oxygen is given by the Faraday formula:

where Δ m is the mass of oxygen consumption; m represents the relative molecular mass of oxygen; n represents the number of electrons consumed by the reaction.

The diffusion of oxygen in concrete under a concentration gradient is described by Fick's second law:

wherein, c_O2Represents the concentration of oxygen; d_O2Representing the diffusion coefficient of oxygen.

The above control equations (9) - (12)) are solved by a Newton-Raphson nonlinear method (Newton-Raphson method) using a finite element method through the PARDISO solver in comsollmultyphysics.

The thermodynamic calculation process and the finite element particle transport calculation process take the particle concentration as an intermediate variable, and are coupled by an operator splitting method, so that a theoretical model of development and evolution of a steel-concrete structure phase field and a pore liquid particle field under the action of a stray electric field is formed.

Example (b):

in fig. 1, two ends of the upper surface of the concrete are assumed to be a flowing point and a flowing point of the stray current respectively, and the lower part is the steel bar.

(1) According to the above theoretical model of thermodynamics, the initial values of the element concentrations of the cement hydration product and the pore fluid can be obtained by using the portland cement shown in table 1 through the above theoretical model (as shown in tables 2 and 3). Further thermodynamic equilibrium calculations were performed on the values in tables 2 and 3, and the resulting ion concentrations were stored in a matrix form, where the pore fluid particles considered in this example included: OH group^-、AlO_2-、CaOH⁺、Ca²⁺、CaSiO₃、CaSO₄、Cl^-、K⁺、KOH、KSO₄ ^-、Na⁺、NaOH、NaSO₄ ^-、SO₄ ^2-、HSiO₃ ^-、SiO₃ ^2-. The diffusion coefficient of the chloride ions in the concrete obtained by the RCM method is 9.2X 10^-12m²Data, and obtaining the diffusion coefficient of the particles in concrete according to the diffusion coefficient of the particles in an aqueous solution given by PHREEQC; the initial porosity was 0.08467 based on thermodynamic calculations. Storing the ion concentration, diffusion coefficient and pore information obtained by the calculation in a matrix form, and using the stored ion concentration, diffusion coefficient and pore information as a model for next calculationIs started.

TABLE 1 Cement chemical analysis results (%)

TABLE 2 thermodynamic calculation results of the element composition and concentration of cement hydration pore liquid

TABLE 3 thermodynamic calculations of phase composition of cement hydrates

(2) And establishing a numerically-calculated geometric model based on COMSOL, wherein the mesh division of the geometric model is shown in FIG. 2, the complete mesh comprises 12176 domain units and 1611 boundary units, the concrete part is divided by adopting a free triangular unstructured mesh, and the steel bar part is divided by adopting a structured mesh. Because the probability of concrete phase change and change of pore liquid ion concentration occurring at the steel bar-concrete interface is higher, and the potential threat to the structural durability is higher, in order to more accurately analyze the change situation of the physical quantity, the grid at the steel-concrete interface is encrypted.

(3) And calling COMSOL based on MATLAB, assigning the solution stored in the form of matrix in the step (1) to each unit grid node in the COMSOL geometric model in a difference function mode, and solving the finite element model under a given time step, wherein the time step in the example is set to be 10 days. The calculation results (particle concentrations) were converted into element concentrations, which were saved in matrix form by MATLAB as initial values for the next calculation.

(4) And (4) calling PHREEQC based on MATLAB, assigning the obtained solution in the step (3) to PHREEQC, and taking the solution as an initial value to perform thermodynamic calculation. Similarly, the calculated ion concentration, diffusion coefficient, pore information, and the like are stored in a matrix form as initial values for the next calculation.

(5) Repeating (3) and (4) until the calculated target time period is reached, the target time period set in the present embodiment is 60 days.

(6) And (4) carrying out post-processing on the numerical calculation result to obtain the concentration of particles at the steel-concrete interface and the change condition of solid phase components.

3-6 are partial numerical results in this example, it can be found that under the action of the stray electric field, the concentration of chloride ions in the cathode region is reduced and enriched in the anode region, and at about 60d, under the combined action of concentration gradient, electromigration and C-S-H surface complexation, the concentration of chloride ions in the cathode and anode regions gradually levels; the concentration of alkali metal ions (potassium ions for example) increases rapidly in the cathode region and decreases slowly in the anode region, and this trend includes, in addition to concentration gradients and electromigration, the dissolution and deposition processes of the NaSiOH component in the CSHQ solid solution; due to the continuous enrichment of chloride ions by stray electric fields, Friedel's salts and Kuzels salts may be produced in the concrete, as shown in FIG. 6, which are the average concentrations of Friedel's salts and Kuzels salts in the concrete, respectively, and it was found that the Kuzels salts are produced at day 10 and the Friedel's salts are produced at day 30.