Prediction method of chloride ion content in concrete structures after surface coating treatment

Abstract

An embodiment of the present application provides a method for predicting the chloride ion content inside a concrete structure after surface coating treatment. The method obtains relevant parameters of the concrete structure after surface coating treatment and the experimental environment, determines the free chloride ion erosion depth inside the concrete structure and the free chloride ion content in the chemically bound chloride ion saturation zone based on the relevant parameters, a first boundary condition, and a second boundary condition. The method analyzes the chloride ion transport mechanism in the surface-treated concrete, considers the effects of chemically bound chloride ions and physically adsorbed chloride ions in the concrete, sets boundary conditions, and uses a series solution to determine the chloride ion penetration depth and free chloride ion content distribution inside the coated concrete structure. This method at least solves the problem of how to efficiently analyze and predict the chloride ion content inside the coated concrete structure in the related art, making the prediction more accurate and greatly reducing the amount of calculation.

Description

Technical Field

[0001] The present application relates to the technical field of surface coating treatment of concrete structures, and in particular to a method for predicting the chloride ion content inside a concrete structure after surface coating treatment. Background Art

[0002] Most of my country's nuclear power plants are built in coastal areas. Concrete structures are exposed to chloride environments for a long time. Excessive chloride ion content may cause depassivation of steel bars and electrochemical corrosion, thereby affecting the durability and safety of the structure. Coating protection measures can effectively reduce the intrusion rate of chloride ions, thereby significantly improving the durability and service life of concrete structures. Based on this engineering background, relevant durability monitoring needs to consider the impact of the coating interface. For example, the distribution of chloride ions will differ from that of conventional concrete structures due to the different diffusion coefficients between the coating interface and concrete. Therefore, studying the chloride ion distribution in concrete structures after coating treatment is of great value and significance.

[0003] Considering the complexity of the concrete structure after coating treatment, the use of numerical solutions for chloride ion diffusion analysis would be very time-consuming and almost impossible for reliability analysis.

[0004] In the current related technologies, there is no reasonable solution to the problem of how to efficiently analyze and predict the chloride ion content inside concrete structures after coating treatment. Summary of the Invention

[0005] The embodiment of the present application provides a method for predicting the chloride ion content inside a concrete structure after surface coating treatment, so as to at least solve the problem in the related art of how to efficiently analyze and predict the chloride ion content inside a concrete structure after coating treatment.

[0006] According to one embodiment of the present application, a method for predicting the chloride ion content inside a concrete structure after surface coating treatment is provided, comprising: obtaining relevant parameters of the concrete structure after surface coating treatment and the experimental environment, wherein the concrete structure after surface coating treatment includes a surface treatment layer and a concrete layer, and the relevant parameters include: the thickness of the surface treatment layer h1, the chloride ion diffusion coefficient D of the surface treatment layer at time t0 10 and the chloride ion diffusion coefficient D of the concrete layer 20 , a first empirical parameter p and a second empirical parameter q determined according to the type of concrete admixture, a chloride ion intrusion time t after surface coating treatment, an absolute temperature T, an atmospheric pressure P, a gas constant R, an activity constant ν, and a total porosity ε of the concrete layer p , Chloride ion content of exposed surface C s , chemically bound chloride ion content C bc, the exposed surface is the surface of the surface treatment layer exposed to the air; according to the relevant parameters, the first boundary condition and the second boundary condition, the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone inside the concrete structure are determined. f , wherein the first boundary condition is: at the free chloride ion corrosion depth ξ(t), the free chloride ion content is zero, and the second boundary condition is: the free chloride ion content on the exposed surface is equal to the chloride ion content C on the exposed surface. s Equal; wherein the total chloride ion content C at any point inside the concrete structure t It consists of three parts: chemically bound chloride ion C bc , physical adsorption of chloride ions C bp and free chloride ions C f .

[0007] In one embodiment, the change of the chloride ion diffusion coefficient D2(t) of the concrete layer over time t is expressed by the following formula:

[0008]

[0009] The change of the chloride ion diffusion coefficient D1(t) of the surface treatment layer with time t is expressed by the following formula:

[0010]

[0011] Among them, t0 is set to 28 days.

[0012] In one embodiment, the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone are determined according to the relevant parameters, the first boundary condition and the second boundary condition. f ,include:

[0013] According to the first boundary condition: at the chloride ion corrosion depth ξ(t), the free chloride ion content is zero: C f | x＝ξ(t) =0(3); x is the linear distance between the chloride ions and the exposed surface;

[0014] Assuming that the pore solution in the concrete layer is an ideal dilute solution, the calculation formula for the chloride ion chemical potential of the pore solution in the chemically bound chloride ion saturated zone can be obtained. Combined with the calculation method of the free chloride ion flow, the local chloride ion mass conservation equation at the free chloride ion corrosion depth ξ(t) is obtained:

[0015]

[0016] Among them, ε pis the total porosity of concrete, D2=νRT / ε p is the chloride ion diffusion coefficient of the concrete layer determined according to environmental conditions;

[0017] According to the relevant parameters, the first boundary condition and the second boundary condition, the analytical method or the numerical method is used to solve the formula (3) and the formula (4) to determine the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone. f .

[0018] In one embodiment, the analytical method or numerical method is used to solve formula (3) and formula (4) to determine the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bound chloride ion saturation zone. f ,include:

[0019] The total chloride ion content C at any point inside the concrete t for:

[0020] C t =C bc +C bp +C f (5)

[0021] For the ion linear binding model, C bp with C f The relationship can be expressed as a linear equilibrium:

[0022] C bp =RC f (6)

[0023] Under the premise that the pore solution in concrete is an ideal dilute solution, according to the law of conservation of chloride ion mass, the chloride ion content C is obtained. f About the countdown of time:

[0024]

[0025] The initial conditions of formula (7) are:

[0026] C f | t＝0 =C0 (8)

[0027] Set the second boundary condition, on the exposed surface, the chloride ion content is:

[0028] C f | x＝0 =C s (9)

[0029] Set the total exposure time to τ m , the interval [0,τ m] is divided into m equal-length subintervals, where τ j =(j-1)τ m / m, for the jth subinterval [τ j ,τ j+1 ], the chloride ion diffusion coefficients of the surface treatment layer and concrete are:

[0030]

[0031] For the jth subinterval [τ j ,τ j+1 ], the penetration depth of free chloride ions is h 2j , according to boundary conditions (9), (3) and separation of variables method, the free chloride ion content is:

[0032]

[0033] Where the step function H(x) is:

[0034]

[0035] Eigenvalue β n Satisfies the following characteristic equation

[0036] λ n2 cos(λ n1 h1)sin(λ n2 h 2j )+λ n1 sin(λ n1 h1)cos(λ n2 h 2j )=0 (13)

[0037] Where λ ni (i=1,2) is defined as:

[0038]

[0039] Characteristic function g n (x) is

[0040]

[0041] It is easy to verify from formula (15) that is a non-zero L 2 The orthogonal function of the module is:

[0042]

[0043]

[0044] Substituting the initial conditions into equation (11) we can obtain E n:

[0045]

[0046] In formula (18), C0(x)=C0;

[0047] For diffusion problems, the penetration depth of free chloride ions is proportional to the square root of time:

[0048]

[0049] Substituting Equation (11) into Equation (4) can jointly obtain the free chloride ion penetration depth ξ(t), and then substituting ξ(t) back into Equation (11) to obtain the free chloride ion content C f .

[0050] In one embodiment, C bc Take it as a constant, the chloride ion diffusion coefficient D of the surface treatment layer at time t0 10 and the chloride ion diffusion coefficient D of the concrete layer 20 The concrete structure is measured in real time by the NEL test method.

[0051] The present invention provides a method for predicting the chloride ion content inside a concrete structure after surface coating treatment, by obtaining relevant parameters of the concrete structure after surface coating treatment and the experimental environment, and determining the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bound chloride ion saturation zone according to the relevant parameters, the first boundary condition and the second boundary condition. f By analyzing the chloride ion transmission mechanism in surface-treated concrete, considering the influence of chemically bound chloride ions and physically adsorbed chloride ions in concrete, and setting boundary conditions, the chloride ion penetration depth and free chloride ion content distribution inside the concrete structure after coating treatment are determined by series solution, so as to at least solve the problem of how to efficiently analyze and predict the chloride ion content inside the concrete structure after coating treatment in related technologies, making the prediction more accurate and greatly reducing the amount of calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0053] Figure 1 This is a schematic diagram of an optional concrete structure treated with a surface coating according to an embodiment of the present application;

[0054] Figure 2 is a schematic diagram of an optional free chloride ion diffusion coefficient changing with time in an embodiment of the present application;

[0055] Figure 3 1 is a schematic diagram of the relationship between the free chloride ion content and the relative exposure surface distance according to an optional embodiment of the present application;

[0056] Figure 4 It is an optional analysis and calculation flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0057] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0058] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the embodiments of the present application have the same meaning as commonly understood by those of ordinary skill in the art to which the present application belongs.

[0059] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0060] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0061] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0062] Figure 1 Schematic diagram of concrete structure treated with surface coating, such as Figure 1 As shown, the concrete structure can be regarded as a double-layer composite material consisting of a surface treatment layer (i.e. the aforementioned "coating") and a concrete layer.

[0063] Driven by the chloride ion concentration gradient, chloride ions in the environment continuously invade into the concrete. They first react chemically with tricalcium aluminate in cement and hydrated calcium aluminate in hydration products to form Friedel salt, forming chemically bound chloride ions C bc Once the chemically bound chloride ions at a certain point in the concrete reach saturation, the free chloride ions continue to diffuse forward. During the diffusion process, a part of the chloride ions are adsorbed on the surface of the hydration product to form physically adsorbed chloride ions C bp The rest is free chloride ions C f In this way, chloride ion transport forms two different areas in concrete, one is the chemically bound chloride ion saturation area, and the other is the chemically bound chloride ion capture area. The dividing line between them is the penetration depth of free chloride ions ξ(t). The total chloride ion content C at any point inside the concrete t It consists of three parts: chemically bound chloride ions, physically adsorbed chloride ions and free chloride ions, namely

[0064] C t =C bc +C bp +C f (5)

[0065] D1(t) and D2(t) are the chloride ion diffusion coefficients of the surface treatment layer and concrete, respectively. They are both functions of the exposure time t after coating treatment, h1 is the thickness of the surface treatment layer, and h2 is the penetration depth of free chloride ions. The change of the chloride ion diffusion coefficient of concrete with time t can be expressed as

[0066]

[0067] Where t0 is usually taken as 28d, t is the exposure time, D 20 is the chloride ion diffusion coefficient of concrete at time t0, and p is an empirical parameter selected according to the type of concrete admixture. D1(t) can be assumed to be an exponential function of exposure time, but after 15 years, the surface treatment layer fails and its chloride ion diffusion coefficient is the same as that of concrete, that is,

[0068]

[0069] Where D 10 is the chloride ion diffusion coefficient of the surface treatment layer at time t0, and q is an empirical parameter that can also be selected according to the admixture type.

[0070] The purpose of the present invention is to provide a method for determining the penetration depth ξ(t) and the free chloride ion content C of a concrete structure after coating. f The calculation method, such as Figure 4 As shown, it includes: Step 1: Determine relevant parameters; Step 2: Determine the invasion depth ξ(t) and the free chloride ion content C f Analytical expression; Step 3: Use the discrete diffusion coefficient D(t) method to obtain the expression of free chloride ion content at different depths; Step 4: Use the analytical solution expression to calculate ξ(t) and C f Solve it.

[0071] Step 1: Determine the relevant parameters of the concrete material and the experimental environment, including the thickness of the surface treatment layer h1, the chloride ion diffusion coefficient D of the surface treatment layer at time t0 10 and the chloride ion diffusion coefficient D of concrete 20 (can be tested by the NEL method), empirical parameter p determined according to the type of concrete admixture, parameter q (determined based on the fact that the chloride ion diffusion coefficient of the surface treatment layer is the same as that of the concrete after 15 years. These two parameters generally vary with the concrete mix ratio. For the same type of concrete, they are constants. In actual engineering, they can be determined through experiments), chloride ion invasion time t, absolute temperature T, atmospheric pressure P, gas constant R, activity constant ν, total porosity of concrete ε p , Chloride ion content of exposed surface C s (Changed to "chloride ion content of exposed surface", which needs to be determined according to the engineering conditions of the concrete structure surface.) Chemically bound chloride ion content C bc (According to the irreversible nature of chemically bonded chloride ions, C bc (taken as a constant)

[0072] Step 2: At the chloride ion erosion depth ξ(t), the free chloride ion content is zero.

[0073] C f | x＝ξ(t) =0 (4)

[0074] Assuming that the pore solution in concrete is an ideal dilute solution, the calculation formula for the chloride ion chemical potential of the pore solution in the chemically bound chloride ion saturated zone can be obtained. Combined with the calculation method of the free chloride ion flow rate, the local chloride ion mass conservation equation at the front end of free chloride ion invasion (chloride ion corrosion depth ξ(t)) is obtained, that is, formula (5)

[0075]

[0076] Where, ε p is the total porosity of concrete, D2=νRT / ε p is the chloride ion diffusion coefficient of concrete determined according to environmental conditions.

[0077] In this way, by solving equations (4) and (5) using analytical or numerical methods, we can obtain the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bound chloride ion saturation zone. f .

[0078] Step 3: For the ion linear binding model, C bp with C f The relationship can be expressed as a linear equilibrium:

[0079] C bp =RC f (6)

[0080] Under the premise that the pore solution in concrete is an ideal dilute solution, according to the law of conservation of chloride ion mass, the chloride ion content C is obtained. f About the countdown of time:

[0081]

[0082] The initial condition of formula (7) is

[0083] C ft＝0 =C0 (8)

[0084] On the exposed surface, the chloride ion content is:

[0085] C f | x＝0 =C s (9)

[0086] Let the total exposure time be τ m , the interval [0,τ m] is divided into m equal-length subintervals, such as Figure 2 As shown, where τ j =(j-1)τ m / m, for the jth subinterval [τ j ,τ j+1 ], the chloride ion diffusion coefficients of the surface treatment layer and concrete are:

[0087]

[0088] For the jth subinterval [τ j ,τ j+1 ], the penetration depth of free chloride ions is h 2j , based on boundary conditions (9), (4) and separation of variables method, the free chloride ion content can be expressed as:

[0089]

[0090] Where the step function H(x) is:

[0091]

[0092] Eigenvalue β n Satisfies the following characteristic equation:

[0093] λ n2 cos(λ n1 h1)sin(λ n2 h 2j )+λ n1 sin(λ n1 h1)cos(λ n2 h 2j )=0 (13)

[0094] Where λ ni (i=1,2) is defined as

[0095]

[0096] Characteristic function g n (x) is

[0097]

[0098] It is easy to verify from formula (15) that is a non-zero L 2 The orthogonal function of the module, that is

[0099]

[0100]

[0101] Substituting the initial conditions into equation (11) we can obtain E n

[0102]

[0103] In formula (17), C0(x)=C0.

[0104] Step 4: For the diffusion problem, the penetration depth of free chloride ions is proportional to the square root of time. Note that:

[0105]

[0106] Substituting Equation (11) into Equation (5) can jointly obtain the free chloride ion penetration depth ξ(t), and then substituting ξ(t) back into Equation (11) to obtain the free chloride ion content C f .

[0107] The technical solution and effectiveness of the present invention are further illustrated below by comparing with experimental results.

[0108] The experiment was a salt water immersion test of Wacker silane-impregnated concrete. The actual mix ratio of the containment vessel (4RX) of Fuqing Nuclear Power Unit 4 was selected. Details are shown in Table 1.

[0109] Table 1

[0110]

[0111] Unit: kg / m 3

[0112] Three concrete specimens with a diameter of (100±5) mm and a height of at least 45 mm were cast. After one day, the specimens were demolded and placed in a standard curing room for 28 days. After curing, each specimen was coated with the same amount of silane, maintaining the silane-impregnated surface intact, and then dried in an oven at (40±5)°C for 48 hours. The specimens were removed and split axially in half using a pressure testing machine. A water-based fugitive dye was sprayed onto the split section and allowed to stand for 15 minutes. The silane impregnation depth in the non-dye-absorbing areas was measured using a vernier caliper. At least five test points were evenly selected along the length of the specimen test surface. The average Wacker silane impregnation depth was found to be 2.17 mm, indicating a surface treatment layer thickness of h1 = 2.17 mm.

[0113] Three cylindrical concrete specimens with a diameter of 100 mm and a height of 200 mm were cast, demolded after one day, and placed in a standard curing room for 28 days. After curing, six 50 mm high cylinders were cut out from the center of the specimens. Three of these were used to measure the chloride ion diffusion coefficient of ordinary concrete, and the remaining three were used to measure the chloride ion diffusion coefficient of silane-impregnated concrete. The chloride ion diffusion coefficient of ordinary concrete was measured using the resistivity method (NEL method) and was found to be 1.702×10-12 m 2 / s, and the chloride ion diffusion coefficient of silane-impregnated concrete is 1.305×10 -12 m 2 / s, so the chloride ion diffusion coefficient of the surface silane impregnation layer can be calculated to be 2.125×10 -13 m 2 / s.

[0114] Cement slurry samples with the same cement replacement rate of fly ash as in Table 1 and a water-cement ratio of 0.365 were cast. After curing for 28 days, the samples were crushed and several fragments were taken for grinding and sieving. The sieved cement slurry powder was placed in a Yatai LD-2000 intelligent electric vacuum drying oven for vacuum drying for 4 days. After drying, it was placed in a sealed bag and placed for 7 days. Then 6g of cement slurry powder was taken out and immersed in 30ml of NaCl solution, and soaked in solutions with different salt concentrations for 30 days. Finally, the chloride ion concentration in the solution was titrated to obtain the bound chloride ion content. After numerical analysis, it was found that the chemically bound chloride ion content in concrete is C bc =0.1819%, the ratio of physically adsorbed chloride ion content to free chloride ion content is C bp / C f =0.3412.

[0115] Three 100 mm × 90 mm × 50 mm specimens were prepared for the concrete mix proportions shown in Table 1 and coated with Wacker silane. The specimens were then placed in a standard curing room for 58 days. The specimens were removed from the curing room and sealed with epoxy resin on all sides except the silane-impregnated surface. The specimens were then immersed in a 3% NaCl solution for 90 days. The free chloride ion content at each penetration depth was determined by grinding. The results are shown in Table 1. Figure 3 Using the above-measured values of Wacker silane impregnation layer thickness, surface impregnation layer and concrete chloride ion diffusion coefficient, chemically bound chloride ion content, and the ratio of physically adsorbed chloride ion content to free chloride ion content, the series solution proposed in this report was applied to predict the free chloride ion content at each point in the concrete. The results are shown in the figure below. Figure 3 shown.

[0116] Depend on Figure 3 It can be seen that the theoretical predictions are in good agreement with the experimental results, with a correlation coefficient of 0.9835, which preliminarily indicates that the series solution can be used to analyze chloride ion diffusion in surface-treated concrete. Figure 3It also shows that there is an obvious turning point in the free chloride ion content curve at the interface between the surface silane impregnated layer and the concrete. On the left side of the turning point, due to the small chloride ion diffusion coefficient of the silane impregnated layer, the free chloride ion content decreases rapidly, while on the right side of the turning point, the chloride ion diffusion coefficient of the concrete is relatively large and the free chloride ion content decreases slowly, indicating that silane impregnation can greatly reduce the free chloride ion content on the interface layer, thereby improving the service life of coastal concrete structures.

[0117] It should be noted that the above description is merely a preferred embodiment of the present application and is not intended to limit the present application. The technical features in the above embodiments may be combined in any manner. For those skilled in the art, the present application may be subject to various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for predicting the chloride ion content inside a concrete structure after surface coating treatment, characterized in that: include: Obtain relevant parameters of the concrete structure after surface coating treatment and the experimental environment, wherein the concrete structure after surface coating treatment includes a surface treatment layer and a concrete layer, and the relevant parameters include: the thickness of the surface treatment layer h1, the chloride ion diffusion coefficient D of the surface treatment layer at time t0 10 and the chloride ion diffusion coefficient D of the concrete layer 20 , a first empirical parameter p and a second empirical parameter q determined according to the type of concrete admixture, a chloride ion intrusion time t after surface coating treatment, an absolute temperature T, an atmospheric pressure P, a gas constant R, an activity constant v, and the total porosity ε of the concrete layer p , Chloride ion content of exposed surface C s , chemically bound chloride ion content C bc , the exposed surface is the surface of the surface treatment layer exposed to the air; Determine the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone within the concrete structure according to the relevant parameters, the first boundary condition and the second boundary condition. f , wherein the first boundary condition is: at the free chloride ion corrosion depth ξ(t), the free chloride ion content is zero, and the second boundary condition is: the free chloride ion content on the exposed surface is equal to the chloride ion content C on the exposed surface. s equal; The total chloride ion content C at any point inside the concrete structure is t It consists of three parts: chemically bound chloride ion C bc , physical adsorption of chloride ions C bp and free chloride ions C f ; The free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone are determined according to the relevant parameters, the first boundary condition and the second boundary condition. f ,include: According to the first boundary condition: at the chloride ion corrosion depth ξ(t), the free chloride ion content is zero: C f | x＝ξ(t) =0 (3); Assuming that the pore solution in the concrete layer is an ideal dilute solution, the calculation formula for the chloride ion chemical potential of the pore solution in the chemically bound chloride ion saturated zone can be obtained. Combined with the calculation method of the free chloride ion flow, the local chloride ion mass conservation equation at the free chloride ion corrosion depth ξ(t) is obtained: Among them, ε p is the total porosity of concrete, D2=νRT / ε p is the chloride ion diffusion coefficient of the concrete layer determined according to environmental conditions; x is the linear distance of the chloride ion relative to the exposed surface; According to the relevant parameters, the first boundary condition and the second boundary condition, the analytical method or the numerical method is used to solve the formula (3) and the formula (4) to determine the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bonded chloride ion saturation zone. f .

2. The method according to claim 1, characterized in that The change of chloride ion diffusion coefficient D2(t) of the concrete layer with time t is expressed by the following formula: The change of the chloride ion diffusion coefficient D1(t) of the surface treatment layer with time t is expressed by the following formula: Among them, t0 is set to 28 days.

3. The method according to claim 2, characterized in that The analytical method or numerical method is used to solve formula (3) and formula (4) to determine the free chloride ion corrosion depth ξ(t) and the free chloride ion content C in the chemically bound chloride ion saturation zone. f ,include: The total chloride ion content C at any point inside the concrete t for: C t =C bc +C bp +C f (5) For the ion linear binding model, C bp with C f The relationship can be expressed as a linear equilibrium: C bp =RC f (6) Under the premise that the pore solution in concrete is an ideal dilute solution, according to the law of conservation of chloride ion mass, the chloride ion content C is obtained. f About the countdown of time: The initial conditions of formula (7) are: C f | t＝0 =C0(8) Set the second boundary condition, on the exposed surface, the chloride ion content is: C f | x＝0 =C s (9) Set the total exposure time to τ m , the interval [0,τ m ] is divided into m equal-length subintervals, where τ j =(j-1)τ m / m, for the jth subinterval [τ j ,τ j+1 ], the chloride ion diffusion coefficients of the surface treatment layer and concrete are: For the jth subinterval [τ j ,τ j+1 ], the penetration depth of free chloride ions is h 2j , according to boundary conditions (9), (3) and separation of variables method, the free chloride ion content is: Where the step function H(x) is: Eigenvalue β n Satisfies the following characteristic equation l n2 cos(λ n1 h1)sin(λ n2 h 2j )+λ n1 sin(λ n1 h1)cos(λ n2 h 2j )=0 (13) Where λ ni (i=1,2) is defined as: Characteristic function g n (x) is It is easy to verify from formula (15) that is a non-zero L 2 The orthogonal function of the module is: Substituting the initial conditions into equation (11) we can obtain E n : In formula (18), C0(x)=C0; For diffusion problems, the penetration depth of free chloride ions is proportional to the square root of time: Substituting Equation (11) into Equation (4) can jointly obtain the free chloride ion penetration depth ξ(t), and then substituting ξ(t) back into Equation (11) to obtain the free chloride ion content C f .

4. The method according to claim 1, wherein C bc Take it as a constant, the chloride ion diffusion coefficient D of the surface treatment layer at time t0 10 and the chloride ion diffusion coefficient D of the concrete layer 20 The concrete structure is measured in real time by the NEL test method.

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