阅读说明：本技术 混凝土细观氯离子扩散系数预测方法 (Concrete mesoscopic chloride ion diffusion coefficient prediction method ) 是由 龙武剑 冯甘霖 刘铁军 李龙元 叶涛华 郉锋 于 2019-07-30 设计创作，主要内容包括：本发明揭示了一种混凝土细观氯离子扩散系数预测方法,包括获取混凝土中孔结构信息、孔隙率以及孔径分布；通过微观成像技术结合孔隙率以及孔径分布确定混凝土中骨料体积分布,构建所述混凝土的二维细观结构；在所述二维细观结构的基础上确定混凝土的孔隙表面离子浓度及分布；根据质量守恒定律、离子浓度、离子流量、离子表观扩散系数以及离子带电量等,构建多离子传输模型；根据定律所述多离子传输模型计算混凝土中氯离子传输浓度分布；根据氯离子传输浓度分布计算混凝土中氯离子扩散系数。本发明在预测混凝土氯离子扩散系数时,考虑了混凝土微、细观结构以及表面离子对氯离子扩散的影响,较现有的电加速测试方法更准确、也更具科学性。(The invention discloses a method for predicting a mesoscopic chloride ion diffusion coefficient of concrete, which comprises the steps of obtaining the information of a pore structure, the porosity and the pore size distribution of the concrete; determining the volume distribution of aggregates in the concrete by combining a microscopic imaging technology with porosity and pore size distribution, and constructing a two-dimensional microscopic structure of the concrete; determining the concentration and distribution of ions on the surface of the pores of the concrete on the basis of the two-dimensional microscopic structure; constructing a multi-ion transmission model according to a mass conservation law, ion concentration, ion flow, an ion apparent diffusion coefficient, ion charge and the like; calculating the transmission concentration distribution of chloride ions in the concrete according to the law and the multi-ion transmission model; and calculating the diffusion coefficient of the chloride ions in the concrete according to the transmission concentration distribution of the chloride ions. The method considers the influence of micro and microscopic structures of the concrete and surface ions on the diffusion of the chloride ions when predicting the diffusion coefficient of the chloride ions of the concrete, and is more accurate and scientific compared with the conventional electric acceleration test method.)

1. A concrete mesoscopic chloride ion diffusion coefficient prediction method is characterized by comprising the following steps:

Acquiring pore structure information of a microstructure in concrete;

Determining the porosity and pore size distribution of cement slurry in the concrete according to the pore structure information;

Determining the volume distribution of the aggregates in the concrete by combining a microscopic imaging technology with porosity and pore size distribution, and constructing a two-dimensional microscopic structure of the concrete based on an aggregate random distribution model;

determining the surface ion concentration of the concrete according to the two-dimensional microscopic structure; constructing a multi-ion transmission model based on Nernst-Planck/Poisson equation set according to ion concentration, ion flow, ion apparent diffusion coefficient and ion charge;

Calculating the transmission concentration distribution of chloride ions in the concrete according to the mass conservation law and the multi-ion transmission model;

And calculating the diffusion coefficient of the chloride ions in the concrete according to the transmission concentration distribution of the chloride ions.

2. The method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to claim 1, wherein said step of determining the porosity and pore size distribution of the cement slurry in said concrete based on said pore structure information comprises:

and measuring the porosity and pore size distribution of the cement slurry in the concrete by a mercury intrusion method according to the pore structure information of the microstructure.

3. The method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to claim 1, wherein the step of determining the volume distribution of the aggregates in the concrete by using a microscopic imaging technique comprises:

And determining the volume distribution of the aggregate in the concrete by adopting a scanning electron microscope technology.

4. The method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to claim 1, wherein the multi-ion transmission model is as follows:

Formula (1)

Wherein J_kIs the ion flux, D_kIs the apparent diffusion coefficient of ion, C_kis the ion concentration, Z_kF is 96480C/mol, faraday constant, Φ is local potential, R is 8.314J/(mol · K) is ideal gas constant, T is 298K is absolute temperature, subscript K represents kth pore solution ion of cement slurry, and N is the number of pore solution ions in the model.

5. the method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to claim 4, wherein the local potential Φ is determined by all ions in the pore solution and the ions on the surface of the hydration product, and the relationship is as follows:

formula (2)

Wherein epsilon_o＝8.854×10^-12C/(V.m) is the dielectric constant in vacuum, ε_r78.3 is the relative dielectric constant of water at 298K, Z_sThe ionic charge on the surface of the hydration product, C_sis the hydration product surface ion concentration.

6. The method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to claim 4, wherein the concentration of each ion in the pore solution obtained according to the mass conservation law satisfies the following conditions:

Formula (3)

where t is time.

7. The method for predicting the mesoscopic chloride diffusion coefficient of concrete according to claim 6, wherein the step of calculating the chloride diffusion coefficient in concrete according to the chloride transport concentration distribution comprises:

Calculating the average diffusion flux J_Cl ^-：

formula (4)

wherein L is the concrete test speed thickness, x is the calculation direction along the chloride ion transmission in the model, and y is the calculation direction vertical to the chloride ion transmission in the model;

According to the average diffusion flux J_Cl ^-Calculation of the chloride diffusion coefficient D_eff：

formula (5)

wherein C is_bThe boundary chloride ion concentration.

Technical Field

the invention belongs to the field of cement-based composite materials, and particularly relates to a method for predicting a mesoscopic chloride ion diffusion coefficient of concrete.

Background

Chloride-induced corrosion of steel reinforcement is a major cause of deterioration of failure of reinforced concrete structures in most cases, especially in cases where contact with chloride is frequent (e.g., when using deicing salt or a seawater environment). Therefore, from the viewpoint of service life and maintenance work, it is very important to design a concrete protective layer (concrete layer covering steel bars) having a sufficient thickness and excellent permeation resistance. The most important index for quantifying the rate of chloride ion intrusion into concrete is the chloride ion diffusion coefficient. Various laboratory measurement methods are used for determining the diffusion/migration coefficient of chloride ions, and in the past, a natural diffusion experimental method is mainly used, so that a concrete sample is exposed in a chloride solution for a long time, chloride ions permeate the sample under the action of concentration gradient, and the diffusion coefficient is calculated through a Fick diffusion theory.

The traditional rapid chloride ion migration test is predicated on a single ion Nernst-Planck equation, a theoretical model is excessively simplified, and the deviation between a measured chloride ion diffusion concentration curve and the theoretical model is large after the test. The main reasons are two major reasons, on one hand, the concrete material is a multiphase material, has a complex pore structure and pore distribution, and changes along with continuous hydration reaction, the transmission process of chloride ions in the concrete is influenced by the pore connectivity, and meanwhile, a part of chloride ions react with cement hydration products in the transmission process to be adsorbed. On the other hand, many ions exist in the concrete pore solution, the ions can generate mutual influence due to electric field force, a theoretical model cannot only consider single transmission of chloride ions, and simultaneously, surface ions can be formed on cement hydration products due to physical and chemical adsorption, and the ions also can generate influence on the chloride ions transmitted in the pore solution.

the current common concrete chloride ion diffusion coefficient prediction method comprises an empirical method and a theoretical calculation method. However, the input parameters of the existing numerical method are still too simplified, and the experimental result cannot be accurately predicted.

Disclosure of Invention

The invention mainly aims to provide a method for predicting the mesoscopic chloride ion diffusion coefficient of concrete, which can accurately predict the chloride ion diffusion coefficient of the concrete.

In order to achieve the above object, the present invention provides a method for predicting a microscopic chloride ion diffusion coefficient of concrete, the method comprising the steps of:

acquiring pore structure information of a microstructure in concrete;

determining the porosity and pore size distribution of cement slurry in the concrete according to the pore structure information;

Determining the volume distribution of the aggregates in the concrete by combining a microscopic imaging technology with porosity and pore size distribution, and constructing a two-dimensional microscopic structure of the concrete based on an aggregate random distribution model;

Determining the surface ion concentration of the concrete according to the two-dimensional microscopic structure; constructing a multi-ion transmission model based on Nernst-Planck/Poisson equation set according to ion concentration, ion flow, ion apparent diffusion coefficient and ion charge;

Calculating the transmission concentration distribution of chloride ions in the concrete according to the mass conservation law and the multi-ion transmission model;

And calculating the diffusion coefficient of the chloride ions in the concrete according to the transmission concentration distribution of the chloride ions.

Further, the step of determining the porosity and pore size distribution of the cement slurry in the concrete according to the pore structure information includes:

and measuring the porosity and pore size distribution of the cement slurry in the concrete by a mercury intrusion method according to the pore structure information of the microstructure.

Further, the step of determining the aggregate volume distribution in the concrete by microscopic imaging technique comprises:

And determining the volume distribution of the aggregate in the concrete by adopting a scanning electron microscope technology.

Further, the multi-ion transmission model is as follows:

Formula (2)

Wherein J_kis the ion flux, D_kis the apparent diffusion coefficient of ion, C_kis the ion concentration, Z_kF is 96480C/mol, faraday constant, Φ is local potential, R is 8.314J/(mol · K) is ideal gas constant, T is 298K is absolute temperature, subscript K represents kth pore solution ion of cement slurry, and N is the number of pore solution ions in the model.

further, the local potential Φ is determined by all ions in the pore solution and the hydration product surface ions in the relationship:

Formula (2)

Wherein epsilon_o＝8.854×10^-12C/(V.m) is the dielectric constant in vacuum, ε_r78.3 is the relative dielectric constant of water at 298K, Z_sThe ionic charge on the surface of the hydration product, C_sIs the hydration product surface ion concentration.

further, according to the mass conservation law, the concentration of each ion in the pore solution satisfies the following conditions:

Formula (3)

Where t is time.

Further, the step of calculating the diffusion coefficient of chloride ions in concrete according to the chloride ion transmission concentration distribution comprises:

calculating the average diffusion flux J_Cl ^-：

Formula (4)

Wherein L is the concrete test speed thickness, x is the calculation direction along the chloride ion transmission in the model, and y is the calculation direction vertical to the chloride ion transmission in the model;

According to the average diffusion flux J_Cl ^-Calculation of the chloride diffusion coefficient D_eff：

formula (5)

wherein C is_bthe boundary chloride ion concentration.

The invention discloses a method for predicting the mesoscopic chloride ion diffusion coefficient of concrete, which comprises the steps of obtaining the pore structure information of a microstructure in the concrete; determining the porosity and pore size distribution of cement slurry in the concrete according to the pore structure information; determining the volume distribution of the aggregates in the concrete by combining a microscopic imaging technology with porosity and pore size distribution, and constructing a two-dimensional microscopic structure of the concrete based on an aggregate random distribution model; determining the concentration and distribution of ions on the surface of the pores of the concrete on the basis of the two-dimensional microscopic structure; constructing a multi-ion transmission model based on Nernst-Planck/Poisson equation set according to the mass conservation law, ion concentration, ion flow, ion apparent diffusion coefficient, ion charged quantity and the like; calculating the transmission concentration distribution of chloride ions in the concrete according to the law and the multi-ion transmission model; and calculating the diffusion coefficient of the chloride ions in the concrete according to the transmission concentration distribution of the chloride ions. The method considers the influence of micro and microscopic structures of the concrete and surface ions on the diffusion of the chloride ions when predicting the diffusion coefficient of the chloride ions of the concrete, and is more accurate and scientific compared with the conventional electric acceleration test method.

Drawings

FIG. 1 is a schematic flow chart of a method for predicting the mesoscopic chloride diffusion coefficient of concrete according to the invention;

FIG. 2 is a schematic diagram of an experiment for simulating rapid chloride ions based on a two-dimensional mesoscopic model in an embodiment of the method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to the invention;

FIG. 3 is a schematic diagram of mesh division in an embodiment of the method for predicting the mesoscopic chloride ion diffusion coefficient of concrete according to the present invention;

Fig. 4 is a schematic diagram illustrating a chloride ion concentration distribution when t is 1800s in an embodiment of the method for predicting a microscopic chloride ion diffusion coefficient of concrete according to the present invention;

Fig. 5 is a schematic diagram illustrating a chloride ion concentration distribution when t is 3600s in an embodiment of the method for predicting a microscopic chloride ion diffusion coefficient of concrete according to the present invention;

Fig. 6 is a schematic diagram illustrating a chloride ion concentration distribution when t is 5400s in an embodiment of the method for predicting a microscopic chloride ion diffusion coefficient of concrete according to the present invention;

Fig. 7 is a schematic diagram illustrating a chloride ion concentration distribution when t is 7200s in an embodiment of the method for predicting a microscopic chloride ion diffusion coefficient of concrete according to the present invention;

fig. 8 is a schematic view of the flow rate of chloride ions when t is 7200s in an embodiment of the method for predicting the mesoscopic chloride ion diffusion coefficient of concrete of the present invention.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

in the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., which refer to the orientation or positional relationship, are only used for convenience of description and simplification of the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" as appearing herein are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. The specific meaning of the above terms in the present invention can be understood in specific cases for those skilled in the art.

Referring to fig. 1 to 8 (the arrow direction in fig. 8 represents the chloride ion transport direction, and the arrow length represents the relative flow value), the embodiment of the present invention provides a method for predicting the mesoscopic chloride ion diffusion coefficient of concrete, the method comprising the steps of:

S10, acquiring the pore structure information of the microstructure in the concrete;

S20, determining the porosity and pore size distribution of the cement slurry in the concrete according to the pore structure information;

S30, determining the volume distribution of the aggregates in the concrete by combining the microscopic imaging technology with the porosity and the pore size distribution, and constructing a two-dimensional microscopic structure of the concrete based on an aggregate random distribution model;

S40, determining the surface ion concentration of the concrete according to the two-dimensional microscopic structure; constructing a multi-ion transmission model based on Nernst-Planck/Poisson equation set according to ion concentration, ion flow, ion apparent diffusion coefficient and ion charge;

S50, calculating the chloride ion transmission concentration distribution in the concrete according to the mass conservation law and the multi-ion transmission model;

And S60, calculating the diffusion coefficient of the chloride ions in the concrete according to the transmission concentration distribution of the chloride ions.

In the embodiment, the concrete chloride ion diffusion system is an important parameter for measuring the diffusion of chloride ions in concrete, is a key parameter for determining the service life of a concrete structure, and plays an important role in the durability evaluation and design of the concrete structure. When the chloride ion diffusion coefficient in concrete is calculated, the two-dimensional microscopic structure of the pores, the surface ions of the cement paste and the influence of the multi-ion pore solution on the chloride ion diffusion are considered, and compared with the traditional chloride ion diffusion coefficient calculation method, the chloride ion diffusion coefficient can be more accurately measured.

In one embodiment, the step of determining the porosity and pore size distribution of the cement slurry in the concrete comprises:

and measuring the porosity and pore size distribution of the cement slurry in the concrete by a mercury intrusion method according to the pore structure information of the microstructure.

in this embodiment, the mercury intrusion method refers to a method of measuring pore size and pore distribution of a material by allowing mercury to enter pores of the material against surface tension by means of an applied pressure. The additional pressure is increased to allow mercury to enter the smaller pores and the amount of mercury entering the pores of the material is increased. According to the principle that the surface tension of mercury in the air hole is balanced with the applied pressure, the calculation method of the aperture of the material can be obtained. Optionally, the concrete implementation manner of determining the porosity and the pore size distribution of the concrete may also be based on the mixture ratio of the concrete, a three-dimensional microstructure of the concrete at the mixture ratio is simulated, and the porosity and the pore size distribution of the concrete are determined through the three-dimensional microstructure.

In one embodiment, the step of determining the aggregate volume distribution in the concrete by microscopic imaging techniques comprises:

and determining the volume distribution of the aggregate in the concrete by adopting a scanning electron microscope technology.

In the embodiment, the volume distribution of the aggregates in the concrete is determined by adopting a scanning electron microscope technology, wherein the volume distribution of the aggregates mainly comprises the area percentage of the aggregates, an aggregate morphology system, the maximum aggregate diameter and aggregate gradation; alternatively, the aggregate volume distribution may also be determined by an electron probe, an electron spectrometer, or the like.

in one embodiment, the multiple ion transport model is:

formula (3)

Wherein J_kis the ion flux, D_kIs the apparent diffusion coefficient of ion, C_kIs the ion concentration, Z_kfor the ionic charge, F-96480C/mol is the faraday constant, Φ is the local potential, R-8.314J/(mol · K) is the ideal gas constant, T-298K is the absolute temperature, subscript K represents the kth pore solution ion, and N is the number of pore solution ions considered in the model.

in one embodiment, the local potential Φ is determined by all ions in the pore solution and the hydration product surface ions in the relationship:

Formula (2)

wherein epsilon_o＝8.854×10^-12C/(V.m) is the dielectric constant in vacuum, ε_r78.3 is the relative dielectric constant of water at 298K, Z_sthe ionic charge on the surface of the hydration product, C_sis the hydration product surface ion concentration.

in one embodiment, the obtaining of the concentration of each ion according to the mass conservation law satisfies:

Formula (3)

where t is time.

In one embodiment, the step of calculating the chloride diffusion coefficient in concrete from the chloride transport concentration profile comprises:

Calculating the average diffusion flux J_Cl ^-：

Formula (4)

Wherein L is the concrete test speed thickness, x is the calculation direction along the chloride ion transmission in the model, and y is the calculation direction vertical to the chloride ion transmission in the model;

According to the average diffusion flux J_Cl ^-Calculation of the chloride diffusion coefficient D_eff：

Formula (5)

wherein C is_bthe boundary chloride ion concentration.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.