阅读说明：本技术 降低水泥基材料孔道离子传输速率的量化方法 (Quantification method for reducing ion transmission rate of cement-based material pore channel ) 是由 蒋金洋 陈泽 张宇 罗齐 于 2021-06-10 设计创作，主要内容包括：本发明公开了一种降低水泥基材料孔道离子传输速率的量化方法,包括分子动力学模型构建、计算模拟和传输速率量化。分子动力学模型由三部分组成：C-S-H凝胶孔道、十八烷羧酸和盐溶液。本发明可以模拟不同溶液环境下C-S-H孔道中离子的传输行为,量化十八烷羧酸对C-S-H孔道传输速率的影响,计算既定环境下C-S-H内部离子渗透速率,从而为水泥基材料耐久性寿命预测提供依据。(The invention discloses a quantification method for reducing the transmission rate of cement-based material pore ions, which comprises the steps of molecular dynamics model construction, calculation simulation and transmission rate quantification. The molecular dynamics model consists of three parts: C-S-H gel pore canal, octadecane carboxylic acid and salt solution. The method can simulate the transmission behavior of ions in the C-S-H pore channel under different solution environments, quantify the influence of octadecanoic carboxylic acid on the transmission rate of the C-S-H pore channel, and calculate the permeation rate of the ions in the C-S-H pore channel under the established environment, thereby providing a basis for predicting the durability life of the cement-based material.)

1. A quantification method for reducing the ion transmission rate of a cement-based material pore passage is characterized by comprising the following steps:

(1) establishing a molecular dynamics model of C-S-H gel molecules, octadecane carboxylic acid molecules and salt solution, constructing the C-S-H molecules, the octadecane carboxylic acid molecules and the salt solution molecules, and relaxing under an NVT (noise, vibration and harshness) ensemble to enable all parts of the model to be close to each other to form a stable molecular structure;

(2) applying a force to each atom in the molecular model created above, the force field being of the form shown below:

E_total＝E_bond+E_angle+E_torsion+E_vdw+E_coul

in the formula, E_totalRepresents the total potential energy, E_bondIndicating key expansion potential energy, E_angleIndicating the bending potential energy of the key angle, E_torsionRepresenting dihedral torsional potential energy, E_vdwDenotes van der Waals' force, E_coulRepresenting electrostatic potential of coulombs；

(3) Setting preset environment temperature, calculation time step length and the outer edge of the whole molecular model as periodic boundary conditions, ensuring system stability in the simulation process by using a Nose-Hoover constant temperature calculation method, and obtaining an atom motion coordinate trajectory by using a Verlet algorithm;

(4) and (4) according to the atom motion coordinate track obtained in the step (3), obtaining the positions and the penetration depths of the ions in the pore channels at different times, drawing a correlation curve of the penetration depths and the time, and fitting the obtained correlation curve of the penetration depths and the time to obtain the diffusion coefficient.

2. The method for quantifying the reduction in the ion transfer rate of the cement-based material pore canals according to claim 1, wherein when the molecular dynamics model is established in the step (1), octadecanecarboxylic acid molecules are placed on the surface of the inner wall of the C-S-H molecules, and the salt solution molecules are distributed at the spatial positions below the C-S-H molecules.

3. The method for quantifying and reducing the ion transmission rate of the cement-based material pore channels according to claim 1, wherein the C-S-H gel molecular model in the step (1) is usedTobermorite crystal configuration.

4. The method for quantifying the reduction in the ion transport rate of the cement-based material pore channels according to claim 1, wherein the octadecanecarboxylic acid model in the step (1) is the same as the actual molecular structure.

5. The method for quantifying the reduction in the ion transmission rate of the cement-based material pore channels according to claim 1, wherein the salt solution in the step (1) is at least one of a sodium chloride solution, a calcium chloride solution, a cesium chloride solution, a sodium sulfate solution and a magnesium sulfate solution, and the salt solution model is constructed by mixing anions and cations with water molecules, wherein the ratio of the anions to the cations satisfies a chemical molecular formula, so that the salt solution with a certain concentration is obtained.

6. The method for quantifying and reducing the pore ion transport rate of cement-based materials according to claim 1, wherein the field formula of the step (2) is developed as follows:

in the formula, the first, second, third and fourth terms on the right respectively represent key expansion potential energy, key angle bending potential energy, dihedral angle twisting potential energy and non-key energy, specifically, k_1i、k_2i、k_3iRepresenting the elastic constant of the key expansion term; Δ l represents the bond length; Δ θ represents a bond angle; of_ijAnd σ_ijRepresents a potential energy parameter (epsilon)_ijPotential energy difference between reaction atoms, sigma_ijReflecting equilibrium distance between atoms); r is_ijRepresents an interatomic distance; q. q.s_i(j)Represents the charge of the ith (j) ion in the molecule; cos (nw-r) represents the dihedral angle parameter; epsilon₀Representing a potential energy parameter.

Technical Field

The invention relates to calculation of ion transmission rate, in particular to a quantification method for reducing ion transmission rate of a cement-based material pore channel.

Background

Cement concrete is the main material for constructing highways, bridges, houses, tunnels, etc. Cement concrete structures exposed to severe environments such as sea salt areas, frozen areas, saline soil and the like are often degraded prematurely due to invasion of erosion media, and finally the structures are damaged or even fail. Thus, structural durability is closely linked to the microscopic resistance of the cement-based structure to ionic attack. The C-S-H gel is a main product of Portland cement hydration, is a main body of a cement hydration gel phase, exists in a form of gel particles of 1-100 nm, pores among the gel particles provide channels for transmission of an erosion medium, and the hydrophilic property of the surface of the C-S-H gel provides power for capillary transmission, so that the transmission resistance of the traditional cement concrete is further reduced.

For this reason, more and more foreign and domestic scholars start to reduce the transmission of cement concrete by means of nano-doping and surface coating. Mainly comprises the following steps: 1) before the cement-based material is formed, graphene oxide, epoxy, silylene, octadecanecarboxylic acid and the like are doped to participate in the cement hydration process and interact with cement hydration products; 2) after the cement-based material is formed, the nano-dopant is made into a solution to be coated on the surface of the cement-based material. The method can improve the anti-transmission capability of the cement-based material to a certain extent. Particularly, when the octadecanoic carboxylic acid is coated on the cement-based material, the octadecanoic carboxylic acid molecules can be attached to the surfaces of the cement-based material pore canals, the hydrophilicity of the surfaces of the pore canals is reduced to a certain degree, the capillary transmission rate is reduced, and therefore the transmission performance of the cement-based material is greatly reduced, and the research significance is high.

However, the principle of the octadecanoic carboxylic acid for reducing the transmission inhibition of the erosion medium in the cement-based material is still unclear at present, the existing experimental means cannot fully illustrate the action mechanism, and the existing experimental means cannot quantitatively characterize the erosion property of the octadecanoic carboxylic acid for inhibiting the cement-based material, so that the related engineering application of the octadecanoic carboxylic acid for reducing the transmission of the cement-based material is few.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a quantification method for reducing the ion transmission rate of a cement-based material pore passage, and solves the problem that the corrosion of a cement-based material inhibited by octadecanoic carboxylic acid cannot be quantified and characterized.

The technical scheme is as follows: the invention aims to provide a quantification method for reducing the ion transmission rate of a cement-based material pore channel, which comprises the following steps:

(1) establishing a molecular dynamics model of C-S-H gel molecules, octadecane carboxylic acid molecules and salt solution, constructing the C-S-H molecules, the octadecane carboxylic acid molecules and the salt solution molecules, and relaxing under an NVT (noise, vibration and harshness) ensemble to enable all parts of the model to be close to each other to form a stable molecular structure;

(2) applying a force to each atom in the molecular model created above, the force field being of the form shown below:

E_total＝E_bond+E_angle+E_torsion+E_vdw+E_coul

in the formula, E_totalRepresents the total potential energy, E_bondIndicating key expansion potential energy, E_angleIndicating the bending potential energy of the key angle, E_torsionRepresenting dihedral torsional potential energy, E_vdwDenotes van der Waals' force, E_coulRepresenting the coulomb electrostatic potential;

(3) setting preset environment temperature, a calculation time step and the outer edge of an integral molecular model as periodic boundary conditions, ensuring the system stability in the simulation process by using a Nose-Hoover constant temperature calculation method, and obtaining an atom motion trajectory by using a Verlet algorithm;

(4) and (4) according to the atom motion coordinate track obtained in the step (3), obtaining the positions and the penetration depths of the ions in the pore channels at different times, drawing a correlation curve of the penetration depths and the time, and fitting the obtained correlation curve of the penetration depths and the time to obtain the diffusion coefficient.

When the molecular dynamics model is established in the step (1), octadecanecarboxylic acid molecules are placed on the surface of the inner wall of the C-S-H molecule, and the salt solution molecules are fully distributed at the spatial position below the C-S-H molecule.

The C-S-H gel molecule model in the step (1) is usedTobermorite crystal configuration.

The octadecane carboxylic acid model in the step (1) is the same as the actual molecular structure.

In the step (1), the salt solution is at least one of a sodium chloride solution, a calcium chloride solution, a cesium chloride solution, a sodium sulfate solution and a magnesium sulfate solution, and the construction of the salt solution model is to mix a certain amount of anions and cations with water molecules so as to obtain the salt solution with a certain concentration.

The vertical formula of the step (2) is developed as follows:

in the formula, the first, second, third and fourth terms on the right respectively represent key expansion potential energy, key angle bending potential energy, dihedral angle twisting potential energy and non-key energy, specifically, k_1i、k_2i、k_3iRepresenting the elastic constant of the key expansion term; Δ l represents the bond length; Δ θ represents a bond angle; of_ijAnd σ_ijRepresents a potential energy parameter (epsilon)_ijPotential energy difference between reaction atoms, sigma_ijReflecting equilibrium distance between atoms); r is_ijRepresents an interatomic distance; q. q.s_i(j)Represents the charge of the ith (j) ion in the molecule; cos (nw-r) represents the dihedral angle parameter; epsilon₀Representing a potential energy parameter.

Has the advantages that: the invention can reveal the interaction mechanism of octadecanoic carboxylic acid and C-S-H gel pore canal on the molecular scale, quantify the influence of octadecanoic carboxylic acid on the transmission rate of the C-S-H gel pore canal, make up the defect of the molecular scale representation by the experimental means, provide the basis for the durability life of the cement-based material by the obtained data, and have guiding significance for the experimental research and the engineering application of the octadecanoic carboxylic acid for improving the anti-transmission performance of the cement-based material, particularly for the research on the influence of the durability of the cement-based material.

Drawings

FIG. 1 is a general schematic diagram of a molecular dynamics model;

FIG. 2 is a schematic diagram of a C-S-H molecule;

FIG. 3 shows (a) a model of the solution transport through the C-S-H channels, (b) a depth of penetration as a function of time, the percentages representing different octadecanecarboxylic acid loadings, and the C-S-H blank.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The invention discloses a quantification method for reducing the ion transmission rate of a cement-based material pore passage, which comprises the following steps:

(1) establishing a molecular dynamics model of C-S-H gel molecules, octadecane carboxylic acid molecules and salt solution, wherein the model comprises three parts as shown in figure 1: C-S-H gel molecules, octadecanecarboxylic acid molecules and salt solution (water molecules and ions), wherein the octadecanecarboxylic acid molecules are placed on the inner wall surface of the C-S-H molecules, the salt solution molecules are fully distributed at the spatial position below the C-S-H molecules, and all parts of the model are relaxed by 100-200 ps under an NVT (noise, vibration and harshness) ensemble to be close to each other, so that a stable molecular structure is formed;

the C-S-H gel is a main product of Portland cement hydration, is a main body of a cement hydration gel phase and exists in the form of gel particles of 1-100 nm, pores among the gel particles provide channels for transmission of an erosion medium, and the hydrophilicity of the surface of the C-S-H gel provides power for capillary transmission. The C-S-H gel pore channel model is a pore channel model formed by parallelly placing C-S-H gel molecule models serving as substrates and reserving a transmission pore channel in the middle, and is called as a C-S-H gel pore channel model, and the diameter and the length of the pore channel can be adjusted by translating and extending the C-S-H substrates;

the saline solution can be a variety of aggressive media including, but not limited to: sodium chloride solution, calcium chloride solution, cesium chloride solution, sodium sulfate solution and magnesium sulfate solution;

the construction of the saline solution model is to mix a certain amount of anions and cations with water molecules so as to obtain a saline solution with a certain concentration;

the octadecanoic carboxylic acid can be dispersed in ethanol in a nanoscale, one end of the molecular structure of the octadecanoic carboxylic acid is hydrophilic, the other end of the molecular structure of the octadecanoic carboxylic acid is hydrophobic, and the hydrophilic end of the molecular structure of the octadecanoic carboxylic acid can interact with a C-S-H gel pore channel and is adsorbed on the pore channel. The octadecanoic carboxylic acid model has the same structure as the actual molecule, the constructed model C-S-H gel pore canal is perpendicular to the salt solution, and a layer of octadecanoic carboxylic acid molecules is attached to the C-S-H gel pore canal.

(2) Applying force to each atom in the established molecular model, wherein the force field describes potential energy for driving the atom to move in the system, converting the potential energy into acceleration of the movement of each atom through Newton's second law, and under the condition of giving an initial position and speed, the coordinate of each atom at each time point can be calculated, and the force field adopts an empirical force field, and the fundamental form of the empirical force field is shown as formula 1 and comprises bond energy among atoms, van der Waals force action and long coulomb force action;

E_total＝E_bond+E_angle+E_torsion+E_vdw+E_coulequation 1

The expansion formula is as follows:

in the formula 1, E_totalRepresents the total potential energy, E_bondIndicating key expansion potential energy, E_angleIndicating the bending potential energy of the key angle, E_torsionRepresenting dihedral torsional potential energy, E_vdwDenotes van der Waals' force, E_coulRepresenting the coulomb electrostatic potential.

In the expansion formula, the first term, the second term, the third term and the fourth term on the right respectively represent key expansion potential energy, key angle bending potential energy, dihedral angle twisting potential energy and non-key energy. Specifically, k_1i、k_2i、k_3iRepresenting the elastic constant of the key expansion term; Δ l represents the bond length; Δ θ represents a bond angle; of_ijAnd σ_ijRepresents a potential energy parameter (epsilon)_ijPotential energy difference between reaction atoms, sigma_ijReflecting equilibrium distance between atoms); r is_ijRepresents an interatomic distance; q. q.s_i(j)Represents the charge of the ith (j) ion in the molecule; cos (nw-r) represents the dihedral angle parameter; epsilon₀Representing a potential energy parameter.

(3) The method comprises the steps of giving preset environment temperature, calculation time step and periodic boundary conditions, ensuring system stability in a simulation process by using a Nose-Hoover constant temperature calculation method, and obtaining an atomic motion trajectory by using a Verlet algorithm;

(4) and (4) according to the atom motion coordinate track obtained in the step (3), obtaining the positions and the penetration depths of the ions in the pore channels at different times, drawing a correlation curve of the penetration depths and the time, and fitting the obtained correlation curve of the penetration depths and the time to obtain the diffusion coefficient.

When the method is adopted to carry out actual simulation calculation, a molecular dynamics model is established firstly, wherein C-S-H gel is usedThe tobermorite crystal substitution is shown in fig. 2, and the crystallographic parameters of the cells are as follows: α ═ β ═ γ ═ 90 °, including 43 calcium atoms, 24 silicon-oxygen tetrahedrons, and 16 water molecules. The C-S-H gel pore channel is formed by two C-S-H substrates which are arranged in parallel, and the width of the constructed pore channel is 3.4nm and the length is 7 nm; saline solution model: mixing 50 sulfate ions and 50 sodium ions with water molecules to obtain a sodium sulfate solution of 0.6 mol/L; octadecanecarboxylic acid model: the octadecanecarboxylic acid model has the same structure as the actual molecule, and the molecular structural formula is [ CH ]₂]₁₈COOH. Octadecanecarboxylic acid molecules are attached to the C-S-H pore canals, and the attachment rate is 25%.

Establishing a molecular dynamics model, applying a force field on each atom, and performing simulation calculation on LAMMPS, wherein the system temperature is 300K, the pressure is one atmosphere, and the time step is 1 fs. The periodic boundaries are set at X, Y, Z in three directions. The initial velocity of each atom is randomly generated based on the initial temperature. The position of the next moment of the atom is calculated using the Verlet algorithm with a long-range force cutoff radius ofThe simulation process is divided into three steps. Firstly, energy optimization is carried out on the structure through energy minimization; then, a barrier is arranged between the solution and the C-S-H substrate, so that the solution can not enter the pore channel temporarily, and meanwhile, the whole system moves for 1000ps under a normal synthetic method (NVT) to achieve the balance of each part of structure; finally, under the regular system, the barrier is deleted and dissolvedThe liquid enters the pore channel under the action of capillary force and moves 1000 ps. In the simulation process, thermodynamic parameters such as temperature, pressure and the like and the size of the box are output every 1ps, coordinates of all atoms are output once, and the number of atomic coordinate frames is output for 1000 frames in total. The process of solution transmission in the C-S-H pore channel is shown in fig. 3(a), and the ion penetration depth at different times is calculated according to the atomic coordinates, and the obtained graph of the relation between the penetration depth and the time is obtained by an exponential equation (y ═ x)^D+ b) fitting the curve of penetration depth and time to obtain the diffusion coefficient D, wherein b: a regulatory factor; y: the diffusion depth; x: time. And the diffusion coefficient D is used as a characterizing parameter for the transmission rate.

In order to further compare the effect of different amounts of octadecanoic carboxylic acid on the transmission efficiency, the relationship between the penetration depth and time was determined by the method of the present invention for 50%, 75%, and 100% of octadecanoic carboxylic acid, and compared with the blank case, the result is shown in fig. 3(b), from which it can be seen that the ion transmission inhibition effect is larger as the amount of octadecanoic carboxylic acid is increased.