A method for predicting the effective chloride diffusion coefficient of cement paste

Abstract

The application discloses a cement paste chloride ion effective diffusion coefficient prediction method and belongs to the technical field of material and structure medium diffusion simulation. Based on the cement paste microstructure, the components of the cement paste microstructure and the diffusion coefficients of the components are determined, a geometric model of free diffusion of chloride ions containing a high concentration area, a cement paste microstructure and a low concentration area is constructed, the high concentration area, the cement paste microstructure and the low concentration area are discretized to form a material point lattice structure with physical properties and volume, and a near-field dynamics bond list is constructed. On this basis, a near-field dynamics steady-state model of chloride ion diffusion is constructed, an implicit solution method is adopted, the minimum iteration convergence criterion is limited, and the chloride ion concentration distribution under the steady state is obtained. Finally, a method for determining the effective diffusion coefficient of chloride ions in the cement paste is constructed. The application can stably and accurately realize the prediction of the cement paste chloride ion effective diffusion coefficient problem.

Description

Technical Field

[0001] This invention relates to the field of materials and structural media diffusion simulation technology, and in particular to a new method for predicting the effective diffusion coefficient of chloride ions in cement paste based on near-field dynamics theory. Background Technology

[0002] Chloride corrosion of reinforcing steel is one of the main factors contributing to the durability failure of reinforced concrete structures in marine environments. Chloride ions in the service environment diffuse into the concrete through capillary pores and cracks, carried by water, and accumulate on the surface of the reinforcing steel. Once the chloride ion concentration on the steel surface reaches a critical value, the passivation film on the steel surface is destroyed, leading to corrosion. Because the volume of corrosion products is larger than that of the original substrate, corrosion expansion forces are generated at the interface between the steel and the concrete. Ultimately, this leads to cracking and spalling of the protective layer of the steel, severely affecting the service performance of the reinforced concrete structure. Therefore, studying the diffusion properties of chloride ions in concrete is of great significance for assessing the service condition of marine reinforced concrete structures.

[0003] The key to evaluating the diffusion performance of chloride ions in concrete is determining the diffusion coefficient of chloride ions in cement paste, which is currently mostly obtained experimentally. However, due to limitations in experimental methods, these methods cannot shield the chloride ion binding effect, making it difficult to obtain the true chloride ion diffusion coefficient in cement paste. Furthermore, the experimentally obtained chloride ion diffusion coefficient suffers from significant dispersion due to the influence of experimental design and operation. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for predicting the effective diffusion coefficient of chloride ions in cement paste.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for predicting the effective diffusion coefficient of chloride ions in cement paste includes the following steps:

[0007] Step 1: Establish the microstructure of cement paste and determine the distribution of each phase material;

[0008] Step 2: Construct high-concentration and low-concentration regions on the upper and lower sides of the cement paste microstructure, and determine their size;

[0009] Step 3: Discretize the cement microstructure, high-concentration region and low-concentration region at equal intervals to make it a uniform material point lattice structure, and determine the material type of each material point.

[0010] Step 4: Construct a list of material point bonds based on the spacing between material points and the near-field range;

[0011] Step 5: Determine the transport coefficient of each bond based on the bond list and substance point type information;

[0012] Step 6: Based on peri-field dynamics theory, construct the peri-field dynamics equations for steady-state chloride ion transport;

[0013] Step 7: Determine the boundary conditions and initial values, and solve the near-field dynamics equations of steady-state chloride ion transport using an implicit method;

[0014] Step 8: Output the concentration distribution and concentration gradient of the substance points, and calculate the effective chloride ion diffusion coefficient;

[0015] Furthermore, in step one, establishing the microstructure of cement paste includes: the microstructure of cement paste includes unhydrated cement particles, porous structure, high-density hydration products, low-density hydration products and mixed high- and low-density hydration products.

[0016] Furthermore, in step two, the height of the high-concentration region and the low-concentration region is 0.5 to 1 times the height of the cement paste microstructure.

[0017] Furthermore, in step three, the equidistant distance is between 0.1 micrometers and 1 micrometer, and the type of material point is determined by the component with the largest volume proportion among the unhydrated cement particles, pore structures, high-density hydration products, low-density hydration products, or mixed high- and low-density hydration products in the 1 cubic micrometer of material.

[0018] Furthermore, in step four, the near-field range is 3.015 to 6.015 times the spacing between material points, and within the near-field range, each material point is interconnected with other material points to form a bond list.

[0019] Furthermore, in step five, the diffusion coefficient of the bond is the weighted average of the diffusion coefficients of the material points corresponding to the bond. The diffusion coefficients of each substance are as follows: The diffusion coefficients of the substances in the microstructure of cement paste are as follows: unhydrated cement particles 0 m 2 / s, the diffusion coefficient of the pore structure is The diffusion coefficient of high-density hydration products is The diffusion coefficient of low-density hydration products is The diffusion coefficient of the mixed hydration products of high and low density is the weighted average of the diffusion coefficients of the low-density hydration products and the high-density hydration products.

[0020] Furthermore, in step six, a steady-state near-field dynamic equation for chloride ion transport is constructed, where each material point reaches an equilibrium state, and the following equations are obtained:

[0021]

[0022] in, The near-field dynamics micro-diffusion coefficient of the bond type. and For matter points and matter points chloride ion concentration, For matter points volume, For matter points The near-field range.

[0023] Furthermore, in step seven, the chloride ion concentration at the lower boundary of the high-concentration region is 0.1 mol / m³. 3 -1mol / m 3 The chloride ion concentration at the upper boundary of the low-concentration region is 0 mol / m 3 Other boundaries are zero-flux boundaries, and the convergence condition is that the error is less than 10. -9 .

[0024] Furthermore, in step eight, the effective chloride ion diffusion coefficient is determined using the chloride ion flux equivalence method, and the following applies:

[0025]

[0026] Where L represents the size of the microstructure of the cement paste. Let be the diffusion coefficient of substance point i corresponding to the high concentration region. Let i be the concentration gradient of substance point i corresponding to the high concentration region. Let i be the concentration of substance point i corresponding to the high-concentration region. Let be the diffusion coefficient of substance point j corresponding to the high concentration region. Let J represent the concentration gradient of substance point j in the high-concentration region. The concentration of substance point j corresponds to the high concentration region.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] It can economically and accurately predict the effective diffusion coefficient of chloride ions in cement paste under various working conditions, providing a theoretical basis for evaluating the service status of marine reinforced concrete structures. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the high-concentration region, the cement paste microstructure region, and the low-concentration region of the present invention;

[0030] Figure 2 This is a schematic diagram of the microstructure of cement paste with a water-cement ratio of 0.4 in the implementation of this invention;

[0031] Figure 3This is a steady-state distribution diagram of chloride ions in the microstructure of cement paste with a water-cement ratio of 0.4 in the embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the microstructure of cement paste with a water-cement ratio of 0.5 in the implementation of this invention;

[0033] Figure 5 This is a steady-state distribution diagram of chloride ions in the microstructure of cement paste with a water-cement ratio of 0.5 in the embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the microstructure of cement paste with a water-cement ratio of 0.6 in the implementation of this invention;

[0035] Figure 7 This is a steady-state distribution diagram of chloride ions in the microstructure of cement paste with a water-cement ratio of 0.6 in the embodiment of the present invention.

[0036] In the diagram: 01 - High concentration area, 02 - Cement paste microstructure, 03 - Low concentration area, 04 - Low concentration boundary, 05 - High concentration boundary. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0038] Example 1

[0039] A method for predicting the effective diffusion coefficient of chloride ions in cement paste includes the following steps:

[0040] S1 prepares a 100μm x 100μm x 100μm cement paste microstructure with a water-cement ratio of 0.4 and a hydration age of 28 days, as shown in the figure. Figure 2 As shown, the components of the microstructure were determined, and unhydrated cement particles, porous structures, high-density hydration products, low-density hydration products, and mixed high- and low-density hydration products were identified.

[0041] S2 generates a 0.1 mol / m² chloride ion concentration within a 100μm x 100μm x 50μm area directly above the cement paste microstructure. 3 In the aqueous solution region, a chloride ion concentration of 0 mol / m³ is generated in a 100μm x 100μm x 50μm area directly beneath the cement paste microstructure. 3 aqueous solution region, such as Figure 1 As shown;

[0042] S3 discretizes the microstructure of cement paste, the high-concentration chloride ion region, and the low-concentration chloride ion region into a lattice structure of equally spaced material points, each material point being 1 cubic micrometer, and determines the type of material point based on its location.

[0043] S4 constructs a near-field dynamics bond list and assigns diffusion coefficients to different bond types based on material type information. The diffusion coefficient of a bond is the weighted average of the diffusion coefficients of the two material points connecting the bond; unhydrated cement particles 0 m 2 / s, the diffusion coefficient of the pore structure is The diffusion coefficient of high-density hydration products is The diffusion coefficient of low-density hydration products is .

[0044] Based on peri-field dynamics theory, a peri-field dynamics equation for steady-state chloride ion transport is constructed;

[0045]

[0046] in, The near-field dynamics micro-diffusion coefficient of the bond type. and For matter points and matter points chloride ion concentration, For matter points volume, For matter points The near-field range.

[0047] S5 sets the boundary conditions and initial values; the surface chloride ion concentration in the high-concentration region is 1 mol / m³. 3 The chloride ion concentration at the upper boundary of the low-concentration region is 0 mol / m³. 3 .

[0048] S6 uses an implicit method to solve the near-field dynamics equations of steady-state chloride ion transport, with an iteration error set to 10. -10 .

[0049] S7 outputs the concentration distribution of substances at specific points, such as... Figure 3 As shown, the effective chloride ion diffusion coefficient is calculated. The effective chloride ion diffusion coefficient is determined using the chloride ion flux equivalence method, and the following holds:

[0050]

[0051] Where L represents the size of the microstructure of the cement paste. Let be the diffusion coefficient of substance point i corresponding to the high concentration region. Let i be the concentration gradient of substance point i corresponding to the high concentration region. Let i be the concentration of substance point i corresponding to the high-concentration region. Let be the diffusion coefficient of substance point j corresponding to the high concentration region. Let J represent the concentration gradient of substance point j in the high-concentration region. Let be the concentration of substance point j corresponding to the high-concentration region. The calculated effective diffusion coefficient of chloride ions is: .

[0052] Example 2

[0053] A method for predicting the effective diffusion coefficient of chloride ions in cement paste includes the following steps:

[0054] S1 prepares a 100μm x 100μm x 100μm cement paste microstructure with a water-cement ratio of 0.5 and a hydration age of 28 days, such as... Figure 4 As shown, the components of the microstructure were determined, and unhydrated cement particles, porous structures, high-density hydration products, low-density hydration products, and mixed high- and low-density hydration products were identified.

[0055] S2 generates a 0.1 mol / m² chloride ion concentration within a 100μm x 100μm x 50μm area directly above the cement paste microstructure. 3 In the aqueous solution region, a chloride ion concentration of 0 mol / m³ is generated in a 100μm x 100μm x 50μm area directly beneath the cement paste microstructure. 3 aqueous solution region, such as Figure 1 As shown.

[0056] S3 discretizes the microstructure of cement paste, the high-concentration chloride ion region, and the low-concentration chloride ion region into a lattice structure of equally spaced material points, each material point being 1 cubic micrometer, and determines the type of material point based on its location.

[0057] S4 constructs a near-field dynamics bond list and assigns diffusion coefficients to different bond types based on material type information. The diffusion coefficient of a bond is the weighted average of the diffusion coefficients of the two material points connecting the bond; unhydrated cement particles 0 m 2 / s, the diffusion coefficient of the pore structure is The diffusion coefficient of high-density hydration products is The diffusion coefficient of low-density hydration products is .

[0058] Based on peri-field dynamics theory, a peri-field dynamics equation for steady-state chloride ion transport is constructed;

[0059]

[0060] in, The near-field dynamics micro-diffusion coefficient of the bond type. and For matter points and matter points chloride ion concentration, For matter points volume, For matter points The near-field range.

[0061] S5 sets the boundary conditions and initial values; the surface chloride ion concentration in the high-concentration region is 1 mol / m³. 3 The chloride ion concentration at the upper boundary of the low-concentration region is 0 mol / m³. 3 .

[0062] S6 uses an implicit method to solve the near-field dynamics equations of steady-state chloride ion transport, with an iteration error set to 10. -10 .

[0063] S7 outputs the concentration distribution of substances at specific points, such as... Figure 5 As shown, the effective chloride ion diffusion coefficient is calculated. The effective chloride ion diffusion coefficient is determined using the chloride ion flux equivalence method, and the following holds:

[0064]

[0065] Where L represents the size of the microstructure of the cement paste. Let be the diffusion coefficient of substance point i corresponding to the high concentration region. Let i be the concentration gradient of substance point i corresponding to the high concentration region. Let i be the concentration of substance point i corresponding to the high concentration region. Let be the diffusion coefficient of substance point j corresponding to the high concentration region. Let J represent the concentration gradient of substance point j in the high-concentration region. Let be the concentration of substance point j corresponding to the high-concentration region. The calculated effective diffusion coefficient of chloride ions is: .

[0066] Example 3

[0067] A method for predicting the effective diffusion coefficient of chloride ions in cement paste includes the following steps:

[0068] S1 prepares a 100μm x 100μm x 100μm cement paste microstructure with a water-cement ratio of 0.6 and a hydration age of 28 days, such as... Figure 6 As shown, the components of the microstructure were determined, and unhydrated cement particles, porous structures, high-density hydration products, low-density hydration products, and mixed high- and low-density hydration products were identified.

[0069] S2 generates a 0.1 mol / m² chloride ion concentration within a 100μm x 100μm x 50μm area directly above the cement paste microstructure. 3 In the aqueous solution region, a chloride ion concentration of 0 mol / m³ is generated in a 100μm x 100μm x 50μm area directly beneath the cement paste microstructure. 3 aqueous solution region, such as Figure 1 As shown.

[0070] S3 discretizes the microstructure of cement paste, the high-concentration chloride ion region, and the low-concentration chloride ion region into a lattice structure of equally spaced material points, each material point being 1 cubic micrometer, and determines the type of material point based on its location.

[0071] S4 constructs a near-field dynamics bond list and assigns diffusion coefficients to different bond types based on material type information. The diffusion coefficient of a bond is the weighted average of the diffusion coefficients of the two material points connecting the bond; unhydrated cement particles 0 m 2 / s, the diffusion coefficient of the pore structure is The diffusion coefficient of high-density hydration products is The diffusion coefficient of low-density hydration products is .

[0072] Based on peri-field dynamics theory, a peri-field dynamics equation for steady-state chloride ion transport is constructed;

[0073]

[0074] in, The near-field dynamics micro-diffusion coefficient of the bond type. and For matter points and matter points chloride ion concentration, For matter points volume, For matter points The near-field range.

[0075] S5 sets the boundary conditions and initial values; the surface chloride ion concentration in the high-concentration region is 1 mol / m³. 3 The chloride ion concentration at the upper boundary of the low-concentration region is 0 mol / m³. 3 .

[0076] S6 uses an implicit method to solve the near-field dynamics equations of steady-state chloride ion transport, with an iteration error set to 10. -10 .

[0077] S7 outputs the concentration distribution of substances at specific points, such as... Figure 7 As shown, the effective chloride ion diffusion coefficient is calculated. The effective chloride ion diffusion coefficient is determined using the chloride ion flux equivalence method, and the following holds:

[0078]

[0079] Where L represents the size of the microstructure of the cement paste. Let be the diffusion coefficient of substance point i corresponding to the high concentration region. Let i be the concentration gradient of substance point i corresponding to the high concentration region. Let i be the concentration of substance point i corresponding to the high-concentration region. Let be the diffusion coefficient of substance point j corresponding to the high concentration region. Let J represent the concentration gradient of substance point j in the high-concentration region. Let be the concentration of substance point j corresponding to the high-concentration region. The calculated effective diffusion coefficient of chloride ions is: .

[0080] Table 1 shows a comparison between the predicted and experimental values ​​of the effective diffusion coefficient of chloride ions in the above embodiments.

[0081] Table 1

[0082] Serial Number water-cement ratio <![CDATA[Predicted value 10 -12 m 2 / s]]> <![CDATA[Experimental value 10 -12 m 2 / s]]> Implementation 1 0.4 2.79 2.5 Implementation 2 0.5 6.69 7.1 Implementation Three 0.6 10.05 11.2

[0083] As can be seen from Table 1, the numerical simulation prediction of the effective diffusion coefficient of chloride ions is in good agreement with the experimental value, indicating the reliability of the present invention.

[0084] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A method for predicting the effective diffusion coefficient of chloride ions in cement paste, characterized in that, Includes the following steps: Step 1: Establish the microstructure of cement paste and determine the distribution of each phase material; Step 2: Construct high-concentration and low-concentration regions on the upper and lower sides of the cement paste microstructure and determine their size; the height of the high-concentration and low-concentration regions is 0.5 to 1 times the height of the cement paste microstructure. Step 3: Discretize the cement microstructure, high-concentration region and low-concentration region at equal intervals to make it a uniform material point lattice structure, and determine the material type of each material point. Step 4: Based on the distance between material points and the near-field range, construct a material point bond list. The near-field range is 3.015 to 6.015 times the distance between material points. Within the near-field range, each material point is connected to other material points to form a bond list. Step 5: Determine the transport coefficient of each bond based on the bond list and substance point type information; Step 6: Based on peri-field dynamics theory, construct the peri-field dynamics equations for steady-state chloride ion transport, where each material point reaches equilibrium and has the following: ； in, The near-field dynamics micro-diffusion coefficient of the bond type. and For matter points and matter points chloride ion concentration, For matter points volume, For matter points The near-field range; Step 7: Determine the boundary conditions and initial values, and solve the near-field dynamics equations of steady-state chloride ion transport using an implicit method; Step 8: Output the concentration distribution and concentration gradient of the substance points, and calculate the effective chloride ion diffusion coefficient.

2. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, characterized in that: In step one, establishing the microstructure of cement paste includes: the microstructure of cement paste includes unhydrated cement particles, pore structure, high-density hydration products, low-density hydration products and mixed high- and low-density hydration products.

3. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, characterized in that: In step three, the equidistant distance is between 0.1 micrometers and 1 micrometer. The type of material point is determined by the component with the largest volume proportion among the unhydrated cement particles, pore structures, high-density hydration products, low-density hydration products, or mixed high- and low-density hydration products in the 1 cubic micrometer of material.

4. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, characterized in that: In step five, the diffusion coefficient of a bond is the weighted average of the diffusion coefficients of the material points corresponding to the bond. The diffusion coefficients of each substance are as follows: The diffusion coefficients of the substances in the microstructure of cement paste are as follows: unhydrated cement particles 0m 2 / s, the diffusion coefficient of the pore structure is The diffusion coefficient of high-density hydration products is The diffusion coefficient of low-density hydration products is The diffusion coefficient of the mixed hydration products of high and low density is the weighted average of the diffusion coefficients of the low-density hydration products and the high-density hydration products.

5. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, characterized in that: In step seven, the chloride ion concentration at the lower boundary of the high-concentration region is 0.1 mol / m³. 3 -1mol / m 3 The chloride ion concentration at the upper boundary of the low-concentration region is 0 mol / m³. 3 Other boundaries are zero-flux boundaries, and the convergence condition is that the error is less than 10. -9 .

6. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, characterized in that: In step eight, the effective chloride ion diffusion coefficient is determined by the chloride ion flux equivalence method, and the following applies: ； Where L represents the dimensions of the cement paste microstructure. Let be the diffusion coefficient of substance point i corresponding to the high concentration region. Let i be the concentration gradient of substance point i corresponding to the high concentration region. Let i be the concentration of substance point i corresponding to the high-concentration region. Let be the diffusion coefficient of substance point j corresponding to the high concentration region. Let J represent the concentration gradient of substance point j in the high-concentration region. The concentration of substance point j corresponds to the high concentration region.

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