CN-116384046-B - Method for predicting effective diffusion coefficient of chloride ions in cement paste

CN116384046BCN 116384046 BCN116384046 BCN 116384046BCN-116384046-B

Abstract

The invention discloses a method for predicting the effective diffusion coefficient of chloride ions in cement paste, and belongs to the technical field of diffusion simulation of materials and structural media. On the basis of the microstructure of the cement paste, each component of the microstructure of the cement paste and the diffusion coefficient of each component are determined, a geometric model containing a high concentration area, the microstructure of the cement paste and free diffusion of chloride ions in a low concentration area is constructed, the high concentration area, the microstructure of the cement paste and the low concentration area are discretized to form a substance point lattice structure with physical properties and volumes, a near-field dynamic bond list is constructed, on the basis, a chloride ion diffusion near-field dynamic steady-state model is constructed, an implicit solution is adopted, a minimum iteration convergence criterion is limited, and the concentration distribution of the chloride ions in a steady state is obtained. Finally, a method for determining the effective diffusion coefficient of chloride ions in the cement paste is constructed. The method can stably and accurately realize the prediction of the effective diffusion coefficient of the chloride ions of the cement paste.

Inventors

CHEN XUANDONG
GU XIN
ZHANG QING

Assignees

河海大学

Dates

Publication Date: 20260512
Application Date: 20230206

Claims (6)

1. The method for predicting the effective diffusion coefficient of chloride ions in cement paste is characterized by comprising the following steps of: step one, establishing a cement paste microstructure, and determining the distribution of materials of each phase; step two, constructing a high-concentration area and a low-concentration area on the upper side and the lower side of the microstructure of the cement paste, and determining the size of the high-concentration area and the low-concentration area, wherein the heights of the high-concentration area and the low-concentration area are 0.5-1 time of the height of the microstructure of the cement paste; Thirdly, dispersing the cement microstructure, the high concentration region and the low concentration region at equal intervals to form a uniform substance point lattice structure, and determining the substance type of each substance point; step four, according to the material point spacing and according to the near field range, building a material point bond list, wherein the near field range is 3.015-6.015 times of the material point spacing, and each material point is connected with other material points in the near field range to form the bond list; step five, determining the transmission coefficient of each key according to the key list and the material point type information; step six, based on the near field dynamics theory, constructing a steady-state chloride ion transmission near field dynamics motion equation, wherein each object point reaches an equilibrium state, and the method comprises the following steps: ; Wherein, the Is a bonded near field kinetic micro-diffusion coefficient, And Is a point of matter And a point of matter Is used for the concentration of chloride ions, Is a point of matter Is defined by the volume of (a), Is a point of matter Is a near field range of (2); Step seven, determining boundary conditions and initial values, and solving a steady-state chloride ion transmission near-field dynamics equation by adopting an implicit method; And step eight, outputting the concentration distribution and the concentration gradient of the substance points, and calculating the effective chloride ion diffusion coefficient.
2. The method for predicting the effective diffusion coefficient of chloride ions of cement paste according to claim 1, wherein in the first step, the microstructure of the cement paste is established to comprise unhydrated cement particles, a pore structure, a high-density hydration product, a low-density hydration product and a high-low-density mixed hydration product.
3. The method of predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, wherein in the third step, the equidistant distance is between 0.1 μm and 1. Mu.m, and the type of the material particles is determined by the components with the largest volume ratio among unhydrated cement particles, pore structures, high-density hydration products, low-density hydration products or high-low-density mixed hydration products in 1 cubic μm.
4. The method for predicting the effective diffusion coefficient of chloride ions in cement paste as defined in claim 1, wherein in the fifth step, the diffusion coefficient of the bond is a weighted average of diffusion coefficients of substance points corresponding to the bond, and the diffusion coefficients of the substances are respectively 0m 2 /s of unhydrated cement particles and 0m 2 /s of pore structure diffusion coefficient of the substances in the microstructure of the cement paste High density hydration product diffusion coefficient of Low density hydration product diffusion coefficient of The high-low density mixed hydration product diffusion coefficient is a weighted average of the low density hydration product and the high density hydration product diffusion coefficient.
5. The method for predicting the effective diffusion coefficient of chloride ions in cement paste according to claim 1, wherein in the seventh step, the chloride ion concentration at the lower boundary of the high concentration region is 0.1mol/m 3 -1mol/m 3 , the chloride ion concentration at the upper boundary of the low concentration region is 0mol/m 3 , the 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 chloride ion diffusion coefficient of cement paste according to claim 1, wherein in the eighth step, the effective chloride ion diffusion coefficient is determined by a chloride ion flux equivalent method, and the method comprises the following steps: ; wherein L is the size of the microstructure of the cement paste, The diffusion coefficient of the object point i corresponding to the high concentration region, Is the concentration gradient of the corresponding object point i in the high concentration region, The concentration of the object point i is corresponding to the high concentration region, The diffusion coefficient of the object point j corresponding to the high concentration region, Is the concentration gradient of the corresponding object point j in the high concentration region, The concentration of object point j corresponds to the high concentration region.

Description

Method for predicting effective diffusion coefficient of chloride ions in cement paste Technical Field The invention relates to the technical field of diffusion simulation of materials and structural media, in particular to a novel method for predicting the effective diffusion coefficient of chloride ions of cement paste based on a near-field dynamics theory. Background Corrosion of steel bars caused by chlorine salt corrosion is one of the main factors of durability failure of reinforced concrete structures in marine environments. The chloride ions in the service environment of the reinforced concrete structure are diffused into the concrete through capillary pores and cracks by taking water as a carrier and accumulated on the surface of the reinforced steel. Once the chloride ion concentration on the surface of the steel bar reaches a critical value, the passivation film on the surface of the steel bar is destroyed, thereby leading to corrosion of the steel bar. Since the volume of the corrosion product is greater than that of the original body, a corrosive expansion force is generated at the interface between the reinforcing steel bar and the concrete. Finally, it causes cracking and peeling of the reinforcing bar protective layer, seriously affecting the service performance of the reinforced concrete structure. Therefore, the research on the diffusion performance of chloride ions in concrete is of great significance for evaluating the service state of the marine reinforced concrete structure. The key to evaluating the diffusion performance of chloride ions in concrete is to determine the diffusion coefficient of chloride ions in cement paste, and the diffusion coefficient at the present stage is mostly obtained by adopting an experimental method. However, the experimental method is limited by experimental means, can not shield the chloridion combination effect, and the real chloridion diffusion coefficient in the cement paste is difficult to obtain, and the dispersion type of the chloridion diffusion coefficient is large and the like due to the influence of experimental scheme and operation. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a method for predicting the effective diffusion coefficient of chloride ions in cement paste. In order to achieve the above object, the present invention adopts the following technical scheme: a method for predicting the effective diffusion coefficient of chloride ions in cement paste comprises the following steps: step one, establishing a cement paste microstructure, and determining the distribution of materials of each phase; Step two, constructing a high concentration area and a low concentration area on the upper side and the lower side of the microstructure of the cement paste, and determining the size of the high concentration area and the low concentration area; Thirdly, dispersing the cement microstructure, the high concentration region and the low concentration region at equal intervals to form a uniform substance point lattice structure, and determining the substance type of each substance point; Step four, constructing a material dot key list according to the material dot spacing and the near field range; step five, determining the transmission coefficient of each key according to the key list and the material point type information; Step six, constructing a steady-state chloride ion transmission near-field dynamics equation of motion based on a near-field dynamics theory; Step seven, determining boundary conditions and initial values, and solving a steady-state chloride ion transmission near-field dynamics equation by adopting an implicit method; Outputting material point concentration distribution and concentration gradient, and calculating an effective chloride ion diffusion coefficient; further, in the first step, the cement paste microstructure is established, wherein the cement paste microstructure comprises unhydrated cement particles, a pore structure, a high-density hydration product, a low-density hydration product and a high-low-density mixed hydration product. Further, in the second step, the heights of the high concentration area and the low concentration area are 0.5-1 times of the microstructure height of the cement paste. Further, in the third step, the equidistant distance is between 0.1 micrometers and 1 micrometer, and the type of the material points is determined by the non-hydrated cement particles, the pore structure, the high-density hydration product, the low-density hydration product or the components with the largest volume ratio in the high-low density mixed hydration product in the 1 cubic micrometers. In the fourth step, the near field range is 3.015 times to 6.015 times of the substance point distance, and each substance point is connected with other substance points in the near field range to form a bond list. In the fifth step, the diffusion coefficient of the bond is a weighted average o