Construction method of concrete chloride ion diffusion coefficient model

Abstract

The invention provides a construction method of a concrete chloride ion diffusion coefficient model, which comprises the following steps: S1, acquiring a mix proportion of concrete, and acquiring a chloride ion diffusion coefficient of concrete mortar prepared according to the mix proportion; s2, building a two-dimensional three-phase geometric model of the concrete by utilizing finite element software based on the mix proportion; and S3, based on the constructed two-dimensional three-phase geometric model, establishing a chloride ion diffusion coefficient model. According to the method, the influence of large aggregate distribution is considered, concrete erosion can be simulated more accurately, and reliable technical support is provided for durability of large-particle-size aggregate concrete engineering.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete, and in particular relates to a method for constructing a concrete chloride ion diffusion coefficient model. Background Art

[0002] With the rapid development of social economy, the construction speed of port buildings has accelerated. At the same time, as the main material of coastal buildings, concrete, its durability problem has gradually become prominent. In order to ensure that large-volume concrete does not produce cracks during construction, the common practice is to increase the aggregate size and reduce the amount of cementitious materials. Therefore, the aggregate used in concrete has also developed from secondary to tertiary or even quaternary. As the gradation of concrete aggregate increases, the aggregate size increases accordingly. The maximum aggregate size of secondary concrete reaches 40mm, the maximum aggregate size of tertiary concrete reaches 80mm, and the maximum aggregate size of quaternary concrete reaches 120mm. With the increase of aggregate size, some test methods are no longer suitable. The reason is that when forming the test piece, the maximum aggregate size of the concrete mixture should not exceed 1 / 3 of the minimum side length of the test mold. The common practice is to use wet screening method, remove the large-size aggregate, and then test its related performance. This is mentioned in the "Test Procedure for Hydraulic Concrete" (DL / T 5150-2017).

[0003] Although the specification mentions that wet-screened two-stage concrete can be used to prepare fully-graded concrete chloride ion diffusion coefficient specimens, wet-screened two-stage concrete is to screen out large-size aggregates in the fully-graded concrete and leave only small-size aggregates. This practice changes the paste-aggregate ratio in the concrete, resulting in more paste in the molded specimens and a smaller interface transition zone (ITZ) than that of the fully-graded concrete. This practice seriously affects the chloride ion diffusion coefficient of the concrete, and the measured chloride ion diffusion coefficient is smaller than that of the fully-graded concrete.

[0004] The existing rapid chloride ion migration determination methods, the RCM method and the electric flux method, both require that the aggregate particle size should not be greater than 25 mm. Therefore, if these two methods are used to test the chloride ion diffusion coefficient of fully graded concrete, only wet-screened secondary concrete can be used. The chloride ion diffusion coefficient measured by this method is too large. In order to achieve the design indicators, the project often needs to increase the amount of cement or admixtures, which is contrary to the original intention of the design of fully graded concrete. In order to solve the disadvantages brought by wet-screened secondary concrete, there are also existing modeling methods to obtain the chloride ion diffusion coefficient of three-graded equal-proportion concrete. However, the existing models do not consider the influence of large aggregates. Therefore, accurately and quickly establishing a chloride ion diffusion coefficient model for large-size aggregate concrete is the main problem currently faced by engineering and technical personnel. Summary of the invention

[0005] The purpose of the present invention is to provide a method for constructing a concrete chloride ion diffusion coefficient model, which takes into account the influence of large aggregate distribution, can more accurately simulate concrete erosion, and provide reliable technical support for the durability of large-size aggregate concrete projects.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for constructing a concrete chloride ion diffusion coefficient model comprises the following steps:

[0008] S1. Obtaining a mix ratio of concrete, and obtaining a chloride ion diffusion coefficient of a concrete mortar made from the mix ratio;

[0009] S2. Based on the mix ratio, a two-dimensional three-phase geometric model of concrete is constructed using finite element software;

[0010] S3. Based on the constructed two-dimensional three-phase geometric model, a chloride ion diffusion coefficient model is established. The specific steps are as follows:

[0011] S31, determine to create a simulation environment;

[0012] S32, importing a two-dimensional three-phase geometric model into a simulation environment, establishing a three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and constructing them into a union, and using a Boolean algorithm to deduct the aggregate part;

[0013] S33, based on the obtained chloride ion diffusion coefficient of the concrete mortar, set the basic parameters that need to be defined in the model establishment, the basic parameters include the initial chloride ion concentration in the concrete, the initial chloride ion diffusion coefficient of the mortar, the initial chloride ion diffusion coefficient of the interface transition zone, and the attenuation coefficient of the chloride ion diffusion coefficient of the mortar with age;

[0014] S34, setting a time-varying model of mortar diffusion coefficient and a time-varying model of chloride ion concentration on the concrete surface;

[0015] S35, setting a zero flux boundary and a chloride ion inflow boundary of the two-dimensional three-phase geometric model, wherein the zero flux boundary is a boundary that does not allow chloride ions to penetrate or infiltrate, and the chloride ion inflow boundary is a boundary that allows chloride ions to penetrate or infiltrate;

[0016] S36, setting the transfer properties of each component phase in the two-dimensional three-phase geometric model;

[0017] S37. Use ultra-fine grids for grid division to complete the process of establishing the chloride ion diffusion coefficient model.

[0018] Furthermore, based on the mix ratio, the steps of constructing a two-dimensional three-phase geometric model of concrete using finite element software include:

[0019] S21. Based on the mix ratio, determine the model area of the two-dimensional three-phase geometric model, set the geometric shapes of polygonal aggregates with different particle sizes, and use the area fractions of polygonal aggregates with different particle sizes obtained by the Walraven formula as the target area fractions.

[0020] S22. Randomly place polygonal aggregates within the model area and determine whether there is an overlap between the placed polygonal aggregates and the existing polygonal aggregates within the model area.

[0021] S23. If so, delete the newly placed polygonal aggregate and randomly place a polygonal aggregate within the model area again.

[0022] S24. Generate a film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interfacial transition zone between the polygonal aggregate and the matrix.

[0023] S25. Repeat steps S22 to S24 until the area fractions of polygonal aggregates with different particle sizes within the model area all reach the target area fractions, and complete the construction of the two-dimensional three-phase geometric model of concrete.

[0024] Further, in the step of obtaining the area fractions of polygonal aggregates with different particle sizes by using the Walraven formula, the specific formula is:

[0025]

[0026] In the formula, P c is the probability that an inscribed circle with an aggregate diameter D < D0 appears at any point on the two-dimensional cross-section, P k is the percentage of coarse aggregate in the total volume of concrete, D0 is the sieve hole diameter, and D max is the maximum aggregate particle size.

[0027] Further, the step of generating a film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interfacial transition zone between the polygonal aggregate and the matrix includes:

[0028] S241. Set the thickness of the interfacial transition zone and calculate the coordinates of each vertex of the interfacial transition zone. The specific calculation formula is:

[0029] (x′ ITZ , y′ ITZ ) = (x′ i + t ITZ cos(θ i ), y′ i + t ITZ cos(θ i )) (2);

[0030] In the formula, (x′ ITZ , y′ ITZ ) is the coordinate of the i-th vertex in the interface transition zone, (x i ,y i ) represents the coordinates of the i-th vertex of the polygonal aggregate, t ITZ is the thickness of the interface transition zone, θ i is the polar angle of the ith vertex of the polygonal aggregate relative to the center of the polygonal aggregate;

[0031] S242, connecting the vertices in the interface transition zone.

[0032] Furthermore, the step of setting the thickness of the interface transition zone includes:

[0033] S2411. Obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio;

[0034] S2412, randomly selecting a thickness within a preset thickness range as a target thickness;

[0035] S2413, setting the thickness of the interface transition zone to the target thickness, and constructing a two-dimensional three-phase geometric model under the condition that the thickness of the interface transition zone is the target thickness, and establishing a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model;

[0036] S2414, numerical simulation is performed using the established chloride ion diffusion coefficient model to obtain the chloride ion diffusion coefficient of concrete;

[0037] S2415, determining whether the error between the simulated chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient of the concrete slab is within a preset error range, if not, executing steps S2416 to S2417, if yes, executing step S2418;

[0038] S2416, judging whether the chloride ion diffusion coefficient of the concrete obtained by simulation is greater than the chloride ion diffusion coefficient of the concrete slab, if so, reducing the target thickness to obtain a new target thickness, if less, increasing the target thickness to obtain a new target thickness;

[0039] S2417, repeat steps S2413 to S2415;

[0040] S2418. Set the thickness of the interface transition zone to the target thickness.

[0041] Further, the step of obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio includes:

[0042] preparing concrete slabs according to concrete mix proportions;

[0043] Sampling multiple groups of concrete test blocks on the concrete slab;

[0044] The chloride ion diffusion coefficient of each group of concrete specimens was obtained by RCM or natural immersion grinding method;

[0045] The average value of the chloride ion diffusion coefficients of multiple concrete test blocks is calculated to obtain the average value as the chloride ion diffusion coefficient of the concrete slab.

[0046] Furthermore, in the step of setting the time-varying model of the mortar diffusion coefficient and the time-varying model of the chloride ion concentration on the concrete surface, the time-varying model of the mortar diffusion coefficient is as follows:

[0047] D = D0f(m) (3);

[0048]

[0049] Where D is the chloride ion diffusion coefficient of mortar under different erosion times, m is the attenuation coefficient of chloride ion diffusion coefficient of mortar with age, t is the erosion time, t 28 is the curing age of concrete.

[0050] Furthermore, in the step of setting the time-varying model of the mortar diffusion coefficient and the time-varying model of the chloride ion concentration on the concrete surface, the time-varying model of the chloride ion concentration on the concrete surface is as follows:

[0051] C = 0.36 lnt-0.57 (5);

[0052] Where C is the chloride ion concentration on the concrete surface and t is the erosion time.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows: a two-dimensional three-phase geometric model of concrete is established based on the mix ratio, the influence coefficient of large aggregate is fully considered, the accuracy of the chloride ion resistance design value of large aggregate concrete is improved, and a relatively accurate chloride ion diffusion coefficient can be obtained through the established chloride ion diffusion coefficient model, which provides technical support for the durability design of large aggregate concrete, ensures the quality of the project, and makes up for the shortcomings of the existing test methods in the determination of the chloride ion diffusion coefficient of large aggregate concrete. The method is simple and feasible, and the data is accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The present invention is a flowchart of the steps of the method for constructing a chloride ion diffusion coefficient model for concrete;

[0055] Figure 2 It is a schematic diagram of a two-dimensional three-phase geometric model constructed in the method for constructing a concrete chloride ion diffusion coefficient model of the present invention;

[0056] Figure 3 A schematic diagram of boundary condition setting in the method for constructing a concrete chloride ion diffusion coefficient model of the present invention;

[0057] Figure 4 Schematic diagram of model mesh division;

[0058] Figure 5 It is the distribution diagram of chloride ion concentration in the chloride ion corrosion model;

[0059] Figure 6 Schematic diagram of the distribution of chloride ion diffusion coefficient of concrete with the number of simulation times. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0061] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0063] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0064] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0065] See also Figure 1 , Figure 1 The present invention is a flowchart of the steps of the method for constructing a chloride ion diffusion coefficient model of concrete. A method for constructing a chloride ion diffusion coefficient model of concrete comprises the following steps:

[0066] S1. Obtaining a mix ratio of concrete, and obtaining a chloride ion diffusion coefficient of a concrete mortar made from the mix ratio;

[0067] S2. Based on the mix ratio, a two-dimensional three-phase geometric model of concrete is constructed using finite element software;

[0068] S3. Based on the constructed two-dimensional three-phase geometric model, a chloride ion diffusion coefficient model is established. The specific steps are as follows:

[0069] S31, determine to create a simulation environment;

[0070] S32, importing a two-dimensional three-phase geometric model into a simulation environment, establishing a three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and constructing them into a union, and using a Boolean algorithm to deduct the aggregate part;

[0071] S33, based on the obtained chloride ion diffusion coefficient of the concrete mortar, set the basic parameters that need to be defined in the model establishment, the basic parameters include the initial chloride ion concentration in the concrete, the initial chloride ion diffusion coefficient of the mortar, the initial chloride ion diffusion coefficient of the interface transition zone, and the attenuation coefficient of the chloride ion diffusion coefficient of the mortar with age;

[0072] S34, setting a time-varying model of mortar diffusion coefficient and a time-varying model of chloride ion concentration on the concrete surface;

[0073] S35, setting a zero flux boundary and a chloride ion inflow boundary of the two-dimensional three-phase geometric model, wherein the zero flux boundary is a boundary that does not allow chloride ions to penetrate or infiltrate, and the chloride ion inflow boundary is a boundary that allows chloride ions to penetrate or infiltrate;

[0074] S36, setting the transfer properties of each component phase in the two-dimensional three-phase geometric model;

[0075] S37. Use ultra-fine grids for grid division to complete the process of establishing the chloride ion diffusion coefficient model.

[0076] In the above step S1, the mix ratio of the engineering concrete is first confirmed, and then the concrete mortar of the mix ratio is prepared according to the confirmed concrete mix ratio. Specifically, a cylindrical concrete mortar of φ100mm×50mm is formed indoors. After 28 days of standard curing, the chloride ion diffusion coefficient of the concrete mortar is measured by RCM or natural immersion grinding method to obtain the chloride ion diffusion coefficient of the concrete mortar.

[0077] In the above step S2, the finite element software can adopt one of MATLAB, COMSOL, ANSYS, etc. Based on the principle of random placement of aggregates, a two-dimensional three-phase geometric model of concrete with the concrete mix ratio confirmed in step S1 is constructed in the finite element software. The two-dimensional three-phase geometric model generally refers to a model that describes the distribution and interaction of three different phases in a two-dimensional space.

[0078] Further, in step S2, based on the mix ratio, the step of constructing a two-dimensional three-phase geometric model of concrete using finite element software includes:

[0079] S21. Based on the mix ratio, determine the model region of the two-dimensional three-phase geometric model, set the geometric shapes of polygonal aggregates with different particle sizes, and use the Walraven formula to obtain the area fractions of polygonal aggregates with different particle sizes, and use the obtained area fractions as the target area fractions;

[0080] S22, randomly placing polygonal aggregates in the model area, and determining whether the placed polygonal aggregates overlap with existing polygonal aggregates in the model area;

[0081] S23, if yes, then delete the newly placed polygonal aggregates, and randomly place polygonal aggregates in the model area again;

[0082] S24, generating a film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix;

[0083] S25, repeating step 22 to step S24 until the area fractions of polygonal aggregates with different particle sizes in the model region all reach the target area fractions, thereby completing the construction of the two-dimensional three-phase geometric model of concrete.

[0084] In the above step S21, the model region of the two-dimensional three-phase geometric model is first determined. The model region is a rectangular region with a length of L. x , width is L y。The geometric shape of polygonal aggregates can be described by defining the range of the number of sides and the range of particle sizes of the polygons. Among them, the number of sides of the polygonal aggregates can be randomly selected within a preset range of the number of sides, and then all the polygonal aggregates are established according to the randomly obtained number of sides. The particle size range is determined according to the aggregate range in the mix ratio. For example, if the mix ratio is three-stage grading and there are three types of stones in the three-stage grading, the particle size range of each polygonal aggregate is set according to the particle size ranges of the three types of stones. For the set polygonal aggregates, assuming the center coordinates are (x0, y0), the coordinates of each vertex of the polygonal aggregate can be calculated by the following formula:

[0085] (x i , y i ) = (x0 + r i cos(θ i ), y0 + r i sin(θ i )) (6);

[0086] In the formula, r i is the distance from the i-th vertex to the center, and θ i is the polar angle of the i-th vertex;

[0087] In a two-dimensional model, the three-dimensional aggregate proportion cannot be directly adopted. Therefore, the volume fraction of the three-dimensional aggregate is converted into the area fraction on the two-dimensional plane by using the Walraven formula, and the area fractions of the polygonal aggregates with different particle sizes are obtained. The specific formula is:

[0088]

[0089] In the formula, P c is the probability that an inscribed circle with an aggregate diameter D < D0 appears at any point on the two-dimensional cross-section, P k is the percentage of coarse aggregate in the total volume of concrete, D0 is the sieve hole diameter, and D max is the maximum aggregate particle size.

[0090] In the above step S22, the whole of the polygonal aggregates placed in the model area must be within the model area, that is, all vertices of the polygonal aggregates must meet the following conditions: 0 ≤ x i ≤ L x and 0 ≤ y i ≤ L y ; Therefore, during the process of randomly placing polygonal aggregates in the model area, they can be placed in ascending order of particle size, or in descending order of particle size, or one polygonal aggregate in each particle size range can be placed simultaneously. When placing, first randomly generate the center coordinates of the polygonal aggregate, and the center point position of the polygonal aggregate can be randomly generated by the following formula:

[0091] x0=rand(0,L x )(7);

[0092] y0=rand(0,L y )(8);

[0093] In the formula, rand(a, b) represents a uniform random number in the interval [a, b];

[0094] Determine whether all vertices of the generated polygonal aggregate are within the model area. If not, regenerate the center coordinates of the polygonal aggregate. If within the model area, perform collision detection to determine whether the placed polygonal aggregate overlaps with the existing polygonal aggregates in the model area. The collision detection formula is:

[0095]

[0096] Where (x0, y0) is the coordinate of the center point of the polygonal aggregate currently placed, (x 0,i ,y 0,i ) is the coordinate of the center point of the existing i-th polygonal aggregate, and distance represents the distance between the center of the currently generated polygonal aggregate and the center of the already placed polygonal aggregate;

[0097] If the distance is less than 2r, it is considered that a collision occurs, that is, the polygonal aggregate placed overlaps with the polygonal aggregate already in the model area. Otherwise, the polygonal aggregate placed does not overlap with the polygonal aggregate already in the model area.

[0098] In the above step S23, if the polygonal aggregate to be placed overlaps with the existing polygonal aggregates in the model area, the generated polygonal aggregate is deleted, and then a new polygonal aggregate is regenerated and placed according to step S22 until there is no overlap.

[0099] In the above step S24, the step of generating a thin film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix includes:

[0100] S241, setting the thickness of the interface transition zone, and calculating the coordinates of each vertex in the interface transition zone. The specific calculation formula is:

[0101] (x′ ITZ , y′ ITz )=(x′ i +t ITZ cos(θ i ), y′ i +t ITZ cos(θ i )) (2);

[0102] In the formula, (x′ ITZ , y′ ITZ ) is the coordinate of the i-th vertex in the interface transition zone, (x i ,y i ) represents the coordinates of the i-th vertex of the polygonal aggregate, t ITZ is the thickness of the interface transition zone, θ i is the polar angle of the ith vertex of the polygonal aggregate relative to the center of the polygonal aggregate;

[0103] S242, connecting the vertices in the interface transition zone.

[0104] In the above steps S241 and S242, the thickness of the interface transition zone can be set according to experimental data or relevant standards. For each polygonal aggregate, the boundary vertex coordinates of the interface transition zone can be calculated by expanding the vertices of the original polygonal aggregate outward, and then the vertices of the interface transition zone are connected to obtain the interface transition zone on the polygonal aggregate.

[0105] Further, in step S241, the step of setting the thickness of the interface transition zone includes:

[0106] S2411. Obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio;

[0107] S2412, randomly selecting a thickness within a preset thickness range as a target thickness;

[0108] S2413, setting the thickness of the interface transition zone to the target thickness, and constructing a two-dimensional three-phase geometric model under the condition that the thickness of the interface transition zone is the target thickness, and establishing a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model;

[0109] S2414, numerical simulation is performed using the established chloride ion diffusion coefficient model to obtain the chloride ion diffusion coefficient of concrete;

[0110] S2415, determining whether the error between the simulated chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient of the concrete slab is within a preset error range, if not, executing steps S2416 to S2417, if yes, executing step S2418;

[0111] S2416, judging whether the chloride ion diffusion coefficient of the concrete obtained by simulation is greater than the chloride ion diffusion coefficient of the concrete slab, if so, reducing the target thickness to obtain a new target thickness, if less, increasing the target thickness to obtain a new target thickness;

[0112] S2417, repeat steps S2413 to S2415;

[0113] S2418. Set the thickness of the interface transition zone to the target thickness.

[0114] In the above step S2411, the step of obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio includes:

[0115] S24111. Prepare concrete slab according to concrete mix ratio;

[0116] S24112. Sampling multiple groups of concrete test blocks on the concrete slab;

[0117] S24113. Use RCM or natural immersion grinding method to obtain the chloride ion diffusion coefficient of each group of concrete test blocks;

[0118] S24114. Calculate the average value of the chloride ion diffusion coefficients of multiple concrete test blocks, and use the average value as the chloride ion diffusion coefficient of the concrete slab.

[0119] In the above steps S24111 to S24114, a 500mm×400mm×300mm concrete slab is formed indoors according to the concrete mix ratio. After 28 days of standard curing, multiple groups of concrete test blocks are obtained by uniform core sampling on the concrete slab. The specific number can be selected according to the actual situation. In this embodiment, 12 cylindrical concrete test blocks of 100mm×50mm are uniformly extracted from the concrete slab. Then, the chloride ion diffusion coefficients of the multiple groups of concrete test blocks extracted are measured by RCM or natural immersion grinding method to obtain the chloride ion diffusion coefficient of each group of concrete test blocks. Finally, according to the chloride ion diffusion coefficient of each group of concrete test blocks, the average value of the chloride ion diffusion coefficients of the multiple groups of concrete test blocks is calculated, and the calculated average value is used as the chloride ion diffusion coefficient of the concrete slab.

[0120] In the above step S2412, the thickness of the interface transition zone of ordinary concrete is generally between 10-100 μm, so the preset thickness range can be set to 10-100 μm, and then a thickness is randomly selected within the preset thickness range as the target thickness.

[0121] In the above step S2413, the thickness of the interface transition zone is set to the target thickness, and under the condition that the thickness of the interface transition zone is the target thickness, a two-dimensional three-phase geometric model is constructed according to step S2, and a chloride ion diffusion coefficient model is established according to step S3.

[0122] In the above step S2414, after the chloride ion diffusion coefficient model is established, transient calculation is selected, the calculation step size is set, and calculation is performed to obtain the results of the change of chloride ion concentration in concrete with depth. Based on the results of the change of chloride ion concentration in concrete with depth, Fick's second law is used to invert the chloride ion diffusion coefficient of concrete.

[0123] In the above step S2415, the chloride ion diffusion coefficient of the concrete is compared with the chloride ion diffusion coefficient obtained by coring the concrete slab to determine whether the error between the two is within a preset error range. The error range can be set to within 3%. This is to verify whether the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is accurate by using the chloride ion diffusion coefficient obtained by coring the concrete slab.

[0124] In the above step S2416, if the error between the chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient obtained by coring the concrete slab is outside the preset error range, it means that the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is not very accurate, that is, the thickness setting of the interface transition zone is inaccurate and needs to be adjusted. Therefore, a fixed value of reduction or increase of the interface transition zone is pre-set. In this embodiment, the fixed value is set to 10 μm, and then it is determined whether the chloride ion diffusion coefficient of the simulated concrete is greater than the chloride ion diffusion coefficient of the concrete slab. If it is greater than, it is necessary to reduce the thickness of the interface transition zone, that is, to reduce the target thickness by 10 μm, and obtain a new target thickness. If it is less than, it is necessary to increase the thickness of the interface transition zone, that is, to increase the target thickness by 10 μm, and obtain a new target thickness.

[0125] S2417, after obtaining the new target thickness, reset the thickness of the interface transition zone to the new target thickness, repeat steps S2413 to S2415, and continue to determine whether the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is accurate.

[0126] In the above step S2418, if the error between the chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient obtained by coring the concrete slab is within the preset error range, it means that the chloride ion diffusion coefficient model established under the condition that the thickness of the interface transition zone is the target thickness is accurate, that is, the thickness of the interface transition zone is set accurately and does not need to be adjusted, so the thickness of the interface transition zone is set to the target thickness. Further, the set thickness of the interface transition zone obtained can be used in the establishment of chloride ion diffusion coefficient models of other mix ratios.

[0127] In the above step S25, steps 22 to S24 are repeated to place polygonal aggregates in the model area until the area fractions of polygonal aggregates with different particle sizes in the model area reach the target area fractions, thereby completing the construction of the two-dimensional three-phase geometric model of concrete, and saving the constructed two-dimensional three-phase geometric model to a .dxf format file for later use.

[0128] In the above step S3, in the finite element software, based on the two-dimensional three-phase geometric model established previously, chloride salt corrosion is introduced, so as to establish a chloride ion diffusion coefficient model considering large aggregates.

[0129] In the above steps S31 to S32, a simulation environment is created in COMSOL software, and a .dxf file containing two-dimensional three-phase geometric model information is imported into the simulation environment to establish a two-dimensional three-phase geometric model of the concrete slab; and the two-dimensional three-phase geometric model is divided into three different domains of aggregate, interface transition zone and mortar, and constructed into a union. Since aggregate is a path through which chloride ions do not pass, it is necessary to set the aggregate to zero flux, and then the aggregate part is deducted using a Boolean algorithm to complete the creation of the geometric model.

[0130] In the above step S33, the basic parameters and parameter values ​​required to be defined in the numerical simulation are set, the initial chloride ion concentration C0 in the concrete is set to 0%, and the initial chloride ion diffusion coefficient C s It is the chloride ion diffusion coefficient of the concrete mortar obtained in step S1. The initial chloride ion diffusion coefficient of the interface transition zone is a multiple of the chloride ion diffusion coefficient of the concrete mortar. In this embodiment, the initial chloride ion diffusion coefficient of the interface transition zone is set to 12 times the chloride ion diffusion coefficient of the concrete mortar. The attenuation coefficient m of the chloride ion diffusion coefficient of the mortar with age is set to 0.55, referring to the "Quality Control Standard for High-Performance Concrete for Port Engineering" (JTS257-2-2012).

[0131] In the above step S34, the time-varying model of the mortar diffusion coefficient is as follows:

[0132] D = D0f(m) (3);

[0133]

[0134] Where D is the chloride ion diffusion coefficient of mortar under different erosion times, m is the attenuation coefficient of chloride ion diffusion coefficient of mortar with age, t is the erosion time, t 28 is the curing age of concrete;

[0135] The time-varying model of chloride ion concentration on the concrete surface is obtained by fitting the change of chloride ion concentration on the surface of three-graded concrete with erosion time, as described in the following formula:

[0136] C = 0.36 lnt-0.57 (5);

[0137] Where C is the chloride ion concentration on the concrete surface and t is the erosion time.

[0138] In the above steps S35 to S37, the zero flux boundary and the chloride ion inflow boundary of the chloride ion diffusion model are set, including three zero flux boundaries and one chloride ion inflow boundary, such as Figure 3 Then, the transfer properties of each component phase in the chloride ion diffusion model are set, and the mesh is divided using an ultra-fine grid. The mesh division result is shown in Figure 4 As shown in the figure, after meshing, the chloride ion diffusion coefficient model is established. The chloride ion diffusion coefficient model can be used for engineering applications. For different mix ratios, it is only necessary to determine the chloride ion diffusion coefficient of concrete mortar and establish a two-dimensional three-phase geometric model of concrete with the mix ratio. After bringing the above two into the model, the chloride ion diffusion coefficient model of concrete considering large-size aggregate can be obtained, which provides data support for engineering durability design.

[0139] The method for constructing the concrete chloride ion diffusion coefficient model of the present invention is described below by an embodiment:

[0140] For example, the concrete mix ratio of a ship lock project is shown in Table 1 below;

[0141] Table 1 Concrete mix ratio of a ship lock project

[0142]

[0143] According to the concrete mix ratio in Table 1, a 500mm×400mm×300mm concrete slab and a φ100mm×50mm cylindrical concrete mortar were formed indoors. After 28 days of standard curing, 12 100mm×50mm cylindrical concrete test blocks were evenly extracted from the concrete slab. Then, the chloride ion diffusion coefficients of the concrete mortar and the extracted multiple groups of concrete test blocks were measured by RCM or natural immersion grinding method. It was determined that the chloride ion diffusion coefficients of the concrete mortar and concrete slab prepared based on the mix ratio in Table 1 were 8.0×10 -12 m 2 / s, 4.5×10 -12 m 2 / s.

[0144] According to the concrete mix ratio of the ship lock project in Table 1, the Walraven formula is used to calculate the proportion of aggregates in each particle size range in the two-dimensional geometric figure of the three-graded concrete. The calculated proportions of 5-20mm, 20-40mm, and 40-80mm aggregates are 20.13%, 28.35%, and 51.52%, respectively. In addition, the total area ratio of all aggregates (the proportion of the total aggregate area to the cube) can be calculated to be 55.3% based on the mix ratio. Based on the principle of random placement, a two-dimensional three-phase geometric model of the three-graded concrete in .dxf format with a size of 240mm×240mm×240mm (the side length is three times the maximum aggregate particle size) is constructed using MATLAB, as shown in the figure. Figure 2 shown.

[0145] The concrete geometry model was imported into COMSOL and divided into three different domains: aggregate, interface transition zone and mortar, and then constructed into a union. The aggregate part was deducted using the Boolean algorithm to complete the creation process of the geometry model.

[0146] The basic parameters of the chloride ion diffusion coefficient model are set. The initial chloride ion concentration C0 in concrete is set to 0%, the initial chloride ion diffusion coefficient C s Set to 8.0×10 -12 m 2 / s, initial chloride ion diffusion coefficient C in the interface transition zone ITZ Set to 1.2×10 -10 m 2 / s (12 times of the chloride ion diffusion coefficient of the mortar) and the attenuation coefficient m of the chloride ion diffusion coefficient of the mortar with age is set to 0.55.

[0147] The time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on concrete surface are set as described in the following formula:

[0148] D = D0f(m) (3);

[0149]

[0150] Set the time-varying model of chloride ion concentration on the concrete surface as described in the following formula:

[0151] C = 0.36 lnt-0.57 (5);

[0152] Set the boundary conditions of the chloride ion diffusion model, including three zero flux boundaries and one chloride ion inflow boundary, as shown in the schematic diagram Figure 3 As shown in the figure; set the transfer properties of each component phase in the chloride ion diffusion model; use ultra-fine grids for grid division, and the grid division results are shown in the figure. Figure 4 As shown, the establishment of chloride ion diffusion coefficient model is completed.

[0153] After the chloride ion diffusion coefficient model is completed, select transient calculation, set the calculation step to 30d, and perform the calculation. After the calculation is completed, export the concrete chloride ion concentration cloud map, such as Figure 5 As shown in the figure, the chloride ion concentration in concrete changes with depth, and the chloride ion diffusion coefficient of concrete is inverted using Fick's second law. Finally, the distribution law of the chloride ion diffusion coefficient of concrete with the number of simulations is obtained, as shown in Figure 6 As shown by Figure 6 It can be seen that the chloride ion diffusion coefficient results simulated by the concrete chloride ion diffusion coefficient model are consistent with the chloride ion diffusion coefficient obtained by coring the concrete slab, which is 4.5×10 -12 m 2 The relative error of / s is within 3%, which indirectly verifies the accuracy of the concrete chloride ion diffusion model established by the method for constructing the concrete chloride ion diffusion coefficient model of the present invention, and carries out engineering applications. Therefore, the method for constructing the concrete chloride ion diffusion coefficient model of the present invention can obtain a concrete chloride ion diffusion model with a relative error of less than 3% of the chloride ion diffusion coefficient obtained by concrete coring, avoiding the drawbacks of using wet-screened secondary-graded concrete chloride ion diffusion coefficient to evaluate tertiary-graded concrete, and improving the accuracy of durability evaluation of large-size aggregate concrete.

[0154] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for constructing a chloride ion diffusion coefficient model for concrete, characterized in that: The following steps are involved: S1. Obtaining a mix ratio of concrete, and obtaining a chloride ion diffusion coefficient of a concrete mortar made with the mix ratio; S2. Based on the mix ratio, construct a two-dimensional three-phase geometric model of concrete using finite element software; S3. Based on the constructed two-dimensional three-phase geometric model, a chloride ion diffusion coefficient model is established. The specific steps are as follows: S31, determine to create a simulation environment; S32, importing the two-dimensional three-phase geometric model into a simulation environment, establishing a three-phase domain of the two-dimensional three-phase geometric model, including: aggregate, interface transition zone and mortar, and constructing them into a union, and using a Boolean algorithm to deduct the aggregate part; S33, based on the obtained chloride ion diffusion coefficient of the concrete mortar, setting basic parameters that need to be defined in model establishment, the basic parameters include initial chloride ion concentration in concrete, initial chloride ion diffusion coefficient of mortar, initial chloride ion diffusion coefficient of interface transition zone, and attenuation coefficient of chloride ion diffusion coefficient of mortar with age; S34, setting a time-varying model of mortar diffusion coefficient and a time-varying model of chloride ion concentration on the concrete surface; S35, setting a zero flux boundary and a chloride ion inflow boundary of the two-dimensional three-phase geometric model, wherein the zero flux boundary is a boundary that does not allow chloride ions to penetrate or infiltrate, and the chloride ion inflow boundary is a boundary that allows chloride ions to penetrate or infiltrate; S36, setting the transfer properties of each component phase in the two-dimensional three-phase geometric model; S37. Use ultra-fine grids for grid division to complete the process of establishing the chloride ion diffusion coefficient model.

2. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 1, characterized in that: The step of constructing a two-dimensional three-phase geometric model of concrete using finite element software based on the mix ratio includes: S21. Based on the mix ratio, determine the model region of the two-dimensional three-phase geometric model, set the geometric shapes of polygonal aggregates with different particle sizes, and use the Walraven formula to obtain the area fractions of polygonal aggregates with different particle sizes, and use the obtained area fractions as the target area fractions; S22, randomly placing polygonal aggregates in the model area, and determining whether the placed polygonal aggregates overlap with existing polygonal aggregates in the model area; S23, if yes, then delete the newly placed polygonal aggregates, and randomly place polygonal aggregates in the model area again; S24, generating a film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix; S25, repeating step 22 to step S24 until the area fractions of polygonal aggregates with different particle sizes in the model region all reach the target area fractions, thereby completing the construction of the two-dimensional three-phase geometric model of concrete.

3. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 2, characterized in that: In the step of obtaining the area fraction of polygonal aggregates of different particle sizes using the Walraven formula, the specific formula is: where P c is the probability of the occurrence of an inscribed circle with aggregate diameter D < D0 at any point on the two-dimensional cross-section, P k is the percentage of coarse aggregate in the total volume of concrete, D0 is the sieve hole diameter, D max is the maximum aggregate size.

4. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 2, characterized in that: The step of generating a film corresponding to the shape of the polygonal aggregate around the polygonal aggregate to simulate the interface transition zone between the polygonal aggregate and the matrix comprises: S241, setting the thickness of the interface transition zone, and calculating the coordinates of each vertex of the interface transition zone. The specific calculation formula is: (x′ ITZ ,y′ ITZ )=(x′ i +t ITZ cos(θ i ),y′ i +t ITZ cos(θ i )) (2); In the formula, (x′ ITZ ,y′ ITZ ) is the coordinate of the i-th vertex in the interface transition zone, (x i ,y i ) represents the coordinates of the i-th vertex of the polygonal aggregate, t ITZ is the thickness of the interface transition zone, θ i is the polar angle of the ith vertex of the polygonal aggregate relative to the center of the polygonal aggregate; S242, connecting the vertices of the interface transition zone.

5. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 4, characterized in that: The step of setting the thickness of the interface transition zone comprises: S2411, obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio; S2412, randomly selecting a thickness within a preset thickness range as a target thickness; S2413, setting the thickness of the interface transition zone to the target thickness, and constructing the two-dimensional three-phase geometric model under the condition that the thickness of the interface transition zone is the target thickness, and establishing a chloride ion diffusion coefficient model based on the constructed two-dimensional three-phase geometric model; S2414, numerical simulation is performed using the established chloride ion diffusion coefficient model to obtain the chloride ion diffusion coefficient of concrete; S2415, determining whether the error between the simulated chloride ion diffusion coefficient of the concrete and the chloride ion diffusion coefficient of the concrete slab is within a preset error range, if not, executing steps S2416 to S2417, if yes, executing step S2418; S2416, judging whether the chloride ion diffusion coefficient of the concrete obtained by simulation is greater than the chloride ion diffusion coefficient of the concrete slab, if so, reducing the target thickness to obtain a new target thickness, if less, increasing the target thickness to obtain a new target thickness; S2417, repeat steps S2413 to S2415; S2418. Setting the thickness of the interface transition zone to a target thickness.

6. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 5, characterized in that: The step of obtaining the chloride ion diffusion coefficient of the concrete slab made by the mix ratio comprises: preparing concrete slabs according to concrete mix proportions; Sampling multiple groups of concrete test blocks on the concrete slab; The chloride ion diffusion coefficient of each group of concrete specimens was obtained by RCM or natural immersion grinding method; The average value of the chloride ion diffusion coefficients of multiple concrete test blocks is calculated to obtain the average value as the chloride ion diffusion coefficient of the concrete slab.

7. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 1, characterized in that: In the step of setting the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on the concrete surface, the time-varying model of mortar diffusion coefficient is as follows: D = D0f(m) (3); Where D is the chloride ion diffusion coefficient of mortar under different erosion times, m is the attenuation coefficient of chloride ion diffusion coefficient of mortar with age, t is the erosion time, t 28 is the curing age of concrete.

8. The method for constructing a concrete chloride ion diffusion coefficient model according to claim 1, characterized in that: In the step of setting the time-varying model of mortar diffusion coefficient and the time-varying model of chloride ion concentration on the concrete surface, the time-varying model of chloride ion concentration on the concrete surface is as follows: C = 0.36 lnt-0.57 (5); Where C is the chloride ion concentration on the concrete surface and t is the erosion time.

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