Gradation design method for coarse aggregate in asphalt mixture, computer equipment and storage medium

Abstract

The invention discloses a gradation design method for coarse aggregate in an asphalt mixture, computer equipment and a storage medium, and relates to the field of asphalt mixtures. The design method comprises the following steps: constructing a stacking model; the stacking model comprises a second rigid wall body arranged on the radial periphery; replacing the second rigid wall body with a flexible confining pressure wall body, and performing servo to obtain a three-dimensional discrete element model; the flexible confining pressure wall body comprises a plurality of spherical particles capable of transmitting pressure in the radial direction; applying a preset radial load and a preset axial load, and extracting a normal contact force, a tangential contact force, a normal vector, a tangential vector, a branch vector, a normal branch vector and a tangential branch vector of each contact; constructing a constitutive anisotropy coefficient; and determining the optimal gradation of each grade of coarse aggregate according to the relationship between the weighted structure stress coefficient of the second coarse aggregate aggregate and the axial strain of the second coarse aggregate aggregate under the preset axial load and radial load. According to the invention, the defect of poor correlation between a volume design method and pavement performance is overcome, and the designed gradation has excellent mechanical properties.

Description

Technical Field

[0001] The invention relates to the field of asphalt mixtures, and in particular to a coarse aggregate gradation design method in asphalt mixtures, computer equipment and storage media. Background Art

[0002] Asphalt mixture gradation is directly related to its road performance. If the gradation is too fine, flow deformation is likely to occur at high temperature, which will then evolve into rutting disease; if the gradation is too coarse, the void ratio is large, which is not only easy to segregate during construction, but also prone to water damage disease in later use. Therefore, the best design gradation should have excellent mechanical properties, and the gradation design should be carried out based on the mechanical properties.

[0003] However, the current gradation design is mainly carried out based on volume indicators or experience, which can be divided into the following categories: 1. Design using the CAVF method. The basic idea of ​​the CAVF method is to use asphalt mortar as a filler to fill the voids of the main aggregate, so that the sum of the volume of fine aggregate, the volume of asphalt, the volume of mineral powder and the void volume of the designed mixture is equal to the measured void volume of the main skeleton. The idea is that the main aggregate plays an interlocking role and the fine aggregate plays a filling role. However, the proportion of each grade of coarse aggregate is determined by the packed density of different dosages, and the default is that the packed density is the largest and the interlocking is the best. Its disadvantages are: (1) The repeatability error of the packed density test is large; (2) A large packed density does not mean the best interlocking effect; (3) This method is actually designed using the volume method, and whether the designed gradation mechanical properties are optimal is worth discussing.

[0004] 2. Design using the Bailey method. The Bailey method is based on the interference theory and adopts the plane circle model assumption. It is believed that the maximum particle size of the next-level aggregate cannot interfere with the particle aggregate of the previous level. Its main feature is to control the passing percentage ratio of the key sieve hole size of the coarse aggregate and the fine aggregate so that the mineral gradation can obtain a good skeleton structure. Its disadvantages are: (1) The plane circle assumption is far from the three-dimensional aggregate particles, and the design results have a large deviation; (2) It is only applicable to continuous grading; (3) The volume filling effect of mineral powder is not considered.

[0005] 3. Design using the Marshall method. The core of the Marshall method design is the volume index, which is to find a gradation curve that meets the volume parameter requirements within a given gradation range. Its disadvantages are: (1) The gradation curve is not unique. There are several gradation curves that meet the volume parameter requirements within the gradation range. Therefore, the selection of the gradation curve is highly subjective; (2) The road performance of the asphalt mixture obtained by the gradation curve that meets the volume index is not necessarily the best, and the correlation between the volume index and the road performance needs to be discussed. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a design method, computer equipment and storage medium for asphalt mixture gradation, which have a strong correlation with road performance and the designed gradation has excellent mechanical properties.

[0007] In order to solve the technical problem of the present invention, the present invention provides a method for designing the gradation of coarse aggregate in an asphalt mixture, which comprises: Constructing a stacking model of coarse aggregates with different gradation ratios; the stacking model includes a first coarse aggregate assembly, a first rigid wall disposed at the axial end of the first coarse aggregate assembly, and a second rigid wall disposed at the radial periphery of the first coarse aggregate assembly; The second rigid wall is replaced by a flexible confining pressure wall, and the preset contact stiffness is servoed to a preset target void ratio, and the first rigid wall is removed to obtain a three-dimensional discrete element model; the three-dimensional discrete element model includes a second coarse aggregate assembly and a flexible confining pressure wall, and the flexible confining pressure wall is composed of a plurality of spherical particles, each of which can transmit pressure in a radial direction; Applying a preset radial load and a preset axial load to the three-dimensional discrete element model to obtain a mechanical response model; the coarse aggregate particles in the mechanical response model form a plurality of contacts under the action of the radial load and the axial load, and extracting the normal contact force, tangential contact force, normal vector, tangential vector, branch vector, normal branch vector and tangential branch vector of each contact; Constructing a structural anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the tangential vector, the branch vector, the normal branch vector and the tangential branch vector; Constructing a weighted structural anisotropy coefficient of a second coarse aggregate assembly according to the structural anisotropy coefficient; The optimal gradation of each level of coarse aggregate is determined according to the relationship between the weighted structural anisotropy coefficient of the second coarse aggregate assembly and its axial strain under the preset axial load and radial load, and the coarse aggregate mixture is prepared with the optimal grade.

[0008] As an improvement of the above technical solution, the step of constructing a stacking model of coarse aggregates with different grading ratios includes: Extract geometric parameters of coarse aggregate particles; Filling coarse aggregates of various grades with preset gradation ratios into a closed space formed by the first rigid wall and the second rigid wall to obtain a stacking model; The steps of replacing the second rigid wall with a flexible confining pressure wall, servoing to a preset target void ratio according to a preset contact stiffness, removing the first rigid wall, and obtaining a three-dimensional discrete element model include: The second rigid wall is replaced by a flexible confining pressure wall; Using a linear model, each coarse aggregate particle in the first coarse aggregate assembly is given a contact stiffness, and the contact stiffness is servoed to a preset target porosity; The first rigid wall is removed to obtain a three-dimensional discrete element model.

[0009] As an improvement of the above technical solution, the flexible confining pressure wall includes multiple layers of spherical particles distributed along the axial direction; The radius of the spherical particles in each spherical particle layer is calculated according to the following formula:

[0010] Among them, r i is the radius of the spherical particles in the i-th spherical particle layer, R i is the radius of the first coarse aggregate in the accumulation model, N i is the number of spherical particles in the i-th spherical particle layer; The number of spherical particle layers in the flexible confining pressure wall is calculated according to the following formula:

[0011] Among them, C i is the number of spherical granular layers in the flexible confining pressure wall, H i is the height of the flexible confining wall, r i is the radius of the spherical particles in the i-th spherical particle layer.

[0012] As an improvement of the above technical solution, in the step of applying a preset radial load and a preset axial load to the three-dimensional discrete element model to obtain a mechanical response model, when the radial load is applied, the confining pressure on the spherical particles in the spherical particle layer is calculated according to the area equivalence principle.

[0013] As an improvement of the above technical solution, the step of constructing the fabric anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the branch vector, the tangential vector, the normal branch vector and the tangential branch vector includes the steps of calculating the stress tensor and the fabric tensor according to the normal contact force, the normal vector, the tangential vector and the branch vector, and calculating the anisotropy coefficient according to the stress tensor and the fabric tensor; Among them, the stress tensor, fabric tensor, and anisotropy coefficient are calculated according to the following formula group:

[0014]

[0015]

[0016]

[0017] is the stress tensor of the second coarse aggregate, is the fabric tensor of the second coarse aggregate, is the second-order structure tensor of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force of the cth contact, is the branch vector of the cth contact, V is the volume of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

[0018] As an improvement of the above technical solution, the step of constructing the structural anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the tangential vector, the branch vector, the normal branch vector and the tangential branch vector further comprises: calculating the structural tensor of the normal contact force, the structural tensor of the tangential contact force, the structural tensor of the normal branch vector and the structural tensor of the tangential branch vector; Among them, the structural tensor of the normal contact force is calculated as follows:

[0019] in, is the structural tensor of the normal contact force of the second coarse aggregate assembly, is the normal contact force of the cth contact, , are the projections of the unit normal contact force of the cth contact in the i and j directions respectively, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; The structural tensor for the tangential contact force is calculated as follows:

[0020] in, is the structural tensor of the tangential contact force of the second coarse aggregate assembly, is the magnitude of the tangential contact force of the cth contact, , are the projections of the unit tangential contact forces of c contacts in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the normal branch vector is as follows:

[0021] in, is the structural tensor of the normal branch vector of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal branch vector of the cth contact in the i and j directions, respectively. , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the tangent branch vector is as follows:

[0022] in, is the structural tensor of the tangential branch vector of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, , is the projection length of the unit tangential branch vector of the cth contact in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

[0023] As an improvement of the above technical solution, the step of constructing the composition anisotropy coefficient according to the normal contact force, tangential contact force, normal vector, tangential vector, branch vector, normal branch vector and tangential branch vector also includes: the step of calculating the composition anisotropy coefficient of the normal contact force, the composition anisotropy coefficient of the tangential contact force, the composition anisotropy coefficient of the normal branch vector and the composition anisotropy coefficient of the tangential branch vector that characterize the degree of anisotropy distributed in different directions; Among them, the calculation method of the normal contact force component anisotropy coefficient is as follows:

[0024] In the formula, is the normal contact force anisotropy coefficient of the second coarse aggregate, and are the second-order structural tensors of the normal contact force of the second coarse aggregate, and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the normal contact force of the second coarse aggregate The partial tensor of is the average normal contact force of the second coarse aggregate, is the normal contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential contact force component anisotropy coefficient is as follows:

[0025] In the formula, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and They are the second-order structural tensors of the tangential contact force of the second coarse aggregate assembly; and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the tangential contact force of the second coarse aggregate The partial tensor of is the average tangential contact force of the second coarse aggregate, is the magnitude of the tangential contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the normal branch vector structural anisotropy coefficient is as follows:

[0026] In the formula, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the normal branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structure tensor of the normal branch vector The partial tensor of is the average normal branch vector length of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential branch vector structural anisotropy coefficient is as follows:

[0027] In the formula, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the tangential branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structural tensor of the tangential branch vector of the second coarse aggregate The partial tensor of is the average tangential branch vector length of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model.

[0028] As an improvement of the above technical solution, the weighted structural anisotropy coefficient is calculated according to the following formula: ; In the formula, is the weighted structural anisotropy coefficient of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force structural anisotropy coefficient of the second coarse aggregate assembly, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate assembly.

[0029] Correspondingly, the present invention also discloses a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above-mentioned design method when executing the computer program.

[0030] Correspondingly, the present invention also discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the grading design method steps of the above method are implemented.

[0031] The implementation of the present invention has the following beneficial effects: In the method for designing the gradation of coarse aggregate in asphalt mixture of the present invention, a three-dimensional discrete element model, three-dimensional flexible confining pressure, servo control, fabric tensor, structural tensor, and fabric anisotropy coefficient are combined to form a coarse aggregate gradation design process that is consistent with road performance and what you see is what you get. Specifically: the present invention adopts flexible confining pressure control, which can track the multiple mechanical properties of the coarse aggregate assembly within the effective deformation range and comprehensively evaluate the effectiveness of the designed gradation. The present invention adopts a theoretical method to effectively solve the disadvantage that the volume design method has a poor correlation with road performance, and the designed gradation has excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a three-dimensional schematic diagram of a 4.75-9.5 mm coarse aggregate scanned in Example 1 of the present invention; Figure 2 is a three-dimensional schematic diagram of a 9.5-13.2 mm coarse aggregate scanned in Example 1 of the present invention; Figure 3 is a schematic diagram of a confined space in Example 1 of the present invention; Figure 4 is a schematic diagram of a flexible confining pressure wall in Example 1 of the present invention; Figure 5 It is a schematic diagram of the numbering rules of the head balls, regular balls and tail balls of the even-numbered layers when the spherical particles are arranged in an interlaced manner in Example 1 of the present invention; Figure 6 It is a schematic diagram of the numbering rules of the head balls, regular balls and tail balls of the odd-numbered layers when the spherical particles are arranged in an interlaced manner in Example 1 of the present invention; Figure 7 Schematic diagram of the numbering rules of the head ball, the regular ball and the tail ball when the spherical particles are symmetrically arranged in Example 1 of the present invention; Figure 8 Schematic diagram of the calculation rule of unit area when spherical particles are arranged in an interlocking manner in Example 1 of the present invention; Fig. 9is a schematic diagram of the calculation rule of the unit area when the spherical particles are symmetrically arranged in Example 1 of the present invention; Fig.10 is a relationship diagram between the weighted structural stress coefficient and the axial strain under a confining pressure of 0.2 MPa in Example 1 of the present invention; Fig.11 It is a relationship diagram between the weighted structural stress coefficient and the axial strain under the confining pressure of 0.4 MPa in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with specific implementation methods.

[0034] Example 1 This embodiment provides a method for designing the gradation of coarse aggregate in an asphalt mixture, comprising: S1: Construct the stacking model of coarse aggregate with different grading ratios; Specifically, in one embodiment, coarse aggregate refers to aggregate with a particle size ≥ 4.75 mm.

[0035] Specifically, step S1 includes: S11: Scanning coarse aggregates of different particle sizes in each batch using a 3D scanner to form an STL format file, and forming a template with the 3D scanning files of different particle sizes; Specifically, in one embodiment, taking asphalt mixture AC-13 as an example, its coarse aggregate includes two grades of 4.75~9.5mm and 9.5~13.2mm, and the stl files after three-dimensional scanning are as follows: Figure 1 , Figure 2 shown.

[0036] S12: Generate top, bottom and side rigid walls to form a confined space (refer to Figure 3 ), calculate the volume of the confined space; S13: Use clump distribute to read the coarse aggregate particles of different particle sizes in the template in turn, determine the generation volume of each level of coarse aggregate particles according to the preset gradation ratio, and calculate the number of coarse aggregate particles required to generate each level of coarse aggregate according to the volume of a single coarse aggregate particle; the generation order is to generate the coarse aggregate particle model in order from large to small particle size; S14: randomly placing the generated coarse aggregate particle model into a predetermined area of ​​a preset closed space to obtain a stacking model; Specifically, in one embodiment, steps S12 to S14 are completed in the three-dimensional discrete element software PFC.

[0037] S2: replacing the second rigid wall with a flexible confining pressure wall, servoing to a preset target void ratio according to a preset contact stiffness, removing the first rigid wall, and obtaining a three-dimensional discrete element model; Specifically, in one embodiment, step S2 includes: S21: Replace the second rigid wall with a flexible confining pressure wall; It should be noted that it is difficult to effectively apply radial load (confining pressure) in the traditional three-dimensional discrete element model, which makes it difficult to effectively simulate the stress effect on asphalt mixture during real road use. Based on this, the present invention replaces the second rigid wall with a flexible confining pressure wall (refer to Figure 4 ), in order to simulate the influence of radial load on the coarse aggregate. Specifically, the flexible confining pressure wall is composed of multiple spherical particles, each of which can transmit pressure in the radial direction, thereby transmitting the radial load applied to the model to the coarse aggregate particles through the spherical particles. In order to accurately evaluate the above simulation, it is necessary to specify the specific number, diameter, and numbering rules of the spherical particles in the flexible confining pressure wall in detail to achieve accurate extraction of the confining pressure on each spherical particle. The details are as follows: In one embodiment, the flexible confining pressure wall includes multiple spherical particle layers distributed along the axial direction; The radius of the spherical particles in each spherical particle layer is calculated according to the following formula:

[0038] Among them, r i is the radius of the spherical particles in the i-th spherical particle layer, R i is the radius of the first coarse aggregate in the accumulation model, N i is the number of spherical particles in the i-th spherical particle layer; specifically, for the convenience of calculation, the number of spherical particles in each spherical particle layer is set to 10 n , wherein n is a positive integer greater than or equal to 2. Further, the radii of all spherical particles in the flexible confining pressure wall are set to be the same.

[0039] The number of spherical particle layers in the flexible confining pressure wall is calculated according to the following formula:

[0040] Among them, C i is the number of spherical granular layers in the flexible confining pressure wall, H i is the height of the flexible confining wall, r i is the radius of the spherical particles in the i-th spherical particle layer.

[0041] Specifically, in one embodiment, the spherical particles in each spherical particle layer in the flexible confining pressure wall are numbered from large to small. For example, in one embodiment, if the number of spherical particles in each spherical particle layer is 100, the starting number of the spherical particles in the layer can be set to 100000, the last spherical particle is numbered 100099, and so on.

[0042] Furthermore, in order to facilitate the calculation of the confining pressure of each spherical particle after the radial load is applied later, it is also necessary to specify the numbering rules between adjacent layers. Specifically, the spherical particles of adjacent spherical particle layers are arranged in an interlocking arrangement or a symmetrical arrangement; when the spherical particles are arranged in an interlocking arrangement, six spherical particles are arranged around each spherical particle; when the spherical particles are arranged in a symmetrical arrangement, four spherical particles are arranged around each spherical particle (see Figure 5~Figure 7 ). The following is a detailed description of the numbering rules between adjacent layers in each arrangement mode: 1. When spherical particles are arranged in an interlocking manner, the numbering rules of spherical particles in even-numbered layers and odd-numbered layers are different; When spherical particles are arranged in an interlaced manner, they are divided into head balls, regular balls, and tail balls. The head ball is the ball that starts numbering in each layer of balls. Its number N0 can be an integer, and N0 ≥ 10 n (n is a positive integer ≥ 3), such as 10000 or 100000; the tail ball is the ball at the end of each layer of balls, and its number is N e It can be an integer, and N e =N0+N i -1(N i is the total number of spherical particles in the i-th layer), exemplarily 10099 or 100099; the conventional balls are small balls between the head ball and the tail ball, numbered N0+1~N e -1, illustratively, 10001~10098 or 100001~100098 (taking 100 spherical particles in each layer as an example, but not limited to this); the numbering rules for even-numbered layers and odd-numbered layers are different. The details are as follows: 1. Ginseng Figure 5 , the numbering rule for spherical particles in even layers is: (1) When it is the first ball in an even layer, the ball is numbered as bid. The number of the ball to the right of the ball is bid+1. The number of the ball to the left of the ball is bid-1+N i , The number of the ball on the upper right side of the ball is bid+1+N i , The number of the ball on the upper left side of the ball is bid+N i , The number of the ball to the lower right of the ball is bid+1-N i , The number of the ball on the lower left side of the ball is bid-N i .

[0043] (2) When it is the last ball of an even-numbered layer, the ball number is bid. The number of the ball to the right of the ball is bid+1-N i , The ball to the left of the ball is numbered bid-1. The number of the ball on the upper right side of the ball is bid+1. The number of the ball on the upper left side of the ball is bid+N i , The number of the ball to the lower right of the ball is bid+1-N i -N i , The number of the ball on the lower left side of the ball is bid-N i .

[0044] (3) When it is an even-numbered layer of regular balls (the 2nd to the Nth i -1 ball (the ordinary ball), record the ball number as bid, then The number of the ball to the right of the ball is bid+1. The ball to the left of the ball is numbered bid-1. The number of the ball on the upper right side of the ball is bid+1+N i , The number of the ball on the upper left side of the ball is bid+N i , The number of the ball to the lower right of the ball is bid+1-N i , The number of the ball on the lower left side of the ball is bid-N i .

[0045] It should be noted that Figure 5 N i = 100 for legend illustration, but N i The value of is not limited to this.

[0046] (II) Ginseng Figure 6 , the numbering rule for odd-numbered layers of spherical particles is: (1) When it is the first ball in an odd layer, the ball is numbered as bid. The number of the ball to the right of the ball is bid+1. The number of the ball to the left of the ball is bid-1+N i , The number of the ball on the upper right side of the ball is bid+N i , The number of the ball on the upper left side of the ball is bid-1+N i +N i , The number of the ball on the lower right side of the ball is bid-N i , The small ball on the lower left side of the ball is numbered bid-1.

[0047] (2) When it is the last ball of an odd-numbered layer, the ball number is bid. The number of the ball to the right of the ball is bid+1-N i , The ball to the left of the ball is numbered bid-1. The number of the ball on the upper right side of the ball is bid+N i , The number of the ball on the upper left side of the ball is bid-1+N i , The number of the ball on the lower right side of the ball is bid-N i , The ball on the lower left side of the ball is numbered bid-1-N i .

[0048] (3) When it is an odd-numbered layer of regular balls (the 2nd to the Nth i -1 ball (the ordinary ball), record the ball number as bid, then The number of the ball to the right of the ball is bid+1. The ball to the left of the ball is numbered bid-1. The number of the ball on the upper right side of the ball is bid+N i , The number of the ball on the upper left side of the ball is bid-1+N i , The number of the ball on the lower right side of the ball is bid-N i , The ball on the lower left side of the ball is numbered bid-1-N i .

[0049] It should be noted that Figure 6 N i = 100 for legend illustration, but N i The value of is not limited to this.

[0050] 2. When the spherical particles are arranged symmetrically, the numbering rule of the spherical particles is: When the spherical particles are arranged symmetrically, they are divided into head balls, regular balls, and tail balls. The head ball is the ball that starts numbering in each layer of balls. Its number N0 can be an integer, and N0 ≥ 10 n (n is a positive integer ≥ 3), such as 10000 or 100000; the tail ball is the ball at the end of each layer of balls, and its number is N e It can be an integer, and N e =N0+N i -1(N i is the total number of spherical particles in the i-th layer), exemplarily 10099 or 100099; the conventional balls are small balls between the head ball and the tail ball, numbered N0+1~N e -1, illustratively, 10001-100098 or 100001~100098 (taking 100 spherical particles in each layer as an example, but not limited to this); the numbering rules of even-numbered layers and odd-numbered layers are the same, such as Figure 7 As shown, more specific as follows: (1) When it is the first ball of each layer, the ball number is bid, then The number of the ball to the right of the ball is bid+1. The number of the ball to the left of the ball is bid-1+N i , The number of the ball directly above the ball is bid+N i , The number of the ball directly below the ball is bid-N i .

[0051] (2) When it is the last ball of each layer, the ball number is bid, then The number of the ball to the right of the ball is bid+1-N i , The ball to the left of the ball is numbered bid-1. The number of the ball directly above the ball is bid+N i , The number of the ball directly below the ball is bid-N i .

[0052] (3) When the regular balls in each layer (the 2nd to the Nth i -1 ball (the ordinary ball), let the ball be numbered bid, then The number of the ball to the right of the ball is bid+1. The ball to the left of the ball is numbered bid-1. The number of the ball directly above the ball is bid+N i , The number of the ball directly below the ball is bid-Ni .

[0053] It should be noted that Figure 7 N i = 100 for legend illustration, but N i The value of is not limited to this.

[0054] S22: using a linear model to assign contact stiffness to each coarse aggregate particle in the first coarse aggregate assembly, and servoing to a preset target void ratio; Specifically, a linear contact bonding model may be used for simulation, and a preset target void ratio may be achieved under a given contact stiffness.

[0055] S3: applying a preset radial load and a preset axial load to the three-dimensional discrete element model to obtain a mechanical response model; When a radial load is applied, the confining pressure exerted on the spherical particles in the spherical particle layer near the middle is calculated according to the area equivalence principle. Specifically, the center coordinates of each spherical particle are extracted according to the number of each spherical particle, the center vector of each spherical particle is calculated, and the preset area is calculated according to the center vector, and then the confining pressure exerted on each spherical particle is calculated; Exemplarily, the nested arrangement is as follows Figure 8 As shown, the regular hexagon is the calculation unit area, and the regular hexagon is composed of six equilateral triangles. The force applied to the area of ​​the regular hexagon is equivalent to the force applied to the target ball BP_0, F=P*(S1+S2+S3+S4+S5+S6), where P is the confining pressure value, S1, S2, S3, S4, S5, and S6 are the areas of the six equilateral triangles respectively.

[0056] Taking the triangle S1 composed of balls BP_0, BP_UR, and BP_R as an example, the center coordinates of the three balls are extracted, the center vector is calculated, S1 is calculated based on the cross product of the center vectors, and then the force applied to S1 is calculated. When extracting the center coordinates of each ball, the extraction is performed according to the number of each ball. The numbering rules of the balls refer to Figure 5 and Figure 6 .

[0057] Symmetrical arrangement Fig. 9 As shown, the square is the calculation unit area, and the square is composed of four small squares. The force applied to the square area is equivalent to being applied to the target ball BP_0, F=P*(S1+S2+S3+S4), where P is the test confining pressure value, and S1, S2, S3, and S4 are the areas of the four squares respectively.

[0058] Take the square of (S1+S2+S3+S4) enclosed by the balls BP_R, BP_L, BP_U, and BP_D as an example, by extracting the center coordinates of the three balls BP_0, BP_L, and BP_U, calculate the center vector, calculate S1 based on half of the cross product of the center vector, and then calculate the force applied to S1. When extracting the center coordinates of each ball, extract them according to the number of each ball. The numbering rules of the balls refer to Figure 7 .

[0059] Specifically, after applying a preset radial load and a preset axial load to the three-dimensional discrete element model, the coarse aggregate particles form multiple contacts under the action of the radial load and the axial load, and the discrete element software PFC is used for simulation, and then the normal contact force, tangential contact force, branch vector, normal branch vector, tangential branch vector and normal vector of each contact are extracted. It should be noted that the contact here is different from the coarse aggregate particles, and each coarse aggregate particle may form multiple contacts under the action of multiple coarse aggregate particles around it.

[0060] S4: construct the structural anisotropy coefficient according to the normal contact force, tangential contact force, normal branch vector, branch vector, tangential branch vector and normal vector; Specifically, S5 includes: S41: Calculate the stress tensor and the fabric tensor according to the normal contact force, the normal vector, the tangential vector and the branch vector, and calculate the anisotropy coefficient according to the stress tensor and the fabric tensor; Among them, the stress tensor, fabric tensor, and anisotropy coefficient are calculated according to the following formula group:

[0061]

[0062]

[0063]

[0064] is the stress tensor of the second coarse aggregate, is the fabric tensor of the second coarse aggregate, is the second-order structure tensor of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force of the cth contact, is the branch vector of the cth contact, V is the volume of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

[0065] It should be noted that in the present invention, the normal contact force, tangential contact force, normal vector, tangential vector, branch vector, normal branch vector, and tangential branch vector are all vectors, and their magnitudes and lengths refer to the modulus of the vector. The unit normal vector refers to the vector obtained by dividing the normal vector by its modulus, and other unit vectors are calculated in the same way.

[0066] S42: Calculate the structure tensor of normal contact force, the structure tensor of tangential contact force, the structure tensor of normal branch vector, and the structure tensor of tangential branch vector; Among them, the structural tensor of the normal contact force is calculated as follows:

[0067] in, is the structural tensor of the normal contact force of the second coarse aggregate assembly, is the normal contact force of the cth contact, , are the projections of the unit normal contact force of the cth contact in the i and j directions respectively, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; The structural tensor for the tangential contact force is calculated as follows:

[0068] in, is the structural tensor of the tangential contact force of the second coarse aggregate assembly, is the magnitude of the tangential contact force of the cth contact, , are the projections of the unit tangential contact forces of c contacts in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the normal branch vector is as follows:

[0069] in, is the structural tensor of the normal branch vector of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal branch vector of the cth contact in the i and j directions, respectively. , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the tangent branch vector is as follows:

[0070] in, is the structural tensor of the tangential branch vector of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, , is the projection length of the unit tangential branch vector of the cth contact in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

[0071] S43: calculating the normal contact force configuration anisotropy coefficient, the tangential contact force configuration anisotropy coefficient, the normal branch vector configuration anisotropy coefficient and the tangential branch vector configuration anisotropy coefficient, which characterize the degree of anisotropy distributed in different directions; Among them, the calculation method of the normal contact force component anisotropy coefficient is as follows:

[0072] In the formula, is the normal contact force anisotropy coefficient of the second coarse aggregate, and are the second-order structural tensors of the normal contact force of the second coarse aggregate, and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the normal contact force of the second coarse aggregate The partial tensor of is the average normal contact force of the second coarse aggregate, is the normal contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential contact force component anisotropy coefficient is as follows:

[0073] In the formula, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and They are the second-order structural tensors of the tangential contact force of the second coarse aggregate assembly; and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the tangential contact force of the second coarse aggregate The partial tensor of is the average tangential contact force of the second coarse aggregate, is the magnitude of the tangential contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the normal branch vector structural anisotropy coefficient is as follows:

[0074] In the formula, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the normal branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structure tensor of the normal branch vector The partial tensor of is the average normal branch vector length of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential branch vector structural anisotropy coefficient is as follows:

[0075] In the formula, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the tangential branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structural tensor of the tangential branch vector of the second coarse aggregate The partial tensor of is the average tangential branch vector length of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model.

[0076] S5: constructing a weighted structural stress coefficient of the second coarse aggregate according to the structural anisotropy coefficient; Specifically, the weighted structural anisotropy coefficient is calculated according to the following formula: ; In the formula, is the weighted structural anisotropy coefficient of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force structural anisotropy coefficient of the second coarse aggregate assembly, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate assembly.

[0077] S6: Determine the optimal gradation of each level of coarse aggregate according to the relationship between the weighted structural stress coefficient of the second coarse aggregate assembly and its axial strain under a preset axial load.

[0078] Specifically, coarse aggregates of different particle sizes are taken respectively, and after being mixed according to different grading ratios, a three-dimensional discrete element model is generated according to steps S1 to S5, different radial loads and axial loads are changed, the microscopic mechanical properties of the coarse aggregate assembly under different grading ratios are compared and analyzed, and the gradation with the best road performance is selected.

[0079] For example, in one embodiment of the present invention, the relationship between the weighted structural anisotropy coefficients at 9.5-13.2 mm: 4.75-9.5 mm = 3:7, 4:6, 5:5, 6:4 under confining pressures of 0.2 MPa and 0.4 MPa is as follows: Fig.10 , Fig.11 shown.

[0080] according to Fig.10 , Fig.11 When 9.5~13.2mm:4.75~9.5mm=4:6, the mechanical properties of the coarse aggregate assembly are the best, so the ratio of coarse aggregate 9.5~13.2mm and 4.75~9.5mm is determined to be 4:6.

[0081] The above is a preferred embodiment of the invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the invention. These improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A method for designing the gradation of coarse aggregate in asphalt mixture, characterized in that: include: Constructing a stacking model of coarse aggregates with different gradation ratios; the stacking model includes a first coarse aggregate assembly, a first rigid wall disposed at the axial end of the first coarse aggregate assembly, and a second rigid wall disposed at the radial periphery of the first coarse aggregate assembly; The second rigid wall is replaced by a flexible confining pressure wall, and the preset contact stiffness is servoed to a preset target void ratio, and the first rigid wall is removed to obtain a three-dimensional discrete element model; the three-dimensional discrete element model includes a second coarse aggregate assembly and a flexible confining pressure wall, and the flexible confining pressure wall is composed of a plurality of spherical particles, each of which can transmit pressure in a radial direction; Applying a preset radial load and a preset axial load to the three-dimensional discrete element model to obtain a mechanical response model; the coarse aggregate particles in the mechanical response model form a plurality of contacts under the action of the radial load and the axial load, and extracting the normal contact force, tangential contact force, normal vector, tangential vector, branch vector, normal branch vector and tangential branch vector of each contact; Constructing a structural anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the tangential vector, the branch vector, the normal branch vector and the tangential branch vector; Constructing a weighted structural anisotropy coefficient of a second coarse aggregate assembly according to the structural anisotropy coefficient; The optimal gradation of each level of coarse aggregate is determined according to the relationship between the weighted structural anisotropy coefficient of the second coarse aggregate assembly and its axial strain under the preset axial load and radial load, and the coarse aggregate mixture is prepared with the optimal grade.

2. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 1, characterized in that: The steps of constructing a stacking model of coarse aggregates with different gradation ratios include: Extract geometric parameters of coarse aggregate particles; Filling coarse aggregates of various grades with preset gradation ratios into a closed space formed by the first rigid wall and the second rigid wall to obtain a stacking model; The steps of replacing the second rigid wall with a flexible confining pressure wall, servoing to a preset target void ratio according to a preset contact stiffness, removing the first rigid wall, and obtaining a three-dimensional discrete element model include: The second rigid wall is replaced by a flexible confining pressure wall; Using a linear model, each coarse aggregate particle in the first coarse aggregate assembly is given a contact stiffness, and the contact stiffness is servoed to a preset target porosity; The first rigid wall is removed to obtain a three-dimensional discrete element model.

3. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 1 or 2, characterized in that: The flexible confining pressure wall comprises multiple layers of spherical particles distributed along the axial direction; The radius of the spherical particles in each spherical particle layer is calculated according to the following formula: Among them, r i is the radius of the spherical particles in the i-th spherical particle layer, R i is the radius of the first coarse aggregate in the accumulation model, N i is the number of spherical particles in the i-th spherical particle layer; The number of spherical particle layers in the flexible confining pressure wall is calculated according to the following formula: Among them, C i is the number of spherical granular layers in the flexible confining pressure wall, H i is the height of the flexible confining wall, r i is the radius of the spherical particles in the i-th spherical particle layer.

4. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 1, characterized in that: In the step of applying a preset radial load and a preset axial load to the three-dimensional discrete element model to obtain a mechanical response model, when applying the radial load, the confining pressure exerted on the spherical particles in the spherical particle layer is calculated according to the area equivalence principle.

5. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 1, characterized in that: The step of constructing the fabric anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the branch vector, the tangential vector, the normal branch vector and the tangential branch vector comprises the steps of calculating the stress tensor and the fabric tensor according to the normal contact force, the normal vector, the tangential vector and the branch vector, and calculating the anisotropy coefficient according to the stress tensor and the fabric tensor; Among them, the stress tensor, fabric tensor, and anisotropy coefficient are calculated according to the following formula group: is the stress tensor of the second coarse aggregate, is the fabric tensor of the second coarse aggregate, is the second-order structure tensor of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force of the cth contact, is the branch vector of the cth contact, V is the volume of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

6. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 5, characterized in that: The step of constructing the structural anisotropy coefficient according to the normal contact force, the tangential contact force, the normal vector, the tangential vector, the branch vector, the normal branch vector and the tangential branch vector also includes the step of calculating the structural tensor of the normal contact force, the structural tensor of the tangential contact force, the structural tensor of the normal branch vector and the structural tensor of the tangential branch vector; Among them, the structural tensor of the normal contact force is calculated as follows: in, is the structural tensor of the normal contact force of the second coarse aggregate assembly, is the normal contact force of the cth contact, , are the projections of the unit normal contact force of the cth contact in the i and j directions respectively, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; The structural tensor for the tangential contact force is calculated as follows: in, is the structural tensor of the tangential contact force of the second coarse aggregate assembly, is the magnitude of the tangential contact force of the cth contact, , are the projections of the unit tangential contact forces of c contacts in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the normal branch vector is as follows: in, is the structural tensor of the normal branch vector of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal branch vector of the cth contact in the i and j directions, respectively. , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the structure tensor of the tangent branch vector is as follows: in, is the structural tensor of the tangential branch vector of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, , is the projection length of the unit tangential branch vector of the cth contact in the i and j directions, is the second-order structure tensor of the second coarse aggregate, , are the projection lengths of the unit normal vector of the cth contact in the k direction and the l direction, respectively, is the total contact number of coarse aggregate particles in the mechanical response model.

7. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 6, characterized in that: The step of constructing the composition anisotropy coefficient according to the normal contact force, tangential contact force, normal vector, tangential vector, branch vector, normal branch vector and tangential branch vector also includes: calculating the composition anisotropy coefficient of the normal contact force, the composition anisotropy coefficient of the tangential contact force, the composition anisotropy coefficient of the normal branch vector and the composition anisotropy coefficient of the tangential branch vector, which characterize the degree of anisotropy distributed in different directions; Among them, the calculation method of the normal contact force component anisotropy coefficient is as follows: In the formula, is the normal contact force anisotropy coefficient of the second coarse aggregate, and are the second-order structural tensors of the normal contact force of the second coarse aggregate, and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the normal contact force of the second coarse aggregate The partial tensor of is the average normal contact force of the second coarse aggregate, is the normal contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential contact force component anisotropy coefficient is as follows: In the formula, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and They are the second-order structural tensors of the tangential contact force of the second coarse aggregate assembly; and They are all deviatoric tensors of the stress tensor of the second coarse aggregate aggregate; is the structural tensor of the tangential contact force of the second coarse aggregate The partial tensor of is the average tangential contact force of the second coarse aggregate, is the magnitude of the tangential contact force of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the normal branch vector structural anisotropy coefficient is as follows: In the formula, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the normal branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structure tensor of the normal branch vector The partial tensor of is the average normal branch vector length of the second coarse aggregate, is the length of the normal branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model; Among them, the calculation method of the tangential branch vector structural anisotropy coefficient is as follows: In the formula, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, for and The standard value of the double dot product; sign() is the sign function, when >0,sign( ) = 1; when <0, sign( ) = -1; and are the second-order structure tensors of the tangential branch vectors of the second coarse aggregate; and are the deviatoric tensors of the stress tensor of the second coarse aggregate, is the structural tensor of the tangential branch vector of the second coarse aggregate The partial tensor of is the average tangential branch vector length of the second coarse aggregate, is the length of the tangential branch vector of the cth contact, is the total contact number of coarse aggregate particles in the mechanical response model.

8. The method for designing the gradation of coarse aggregate in asphalt mixture according to claim 6, characterized in that: The weighted structural anisotropy coefficient is calculated according to the following formula: ； In the formula, is the weighted structural anisotropy coefficient of the second coarse aggregate, is the anisotropy coefficient of the second coarse aggregate, is the normal contact force structural anisotropy coefficient of the second coarse aggregate assembly, is the normal branch vector structural anisotropy coefficient of the second coarse aggregate, is the structural anisotropy coefficient of the tangential branch vector of the second coarse aggregate, is the structural anisotropy coefficient of the tangential contact force of the second coarse aggregate assembly.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the design method described in any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the design method steps of any one of claims 1 to 8 are implemented.

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