An evaluation method for skeleton structure of asphalt mineral mixture based on accumulation theory

Abstract

The application discloses a method for evaluating the skeleton structure of asphalt mineral mixture based on the accumulation theory and belongs to the technical field of highway analysis and evaluation. In order to solve the problems that the evaluation method for the structure composition of the asphalt mineral mixture lacks the consideration of the contact stress and the contact type between coarse aggregate and fine aggregate, and lacks the intuitive representation and accurate description of the skeleton structure of the asphalt mineral mixture, the application first obtains the real gradation of the mineral mixture; then generates a virtual accumulation model of the mineral mixture by using a discrete element software based on the accumulation theory and carries out a uniaxial constraint compression test simulation; meanwhile, the solid is selected to verify the real model, and the internal structure difference between the real model and the virtual model is clarified by using the X-ray CT technology; finally, the probability density distribution diagram of the contact stress of the mineral mixture and the contribution diagram of the contact type to the external load are constructed by the model test to evaluate the skeleton structure type of the mineral mixture.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of highway analysis and evaluation, and relates to a method for evaluating the skeleton structure of asphalt mineral mixture. BACKGROUND

[0002] Asphalt mixture is a multiphase non-uniform system composed of mineral mixture and asphalt cement, and is used in the construction of asphalt pavement. The mineral mixture is formed by the accumulation of coarse and fine aggregates according to a certain gradation ratio. It is generally believed that the coarse aggregate forms a skeleton structure, and the fine aggregate fills in the skeleton structure, and both of them participate in the stress process. The mineral mixture accounts for more than 90% of the volume of the asphalt mixture, and plays a decisive role in the service performance of the asphalt pavement. As for the bearing capacity of the asphalt mineral mixture, it is largely dependent on the skeleton structure formed by the mineral mixture in the asphalt mixture. However, for the structural composition of the asphalt mineral mixture, the existing research and specifications mostly use macroscopic volume parameters such as mineral aggregate void ratio and air void ratio to characterize the structure, and the contact stress and contact type between the coarse and fine aggregates are not considered enough, and there is a lack of intuitive characterization and accurate description of the skeleton structure of the asphalt mineral mixture, and there is a lack of effective evaluation method for the composition structure of the asphalt mineral mixture. Due to the complexity of the composition and structure of the asphalt mineral mixture, it is necessary to study the micromechanics behavior of the aggregate. In recent years, the rapid development of computer technology and digital virtual technology provides a more convenient method for describing the skeleton structure characteristics in the asphalt mineral mixture. Therefore, for the mineral mixture formed by the accumulation of coarse and fine aggregates, it is necessary to start from the micromechanics to propose an evaluation method for the skeleton structure of the asphalt mineral mixture based on the accumulation theory. SUMMARY

[0003] In order to solve the problem that the evaluation method for the structural composition of the asphalt mineral mixture lacks consideration of the contact stress and contact type between the coarse and fine aggregates, and lacks intuitive characterization and accurate description of the skeleton structure of the asphalt mineral mixture.

[0004] An evaluation method for the skeleton structure of the asphalt mineral mixture based on the accumulation theory, comprising the following steps:

[0005] S1, obtaining the true gradation of the asphalt mineral mixture, and dividing the particles into fine aggregates and coarse aggregates according to the particle size of the aggregate particles; and then performing steps S2 and / or S3;

[0006] S2, using a discrete element software to build a cylindrical container, using a dropping method, generating a certain number of spherical particles according to the obtained true gradation of the mineral mixture, and allowing the particles to freely accumulate in the container under the influence of gravity to form a layer of mineral mixture accumulation body, and using a multi-layer generation method to obtain a uniform mineral mixture accumulation model, and applying a sinusoidal vibration on the mineral mixture accumulation model after completing the accumulation of each layer of mineral mixture;

[0007] For the generated mineral aggregate pile-up model, vertical load is applied to simulate uniaxial constraint compression test, and data is obtained by discrete element software: virtual particle contact number and particle number of coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles, contact stress between mineral aggregate particles and boundary wall, and vertical contact stress of coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles;

[0008] S3, selecting entities for real model verification, including the following steps:

[0009] Step 301, selecting material balls with density close to that of mineral aggregate;

[0010] Step 302, using discrete element software to build a cylindrical container, using a drop method to generate a certain number of material ball particles, allowing them to freely pile up in the container under the influence of gravity to form a layer of material ball pile-up body, and using a multi-layer generation method to obtain a uniform material ball virtual pile-up model, and applying sinusoidal vibration to the pile-up model after completing each layer of material ball pile-up;

[0011] Step 303, selecting a real cylindrical barrel with the same size as the material ball virtual pile-up model to fill the material ball solid pile-up model; using CT technology to scan the material ball solid pile-up model to obtain a tomographic image; and performing computer image processing on the scanned image to obtain particle spatial position information of the tomographic image;

[0012] Step 304, accurately identifying the contacted material ball particles according to the particle spatial position information of the tomographic image; finally, counting the tomographic real particle contact number and particle number to obtain the distribution of the real particle contact number and particle number of the material ball solid pile-up model with the change of the tomographic height;

[0013] Step 305, performing virtual slicing processing on the material ball virtual pile-up model to count the material ball particle contact number and particle number on the virtual slice; taking the particle contact number and particle number as indicators, verifying the structural differences between the material ball virtual pile-up model and the material ball solid pile-up model, and adjusting the number of sinusoidal vibrations applied to the pile-up model corresponding to each layer of material ball in step 302 to obtain a material ball virtual pile-up model and a material ball solid pile-up model that meet the difference verification requirements;

[0014] Step 4, evaluating the skeleton structure of asphalt mineral aggregate, including the following steps:

[0015] Step 401, the contact stress network in the mineral mixture is complex, and the contact stress between the mineral mixture particles can be further divided into strong contact stress and weak contact stress; the strong contact stress refers to the contact stress between the mineral mixture particles being greater than the average contact stress between the mineral mixture particles, and the weak contact stress refers to the contact stress between the mineral mixture particles being less than the average contact stress between the mineral mixture particles; the contact stress between the mineral mixture particles and the boundary wall collected in step S2 and the contact stress data of the aggregate particles are quantitatively analyzed, and a probability density distribution diagram of the contact stress of the mineral mixture is drawn;

[0016] and / or,

[0017] Step 402, according to the difference of the two ends of the contact point, the contact types in the mineral mixture are respectively characterized as coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact; the proportion of the contact stress of different contact types in the total contact stress in the vertical direction reflects the contribution of different contact types of the mineral mixture to the external load; the contribution of different contact types to the external load is quantitatively analyzed by using mathematical statistics technology, and a graph of the contribution of the contact type of the mineral mixture to the external load related to the fine aggregate content is drawn; the skeleton structure of the asphalt mineral mixture is evaluated according to the contribution graph of the contact type of the mineral mixture to the external load.

[0018] Further, the process of obtaining the true gradation of the asphalt mineral mixture in step S1 is determined by the screening experiment of the mineral mixture.

[0019] Further, in the process of dividing the particles into fine aggregate and coarse aggregate according to the particle size of the aggregate particles, the aggregate particles with a particle size of 2.36-4.75 mm are regarded as fine aggregate, and the aggregate particles with a particle size of 4.75 mm and above are regarded as coarse aggregate.

[0020] Further, step S2 applies a sinusoidal vibration in the horizontal direction when applying a sinusoidal vibration on the mineral mixture accumulation model.

[0021] Further, the material balls in step 301 are glass balls.

[0022] Further, when steps S2 and S3 are performed after step S1, the size of the cylindrical container in step 302 is the same as the cylindrical container in step S2, the number of material balls is the same as the number of mineral mixture particles in step S2, the number of layers of material ball accumulation is the same as the number of layers of mineral mixture accumulation in step S2, and the diameter of the material ball is the median value of the particle size of the mineral mixture in step S2.

[0023] Further, the quantity of material balls, the number of material ball stacking layers and the diameter of material balls in the process of forming the material ball entity stacking model in step 303 are the same as the quantity of material balls, the number of material ball stacking layers and the diameter of material balls in step 302.

[0024] Further, in the process of evaluating the skeleton structure of the asphalt mineral mixture in step 401, the stability of the skeleton structure of the mineral mixture is determined by the probability density of strong and weak contact stresses in the mineral mixture. The more the proportion of weak contact stress, the better the filling effect of fine aggregate on the skeleton gap, the better the synergistic bearing capacity of coarse and fine aggregates, the stronger the evaluation of asphalt mixture against external load and deformation, and the better the stability performance.

[0025] Further, the process of evaluating the skeleton structure of the asphalt mineral mixture according to the contribution graph of the contact type of the mineral mixture to the external load in step 402 comprises the following steps:

[0026] In the contribution graph of the contact type to the external load, different curves represent the change trend of different contact types, and the intersection points of different curves in the contribution graph of the contact type are determined; according to the position, number and adjacent curves of the intersection points, the contribution graph is divided into three typical regions; when the contribution values of coarse-coarse aggregate particle contact are all higher than those of coarse-fine aggregate particle and fine-fine aggregate particle contact, it is regarded as typical region I; when the contribution value of coarse-coarse aggregate particle contact is between the contribution values of coarse-fine aggregate particle and fine-fine aggregate particle contact, it is regarded as typical region II; when the contribution value of coarse-coarse aggregate particle contact is lower than both the contribution value of coarse-fine aggregate particle contact and the contribution value of fine-fine aggregate particle contact, it is regarded as typical region III.

[0027] According to the typical regions in the contribution graph of the contact type of the mineral mixture to the external load, the skeleton structure of the asphalt mineral mixture is evaluated; when the contribution value of coarse-coarse particle contact is the highest, i.e. typical region I, it indicates that the proportion of coarse aggregate in the mineral mixture is large, and the asphalt mixture is not easy to deform or damage under external force, and can exhibit good bearing capacity.

[0028] Further, the vertical direction contact total stress in step 402 is:

[0029] σ = σ CC + σ CF + σ FF

[0030] In the formula, σ is the sum of the contact stresses between the mineral mixture particles in the vertical direction, i.e. the total contact stress; σ CC is the sum of the contact stresses between coarse-coarse aggregate particles in the vertical direction; σ CF is the sum of the contact stresses between coarse-fine aggregate particles in the vertical direction; and σ FF is the sum of the contact stresses between fine-fine aggregate particles in the vertical direction.

[0031] Compared with other prior arts, the present application has the following advantages:

[0032] The present application provides a skeleton structure method of asphalt mineral mixture based on packing theory, by constructing the contact stress probability distribution graph of asphalt mineral mixture and the contribution graph of contact type to external load, the present application can intuitively characterize and describe the skeleton structure of asphalt mineral mixture, and can quickly, effectively and accurately evaluate the skeleton structure of asphalt mineral mixture.

[0033] The present application scans the particle entity packing model by CT technology, and provides the optimization basis of the constructed virtual packing model of asphalt mineral mixture by comparing with the virtual packing model of glass ball constructed by discrete element, so as to ensure the accuracy of model evaluation.

[0034] The present application can intuitively reveal the influence of coarse and fine aggregate composition of mineral mixture on the skeleton structure, and provide reference for the gradation design of mineral mixture, so as to effectively improve the production efficiency of asphalt mixture and the construction quality of asphalt pavement. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is the gradation graph of AC-16 mineral mixture with different passing rates;

[0036] Figure 2 is the assembly generation graph of mineral mixture;

[0037] Figure 3 is the uniaxial constraint compression process graph of mineral mixture;

[0038] Figure 4 is the X-ray CT scanning graph and virtual packing model graph of filled glass ball;

[0039] Figure 5 is the horizontal section image schematic diagram of X-ray CT scanning three-dimensional reconstruction model and discrete element virtual packing model;

[0040] Figure 6 is the distribution graph of particle contact number along sample height;

[0041] Figure 7 is the distribution graph of particle number along sample height;

[0042] Figure 8 is the probability density distribution graph of contact stress of mineral mixture (probability density of strong contact stress);

[0043] Figure 9 is the probability density distribution graph of contact stress of mineral mixture (probability density of weak contact stress);

[0044] Figure 10 The contribution of the contact type of the mineral mixture related to the fine aggregate content to the external load. DETAILED DESCRIPTION

[0045] The application will be described in further detail below with reference to the drawings and specific implementation cases. DETAILED DESCRIPTION

[0047] The embodiment is a method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory, comprising the following steps:

[0048] Step 1, obtaining the real gradation of the asphalt mineral mixture;

[0049] The process of obtaining the real gradation of the asphalt mineral mixture is determined by the screening experiment of the mineral mixture. In the embodiment, the aggregate particles with a particle size of 2.36-4.75 mm are regarded as fine aggregate, and the aggregate particles with a particle size of 4.75 mm and above are regarded as coarse aggregate. The aggregate particles with a particle size of less than 2.36 mm are not introduced into the analysis model.

[0050] Step 2, generating a discrete element model of the mineral mixture based on the packing theory using a discrete element software, and performing a uniaxial constraint compression test simulation, comprising:

[0051] Step 201, using the interaction between the contact forms of the calculation objects, which are the mineral mixture particles and the boundary wall, of the discrete element method.

[0052] In the process of the interaction between the contact forms of the calculation objects, the object motion and the contact stress are calculated and iterated based on the Newton's second law and the force-displacement law.

[0053] Step 202, considering that there is no cohesive force action between the particles-particles and the particles-boundary wall in the dry particle packing system, selecting a linear contact model as the particle-particle contact model and the particle-boundary wall contact model.

[0054] When the linear contact model is selected as the particle-particle contact model and the particle-boundary wall contact model, the mesoscopic parameters that need to be determined include the normal contact stiffness k n , the tangential contact stiffness k s and the friction coefficient μ of the contact, etc. These mesoscopic parameters are used in the model establishment process, and the purpose is to make the virtual model consistent with the actual situation.

[0055] Step 203, using discrete element software to build a cylindrical container, using the drop method, according to the real gradation of the mineral aggregate mixture obtained in step 1, a certain number of spherical particles are generated, which are allowed to freely accumulate in the container under the influence of gravity to form a layer of mineral aggregate accumulation body, and a multi-layer generation method is used to obtain a uniform mineral aggregate accumulation model for subsequent loading simulation.

[0056] During the generation of the mineral aggregate accumulation model, after each layer of accumulation is completed, a certain number of sinusoidal vibrations are applied to the mineral aggregate accumulation model in the horizontal direction to ensure that the mineral aggregate accumulation model is in a dense state.

[0057] Step 204, for the generated mineral aggregate accumulation model, vertical load is applied for uniaxial constraint compression test simulation, and data such as the number of virtual particle contacts and the number of particles of coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles, the contact stress (contact force) between the mineral aggregate particles and the boundary wall, and the contact stress (contact force) of vertical coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles are obtained by discrete element software;

[0058] The number of virtual particle contacts and the number of particles are subsequently used to compare the real number of contacts and the number of particles scanned from the physical accumulation model (real model) to verify the difference between the virtual model and the real model;

[0059] The contact stress between the mineral aggregate particles and the boundary wall, and the contact stress of the aggregate particles, are subsequently used to evaluate the skeleton structure of the asphalt mixture.

[0060] Step 3, select entities for real model verification, compare the internal particle space position difference between the discrete element virtual accumulation model and the real accumulation model by X-ray CT technology, including the following steps:

[0061] Step 301, select a material ball with a density close to that of the mineral aggregate mixture as the carrier for optimization and verification of the mineral aggregate accumulation model. In this embodiment, the material ball with a density close to that of the mineral aggregate mixture is selected as a glass ball, and the density of the glass ball is generally 2.5 g / cm 3 , and the density of the mineral aggregate mixture is generally 2.7 g / cm 3 .

[0062] Step 302, using discrete element software to build a cylindrical container, using the drop method, a certain number of glass ball particles are generated, which are allowed to freely accumulate in the container under the influence of gravity to form a layer of glass ball accumulation body, and a multi-layer generation method is used to obtain a uniform glass ball virtual accumulation model for subsequent model verification. During this process, a sinusoidal vibration needs to be applied to the accumulation model in the horizontal direction after each layer of glass ball accumulation is completed.

[0063] The cylindrical container has the same size as the cylindrical container in step 203, the number of glass balls is the same as the number of mineral mixture particles in step 203, the number of glass ball layers is the same as the number of mineral mixture layers in step 203, and the diameter of the glass balls is the median of the particle size of the mineral mixture in step 203.

[0064] In step 303, a real cylindrical barrel with the same size as the virtual glass ball packing model is selected to fill the glass ball physical packing model. The number of glass balls, the number of glass ball layers, and the diameter of the glass balls are the same as those in step 302.

[0065] The glass ball physical packing model is scanned using CT technology to obtain clear tomographic images. The scanned images are processed by computer to obtain spatial position information of the particles in the tomographic images.

[0066] In step 304, the glass ball particles in contact are accurately identified based on the spatial position information of the particles in the tomographic images. The number of real particle contacts and the number of particles are finally counted to obtain the distribution of the number of real particle contacts and the number of particles in the glass ball physical packing model with the change of the tomographic height.

[0067] In step 305, the glass ball virtual packing model is virtually sliced to count the number of glass ball particle contacts and the number of particles on the virtual slices. The number of particle contacts and the number of particles are used as indicators to verify the structural differences between the virtual model (glass ball virtual packing model) and the real model (glass ball physical packing model).

[0068] In step 306, if there is no significant difference between the virtual particle contact number and the real result, it means that the verification result meets the expected standard, and the evaluation of the asphalt mineral mixture skeleton structure can be carried out. Otherwise, if the difference is large, it means that the verification result does not meet the standard, and the number of sinusoidal vibrations applied to the packing model after each layer of glass ball packing in step 302 needs to be increased to improve the density of the packing model until it is consistent with the actual situation. The final determined vibration number is the number of sinusoidal vibrations applied to the packing model after each layer of mineral mixture packing in step 203.

[0069] In step 4, based on the results of the mineral mixture virtual packing test, a contact stress probability distribution diagram and a contact type contribution diagram to external load are constructed to evaluate the asphalt mineral mixture skeleton structure, including the following steps:

[0070] Step 401, the contact stress network in the mineral mixture is complex, and the contact stress between the mineral mixture particles can be further divided into strong contact stress and weak contact stress. The strong contact stress refers to the contact stress between the mineral mixture particles being greater than the average contact stress between the mineral mixture particles, and the weak contact stress refers to the contact stress between the mineral mixture particles being less than the average contact stress between the mineral mixture particles. According to the packing theory, the strong contact stress is mainly generated by coarse aggregate, and the fine aggregate mainly bears the weak contact stress. Mathematical statistics techniques are used to quantitatively analyze the contact stress between the mineral mixture particles and the boundary wall collected in step 204, and the contact stress data of the aggregate particles, and a probability density distribution diagram of the contact stress of the mineral mixture is drawn. The probability density distribution diagram of the contact stress of the mineral mixture is used to illustrate the influence of the content of coarse and fine aggregate particles in the mineral mixture on the stability of the packing structure, and then the skeleton structure of the asphalt mineral mixture is evaluated. If the probability density of the weak contact stress in the mineral mixture is large, that is, the filling effect of the fine aggregate on the skeleton gap is good, and the cooperative bearing capacity of the coarse and fine aggregates is good, it indicates that the asphalt mixture can effectively resist external load and deformation, and shows high structural stability.

[0071] Step 402, according to the difference of the two ends of the contact point, the contact types in the mineral mixture can be respectively characterized as coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact. The proportion of the stress generated by different contact types in the vertical direction contact total stress reflects the contribution degree of the contact type to the externally applied load. The contact total stress is the sum of the stresses of different contact types:

[0072] σ = σ CC + σ CF + σ FF

[0073] In the formula, σ is the sum of the contact stresses between the mineral mixture particles in the vertical direction; σ CC is the sum of the vertical coarse-coarse aggregate particle contact stresses; σ CF is the sum of the vertical coarse-fine aggregate particle contact stresses; and σ FF is the sum of the vertical fine-fine aggregate particle contact stresses.

[0074] The ratio of stress of different contact types to the total stress of vertical direction contact reflects the contribution of different contact types of mineral mixture to external load. The contribution of different contact types to external load is quantitatively analyzed by using mathematical statistics technology, and the contribution graph of contact types of mineral mixture to external load related to fine aggregate content is drawn. In the contribution graph of contact types to external load, different curves represent the variation trend of different contact types, and the intersection of different curves in the contact type contribution graph is observed. According to the position, number and adjacent curve of the intersection, the contribution graph is divided into three typical regions. When the contribution value of coarse-coarse aggregate particle contact is higher than that of coarse-fine aggregate particle and fine-fine aggregate particle contact, it is regarded as typical region I; when the contribution value of coarse-coarse aggregate particle contact is between the contribution value of coarse-fine aggregate particle and fine-fine aggregate particle contact, it is regarded as typical region II; when the contribution value of coarse-coarse aggregate particle contact is lower than that of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical region III.

[0075] Therefore, the skeleton structure of asphalt mineral mixture can be evaluated according to the typical region in the contribution graph of contact types of mineral mixture to external load. When the contribution value of coarse-coarse particle contact is the highest, that is, typical region I, it indicates that there is more coarse aggregate in the mineral mixture, and the asphalt mixture is not easy to deform or damage under external force, and can exhibit good bearing capacity.

[0076] Embodiment:

[0077] The simulation is performed by using the asphalt mineral skeleton structure evaluation method based on the packing theory:

[0078] An asphalt mixture with a nominal maximum particle size of 16 mm (AC-16) is used for numerical analysis. Five mixtures with different fine aggregate contents are considered, as shown in Figure 1 The passing rate of 2.36 mm aggregate particles (mass percentage passing through a 2.36 mm sieve size) is 20%, 27%, 34%, 41% and 48%, respectively.

[0079] In the numerical simulation, the contact is automatically created and deleted in the loop process, and the contact between particles-particles and particles-wall is taken as a linear elastic contact mode. The micro parameters used in the simulation are shown in Table 1.

[0080] Table 1 Micro parameters for numerical simulation

[0081]

[0082] In mineral mixture packing structures with sieve aperture sizes of 2.36 mm and passing rates of 20%, 27%, 34%, 41%, and 48%, the equivalent proportions of 2.36-4.75 mm aggregate particles were 0%, 12%, 21%, 29%, and 35% of the total mass of the mineral mixture, respectively. Before preparing the mineral mixture, a cylindrical container with a diameter of 101.6 mm and a height of 250 mm was constructed to generate particles. The mineral mixture particles were generated in three stages using a drip method, and each stage was allowed to fall freely to obtain a uniform mineral mixture packing model for subsequent discrete element simulation and data extraction. Figure 2 As shown. After each layer of accumulation is completed, a certain number of sinusoidal vibrations with a frequency of 8Hz and an amplitude of 50mm are applied to the mineral mixture accumulation model in the horizontal direction to ensure that the accumulation model is in a dense state.

[0083] To apply a vertical load to the mineral mixture, a virtual loading plate with a diameter of 120 mm was generated. A uniaxial constrained compression test simulation was conducted by applying a constant pressure of 600 kPa to the plate until the mineral mixture reached a steady state. Figure 3 As shown.

[0084] The loading of mineral mixtures is a dynamic equilibrium process, accompanied by the generation and elimination of contact. When the ratio of the average magnitude of unbalanced forces to the average sum of contact stresses is less than 10... -5 At this point, the loading system is considered to have reached equilibrium. The simulation can then be stopped.

[0085] To verify the consistency between the real and virtual models, X-ray CT technology was used to elucidate the differences in their internal structures. Glass spheres with a diameter of 10 mm (the median particle size of the AC16 type mineral mixture packing model) were used as the medium for model verification. Figure 4 As shown, the measured density of the glass sphere is 2.479 g / cm³. 3The computer tomography test was carried out by using Phoenix v|tome|x s industrial high-resolution X-ray CT produced by General Electric Sensing & Detection Technology Company to obtain clear tomography images. The scanned images were processed to obtain the spatial position information of the particles in the tomography images, and the spatial position information of the particles mainly included the number of particle contacts and the distribution of particle numbers. The real particle contact number and the particle number were taken as indexes to compare the virtual particle contact number and the particle number obtained by the discrete element method to determine that the number of sine vibrations applied to the accumulation model was 30 times for each completed layer of mineral mixture accumulation. The two-dimensional images and the simulation model output by the X-ray CT technology were used to quantitatively calculate the changes in the internal structure parameters when the distance in the vertical direction increased by 2 mm. The same observation interval was selected to process the virtual slice of the glass sphere discrete element accumulation model, and the number of glass sphere particle contacts and the number of glass spheres on the virtual slice were counted. The horizontal sections corresponding to the X-ray CT scanning three-dimensional reconstruction model and the discrete element virtual accumulation model are shown in Figure 5 . Figure 6-7 The particle contact number and the particle number distribution of the real and virtual particle accumulation models are shown. By comparing the particle contact number and the particle number distribution characteristics, it is shown that the virtual accumulation structure is similar to the real sample, and therefore the internal structure of the mineral mixture can be reasonably obtained by numerical simulation.

[0086] The contact stress network in the mineral mixture is complex and varies greatly in value. The contact stress distribution is described by the probability density distribution represented by the logarithmic-linear and linear-logarithmic coordinate systems. The contact stress of the mineral mixture can be further divided into strong contact stress and weak contact stress. The strong contact stress refers to the contact stress of the mineral mixture greater than the average contact stress of the mineral mixture and the weak contact stress refers to the contact stress of the mineral mixture less than the average contact stress of the mineral mixture. According to the accumulation theory, the strong contact stress is mainly generated by coarse aggregates, and fine aggregates mainly bear weak contact stress. Therefore, the probability density distribution of the contact stress describes the skeleton structure of the asphalt mineral mixture, as shown in Figure 8-9 , Figure 8-9 The data are the same, only the logarithmic coordinate form is changed. The x-axis coordinate represents the ratio of the normal contact stress to the average contact stress and the y-axis coordinate represents the percentage of the ratio to the total number of particle contacts. Figure 8 is to describe the probability density of the strong contact stress, so it focuses on the part of the entire horizontal coordinate greater than 5. Figure 9 is to describe the probability density of the weak contact stress, so it focuses on the part of the entire horizontal coordinate less than 0.1. It can be seen from Figure 8-9 that the probability density of the strong contact stress (i.e. ) decreases with the increase of the fine aggregate content, and a larger The extreme value indicates that with the increase of fine aggregate particle content, the void between coarse aggregate particles is obviously filled, and together with coarse aggregate particles, it bears external load. By comparing the probability distribution change of weak contact stress (i.e. ), it can be seen that in this case, the mineral mixture containing 12% fine aggregate has the highest probability density of weak contact stress. When the fine aggregate content continues to increase, it will gradually reduce the probability density of weak contact stress. This is mainly because when the fine aggregate content is less than 12%, the coarse aggregate is the main body of the accumulation structure, the skeleton structure is good, the size of the inter-particle contact stress is relatively uniform, and the weak contact stress is mainly in the form of strong contact stress, resulting in a low probability density of weak contact stress. With the increase of the number of fine aggregate particles, the filling effect of fine aggregate on the void between coarse aggregate particles is more and more obvious, and the number of weak forces that provide stability to the skeleton of the mineral mixture gradually increases. When the fine aggregate content is 12%, the probability of weak contact stress reaches the maximum value, and the particle accumulation structure is the most stable. After that, with the further increase of fine aggregate content, fine aggregate further participates in bearing external load, and the accumulation skeleton structure of coarse aggregate is obviously interfered. Thus, the number distribution of strong and weak contact stresses of the mineral mixture accumulation structure can be determined.

[0087] According to the different minerals on both ends of the contact point, the contact types in the mineral mixture can be characterized as coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact. In-depth analysis of the mechanical properties of the mineral mixture shows that the proportion of vertical stress generated by different contact types in the total contact stress reflects the contribution of the contact type to the externally applied load. The total contact stress can be divided into the sum of different contact type stresses:

[0088] σ = σ CC + σ CF + σ FF

[0089] In the formula, σ is the sum of the vertical inter-particle contact stress of the mineral mixture; σ CC is the sum of the vertical coarse-coarse aggregate particle contact stress; σ CF is the sum of the vertical coarse-fine aggregate particle contact stress; and σ FF is the sum of the vertical fine-fine aggregate particle contact stress.

[0090] Figure 10The curves of the contribution ratio of different contact types to the external load in the vertical direction of the mineral mixture are shown. As shown in the figure, with the increase of the fine aggregate content, the proportion of coarse-coarse aggregate contact gradually decreases, and the proportion of fine-fine aggregate contact gradually increases. In terms of the stress proportion of coarse-fine aggregate contact type, the overall curve shows a trend of first increasing and then decreasing, and the turning point of the fine aggregate content is about 28%. In addition, the typical regions can be divided according to the intersection points of different curves. When the fine aggregate content is <24%, coarse-coarse aggregate contact plays a major role in providing strength, coarse-fine aggregate contact plays a secondary role, and fine-fine aggregate contact does not play an important role. When 24% < fine aggregate content < 33%, coarse-fine aggregate contact begins to dominate the strength, coarse-coarse aggregate contact plays a secondary role, and fine-fine aggregate contact type still plays the smallest role. When the fine aggregate content is >33%, coarse-fine aggregate contact still occupies the dominant position, and fine-fine aggregate contact begins to play a more important role than coarse-coarse aggregate contact type. In this way, the type of the skeleton structure of the asphalt mineral mixture can be evaluated.

[0091] The present application can also have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application. However, these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A method for evaluating the skeleton structure of an asphalt mineral mixture based on the packing theory, characterized in that, Comprising the following steps: S1, obtaining the real gradation of asphalt mineral aggregate mixture, and dividing the particles into fine aggregate and coarse aggregate according to the particle size of the aggregate particles; then performing steps S2 and S3; S2, using discrete element software to build a cylindrical container, using the drop method, and generating a certain number of spherical particles according to the obtained real gradation of mineral aggregate mixture, so that they are freely stacked in the container under the influence of gravity to form a layer of mineral aggregate stacking body, and using the multi-layer generation method to obtain a uniform mineral aggregate stacking model, and a sinusoidal vibration needs to be applied to the mineral aggregate stacking model for each completed layer of mineral aggregate stacking; For the generated mineral aggregate stacking model, a vertical load is applied for uniaxial constraint compression test simulation, and the discrete element software is used to obtain data: the virtual particle contact number and particle number of coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles, the contact stress between mineral aggregate particles and boundary wall, and the contact stress of vertical coarse-coarse aggregate particles, coarse-fine aggregate particles and fine-fine aggregate particles; S3, selecting entities for real model verification, comprising the following steps: Step 301, selecting material balls with a density close to that of the mineral aggregate mixture; Step 302, using discrete element software to build a cylindrical container, using the drop method to generate a certain number of material ball particles, so that they are freely stacked in the container under the influence of gravity to form a layer of material ball stacking body, and using the multi-layer generation method to obtain a uniform material ball virtual stacking model, and a sinusoidal vibration needs to be applied to the stacking model for each completed layer of material ball stacking; Step 303, selecting a real cylindrical barrel with the same size as the material ball virtual stacking model to form a material ball solid stacking model; using CT technology to scan the material ball solid stacking model to obtain a tomographic image; and performing computer picture processing on the scanned image to obtain the spatial position information of the particles in the tomographic image; Step 304, accurately identifying the contacted material ball particles according to the spatial position information of the particles in the tomographic image; finally, counting the real particle contact number and particle number of the tomographic image to obtain the distribution of the real particle contact number and particle number of the material ball solid stacking model with the height of the tomographic image; Step 305, performing virtual slicing processing on the material ball virtual stacking model, and counting the material ball particle contact number and particle number on the virtual slice; taking the particle contact number and particle number as indicators, verifying the structural differences between the material ball virtual stacking model and the material ball solid stacking model, and adjusting the number of sinusoidal vibrations applied to the stacking model for each layer of material ball in step 302 to obtain a material ball virtual stacking model and a material ball solid stacking model that meet the difference verification requirements; Step 4, evaluating the skeleton structure of the asphalt mineral aggregate mixture, comprising the following steps: Step 401, the contact stress network in the mineral mixture is complex, and the contact stress between the mineral mixture particles can be further divided into strong contact stress and weak contact stress; the strong contact stress refers to the contact stress between the mineral mixture particles being greater than the average contact stress between the mineral mixture particles, and the weak contact stress refers to the contact stress between the mineral mixture particles being less than the average contact stress between the mineral mixture particles; the contact stress between the mineral mixture particles and the boundary wall collected in step S2 and the contact stress data of the aggregate particles are quantitatively analyzed, and the probability density distribution diagram of the contact stress of the mineral mixture is drawn; in the process of evaluating the skeleton structure of the asphalt mineral mixture, the stability of the skeleton structure of the mineral mixture is determined by the probability density of the strong and weak contact stresses in the mineral mixture, the more the proportion of the weak contact stress, the better the filling effect of the fine aggregate on the gap between the coarse aggregate particles, the better the synergistic bearing capacity of the coarse and fine aggregates, the stronger the ability of the asphalt mixture to resist external load and deformation, and the better the stability performance; And, Step 402, according to the difference of the two ends of the contact point, the contact type in the mineral mixture is respectively characterized as coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact three contact types; the proportion of the contact stress of different contact types in the total contact stress in the vertical direction reflects the contribution of different contact types of the mineral mixture to the external load; the contribution of different contact types to the external load is quantitatively analyzed by using mathematical statistics technology, and the contribution diagram of the contact type of the mineral mixture to the external load related to the fine aggregate content is drawn; the skeleton structure of the asphalt mineral mixture is evaluated according to the contribution diagram of the contact type of the mineral mixture to the external load.

2. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, The process of obtaining the true gradation of the asphalt mineral mixture in step S1 is determined by screening experiment of the mineral mixture.

3. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, In the process of dividing the particles into fine aggregate and coarse aggregate according to the particle size of the aggregate particles, the aggregate particles with a particle size of 2.36-4.75 mm are regarded as fine aggregate, and the aggregate particles with a particle size of 4.75 mm and above are regarded as coarse aggregate.

4. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, Step S2 applies a sinusoidal vibration in the horizontal direction when a sinusoidal vibration is applied to the mineral mixture accumulation model.

5. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, The material balls in step 301 are selected as glass balls.

6. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, The number of material balls, the number of material ball accumulation layers and the diameter of material balls in the process of forming the material ball solid accumulation model in step 303 are the same as the number of material balls, the number of material ball accumulation layers and the diameter of material balls in step 302.

7. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 1, characterized in that, When steps S2 and S3 are performed after step S1, the size of the cylindrical container in step 302 is the same as the cylindrical container in step S2, the number of material balls is the same as the number of mineral mixture particles in step S2, the number of material ball accumulation layers is the same as the number of mineral mixture accumulation layers in step S2, and the diameter of the material balls is the median of the particle size of the mineral mixture in step S2.

8. A method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to any one of claims 1 to 6, characterized in that, The process of evaluating the skeleton structure of the asphalt mineral mixture according to the contribution diagram of the contact type of the mineral mixture to the external load in step 402 includes the following steps: In the contribution graph of contact types to external load, different curves represent the variation trend of different contact types, and the intersection points of different curves in the contribution graph of contact types are determined; according to the position, number and adjacent curves of the intersection points, the contribution graph is divided into three typical regions; when the contribution values of coarse-coarse aggregate particle contact are all higher than those of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical region I; when the contribution values of coarse-coarse aggregate particle contact are between those of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical region II; when the contribution values of coarse-coarse aggregate particle contact are lower than those of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical region III; According to the typical regions in the contribution graph of contact types of mineral mixture to external load, the skeleton structure of asphalt mineral mixture is evaluated; when the contribution value of coarse-coarse particle contact is the highest, that is, typical region I, it indicates that the proportion of coarse aggregate in the mineral mixture is large, and the asphalt mixture is not easy to deform or damage under external force, and can exhibit good bearing capacity.

9. The method for evaluating the skeleton structure of asphalt mineral mixture based on the packing theory according to claim 8, characterized in that, The vertical direction contact total stress in step 402: σ = σ CC + σ CF + σ FF where σ is the total contact stress between the particles of the mineral mixture in the vertical direction, i.e. the total contact stress; σ CC is the sum of the contact stresses between the particles of the coarse-coarse aggregate in the vertical direction; σ CF is the sum of the contact stresses between the particles of the coarse-fine aggregate in the vertical direction; σ FF is the sum of the contact stresses between the particles of the fine-fine aggregate in the vertical direction.

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