Asphalt mineral mixture skeleton structure evaluation method based on accumulation theory

Abstract

The invention discloses an asphalt mineral mixture skeleton structure evaluation method based on a stacking theory, and belongs to the technical field of road analysis and evaluation. In order to solve the problems of insufficient consideration of contact stress and contact types between coarse and fine aggregates and lack of visual representation and accurate description of a skeleton structure of the asphalt mineral mixture in an evaluation mode of structural composition of the asphalt mineral mixture, the method comprises the following steps: firstly, obtaining real gradation of the mineral mixture; then generating a mineral mixture virtual accumulation model by using discrete element software based on an accumulation theory, and performing uniaxial constraint compression test simulation; meanwhile, an entity is selected for real model verification, and the internal structure difference between the real model and the virtual model is illustrated through the X-ray CT technology; and finally, constructing a probability density distribution diagram of the contact stress of the mineral mixture and a contribution diagram of the contact type to an external load through a model test to evaluate the skeleton structure type of the mineral mixture.

Description

Technical Field

[0001] The invention 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 Art

[0002] Asphalt mixture is a multiphase heterogeneous system composed of mineral mixture and asphalt binder, which is used in the construction of asphalt pavement. Mineral mixture is formed by stacking coarse and fine aggregates in a certain gradation ratio. It is generally believed that coarse aggregate forms a skeleton structure, and fine aggregate fills it, and the two participate in the force process together. Mineral mixture occupies more than 90% of the volume of asphalt mixture and plays a decisive role in the service performance of asphalt pavement. As far as the bearing capacity of asphalt mineral mixture is concerned, it depends to a large extent on the skeleton structure formed by the mineral mixture in the asphalt mixture. However, for the structural composition of asphalt mineral mixture, existing research and specifications mostly use macroscopic volume parameters such as mineral interstitial ratio and void ratio to characterize it, and the contact stress and contact type between coarse and fine aggregates are not considered enough. There is a lack of intuitive characterization and accurate description of the skeleton structure of asphalt mineral mixture, and there is a lack of effective evaluation method for the composition structure of asphalt mineral mixture. Due to the complex composition and structure of asphalt mineral mixture, it becomes very necessary to study the micromechanical behavior of aggregates. In recent years, the rapid development of computer technology and digital virtual technology has provided a more convenient method for describing the skeleton structure characteristics of asphalt mineral mixtures. Therefore, for mineral mixtures composed of coarse and fine aggregates, it is necessary to start from micromechanics and propose an evaluation method for the skeleton structure of asphalt mineral mixtures based on the accumulation theory. Summary of the invention

[0003] In order to solve the problem that the evaluation method of the structural composition of asphalt mineral mixtures does not adequately consider the contact stress and contact type between coarse and fine aggregates, and lacks an intuitive representation and accurate description of the skeleton structure of asphalt mineral mixtures.

[0004] A method for evaluating the skeleton structure of asphalt mineral mixture based on stacking theory comprises the following steps:

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

[0006] S2. Use discrete element software to build a cylindrical container, adopt the dropping method, and generate a certain number of spherical particles according to the actual gradation of the obtained mineral mixture, so that they can be freely stacked in the container under the influence of gravity to form a layer of mineral mixture accumulation body, and adopt a multi-layer generation method to obtain a uniform mineral mixture accumulation model. Each time a layer of mineral mixture accumulation is completed, sinusoidal vibration needs to be applied to the mineral mixture accumulation model;

[0007] For the generated mineral mixture stacking model, a vertical load was applied to simulate the uniaxial restrained compression test, and the following data were obtained through discrete element software: 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 between mineral mixture particles and the boundary wall, and the vertical contact stress of coarse-coarse aggregate particles, coarse-fine aggregate particles, and fine-fine aggregate particles;

[0008] S3. Select an entity for real model verification, including the following steps:

[0009] Step 301, selecting a material ball having a density close to that of the mineral mixture;

[0010] Step 302: Use discrete element software to build a cylindrical container, use the dropping method to generate a certain number of material ball particles, and make them freely accumulate in the container under the influence of gravity to form a layer of material ball accumulation body. Use a multi-layer generation method to obtain a uniform material ball virtual accumulation model. After each layer of material ball accumulation is completed, sinusoidal vibration needs to be applied to the accumulation model;

[0011] Step 303: select a real cylindrical barrel of the same size as the virtual stacking model of the material balls, fill it with material balls to form a physical stacking model; use CT technology to scan the physical stacking model of the material balls to obtain a tomographic image; and perform computer image processing on the scanned image to obtain spatial position information of particles in the tomographic image;

[0012] Step 304, accurately identify the contacting material ball particles according to the spatial position information of the particles in the tomographic image; finally count the real contact number of particles and the number of particles in the tomographic image, and obtain the distribution of the real contact number of particles and the number of particles of the material ball solid accumulation model as the tomographic height changes;

[0013] Step 305, perform virtual slicing on the virtual stacking model of the material balls, and count the number of material ball particle contacts and the number of particles on the virtual slices; use the number of particle contacts and the number of particles as indicators to verify the structural difference between the virtual stacking model of the material balls and the physical stacking model of the material balls, and obtain the virtual stacking model of the material balls and the physical stacking model of the material balls that meet the difference verification requirements by adjusting the number of sinusoidal vibrations applied to the stacking model for each layer of the material balls in step 302;

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

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

[0016] and / or,

[0017] Step 402: According to the difference of mineral mixtures at both ends of the contact point, the contact types in the mineral mixture are characterized as three contact types: coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact; the proportion of contact stress of different contact types to the total contact stress in the vertical direction reflects the contribution of different contact types of the mineral mixture to the external load; mathematical statistics technology is used to quantitatively analyze the contribution of different contact types to the external load, and a contribution diagram of the mineral mixture contact type related to the fine aggregate content to the external load is drawn; the skeleton structure of the asphalt mineral mixture is evaluated according to the contribution diagram of the mineral mixture contact type to the external load.

[0018] Furthermore, the process of obtaining the actual gradation of the asphalt mineral mixture in step S1 is determined by performing a screening experiment on the mineral mixture.

[0019] Further, in the process of classifying 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] Furthermore, step S2 applies sinusoidal vibration along the horizontal direction when applying sinusoidal vibration to the mineral mixture stacking model.

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

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

[0023] Furthermore, in step 303 , the number of material balls, the number of material ball stacking layers, and the material ball diameter in the process of filling and forming the material ball solid stacking model are the same as the number of material balls, the number of material ball stacking layers, and the material ball diameter described in step 302 .

[0024] Furthermore, in the process of evaluating the skeleton structure of the asphalt mineral mixture described 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 larger the proportion of weak contact stress, the better the filling effect of fine aggregate on the skeleton gap, the better the coordinated bearing capacity of coarse and fine aggregates, the stronger the asphalt mixture is able to resist external loads and deformation, and the better the stability performance.

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

[0026] In the contact type contribution diagram to the external load, different curves represent the changing trends of different contact types, and the intersection points of different curves in the contact type contribution diagram are determined; the contribution diagram is divided into three typical areas according to the position, number and adjacent curves of the intersection points; when the contribution values ​​of the coarse-coarse aggregate particle contact exceed the contribution values ​​of the coarse-fine aggregate particle contact and the fine-fine aggregate particle contact, it is regarded as the typical area I; when the contribution value of the coarse-coarse aggregate particle contact is between the contribution values ​​of the coarse-fine aggregate particle contact and the fine-fine aggregate particle contact, it is regarded as the typical area II; when the contribution value of the coarse-coarse aggregate particle contact is lower than both the contribution value of the coarse-fine aggregate particle contact and the contribution value of the fine-fine aggregate particle contact, it is regarded as the typical area III;

[0027] The skeleton structure of asphalt mineral mixture is evaluated according to the typical areas in the graph of the contribution of mineral mixture contact type to external load. When the contribution value of coarse-coarse particle contact is the highest, that is, typical area I, it means that the coarse aggregate accounts for a large proportion in the mineral mixture, and the asphalt mixture is not easy to deform or damage under the action of external force, and can show good bearing capacity.

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

[0029] σ=σ CC +σ CF +σ FF

[0030] Where, σ is the sum of the contact stresses between the particles of the mineral mixture in the vertical direction, that is, the total contact stress; σ CC is the sum of the contact stress between coarse-coarse aggregate particles in the vertical direction; σ CF is the sum of the contact stress between coarse and fine aggregate particles in the vertical direction; σ FF It is the sum of the vertical fine-fine aggregate particle contact stresses.

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

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

[0033] The present invention uses CT technology to scan the particle entity stacking model, and by comparing it with the glass ball virtual stacking model constructed by discrete elements, provides an optimization basis for the constructed asphalt mineral mixture virtual stacking model and ensures the accuracy of model evaluation.

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

[0035] Figure 1 The gradation diagram of AC-16 mineral mixture with different pass rates;

[0036] Figure 2 Generate diagrams for the assembly of mineral mixes;

[0037] Figure 3 It is the uniaxial constrained compression process diagram of the mineral mixture;

[0038] Figure 4 The X-ray CT scan and virtual stacking model of the filled glass spheres are shown;

[0039] Figure 5 It is a schematic diagram of horizontal cross-sectional images corresponding to the X-ray CT scanning three-dimensional reconstruction model and the discrete element virtual stacking model;

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

[0041] Figure 7 is the distribution diagram of the number of particles along the sample height;

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

[0043] Fig. 9 is the probability density distribution diagram of contact stress of mineral mixture (probability density of weak contact stress);

[0044] Fig.10 Contribution of mineral mixture contact type to external load related to fine aggregate content. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation examples. Specific implementation method one:

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

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

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

[0050] Step 2: Generate a discrete element model of the mineral mixture using discrete element software based on the stacking theory and perform a uniaxial constrained compression test simulation, including:

[0051] Step 201: using a discrete element method to calculate the interaction between objects in the form of contact, the objects being mineral mixture particles and boundary walls.

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

[0053] Step 202: Considering that there is no cohesive force between particles and between particles and boundary walls in the dry particle stacking system, a linear contact model is selected as a particle-particle contact model and a particle-boundary wall contact model.

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

[0055] Step 203, use discrete element software to build a cylindrical container, adopt the dropping method, and generate a certain number of spherical particles according to the actual gradation of the mineral mixture obtained in step 1, so that they can be freely accumulated in the container under the influence of gravity to form a layer of mineral mixture accumulation body, and adopt a multi-layer generation method to obtain a uniform mineral mixture accumulation model for subsequent loading simulation.

[0056] In the process of generating the mineral mixture stacking model, each time a layer of stacking is completed, a certain number of sinusoidal vibrations are applied to the mineral mixture stacking model in the horizontal direction to ensure that the mineral mixture stacking model is in a dense state.

[0057] Step 204: for the generated mineral mixture stacking model, a vertical load is applied to perform a uniaxial constrained compression test simulation, and data are obtained through discrete element software: 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 mixture particles and the boundary wall, and the vertical contact stress (contact force) of coarse-coarse aggregate particles, coarse-fine aggregate particles, and fine-fine aggregate particles;

[0058] The virtual particle contact number and particle number are subsequently used to compare with the real contact number and particle number scanned by the physical accumulation model (real model) to verify the difference between the virtual model and the real model;

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

[0060] Step 3: Select an entity to verify the real model, and compare the internal particle space position difference between the discrete element virtual stacking model and the real stacking model by X-ray CT technology, including the following steps:

[0061] Step 301: Select material balls with a density close to that of the mineral mixture as carriers for optimizing and verifying the mineral mixture stacking model. In this embodiment, the material balls with a density close to that of the mineral mixture are glass balls, and the density of glass balls is generally 2.5 g / cm 3 The density of mineral mixture is generally 2.7g / cm 3 .

[0062] Step 302: Use discrete element software to build a cylindrical container, use the dropping method to generate a certain number of glass ball particles, and make them freely stack in the container under the influence of gravity to form a layer of glass ball stacking body. Use a multi-layer generation method to obtain a uniform glass ball virtual stacking model for subsequent model verification. In this process, sinusoidal vibration needs to be applied to the stacking model in the horizontal direction for each layer of glass ball stacking.

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

[0064] Step 303: Select a real cylindrical barrel of the same size as the virtual glass ball stacking model and fill it with glass balls to form a real glass ball stacking model. The number of glass balls, the number of glass ball stacking layers, and the diameter of the glass balls are the same as those described in step 302.

[0065] The CT technology is used to scan the glass ball solid stacking model to obtain a clear tomographic image. The scanned image is processed by computer image processing to obtain the spatial position information of the tomographic image particles.

[0066] Step 304: accurately identify the contacting glass ball particles according to the spatial position information of the particles in the tomographic image. Finally, the real contact number of particles and the number of particles in the tomographic image are counted to obtain the distribution of the real contact number of particles and the number of particles in the glass ball solid accumulation model as the tomographic height changes.

[0067] Step 305: Virtually slice the glass ball virtual stacking model, and count the number of glass ball particle contacts and the number of particles on the virtual slice. The number of particle contacts and the number of particles are used as indicators to verify the structural difference between the virtual model (glass ball virtual stacking model) and the real model (glass ball physical stacking model).

[0068] Step 306: If the virtual particle contact number and particle number are not significantly different from the real results, it means that the verification result meets the expected standard, and the evaluation of the asphalt mineral mixture skeleton structure can be carried out; on the contrary, if the difference is large, it means that the verification result does not meet the standard, and it is necessary to increase the number of sinusoidal vibrations applied to the stacking model after each layer of glass ball stacking is completed in step 302, and improve the density of the stacking model until it is consistent with the actual situation. The final number of vibrations is actually the number of sinusoidal vibrations applied to the stacking model after each layer of mineral mixture stacking is completed in step 203.

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

[0070] Step 401, the contact stress network in the mineral mixture is complex, and the contact stress between the particles of the mineral mixture can be further divided into strong contact stress and weak contact stress. Strong contact stress refers to the contact stress between the particles of the mineral mixture being greater than the average contact stress between the particles of the mineral mixture, while weak contact stress refers to the contact stress between the particles of the mineral mixture being less than the average contact stress between the particles of the mineral mixture. According to the accumulation theory, strong contact stress is mainly generated by coarse aggregate, while fine aggregate is mainly subjected to weak contact stress. Mathematical statistics techniques are used to quantitatively analyze the contact stress between the particles of the mineral mixture and the boundary wall collected in step 204, as well as 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 accumulation structure, and then the skeleton structure of the asphalt mineral mixture is evaluated. If the probability density of weak contact stress in the mineral mixture is large, that is, the fine aggregate has a better filling effect on the skeleton gap, and the coordinated bearing capacity of coarse and fine aggregates is better, it means that the asphalt mixture can effectively resist external loads and deformations and show higher structural stability.

[0071] Step 402: According to the different mineral mixtures at both ends of the contact point, the contact types in the mineral mixture can be characterized as three contact types: 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 total vertical contact stress reflects the contribution of the contact type to the externally applied load. The total contact stress is the sum of the stresses of different contact types:

[0072] σ=σ CC +σ CF +σ FF

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

[0074] The proportion of stress of different contact types to the total contact stress in the vertical direction 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 mathematical statistics technology, and the contribution diagram of contact type of mineral mixture to external load related to fine aggregate content is drawn. In the contribution diagram of contact type to external load, different curves represent the change trend of different contact types, and the intersection of different curves in the contact type contribution diagram is observed. According to the position, number and adjacent curves of the intersection, the contribution diagram is divided into three typical areas. When the contribution value of coarse-coarse aggregate particle contact exceeds the contribution value of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical area I; when the contribution value of coarse-coarse aggregate particle contact is between the contribution value of coarse-fine aggregate particle contact and fine-fine aggregate particle contact, it is regarded as typical area 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 area III.

[0075] Therefore, the skeleton structure of asphalt mineral mixture can be evaluated according to the typical area in the contribution diagram of the mineral mixture contact type to the external load. When the contribution value of the coarse-coarse particle contact is the highest, that is, the typical area I, it means that there are more coarse aggregates in the mineral mixture, and the asphalt mixture is not easy to deform or damage under the action of external force, and can show good bearing capacity.

[0076] Example:

[0077] The simulation was performed using the asphalt mineral skeleton structure evaluation method based on the stacking theory:

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

[0079] In the numerical simulation, contacts are automatically created and deleted during the cycle, and the contacts between particles and particles and between particles and walls are treated as linear elastic contact modes. The microscopic parameters used in the simulation are shown in Table 1.

[0080] Table 1 Microscopic parameters of numerical simulation

[0081]

[0082] In the mineral mixture stacking structure with a pass rate of 20%, 27%, 34%, 41% and 48% corresponding to the 2.36mm sieve size, the equivalent proportion of 2.36-4.75mm aggregate particles is 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 101.6mm and a height of 250mm was built to generate particles. The dropping method was used to generate the mineral mixture particles in three times, and they were allowed to fall freely to obtain a uniform mineral mixture stacking model for subsequent discrete element simulation and data extraction, such as Figure 2 When each layer of stacking is completed, a certain number of sinusoidal vibrations with a frequency of 8 Hz and an amplitude of 50 mm are applied to the mineral mixture stacking model in the horizontal direction to ensure that the stacking model is in a dense state.

[0083] In order to apply vertical load to the mineral mixture, a virtual loading plate with a diameter of 120 mm was generated. A compressive force was applied to the plate at a constant pressure of 600 kPa to simulate the uniaxial restrained compression test until the mineral mixture reached a stable state, as shown in Figure 2. Figure 3 shown.

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

[0085] In order to verify the consistency between the real model and the virtual model, X-ray CT technology was used to clarify the internal structural differences between them. Glass balls with a diameter of 10 mm (the median particle size of the AC16 type mineral mixture accumulation model) were used as the medium for model verification. Figure 4 The measured density of the glass ball is 2.479 g / cm 3. The Phoenix v|tome|xs industrial high-resolution X-ray CT produced by General Electric Sensing and Inspection Technologies was used for computer tomography testing to obtain clear tomography images. The scanned images were processed to obtain the spatial position information of the particles in the tomography image. The spatial position information of the particles mainly includes the distribution of the number of particle contacts and the number of particles. Taking the real number of particle contacts and the number of particles as indicators, the virtual number of particle contacts and the number of particles obtained by the discrete element method were compared to determine that the number of sinusoidal vibrations required to be applied to the stacking model to complete each layer of mineral mixture stacking is 30 times. Using the two-dimensional images and simulation models output by X-ray CT technology, the changes in internal structural parameters with each increase of 2 mm in the vertical distance were quantitatively calculated. The same investigation spacing was selected to perform virtual slicing on the glass ball discrete element stacking model, and the number of glass ball particle contacts and the number of glass balls on the virtual slices were counted. The horizontal sections corresponding to the X-ray CT scanning three-dimensional reconstructed model and the discrete element virtual stacking model are shown in the figure. Figure 5 shown. Figure 6-Figure 7 The particle contact number and particle number distribution of the real and virtual particle packing models are shown. The comparison of the particle contact number and particle number distribution characteristics shows that the virtual packing structure is similar to the real sample, so the internal structure of the mineral mixture can be reasonably obtained through numerical simulation.

[0086] The contact stress network in the mineral mixture is complex and the values ​​vary greatly. The contact stress distribution is explained 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. Strong contact stress refers to the contact stress of the mineral mixture. Greater than the average contact stress of the mineral mixture Weak contact stress refers to the contact stress of mineral mixture is less than the average contact stress of mineral mixture. According to the accumulation theory, strong contact stress is mainly generated by coarse aggregate, while fine aggregate mainly bears weak contact stress. Therefore, the probability density distribution of contact stress is used to explain the skeleton structure of asphalt mineral mixture, such as Figure 8-Figure 9 As shown, Figure 8-Figure 9 The data is the same, only the logarithmic coordinate format is changed. The x-axis coordinate represents the ratio of the normal contact stress to the average contact stress. The y-axis coordinate represents the percentage of the number of contacts between particles corresponding to the analog value to the total number of contacts between particles. Figure 8 In order to illustrate the probability density of strong contact stress, we focus on the entire part where the horizontal axis is greater than 5. Fig. 9 In order to illustrate the probability density of weak contact stress, we focus on the entire part where the horizontal axis is less than 0.1. Figure 8-Figure 9 It can be seen that strong contact stress (i.e. ) decreases with the increase of fine aggregate content, and a larger This indicates that as the content of fine aggregate particles increases, the gaps between coarse aggregate particles are significantly filled, and the fine aggregate particles and the coarse aggregate particles share the external load. ), it can be seen that in this case, the probability density of weak contact stress of the mineral mixture containing 12% fine aggregate is the highest. When the fine aggregate content continues to increase, the probability density of weak contact stress will gradually decrease. This is mainly because when the fine aggregate content is less than 12%, the coarse aggregate is the main body of the stacking structure, the skeleton structure is good, the size of the contact stress between particles is relatively uniform, and strong contact stress is dominant, resulting in a low probability density of weak contact stress. With the increase in the number of fine aggregate particles, the filling effect of fine aggregate on the gaps between coarse aggregates becomes more and more obvious, and the number of weak forces that provide stability for 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 at this time, and the particle stacking structure is the most stable. Afterwards, as the fine aggregate content increases further, the fine aggregate further participates in bearing the external load until it significantly interferes with the stacking skeleton structure of the coarse aggregate. From this, the distribution of the number of strong and weak contact stresses in the stacking structure of the mineral mixture can be determined.

[0087] According to the different mineral mixtures at 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 the in-depth analysis of the mechanical properties of mineral mixtures, it is found 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 external applied load. The total contact stress can be divided into the sum of stresses of different contact types:

[0088] σ=σ CC +σ CF +σ FF

[0089] Where, σ is the sum of the contact stress between the particles of the mineral mixture in the vertical direction; σ CC is the sum of the contact stress between coarse-coarse aggregate particles in the vertical direction; σ CF is the sum of the contact stress between coarse and fine aggregate particles in the vertical direction; σ FF It is the sum of the vertical fine-fine aggregate particle contact stresses.

[0090] Fig.10The contribution ratio curves of different contact types to the external load in the vertical direction of mineral mixtures are shown. As shown in the figure, with the increase of fine aggregate content, the ratio of the number of coarse-coarse aggregate contacts gradually decreases, and the ratio of the number of fine-fine aggregate contacts gradually increases. In terms of the force ratio of the 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, typical areas can be divided according to the intersection of different curves. When the fine aggregate content is <24%, the coarse-coarse aggregate contact plays a major role in providing strength, the coarse-fine aggregate contact type plays a minor role, and the fine-fine aggregate contact does not play an important role. When 24% < fine aggregate content <33%, the coarse-fine aggregate contact begins to dominate the strength, the coarse-coarse aggregate contact plays a minor role, and the role of the fine-fine aggregate contact type is still the smallest. When the fine aggregate content is >33%, the coarse-fine aggregate contact still dominates, and the fine-fine aggregate contact begins to play a more important role than the coarse-coarse aggregate contact type. This can be used to evaluate the skeleton structure type of asphalt mineral mixture.

[0091] The present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for evaluating the skeleton structure of asphalt mineral mixture based on stacking theory, characterized in that: The following steps are involved: S1, obtaining the real gradation of the asphalt mineral mixture, and dividing the particles into fine aggregate and coarse aggregate according to the particle size of the aggregate particles; then proceeding to step S2 and / or S3; S2. Use discrete element software to build a cylindrical container, adopt the dropping method, and generate a certain number of spherical particles according to the actual gradation of the obtained mineral mixture, so that they can be freely stacked in the container under the influence of gravity to form a layer of mineral mixture accumulation body, and adopt a multi-layer generation method to obtain a uniform mineral mixture accumulation model. Each time a layer of mineral mixture accumulation is completed, sinusoidal vibration needs to be applied to the mineral mixture accumulation model; For the generated mineral mixture stacking model, a vertical load was applied to simulate the uniaxial restrained compression test, and the following data were obtained through discrete element software: 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 between mineral mixture particles and the boundary wall, and the vertical contact stress of coarse-coarse aggregate particles, coarse-fine aggregate particles, and fine-fine aggregate particles; S3. Select an entity for real model verification, including the following steps: Step 301, selecting a material ball having a density close to that of the mineral mixture; Step 302: Use discrete element software to build a cylindrical container, use the dropping method to generate a certain number of material ball particles, and make them freely accumulate in the container under the influence of gravity to form a layer of material ball accumulation body. Use a multi-layer generation method to obtain a uniform material ball virtual accumulation model. After each layer of material ball accumulation is completed, sinusoidal vibration needs to be applied to the accumulation model; Step 303: select a real cylindrical barrel of the same size as the virtual stacking model of the material balls, fill it with material balls to form a physical stacking model; use CT technology to scan the physical stacking model of the material balls to obtain a tomographic image; and perform computer image processing on the scanned image to obtain spatial position information of particles in the tomographic image; Step 304, accurately identify the contacting material ball particles according to the spatial position information of the particles in the tomographic image; finally count the real contact number of particles and the number of particles in the tomographic image, and obtain the distribution of the real contact number of particles and the number of particles of the material ball solid accumulation model as the tomographic height changes; Step 305, perform virtual slicing on the virtual stacking model of the material balls, and count the number of material ball particle contacts and the number of particles on the virtual slices; use the number of particle contacts and the number of particles as indicators to verify the structural difference between the virtual stacking model of the material balls and the physical stacking model of the material balls, and obtain the virtual stacking model of the material balls and the physical stacking model of the material balls that meet the difference verification requirements by adjusting the number of sinusoidal vibrations applied to the stacking model for each layer of the material balls in step 302; Step 4, evaluating the asphalt mineral mixture skeleton structure, including the following steps: Step 401: The contact stress network in the mineral mixture is complex, and the contact stress between the particles of the mineral mixture can be further divided into strong contact stress and weak contact stress; strong contact stress refers to the contact stress between the particles of the mineral mixture being greater than the average contact stress between the particles of the mineral mixture, while weak contact stress refers to the contact stress between the particles of the mineral mixture being less than the average contact stress between the particles of the mineral mixture; quantitatively analyzing the contact stress between the particles of the mineral mixture and the boundary wall and the contact stress data of the aggregate particles collected in step S2, and drawing a probability density distribution diagram of the contact stress of the mineral mixture; and / or, Step 402: According to the difference of mineral mixtures at both ends of the contact point, the contact types in the mineral mixture are characterized as three contact types: coarse-coarse aggregate particle contact, coarse-fine aggregate particle contact and fine-fine aggregate particle contact; the proportion of contact stress of different contact types to the total contact stress in the vertical direction reflects the contribution of different contact types of the mineral mixture to the external load; mathematical statistics technology is used to quantitatively analyze the contribution of different contact types to the external load, and a contribution diagram of the mineral mixture contact type related to the fine aggregate content to the external load is drawn; the skeleton structure of the asphalt mineral mixture is evaluated according to the contribution diagram of the mineral mixture contact type to the external load.

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

3. The method for evaluating the skeleton structure of asphalt mineral mixture based on stacking theory according to claim 1, characterized in that: In the process of classifying 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 stacking theory according to claim 1, characterized in that: Step S2 applies sinusoidal vibration along the horizontal direction when applying sinusoidal vibration to the mineral mixture stacking model.

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

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

7. The method for evaluating the skeleton structure of asphalt mineral mixture based on stacking 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 that of 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 stacking layers is the same as the number of mineral mixture stacking layers in step S2, and the material ball diameter 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 stacking theory according to any one of claims 1 to 7, characterized in that: In the process of evaluating the skeleton structure of the asphalt mineral mixture described 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 larger the proportion of weak contact stress, the better the filling effect of fine aggregate on the gaps between coarse aggregate particles, the better the coordinated bearing capacity of coarse and fine aggregates, the stronger the asphalt mixture is able to resist external loads and deformation, and the better the stability performance.

9. A method for evaluating the skeleton structure of asphalt mineral mixture based on stacking theory according to any one of claims 1 to 7, characterized in that: Step 402: The process of evaluating the asphalt mineral mixture skeleton structure according to the contribution diagram of the mineral mixture contact type to the external load includes the following steps: In the contact type contribution diagram to the external load, different curves represent the changing trends of different contact types, and the intersection points of different curves in the contact type contribution diagram are determined; the contribution diagram is divided into three typical areas according to the position, number and adjacent curves of the intersection points; when the contribution values ​​of the coarse-coarse aggregate particle contact exceed the contribution values ​​of the coarse-fine aggregate particle contact and the fine-fine aggregate particle contact, it is regarded as the typical area I; when the contribution value of the coarse-coarse aggregate particle contact is between the contribution values ​​of the coarse-fine aggregate particle contact and the fine-fine aggregate particle contact, it is regarded as the typical area II; when the contribution value of the coarse-coarse aggregate particle contact is lower than both the contribution value of the coarse-fine aggregate particle contact and the contribution value of the fine-fine aggregate particle contact, it is regarded as the typical area III; The skeleton structure of asphalt mineral mixture is evaluated according to the typical areas in the graph of the contribution of mineral mixture contact type to external load. When the contribution value of coarse-coarse particle contact is the highest, that is, typical area I, it means that the coarse aggregate accounts for a large proportion in the mineral mixture, and the asphalt mixture is not easy to deform or damage under the action of external force, and can show good bearing capacity.

10. The method for evaluating the skeleton structure of asphalt mineral mixture based on stacking theory according to claim 9, characterized in that: The total contact stress in the vertical direction in step 402 is: s = s CC +s CF +s FF Where, σ is the sum of the contact stresses between the particles of the mineral mixture in the vertical direction, that is, the total contact stress; σ CC is the sum of the contact stress between coarse-coarse aggregate particles in the vertical direction; σ CF is the sum of the contact stress between coarse and fine aggregate particles in the vertical direction; σ FF It is the sum of the vertical fine-fine aggregate particle contact stresses.

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