Each damage of cement mixture is closely related to the heterogeneity and discontinuity of its internal materials. It is very important to analyze the mechanical evolution behavior of cement mixture with the theory of meso-mechanics to reveal the failure mechanism of cement mixture structure. In this paper, the microscopic parameters of the discrete element model are obtained in the compressive tests of concrete mixture cubes. The three-dimensional discrete element model of cement mixture was established by using these microscopic parameters. Under the action of a certain rate load, the generation and propagation process, stress distribution, transfer and displacement field evolution behavior of the meso-fracture between the cement mixture particles are analyzed. The results show that the error between the simulated discrete element flexural strength test and the actual standard test (flexural strength, micro-strain at the bottom of the specimen) is within 10%, which indicates that the discrete element method can well simulate the discontinuous and heterogeneous materials. When the external load acts, the horizontal and vertical displacement of the cementitious material is greater than that of the coarse aggregate, and the displacement angle of the coarse aggregate is greater than that of the cementitious material. When the horizontal tensile stress between the particles exceeds the bond strength of the material, the bond between the particles will break. There are few micro-cracks at the initial stage. In late stage, the micro-cracks penetrate each other and form larger cracks. Micro-cracks usually occur at the weak bonding position between coarse aggregate and cementitious material. The upper particle changes from compressive stress to tensile stress gradually with the duration of load. The bottom particles are in the non-uniform distribution of tensile stress and compressive stress, and the stress values between the particles are also in the non-uniform distribution.

The damage of asphalt mixture is closely related to its internal material heterogeneity and discontinuity. The mechanical evolution of asphalt mixture is analyzed by meso-mechanics theory, which is very important for revealing the failure mechanism of asphalt pavement. In this paper, the two-dimensional (2D) bending discrete-element model of asphalt mixture was established based on the meso parameters and pictures of the model determined by practical experiments. The process of meso-crack formation and propagation between particles of asphalt mixture under a certain load rate was analyzed. The distribution and transmission of stress and the evolution of the displacement field were also analyzed. The results show that the error between the model bending test and the actual standard test is within 10% (maximum bending strength and maximum bending strain). The model test results show that the discrete-element method can simulate discontinuous and heterogeneous materials well. Under the action of external load, the vertical displacement of coarse aggregate particles is much larger than the horizontal displacement. The displacement of asphalt cement granules is slightly larger than that of coarse aggregate granules. The number of microcracks in the model increases slowly in the early stage and quickly in the later stage. Finally, macroscopic cracks are generated. These macroscopic cracks generally extend along the edges of coarse aggregate particles and where the adhesion of asphalt mortar particles is weak. The force chain diagram between particles in the discrete-element model had both regularity and great discreteness. The results showed that the discrete-element method could not only obtain the internal stress and displacement of the asphalt mixture, but also reveal the mechanical evolution behavior between the particle flows of the asphalt mixture.

Currently, most experts only focus on the surface failure characteristics of material structures. Moreover, previous damage constitutive models were unable to simulate the nonlinear deformation characteristics of cement crushed stone during the initial compaction stage. To study the microdamage of cement crushed stone after freeze–thaw cycles and uniaxial compression, further exploration was conducted on the changes in displacement, number of microcracks, relationship between acoustic emission events and microcrack development after freeze–thaw cement gravel loading, as well as the number of force chains before and after loading. Based on the theory of damage mechanics, this article establishes a damage constitutive model that can simulate the entire deformation process of cement crushed stone under uniaxial compression conditions using a particle flow program. Based on the numerical model created by the discrete element method, this article reproduces the entire process of internal fracture of cement crushed stone from a microscopic perspective, which has certain advantages in studying the complex mechanical behavior of cement crushed stone. After freeze–thaw treatment, irreversible damage occurs inside the cement-stabilized crushed stone. The more freeze–thaw cycles, the lower the compressive strength of cement-stabilized crushed stone.

The various damages of asphalt pavement are closely related to the mesomechanical gradual behavior of asphalt materials, and it is very important to study the mesoscopic response under vibration loading in order to reveal the failure mechanism of asphalt pavement. The semisinusoidal vertical load is applied to the subgrade‐surface discrete element model in this paper, and we use the model to analyze the evolution behavior of microcrack generation and expansion processes, stress distribution and stress transfer, and displacement field in various structural layers of asphalt pavement. The results show that the number of cracks increases rapidly on both sides of the vibration load, the rut is generated due to repeated load on the wheel, the asphalt mixture has bulging phenomenon on both sides of the rut and formed macroscopic cracks at the ridge, the microcracks extend mainly along the weak joints of the edges of the coarse aggregate and the asphalt cement, the number of microcracks increases slowly at the initial stage of the vibration load, the microcracks increase sharply until macroscopic cracks appear with the vibration load increases, the direction of compressive stress extends parallel to the microcrack, and the direction of tensile stress extends perpendicular to the microcracks inside the asphalt pavement. The results show that the discrete element method can not only obtain the stress and displacement of each structural layer, but also reveal the microcrack gradual behavior between particle flows.

An asphalt mixture is a heterogeneous material composed of coarse/fine aggregate, asphalt, and admixtures. The damage of asphalt mixtures under vehicle load is closely related to the movement law of various materials. In order to study the mechanical response of each structural layer of asphalt pavement and the movement velocity of particles in the upper layer under vehicle load, the vehicle–road coupling model was established in this paper using commercially available software. The dynamic force of the tire is obtained in the model. Then, in the discrete-element software, a three-dimensional discrete-element model of asphalt pavement with random distribution of coarse aggregate is constructed according to the material gradation and porosity. Finally, the dynamic force of the tire is loaded into the discrete metamodel by means of moving load. The dynamic response of each structure layer and the moving speed of particles of the asphalt pavement can be solved under the action of vehicle load. The results show that the vertical displacement response of each pavement structure layer is solved by the discrete-element method, and the trend is similar by comparing its vertical displacement curve with the curve obtained by the finite-element method. The difference between the two is 8.9%, which indicates that it is feasible to use the discrete-element method to establish the pavement model in this paper. The following data are obtained by the discrete-element method: as the depth of the pavement structure layer increases, the vertical displacement continues to decrease, and the vertical displacement above the base layer accounts for 75% of the total displacement. The pavement bears both compressive stress and tensile stress in the horizontal and vertical directions. The largest transverse and longitudinal compressive stresses appear in the upper layer, but the largest transverse and longitudinal tensile stresses appear in the middle layer. When the vehicle load crosses the measuring point, the shear stress changes in both ${\tau }_{xz}$ and ${\tau }_{xy}$ directions, but does not change in the ${\tau }_{yz}$ direction. At the beginning and end of the vehicle, the lateral, longitudinal, and vertical velocities of the upper-layer particles change dramatically. In the process of stable vehicle running, the velocity value of particles in each structural layer is small. The transverse and vertical velocity curves of particles are arranged in an antisymmetric way, whereas the longitudinal velocity curves of particles are symmetric. To sum up, under the action of vehicle load, the movement of particles in each structural layer of asphalt pavement has certain rules. The movement behavior of particles will damage the asphalt pavement to a certain extent.