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.

Asphalt mixture is composed of coarse aggregate, fine aggregate, mineral powder, asphalt, etc., with heterogeneous, discontinuous characteristics. The mechanical behavior of asphalt mixture particles under vehicle load is very complicated. And the asphalt pavement will be damaged in the early bearing stage, which is closely related to the mechanical behavior between the particles of the mixture. In order to study the mechanical response of asphalt mixture particles under vehicle load, a 2 DOF (degrees of freedom) 1/4 vehicle model composed of mass block–spring-damper was constructed in this paper. In this model, the mechanical response and velocity of particles in pavement structure layer are solved by programming. The results show that the vertical displacement of the pavement calculated by the discrete element method is less than 8.9% of that calculated by the finite element method, which indicates that the discrete element method is more feasible.

The effect of temperature on the meso-mechanical properties of each structural layer of the pavement was studied in this paper. Fitting standard indoor uniaxial compression tests, meso-scale parameters of the material were obtained. With the mesoscopic parameters of each structural layer, a two-dimensional discrete element model of the pavement was constructed. This discrete element model of the road surface was coupled with the 2 DOF 1/4 vehicle model, and the unevenness of the road surface provided incentives for vehicles. At different temperatures, the meso-mechanical response of each structural layer of the road surface was solved under the action of vehicle loads. The movement of particles at different temperatures was analysed. The results show: compared with the finite element model, the vertical displacement produced by the discrete element model is 4.8% larger than the finite element model. That shows that the discrete element model data has certain credibility. The vertical displacement decreases as the depth of the structural layer increases and increases as the road surface temperature increases. And the vertical stress decreases as the depth of the structural layer increases, and increases as the road surface temperature increases. The horizontal stress of the upper layer is compressed, the horizontal stress of the lower layer is stretched, and the horizontal stress of the remaining structural layers does not change significantly. The horizontal stress decreases as the road surface temperature increases. The tangential stress of each structural layer is in anti-symmetric state, both tensile state and compressed state. Tangential stress decreases with increasing road surface temperature. The higher the temperature, the smaller the tangential stress. The effect of temperature on the velocity of particles in the early stage is greater than that in the late stage.

To study the mechanical relationship between vehicles and bridge decks, a bridge model, a rubber tyre model and a bridge deck pavement (BDP) model were constructed based on vehicle–bridge dynamic coupling theory. The rationality of the rubber tyre model was verified, and the rubber tyre and bridge models were coupled. The research results indicate that, regarding the maximum vertical displacement in the middle of spans, first span > second span > third span. For the equivalent stress in the middle of spans, first span > second span > third span. For the transverse stress in the middle of spans, first span < second span < third span. For the longitudinal stress in the middle of spans, second span > third span > first span. With an increase in the depth of the bridge deck, the vertical displacement of the BDP gradually decreased. With an increase in vehicle speed, the vertical displacement in the middle of the bridge span decreased. Therefore, the rubber tyre model using the discrete-element method can accurately simulate vehicle loads.

Water can cause a certain degree of damage to cement-stabilised macadam (CSM), and the degree of damage is greater if CSM is immersed in water for a long time. In order to study CSM damage after lengthy water immersion, a discrete-element model of CSM was established. The Weibull distribution function was used to simulate the heterogeneous contacts between particles. The parallel bond model was used to simulate the material constitutive relationship. The microscopic parameters of CSM were obtained by trial-and-error method. The stress–strain curve was obtained from immersion tests. The micromechanical behaviour of the CSM after immersion was analysed. The results showed that the contact area and strength of the CSM immersed for 30 days were, respectively, 31.4% and 46% less than those of the non-immersed macadam. The force chains between particles were evenly distributed. At peak loading, the normal contact force between particles was much larger than the tangential contact force, and the vertical force chain was much larger than the transverse force chain. The distributions of cementation energy, friction energy and impact energy were not uniform in the middle/peak loading stage.