Research On Virtual Tests Of Asphalt Mixture Based On PFC3D

Asphalt mixture is a typical heterogeneous material, which has complex mechanical characteristics related to temperature, it’s difficult to observe the stress and deformation of the internal structure of asphalt mixture by means of macro scale analysis. Discrete element numerical simulation as a new method, with its advantages on processing of discontinuous media and large deformation of material, can well simulate and monitor the actual stress state of asphalt mixture instead of laboratory test. Thus, research on the simulation of asphalt mixture performance from low to high temperature based on the discrete element method is necessary. The main steps are as follows:First of all, coarse aggregate volume fraction of virtual specimen and the density of asphalt mortar can be deduced by the aggregate gradation, oil-stone ratio and porosity, balls with the same aggregate particle size are put into the virtual specimen, which could be checked by voids in mineral aggregate. After extracting the geometry information for aggregate initial parameters, and considering irregular polyhedron aggregate and actual distribution of the air voids, three-dimensional digital structure of asphalt mixture can be generated, which is regarded the same as trial sample.Secondly, the suitable microscopic contact model could be chosen according to the test temperature and failure mode, asphalt mortar macroscopic viscoelastic parameters under different temperature are captured by the uniaxial creep test. The appropriate area of temperature and load with Burgers model can be verified. According to transformation relationship between macro and micro parameters, the microscopic parameters among asphalt mortar internal units, asphalt mortar and aggregate unit, aggregate unit are obtained.Finally, simulating asphalt mixture fracture in low temperature, observing the initiating specimen cracking and crack propagation characteristics, then analyzing the internal fracture mechanism and influence factors of three point bending trabecular. Four-point bending fatigue test is simulated, which can make an observation on internal stress and strain change state of specimen at every second, also, fatigue cracking mechanism and virtual fatigue lifespan can be analyzed. And then, simulating uniaxial creep test under reducing time parameters, while Burgers model is applied to simulate two early stages of creep test without damage, the damage factor is used to cause the degradation of material parameters, which can realize the third stage of virtual creep test.Results show that the volume fraction of aggregates, asphalt mortar strength, temperature, the micro contact model and the way of load stress all have significant impacts on low to high temperature and fatigue performance of asphalt mixture.