Effect of aggregate shape representation and deformability on the bituminous mixture stiffness properties using 3D DEM modelling

Abstract

Given the recognised importance of aggregate shape in the performance of bituminous mixtures, there has been growing interest in developing numerical models that accurately capture the material’s mesostructural characteristics. This paper presents a methodology for incorporating complex aggregate shapes into three-dimensional (3D) Discrete Element Method (DEM) models of bituminous materials and investigates the impact of representing coarse aggregates as deformable bodies on both the geometry and mechanical response of DEM assemblies. This approach was implemented in VirtualPM3DLab, a 3D DEM software that employs Laguerre–Voronoi diagrams to define spherical particle contacts and contact areas, together with a generalised Kelvin contact model to simulate the viscoelastic behaviour of bituminous materials. The mechanical response of DEM assemblies, using rigid single-spherical particle aggregates versus deformable multi-spherical particle aggregates, was analysed through simulated uniaxial tension–compression cyclic tests at various frequencies. The results show that discretising the aggregate volume using a distribution of smaller-radius spherical particles effectively captures aggregate geometry, although the sphere size distribution must be carefully selected to ensure high-fidelity representation. Virtual asphalt specimens with deformable multisphere aggregate particles exhibited higher stiffness moduli and lower phase angles across the tested frequencies compared to rigid single-sphere specimens. These variations in viscoelastic properties were more pronounced with finer aggregate discretisation, due to the increased number of aggregate–aggregate and aggregate–mastic contacts. In contrast, the total number of contacts and their distribution among constituents were very similar for assemblies with irregular particle models (realistic) and subdivided icosahedron models (close to spherical), resulting in a minimal effect of aggregate shape on the overall DEM simulation results.