H.L. ter Huerne

Simulation of HMA Compaction by using FEM

This paper introduces a simulation tool for the compaction process of hot mix asphalt (HMA) using a roller under varying external conditions. The focus is on the use of the finite element model (FEM) with code DiekA, on its necessary requirements and on the presentation of simulation results. The approach requires the availability of a suitable material model, equipment to measure material parameters and a laboratory-testing program for fitting the correct material parameters. Subsequently, in discussing the simulation results attention is paid to; the principal stresses, strains and shear stresses inside the material during rolling, and the incremental displacements of the material. Furthermore, the simulated density path as a function of depth inside the layer is presented for a series of applied roller passes. In conclusion it can be stated that FEM approaches in general are well suited to simulate compaction processes of HMA on condition that the selected FEM comprises the right features.

Asphalt durability and self-healing modelling with discrete particles approach

Asphalt is an important road paving material, where besides an acceptable price, durability, surface conditions (like roughening and evenness), age-, weather- and traffic-induced failures and degradation are relevant aspects. In the professional road engineering branch empirical models are used to describe the mechanical behaviour of the material and to address large-scale problems for road distress phenomena like rutting, ravelling, cracking and roughness. The mesoscopic granular nature of asphalt and the mechanics of the bitumen between the particles are only partly involved in this kind of approach. The discrete particle method is a modern tool that allows for arbitrary (self-)organization of the asphalt meso-structure and for rearrangements due to compaction/cyclic loading. This is of utmost importance for asphalt during the construction phase and the usage period, in forecasting the relevant distress phenomena and understand their origin on the grain-, contact-, or molecular scales. Contact models that involve visco-elasticity, plasticity, friction and roughness are state-of-the art in fields like particle technology and can now be modified for asphalt and validated experimentally on small samples. The ultimate goal is then to derive micro- and meso-based constitutive models that can be applied to modellingbehaviour of asphalt pavements on the larger scales. Using the new contact models, damage and crack formation in asphalt and their propagation can be modeled. Furthermore, the possibility to trigger self-healing in the material can be investigated from a micromechanical point of view.