Microstructure characterisation of field and laboratory roller compacted asphalt mixtures

This study investigates the effect of field and laboratory roller compaction methods on the microstructure of asphalt mixtures. Loose material of varying hot mix asphalt (HMA) types was compacted in the laboratory using the steel-segmented roller compactor. Multiple compaction regimes were implemented by adjusting the compaction effort, temperature and mode. The internal structure of the laboratory roller compacted specimens was characterised in terms of the aggregate contact points, orientation and segregation by means of two-dimensional image analysis. The investigation in the laboratory demonstrated that the dominant parameters controlling the formation of the asphalt mixture microstructure are the compaction temperature and effort. In addition, the comparative evaluation of the field cores and laboratory compacted specimens revealed that the laboratory roller compaction method reproduces the microstructure induced by the field compaction. To conclude several laboratory compaction regimes may be established to closely duplicate the internal structure characteristics of field cores.