Quantification of impact compaction locking point for asphalt mixture

Abstract The volumetric properties of asphalt mixture are main elements of the interaction of asphalt and aggregate. To ensure a stable structure of compacted asphalt mixture, the concept of locking point was developed to characterize the amount of compaction efforts which are needed to achieve a stable compaction state. The traditional way of defining locking point was based on the change of volume of mixtures during compaction. In this study, the locking point was defined based upon compaction curves from impact compaction. The locking point for two types of dense-graded asphalt mixtures (AC-20C and AC-13C)and one type of open graded asphalt mixture (SMA13) was evaluated by both impact compaction and gyratory compaction. The influence of compaction temperature and asphalt content on locking points was also investigated. Results showed that it was feasible to identify the locking points for impact compaction. The locking point of impact compaction could be analogically determined according to the locking point of the gyratory compaction. The size of Marshall mold may influence impact compaction curves.