Effect of aggregate contact characteristics on densification properties of asphalt mixture

Abstract The densification properties of asphalt mixture are an external manifestation of aggregate contact action, including the friction, interlocking and dislocation of aggregates as well as the cohesion of asphalt binder during compaction. The asphalt binder also has a lubrication effect on the contact action at the high temperature. To investigate the effect of aggregate contact characteristics on the densification properties of asphalt mixture, an aggregate contact device was developed and aggregate contact tests were conducted on different conditions. Two parameters, F that refers to the maximum contact force composed of friction and interlocking force and E that refers to the required energy during the whole test, were gained according to the contact test curve. Considering the lubrication of asphalt binder at the high temperature, the MF and ME refer to the dry mixture, while the AMF and AME refer to the asphalt mixture. The densification parameters were obtained by means of analyzing the densification curves. Then the relationships between the parameters of aggregate contact and those of densification of asphalt mixture were discussed. The results indicate that the aggregate contact action composed of friction and interlocking force increases with the enlargement of nominal maximum aggregate size ( NMAS ) of the asphalt mixture, and the values of MF and ME increase with the increase of NMAS . The asphalt binder has a significant lubrication effect on the aggregate contact at the high temperature. The contact action of asphalt mixture with a dense gradation is lubricated enough is prone to be compacted. Comparing to test temperature and asphalt content, the gradation of mixture and its NMAS are more easily to affect the contact action, which has the significant effect on the densification properties of the asphalt mixture.