Research on microscopic contact characteristics of aggregates during compaction of asphalt mixtures

The compaction process is the stage when the skeleton structure and strength of asphalt mixture are developed. In order to explore the strength development mechanism of asphalt mixture skeleton, the microscopic contact characteristics of aggregates during asphalt mixture compaction process were evaluated. Firstly, the CT scanning and image processing techniques were employed to obtain digital images of the asphalt mixture during the compaction process. Then, the processed digital images were reconstructed in three dimensions to achieve dynamic simulation of the asphalt mixture compaction process. A novel index of contact chains was proposed to characterize the different state of aggregate contact within the asphalt mixture, and then, the characteristic parameters of contact chains during compaction, such as the number of contact chains, contact chain length, and contact chain angle, were analyzed. The results showed that for the typical used SMA-13 asphalt mixture, the primary role of 13.2-16 mm grade aggregates in the asphalt mixture was to form the main skeletal structure, and 4.75-9.5 mm and 9.5-13.2 mm grade aggregates provided more than 90% of the contact points for the asphalt mixture. The contact chains formed by the aggregates of 4.75-9.5 mm and 9.5-13.2 mm were the main source of strength of the asphalt mixture. The aggregate was dominated by migrating movements in the early and middle stages of compaction, and rotating movements in the later stages of compaction dominated the aggregate.