The movement property characterization of coarse aggregate during gyratory compaction based on 3D-printed aggregate

The quality, as well as the formability of asphalt mixture compaction, are dominantly determined by the movement characteristics of coarse aggregate during compacting. In this paper, the discrete features of the mixture in the compaction process are studied by repeatedly and continuously compacting the same batch of mixture. Furthermore, the three-stage compaction method is used to analyze the movement of the round ag-gregates. X-ray Computed Tomography (CT) images of the specimen acquired before and after each compaction stage are compared to track the position of three-dimensional printed (3D-printed) aggregates. During the compaction process, the results obtained from the imaging analysis method VG STUDIO MAX 3.0 are applied to describe the displacement and the angle of the round aggregate of the mixture with different bitumen contents, asphalt types, and mixture gradations. The rotation angle of aggregates, namely the Percentage of Vertical Displacement of Round aggregates (PVDR), and the Percentage Horizontal Displacement of Round aggregates (PHDR) are proposed to quantify the aggregate movement property. The results suggest that the aggregates with good angularity and better interlocking frame could increase the discreteness in the early compaction process, though this structure is more conducive to the stability of the pavement structure. Moreover, the main differ-ences in round aggregates movement in different asphalt mixtures are observed. The mixture with Styrene-Butadiene-Styrene (SBS) initially shows a slight increase in vertical displacement accumulation, while later this increase dramatically happens, especially in the active force part. For different gradations, the PVDR of the dense skeleton structure in the second stage of compaction is greater than that of the dense suspension structure, yet the PHDR represents the opposite results. In addition, in the compaction process, the elongated aggregates tend to transform into round-shaped aggregates due to breakage to achieve greater compactness and structural stability, especially when the angle between the elongated aggregate and the horizontal direction is less than 60 degrees.