_Article_  
**Algorithm for Virtual Aggregates' Reconstitution**  
**Based on Image Processing and**  
**Discrete-Element Modeling**  
**[PERSON] 1, [PERSON] 2, [PERSON] 2,*, [PERSON] 2 and [PERSON] 3**  
1 School of Computer Engineering, Nanjing Institute of Technology, Nanjing 211167, China; [EMAIL_ADDRESS]  
2 School of Transportation, Southeast University, 2 Sipailou, Nanjing 210096, China; [EMAIL_ADDRESS] (X.D. ); [EMAIL_ADDRESS] (W.Z.) 3 School of Engineering and Architecture, Nanjing Institute of Technology, Nanjing 211167, China; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS]; Tel. : +86-158-0516-0021
* 2018 20  
following shape acquisition, which is the basis to guarantee the results [7; 8]. The discrete-element method (DEM) was proposed by the [PERSON] [9] firstly, and then, a software program named Particle Flow Code (PFC) was developed to help the mechanical calculation of heterogeneous materials, which has been widely used in many fields [10; 11; 12]. As the basic calculation elements, the balls in the software (PFC2D, Itasca Consulting Group: Minneapolis, USA) are all round shaped without any angular shape, which is not consistent with the realistic particles in pavement construction. Therefore, prior to numerical simulation, it is important to rebuild the realistic particle shape, which will influence the simulation results obviously [13; 14; 15]. Many modeling methods have been proposed within PFC to characterize the shape features by some researchers. [PERSON] et al. [16] regarded the aggregate particles as hexahedrons, pentahedrons and tetrahedrons within PFC, respectively. Then, the equal-radius balls were arranged regularly within the particles and were defined as a rigid body. CPA (Computerized Particle Analysis) was utilized to help develop the virtual shape within PFC by [PERSON] and [PERSON] [17]. The input index, known as the grain-shape coefficient, was used to redefine the particle contour. Then, numerical particles were reconstructed by filling the redefined area with balls. [PERSON] [18] reconstructed 3D ballast particles with three images (top, side and front) of the particles with the help of the image processing technology. Similar methods can also be found in the works of [PERSON] and [PERSON] [19; 20], [PERSON] et al. [21] and [PERSON] and [PERSON] [22; 23; 24], as well. Most of the existing modeling methods can only model the shape roughly with excessive simplification. Although some virtual models were rebuilt precisely by X-ray scanning, the angular shape could not be quantified precisely [25; 26; 27; 28; 29]. [PERSON] scanned the particles and rebuilt their virtual shapes according to the acquired images [30; 31]. In their studies, the stl-format file were developed, which can reflect the shapes of aggregates precisely. By the designed routine, the virtual particles in three dimensions were developed successfully with enough balls filled. However, their methods can only model the realistic shapes, but cannot evaluate the shape properties of mixtures by a specific index. Therefore, the simulation accuracy mainly depends on the samples' selection and cannot model the material heterogeneity well. Compared to X-ray scanning, the Aggregate Imaging Measurement System (AIMS) apparatus is a promising way for performing particle shape modeling and has been utilized gradually in material analyses [32]. It can capture the morphological characteristics of aggregates and quantifies the shape properties by some design indices such as the angularity index, texture index, size, and so on. However, this apparatus is mainly used for pavement skid resistance measurements nowadays [33; 34; 35]. More uses of it should be explored, especially combined with other technologies. The objective of this study is to propose an algorithm for the virtual aggregates' reconstitution based on the Discrete-Element Method (DEM). To achieve this, the AIMS apparatus with the image processing technology were utilized before the simulations.