State-of-the-art review of DEM-based modeling of polymer-modified asphalt mixtures: Material properties, performance, and applications

The increasing demand for durable and high-performance pavements has led to the widespread use of polymer-modified asphalt (PMA) mixtures owing to their enhanced elasticity, rutting resistance, and fatigue performance. However, the complex multi-phase and heterogeneous nature of these materials limits the effectiveness of conventional experimental and continuum-based modeling approaches in fully capturing their mechanical behavior. The discrete element method (DEM) has emerged as an effective mesoscale numerical tool for modeling particle interactions, contact behavior, and internal structural development in asphalt mixtures. This paper presents a critical state-of-the-art review of DEM-based modeling of polymer-modified asphalt mixtures, focusing on material properties, modeling techniques, and applications. It examines polymer modification mechanisms, including network formation, viscoelastic behavior, temperature susceptibility, and aging effects, and assesses their implications for DEM contact modeling and parameter calibration. Because the literature identified for this review is overwhelmingly dominated by styrene-butadiene-styrene (SBS) modification, findings are explicitly flagged throughout as SBS-specific or as more broadly applicable to PMA. In this review, DEM model-generation techniques, contact constitutive laws, and calibration strategies are compared, and key applications, including compaction, rutting, fatigue cracking, moisture damage, and pavement maintenance, are discussed. A bibliometric analysis was used to map current research trends and identify gaps, particularly the limited incorporation of polymer microstructures and rheology into DEM models. This review outlines priority directions for future research, including multiscale modeling, DEM-FEM coupling, CT-based reconstruction, and AI-assisted parameter calibration, and proposes a framework linking polymer-modified material behavior to DEM modeling requirements to support future improvements in simulation accuracy and pavement design.