Meso-Scale Breakage Characteristics of Recycling Construction and Demolition Waste Subgrade Material Under Compaction Effort

The application of construction and demolition waste (CDW) as roadbed filler faces challenges due to the variable mechanical properties caused by fragile recycled brick aggregates. This study elucidates the breakage mechanism of CDW fillers under compaction effort through a combination of standardized laboratory compaction tests and discrete element method (DEM) simulations. Furthermore, the breakage evolution patterns of mixed fills comprising recycled concrete and brick aggregates at various mixing ratios were revealed. A DEM model was developed to characterize recycled concrete and brick aggregates, adopting polygonal clumps for particles >4.75 mm and spherical clumps for finer fractions. The results indicate that particle breakage progresses through three distinct stages: linear fragment stage (0-200 kJ/m³, 50% of total breakage), deceleration growth stage (200-1000 kJ/m³, 38% of total breakage), and residual crushing stage (1000-2684.9 kJ/m³, 12% of total breakage). Recycled concrete aggregates form a skeleton restraining deep cracks, while brick aggregates enhance stability through energy dissipation and void filling. However, exceeding 30% brick content impedes skeleton development. Critically, a 30% brick content optimizes performance, achieving peak dry density with 25% lower compression deformation than concrete-only fillers, while limiting breakage index rise. These results provide a science-based strategy to optimize CDW roadbed design, improving recycling efficiency and supporting sustainable infrastructure.