Optimizing aggregate content and size distribution in low-carbon 3D-printed concrete via DEM simulation

To mitigate the reduced extrudability typically associated with low-carbon concrete formulations of 3D-printed concrete, this study focuses on optimizing aggregate content and size distribution through discrete element method (DEM) simulations. A two-phase soft shell-hard core model was adopted to simulate the extrusion process, where aggregates (hard cores) and cement paste (soft shells) were explicitly represented. The effects of binder-to-aggregate ratios (0.4-1.0) and aggregate fineness moduli (2.5-3.3) on extrusion pressure, surface quality, and clogging behavior were systematically investigated. Results demonstrated that higher aggregate content and coarser gradation increased extrusion pressure remarkably, leading to nozzle blockages, while finer aggregates improved flow uniformity and filament consistency. Optimal extrudability was achieved at a binder-to-aggregate ratio of 0.8 with a fineness modulus of 2.5, balancing material sustainability and extrudability. This work provides a computational framework for designing low-carbon 3D-printed concrete by tailoring aggregate characteristics, reducing reliance on high cement content without compromising extrudability.