A unified fluid-solid elasto-viscoplastic finite element model for the simulation of 3D concrete printing across process scales

• PFEM framework simulating full 3DCP process from extrusion to buildability. • Extension of Saramito constitutive model to cementitious materials. • Numerical and laser-scanned cross-sections reveal elastic effects during extrusion. • Experimental validation of out-of-plane collapse in inclined 3D printed walls. • Simulation of a structural component with in-plane layer merging. An advanced computational approach is presented for the high-fidelity simulation of 3D Concrete Printing (3DCP) across process- and length-scales, encompassing extrusion, layer deposition, and buildability. The framework couples a flexible finite element environment with a novel constitutive model, extending Saramito elasto-viscoplastic formulation to cementitious materials for the first time. Using a limited set of experimentally identifiable parameters, the model reproduces elastic behaviour in the solid regime and provides a smooth, thermodynamically consistent transition between fluid- and solid-like states. To account for the pressure-dependent response of early-age concrete, a Drucker-Prager yield criterion is adopted, while thixotropy and structural build-up are modelled through time-dependent material properties. Large deformations and free-surface evolution, critical in the fluid regime, are resolved using the Particle Finite Element Method (PFEM), which combines an updated Lagrangian formulation with Delaunay remeshing. Additional numerical strategies are introduced to handle the complex boundary conditions associated with extrusion and layer deposition. The model is validated against 3D printing experiments involving single- and multi-layer walls, both vertical and inclined. The simulated geometries show excellent agreement with laser-scanned data and provide insight into the role of elasticity during layer deposition. Out-of-plane collapse mechanisms observed experimentally were also reproduced numerically with good reliability. Finally, full-scale simulation of a printed structural component is conducted, demonstrating the model capacity of capturing extrusion dynamics, interlayer merging, junction formation, and the overall mechanical response of the built object.