Multiphase computational modeling of gravitational asymmetry in direct ink writing of cementitious materials

Direct Ink Writing (DIW) of cementitious materials presents a transformative approach for additive manufacturing in construction, enabling the fabrication of geometrically complex and material-efficient structures. However, the fidelity and structural performance of printed components are often compromised by gravitational asymmetries, especially during the deposition of overhangs, slanted contours, or unsupported geometries. The non-linear interactions among material rheology, extrusion dynamics, and gravity are not yet fully evaluated in open literature. To address this knowledge gap, this work develops a multiphase computational framework to simulate the coupled behavior of the extruded fluid and the surrounding air phases during DIW of cement-based inks. The incorporation of non-Newtonian rheology, transient behavior, and gravity-driven deformation allows the model to capture the temporal and spatial evolution of asymmetric layer shapes and structural instability. Validation is performed against experimental builds using high-resolution imaging and cross-sectional strand geometry analysis. The results reveal that gravitational asymmetries have an observable impact on strand morphology including strand height, width, and cross-sectional properties. In conclusion, this study offers a mechanistic understanding of printed strand morphology in DIW of cementitious materials and provides a simulation-guided pathway toward structurally robust, gravity-aware additive construction.