Layer pressing in concrete extrusion-based 3D-printing: Experiments and analysis

The Layer Pressing Strategy is widely used in large-scale concrete 3D Printing for its capacity to provide good control over the layer cross-section geometry and, consequently, the final overall printed element geometry. However, although layer pressing ensures exact positioning of the extruded layer upper surface, it may be at the origin of some deformation of the sub-layers, due to the squeezing of the material under the nozzle. In such a complex flow typology, the setting of the printing parameters, namely layer thickness, printing velocity and material flow rate, still mainly result from time-costly experimental trial-and-errors procedures rather than from a rational understanding of the underlying mechanics. The aim of this article is therefore to provide insights on the effects of the printing parameters on the geometry and local stability of the extruded layer. Some upper and lower bound requirements for controlled layer pressing are discussed from the study of the influence of geometric and kinematic parameters, along with fresh material properties. Finally, a generic printing parameters map is proposed, allowing for the classification of the behaviour of the extruded material.