2D Numerical Modelling of Particle-Bed 3D Printing by Selective Paste Intrusion

Additive manufacturing of concrete and cement based materials is expected to revolutionize how structures are built. 3D printing processes by means of extrusion-deposition have recently been developed at the scale of few meters for houses or structural elements but not yet for several floors. Among the 3D printing processes which have also gained attention, particle-bed methods could be designated as an innovative one. In the case of the selective paste intrusion technique, the nozzle of the 3D printer applies the binder composed of water, mineral material and admixtures to a particle bed of sand particles. To reach a homogeneous material using the selective paste intrusion method, the aggregate layer made of sand must be completely penetrated by the cement paste to bond with the other layers. Such an issue is challenging regarding the rheological requirements of the binder to ensure the complete penetration of the aggregates layer. Therefore, this paper aims to provide and validate the penetration of yield stress fluids through sand particle layers using numerical simulation. A 2D numerical analysis is carried out to study the preferential flow path comparing to previous unidirectional modeling. A level-set method and a continuous viscoplastic model have been used to simulate the penetration and to compare the numerical results with experimental and analytical models from the literature. We describe the penetration as a function of the yield stress, the contact angle at the interface, the medium diameter of the sand particles, the void fraction of the sand packing and the dimension of the sand layer. We show that the numerical modelling is able to predict the evaluation of penetration depth as a function of the yield stress of the fluid measured from rheological measurements and the sand particles bed properties.