Rheological requirements for printable concretes

We study in this paper the rheological requirements for printable concrete in terms of yield stress, viscosity, elastic modulus, critical strain, and structuration rate. We first discuss the extrusion/deposition process at the level of the nozzle from a material perspective. We then focus on the rheological requirements needed to prevent the flow of one layer or the strength-based failure of the rising printed element. We moreover discuss the rheological requirements needed to control the final geometrical dimensions of one layer and of the entire object, including buckling stability and surface cracking. We finally describe the requirement for a proper intermixing of the layers interface and also note that drying of the upper surface of the layer at rest could also play a major role on the interlayer bond. Finally, we evaluate the effect of the use of printing supports (i.e. non-direct printing) on the above rheological requirements.