Characterizing Extrudability for 3D Concrete Printing Using Discrete Element Simulations (2020-07)¶

3D Concrete Printing (3DCP) is a novel automation construction technique, which interested many researchers extensively in the past few years. Among the major research interests in the specific area, the rheology of 3DCP material attracted more researchers recently. Due to the significantly different rheological requirements in extrusion and layer-wise construction stages, proper understanding and characterization of the rheology of 3D printable concrete are required. Extrudability criteria of the material highly depend on the extrusion geometry, extrusion parameters, and the flow type occurring while extruding (i.e. plug flow or highly sheared flow). Hence, numerical simulation tools may be important to understand the flow behavior and extrudability criteria of 3DCP. Therefore, in the current study, the Discrete Element Method (DEM) was used to model the flow behaviour of 3D printing concrete and to characterize the extrudability. A user-defined two-phase hardcore-softshell contact model was developed for particle interactions and the model was calibrated using the experimental orifice extrusion test results. The developed model was then used to simulate the flow inside a hopper with rotating augur. The extrusion pressure in the simulation was compared with the experimental relative power consumption to discharge ratio (pressure) for different rotational speeds. The results for the simulation show good agreements with the experimental pressure values. Based on the results, suggestions were provided to improve the numerical model predictions and the developed numerical model can be used to quantify the extrudability of 3DCP material using either ram-type or rotating screw-type extruders.