Extrusion rheometer for 3D concrete printing

An ability to measure and monitor the rheological characteristics of concrete is important for 3D printing applications. Printable concretes need to have high yield stress and viscosity for buildability. The common rheological testing methods, such as slump tests and rheometers are not sensitive for these highly stiff concretes. In this study, the suitability of the orifice extrusion method in measuring rheological parameters of 3D printable concrete was explored for different concrete mixes with varying aggregate proportions. Further, a Discrete Element Model (DEM) was developed to simulate the particle flow in an orifice extruder with a user-defined contact model. The DEM parameters were calibrated using the experimental results from the orifice extruder and validated further using the slump test data. Finally, using the calibrated model, the 3D printing extrusion process with different print velocities was simulated to validate the applicability of the developed model to simulate the extrusion-based 3D concrete printing process. The results and observations from a DEM simulation were confirmed using the 3D concrete printing experiments, which were conducted using a laboratory-scale 3D printer.