Relating print velocity and extrusion characteristics of 3D-printable cementitious binders: Implications towards testing methods

This study aims to relate print velocity to critical parameters extracted from a controlled ram extrusion test, towards a test method to expedite the selection of materials and process parameters for 3D-printing of cementitious materials. Higher print velocities, while aiding faster construction, results in a need for higher extrusion pressure, while lower velocities interfere with extrudate quality through effects such as water filtration. Steadystate pressures and dead-zone lengths corresponding to a chosen barrel-die geometry and print velocity are extracted from extrusion force-ram displacement relationships. The steady state pressure increases with print velocity, while the dead-zone length decreases. The deposition pressure between the nozzle exit and the print bed increases with increase in print velocity, and is proportional to the extrusion pressure. These results are used to define a range of desirable print velocities for the chosen geometry and the printer system, so that the extrusion pressure and dead-zone lengths are simultaneously optimized. The lower limit of the print velocity range, steadystate pressure, and dead-zone lengths are all lower when the material microstructural parameter (ratio of particle volume fraction to square of mean size) is higher, indicating the importance of appropriate material design in ensuring efficient 3D printing of cementitious binders.