A Rheological test method for determining the printability zone of cementitious 3D printers

This study establishes a standardized methodology for defining the printability zone of a manually fed extruder using a delta 3D printer. Portland cement-based reference materials were prepared by varying the water-cement ratios from 0.32 to 0.36 and superplasticizer content ranging from 0.1 to 0.5 percent. A successful 3D model was designed based on the printer and extruder specifications and transferred to the 3D printer using Geometric Code (G-Code). The controlled Shear Stress (CSS) method was employed to determine the rheological properties of all mixtures, such as static yield stress and viscosity at a critical shear rate of 0.02 s -1 . Concurrently, the printability factors - extrudability, shape retention, and minimum buildability were studied and evaluated. The results revealed that nozzle diameter significantly affects shape retention behaviour. Reducing the nozzle diameter to 6 mm increased the velocity at the nozzle tip, resulting in wider extrusions and is unsuitable for 3D printing. Conversely, the 8 mm nozzle with an 8 mm layer height encountered challenges extruding materials and underwent excessive plastic deformation; however, the 4 mm layer height allowed for printing a wide range of rheological properties. The printability zone was determined based on four limits: minimum and maximum printable yield stresses and minimum and maximum printable viscosities. Ultimately, a plot correlating yield stresses and viscosities with printability factors was created to determine the printability zone of the 8 mm nozzle with 4 mm and 8 mm layer height for the manual feeding extruder. • Developing a standardized methodology to define the printability zone for manually fed extruders using a Delta 3D printer. • Showing how nozzle size and layer height influence extrudability, shape retention, and buildability, with an 8 mm nozzle and 4 mm layer height providing optimal printability. • Identifying minimum and maximum printable yield stresses and viscosities, ensuring successful 3D printing of a single layer without deformation. • Mapping extrudable vs. non-extrudable regions and paving the way for future research on pressurized extruders and material modifications.