Development of a Standardized Methodology for Identifying the Printability Zone of Cementitious 3D Printer and Object Design

Abstract

The construction industry faces significant challenges in achieving sustainability and embracing digitalization. A key development area involves the integration of 3D printing into the construction process. The success of printing a well-designed 3D model critically depends on the rheological characteristics and density of the material used. However, a major limitation in current 3D printing is the absence of standardized methods for defining the printability zone of 3D printers. This master's study establishes a standard methodology to determine the printability zone of a manually fed extruder using a Delta WASP 3D printer, targeting design heights of 40 mm and 120 mm. A Controlled Shear Stress method was applied to characterize the rheological properties, such as static yield stress and viscosity at a critical shear rate of 0.02 s⁻¹. In the first phase of the study, the extrudability, shape retention, and buildability of a single layer were evaluated. It was observed that reducing the nozzle diameter from 8 mm to 6 mm increased the tip velocity, resulting in wider extrusions of approximately 25 percent. Additionally, the layer printed at an 8 mm layer height experienced excessive plastic deformation compared to those printed with a 4 mm layer height. The printability zone was determined based on printability limits, and 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. The second phase focused on assessing the effect of different printing materials (Portland Cement and Alkali-Activated Material) on buildability at the target design heights and their corresponding impact on the printability zone. The concept of minimum specific yield strength was introduced in this study. Among the materials tested, Alkali-Activated Material (AAM) demonstrated superior buildability, successfully printing up to 35 layers - significantly higher than the 11 layers achieved with Portland Cement under comparable rheological properties. This enhanced performance is attributed to its lower density and higher specific yield strength. Finally, buildability plots for 40 mm and 120 mm were developed by correlating specific yield strength and viscosity, in accordance with the established buildability factor criteria.