Date of Award

Fall 5-3-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Luis Zambrano Cruzatty

Second Committee Member

Aaron Gallant

Third Committee Member

Roberto Lopez-Anido

Abstract

Recently, additive manufacturing (AM) using earthen materials (natural earth components such as clay, silt, and sand) has been proposed as a sustainable alternative to conventional concrete-based construction practices for its potential to reduce carbon footprint. Some research groups suggest zero-transportation construction can be achieved using local or “indigenous" soils. However, the heterogeneous nature of these soils can impose significant challenges associated with fine-tuning the soil mixture and the printing parameters for the extrusion, deposition, and curing process. Understanding the mechanical links between the extrusion process and the behavior of earthen materials is critical to developing the potential of AM using earthen materials. Among the components of earthen mixtures, the percent of clay plays a key role, providing cohesive binding and flexibility to the mixture required to pump and extrude the material. Thus, studying the isolated parameters of the clay is essential to developing the design of earthen mixtures that fulfill the stringent criteria that materials need for AM purposes.

This research elucidates the role of Atterberg limits and liquidity index in optimizing the extrudability and quality of 3D-printed clay objects. Three mathematical models are proposed to capture the role of the mentioned parameters in the extrusion process: first, one linking threshold pressure on the piston to initiate clay paste extrusion with liquidity index and geometry of the tank; second, linking printing pressure with liquidity index, extrusion velocity, bead height and width, and geometry of the equipment parts involved in the printing process; and third, one for predicting post-drying shrinkage based on water content and Atterberg’s limits. An extensive experimental program was conducted with three different types of clay (Kaolinite, Cibas, and Presumpscot), using a WASP 40100 clay 3D printer to validate the model. The findings indicate that the liquidity index significantly influences the extrusion pressure due to its correlation with the undrained shear strength of the clay. It was also found that a simple flow rate test can be used to determine the optimum printing pressure vs. liquidity index, to avoid under and over-extrusion of clay paste. It is also found that the optimum range of clay consistency is between a liquidity index of 50-80%, correlating to a defined pressure range of 250-850 kPa in the WASP 40100 clay printer. This research contributes valuable insights into the use of Atterberg limits and soil mechanics principles to characterize the use of clay in the AM process and opens research opportunities oriented to studying the behavior of soil mixtures for AM.

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