2025 Theses Doctoral

Facilitating Earthen Construction through Bio-Based Materials and Additive Manufacturing Technologies

Yierfan, Maierdan

The urgent demand for sustainable, low-carbon alternatives in the construction industry has renewed interest in earthen materials due to their local availability, low embodied carbon, and potential to enhance indoor environmental quality. However, the widespread adoption of earth-based construction remains limited due to its poor flowability, low mechanical performance, and slow drying process. These limitations can be addressed through the integration of additive manufacturing and bio-based stabilizers. Additive manufacturing increases freedom in architectural design, which makes it possible to increase the surface area of the deposited earthen material and, in turn, accelerate the dehydration process, while biopolymer stabilizers improve rheological performance and mechanical properties without the environmental drawbacks of cementitious additives.

This dissertation investigates micro-level particle interactions between clay and biopolymers and their influence on meso-scale rheological behavior and macro-scale 3D printability and mechanical performance. Kaolinite clay—the most abundant clay mineral on Earth—is selected as a model system due to its widespread availability and well-characterized structure. Four naturally derived polysaccharide biopolymers are examined: two anionic (sodium alginate (SA) and xanthan gum (XG)) and two non-ionic (locust bean gum (LBG) and guar gum (GG)), reflecting the fact that most of the water-soluble polysaccharides in nature fall into these two categories. A micro-to-meso-to-macro experimental framework is employed to systematically evaluate how clay–biopolymer interactions evolve across varying water-to-clay ratios, polymer chemistries and concentrations, and controlled chemical environments, with the goal of optimizing the fresh-state and hardened performance of bio-stabilized, 3D-printable earthen materials.

Chapters 2 and 3 examine the particle interactions, rheology, and 3D printability of kaolinite-based earth concrete stabilized with two anionic biopolymers: SA and XG. Neither biopolymer exhibited strong binding affinity to kaolinite (referred to as non-binding biopolymers throughout this dissertation) and induce a two-phase rheological response. At low concentrations, they reduce yield stress and storage modulus due to strong electrostatic repulsion between the negatively charged clay surfaces and the anionic polymers. As the polymer content increases beyond a critical concentration, rheological properties begin to rise again due to the formation of a three-dimensional polymer network. This superplasticizing effect shifts the “printability window” to higher clay contents, enabling smooth extrusion of mixtures with higher solid content, potentially reducing the drying shrinkage and increasing the strength of printable mixtures.

Chapter 4 investigates the rheology, particle interactions, and 3D printability of kaolinite-based earth concrete stabilized with LBG, a non-ionic polysaccharide, in contrast to the anionic biopolymers studied in Chapters 2 and 3. While SA and XG exhibited non-binding behavior with kaolinite and followed a two-phase rheological trend, LBG showed strong binding affinity to kaolinite and exhibited a three-phase rheological response. At low concentrations, LBG increased yield stress and storage modulus while reducing creep compliance through a polymer bridging mechanism, resulting in enhanced buildability. At intermediate concentrations, excessive adsorption disrupted the clay’s original self-assembly structure; although yield stress continued to rise, the stiffness and buildability of the mixtures declined. At high concentrations, polymer chain overlapping was restored and enhanced both yield stress and viscoelasticity, leading to improved buildability. These findings underscore that buildability in 3D-printed earthen materials depends not on yield stress alone, but on its interplay with viscoelastic behavior.

Chapter 5 investigates how tuning kaolinite self-assembly through controlled chemical environment and biopolymer addition influences the performance of 3D-printable, bio-stabilized earthen materials. GG, a non-ionic polysaccharide, was selected for its chemical and rheological stability across a broad pH range. Kaolinite, on the other hand, exhibits pH-sensitive surface charge behavior, allowing its self-assembly structure to be systematically modulated. This chapter leverages that contrast to explore how variations in clay self-assembly affect particle interactions, fresh-state rheology, and hardened mechanical performance. A multiscale experimental framework revealed that although similar microstructures can be achieved across pH at sufficient GG content, their formation mechanisms differ. Crucially, networks formed via biopolymer bridging exhibited more than 110% higher compressive strength than those formed through colloidal interactions (van der Waals and electrostatic interactions), despite displaying comparable rheology, crystalline structure and printing properties.

This dissertation aims to contribute fundamental understanding of how micro-scale particle interactions govern meso-scale rheological behavior and ultimately influence macro-scale 3D printability and mechanical performance in bio-stabilized earthen materials. Focusing on kaolinite clay and representative anionic and non-ionic polysaccharides, it establishes a multiscale experimental framework to explore how biopolymer-clay interaction shape the structure–property relationships critical to additive manufacturing. By bridging these scales, the work seeks to inform the rational design of sustainable, high-performance materials and provide a scientific basis for advancing the use of natural biopolymers in 3D printing applications for earthen construction.