Variations in rheological properties and fundamental processing of potassium-based geopolymers for optimal 3D printed layer adhesion for applications in extreme environment

Brandvold, Allison S.

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https://hdl.handle.net/2142/129370 Copy

Description

Title

Variations in rheological properties and fundamental processing of potassium-based geopolymers for optimal 3D printed layer adhesion for applications in extreme environment

Author(s)

Brandvold, Allison S.

Issue Date

2025-03-03

Director of Research (if dissertation) or Advisor (if thesis)

Kriven, Waltraud

Doctoral Committee Chair(s)

Kriven, Waltraud

Committee Member(s)

• Ewoldt, Randy
• Stinville, Jean-Charles
• Garg, Nishant
• Shoemaker, Daniel

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Geopolymer
• Rheology
• 3D printing
• Adhesion
• Squeeze Flow
• Thixotropy

Abstract

Geopolymers are an alkali activated, amorphous, inorganic, polymeric material that has significant applications in building materials and is a viable alternative material to Ordinary Portland Cement. Given their ability to be easily shaped and cured at ambient temperatures, there has been significant interest in the past few decades to further investigate applications of geopolymers in 3D printing. Underlying basic rheological properties of the geopolymer pastes and composites were largely lacking in literature and deemed essential to fully understand how to optimally print geopolymers. Given the unique layer by layer structure of 3D printed parts, the mechanical properties of these composites would be easily influenced by various processing and reinforcement-based variables. Further exploration into critical changes in adhesion strength provides a roadmap for designing optimal 3D printed composites for many different applications. The work outlined in this thesis has three major parts simplified as: basic rheological properties and characterization, complex rheological properties of reinforced geopolymer pastes and investigations into factors influencing the adhesion strength of 3D printed composites. For the basic rheological properties and characterization, geopolymers were found to strong show evidence of thixotropic properties. The underlying rheological changes were found to result from two competing mechanisms: reversible physical restructuring due to thixotropy and irreversible chemical setting due to the ongoing geopolymerization reaction. The behavior of thixotropy was found to be driven primarily by physical restructuring of silica and alumina tetrahedra via hydrogen bonding intermolecular forces. In addition, the elevated temperatures led to rapid polymerization rates, decreasing solidification time from approximately 26 hrs at 25 °C to 2 hrs at 55 °C, indicating a significant reduction in viable printing time. The sand and basalt fiber geopolymer composites exhibited a strong dependence on solid to liquid ratio to increase deformation resistance proving the reliance on necessary liquid bridges between particles and the impact of particle-to-particle collisions to hold subsequent layers. The inclusion of fiber also significantly improved shape retention via flow table testing results. The alumina platelet composition, however, had significant dependence on weight percent, specific surface area and deformation rate to determine the force response. Elevated deformation rates, such as 3.0 mm/s, forced the composite to deform much more homogeneously as particle interactions were unable to occur as strongly during rapid flow. Slower deformation rates allowed for interconnected normal force contacts to consistently develop and cumulatively increase the force response, further resisting deformation. The weight percent allowable in terms of workability limits was dominated by the specific surface area, with the smallest platelet size of 5 m, limited by a maximum of 34wt% of reinforcement for potassium geopolymers. Lastly, the adhesion strength of various processing and reinforcement-based variables were investigated. Time between layer deposition critically impacted the adhesion between layers as exposed geopolymer surface material was unable to fully polymerization. However, adherence to a fully cured geopolymer was deemed as effective as adhering to a fresh geopolymer paste. Fibers were found to increase crack deflection and crack bridging to act as strengthening mechanisms between layers for ambient temperatures but performed poorly at elevated temperatures. In addition, loss of internal water (600°C) and crystallization to leucite (~1000 °C) severely compromised adhesion strength due to microstructural cracking, enhanced porosity and brittleness. Lastly, an optimal composite ratio of 50 wt% sand and 3 wt% basalt fiber were found for maximizing stress and reliability of fracture. Overall, many factors must be considered when designing a 3D printed composite material for any application.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129370

Copyright and License Information

Copyright 2025 Allison Brandvold

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