Unveiling the critical role of rheology modifiers in additive manufacturing of geopolymers and their mechanical properties

Optimal selection of rheology modifiers is a crucial prerequisite for designing ideal geopolymer inks for high-precision material extrusion (ME). In this study, we shed light on this issue by exploring two-component rheology modifiers systems for ME, including Triton+Kaolin, Polyethylene Glycol (PEG)+Kaolin, and Polyvinyl Alcohol (PVA)+Kaolin. We find that the type and dosage of rheology modifiers are versatile control knobs for fine-tuning the printing open time and mechanical properties of actual printed Na-based geopolymers. By carefully adjusting the rheology modifier dosage, the printing open time of Na-based geopolymers can be extended to 180 mins. Fluid simulations reveal that the ink viscosity plays a key role in determining printing accuracy by affecting the pressure concentration stage during extrusion. Furthermore, the mechanical properties of geopolymers with the same rheology modifier composition gradually decreased with increasing printing open time. At 0 min printing open time, Na-based geopolymer containing 10% Kaolin + 1.25% Triton shows the highest compressive strengths of 68.6 ± 2.7 MPa. The Triton-Kaolin rheology modifier combination demonstrates universality in rheological control of Na+, K+, and Cs+ based geopolymer inks, with the corresponding minimum slump rates of 0.7%, 0.4%, and 0.8%, respectively. Our findings provide clear guidelines for the design of high-quality metakaolin-based geopolymer inks for ME, crucial for their practical application and sustainable development.