Multiscale characterization and CFD-driven optimization of 3D-printed geopolymer composites for high-temperature molds

This study investigated the development of geopolymer formulations suitable for additive manufacturing, with a particular focus on their thermo-mechanical performance under high-temperature service conditions. The materials were designed to withstand temperatures up to 800°C while exhibiting flexural strengths exceeding 15 MPa. Such properties make these formulations promising candidates for various high-temperature applications, including, among others, the fabrication of 3D-printed geopolymer insert molds intended for thermally demanding processes. To address these requirements, a multiscale framework was developed, coupling material formulation, rheological optimization, and Computational Fluid Dynamics (CFD) simulation to link flow behavior with extrusion accuracy. The designed geopolymer composite combined a potassium-based binder with thermally stable fillers and rheology modifiers to ensure both printability and high-temperature performance. The CFD model, calibrated from experimental rheological data, accurately captured the non-Newtonian and viscoelastic response of the geopolymer paste, and was used to identify an optimal printing regime characterized by a dimensionless inlet-to-substrate velocity ratio (Formula presented) and a gap-to-diameter ratio (Formula presented), within which the predicted strand geometry deviated by less than 6.98% from experimental measurements. This dimensionless framework ensured a balanced material deposition and provided a robust, scalable basis for selecting printing parameters such as infill density, orientation, and nozzle-to-substrate gap, thereby ensuring the structural integrity of the printed parts. The optimized formulations exhibited flexural strengths up to 34MPa and structural stability after exposure to 1000°C, surpassing the initial industrial targets by 40%. The workflow was validated through the successful fabrication and thermal testing of a complex industrial prototype, demonstrating a rigorous experimental-computational approach that connects material design, process control, and application performance for sustainable, high-temperature geopolymer additive manufacturing.