This work reports the development of a phosphoric acid-activated geopolymer (PAGP) formulated for extrusion-based additive manufacturing via direct ink writing. To our knowledge, this is the first demonstration of 3D printing of an acid-activated geopolymer, broadening geopolymer chemistry beyond alkaline systems. Metakaolin-based formulations were modified with bentonite (PAGP-BT) and laponite (PAGP-LP) to adjust viscosity, yield stress, and thixotropy. Both showed shear-thinning behavior, with PAGP-LP displaying superior flowability and recovery, ideal for DIW. Imaging revealed low porosity in PAGP, high porosity but preserved geometry in PAGP-BT, and moderate porosity with excellent stability in PAGP-LP. A Central Composite Rotatable Design optimized curing, showing that lower temperatures with extended times enhanced strength (up to 43 MPa), while higher temperatures promoted porosity but reduced integrity. FTIR and XRD confirmed a polycondensed phospho-aluminosilicate network with quartz crystallites. These results establish phosphoric acid-based geopolymers as promising materials for additive manufacturing with tunable structural and functional properties.
Development and characterization of phosphoric acid-activated geopolymers for extrusion-based additive manufacturing
Colombo P.
2026
Abstract
This work reports the development of a phosphoric acid-activated geopolymer (PAGP) formulated for extrusion-based additive manufacturing via direct ink writing. To our knowledge, this is the first demonstration of 3D printing of an acid-activated geopolymer, broadening geopolymer chemistry beyond alkaline systems. Metakaolin-based formulations were modified with bentonite (PAGP-BT) and laponite (PAGP-LP) to adjust viscosity, yield stress, and thixotropy. Both showed shear-thinning behavior, with PAGP-LP displaying superior flowability and recovery, ideal for DIW. Imaging revealed low porosity in PAGP, high porosity but preserved geometry in PAGP-BT, and moderate porosity with excellent stability in PAGP-LP. A Central Composite Rotatable Design optimized curing, showing that lower temperatures with extended times enhanced strength (up to 43 MPa), while higher temperatures promoted porosity but reduced integrity. FTIR and XRD confirmed a polycondensed phospho-aluminosilicate network with quartz crystallites. These results establish phosphoric acid-based geopolymers as promising materials for additive manufacturing with tunable structural and functional properties.
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