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<p>Additive manufacturing of geopolymer-based materials requires a careful balance between flowability, structural build-up, and interlayer cohesion. In this study, sustainable geopolymer binders derived from untreated ceramic sludge were developed and evaluated for extrusion-based 3D printing under both ambient and sub-ambient (0–5&#xa0;°C) conditions. Bentonite and citric acid were introduced as functional additives to tailor fresh-state rheological behaviour and process stability. Rheological performance was characterised using steady-shear measurements and interpreted through Bingham and Herschel–Bulkley models, with parameters extracted from the downward branch of the hysteresis loop to represent the post-shear structural state relevant to extrusion–deposition processes. At room temperature, the formulations exhibited well-defined yield-stress behaviour and controlled shear-thinning response, enabling stable filament formation. Under cold conditions, a reduction in apparent viscosity was observed, attributed to delayed geopolymerisation kinetics and limited early-stage network connectivity. Despite these effects, selected compositions maintained sufficient green-state cohesion to ensure layer stability. By correlating rheological descriptors with extrusion trials and microstructural observations, a process window for printable waste-derived geopolymer inks is proposed. The results highlight the feasibility of temperature-sensitive additive manufacturing using unprocessed ceramic waste, contributing to the development of sustainable and scalable geopolymer-based 3D printing systems.</p>

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Sustainable geopolymer binders for extrusion-based 3D printing: rheology, microstructure, and printability under ambient and sub-ambient conditions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月21日

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  • Laura Ricciotti,
  • Daniele Lucariello,
  • Valeria Perrotta,
  • Antonio Apicella,
  • Raffaella Aversa

摘要

Additive manufacturing of geopolymer-based materials requires a careful balance between flowability, structural build-up, and interlayer cohesion. In this study, sustainable geopolymer binders derived from untreated ceramic sludge were developed and evaluated for extrusion-based 3D printing under both ambient and sub-ambient (0–5 °C) conditions. Bentonite and citric acid were introduced as functional additives to tailor fresh-state rheological behaviour and process stability. Rheological performance was characterised using steady-shear measurements and interpreted through Bingham and Herschel–Bulkley models, with parameters extracted from the downward branch of the hysteresis loop to represent the post-shear structural state relevant to extrusion–deposition processes. At room temperature, the formulations exhibited well-defined yield-stress behaviour and controlled shear-thinning response, enabling stable filament formation. Under cold conditions, a reduction in apparent viscosity was observed, attributed to delayed geopolymerisation kinetics and limited early-stage network connectivity. Despite these effects, selected compositions maintained sufficient green-state cohesion to ensure layer stability. By correlating rheological descriptors with extrusion trials and microstructural observations, a process window for printable waste-derived geopolymer inks is proposed. The results highlight the feasibility of temperature-sensitive additive manufacturing using unprocessed ceramic waste, contributing to the development of sustainable and scalable geopolymer-based 3D printing systems.