Extending Applicability of 3D Printable Geopolymer to Large-Scale Printing Scenario via Combination of Sodium Carbonate and Nano-Silica (2023-10)¶

Adequate printable time is crucial for the application of extrusion-based concrete 3D printing. 3D-printing geopolymer concrete (3DPGC) possesses a rapid hardening feature intrinsically, limiting its applicability in large-scale printing scenarios. Herein, we jointly use Na2CO3 (Nc) and nano-silica (Ns) to improve the printability (particularly extending printable time) and mechanical properties of 3DPGC. We first evaluated the effects of Nc replacement to a traditional activator (waterglass) on the 3D-printing-related rheology and mechanical properties to obtain an optimum Nc dosage. Subsequently, the influences of Ns incorporation on rheology, extrudability, buildability, bulk mechanical strengths, and interlayer properties were investigated based on the optimum Nc dosage. The combination of Nc and Ns (Nc-Ns) manifested a much better extrudability with a sixfold longer printable time (>120 min) due to the decreased hardening rate. Better buildability, higher compressive strengths and a stronger interlayer strength retention capacity were further achieved simultaneously. Nc adoption enables a slower hardening process owing to the lower solution alkalinity and the existence of carbonate, while the overall hardening profile can be adjusted with Ns addition. We successfully printed a special-shaped structure for validation, which requires a long printable time (>40 min). It demonstrates the exceptional printability of the proposed mixture formulation. This work contributes a feasible solution for 3DPGC in large-scale printing scenarios from the material perspective.