Cost-Effective 3D Printing of Geopolymer Concrete Enhanced by Na-CMC as a Viscosity Modifier.

This study presents an experimental investigation into the development of a broadly accessible, research-scale geopolymer concrete (GPC) 3D printing platform and formulation. Concrete 3D printing is a rapidly emerging production method that remains underutilized, largely due to legal and regulatory restrictions and, to a degree, the high barrier to entry in the associated research stemming from expensive specialized hardware. In this work, a low-cost tabletop clay printer was modified for GPC production, demonstrating that a dedicated geopolymer formulation can be effectively utilized for additive manufacturing as a low-carbon alternative to conventional concrete. The mix design was engineered to favor geopolymerization while maintaining printability, employing sodium carboxymethyl cellulose (Na-CMC) as a viscosity-modifying additive to enable a low water-to-solid ratio while maintaining workability. The influence of formulation and processing on extrusion behavior and defect formation is discussed. The printer modification protocol and recipe mix design are described in detail to ensure reproducibility and interstudy comparability. The resulting material demonstrated successful polymerization and solid mechanical performance, confirmed by 7-day direct tensile testing of 3D-printed dog-bone specimens (1.1 ± 0.2 MPa), multiscale defect analysis, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.