Study on the workability and mechanical influencing factors of 3D-printed coal gangue-fly ash-based geopolymers

Geopolymers have attracted increasing attention as low-carbon materials with good mechanical properties. This study explores the development of geopolymer materials using coal gangue (CG) and fly ash (FA) as primary raw materials, combined with 3D printing technology. The effects of CG content, water-to-binder ratio (W/B), binder-to-sand ratio (B/S) and alkali activators on the workability and mechanical properties of both cast and 3D-printed CG–FA geopolymers are systematically investigated. The results indicate that the flowability reaches a slight peak at 20% CG content, whereas further increases lead to a clear decline. Optimal W/B ratios (0.365–0.38) and B/S ratios (0.9–1.2) were found to enhance both the mechanical properties and workability of the material. Furthermore, the dosage and modulus of the alkali activator substantially influenced paste flowability, setting time, and long–term strength. Compared to cast specimens, 3D–printed specimens exhibited pronounced anisotropy in mechanical performance across different loading directions. This study provides guidance for optimizing mix design and process parameters of 3D–printed geopolymers. • A detailed study was conducted on the workability and mechanical influencing factors of coal gangue-fly ash-based geopolymers for 3D printing. • Optimal coal gangue content, water-to-binder ratio, and binder-to-sand ratio significantly enhance the flowability and compressive strength of the geopolymer paste. • The alkali activator content and modulus notably affect the flowability, setting time, and long-term strength of the geopolymer paste. • Compared to cast specimens, 3D printed specimens exhibit significant anisotropy in mechanical performance under different loading directions.