Development of High-CaO Fly Ash-Based Alkali-Activated Mortar for 3D Printing Technology (2026-02)¶

A one-part alkali-activated mortar was developed for 3D printing technology (3DPT). High-CaO fly ash (FA) served as a binder, while sodium metasilicate (SM) was added as the alkali activator at dosages between 3.0% and 9.0% by weight of the binder. Moreover, bottom ash (BA) was used to replace the fine aggregate at substitution rates of 50% and 100% by volume of fine aggregate, serving as an internal curing material and reducing mortar density. Micro polypropylene fibers (PPF) with lengths of 6 and 9 mm were also added to the mixture at a rate of 0.2% by volume to improve the buildability of 3D printing mortar (3DPM). The flowability of the mortar was maintained between 180 and 190 mm by varying the water-to-binder (W/B) ratio. The mortar’s fresh and hardened properties, mechanical properties, and microstructure were investigated. The results indicated that increasing the SM content required a lower W/B ratio to maintain the target flowability, which in turn shortened the setting times and enhanced the compressive strength of the mortar. Increasing the replacement level of fine aggregate with BA resulted in slightly shorter setting times, lower density, and reduced length change behavior. The 4.5SM mortar exhibited optimal 3DPM properties, resulting in superior buildability, shape stability, and filament consistency, while also achieving the highest 90-day compressive strength of 22.7 MPa. The addition of PPF significantly improved the buildability and interlayer bonding. The microstructural analysis revealed that the main reaction products in the paste were aluminosilicate hydrates (N, C-A-S-H) and calcium silicate hydrate (C-S-H), which contributed to improved mechanical performance.