Development of Heat-Triggered Sulfate Capsule for on-Demand Setting 3D Printing Phosphogypsum-Based Cement (2026-04)¶

Extrusion-based 3D printing of cementitious materials demands sufficient pumpability during transportation, while rapidly developing buildability after extrusion and deposition, which remains challenging. In this study, a heat-triggered capsule (HTC) system is developed to achieve on-demand setting and buildability of phosphogypsum-based sulfate cement (GSS) for 3D printing. The results demonstrated that the HTCs remained structurally intact under unheated conditions, ensuring good workability and pumpability of the slurry during extrusion and transportation. Upon heat triggering, the capsules rapidly breakdown and the encapsulated potassium sulfate accelerator is released. The released sulfate species (SO42−) preferentially promotes the formation of needle-like dihydrate gypsum, leading to a pronounced increase in static yield stress and the gradual establishment of a load-bearing skeletal structure. Meanwhile, the introduction of potassium ions (K+) contributes to maintaining a mildly alkaline environment. In the pore solution, K+ participates in the formation of KOH, leading to a moderate increase in alkalinity, which promotes the dissolution of reactive phases in ground granulated blast furnace slag (GGBFS) and steel slag (SS). This alkaline environment further promotes the formation of ettringite (AFt), contributing to the stabilization of the early-age microstructure during hydration. The proposed HTC-based strategy enables precise control over setting and structural evolution, offering a feasible and intelligent approach for the high-value utilization of phosphogypsum via extrusion-based 3D printing technique.