Resource-aware direct ink writing of lunar regolith simulant pastes through milling-controlled rheology and activator reduction

Lunar construction requires processing routes that reduce imported consumables while retaining application-relevant printability and performance. This study developed a two-stage strategy for direct ink writing of alkali-activated CUG-LRS-1 pastes. In Stage I, milling for 1, 4, and 10 h yielded D 50 values of 25, 6, and 0.9 μm, respectively. Without a rheology modifier, prolonged milling enhanced viscosity recovery and time-dependent structural build-up. The 0.9 μm paste exhibited an apparent structural build-up rate, A thix , of 1.424 Pa/min, a printing window of 45–145 min, and a maximum of 43 layers before collapse. In Stage II, reducing the activator from 9 to 5 wt% (44.4%) produced 71.4% viscosity recovery and 32 layers before collapse. At 28 days, flexural strength decreased from 6.48 to 5.99 MPa, while compressive strength decreased from 45.03 to 15.15 MPa. XRD showed that the crystalline phases persisted, whereas FTIR and SEM revealed a less developed amorphous network and a less continuous matrix after activator reduction. Overall, milling history governed the time-dependent printing window, while activator dosage set the trade-off among material input, buildability, and strength. The results support application-specific formulation rather than maximizing strength alone.