Hybrid 3D Printable Mixtures Incorporating Fine Earth, Portland Cement, and Fly Ash (2025-12)¶

3D printing offers efficiency and design flexibility in construction, but its sustainability is limited by the carbon footprint of cement-based materials. In this sense, the present study proposes hybrid printable matrices with Portland cement (30%–50%), fine earth (50%–70%), and fly ash (0–10%). Hydration and rheology of pastes were analyzed using isothermal calorimetry, thermogravimetric analysis (TGA), and rheometry, while printable mortars were evaluated using a flow table, cone penetration, and uniaxial compression. Environmental performance was assessed through cradle-to-gate life cycle assessment (LCA). Cone penetration tests showed that increasing earth from 50% to 70% raises the structuration rate from 8.6 to 33.1 Pa/min, enhancing buildability but narrowing the open time. Fly ash mitigated this effect by reducing structuration and extending open time. In compression, increasing the mass fraction of earth from 50% to 70% reduced the strength from 19.2 MPa to 5.6 MPa. The mixture containing 60% earth and 10% fly ash achieved 10.7 MPa, showing improved strength at equivalent cement content. Regarding environmental impacts, the climate change potential decreased from 355.1 kg CO₂eq/m3 (50% earth, 50% cement) to 243.1 kg CO₂eq/m3 (60% earth, 30% cement, and 10% fly ash), 32% lower and below the 500–583 kg CO₂eq/m3 reported in the literature for printable mortars. These findings show the potential of earth–fly ash–cement hybrid matrices for eco-friendly, 3D printable mortars with balanced rheological, mechanical, and environmental performance.