Printability, engineering properties and environmental implications of 3D-printed cementitious mortars incorporating hydrated lime, tile powder and accelerator

3D printing offers transformative potential in construction, yet optimising the performance of cementitious materials before and after extrusion remains a critical challenge. This study presents a performance-based mix design framework targeting extrudability, buildability, and layer stability, while evaluating the individual and combined effects of cement (C), hydrated lime (L), recycled tile powder (T), and chemical accelerators (A). Results reveal that their synergy significantly enhances rheology, yield stress, and print stability, while maintaining sufficient flowability. A specifically optimised mix, CLTA, achieved a 40% reduction in shrinkage, improved interlayer bonding, and markedly increased mechanical strength, modulus of toughness, and failure strain, key for energy absorption in printed structures. Environmentally, CLTA reduced raw material demand and improved eco-strength and costefficiency by up to 20%, promoting circularity and resource efficiency. The findings provide a robust pathway for designing high-performance, sustainable 3D-printed mortars, integrating engineering functionality with ecological resilience, paving the way for broader adoption of additive manufacturing in construction.