Sustainably 3D-Printing Mortar with Construction Residue Sand: Printability, Mechanical Properties, and Microstructural Mechanisms

This study addresses the technical challenges of using construction residue sand (CRS) with high mud content in 3D printing by developing a novel sustainable mortar system. The key novelty lies in optimizing the mix design with calcium sulfoaluminate cement (CSA) and defining a quantitative printability window. Results show that at a CSA dosage of 10–15% and a sand–binder ratio of 1.4–1.5, the mortar achieves excellent printability, with a fluidity of 165–195 mm and a slump of 10–40 mm. Mechanistically, CSA promotes AFt formation, refining pore structure, and enhancing mechanical strength. This work provides a high-value pathway for recycling construction waste and advancing green intelligent construction.