Recovery of Stone Slurry Waste as an Ultrafine Filler in 3D-Printable Cementitious Mortar for Sustainable Construction

This study investigates the feasibility of utilizing stone dust waste, an industrial by-product generated during ornamental-stone quarrying processing, as a raw material for 3D-printing mortar. This approach reduces waste disposal and promotes a circular economy. Several high-strength cementitious mixtures were screened and optimized by varying raw materials as a function of slump flow evolution over time, which served as indirect assessment of open time and extrudability. Following the identification of the most suitable mixture for 3D printing, one of the raw materials (an ultrafine limestone filler) was subsequently replaced on a 1:1 mass basis with stone waste, selected due to its comparable particle-size distribution, to assess its feasibility as an alternative filler. Fresh-state properties were evaluated based on flowability, with slump values ranging from 16 cm to 13 cm over time, and extrusion tests on a screw pump, used to validate extrusion stability and shape retention. Hardened-state properties were determined at different curing ages. The incorporation of Apricena stone waste resulted in similar fresh-state and extrusion behaviour of mortar, without additional changes to the mix design, and the intended 30 min qualitative extrusion window was met. At 28 days, the mixture incorporating stone dust waste achieved flexural and compressive strength of 12.51 MPa and 79.72 MPa. The incorporation of stone dust waste resulted in an extrudable mixture for 3D printing, with the intended open time and fresh-state behaviour, as well as mechanical properties complying with high-strength applications. However, the full replacement of one of the limestone fillers led to an 8% reduction in 28-day compressive strength. Overall, the findings demonstrate that the recovery of stone dust slurry as viable supplementary cementitious material for 3D-printed concrete is viable. The data support the use of this stone waste as a raw material for 3D printing, and specific mortar development and mix optimization for different applications are recommended, including the quantitative assessment of buildability, printed mechanical properties, durability, and leaching and life-cycle assessment.