Investigation into the Effect of Full Replacement with Portland Slag Cement and Screened Slag Sand for Development of Sustainable 3D Printed Concrete (2026-02)¶

This study evaluates the use of Portland slag cement (PSC) and slag sand (SS) as sustainable alternatives to conventional binders and aggregates for extrusion-based 3D concrete printing (3DCP), with emphasis on their influence on fresh-state printability, hardened state properties, pore microstructure, and coupled thermal and moisture–transport properties. Printing results demonstrated stable extrusion and significantly enhanced buildability due to increased inter-particle friction from angular SS and improved cohesion from the finer and more reactive PSC; however, the open time was reduced to 20 minutes compared to 40 minutes for the OPC–river sand control mix. Despite a moderate increase in total porosity, slag-based mixes exhibited a refined and spatially homogenized pore size distribution, resulting in reduced mechanical anisotropy (0.19), lower sorptivity (0.003 mm/s½), and reduced thermal conductivity (∼0.87 W/mK). This pore refinement reduced preferential moisture transport pathways, and increased phonon scattering, thereby linking improved isotropic load transfer with enhanced resistance to moisture ingress and heat flow. PSC further contributed to improved early-age carbon sequestration through decalcification of secondary hydration products. These findings were substantiated by microstructural analyses, including X-ray diffraction (XRD), thermo-gravimetric analysis (TGA/DTG), and mercury intrusion porosimetry (MIP). Although slag sand increased material cost, sustainability assessment revealed the lowest equivalent CO2 emissions (327 kg/m3) for mixes incorporating both PSC and SS. Overall, the results demonstrate that PSC–SS-based printable concretes achieve a balanced trade-off between buildability, isotropic mechanical response, thermal insulation, and environmental sustainability.