Effects of different silica sources on rheological properties and 3D printability of magnesium-based cements

Abstract

This research explores the usability of reactive MgO (RM)-based materials as sustainable, low-carbon alternative binders for 3D concrete printing. Specifically, RM was substituted with 25 wt% of diverse silica sources to assess their potential: micro-silica (MS), metakaolin (MK), fly ash (FA), and basalt powder (Bst). By evaluating rheology, buildability, and 28-day compressive strength under a constant initial consistency, results reveal that the MK blend exhibited optimal rheological behavior. It combined low initial dynamic yield stress for smooth extrusion with substantial time-dependent viscosity build-up, completely preventing filament deformation. All mixtures demonstrated excellent buildability, successfully sustaining 20-layer structures without collapse. Furthermore, XRD analysis confirmed that highly amorphous silica in MS and MK facilitated extensive precipitation of magnesium silicate hydrate (M-S-H) gels. This microstructural improvement yielded the highest compressive strengths of 16.5 MPa and 13.9 MPa, respectively. Ultimately, RM-SiO₂ systems emerge as highly promising, low-carbon materials for digital construction.