Magnesium phosphate cement for powder-based 3D concrete printing: Systematic evaluation and optimization of printability and printing quality

With the advantages of fast hardening, high early strength, excellent bonding strength and room temperature curing, magnesium phosphate cement (MPC) is highly preferable for powder-based 3D concrete printing. In this paper, a systematic approach via comprehending parametric analysis, visualizing techniques (SEM, XRD and XRay CT) and mechanical testing is developed to evaluate and optimize printability and printing quality of powder-based 3D MPC printing. The test printing results show that appropriately mapped proportions of ingredients will orient the specific properties towards the target objectives through navigating different combinations of proportions comprehensively. Specifically, 1,2-propylene glycol is able to significantly increase the viscosity of the binder, and Surfynol 465 can substantially reduce the surface tension of the binder. 25 wt% quartz sand can remarkably improve spreadability and surface flatness of the powder bed. In addition, the penetration and diffusion of the binder in the powder bed is effectively controlled by appropriate content of polyvinyl alcohol (PVA) due to the properties of high viscosity and good film-forming, thus remarkably improves printing accuracy. The compactness and hydration degree of the powder-based 3D printed MPC are optimized by 5 wt% PVA (MPC5) with the total porosity reduced by 2.86% compared to that of MPC0 (without PVA). High printing precision of the printed complex geological canyon river model indicates that MPC with appropriate contents of modulators, such as 1,2-propylene glycol and Surfynol 465 for binder and PVA and quartz sand for base powder, is desirable powder-based 3D printable material.