3D Printing with Stabilized Earth (2024-07)¶

This research examines the feasibility of using excavated soil (clay content of 44 %) as 25 % and 50 % replacement of natural sand in 3D printable formulations. A combination of ordinary Portland cement (OPC) and fly ash (FA) are used as binders for stabilization. The development of engineering properties subject to two curing conditions – normal curing and CO2 curing (5 % concentration for 5 h) are investigated. Experimental findings suggest that a combination of FA and clay (mainly kaolinite) in the used soil reduces plastic viscosity and improves flow retention, thus enhancing the extrusion quality and stability. The flocculation of clay at rest accelerates the evolution of static yield stress after extrusion, imparting 18–30 % better thixotropy. As a result, OPC-FA-soil mixes could be stacked to a height of 1.20 m compared to 0.48–0.54 m for OPC-sand and OPC-FA-sand mixes. Carbon sequestration via CO2 curing leads to an increase in wet compressive strength of OPC-25 % soil and OPC-FA-25 % soil by 29–38 % and 26–47 % respectively at 1-day age, which is ascribed to the densification effect of mineral carbonates. This is also reflected in the reduction in water sorptivity through the inter-layer zones and total shrinkage by 20 % and 16 % respectively. Due to reduced shrinkage and capillary sorption, inter-layer bond strengths in CO2-cured OPC-25 % soil are also improved by 20–50 % than the normally cured counterpart. In summary, the research demonstrates a feasible pathway to develop carbon-sequestering earth-based materials (CO2 uptake of 9–11 wt% of OPC) for additive manufacturing of masonry building and infrastructural members.