3D printing with geopolymer-stabilized excavated earth: Enhancement of printability and engineering performance through controlled retardation

Excavated soil from widescale tunneling and excavation can be used in 3D-printed constructions. This research investigates the feasibility of 3D printing using geopolymer stabilized excavated soil (GP-E) containing 42% clay rich in kaolinite minerals. At dosages 0.50–1.5 wt%, sucrose is added to control the hydration and time-dependent rheological properties, enabling adequate open printing time (OPT) for large-scale printing. Experimental findings show that 1% and 1.5% sucrose addition to GP-E offers OPT of 130 min and 170 min respectively compared to 32 min for GP-E. By enabling better dispersion, the addition of sucrose allows smooth extrusion with shape retention of 90 – 92% at a lower NaOH solution-to-binder ratio (0.68) than GP-E (0.75). Sucrose and clay (in the soil) act synergistically to reduce the time-dependent static yield stress but maintain it at an adequate level of 5–8 kPa required for stacking up the layers without collapse. Flow retention and thixotropy are maintained at 100% during the printing window, which balances extrusion and buildability. As a result, the sucrose-GP-E mix could be built up to a height of 1.05 m compared to 0.19 m for GP-E. 1 % sucrose-added GP-E possesses 28 – 40% and 70% higher wet compressive strength and inter-layer bonding respectively compared to GP-E depending on the loading direction. These are linked to the refinement of capillary porosity and a 13–15% reduction in shrinkage. In summary, the findings present a potential route for controlling the printing time of geopolymer-stabilized earthen materials while reducing the embodied carbon and enhancing the mechanical performance.