Low-clay soil as fine aggregate in 3D printed concrete: insights into fresh and hardened properties

Earth-based 3D printed concrete (3DPC) was developed using soil as an alternative to fine aggregates. Locally sourced excavated soil with 4% clay content was used to replace 30-50% of natural sand by weight, as a partial replacement and as an additive. The effect of soil inclusion on the fresh and hardened properties of 3DPC was analyzed. The inclusion of soil led to a reduction of up to 15% in the flow value required for printing and increased open time by 13-60% compared to the control mix. Both extrudability and buildability improved, enabling crack-free printing of more than 30 layers. Isothermal calorimetry showed accelerated hydration, correlating with faster structuration and extended open time. Green strength results showed that soil inclusion delayed the onset of cracks by 30-50%. Compressive strength and bond load values for printed specimens at 28 days showed a reduction of 11-58% and 3-10%, respectively.