Earth-based additive manufacturing: A field-oriented methodology for evaluating material printability

The recent convergence of earth construction with technology focuses on additive manufacturing using extrudable earth-based materials. The printability of these materials can be defined by their pumpability, extrudability, and buildability. We present a field-oriented methodology for the design of printable local mixtures suitable for various printers. Three tests were defined to characterize the flowability, pumpability and extrudability, and buildability of such materials in their fresh or ‘green’ state, and used to optimize the workability of a sample material for printability. Based on the outcomes, two indices are proposed for the classification and control of the printability of earthen mixtures: flowability and green strength. Our results demonstrate that adjusting water content for consistency and adjusting plasticity for cohesiveness are both vital for tuning printability, although the necessary modifications can negatively affect the material's strength in its hardened state; incorporating cellulose microfibres can counter this by increasing flowability, plasticity, and compressive strength.