Evaluating the printability and buildability of earth-based fiber-biopolymer composites for 3D printing applications

The integration of 3D printing technology in construction has gained significant attention due to its potential to utilize sustainable, earth-based materials. This innovative approach offers a fast, cost-effective, and environmentally friendly alternative to conventional construction methods. Moreover, 3D printing presents promising applications in extreme environments, as well as for rapidly deployable structures, including temporary military or disaster-relief housing. This study investigates the fresh properties, printability, and compressive strength of 3D-printed earth mixtures composed of locally available soil, sand, biopolymers, and fibers (polypropylene and hemp). The experiments investigate how variations in composition and proportion affect performance, enabling the optimization of these mixtures for 3D printing. A multi-scale characterization approach is employed. Index properties such as liquid limit, plastic limit, particle size distribution, optimum moisture content, and maximum dry density are measured. Rheological properties, including viscosity, are evaluated using the viscometer to assess workability and extrudability. Printability is analyzed through extrusion quality and buildability, with emphasis on discontinuities, deformation, and layer count. The results indicate that biopolymer and water content, along with fiber reinforcement, have a significant effect on printability. Notably, the mixture containing 1% xanthan gum and 0.5% polypropylene fiber at a water-to-dry ratio of 0.635 was identified as the optimal formulation. This mixture exhibited consistent extrusion with an average filament width of 10.13 mm (10 mm nozzle, triangular bag test) and a printing width of 20.19 mm (15 mm printer nozzle, 2D square structure test), satisfying both extrudability and buildability requirements. Upon drying, the 3D-printed sample showed a 12.66% reduction in total height. Unconfined compression tests revealed that the inclusion of fibers and biopolymers increased the compressive strength by [Formula: see text]. Additionally, water resistance testing showed a marginal weight reduction of only 0.33%. An increase in nozzle diameter resulted in a decrease in the total build height, with the 10 mm nozzle producing the highest number of stable layers. Overall, the findings highlight the potential of well-engineered biopolymer-fiber-soil mixtures to facilitate sustainable and durable 3D-printed earthen construction.