Evaluation of Workability Parameters of Straw-Reinforced Earth-Based Materials for Extrusion-Based 3D Printing

Despite increasing interest in earth-based materials for additive manufacturing in construction, limited research has systematically investigated the workability parameters governing their suitability for extrusion-based 3D printing. This study evaluates the influence of wheat straw fiber content on the flowability, pumpability, extrudability, and buildability of earth-based mixtures for extrusion-based 3D printing applications. Four mixtures containing varying proportions of clay (76–100 wt%), wheat straw fiber (0–20 wt%), additives (0–4 wt%), and water were experimentally assessed and subsequently evaluated for compressive strength. Flowability was determined using modified flow tests; pumpability and extrudability were assessed through manual extrusion tools (triangular bag and grout gun), and buildability was evaluated using a modified compression test measuring green strength. Results showed that increasing the wheat straw fiber content from 5% to 20% reduced the flowability from 31.42% to 11.42%, despite corresponding increases in water content. The SP15 mixture (82% clay, 15% wheat straw fiber, 3% additive, and 35% water) exhibited the most balanced performance, achieving the lowest height reduction (17.14%) during buildability testing and demonstrating superior structural stability and compressive performance. The proposed methodology provides practical guidance for developing printable earth-based materials and supports the adoption of locally available, low-carbon materials in sustainable additive manufacturing for construction.