Suction-Based Framework of 3D-Printed Earthen Materials (2026-04)¶

Extrusion-based additive manufacturing using earth materials offers a promising solution for on-site construction. However, its feasibility depends on soil composition, rheological characteristics, geotechnical properties, and unsaturated characteristics. This study proposes a suction-based framework for evaluating printable soil mixtures and predicting buildability through a diffusion-based analytical model linking matric suction evolution to shear strength. Three clay-sand mixtures with 30, 50, and 70% clay (K30, K50, K70) were investigated, achieving maximum buildability of 21, 16, and 15 layers at static yield stresses of 4.19, 2.53, and 1.70 kPa, respectively. Suction was measured during drying using HYPROP-WP4C and incorporated into the Fredlund shear strength framework. Model-predicted buildability matched experimental measurements at 25 °C and 70% RH. Suction-mobilized friction contributed 80–90% of total shear strength after 7 days curing, with clay-rich mixtures achieving 9–48 kPa depending on interlayer intervals (300–3600 s) and relative humidity (10–95%). Buildability is governed primarily by cohesion and interparticle friction at placement, while long-term strength is driven by suction mobilized friction development. Longer time gaps between layers increased buildability through enhanced suction gain, while higher relative humidity reduced it; temperature effects were comparatively minor. The framework provides a physically grounded basis for evaluating binder-free earthen mixtures for extrusion-based additive manufacturing.