Evaluating Clay Characteristics for Printable Geo-Materials: A Case Study of Clay–Sand Mixes

Extrusion-based 3D Construction Printing (3DCP) involves developing novel material mixtures that incorporate local geo-materials. Given that clay minerals and silt are major causes of soil variability, this study focuses on the fine fraction of soil to facilitate purpose-oriented design, classification, and standardization. We begin with an overview of current research in the field and general information about clays. Subsequently, we establish an evaluation methodology, examining various clay–sand mix ratios, along with locally sourced material to gain general insights into the material’s clay-dependent macro-printability characteristics. The findings are then correlated and discussed in relation to the microcharacteristics of the clays, emphasizing the significance of both intraparticle and interparticle swelling for strength and cohesiveness. Factors such as swelling ability, and charge, which may be reflected by pH, are pivotal for strength; while the quantity of clay and its interparticle swelling ability, denoted by the plasticity index (PI), delineate cohesiveness, which is essential for pumpability and extrudability. Furthermore, the presence of organic material and other minerals is observed to have a significant impact on these properties.