Geomechanical and geophysical properties of gypsum-based 3D printed geomaterials

Employing the use of 3D printed geomaterials enables us to overcome sample-to-sample variability of natural materials with reproducible mechanical properties. In this work, cylindrical samples are manufactured with bassanite powder-based 3D printing technique. Printing directions and binder amount are changed to evaluate the impact of printing conditions on mechanical properties of 3D printed samples. Transformation of bassanite powders to gypsum via chemical reaction is identified and printed samples are stored at three different humidity conditions from dry to 80% relative humidity to evaluate the impact of moisture on mechanical properties. Wave velocity is measured in different directions to evaluate directional elastic moduli. Unconfined compression strength (UCS) testing of cylindrical samples is performed to evaluate the consistency of printing process and the variation of mechanical property. Micro-computed tomography (micro-CT) images the printed samples before and after UCS tests. Overall, peak strength and wave velocities show strong directional properties. Because hydration of printed materials weakens the bonding strength of grains, samples stored in the dry condition tend to have stronger UCS strengths than samples stored in higher relative humidity. MicroCT and scanning electron microscopy images reveal that both texture orientation associated with binder spray direction and depositional direction govern the anisotropic (or orthotropic) mechanical properties. The applicability of powder-based printing technique is further discussed to suggest optimal printing conditions for reproducible geomaterials. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.