Fractured rock analogs by binder jetting 3D printing using cement: Improvements in geometric similarity and mechanical performance

Reliable evaluation of the mechanical contribution of fracture networks and deformation parameters of rock matrices is a prerequisite for stability analysis for the safe operation of practical geomechanical engineering projects. Current research for evaluation is underscored by three-dimensional (3D) cementitious printing, particularly binder jetting, to reproduce fracture networks with high fidelity in geometries and deformation/strength parameters of the matrix to those of their natural counterparts. Nevertheless, it has been argued that current 3D printing techniques are inadequate in terms of precision in capturing the geometric features of fractures, and the strength of the printed matrix is generally lower than that of some natural hard rock matrices. To this end, this study developed a 3D binder-jetting cementitious printing methodology with high precision for constructing a fractured rock analog. 3D fractures were fabricated by extracting practical fracture network geometries from scanned computed tomography (CT) images, demonstrating less than 5 % error in key geometric parameters, including the maximum inclination angle, maximum area, porosity, and fractal dimension. High printing precision and mechanical properties of the printed samples were achieved by optimizing the printing parameters and dry-heat curing process. The accuracy of the printed internal fractures was evaluated using CT and dimensional measurements. The mechanical properties of the specimens were tested using uniaxial compression and Brazilian splitting experiments. The microscopic compositions and microstructures of the specimens were obtained using scanning electron microscopy, X-ray diffraction, and thermal analysis techniques. The test results showed that optimizing the binder saturation can significantly improve the dimensional accuracy and effectively reduce the mechanical anisotropy. Dry heat curing enhances both geometric accuracy and mechanical performance by accelerating hydration and restraining binder diffusion. Specimens cured at 40 °C for 3 d yields significantly improved dimensional accuracy and a 40 %–60 % increase in mechanical properties compared to those without thermal curing. These specimens closely approximated natural sandstone with respect to compressive strength, elastic modulus, splitting strength, brittleness index, and failure patterns. The experimental results demonstrate the effectiveness of the proposed CT data-based binder jetting 3D printing methodology in reliably replicating complex fractured rock geometries and mechanics.