Fabrication of internal 3D open-type fractures in binder jetting 3D printed rock matrix using emulsion-based proppants

Fractures/joints of various forms are ubiquitous in natural rocks. A key challenge in rock geomechanics is the 3D additive-subtractive fabrication of internal fractures in printed analogs that replicate natural geometries and mechanical behaviors. Nevertheless, challenges remain in fabricating internal 3D open-type fractures in 3D printed specimens due to the intrinsic limitations in additive layer-by-layer construction process. To this gap, this study introduces an innovative approach to fabricate internal 3D open-type fractures in binder jetting 3D printed brittle magnesium phosphate cement specimens. The 3D open-type fractures are fabricated through layer-wise embedding of self-developed evaporative emulsion-based proppants. To investigate printing accuracy, four patterns of square, elliptical, circular, and non-straight internal 3D open-type fractures are constructed. Maximum geometric similarity of 0.92 is achieved for non-straight fractures. Uniaxial compression tests revealed that filling-type fractured specimens exhibit higher peak strength than open-type fractured specimens. Analysis of crack propagation patterns demonstrate that open-type fractures are dominated by wing crack extension, while filling-type fractures are governed by the fillers. Substituting open-type fractures with filling-type factures may overestimate the strength of fracture rock mass, especially for large opening width fractures, registering a potential threat to safety in rock engineering. The current study lays technical groundwork for the basic relationship between 3D fractured geometry, filler interaction and mechanical responses, advancing application of 3D printing technology in fractured rock studies and practical engineering.