Additive manufacturing of biocemented porous structures using selective binding and active print bed compaction

This paper presents a method for 3D printing bio-concrete components with a compacted, heterogeneous sand mixture, to achieve geometrically complex biomineralized spatial structures with high compressive strength. The presented process uses a moist sand mixture (0.063–2 mm) and additional compaction to achieve high packing density. Bacteria suspension was selectively applied along predetermined paths by a peristaltic pump. Parameter studies established that a CaCl 2 fixation solution concentration of 0.2 M and bacteria dispensing rates between 4 and 12 μL/mm were suitable to control bacterial localization and diffusion depth within the sand mixture. Unconfined compressive strength tests on 3D printed small-scale cylinders (D × h = 25 × 30 mm) yielded mean unconfined compressive strength values of 11 MPa and 17 MPa. A geometrically complex structure (D × h = 90 × 80 mm) was produced and showed dimensional deviations of −4 to +4 mm, attributable to compaction-induced deformations in both the horizontal plane and in the vertical axis.