University of Stuttgart researchers 3D print bio-concrete structures using bacteria
A new additive manufacturing method combines microbial cementation with layer-by-layer sand compaction to produce geometrically complex, low-carbon concrete structures, without conventional cement
Researchers at the University of Stuttgart have developed a 3D printing method for bio-concrete that uses live bacteria to bind compacted sand into load-bearing structures — without conventional cement. The work, published in npj Advanced Manufacturing, targeted a prevalent issue in the field, which is that cement production currently accounts for approximately 8% of global CO₂ emissions.
The process draws on microbially induced calcium carbonate precipitation (MICP), a biological mechanism in which bacteria break down urea and trigger the formation of calcium carbonate crystals that bind sand grains together. While MICP has been studied for applications such as soil stabilization and simple brick production, the Stuttgart team sought to extend it to geometrically complex, additively manufactured forms.
The production process
The method is built around a modified consumer-grade 3D printer fitted with a peristaltic pump dispensing head. Rather than extruding material, the printer selectively deposits a suspension of Sporosarcina pasteurii bacteria along predetermined paths within a moistened sand mixture spanning particle sizes from 0.063 to 2mm.Â
A key departure from earlier bio-concrete printing approaches is the introduction of active print bed compaction: after each sand layer is added, a pneumatic piston vibrator compacts it before bacterial suspension is applied. This increases packing density and, in turn, compressive strength.
To prevent bacteria from migrating during subsequent cementation flooding cycles, the sand mixture was pre-wetted with a calcium chloride (CaClâ‚‚) fixation solution. After printing, the sealed bed underwent 20 immersion cycles in a urea and CaClâ‚‚ solution over several days to complete solidification.
Results and limitations
Compressive strength testing on two sets of small-scale printed cylinders — 25mm in diameter and 30mm tall — produced mean unconfined compressive strength (UCS) values of 11 MPa and 17 MPa, respectively. Those figures exceed the 2.5 MPa minimum required for aggregate concrete masonry units under German standards, though they fall short of the 20 MPa threshold for reinforced precast concrete components.
A more geometrically complex test structure, measuring 90mm in diameter and 80mm in height, was also produced and 3D scanned. Dimensional deviations ranged from −4 to +4mm, with compaction-induced deformation in both the horizontal plane and vertical axis identified as the primary source of inaccuracy.Â
The researchers noted that thin, porous structures with high surface area-to-volume ratios were best suited to the current process due to constraints on how far cementation solution could penetrate denser geometries.
The team identified façade panels as a near-term application given the process’s current load-bearing limitations, and flagged extraterrestrial construction — specifically lunar habitat fabrication — as a longer-term possibility, given prior research into MICP-based brick production from lunar regolith.
