Investigation of Bacterial Cells and Clays as Rheology Modifiers in 3D Concrete Printing

The developments in digital concrete production placed the concrete industry in a paradox for achieving optimization among improved performance, cost, and sustainability. The three-dimensional (3D) printing material design contradicts the sustainability goal of reducing raw material consumption. This study investigates the role of bacterial cells as rheology-modifying agents (RMA) to enhance the performance of cement-based mortars used in 3D concrete printing. Two bacterial species, Bacillus megaterium and Sporosarcina pasteurii, were incorporated with clays (nanomontmorillonite and sepiolite) in fly ash-amended mix designs. Rheological analysis demonstrated that the inclusion of bacterial cells reduced dynamic yield stress by up to 30%. Incorporation of cells with clays improved the development of static yield stress and increased thixotropy by a factor of ten compared to that of the control samples. The synergistic effect of the bacterial cells and clays further enhanced buildability, with nanomontmorillonite improving shape retention by 6%–9% relative to control mixes, whereas sepiolite contributed to better interlayer bonding. Modular prototypes with optimized mixes achieved layer heights that retained 92%–93% of the target dimensions, indicating improved geometric stability and surface finish. The results of this study will provide a better understanding of the influence of B. megaterium and S. pasteurii cells on the rheology of the fly-ash-amended clay containing printable cement-based mortars. This research provides insight into the potential of biobased RMAs to enhance extrusion, shape retention, and sustainability in 3D concrete printing, paving the way for scalable applications within the construction industry.