Microbial-induced carbonate reinforcement for 3D-printed concrete: testing in printable and mechanical strength

This study introduces a microbial-induced calcium precipitation technique into cement-based 3D printing by incorporating Bacillus pasteurii into 3D printing (3DP) mortar. The printability, physical–mechanical properties, and microstructure are analyzed to compare the differences between control concrete and bacterial concrete. Experimental results demonstrated that mixing bacteria in 3DP mortars can enhance printability and increase the uniaxial compressive strength (UCS) and Brazilian splitting tensile strength of printed specimens. Particularly, this method significantly improved the interlayer strength of 3DP concrete. With a bacterial concentration of 1 × 10^7 cells/ml, the UCS improved by 35.8% and 57.3% in the YZ and XY directions, respectively, compared to the control concrete UCS. The tensile strength in the YZ direction improved by 23.65% compared to control concrete at the same bacterial concentration. Moreover, the tensile strength in the XY direction continued to improve with increasing bacterial concentration, while it decreased in the YZ direction, indicating that incorporating bacteria is an effective method for enhancing interlayer tensile strength. Additionally, nitrogen adsorption results revealed that mixing bacteria reduced pore volume and surface area of printed specimens, leading to denser microstructure by filling granular calcium carbonate precipitates at internal pores of 3D-printed concrete, as observed by SEM and XRD. These findings offer a new approach for modifying cement-based 3D-printing mortars and provide valuable insights for enhancing the mechanical performance of architectural 3DP concrete, thereby promoting the advancement of cement-based 3DP technology.