Microbial-Induced Calcareous Precipitation Effect on Tensile Strength and Early Age Shrinkage of 3D Printed Concrete (2025-04)¶

3D printed concrete (3DPC) is more susceptible to occur early age shrinkage as well as form pores from entrapped air due to absence of formwork which affects its long-term durability and strength. This paper investigates the effects of microbial-induced calcareous precipitation (MICP) on the early age plastic shrinkage, pore structure and tensile strength of 3DPC. Through the observation of early age shrinkage and the analysis of the microstructure, it is revealed that the incorporation of bacteria can effectively inhibit the early age shrinkage of 3D printed concrete and reduce the porosity of the specimens, especially the interlayer pore fraction. Meanwhile, it is found that there are three ways to filling the pores of MICP: completely filling, surface filling and local bonding on pores, which can explain the reinforcement mechanism of MICP on 3DPC. The reinforcement mechanism is revealed by numerical simulation. The oriented flat pores in the interlayer makes more easier to form “Z” stress concentration and then expand into a strip-like stress concentration situation until the specimen failure. From the two-way ANOVA analysis, the interlayer pore fraction of 3DPC has a higher impact on its tensile strength than its interlayer slip.