Microbial-induced carbonate precipitation (MICP) modified biochar for low-carbon cementitious materials

To foster sustainable construction, biochar has gained prominence as a filler or aggregate in concrete to mitigate carbon emissions. However, relatively weak strength of porous biochar is often a limitation. To improve the performance of biochar-containing matrices, this study proposed microbial-induced carbonate precipitation (MICP) for pore densification and surface modification of biochar. The MICP-modified biochar was employed as a filler to assess its mechanical performance, hydration processes, and microstructural characteristics. Our findings indicate that MICP modification of biochar yielded a more homogeneous and effective filler by enhancing the hydration rates, elevating the mechanical properties, and increasing the matrix compatibility. These improvements could be attributed to the increased compactness of MICP-modified biochar and its role in regulating the formation of an ettringite shell structure. As a result, the ettringite content was doubled surrounding the MICP-modified biochar. This study sheds light on the potential of MICP-modified biochar to actively participate in the regulation of hydration products for producing low-carbon construction materials. • MICP formed carbonates that could fill biochar pores and reduce its surface charge density. • Achieved a substitution rate of up to 10 % biochar, balancing hydration products and doubling AFt content. • MICP-modified biochar accelerated the early-stage cement hydration, especially for C 3 A. • MICP modification inhibited AFt to AFm conversion, stabilizing AFt near the biochar. • MICP modification enhanced biochar compatibility by embedded carbonates and exterior hydration products.