Microalgae-assisted biomineralization of Lysinibacillus sp. WH for sustainable low-carbon biocement Production

Microbially induced calcium carbonate (CaCO 3 ) precipitation (MICP) is a promising biochemical process for improving cement strength and durability of cementitious materials through biomineralization of CaCO 3 . This study investigates the use of bacteria Lysinibacillus sp. WH bacteria and microalgae Chlorella vulgaris ( C. vulgaris ), both in monoculture and co-culture, for biocement production and micro-crack remediation. Synergistic effects of these microbes on the mechanical properties and microstructural development were examined for the first time. Incorporating Lysinibacillus sp. WH with C. vulgaris resulted in maximum cement strength of ∼58 MPa, accounting for ∼14 % increment compared to the control, and promoted microcrack healing starting from 9 days of treatment. Conversely, incorporation of C. vulgaris solely inhibited the main hydration phase of tricalcium silicate (C 3 S), as confirmed by TGA-DTG and XRD-Rietveld refinement analysis, which reduced cement quality. However, the co-culture system with Lysinibacillus sp. WH minimized this detrimental effect and improved overall cement quality. SEM-EDS analysis confirmed that the morphology of the precipitated bio-CaCO 3 was influenced by the microbial species present. The formation of this crystal effectively seals the crack, particularly with the presence of Lysinibacillus sp. WH. Overall, this work provides an effective method to develop durable and eco-friendly cement paste by leveraging a renewable biological source to achieve enhanced performance and sustainability. • Coculture of microalgae and calcifying bacteria enhanced strength up to 58 MPa (14 % increment). • Microalgae alone inhibited C 3 S formation, resulting in less C-S-H than co-cultured biocement. • Microcrack was sealed within 9 days of observation, especially in the bacterial-added biocement.