Bio-cementation of coral sand using microbial-induced calcite precipitation with sodium alginate

Coral sand with microbial-induced calcite precipitation (MICP) is a promising material for practical engineering. This study attempts to improve the precipitation efficiency by using a modified bio-cement method based on MICP and sodium alginate (SA). It was found that adding an appropriate amount of SA in the bacterial solution could greatly improve the ability of immobilising bacteria, thus achieving an effective precipitation of calcium carbonate on the aggregate surfaces. As the SA content increased, the weight increment and unconfined compressive strength of each sample after MICP cementation initially increased and then decreased. Three main failure modes were observed, i.e., the particle unbroken failure, stepped failure, and steep drop failure. Owing to the macro pores of coral sand, the specific loss of calcium carbonate crystals produced by MICP had a significant effect on the cementation performance, while prolonging the single soaking time could favourably reduce the crystal loss. The calcium carbonate crystals occupied part of the pores between sand aggregates, but did not change the compression strength of a single aggregate significantly.