Microstructure of Bio-Cemented Coarse Sand-Paper

Paper

Pdf Summary

The study investigates microbial-induced calcium carbonate precipitation (MICP) as a means of strengthening coarse sand columns, a potential alternative to conventional cement-based ground improvement. Coarse sand was treated with <em>Sporosarcina pasteurii</em> bacteria and urea–calcium chloride solutions using three treatment levels: 4, 8, and 16 biochemical treatments. Unconfined compressive strength (UCS) tests assessed strength, while X-ray computed tomography (XRCT) was used to examine the material’s internal structure.

Increasing the number of treatments increased calcium carbonate content and UCS. Strength rose from approximately 200 kPa under light treatment to 1,000 kPa under moderate treatment and 5,500 kPa under heavy treatment. XRCT images showed calcium carbonate deposited in the pore spaces, forming layers that surrounded and connected sand particles. With heavier treatment, these layers thickened, pores decreased, and the distribution of cementation became less uniform.

XRCT estimates of calcium carbonate content closely agreed with measurements from laboratory acid washing. The imaging-derived void ratio, dry density, and porosity also corresponded well with laboratory data, supporting XRCT as a reliable, non-destructive method for assessing cementation and microstructure.

The findings indicate that MICP can substantially improve the strength of coarse sand, with strength associated with the amount and distribution of precipitated calcium carbonate. Further work is needed to assess its practical application in sand or stone columns in soft soils.

Keywords

microbial-induced calcium carbonate precipitation

MICP

coarse sand columns

Sporosarcina pasteurii

urea-calcium chloride

unconfined compressive strength

X-ray computed tomography

calcium carbonate precipitation

soil improvement

cementation