Large-scale soil improvement tests using microbially induced carbonate precipitation

Bacterial biomineralization provides a greener solution to a diverse range of civil engineering applications, reducing the carbon footprint of construction. Most successful to-date is microbially induced carbonate precipitation (MICP). MICP is being developed for a diverse range of applications including plugging fractures, stabilising soils and repairing building surfaces. In MICP, bacteria are injected within the soil, followed by injection of a fluid containing urea and calcium chloride. The bacteria hydrolyse the urea, which generates bicarbonate ion, increases pH and precipitates calcite. Advantages of MICP include: better penetration due to the low viscosity of the fluids, the ability to maintain free drainage in treated materials and the thousand-year durability of calcite.

Despite the growing interest in MICP for geotechnical applications, MICP still remains largely confined to the laboratory with only a very small number of large-scale experiments having been completed and one commercial project. Use is constrained by (1) the ability to grow bacteria at a commercial scale and (2) the need to ensure homogeneous soil strengthening at a large-scale. In this research, conducted in collaboration with BAM Nuttall, we present the results of large-scale test for MICP treated sand. We treat a 1 m diameter cylinder of loose sand using multiple cycles of MICP. Unconfined compressive strength tests and triaxial tests of cores taken from the treated sand result in strengths of several MPa. Our results show that bacterial biomineralization could be a viable, low carbon alternative to cement and concrete for a range of earth infrastructure applications.