Geotechnical Engineering Properties of Soils Solidified by Microbially Induced CaCO₃ Precipitation (MICP)

Table 2

Impact of pH on some factors.

Factors	pH	Conclusion	Reference
Growth of bacteria	pH = 7, 8, 9	The bacterial concentration is highest at pH of 9	[59]
Bacterial metabolic activity	pH = 9.31, 11.15, 11.95, 12.24, 12.48	The pH is kept above 12; the urease-producing bacteria are inactivated	[52]
Urease activity	pH = 6, 7, 8, 9, 10	The enzyme activity increased at fast rate, peaking at pH of 8.0 and then decreasing slowly at higher pHs	[14]
	pH = 7, 8, 9	The highest urease activity occurred at pH = 9	[59]
CaCO3 morphology	pH = 6.0, 6.5, 7.0, 8.0	High pH promoted CaCO3 precipitation, and precipitates were mainly calcite crystals, gradually changing from prism to pyramid-like or irregular polyhedral shapes	[54]
CaCO3 precipitation	pH = 3.5, 7, 9.5	The maximum CaCO3 deposition at pH = 9.5	[55]
	pH = 9.31, 11.15, 11.95, 12.24, 12.48	The initial pH decreased to below 11.15, and the Ca^2+ concentration begins to decrease, hence CaCO3 precipitation	[52]
	pH = 5, 6, 8, 9	The increase in pH increased the CaCO3 precipitation	[56]
Strength	pH = 5, 6, 8, 9	The compressive strength of silty clay soil samples increased steadily as pH increased from 5 to 9	[56]