Microbial Calcite Precipitation (MCP) is a technique that utilizes the concept of microbial involvements in calcium carbonate precipitation within the soil matrix structure. This leads to the cementation of the soil particles and consequently improving the strength and stiffness of the soil. In this study microbial carbonate precipitations were induced in tropical residual soil via urea hydrolysis and effects of curing time on the strength improvement after treatment was determined. An isolate of urease active strain named Klebsiella pneumoniae was used to precipitates calcite into the soil with the aim of improving the engineering properties of the soil. Bacteria concentrations of 1.5×105 cfu/ml and 2.9×106 cfu/ml and 0.5 M cementation reagents concentrations were used to evaluate the shear strength of the soil. Treatment durations of 24, 36, 48 and 60 hours were used in the study and biotreated specimens were cured for 1, 3, 7, 14 and 21 days. The results obtained indicated that higher bacteria concentrations of 2.9×106 cfu/ml provided better strength improvement than the lower concentrations of 1.5×105 cfu/ml. Likewise, the strength also increases proportionally with the increase in curing time up to 14 days. Hence, the optimum curing period of biotreated residual soil was found to be 14 days. The results obtained revealed that the higher the amount of calcite precipitated the more the strength improvement up to 48 hours treatment duration.
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