مهندسی عمران شریف (Nov 2021)
Determination of the role of retention time under different temperature conditions In the improvement of sandy soils by bio-cementation
Abstract
The mechanical properties of soils often do not fulfill human needs and expectations due to world population growth. Preventing damage to buildings and infrastructures requires basic measures or ongoing maintenance. For this issue, construction of any structure needs to be on a good soil bed with favorable strength parameters. So far, some improvement methods have been studied and applied. In geotechnical engineering, finding a low-cost and environmentally friendly method is the most improvement challenging problem. Microbial geo-technology is a new branch of geotechnical engineering that deals with the microbiological applications. Microbial sedimentation method (MICP) is a new and emerging method that uses microorganisms in the soil and chemical processes and, thus, the production of calcite sediment increases shear strength and hardness as well as reduces permeability. In this research, we focus on microbial catalysis of urea hydrolysis, which has led to the deposition of calcium carbonate in sand using Bacillus Pasteurii. However, recent researches have not addressed the effects of some parameters such as temperature and material concentration and various bacterial concentrations simultaneously. In this study, under different temperature conditions, different material concentrations, and different bacterial concentrations (different ODs), the reaction completion time is obtained. Significant experimental results show that OD changes have little effect on the result. Also, it is demonstrated that by increasing temperature, the amount of calcium carbonate deposits has also increased. Moreover, the higher the concentration of the material raises, the greater the amount of calcium carbonate deposits, making its formation faster. Also, samples with higher concentrations need a longer time to complete their reaction. High-temperature samples have a higher reaction rate from the earliest hours, but low-temperature samples require more time to precipitate calcium carbonate. Also, with the help of electron scanning, the effect of material concentration on the way of connection bonding and bonding between particles has been investigated.
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