Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Aaron Gallant

Second Committee Member

Luiz Sambrano-Cruzatty

Third Committee Member

Shaleen Jain

Abstract

The production of lime and cement used as additives in the chemical stabilization of soil emits 9% of the total CO2 emissions. The utilization of lime in soil carbonation has a potential for soil improvement via the formation of calcium carbonate and also helps in the sequestration of an appreciable percentage of the process-related CO2 (67% of the total emissions) emitted during the production of this alkali, which would help to reduce the carbon footprint associated with the production of alkali such as calcium and magnesium bearing materials used in chemical stabilization. The research focuses on understanding the optimum soil condition for soil carbonation which would help in the improvement of the engineering properties of weak, frost-susceptible, and expansive subgrade soil due to the modification of the soil fabric caused by the formation of calcite. This study investigates some factors affecting the formation of calcite and degree of carbonation such as lime content, degree of saturation, and density. It also investigates how the degree of saturation and the flow rate at which CO2 is introduced influences the efficiency of CO2 consumption and the formation of calcite during soil carbonation. Silt samples were treated with lime and varying lime content by weight of silt was used for the stabilization of silt which includes 1% lime by weight of silt, 5% lime by weight of silt, and 10% by weight of silt. The lime-treated silt samples were prepared at various densities to capture the effect of density on the degree of carbonation. To capture the effect of increasing degree of saturation on the efficiency of CO2 consumption, lime-treated silt samples were tested at different degrees of saturation and tested at an increased flow rate to check the effect of flow rate on the efficiency of CO2 consumption. It was observed from the study that the degree of carbonation reduces as the lime content in the mix increases from 1% to 10%. It was also found from the study that the increasing degree of saturation enhances the formation of calcite and the degree of carbonation in samples treated with 5% and 10% lime by weight of silt but leads to the elongation of the mineral reaction time when the degree of saturation exceeds 50% due to gas mobility problem. The increasing density has a minor influence on the degree of carbonation, but elongates the duration for the completion of the mineral reaction. The elemental study also unveils that 60 % to 98% of the process-related CO2 emissions can be sequestrated via soil carbonation at optimum soil conditions with the degree of saturation and flowrate having a huge influence on the efficiency of CO2 consumption.

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