Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Advisor

Aaron Gallant

Second Committee Member

Dana N. Humphrey

Third Committee Member

Eric N. Landis

Additional Committee Members

Carlos A. Vega-Posada

Abstract

Challenging subsurface conditions often dictate the need to augment subgrade soils’ in-situ properties via chemical stabilization, a simple method of construction that is widespread globally. Chemical stabilization typically involves the field mixing of calcium-based additives like cement, lime, or fly ash. However, there is increasing awareness of the large carbon footprint associated with typical stabilizing agents. The cement and lime industries currently contribute approximately 10% of all anthropogenic carbon dioxide emissions worldwide each year and are expected to increase. Thus, the development of approaches to chemically stabilize subgrade soils that reduce net carbon emissions would be desirable and align with larger societal initiatives to reduce the rate of global warming. Accelerated carbonation is a nascent approach to chemically stabilize materials. Soil carbonation describes the process whereby carbon dioxide is introduced into soil mixed with chemical additives and sequestered to generate a carbonate binder. However, aside from small elemental and bench-scale experiments, little has been done to evaluate potential methods that would enable carbonation in the field. Lime is a material that’s readily available in the United States but relatively unexplored with respect to carbonating soil. Hydrated lime in particular is a calcium-based additive with relatively high solubility in water and high efficiency with respect to the absorption of dissolved CO2 to precipitate carbonate minerals. Thus, it is a resource that may be relied on to carbonate soil. In this study, an elemental testing phase was carried out to evaluate the use of hydrated lime as a chemical stabilizing agent, as well as the state parameters influencing the rate of binder formation and degree of mechanical improvement. This initial study informed an experiment evaluating surface carbonation, a method with the potential to be scaled and applied across large areas. The experiments were carried out with highly frost-susceptible silt in a large soil box. The durability of the carbonated material was tested in a large environmental chamber, where the effects of soaking and frost action were examined. Carbonation with hydrated lime was shown to be a rapid method to stabilize soil, with equivalent mechanical properties as soils stabilized with conventional cement-based additives like cement, and durable under freeze-thaw conditions. It was demonstrated that surface carbonation has the potential to carbonate soil thicknesses typically associated with the stabilization of foundation materials for surface transportation infrastructure. Moreover, carbonation could substantially reduce net carbon dioxide emissions associated with lime production. Recent policy shifts in the United States, most notably the passage of The Inflation Reduction Act, are providing significant incentives for use of construction materials and products that result in substantially lower levels of embodied greenhouse gas emissions. Thus, soil carbonation technology is ripe for development.

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