Accelerated surface carbonation of non-plastic silt mixed with hydrated lime

Abstract

Chemical stabilization via hydration reactions with cement or lime is a universally applied method to improve the mechanical properties of shallow soils. Accelerated soil carbonation is a nascent approach intended to bypass this reaction. Carbon dioxide gas is deliberately introduced at high concentrations to react with the alkali additives and precipitate a carbonate binder that permanently sequesters carbon dioxide in the process. A large soil box experiment was performed to examine the efficacy of an accelerated surface carbonation approach, which has the potential to be applied over large areas. High concentrations of carbon dioxide gas were introduced at grade beneath a seal to facilitate vertical penetration into lime-mixed silt. The real-time progression of accelerated soil carbonation was captured with a gas flowmeter and a distributed array of embedded thermocouples and bender elements for the first time. Post-carbonation measurements of binder content and California Bearing Ratio (CBR) verified the degree of carbonation and associated mechanical improvement. Synthesis of real-time monitoring data and post-carbonation measurements indicate carbonation progressed top-down 150 to 200 mm below grade within 5 h, resulting in a substantial increase in strength and stiffness. Potential challenges and benefits associated with adoption of accelerated surface carbonation are discussed.