Accelerated carbonation of non-plastic soils mixed with hydrated lime: index properties influencing binder formation rate and mechanical improvement

Abstract

Chemical stabilization—the mixing of additives like cement, lime, or fly-ash with soil to improve its mechanical properties—conventionally relies on hydration reactions to generate a binder. Accelerated soil carbonation is a nascent alternative method, whereby carbon dioxide is intentionally introduced in soil mixed with alkali additives to generate a carbonate binder and sequester carbon dioxide. Non-plastic sand and silt specimens mixed with hydrated lime were carbonated for varying amounts of time at different water contents and densities to evaluate the index properties influencing the rate of carbonation and degree of mechanical improvement. It was demonstrated that volumetric air and water contents primarily govern the rate of binder formation and that mechanical properties are influenced by the carbonate binder content and density. Under optimum conditions, soil specimens could be fully carbonated within 3 to 24 hours and unconfined compressive strengths as great as 3 to 4 MPa were achieved. The degree of strength improvement is comparable to cement-stabilized materials with similar dependence on soil type, density, and binder content. If techniques are developed that enable carbonation at scale, the sequestration of carbon dioxide would offset emissions associated with production of chemical additives used for chemical stabilization.