Accelerated carbonation of lime-treated clayey geomaterials: A synergistic strategy for sustainable earthworks and carbon capture applications

Lime is a popularly adopted binder for improving the mechanical properties and controlling the volume change behavior of problematic clayey soils. However, lime treatment offers certain limitations due to the durability issues arising from varying physico-chemical conditions exacerbated by climatic stresses or clay mineralogy. Lime-treated soils rich in mineral montmorillonite have experienced severe durability issues, with considerable strength decline, eventually falling below the minimum standards required for its application as a construction material. In this study, the innovative approach of "carbon mineralization" is adopted to augment the inadequate mechanical strength in the treated soil rich in mineral montmorillonite through carbonate cementation. Extensive mechanical and microstructure characterization techniques comprising unconfined compressive strength tests, scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and mercury intrusion porosimetry (MIP) techniques were performed to identify the mechanism behind strength deterioration in lime-clay composites cured for 24 months in ambient conditions (99 % relative humidity and temperatures of 25 degrees C and 40 degrees C). The results show that the unconfined compressive strength of treated soils reduced drastically beyond 9 months of curing. The newly derived parameter, effective precipitation factor from cementation levels, and macroporosity measurements at varying curing periods helped reveal the deterioration mechanism in the lime-clay composites. Accelerated carbonation of these composites resulted in a maximum of 74 % strength increment with a corresponding 15 % decrease in macroporosity. Carbonation enabled the nucleation of voluminous carbonates that fill and bridge the inter-aggregate pores of these composites via contact cementation, as evidenced by the micro-level images. In addition to rehabilitating deteriorated earthwork due to aging, the technique mitigates carbon emissions by capturing 37 % of CO2 released during lime production into stable carbonate minerals, promoting environmental sustainability.