Treatment Low CO 2 Low Temp Low CO 2 High Temp High CO 2 Low Temp High CO 2 High Temp Enriched Control δ 15 N (‰)

Unconsolidated artificial ground is an ever‐increasing feature on the Earth's surface but it poses various challenges such as pollutant release and ground instability. The process of lithification could be an important factor in changing the properties of artificial ground and ameliorating these challenges. In this study, a lithified deposit of a furnace slag associated with a former iron and steel works in Scotland was analysed to determine the mechanisms and drivers of lithification. Scanning electron microscope analysis showed that Ca leached from around the edges of clasts of slag through reaction of the chemically unstable slag with water from an adjacent water body. Dissolution of Ca (and OH−) from the slag caused the water in contact with the slag to become hyperalkaline, facilitating ingassing and hydroxylation of CO2 from the atmosphere (fingerprinted through carbon isotope analysis). Reaction of the dissolved Ca and CO2 led to precipitation of calcite. Scanning electron microscope analysis showed the calcite is distributed between slag clasts, forming rims around clasts and cementing clasts together into a solid rock‐like mass. Understanding the mechanisms and drivers of lithification in artificial ground will be important, given its widespread nature particularly in urban areas where artificial ground is the substrate of most development.

No abstract