Due to stringent environmental regulations, embodied carbon estimates are being used increasingly to assess the environmental impact of major building and infrastructure projects, including their geotechnical components. The focus of this paper is on the ground improvement technique of soil-mixing. While it is established that improper management of excavated peat can cause it to lose the majority of its carbon to the atmosphere as CO2, the carbon response of peat mixed in situ is unknown and has prompted this study. Under accelerating conditions in the laboratory, emissions were recorded from columns of parent peat (high and low water tables) and cement-stabilised peat. While the parent peat was found to be a source of CO2 influenced by water levels and temperature, stabilised peat appears to act as a net carbon sink. This is an important finding for carbon calculations relevant to soil-mixing applications. The first author acknowledges the financial support (College Fellowship) provided by the College of Engineering and Informatics at NUI Galway.