Stabilisation for peat improvement: Extent of carbonation and environmental implications

Abstract

The construction industry is a large contributor to global greenhouse gas emissions. In recent years, the industry has begun to consider sustainability alongside technical merit, cost and programme when analysing construction options. Construction on peaty soils is challenging and often requires extensive ground improvement which can in itself be carbon intensive, while also generating further emissions where peat is removed. Stabilisation (soil mixing) is a ground improvement technique in which a soft soil such as peat is mixed with a cementitious binder in situ. While life cycle assessments have been carried out on soil mixing scenarios from cradle-to-site, the effect of the process on carbon stocks post-construction has not been considered to date, hindering cradle-to-grave assessments. In this research, stabilised peat has been shown to be a small sink of CO2. An extensive laboratory study has investigated the key factors impacting carbonation rates (and thus CO2 intake rates) in stabilised peats. The study revealed that time and a greater surcharge magnitude contributed to a greater carbonation depth, while increased cement content and the presence of a high water table decreased carbonation depth. Carbonation k-rate factors exceed those typical of concrete. This quantitative evidence of the impact of peat stabilisation on embodied carbon levels post construction will enable geotechnical engineers to carry out more representative environmental appraisals of soil mixing schemes. In broader terms, data of this type are important in steering engineers and policy makers towards cleaner production and sustainable practices.