Geotechnical requirements for capturing CO₂ through highways land

Roadside verges in Britain support 238,000 hectares of vegetated land and approximately 10 hectares of vegetated central reserves. These areas have the potential to be engineered in such a way that they deliver a range of ecosystem services including flood regulation and biodiversity conservation in addition to their primary functions such as comfort of sidewalk users (mostly un-vegetated), protection of spray from passing vehicles, a space for benches, bus shelters, street lights and other public amenities, and visual improvement of the roads and designated green belts. Previous research has shown that in soils, calcium-rich materials such as recycled crushed concrete or natural crushed dolerite undergo carbonation. This effectively captures CO2 from the atmosphere and stores it in the form of CaCO₃ precipitated between soil particles. Engineering this process can potentially assist the UK in achieving its ambitious target to reduce CO₂ emissions by 80% of 1990 levels by 2050. Rates of carbonation measured at urban brownfield sites in the UK suggest that treating 12,000 hectares of land containing suitable amendments could remove 1 million tonne CO₂ annually. However, brownfield sites are often subjected to re-construction activities which would reduce the rate of CO₂ absorption from the atmosphere by sealing. To optimize the rate of carbonation, engineered soils need to be constructed at locations subjected to least post-construction activities and roadside verges and central reserves represent a key opportunity in this regard. This paper calculates limits to CaCO3 formation within the first 1 m of pore spaces of soils at roadside verges and central reserves in Britain considering a soil porosity of 20%.