Biochar amendment for improved and more sustainable peat stabilisation

Carbon-intensive binders such as cement are traditionally employed to stabilise peat. Few studies have investigated alternative materials such as biochar to improve peat stability while simultaneously sequestering carbon dioxide (CO2). This study explored biochar produced through pyrolysis of clean wood and leaves to stabilize peat from Tiller-Flotten, Norway. Unconfined compressive strength (UCS), water content and pH measurements on biochar, Portland composite cement (CEM II) and peat compositions and a sustainability assessment were conducted. It was found that biochar amendment increased strength and stiffness of peat and cement-stabilised peat. Biochar showed the potential to reduce the cement amount when stabilising peat while retaining geotechnical properties. Peat stabilised with 200 kg/m3 of biochar and 100 kg/m3 of cement exhibited comparable strength (63.3±4.2 kPa, n = 3) as samples with 200 kg/m3 of cement (63.2±1.3 kPa, n = 3), but with a negative carbon footprint. Adding biochar quantities greater than 27% of the cement quantities resulted in a climate-neutral stabilisation. At a carbon price of approximately 85 €/tonne, the biochar costs equalled the cement costs. The cement-only samples outperformed the ones with additional biochar in terms of shear strength/€, while future carbon prices increased the competitiveness of biochar amendments.