Cbr-based performance assessment of feedstock-specific biochars for sustainable clay soil stabilization under soaked and freeze-thaw conditions

This study presents a comparative assessment of three regionally abundant waste-derived biochars: mustard stalk (agricultural residue), Prosopis juliflora (invasive weed), and bamboo (industrial byproduct), for sustainable clay soil stabilization. Through rigorous physicochemical, mineralogical, and microstructural characterization (XRD, FTIR, EDX, FESEM) and geotechnical testing (per IS codes), soils amended with 5% to 15% biochars demonstrated significantly modified properties. All biochars reduced specific gravity, plasticity index, and maximum dry unit weight, while increasing optimum moisture content, pH, and electrical conductivity. Prosopis biochar achieved the highest unsoaked California Bearing Ratio through cationic bridging via amine groups and micro-roughness-enhanced friction. Bamboo biochar dominated moisture resistance with 9.2% soaked CBR through amorphous carbon-regulated hydroscopicity and further demonstrated superior durability under freeze-thaw cycling, retaining the highest CBR value, while enriching carbon at 15% amendment. Quantitative linear models further established feedstock-specific performance trends, confirming Prosopis biochar’s better efficiency in strength development and bamboo biochar’s superior hydraulic and freeze-thaw regulation. These improvements stem from biochar’s porous architecture, charged functional groups, and carbon-mineral balance, enabling lighter, stronger infrastructure. We establish Prosopis biochar as best for pavements and embankments, and bamboo biochar for flood- and frost-prone slopes, valorizing waste streams while supporting UN Sustainable Development Goals 9, 11, and 13. This work provides a novel framework integrating material characterization and performance prediction for feedstock-specific biochar selection in geotechnical applications.