The problem of expansive soils is common worldwide in arid and semi-arid regions where soils are exposed to frequent extreme wet and dry seasons. Expansive soils, having a high affinity for water, easily absorb moisture, undergo significant expansion during wet seasons, and shrink during dry seasons. This cyclic shrink-swell ground movement causes considerable damage to lightweight structures. Lime stabilisation has become a globally popular approach for stabilising flexible pavement subgrades susceptible to expansive soil damage. However, with rising global concerns for sustainability and significant lime shortages, exploring the reuse of industrial byproducts and waste materials as substitutes for lime subgrade stabilisation has emerged as a significant research objective. This study evaluates the suitability of Recovered Carbon Black (rCB) for expansive subgrade treatment through a series of laboratory tests. rCB is a solid powdered residue from the pyrolysis process of end-of-life tyres (ELT). rCB has enabled various reuse options and provides a sustainable solution for managing the increasing tyre waste generated. To achieve the objective, rCB was mixed with soil in proportions of 5%, 10%, 15%, and 20%, and tested. Then, the results were compared to soil mixed with lime in proportions of 5%, 10%, and 15%. The 1-D Oedometer-based swell test results exhibit a significant reduction in swelling with increasing rCB dosage, with near-zero swelling observed at 20%. However, the performance is slightly lower than that of lime. Unconfined Compressive Strength (UCS) revealed that an rCB mixture achieves comparatively higher strength than pure expansive soil and performs better than lime at the exact dosage. The findings of this study demonstrate that rCB is a potential and sustainable alternative to traditional lime treatment while addressing the increasing tyre waste problem. However, as suggested by this study, further research is required to fully evaluate the feasibility and effectiveness of successful field implementations.