Sustainable Stabilization of Clayey Soils: The Influence of Recycled Rubber and Eucalyptus Ash

Clayey soils often exhibit low strength and high plasticity, challenging subgrade stability in road infrastructure and prompting the search for sustainable stabilization solutions. This study evaluated the efficacy of recycled crumb rubber (CR) and eucalyptus ash (EA) as additives to improve the geotechnical properties of a problematic clayey soil. A laboratory program involving Atterberg limits, compaction, unconfined compressive strength (UCS), and California Bearing Ratio (CBR) tests was conducted on samples with varying percentages of CR, EA, and their combinations. Key results demonstrated that CR addition, particularly at 15%, significantly enhanced soil strength, increasing CBR by 41.3% and UCS by 38.9% relative to untreated soil. Optimized CR-EA combinations (e.g., 10% CR + 10% EA) also yielded substantial improvements, with CBR increasing by 30.9% and UCS by 26.3%. However, EA addition generally increased the optimum moisture content, which may cause a potential practical inconvenience, and excessive overall additive levels could negatively impact performance. The findings highlight CR and EA's potential as effective soil stabilizers, emphasizing the critical role of optimizing additive proportions for enhancing clayey soils in road subgrades.