EFFECT OF METAKAOLIN ON THE STRENGTH CHARACTERISTICS OF BAGASSE ASH STABILIZED BLACK COTTON SOIL

Black cotton soil (BCS), a highly expansive soil, poses significant challenges to civil engineering infrastructure due to its poor strength and excessive volume change characteristics. While traditional stabilizers like lime and cement are effective, their use is economically and environmentally costly. This study investigated the potential of enhancing the stabilization of BCS using industrial and agricultural by-products to create a sustainable alternative. The efficacy of sugarcane bagasse ash (SCBA), a pozzolanic waste material, was improved by incorporating high-reactivity metakaolin (MK) to address the limitations of slow and inconsistent strength development. The natural BCS was characterized for its index and engineering properties. An optimum content of 4% lime was determined for initial stabilization. SCBA was added in varying proportions (5-20%), with 10% identified as the optimum dosage based on unconfined compressive strength (UCS) tests. Metakaolin was then introduced into the optimum lime-SCBA mix at dosages of 2-8% to form a ternary stabilized system. The strength characteristics were evaluated through UCS and California Bearing Ratio (CBR) tests on samples cured for 7, 14, and 28 days. Microstructural changes were analyzed using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS). The results demonstrated a remarkable synergistic effect. The ternary mix with 4% lime, 10% SCBA, and 6% metakaolin yielded a peak 28-day UCS of 2280 kPa, a 133% increase over the lime-SCBA mix and a 1126% improvement over the untreated soil. Soaked CBR values increased significantly, confirming the formation of a water-resistant matrix. Microstructural analysis revealed a dense fabric with abundant cementitious gels (C-S-H and C-A-H), explaining the macro-strength gain. The study conclusively proves that metakaolin effectively potentiates the pozzolanic reaction in SCBA-lime stabilized soil, delivering a high-performance, sustainable, and economically viable stabilizer for problematic black cotton soils.