Improving shear strength penetration resistance and microstructural behaviour of expansive subgrade soil using scoria

This study investigates the suitability of Scoria as a modifier for enhancing the engineering properties of expansive soil. Scoria was incorporated at varying percentages (5%, 10%, 15%, 20%, 25%, and 30%), and the resulting soil-Scoria Blend were cured for 7, 14, and 28 days. During the early phases, experiments were performed to assess the Geotechnical and index behaviours of untreated soil, including compaction, Atterberg limits, California Bearing Ratio (CBR) and unconfined compressive strength (UCS). The influence of Scoria inclusion on expansive soil was analyzed through modified Proctor compaction, Atterberg limits, split tensile strength (STS), CBR, UCS tests. The results indicate that partial replacement of expansive soil with Scoria significantly reduces the liquid limit and plasticity index while increasing UCS, STS, and CBR values. However, beyond an optimal Scoria content, a decline in performance is observed. Strength improvements in Scoria-stabilised soil are further enhanced with curing time. Microstructural analyses using SEM (scanning electron microscope) and XRD (X-ray diffraction) revealed changes in clay soil morphology and development of cementitious phases in Scoria-treated clay soil, confirming stabilisation mechanisms. At an optimal scoria content of 25% and 28 days of curing, the UCS reached 493.65 kPa, surpassing the target compressive strength of 345 kPa. Furthermore, Soaked CBR values at the optimal Scoria content satisfied the subgrade material requirement for low-traffic rural roads as per IRC: SP-72:2015 standards, contributing to reduced pavement thickness and construction costs. A predictive statistical model for CBR values was developed using IBM SPSS. Finally, comprehensive flexible pavement design along with a comparative cost analysis, were developed to assess the economic viability of scoria in soil stabilisation. This study provides a sustainable and cost-effective approach to mitigating expansive soil challenges in road construction, bridging the gap between laboratory findings and practical application.