Comparative Assessment of Lime–Fly Ash Stabilization of Expansive Soil for Pavement Subgrades: A Secondary-Data Study

Abstract

Expansive soils create significant challenges in pavement construction because of their high plasticity, low bearing capacity and moisture-induced swelling and shrinkage. Sustainable stabilization using industrial by-products such as fly ash, particularly in combination with lime, provides a potential alternative to conventional soil replacement. This study presents a comparative secondary-data analysis of real experimental results reported in peer-reviewed literature on fly ash and lime–fly ash stabilization of expansive soils. Key parameters including California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), free swell and swelling pressure were examined. Published results for black cotton soil treated with 10% fly ash showed an increase in CBR from 2.189% to 2.33% and UCS from 0.1688 to 0.333 N/mm². Another peer-reviewed study on expansive soil from Nashik reported substantial improvement with lime–fly ash treatment, including a CBR value of up to 28% for a specific tested mixture compared with approximately 4% for untreated soil. Swelling pressure was also reported to decrease from approximately 147 to 70 kPa for a selected mixture. The findings indicate that lime–fly ash stabilization can significantly improve the engineering performance of problematic soils, although optimum proportions are soil-specific and require laboratory validation before field application. Keywords: Expansive soil, fly ash, lime, soil stabilization, CBR, UCS, pavement subgrade, sustainable construction.