Soil Stabilization in Flexible Pavements by Using Industrial Waste Materials

This research explores the use of industrial by-products—ground granulated blast furnace slag (GGBS), fly ash, and lime—for improving the engineering properties of fine-grained soils in flexible pavement applications. The study was designed to evaluate how these stabilizers influence soil strength, density, and moisture resistance, which are critical for developing durable and sustainable pavement subgrades. Five soil samples were prepared, comprising one natural soil and four stabilized mixes. Each stabilized mix contained a constant 10% fly ash, while GGBS was varied at 5%, 10%, 15% and 20%. Additionally, 1.0% lime was incorporated to enhance chemical reactivity. Laboratory investigations included Modified Proctor Compaction, California Bearing Ratio (CBR), and Direct shear tests. Results indicated that untreated soil achieved a maximum dry density (MDD) of ~1.83 g/cc at an optimum moisture content (OMC) of ~16%. The fly ash-only mix reduced density due to its low specific gravity. However, the inclusion of GGBS significantly improved compaction characteristics, with higher GGBS contents producing denser soil matrices. The CBR values increased consistently with GGBS, peaking in the 15% GGBS + 10% fly ash + 1.0% lime mix. Plastic limit results showed reduced moisture sensitivity across all stabilized samples. The findings confirm that GGBS-fly ash-lime stabilization provides a cost-effective, sustainable method to enhance subgrade performance while promoting eco-friendly reuse of industrial waste materials.