Effect of Lime and GGBS on Geotechnical Properties of Fly Ash

Fly ash, a fine by product from coal combustion in thermal power plants, constitutes about 80% of the total ash produced, with the rest being bottom ash. In recent years, India has significantly improved its fly ash management. As per national trends for 2023-24, approximately 100% of newly generated fly ash and a large portion of legacy stock have been successfully utilized in construction, reclamation, and soil stabilization activities up from ~61% in 2014-16. This study explores the geotechnical improvement of class-F fly ash, collected from Godawari Power & Ispat Ltd., Raipur, by stabilizing it with lime and ground granulated blast furnace slag (GGBS). Fly ash was blended with lime (0%, 2%, 4%, 8%, 12%) and GGBS (0%, 5%, 10%, 15%, 20%), resulting in 25 combinations. Standard Proctor tests were performed to determine the optimum moisture content (OMC) and maximum dry density (MDD), followed by unconfined compressive strength (UCS) tests after curing for 0, 7, 14, and 28 days at 28 °C. Results indicated that untreated fly ash had high OMC, low MDD, and negligible strength. Lime addition improved compaction and strength with curing. GGBS, when used with lime, enhanced pozzolanic and latent hydraulic reactions, resulting in significantly higher UCS. The best performance was observed at 12% lime and 20% GGBS after 28 days of curing. This confirms that combining lime and GGBS effectively transforms fly ash into a sustainable geotechnical material suitable for sub-base, embankments, and pavement layers.