Evaluation of Expansive Soil Amended with Fly Ash and Liquid Alkaline Activator

This paper presents the use of fly ash (FA) and liquid alkaline activator (LAA) to amend the engineering behavior of expansive soil (ES) based on a series of unconfined compressive strength (UCS), expansion ratio (ER), California bearing ratio (CBR), and free swell index (FSI) tests conducted on various sets of natural and amended ES with different proportions of FA with LAA at different curing periods of 7, 14, and 28 days. Microstructure analysis was carried out by field emission scanning electron microscopy. This study also evaluates the performance of pavement subgrade with amended ES. The LAA is a mixture of 1.0 molar sodium metasilicate and 10.0 molars of sodium hydroxide solution mixed in the proportion of 70:30, respectively. The results indicate that ER and FSI decrease when FA content increases with optimum alkaline activator content (OLC) in the combination, whereas UCS and CBR values initially increase with an increase in FA content up to 25% and after which they decrease. It is also observed that, with an increase in curing periods, the ER and FSI decrease, whereas UCS and CBR values increase. Also, the flexible pavement’s total thickness and initial cost first decrease up to optimum FA content (25%) with OLC after that increases.