Evaluation on Stabilization Role of Lime and Cement in Expansive Black Clay–Oyster Shell Ash Composite

This research presents an experimental study to analyse the role of lime and cement in amelioration protocols of expansive black clay (EBC) in the presence of oyster shell ash (OSA) as admixtures. An optimal blend of 10%OSA was admixed with cement and lime independently in stepped threshold of 2, 4, 6 and 8%, respectively. The Atterberg limit, compaction properties, California bearing ratio (CBR), unconfined compressive strength (UCS) and shear strength performance of both EBC-OSA-cement and EBC-OSA-lime, respectively, were evaluated. With the increase in cement and lime content in EBC-OSA mixtures, the Atterberg’s limit decreased; meanwhile, the strength properties comprising of CBR, UCS and shear strength performance of soil mixtures were enhanced. In view of the soil engineering performance, the CBR value at 10%OSA content in 8% lime-EBC mixtures was far beyond the satisfactory range for usage as sub-base material of light-traffic roads. The 7-day UCS at 10%OSA/8%lime and 10%OSA/8% cement stabilized expansive soil fell within the satisfactory benchmark as detailed by Ingles and Metcalf for use as sub-base materials. Higher durability and lower swell values of OSA-lime-EBC composites endorse lime/OSA admixture as more effective than cement/OSA admixture in stabilizing EBC soil. The microstructural results from the Fourier transform infrared approach confirmed the variation bands of the significant functional groups of the EBC material in their natural and stabilized forms. The XRD and SEM/EDS confirmed the presence of calcium silicate and calcium aluminate hydrate responsible for strength improvement.