Utilization of Rubber Wood Ash–Clay Mixes as Bottom Liner Material in Solid Waste Landfills: Engineering Properties and Microstructural Characteristics

This research addresses the challenge of finding suitable clay for landfill liners by exploring the utilization of rubber wood ash (RWA) as an improvement for local clay. Landfill compacted soil liners play a crucial role in preventing leachate leaks into groundwater, necessitating an exploration of alternative materials. Laboratory tests were conducted on clay samples mixed with RWA at 0% and 20% ratios, with curing times of 0-, 7-, and 28-days. Three key design parameters were investigated: hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. The study involved examining index and chemical properties, assessing engineering properties, conducting microstructural analysis, and creating plots illustrating the overall acceptable zone of the compacted local clay liner with rubber wood ash. Adding RWA to the clay decreased its hydraulic conductivity, which translated to reduced plasticity and greater unconfined compressive strength. Microstructural analysis revealed increased reactive particles and agglomerated structures, resulting in fewer voids, enhanced strength, and reduced permeability. The results of the analysis of the crystal structure and chemical composition of the material supported the formation of beneficial compounds like calcium silicate hydrate, calcium aluminum silicate hydrate, and calcium aluminum oxide hydrate, contributing to increased strength and durability. The results indicate that a 20% rubber wood ash mixture at a 28-day curing time can be effectively utilized as liner materials if more acceptable materials are not readily available. The mixture meets the criteria for an effective landfill liner, offering enhanced durability attributed to improved soil structure and cementation development.