Assessing the Suitability of Compacted Bentonite-Pond Ash Mixes as Landfill Liner

Abstract

The use of compacted bentonite-sand mixes as landfill liner has been accepted worldwide. However, the non-availability of sand at all landfill sites triggers a search for an alternate material. Pond ash is an industrial waste and has the distinct advantage of a geotechnical material as it resembles the natural earth material. Moreover, it has the similar mineralogical composition to conventional earth materials and needs special attention for its effective utilization rather than disposing of it by consuming large land area leading to the loss of agricultural production. With the addition of bentonite to the pond ash, the plasticity, and strength is expected to increase whereas the permeability is expected to decrease. Further, as pond ash is non-plastic and possesses very low shrinkage, it is expected to reduce the swelling and shrinkage, preventing the formation of any cracks in the compacted liner material. The present study examines the suitability of compacted bentonite-pond ash mixes as landfill liner material. The proportion of bentonite in the pond ash-bentonite mix is varied from 5 to 30% by weight at 5% intervals. The plasticity characteristics, compaction properties, strength and permeability properties of pond ash-bentonite mixes are evaluated. It is observed that with the addition of bentonite the plasticity index, maximum dry density, differential free swell index, cohesion, and compressive strength increases gradual and on the other hand the optimum moisture content, hydraulic conductivity, and frictional angle decreases. It is also found that an addition of 5% bentonite has no effect on the geotechnical properties of pond ash. The designed mixture with 20% bentonite attained its plasticity index, strength and permeability values as per the requirements of a suitable landfill liner material as per the EPA regulatory act.