A feasibility study of fly ash and bentonite composite mix for assessing its suitability as landfill liner material

Most of the materials used in landfill liners are not based on the local soil conditions which increases the cost of landfill construction. It is essential to develop a composite mix based on local soil that fulfills the design parameters of the municipal solid waste (MSW) landfill at a reasonable cost as per USEPA 1989 guidelines. The current study investigates the use of local soil, fly ash, and bentonite mixtures to obtain an optimum composite mix with specific properties for landfill liners. The experimental investigation was conducted on different proportions of local soil-bentonite-fly ash mixes to evaluate the optimum mix proportion for liner materials. The curing period of different mixes is also considered. The geotechnical properties like liquid limit (LL), free swell index (FSI), and optimum moisture content (OMC) increased whereas the maximum dry density (MDD) and permeability decreased with an increase in bentonite content up to 20% with soil. It was also observed that fly ash mixed with soil in proportion (80:20) meets the optimum range of landfill liner properties. And, the composite mix comprised of soil–bentonite–fly ash in proportion (65:15:20) directs toward the optimum design parameters of landfill liner. These mixes were compacted at OMC and MDD satisfying plasticity (i.e., LL ≥ 20% and plasticity index, PI ≥ 7%) and permeability criteria (k ≤ 1 × 10⁻⁷ cm/s) as well as unconfined compressive strength criteria. Moreover, the scanning electron microscopy of local soil–bentonite–fly ash mixes was investigated for the optimum mixes for a comparative assessment of results.