Application of Coal Ash-Bentonite Mixtures as Landfill Liner

Abstract

Landfills are the most popular municipal solid waste disposal system. The landfill liner is designed to isolate the waste from the soil beneath to minimize the passage of leachate into the groundwater. Usually compacted liner materials consist of soil rich in clay minerals for their low hydraulic conductivity. This study is an attempt to assess the use of a waste material, coal ash(fly ash and pond ash) as a potential liner material by mixing it with bentonite in various percentages ranging from 2-20%. Both pond ash and fly ash are non-plastic and possess very low shrinkage. With the addition of bentonite in the mixture, the plasticity is expected to increase and the coal ash is expected to reduce the swelling and shrinkage, preventing formation of any cracks. Due to its swelling properties,bentonite in the mixture is expected to act as a self-sealing, low permeability hydraulic barrier.To determine the viability of coal ash- bentonite mixture as a liner material, the mixture was compacted at its optimum moisture content and maximum dry density and laboratory tests were conducted to obtain the various geotechnical parameters such as plasticity, shrinkage, permeability, free swell index, c,  and unconfined compressive strength.It was found that a compacted mixture of bentonite with fly ash and pond ash with the percent of bentonite in the mixture between 12-20% had the required hydraulic conductivity and strength properties to be used as a liner material.