| Summary: | Landfill sealing layers protect groundwater and soil against contamination from waste leachate. Fly ash, which is a coal combustion by-product, might be used as a substitute material for natural soils to build sealing layers. To improve its properties, different additives can be used. In this study, bentonite in the amounts of 5%, 10% and 15% of the dry mass of fly ash was used as an addition. Compacted fly ash and fly ash-bentonite mixtures were tested in order to verify how bentonite and the amount of addition affect the properties of the materials. Therefore, hydraulic conductivity, as the most important parameter, which determines the suitability of a material for construction landfill sealing layers, were tested. Results indicate that bentonite changes the properties of fly ash and allows the achievement of smaller hydraulic conductivity values. To provide a comparison to the natural soil, sandy silty clay that meets the criteria for natural soils for sealing layers was tested and the differences are presented. Fly ash with 15% of bentonite addition reached a value of hydraulic conductivity for the material suitable to build compacted landfill sealing layers.
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