Evaluation of Bentonite-Fly Ash Mix for Its Application in Landfill Liners

Abstract Compacted landfill liners are required to minimize the migration of harmful contaminants to the surrounding geoenvironment and groundwater. This is mainly achieved by restricting hydraulic conductivity of the compacted liners within a permissible limit of 10−7 cm/s. For geomaterials used in liners, it is important to determine the appropriate range of compaction parameters (water content and dry unit weight) that would ensure hydraulic conductivity and strength characteristics within safe limits. There are not many studies in the literature for specifying such a range for bentonite-fly ash mixes. The addition of cohesionless fly ash would improve the strength and reduce the shrinkage behavior of bentonite but at the same time would increase the hydraulic conductivity. Therefore, it is of utmost importance to determine the ranges of water content and dry unit weight for different bentonite-fly ash mixes that would satisfy the desired ranges of hydraulic conductivity and strength. The objective is to identify the bentonite-fly ash mix that enables maximum use of fly ash, which is advantageous from an environmental perspective. The performance evaluation of different compacted mixes has been done using hydraulic conductivity and unconfined compressive strength as the two reference parameters. The study clearly demonstrates the utility of a bentonite-fly ash mix as a compacted landfill liner. On the basis of the results, it can be noted that up to 70 % by weight of fly ash can be mixed with bentonite for satisfying the requirements of compacted landfill liners.