A Study on the Water Retention and Contaminant Retention Behavior of Fly Ash, Bentonite and Its Mixes

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A need to explore cost-effective and environmentally sustainable alternate materials that can be used in multi-layered hydraulic and contam inant barriers has motivated this research. Natural clays or expansive soils like bentonite mixed with cohesionless soil like sand is used for the construction of low permeable waste containment liners and covers. Sand is a costly construction material that would obviously need replacement in waste management projects such as liners and covers. Fly ash can be a viable alternative to sand in these projects. Unsaturated characteristics and contaminant interaction are important for the behavioral modeling and performance assessment of geomaterials used in liners and covers. This research was planned to investigate the unsaturated behavior and contaminant interaction of fly ash-bentonite mix. The unsaturated behavior was established in terms of water retention characteristics curve (WRCC) for four Indian fly ashes, bentonites and fly ash-bentonite mix. The study brings out the measurable range of suction in fly ash, which is otherwise missing in the literature. The importance of volumetric shrinkage curve and mandatory approach for WRCC parameterization of bentonite has been demonstrated in this study. The influence of fly ash type and content on the WRCC of fly ash-bentonite mix was investigated. The sensitivity of variation in WRCC parameters on unsaturated seepage modeling was studied for specific cases of measured WRCC. The contaminant retention capacity of fly ash, bentonite and selected fly ash-bentonite mix was determined by considering lead as a model contaminant. The study highlights the usefulness of fly ash in combination with bentonite for waste containment liners and covers. This would help in the mass utility of waste fly ash for a meaningful environmental application such as waste containment and also relieve the burden of storage space.
Supervisor: Sreedeep Sekharan