Geotechnical Behaviour of Fly Ash-Bentonite Mixture as a Liner Material

The landfill liners are used to barrier the flow of leachate and hence prevent the migration of contaminants. Clay liners are increasingly used due to their low permeability and high attenuative capacity. The shrinkage of these liners during unsaturated state may cause cracking, and that lead to the leakage of leachate. Hence, it is needed to develop an alternative material having low shrinkage potential and low permeability. Treated fly ash is a good alternative and can be used as landfill liners. Fly ash is a by-product generated due to coal combustion and contains silt-sized hollow spherical particles. In the current study, an attempt has been made to reduce the permeability of fly ash by addition of bentonite and evaluate the suitability of this mixture as a liner material. Different percentages of bentonite (0, 2, 4, 6, 8, 10 and 12%) were mixed in the fly ash, and the geotechnical properties of this mixture were examined through various experiments such as liquid limit, unconfined compression and consolidation tests. The results of liquid limit tests indicated that water holding capacity of fly ash is increasing with the increase in bentonite content. The unconfined compressive strength and stiffness of the specimens were observed to be increased with the addition of bentonite till 8%, after that it started reducing. Swell pressure and permeability of these mixtures were determined through consolidation tests along with compressibility characteristics. Permeability was observed to reduce below 1*10⁻⁹ m/s with the increase in bentonite content in the fly ash indicating its suitability as a liner material.