Feasibility Study of Fly Ash-Bentonite Mixture as an Alternate Liner Material

Abstract

Lining systems are primarily used to prevent a potential pollutant in a waste containment from migrating to surface water, ground water and thus polluting them. Even though compacted sand-bentonite mixture is most widely used as liner material in hazardous and nuclear waste containment, use of large quantities of sand is limited keeping in view of the economic and environmental concern. This forms the scope to explore the alternative liner material. Fly ash is generated in huge quantities from thermal power plants. Effective disposal of fly ash is always a concern. Using fly ash as an alternate material to sand in hydraulic barrier can address two problems: 1. Effective disposal of fly ash and, 2. Alternate liner material to sand.

Hydraulic conductivity and strength characteristics are essential for performance assessment of liner materials. This work was planned to investigate the potential of fly ash-bentonite mixture as effective alternate liner material. In this investigation, fly ash and bentonite are blended in different proportions by weight percentage i.e., 85:15, 90:10 and 95:5 respectively. For this, prepared samples were compacted at optimum moisture content and maximum dry density which are obtained from four different compaction energy such as reduced standard Proctor, standard Proctor, reduced modified Proctor and modified Proctor; and their corresponding coefficient of permeability were determined. It was found that, with increase in bentonite content, the hydraulic conductivity of fly ash and bentonite mixture has decreased. And with increase in compaction energy, the hydraulic conductivity for a fly ash-bentonite mix has decreased. To determine the effect of bentonite on the unconfined compressive strength of fly ash and bentonite mixtures, UCS tests were conducted on fly ash-bentonite samples with bentonite content 5%, 10% and 15% by weight. It was found that the unconfined compressive strength has increased with increase of bentonite content and compaction energy. Geotechnical laboratory tests such as plasticity, shrinkage, free swell index have been carried out and it was found that increase in bentonite content has increased the plasticity and swelling characteristics of the mix.