Pozzolanic fly ash as a hydraulic barrier in land fills

The liner plays an important role in controlling migration of contaminants present in the leachate in waste containment systems such as land fills and impoundments, Although questions have been raised about the performance of clay liners, they are increasingly used singly or as double liners in disp osal sires. Though the clay liners possess many advantages such as low perm eability and large attenuative capacity, they also possess high shrinkage p otential and hence can crack under unsaturated conditions causing instabili ty and increase in leakage rates. Further, the permeability of the clay lin ear can increase due to clay-pollutant interaction. This study examines the potential of pozzolanic fly ash as a hydraulic barrier in land fill. The b ehaviour of three different types of fly ashes, showing a range of physical properties and chemical composition from three different sources are repor ted in the study, Geotechnical properties, needed to evaluate the use of fl y ashes as barriers, such as shrinkage, compaction, permeability, consolida tion and strength characteristics are reported. The results show that Ay as hes possess low shrinkage and hence do not crack, Compacted fly ashes under go very little volume changes. They also show that pozzolanic fly ashes dev elop good strength properties with time, Pozzolanic fly ashes containing su fficient lime develop strength even without addition of lime, Non-pozzolani c fly ashes do not develop strength even on addition of lime. Fly ashes gen erally consist of silt size particles and consequently possess high permeab ility. However, pozzolanic fly ashes with lime exhibit low permeability on curing because of the formation of gelatinous compounds which block the por es. Thus, pozzolanic fly ashes appear to be promising for construction of l iners to contain alkaline leachate. (C) 2001 Elsevier Science B,V, All righ ts reserved.