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.