Permeability of Sand-bentonite and Sand-fly Ash Mixtures

Laboratory hydraulic conductivity (HC) tests have been conducted on mixtures of fine sand with bentonite and fly ash with four fluids with different pH and metal concentrations with a view to assess their suitability for liner constructions for waste containment facilities. HC of sand-bentonite mixtures which was low, due to effective reduction void ratio because of swelling of negatively charged bentonite particles, further reduces with increase in the density and with increase in the pH of the fluid by increase in the cation exchange capacity and fabric of the clay assuming relatively more dispersed structure. The hydraulic conductivity of mixtures of fly ash sand were higher and were in the range of 1 x 10(-5) cm/s which however decreases slightly with increase in the density. HC of sand fly ash mixtures with increase in pH of the solution due to increase in the reactivity of fly ash in alkaline medium produces more pozzolanic compounds leading to reduction in the void ratio. It is also found, however, that hydraulic conductivity of fly ash mixtures is not suitable for liner application. The precipitation of metal ions at higher pH in sand fly ash mixtures may reduce the HC depending on the concentration of metal ions. However, bentonite needs to be incorporated to lower the HC range required for liner application. Thus both sand bentonite and sand fly ash-bentonite mixtures can be used for liner application for waste containment facilities.