Mass transport through defected bentonite plugs

Compacted bentonite-based materials are important barriers in many waste containment strategies. To function as effective barriers, however, these materials must maintain their low water permeability and molecular diffusivity for long periods of time under a variety of environmental conditions. Here we examine the permeability and diffusivity of compacted bentonite plugs that were either slotted, to mimic fractures, parallel to the direction of mass flow or heated at 150 and 250°C for several weeks at various moisture contents before testing. The dry density of the plugs ranged from about 0.9 to 1.3 Mg/m3. The results show that the saturated hydraulic conductivity and diffusivity (for I− and Cs+) of the treated or ‘defected’ bentonite plugs are essentially the same as those of untreated plugs at similar densities. This provides confidence that compacted bentonitic materials can funntion effectively as barriers for long periods of time under a range of environmental conditions.