Concentration dependency of the prehydration effect for a geosynthetic clay liner

Abstract

Both prehydrated and non-prehydrated specimens of a geosynthetic clay liner (GCL) are permeated with chemical solutions containing 5, 10, 20, 50, and 100 mM calcium chloride (CaCl2) to determine the concentration dependency of the prehydration effect on the hydraulic conductivity (k) of the GCL. The tests for k are not terminated before chemical equilibrium between the influent and effluent solutions has been established, resulting in testing durations ranging from 14hrs to 502 days, depending on the CaCl2 concentration and whether or not the specimen was prehydrated. The results are presented in terms of the ratio of k for a non-prehydrated specimen (kNP) relative to k for a separate but identical prehydrated specimen (kP) permeated with the same chemical solution. Prehydration is shown to have little, if any, effect on the hydraulic conductivity of the GCL for specimens permeated with solutions containing from 5 to 50 mM CaCl2 (i.e., 0.5 ≤ kNP/kP ≤ 1.1), whereas the effect of prehydration for specimens of the GCL permeated with the 100 mM CaCl2 solution is more significant (i.e., kNP/kP ≈ 3.0). The results provide evidence that the previously reported prehydration effect is concentration dependent, and may be insignificant when the permeant liquid contains relatively low concentrations of inorganic solutes, i.e., provided permeation is continued until chemical equilibrium is achieved.