Calcium and sodium bentonite for hydraulic containment applications

The hydraulic conductivity of calcium and sodium bentonites was investigated for sand-bentonite mixtures, a thin bentonite layer simulating a geosynthetic clay liner (GCL), and bentonite-cement mixtures simulating backfill for a vertical cutoff wall. The permeant liquids were tap water and distilled water containing 0.25 M calcium chloride. In general, the hydraulic performance of calcium bentonite was not significantly better than the performance of sodium bentonite for either the clay-amended sand or the GCL application, and was substantially worse than the performance of sodium bentonite in the bentonite-cement mixture. A drained angle of internal friction of 21 degrees was measured for calcium bentonite, compared to 10 degrees for sodium bentonite. Except for a larger drained shear strength, no advantage of calcium bentonite over sodium bentonite could be identified from the results of this study.