Permeation of Sand-Processed Clay Mixtures with Calcium Chloride Solutions

The hypothesis that the substitution of attapulgite clay for bentonite in an otherwise sand-bentonite (S-B) mixture will improve the resistance to change in hydraulic conductivity of the mixture upon permeation with calcium chloride (CaCl2) solutions relative to permeation with a processed tap water is tested. For mixtures with the same clay soil content, complete substitution of attapulgite clay for bentonite significantly decreases the change in hydraulic conductivity relative to that observed for the S-B mixtures upon permeation with a 0.5 M CaCl2 solution. In addition, the resistance to change in hydraulic conductivity of the sand-attapulgite clay-bentonite (S-AC-B) mixtures containing 20 clay soil is improved by increasing the percentage of attapulgite clay in the clay soil admixture from 50 to 100, and by decreasing the concentration of the CaCl2 solution from 0.5 M to 0. The first exposure effect also decreases with increasing amount of attapulgite clay in S-AC-B mixtures containing 20 clay soil. However, the resistance to change in hydraulic conductivity resulting from substituting only half of the bentonite in the S-B mixtures with an equal amount of attapulgite clay is not improved substantially due to the dominating influence of the bentonite portion of the sand-clay mixture.