Hypothetical models for the crystalline, interlayer swelling of mixed‐ion (Na+ and Ca2+) saturated montmorillonites in water were developed for two types of cationic distributions on the clay minerals; namely, for complete demixing and for complete random mixing of cations. In addition, the model for demixing was expanded to include both the alternate layering of Ca‐ and Na‐saturated platelets and the complete demixing of cations into separate Na‐ and Ca‐domains. The theoretical development is based on the accepted principles of limited interlayer swelling (10Å maximum) for Ca‐montmorillonite, and free‐swelling for Na‐montmorillonite as the water content of the system is increased beyond approximately 120%. Experimental measurements of interlayer swelling using a low‐angle X‐ray diffraction technique showed that the relative distribution of Na+ and Ca2+ ions on the clay exchange complex was a function of the exchangeable sodium percentage (ESP): (i) the two cations were randomly mixed for ESP values greater than approximately 50%; (ii) they were partially demixed for ESP values between approximately 50 and 15%; and (iii) for ESP values less than approximately 10 to 15% no cation demixing in interlayer regions was evident, but the results did suggest that the interlayer exchange complex was predominantly Ca‐saturated and the exchange complex on external surfaces was predominantly Na‐saturated. Although the experimental techniques could establish that demixing occurred within certain ranges of ESP values, it was not sensitive enough to differentiate between demixing by domains and demixing by alternate layers.

Water repellency and infiltration resistance of porous soils coated with a variety of thin, organic films were examined. Water repellency was determined by measuring the effective contact angle of water resting on the soil surface and infiltration resistance was determined by measuring the breakthrough pressure, i.e., the threshold pressure required to force water into the soil pore structure of these water‐repellent soils. The effective contact angle of water on these treated soils was found to be a function of (i) the structure of the hydrophobic portion of the organic admolecules, and (ii) the proportion of soil surface covered with the organic film, but was relatively independent of soil chemical and physical properties. Effective angles as high as 150 to 160° were recorded for several types of organic materials. These included several silicone water repellents, an amine‐ and a hydroxy‐substituted phenol, and an acetic acid salt of a long‐chain fatty amine. The breakthrough pressure was directly affected by the factors that controlled the contact angle, and was inversely related to the effective pore radii of the porous, water‐repellent soils.

No abstract

No abstract

Swelling properties of several montmorillonites (Li‐, Na‐, or Ca‐saturated) in water systems were studied using low‐angle X‐ray diffraction. All Li‐montmorillonites expanded linearly with water contents greater than 35%. Sodium‐hectorite also exhibited similar expansion. Sodium‐saturated Otay and Wyoming bentonites and nontronite, however, showed step‐wise expansion to about 110% water, and linear expansion at higher water contents. All calcium montmorillonites expanded in a step‐wise manner to a maximum spacing of about 20Å. The experimental techniques also were applied to the swelling properties of soil clays known to be high in montmorillonite. Results suggest that the poor crystallinity of soil montmorillonites is much more apparent at high water contents.