Expansion of Montimorillonite Due to Adsorption of Water Vapor

Expansions of pure sodium and calcium montmorillonites due to absorption of water vapor were studied and the results were correlated with X-ray diffraction and free swelling studies. Specimens of various porosities were used. Results indicate that the uptake of water is a multimolecular physical adsorption phenomenon which justifies application of BET theory. Porosity of specimens did not appreciably affect their expansions due to adsorption of water vapor. Sodium montmorillonite expanded appreciably more than calcium montmorillonite. At near saturation vapor pressure, calcium montmorillonite has attained practically its maximum swelling, while sodium montmorillonite will expand further if exposed to liquid water. Free energies of wetting, calculated from adsorption isotherm data, do not directly reflect the extent of swelling but do reflect the uplift pressures developed. Sodium montmorillonite presents the more serious problem with respect to settlement, and calcium montmorillonite presents the more serious problem with respect to uplift pressures