1 Effect Of Clay-Water Interactions On Swelling In Montmorillonite Clay Kalpana Katti * and Dinesh Katti Department of Civil Engineering and Construction North Dakota State University, Fargo, ND 58105 e-mail: Kalpana.Katti@Ndsu.Nodak.Edu ABSTRACT This paper describes effect of clay-water interactions on swelling of montmorillonite using a new controlled uniaxial swelling (CUS) cell developed by the authors. Using the CUS cell, a simultaneous measurement of swelling and swelling pressure is done. Undisturbed clay samples at well defined swelling (0%-75%) were removed from the CUS cell and analyzed using scanning electron microscopy and fourier transform infrared (FTIR) spectroscopy and also orientation dependant micro-attenuated total reflectance (ATR) spectroscopic investigations. Significant changes in the silicate (Si-O) stretching region (1150 to 950 cm -1 ) have been observed with changes in swelling and orientation. Our results indicate that the reduced particle size with increased swelling is related to increased misorientation of the clay platelets. At 0% swelling the clay platelets are most oriented and have largest particle size. The rearrangement of clay platelets as seen in the orientation dependant spectra are a direct result of the breakdown of the clay particles with increased hydration resulting from increased swelling. Keywords: Swelling Clay, Montmorillonite, Vibrational Spectroscopy, Electron Microscopy INTRODUCTION The understanding, modeling and prediction of interaction of clays with water and other environmental fluids is an important issue in the field of geotechnical engineering, geoenvironmental engineering as well as industrial applications such as muds for oil well drilling and water treatment. The swelling response of montmorillonite clay and corresponding development of swelling pressure when swelling is restrained is a result of fairly complex clay-water interactions between particles and within the particles itself. The understanding and quantitative modeling of these fundamental interactions are extremely important for modeling these systems. The scanning electron microscope (SEM) is a useful tool for the study of microstructural changes in clays with high spatial resolution. Vibrational spectroscopy yield useful information about hydration characteristics, interlayer cations and moisture content in clays. The excitation of a purely vibrational transition by infrared light obeys the selection rules for electric dipole transitions as described by classical electromagnetic theory. Interaction of infrared light with a molecule yields a spectrum that is characteristic of the symmetry and molecular structure of the molecule. Infrared vibrational spectroscopy is a useful tool for studying the bonding of water molecules on clay surfaces. In addition, vibrational spectroscopy is useful to study changes in the Si-O vibrations resulting from changes in crystal symmetry due to swelling.