Atterberg Limits of Sand-Bentonite Mixes and the Influence of Sand Composition

Sand-bentonite mixtures are assuming greater importance as geotechnical barrier materials in waste disposal schemes around the world, and like with any other geotechnical soil structure, a comprehensive understanding on the engineering behavior of various components used in the making of a geotechnical barrier becomes a necessity. A review of the literature indicated a host of variables influencing the engineering behavior of a barrier to various degrees, including and not limited to mineralogy of the soil, size, and shape of particles, their interactions among themselves, interactions with water, interactions with any other pore fluid that may exist in the soil, pH, temperature, cation exchange capacity, and quantity of cations in the soil pore fluid. Upon scrutiny, it has been observed that most of the studies conducted were primarily focusing on the role of bentonite in the sand-bentonite mixture, and studies highlighting the contributions of sand particle size, sand gradation, etc., were very few even though sand forms the major component in most of the sand-bentonite mixtures being employed around the world. This study sheds some light on the plasticity characteristics of sand-bentonite mixtures with varying bentonite proportions and sand compositions. In the current study, locally available sand has been washed thoroughly and sieved for different particle sizes (fine sand and medium sand) and two commercially available bentonites were procured. Fine sand-bentonite (FS-B), medium sand-bentonite (MS-B), and fine sand-medium sand-bentonite (FS-MS-B) mixtures were made with bentonite proportion varying from 10 to 50% by dry weight in the mix and were tested for Atterberg limits. Liquid limit results indicated that, for a given bentonite content, FS-B, MS-B, and FS-MS-B mixes exhibited different liquid limits and sand composition has a little influence on the liquid limits. Shrinkage limit results indicated that sand composition has a notable influence on the shrinkage characteristics of the sand-bentonite mixtures.