Effect of Aging Time on Consistency Limits of Bentonites

Abstract

The water contents of clay soils at liquid limit, plastic limit, and shrinkage limit are the three consistency limits and are used as fundamental index parameters for assessing the geotechnical behavior. The extensive application of highly plastic clays, such as bentonites, in the waste containment facilities and improvements in understanding of the double-porosity structure of plastic clays prompted the present work to relook into the determination of these consistency limits. The liquid limit water contents of three Indian bentonites were estimated using percussion and cone penetration tests; undrained shear strength at different clay-water interaction periods. The liquid limit water content obtained by the percussion method increased with the aging time. The variation in the liquid limit water contents with time was obtained for three different bentonites and mixtures of different percentages of sand and kaolinite. The results were analyzed based on the double-porosity hypothesis. The influence of aging time on the plastic limit and shrinkage limit was also observed. Simple linear equations were proposed to predict the equilibrium water contents at different consistency limits based on the routine testing that are valid for different plastic clays. Further, the significance of equilibrium consistency limits in understanding the soil–water characteristic relationships of the studied bentonites was presented.