Particle Size Effects on the Volumetric Shrinkage of Bentonite-Sand Mixtures

Tests were conducted on bentonite-silica fume mixtures (BSFMs) to determine how particle size affects the volumetric shrinkage of bentonite-sand mixtures (BSMs) used as hydraulic barriers in waste disposal facilities. Free desiccation tests, liquid limit tests, plastic limit tests, and direct shear tests were conducted to compare the soil shrinkage characteristic curves, shrinkage limits, plasticity, and shear strength of BSFMs to that of the commonly used bentonite-standard sand mixtures (BSSMs) at 30% sand percentage. BSFMs exhibited higher air entry values (up to 55.9% higher), shrinkage limits (up to 14.6% higher), final void ratio (up to 43.6% higher), peak shear strength (up to 115% higher), and a smaller percentage of volumetric shrinkage (10.8%) than BSSMs due to the particle contact and constrained particle movement. The liquid and plastic limits of BSFMs, in contrast, were also higher (up to 99.2% and 27.1%) than that of BSSMs. Particle size plays a critical role in controlling the shrinkage limits of BSMs compared to clay fractions.