Characterization of water repellency for hydrophobized grains with different geometries and sizes

Capillary barrier cover systems (CBCSs) are useful and low-cost earthen cover systems for preventing water infiltration and controlling seepage at solid waste landfills. A possible technique to enhance the impermeable properties of CBCSs is to make water repellent grains by mixing the earthen cover material with a hydrophobic agent (HA). In this study, six different grains with different geometries and sizes were used to prepare dry hydrophobized grains by mixing with different contents of oleic acid as a HA. Wet hydrophobized grains were prepared by adjusting the water content ( θ g ; kg kg −1 ) of dry hydrophobized grains. To characterize the water repellency (WR) of dry and wet hydrophobized grains, initial solid-water contact angles ( α i ) were measured using the sessile drop method (SDM). Based on SDM results from the α i –HA content and α i – θ g curves, useful WR indices were introduced as “Area_ dry ” and “Area_ wet ” (areas under the α i –HA content and α i – θ g curves, respectively), “HA_ zica ” and “θ g_zica ” (maximum HA content and θ g at which WR disappears, respectively), and “α i,peak ” and “HA_ αi,peak ” (peak α i in the α i –HA content curve and corresponding HA content to α i,peak , respectively). Pearson correlation analysis was performed to identify correlations between proposed WR indices and basic grain properties. Results showed that WR indices correlated well to d 50 and coefficient of uniformity ( C u ) and regression equations for WR indices were obtained as functions of d 50 and C u ( r 2 > 0.7).