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 (θg; kg kg−1) of dry hydrophobized grains. To characterize the water repellency (WR) of dry and wet hydrophobized grains, initial solid-water contact angles (αi) were measured using the sessile drop method (SDM). Based on SDM results from the αi–HA content and αi–θg curves, useful WR indices were introduced as “Area_dry” and “Area_wet” (areas under the αi–HA content and αi–θg curves, respectively), “HA_zica” and “θg_zica” (maximum HA content and θg at which WR disappears, respectively), and “αi,peak” and “HA_αi,peak” (peak αi in the αi–HA content curve and corresponding HA content to αi,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 d50 and coefficient of uniformity (Cu) and regression equations for WR indices were obtained as functions of d50 and Cu (r2 > 0.7).