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).