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 (theta(g); kg kg(-1)) of dry hydrophobized grains. To characterize the water repellency (WR) of dry and wet hydrophobized grains, initial solidwater contact angles (alpha(i)) were measured using the sessile drop method (SDM). Based on SDM results from the aiHA content and alpha(i)-theta(g) curves, useful WR indices were introduced as "Area_(dry)'' and "Area_(wet)'' (areas under the alpha(i)-HA content and alpha(i)-theta(g) curves, respectively), "HA_(zica)'' and "theta(g)_(zica)'' (maximum HA content and theta(g) at which WR disappears, respectively), and "alpha(i,peak)'' and "HA_alpha(i,peak)'' (peak alpha(i) in the alpha(i)-HA content curve and corresponding HA content to alpha(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).