Chemical Compatibility of Fly Ash–Bentonite Based Hydraulic Barrier

To assess the durability of a liner material, it is important to study its chemical compatibility. In an attempt to define the hydraulic conductivity characteristics of clay liners, use of normal water is far from being representative of the in situ conditions. Therefore, the influence of chemical solutions (inorganic) of different concentrations on hydraulic conductivity of fly ash–bentonite mixtures used as hydraulic barriers was examined. The bentonite content in the fly ash–bentonite mixture was taken up to 15% @ 5% increment starting from 5%. The permeant solutions used include NaCl, NaOH and HCl, at different concentrations, i.e. 0, 0.01, 0.1, 0.5 and 1 M (where ‘M’ represents Molarity), which were chosen to best represent the acidic, basic and neutral nature of the landfill leachate as well as to better portray the effect of monovalent cations present in the in situ landfill leachate. Based on the test results, NaCl proved to have more effect on hydraulic conductivity than NaOH and HCl, considering an overall increase in hydraulic conductivity. Irrespective of the nature of the permeant solution (acidic/basic/neutral), the hydraulic conductivity of all the fly ash–bentonite mixtures increased with the increase in chemical concentrations. Thus, hydraulic conductivity of fly ash–bentonite liner material proved to be more sensitive to the permeant solution.