Effect of wet-and-dry ageing in seawater on the swelling properties and hydraulic conductivity of two amended bentonites

Abstract Amended bentonites have been proposed with the primary purpose of improving their chemical compatibility relative to conventional bentonite. As these materials are relatively new, their durability and long-term performance need to be evaluated. Wet-dry conditions may occur in many applications where bentonite liners are in use. In this study, two amended materials, the MultiSwellable bentonite and a DPH (Dense Prehydrated) GCL were subjected to simulated wet-dry ageing. Distilled water (DW) and natural seawater (NSW) were used as permeant liquids. After five wet-dry cycles, the hydraulic conductivity of both materials increased by two to three orders of magnitude. Unhealed desiccation cracks were identified as responsible for the increase in permeability. Conversely, wet-dry ageing in DW did not impact significantly the permeability of the DPH GCL. For both materials, post-test swell index and XRD diffraction indicated a loss of the chemical amendment, likely solubilised and/or eluted during the wet phases. The results point out that further investigation is necessary to fully address the permanence of swelling and permeability performances of these amended clays after long-term field service. Adequate measures are recommended to prevent or limit desiccation damage for use in applications where aggressive inorganic permeant liquids (e.g., NSW) are present.