Effect of wet-dry cycles on polymer treated bentonite in seawater : swelling ability, hydraulic conductivity and crack analysis

Abstract

Waste disposal facilities are often isolated by clay liners in order to prevent pollutant migration into the ground. Bentonite is used as barrier material thanks to the low conductivity to water. However, the hydraulic performance may be impaired by contact with aggressive liquids due to cation exchange and highly concentrated solutions. Moreover, the combination of cation exchange and wet-dry cycles can further affect the efficiency of the bentonite as barrier material. This study was carried out to evaluate the effect of wet-dry cycles with seawater on untreated sodium bentonite and HYPER clay. HYPER clay is a polymer modified bentonite with enhanced performance in presence of electrolyte solutions. Bentonite and bentonite treated with 2% and 8% polymer by dry weight of the clay were evaluated for their swelling ability, self-healing capacity, crack formation and hydraulic conductivity by means of one-dimensional swell test, μCT scanning and hydraulic conductivity tests. The specimens were subjected to 6 wet-dry cycles for the swell tests and to 4 cycles for the hydraulic conductivity tests. One-dimensional swell tests results showed that HYPER clay 8% had swollen the most and that its thickness after the 6th wet-dry cycle was comparable to the original thickness of untreated bentonite during its maximum swelling in deionised water. μCT analysis demonstrated the better self-healing capacity and the smaller volume of cracks of HYPER clay compared to untreated bentonite. Unlike the untreated clay, HYPER clays maintained low permeability to seawater throughout the wet-dry cycles.