Hydraulic and mechanical behaviour of cement-bentonite mixtures containing HYPER clay: impact of sulfate attack

Cemented clays are regularly employed as cut-off walls to isolate polluted soils or in ground improvement technologies. The objective of this research was to evaluate the performance of a polymer-treated bentonite (HYPER clay) and its impact on hydraulic and mechanical properties of cement-bentonite (CB) mixtures in contact with sulfates. In this research, bender elements were installed in a hydraulic conductivity cell, to simultaneously monitor the small- strain shear modulus (G0) and the hydraulic conductivity (k) of cement-bentonite mixtures. Initially, during permeation with deionized water, an increase of G0 with time was observed, due to cement hydration (hardening). Conversely, after prolonged permeation with sulfates, a decrease of G0 and a gradual increase of k are expected due to degradation of the cemented material. Preliminary results show that k of mixtures containing untreated bentonite increases due to contact with sulfates; conversely, k of mixtures containing HYPER clay remains unaffected. The stiffness modulus G0 was not significantly affected after a sulfate contact period of about 100 days in none of the cement-bentonite mixtures. More extensive monitoring is required for evaluating long-term mechanical degradation. These observations suggest that the use of polymer-treated bentonites could improve the resistance of cement-bentonite mixtures to sulfate attack maintaining a low hydraulic conductivity.