Performance of a cement-bentonite cut-off wall in an acidic sulphate environment

An experimental investigation on contaminant-cement bentonite (CB) mixture interactions is described and discussed. The mixture is a typical water-cement-bentonite mixture to be used for a cut-off wall to isolate a hazardous waste landfill. The landfill leachate is a very acidic inorganic solution that can be very aggressive for cement mixtures. Laboratory tests were performed on samples both prepared in the laboratory and taken from in situ trial panels. The samples were stored and tested under different chemical conditions to simulate those expected in the field and to accelerate any chemical reaction. The results showed that immersion tests can be too severe for assessing the efficiency of a cement-bentonite cut-off wall; hydraulic conductivity tests performed with leachate under a high hydraulic gradient and chemical conditions that are more aggressive than those expected in the field may accelerate the contaminant-mixture interaction thus allowing assessment of the long-term efficiency of a cement-bentonite barrier. From a practical point of view, the results of all the tests, but primarily the hydraulic conductivity tests, indicated good long-term hydraulic performance of the mixture.