Sorption and hydraulic performance of cement-bentonite cutoffs in saline sulphatic solutions

The paper discusses the results of an experimental research on the short and long term hydraulic performance and sorption of cement-bentonite mixtures in saline sulphate solutions. Batch tests at different curing times and permeation tests were performed on three cement-bentonite mixtures with solutions of K2SO4. The results show that permeation can adversely affect the hydraulic performance of cement-bentonite mixtures depending on the sulphate concentration and mixture composition and that the choice of a very low permeable mixture is essential to limit adverse effects of interaction with SO42- on the hydraulic performance. Sorption of K+ was found to be significant, well described by a linear isotherm in a wide range of concentration and nearly constant with curing. Sorption of SO42 was found to decreases with mixture porosity. Since sorption of SO42- means negative interaction, batch tests were found to be useful for a rapid estimation of possible negative effect of SO42- on the hydraulic behaviour in the long term, when selecting a mixture in the design phase. All the results point out the importance of selecting a mixture to be used for cut-off walls with a low hydraulic conductivity already at brief curing and of carefully considering interaction with solute pollutants and sorption capacity