Migration parameters and interaction of saline solutions through cement-bentonite cutoffs

Abstract

The paper discusses the results of an experimental research on hydraulic conductivity, sorption, diffusion and long-term performance of cement-bentonite mixtures in saline sulphate solutions as a function of their composition and curing time. The results show that permeation with solutions of K 2 SO 4 can adversely affects the hydraulic performance of cement-bentonite mixtures depending on sulphate concentration and mixture composition. Choosing a very low permeable mixture at brief curing time is essential to limit adverse effects of interaction with SO 42- on the hydraulic performance. Linear isotherms were found to model sorption of K + , with distribution coefficients resulted not to be significantly influenced with curing, allowing testing, usefully and safely, at brief curing. Values of the distribution coefficient in the range of those of cement paste were obtained. On the contrary, diffusion coefficients of K + and of SO 42- higher than those documented in the literature for cement pastes were found. In designing cut-off walls the results point out the importance of selecting a mixture with very low hydraulic conductivity values at brief curing and of considering its specific diffusion coefficients, as well as interaction and sorption capacity.