Heating and hydration of a column of bentonite pellets for 10 years: postmortem characterisation

Abstract

With the aim of simulating in the laboratory the conditions of the barrier used in the HE-E in situ test, a 50-cm long column of MX-80 bentonite pellets was heated at its base to 140°C while Pearson water was supplied through its upper surface. The mineralogical, chemical, physico-chemical and hydro-mechanical characterisation of the treated bentonite is presented. No relevant mineralogical changes were observed, and although there were some changes in the exchangeable cation complex, it continued to contain predominantly sodium. Close to the heater precipitation of calcite and sulphate and dissolution of cristobalite were observed. The pore size distribution and the way in which particles aggregated were affected by hydration and heating (desiccation), but no worsening of the hydro-mechancial properties of the bentonite was observed in the hydrated areas. Overall, the processes described are similar to those observed in other large-scale tests simulating the conditions of a bentonite barrier where compacted blocks instead of pellets were used.