CB mixtures for cut-off walls used in encapsulation of polluted soils

Working Group
Evelina Fratalocchi, Francesco Mazzieri. Marta di Sante, Jonathan Domizi, Erio Pasqualini
This study has been ongoing for more than a decade and aims at characterizing the hydraulic and mechanical properties of cement bentonite (CB) mixtures employed as hydraulic and pollutant barriers in cut-off walls for the encapsulation of polluted sites. The study analyzes the influence of intrinsic, construction-related and environmental factors on the hydraulic behaviour of the cut-off walls with time, with the purpose of optimizing the performance of the material. In particular, a correlation has been established which allows estimating the long-term hydraulic conductivity as a function of the type and dosage of the components. Furthermore the study investigates the chemical compatibility  of CB mixtures to sulphatic and acidic solutions, which represent the two main classes of potentially aggressive liquids for the considered materials. Special apparatus and testing protocols are utilized  to carry out long-term permeation tests with liquid different than water; sorption of solutes to the CB solids can be separately investigated by means of batch testing. Permeation tests are interpreted by analytical and numerical models in order to assess the migration parameters of the pollutant species. The study has obtained important results on the behaviour of CB mixtures in aggressive conditions; a procedure has been developed that allows to estimate the durability of the material, based on laboratory tests which can be completed in times compatible with the design phase.
La ricerca ha fornito fino ad oggi importanti risultati sul comportamento delle miscele acqua-cemento-bentonite in ambiente aggressivo; è stata inoltre messa a punto una procedura per la stima della durabilità di tali materiali, ottenuta mediante sperimentazione di laboratorio di durata compatibile con la fase di progetto.