The mechanical behaviour of clays is strongly influenced by pore fluid composition. Moreover, exposure to fluids different from their pore fluid may produce a transient stage during which the clays undergo noticeable volume changes. The aim of this paper is to investigate these phenomena and their causes. To this end, a large number of water-saturated specimens of Ponza bentonite (mainly composed of Namontmorillonite) were exposed, alternately, to distilled water and to saturated NaCI, KCl or CaC12 solutions in the course of laboratory direct shear tests and oedometer tests. Exposure to any of the three electrolytes produced consolidation of the specimens, a large decrease in deformability and an equally large increase in residual shear strength. At equilibrium, the mechanical behaviour became very similar to that exhibited by specimens that had been directly prepared with the appropriate salt solution as pore fluid. For both types of specimen (i.e. those prepared with the electrolyte and those exposed to it) NaCI effects were reversible when the specimens were re-exposed to water, while KCI and CaCl2 effects persisted even after some months of continuous testing. The experimental results were consistent with the hypothesis that changes in the thickness of the diffuse double layer were produced by ions diffusing into or out of the clay. X-ray diffraction analysis showed that, in the cases of KCl and CaCl2, the inward diffusion had produced ion exchange. Hence, the decrease of the diffuse double layer was permanent, under the given experimental conditions, and it rendered subsequent osmotic phenomena practically negligible.

Exposure of bentonite to salt solutions: osmotic and mechanical effects

DI MAIO, Caterina
1996-01-01

Abstract

The mechanical behaviour of clays is strongly influenced by pore fluid composition. Moreover, exposure to fluids different from their pore fluid may produce a transient stage during which the clays undergo noticeable volume changes. The aim of this paper is to investigate these phenomena and their causes. To this end, a large number of water-saturated specimens of Ponza bentonite (mainly composed of Namontmorillonite) were exposed, alternately, to distilled water and to saturated NaCI, KCl or CaC12 solutions in the course of laboratory direct shear tests and oedometer tests. Exposure to any of the three electrolytes produced consolidation of the specimens, a large decrease in deformability and an equally large increase in residual shear strength. At equilibrium, the mechanical behaviour became very similar to that exhibited by specimens that had been directly prepared with the appropriate salt solution as pore fluid. For both types of specimen (i.e. those prepared with the electrolyte and those exposed to it) NaCI effects were reversible when the specimens were re-exposed to water, while KCI and CaCl2 effects persisted even after some months of continuous testing. The experimental results were consistent with the hypothesis that changes in the thickness of the diffuse double layer were produced by ions diffusing into or out of the clay. X-ray diffraction analysis showed that, in the cases of KCl and CaCl2, the inward diffusion had produced ion exchange. Hence, the decrease of the diffuse double layer was permanent, under the given experimental conditions, and it rendered subsequent osmotic phenomena practically negligible.
1996
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/3141
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 364
  • ???jsp.display-item.citation.isi??? 304
social impact