Observations of unsaturated soils by Environmental Scanning Electron Microscopy in dynamic mode

Abstract

The Environmental Scanning Electron Microscope (ESEM) allows observation of hydrated samples in their original state. Imaging can be done at a constant vapour pressure and temperature or in dynamic conditions to observe a sample response to changes of water vapour pressure and/or temperature. This paper focuses on the use of the dynamic 'mode' for unsaturated soils studies. Examples are presented on the hydraulic and structural response of kaolin and silica microspheres to cycles of relative humidity at constant temperature. Qualitative observations were made throughout the cycles and focused on the particle level phenomena (e.g., meniscus shape) and mesoscale phenomena (e.g., particle re-arrangements and emptying and filling of pores). Some quantification was also possible: the contact angle between the air-water and water-solid interfaces was measured. Other applications of the ESEM technique to unsaturated soils and limitations are discussed. © 2008 Taylor & Francis Group, London.