Free porosity investigation of compacted Bentonite using XRD

Many countries intend to use compacted bentonite as abarrier in their deep geological repositories for nuclearwaste. In order to describe and predict hydraulicconductivity or radionuclide transport through thebentonite barrier, fundamental understanding of themicrostructure of compacted bentonite is needed. Thisstudy examined the interlayer swelling and overallmicrostructure of Wyoming Bentonite MX-80 and thecorresponding homo-ionic Na+ and Ca2+ forms, usingXRD with samples saturated under confined swellingconditions and free swelling conditions. For thesamples saturated under confined conditions, theinterparticle, or so-called free porosity was estimatedby comparing the experimental interlayer distancesobtained from one-dimensional XRD profile fittingagainst the maximum interlayer distances possible forthe corresponding water content. The results showedthat interlayer porosity dominated total porosity,irrespective of water content, and that free porositywas lower than previously reported in the literature. Atcompactions relevant for the saturated bentonitebarrier (1.4-1.8 g/cm3), the free porosity was estimatedto ≤ 3%.QS 2011 QS 2012032