Analysis of the structural changes of a pellet/powder bentonite mixture upon wetting by X-ray computed microtomography

Agustín Molinero Guerra (1, 2) , Patrick Aimedieu (1) , Michel Bornert (1) , Yu-Jun Cui (1) , Anh Minh A.M. Tang (1) , Zhao Sun (3) , Nadia Mokni (4) , Pierre Delage (1) , Frédéric Bernier (5)

1 navier umr 8205 - Laboratoire Navier
2 IRSN/PRP-DGE/SRTG/LETIS - Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols
3 Tongji University
4 IRSN/PSE-ENV/SEDRE/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols
5 AFCN - Agence fédérale de contrôle nucléaire

Pellet/powder bentonite mixture is one of the candidate materials for sealing plugs in deep geological high-level radioactive waste disposal. This note presents an investigation on the structure changes of this mixture occurring during the saturation process by means of X-ray computed micro-tomography. The test was performed in an infiltration column (60 mm in inner diameter and 120 mm in height). Water was supplied to the two ends of the column and the changes of the sample morphology were observed during a period of 100 days of hydration. Digital Volume Correlation (DVC) technique was used to determine the vertical displacement field of the bentonite powder. A pressure transducer was used to measure the axial swelling pressure during the hydration. The results show that the initial distribution of powder in the inter-pellet pores was not homogeneous; the powder filled almost completely the pores in the zones close to the two ends while air-filled inter-pellet voids were observed in the middle of the column specimen. When water started to infiltrate inside the specimen from both ends, the pellets and the powder grains started to swell (because of the swelling properties of smectite, the principal mineral of bentonite) and filled the voids. That induced at the same time increase of swelling pressure and downward movement of powder grains. The results allowed a better understanding on the hydro-mechanical couplings, at the pellet scale, in the pellet/powder bentonite mixture upon wetting

Keywords: Initial heterogeneity; Digital volume correlation; Water saturation; Homogenizatio; Pellet/powder bentonite mixture; X-ray computed microtomography

Domains: Géotechnique; Génie civil nucléaire; Mechanics of materials [physics.class-ph]

Agustín Molinero Guerra, Patrick Aimedieu, Michel Bornert, Yu-Jun Cui, Anh Minh A.M. Tang, et al.. Analysis of the structural changes of a pellet/powder bentonite mixture upon wetting by X-ray computed microtomography. Applied Clay Science, 2018, 165, pp.164-169. ⟨10.1016/j.clay.2018.07.043⟩. ⟨hal-02130370⟩