Experimental Investigation on Drying and Wetting of GMZ Bentonite Using X-Ray Tomography and Volumetric Digital Image Correlation Technique

Liufeng Chen,Diansen Yang,Kang Li,Pingye Guo

doi:10.1155/2020/6634246

Abstract

To investigate the shrinking and swelling properties of Gao-Miao-Zi (GMZ) bentonite, which has been considered as engineering barriers for high-level radioactive nuclear waste disposal in China, drying and wetting tests were carried out. The microstructure of the material at each hydric state was recorded using X-ray tomography (X-CT). The 3D images of the material were analyzed using digital volume correlation (DVC) technique, and the full-field strains at mesoscale (i.e., in the order of clay aggregate) during drying and wetting were quantified. The results show that the GMZ bentonite exhibits notable swelling characteristics during wetting and the swelling strain of the material is up to 8% at mesoscale. The full-field strain in 3D of the material is heterogeneous, anisotropic, and irreversible during drying and wetting. The corresponding deformation mechanisms are discussed. Two different swelling mechanisms were also identified: traction occurs in the interface between the matrix and inclusions during swelling; pre-existing fissure closes during swelling.

Highlights

Bentonite clay is often chosen as a buffer and backfill material between the waste canister and the host rock or as seals in excavated disposal galleries in geological disposal of highlevel radioactive waste
We present a new procedure to conduct drying and wetting tests combined with X-CT measurements. e shrinking and swelling properties of the GMZ bentonite at mesoscale are quantified and analyzed by digital volume correlation technique. e measured full-field strain of the GMZ bentonite in 3D allows to follow the evolution of damage. e deformation mechanisms of the material during wetting and drying are revealed by analyzing the microstructure changes
digital volume correlation (DVC) is a quantitative image analysis technique for measuring internal deformation of a volume from image slices acquired via an X-ray or CT scanner. e principle of DVC is similar to that of two-dimensional and three-dimensional Digital Image Correlation (DIC), except the z dimension is added allowing for full characterization of the material. e principle of the DIC method consists of tracking the grey-level distributions in subsets of images and pairing the homologous subsets between the reference image and the deformed images by optimizing a correlation coefficient that measures the similarity of the grey-level distribution in a small domain around these points [19, 22]

Summary

Introduction

Bentonite clay is often chosen as a buffer and backfill material between the waste canister and the host rock or as seals in excavated disposal galleries in geological disposal of highlevel radioactive waste. 3. Results and Discussion e X-CT scanning of the material shows that the microstructure of the compacted GMZ bentonite is complex.

Results

Conclusion