InterPore2025

Powder X-Ray Diffraction data for swelling pressure interpretation

22 May 2025, 15:45

1h 30m

Poster Presentation (MS04) Swelling and shrinking porous media Poster

Speaker

Svetlana Babiy

Description

In the scope of nuclear waste disposal facilities active clays are beneficial in comparison to other materials due to their higher swelling and sealing abilities. A unique correlation has previously been established between the final swelling pressure and the dry density of MX-80 bentonite. Additionally, it has been demonstrated that the final swelling pressure is independent of the material's fabric. However, validating these findings regarding swelling pressures in the presence of saline solutions remains a significant challenge. Saline solutions are known to induce chemical consolidation in bentonites, reducing the attractive forces within the diffuse double layer (DDL) and increasing shear strength. This process potentially impacts the final swelling pressure of bentonites. However, the existing data are insufficient to establish a consistent relationship across various fabric types at the same salinity level. Furthermore, the extensive variability in bentonites and their mixtures complicates the aggregation of data across different materials. As a consequence, this study proposes a methodology to utilize available swelling data from different types of sodium-bentonite at varying sodium chloride concentrations to derive a unified swelling pressure-dry density curve. This methodology includes (i) use of the montmorillonite dry density rather than the conventional dry density of bentonite, and (ii) integration of experimental results from Powder X-ray Diffraction (PXRD) to assess the influence of saline solutions on montmorillonite spacing. Using PXRD data, this methodology initially was able to predict the liquid limit across a broad spectrum of saline solutions and to identify a mechanical equivalent of chemical loading. By incorporating the latter, the swelling pressure curve for distilled water was reconstructed from each curve corresponding to a specific salinity level. This approach has been demonstrated to be effective for dry densities above 1.2 Mg/m³, enabling the derivation of a unified swelling pressure versus dry density curve for MX-80 and Gaomiaozi bentonites. For lower compactions, a coefficient that accounts for scaling from the nano- to macroscale effects of salinity has been proposed.