Long-term effect of water chemistry on the swelling pressure of a bentonite-based material

Abstract

International audienceCompacted bentonite-based materials have been proposed as possible sealing and backfill materials in geological repositories for the high-level radioactive waste disposal in several countries. During the long time lifespan of a repository, as the chemical composition of pore water can change, the swelling and sealing capacity of the material may also change. From a point of view of storage safety assessment, it is important to evaluate this possible change of swelling capacity. In this study, a mixture of bentonite and crushed Callovo-Oxfordian claystone was investigated. The long-term effect of pore water chemistry on the swelling pressure was studied at constant-volume conditions for 700 days. Distilled water and synthetic water having the chemical composition similar to that of in-situ pore water were used for hydration. The results obtained in an initial period of 100 h revealed no significant influence of the water composition on the swelling pressure evolution, and the maximum swelling pressures observed were close to 4.30 MPa for a dry density of 1.70 Mg/m3. Over a longer time period, on the contrary, the swelling pressure eventually decreased for all samples, especially for the sample saturated with synthetic water. In addition, comparison of a one-step soaking test with a multi-step soaking test showed no wetting procedure effect on the long term swelling behaviour. All the results are analysed by considering the physico-chemical interaction between the minerals of claystone, minerals of bentonite and different fluids involved

Factors Affecting the Swelling‐Compression Characteristics of Clays in Yichang, China

“…e relation of expansive stress and suction has been demonstrated by Agus et al [8]. Wang et al [9] studied the influence of distilled water and synthetic water on the swelling characteristics of a claysand mixture. Chen et al [10] clarified the different NaCl concentration and vertical pressure effects on swelling feature of compacted clay.…”

Experimental Study on the Swelling Behavior of Expansive Soil at Different Depths under Unidirectional Seepage

“…Several scholars have pointed out that different kinds and concentrations of electrolyte can cause the expansion of swelling clays to varying degrees [12][13][14][15]. It was demonstrated that different pore solutions have a significant effect on the swelling characteristics of bentonite [16][17][18][19][20][21]. Lee et al [17] demonstrated that the swelling pressure of Ca-bentonite is distinct from that of Na-bentonite, and this difference depends on the concentration of electrolyte, which can be ascribed to changes to the thickness of diffuse double-layer (DDL) or cation exchange [22].…”

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

“…The saturation fluid was obtained by mixing the chemical components presented in Table 1 with distilled water until full dissolution. The resulting synthetic water had the same chemical composition as the pore water of the Callovo-Oxfordian claystone (a possible geological host rock for radioactive waste disposal in France) from the underground research laboratory in Bure (Wang et al, 2013a). The table shows a total mass of 5.677 g of salt per liter of solution, that corresponded to a salinity (mass of salt per mass of solution) lower than 1%.…”