Comparison of the swelling pressure of bentonite pellet-contained materials and powder

Bentonite pellet-contained material (PCM) has been recognized as a candidate for the buffer/backfill material in deep geological high-level radioactive waste repository. The PCM has a more complex initial structure comparing with bentonite powder (BP). The difference in the initial structure may cause a difference in the swelling response. In the current work, the swelling pressure of the PCM and BP specimens with varying dry densities was investigated using the zero-swell method. The results showed that the swelling pressure of BP continuously increased. However, the swelling pressure of the PCM increased initially, followed by a decreasing period (i.e., collapse), and reincreased again until the final swelling pressure reached. Besides, the final swelling pressure of the PCM was larger than that of the corresponding BP. The deviation was further discussed based on the scanning electron microscopy images, pore size distribution curves, and the swell index tests.