Effects of hyperalkaline solutions on the swelling pressure of compacted Gaomiaozi (GMZ) bentonite from the viewpoint of Na+ cations and OH- anions

In China, Gaomiaozi (GMZ) bentonite has been selected as a suitable buffer material for high-level nuclear waste disposal. Groundwater in Beishan area, which has been considered as a potential site for the construction of the repository, may reach a high pH value because of its chemical background and possible concrete degradation during the operation of the repository. In order to investigate the independent effects of Na+ cations and OH- anions on the behavior of compacted GMZ bentonite, a series of swelling pressure tests with NaOH and NaCl solutions infiltration was conducted. The mercury intrusion porosimeter (MIP) and the X-ray diffraction (XRD) explorations were performed on the specimens before and after experiencing the swelling pressure tests in order to find out the influences of infiltration solution chemistry on the microstructure and mineralogy of compacted GMZ bentonite. The results showed that high Na+ cations concentration can inhibit the crystalline swelling and the double-layer swelling; high OH- anions concentration can facilitate the double-layer swelling and fabric rearrangement; the effects of NaOH solutions with different concentrations on the swelling pressure present the interaction of Na+ cations and OH- anions.