Direct pH measurement of porewater in compacted bentonite (III); Influence of low alkalinity cement on bentonite porewater

Isogai, Takeshi*; Oda, Chie  

Porewater chemistly in compacted bentonite would affect a performance of engineered barrier system in a high-level radioactive waste repository, whereas there are little information of the porewater based on experimental data. The previous study provided a new method of direct pH measurement for highly compacted bentonite system and demonstrated some tests for compacted bentonite samples (the dry densities: 1.6 [g/cm] and 1.8 [g/cm]) both with the de-ionized water and with the NaCl solution. In this study, the solution equilibrated with low alkalinity cement were used in the direct pH measurement to see the effect of the composition of the external solutions, in which the bentonite column immersed. The result showed that the pH value of porewater in the cementitious condition was around 9 during the immersed time 1 to 3 months, while after 6 months became the porewater pH 10.6, which was equal to pH of the external solution.