Determination of the Porewater Compositions in Compacted Bentonite -Results of Experiment using Distilled Water, Synthesized Seawater and a Low-Alkaline Cement Solution-

Isogai, Takeshi*; Jintoku, Takashi; Sasamoto, Hiroshi   

We determined the pH and chemical compositions of porewaters in compacted bentonite as a function of time. The experiments were carried out using the low-decolorant pH test papers and high-absorbancy pads embedded in compacted bentonite (Kunigel-V1R=100[%]) having dry densities of 1.6 [g/cm]. We also measured the chemical composition and exchangeable cation concentrations of the bentonite after the experiments. The experiments were conducted in a controlled-atmosphere glove box (O(g) content is less than 1[ppm]) using distilled water, synthesized seawater and a low-alkaline cement porewater (i.e., HFSC: High Flyash contained Silica fume Cement) as initial solutions. The pH of the distilled water and synthesized seawater was adjusted to pH=9 by adding NaOH solution. Distilled water was reacted with crushed HFSC to produce a solution representing low-alkaline cement solution (pH= about 11). - Distilled water: The pH of porewaters further away from the interface did not vary significantly (pH = 8.0 to 9.0), but the pH of porewaters near the infiltration interface slightly decreased (pH = 7.5-8.5 pH = 7.0-8.0). - Synthesized seawater: The pH values were roughly constant at the interface between 6.5 and 7.0, but the pH of porewaters further away from the interface slightly decreased with time (pH = 6.5-7.0 pH = 6.0-6.5). - HFSC solution: Like the experiment with involving distilled water, the pH of porewaters contacted with HFSC solution further away from the interface were roughly constant between 8.5 and 10.0, but the pH of porewaters near the infiltration surface significantly decreased with time from pH = 9.5 to pH = 7.5-8.5. Although the determination of porewater chemistry in compacted bentonite was carried out, it was difficult to obtain the quantitative profile for variation during the experiment except the experiment using synthesized seawater.