Long-term immersion tests of engineered materials in the Tono mine; Results for glass material

Hama, Katsuhiro ; Mitsui, Seiichiro  ; Aoki, Rieko*; Hirose, Ikuro

Long-term immersion tests of glass material at ambient temperature (about 18 C) for 10 years were performed in a gallery at the Tono mine in Japan, in order to assess durability of glass matelial contacted with natural groundwater. The gallery was constructed at a depth of 130 m below ground surface in the Toki Granite. Monolithic glass blocks with dimensions of 10 10 10 mm (cubic type) and of 25 mm in diameter and 8 mm in thickness (disk type: The wall of sample was covered by stainless steel of 1 mm thick.) were used for the tests. Both type of samples with and without clay were put in Teflon vessels, which have small holes on the wall, and inserted into boreholes excavated at the gallery floor. In addition to the immersion tests, static leaching test with cubic type glass and ground water was also performed at the gallery. The samples of each test were collected in time intervals of 6 months, 1 year, 2 years, 3 years and 10 years and were subjected to weight loss measurement and several surface analyses. The results were as follows: (1)Weight losses of each sample were proportional to time intervals. This result is attributable to constant dissolved silica concentration in the ground water during tests. (2)The weight losses of disk type glass were slightly larger than those of cubic type glass. This result is attributable to elemental release from internal cracks of disk type glass, instead of effect of stainless steel on the glass dissolution. (3)The weight losses for the tests with clay were slightly smaller than those for tests without clay. This result is attributable to higher concentration of dissolved silica in pore water of clay.