Thermal effects on the engineering behavior of sand-bentonite and zeolite-bentonite mixtures for nuclear waste repositories

Bentonite/bentonite-containing mixtures are used as an impermeable engineering barrier and backfilling undergoes temperature and hydraulic changes over time. Soils around energy geo-structures should preserve their engineering characteristics under different thermal, mechanical, and hydraulic conditions. The present study reports the impact of temperature (25 and 80 degrees C) and temperature cycles on the hydraulic conductivity and volume deformation properties of compacted sand-bentonite and zeolite-bentonite mixtures. In addition, the effect of tincal, a boron mineral with high thermal resistance, on the behavior of these mixtures at high temperatures was investigated. The conventional test apparatuses were modified to perform consolidation and hydraulic conductivity tests at high temperature. The results have shown that the tincal additive had a negative effect by increasing the deformation. Moreover, high temperature caused irreversible contraction under the thermal cycle. An increase in temperature created an increase in hydraulic conductivity. However, tincal added mixtures were more hydraulically stable against high temperature.