| Abstrakt: |
The French national radioactive waste management agency (Andra) is studying the building of a deep geological disposal for High and Intermediate Level radioactive waste. If accepted, the disposal will lead all along the operating period to the excavation of a large amount of host rock, mainly constituted by argillite. With the aim of using this by-product, alkali-activated materials have been prepared and studied, involving two different alkaline silicate sources (solution and powder). In order to increase the thermal resistance, the addition of sand, as filler, has been studied. A standard test and a thermal shock, both up to 800 °C, are used to study the physical stability of the samples under these thermal constraints. Analyses by XRD and SEM allow correlating the thermal resistance to the structural evolution occurring during the thermal tests. It was shown that the alkaline-silicate solution composition is the main parameter to control the reactions during the thermal treatment. The use of the powder-based solution, containing sodium, leads to the formation of more viscous flow and less crystalline phases, which reduces the thermal resistance and the mechanical properties. The addition of filler in the samples increases the resistance to thermal sudden increase, but is not sufficient to obtain a correct resistance to shock. The utilization of flash-calcined argillite, containing carbonate species, gives a better crystallization during the thermal treatment and leads to more cracks but an increase of the mechanical properties. Using, these different compositions, a value of 20 MPa can be reached after thermal treatment. [ABSTRACT FROM AUTHOR] |
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