Geopolymer local network evolution under time and temperature

This study was undertaken in the context of Cigéo project to investigate the use of geopolymer for potential applications in high level waste cell. The aim was to evaluate the structural evolution of potassium metakaolin based geopolymer as a function of time and temperature for geological nuclear waste disposal applications. The evolution of mechanical properties, local structure, and porosity of geopolymer binder and composites stored at 0.5 and 20 months at 20 and 90 °C were studied. It was shown a decrease of density and stability of mechanical strength over time at 20 °C and a slight decrease at 90 °C. Moreover, it was evidenced the stability of the structure over time at 20 °C and the nucleation of a small amount of zeolite type phase at 90 °C. The mesoporosity was favored over time. However, an increase of porosity and pore size was evidenced at 90 °C due to pore coalescence and water removal. A model of aging was proposed in order to elucidate the structural changes over time and temperature. It has been shown that the aging of geopolymer at 20 and 90 °C induces changes of porosity and pore size distribution but seems not to degrade the structure and properties of the final material.