HIGH-TEMPERATURE, RESISTANT, ARGILLITE-BASED, ALKALI-ACTIVATED MATERIALS WITH IMPROVED POST-THERMAL TREATMENT MECHANICAL STRENGTH

Fire resistance performance is one of the most important requirements in geological storage conditions in order to improve the resistance of storage packages to high thermal constraints (in the case of a fire for example). With the need to develop new fire-resistant materials, the aim of the present study was to develop fire-resistant geopolymer binders based on Callovo-Oxfordian (COx) argillite. Two types of kaolin with different degrees of purity were mixed with argillite in various proportions. These mixtures were calcined at 600 or 750°C. In order to assess the fire resistance of activated materials, thermal treatment at 1000°C was performed. The compressive strength and mineralogical composition of the samples were investigated before and after heat treatment. The results showed that the addition of argillite improved significantly the thermomechanical properties of kaolin-based geopolymers containing impurities, especially the mixture containing 67% argillite and calcined at 750°C. This phenomenon was not observed for the pure-kaolin geopolymer. Improvement of fire resistance was due to the formation in situ of leucite and zeolite-type phases (KAlSi2O6 and KAlSiO4) and of wollastonite (CaSiO3) at high temperature, which is linked to the Ca available in the raw materials.