Formation of chabazite in mixes of calcium aluminate cement and silica fume used for caesium immobilization

The immobilization of caesium with a mix of calcium aluminate cement (CAC) and silica fume (SF) was studied at 50°C. The presence of caesium within the hydration solution leads to the formation of a zeolitic phase of the chabazite family, which immobilizes caesium within the cementitious mix. A severe leach test shows that the immobilization is efficient. Chabazite is also formed when a Cs solution is in contact with an already hydrated CAC-SF mix. The structure of zeolites involves ceramic bonds that are more stable with heat treatment than hydrate bonds, which explains why chabazite is not destroyed by heat treatment at a temperature as high as 750°C. The presence of chabazite is therefore interesting for any application that requires thermal treatment.