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Calcium aluminate cements (CACs) are used in combination with calcium sulfates as binders in self-levelling mortars. The influence of commercial CAC/anhydrite ratio on the solid phase assemblage and pore solution at water to binder (w/b) ratios of 0•40 and 0•72 was investigated between 1•5 h and 91 d of hydration using a multi-method approach including x-ray diffraction, thermogravimetric analysis and thermodynamic calculations. The reduction of the extent of hydration at the lower w/b ratio can be explained by a lack of water for complete hydration and lack of space. In the system with a CAC/anhydrite weight ratio of 1, ettringite and AH 3 were the main hydration products, whereas in the case of a CAC/anhydrite ratio of 2•3, in addition to ettringite and AH 3 , monosulfate was present along with strätlingite and at a later age. In contrast to the thermodynamic modelling results, anhydrite persisted even at low calcium sulfate contents as the precipitation of AH 3 around the anhydrite grains seemed to lead to a chemical blocking.

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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.

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