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Preparation and characterization of dicalcium aluminate hydrate (C2AH8)

Although the hydration process of calcium aluminate cement (CAC) represents a process of commercial and industrial importance, the chemical processes involved during the hydration are not yet well understood. With the aim of developing realistic CAC hydration model for defined cylindrical geometry, which includes heat and mass balances, it is necessary to accurately determine composition of hydration products. Due to a poor crystallinity of the hydration products, the methods of combined thermal analysis are a promising ones regarding their characerization. Previous work indicated various interpretations of the results of thermal analysis of CAC hydration products, especially regarding the dehydration of C2AH8 phase. Part of the problem follows from the difficulty of preparing pure C2AH8, which is metastable with respect to C3AH6 and AH3. Thus, research has been carried out in order to contribute to a better understanding of properties of hydration product dicalcium aluminate hydrate, C2AH8. Monocalcium aluminate (CA)and mayenite (C12A7) were synthesized and used for hydration reactions: CA + C + 8 H -> C2AH8 C12A7+ 2C + 56 H -> 7 C2AH8 For the syntheses of CA and C12A7, calcite (CaCO3) and gibbsite (Al(OH)3) have been wet homogenized in planetary mill, dried and fired. Hydration products were investigated by X-ray diffraction analysis (XRD), simultaneous differential scanning calorimetry and thermo gravimetric analysis (DSC/TGA) and transmission Fourier transformed infrared spectroscopy (FTIR). Results of XRD analysis indicated good crystallinity of the obtained C2AH8, but also a presence of minor amounts of calcium carboaluminate hydrate. This indicated accidental contamination by atmospheric CO2, which is in accordance with the results of FTIR analysis. The results of XRD analysis of partially dehydrated C2AH8 together with the results of simultaneous DSC/TGA thermal analysis contribute to the better understanding of the dehydration process of CAC hydration products.

dicalcium aluminate hydrate; FTIR; XRD; DSC/TGA

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