Characterization of phase assemblage in ettringite-forming pastes as a function of calcium aluminate cement variation

The study concentrates on the examination of crystalline and amorphous phase assemblage formed in ettringite-rich systems as a function of calcium aluminate cement variation. Three kind of CACs with different monocalcium aluminate (CA) contents were used in PC/CAC/C mixtures. The effect of CACs variation on the phase formation was investigated by terms of calorimetry, XRD, TGA and SEM. The phase assemblage was followed quantitatively at discrete ages of 1, 7, 28, 56 and 90 days. Experimental results from XRD and TGA showed ettringite, monosulpahte and AH3 as main hydration products. Quantitative X-ray analysis confirmed that the amounts of ettringite, monosulphate and amorphous content varied depending on the type of CAC. However, monosulphate was found to be X-ray detectable only when CAC with low CA content was used. For compositions where CAC with high amount of CA were used, monosulphate was X-ray amorphous and its presence was confirmed by thermal analysis. Furthermore, depending on the used CACs SEM investigation indicated morphological differences in between the hydration products.

Author: E. Qoku, T. Bier, G. Schmidt

Section: Science and production

Keywords: hydration, ettringite, calcium aluminate cement, gypsum, Portland cement.