Studies of Early Stages of Paste Hydration of Cement Compounds, I

The paste hydration of C 4 AF with and without the addition of lime and/or gypsum was studied by means of electron‐optical and X‐ray diffraction techniques. It was found that in the paste hydration of C 4 AF iron did not separate out but remained in the structure of the hydrated compounds, probably substituting for aluminum. In a neat paste of C 4 AF and H 2 O, at first di‐ and tetracalcium aluminate hydrate crystals formed, but later cubic C 3 AH 6 crystals appeared. In the presence of Ca(OH) 2 , C 2 AH x crystals did not form; otherwise the course of the reaction was the same as without lime. Any CO 2 present formed monocarboaluminate. When gypsum alone was present, ettringite crystals first appeared which later changed to monosulfate hydrate. In the presence of both lime and gypsum, the reactivity of C 4 AF was much reduced. Ettringite crystals were somewhat stabilized by lime. The formation of monocarboaluminate was hindered in the presence of gypsum.