X-ray diffraction studies of hydration reaction of cement components and sulfoaluminate (C 4A 3S̄) Part IA. Silicates mixed with different components

Abstract

The purpose of this investigation is to determine the reaction of different cement components and sulfoaluminate in mixtures and their mutual influence on the hydration. The components used are silicates, C 3S and β-C 2S, aluminates, C 3A, C 12A 7 and CA 2, ferrites, C 4AF and C 2F, and sulfoaluminate, C 4A 3S̄. The investigation includes separate components as well as combinations of two components. These combinations include one component from each of the following groups: silicate, aluminate, ferrite and sulfate. All combinations have been made with or without addition of gypsum. All eight hundred different combinations of the components have been investigated for one day, seven days, twenty-eight days and one year. The relations between the products of hydration and the oxide compositions of the cement components in system CaO  SiO 2  Al 2O 3  Fe 2O 3 were explored. The different components were mixed at water/solid ratio of 0.5. The specimens were not protected from CO 2, consequently monocarboaluminate, C 4AC̄H 11, was formed. The hydrate phases developing during hydration have been observed qualitatively by X-ray diffraction technique. In a neat paste of C 3A, di- and tetracalcium aluminate hydrates were formed. After a while C 3AH 6 crystals appeared, according to the following scheme: ▪ High-sulfate form (ettringite) forms in hardened cement, a result of interaction of calcium sulfate with aluminates or ferrites, changing to monosulfate hydrate with time. When there are both gypsum and lime (the lime that is released from C 3S or β-C 2S during the hydration) the reactivity of C 4AF is reduced. The lime seems to stabilize the ettringite crystals somewhat. In the presence of C 3S and gypsum, the hydration of the sulfoaluminate yields a product with a greater quantity of ettringite than that from the pastes without C 3S. The new phase of gehlenite hydrate, C 2ASH 8, found in a different system, seems to be a result of the hydration of C 3S or β-C 2S in alumina saturated solution (alumina components), C 4A 3S̄.