Formation of ettringite, Ca6Al2(SO4)3(OH)12•26H2O, AFt, and monosulfate, Ca4Al2O6(SO4)•14H2O, AFm-14, in hydrothermal hydration of Portland cement and of calcium aluminum oxide -: calcium sulfate dihydrate mixtures studied by in situ synchrotron X-ray powder diffraction

In the hydration of calcium aluminum oxide-gypsum mixtures, i.e., Ca3Al2O6, Ca12Al14O33 and CaSO(4)(.)2H(2)O, the reaction products can be ettringite, Ca6Al2(SO4)(3)(OH)(12)(.)26H(2)O, monosulfate, Ca4Al2O6(SO4)(.)14H(2)O, or the calcium aluminum oxide hydrate, Ca4Al2O7 - 19H(2)O. Ettringite is formed if sufficient CaSO(4)(.)2H(2)O is present in the mixture. Ettringite is converted to monosulfate when all CaSO(4)(.)2H(2)O is consumed in the synthesis of ettringite. The reactions were investigated in the temperature range 25-170degreesC using in situ synchrotron X-ray powder diffraction. This technique allows the study of very fast chemical reactions that are observed here under hydrothermal conditions. A new experimental approach was developed to perform in situ mixing of the reactants during X-ray data collection. (C) 2004 Elsevier Inc. All rights reserved.