Hydration of polyphase Ca3SiO5-Ca3Al2O6 in the presence of gypsum and Na2SO4

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Alite (Ca3SiO5: C3S*) and calcium aluminate (Ca3Al2O6: C3A) are the major phases in Portland cement, which have an essential role in the development of early age properties. The effects of gypsum content, fineness, and Na2SO4 addition on the early-stage hydration kinetics are investigated for polyphase (co-sintered) Ca3SiO5-Ca3Al2O6 model systems using calorimetry, X- ray diffraction, thermal analysis, and solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy. The results demonstrate that the hydration of C3A significantly affects the hydration of C3S. The C3S and C3A hydration is hindered considerably in severely over-sulfated systems (where C3A hydration is suppressed due to a very high gypsum content) and systems with additional Na2SO4. Although there is a considerable amount of Al incorporation in the C-S-H phase, no clear trends with respect to gypsum content, hydration age or Na2SO4 addition are observed for the AlIV/Si ratios of the C-S-H phase determined from 29Si NMR. With the addition of Na2SO4, recrystallization of ettringite from the AFm phases is postponed from 1 day to 7 days. *Cement chemistry notation: C-CaO, S-SiO2, A-Al2O3, (Formula presented.) -SO3, N-Na2O.

TidsskriftJournal of the American Ceramic Society
Sider (fra-til)6461-6474
StatusUdgivet - nov. 2020

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