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Influence of water activity on hydration of tricalcium aluminate‐calcium sulfate systems
Author(s) -
Lapeyre Jonathan,
Ma Hongyan,
Okoronkwo Monday,
Sant Gaurav,
Kumar Aditya
Publication year - 2020
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17046
Subject(s) - ettringite , aluminate , isothermal microcalorimetry , chemistry , cement , isothermal process , solubility , precipitation , sulfate , phase (matter) , calcium silicate , chemical engineering , kinetics , calcium , solubility equilibrium , inorganic chemistry , mineralogy , portland cement , materials science , thermodynamics , metallurgy , organic chemistry , physics , quantum mechanics , meteorology , engineering , enthalpy
The hydration of tricalcium silicate (C 3 S)—the major phase in cement—is effectively arrested when the activity of water ( a H ) decreases below the critical value of 0.70. While it is implicitly understood that the reduction in a H suppresses the hydration of tricalcium aluminate (C 3 A: the most reactive phase in cement), the dependence of kinetics of C 3 A hydration on a H and the critical a H at which hydration of C 3 A is arrested are not known. This study employs isothermal microcalorimetry and complementary material characterization techniques to elucidate the influence of a H on the hydration of C 3 A in [C 3 A + calcium sulfate (C$) + water] pastes. Reductions in water activity are achieved by partially replacing the water in the pastes with isopropanol. The results show that with decreasing a H , the kinetics of all reactions associated with C 3 A (eg, with C$, resulting in ettringite formation; and with ettringite, resulting in monosulfoaluminate formation) are proportionately suppressed. When a H ≤0.45, the hydration of C 3 A and the precipitation of all resultant hydrates are arrested; even in liquid saturated systems. In addition to—and separate from—the experiments, a thermodynamic analysis also indicates that the hydration of C 3 A does not commence or advance when a H ≤0.45. On the basis of this critical a H , the solubility product of C 3 A ( K C3A ) was estimated as 10 −20.65 . The outcomes of this work articulate the dependency of C 3 A hydration and its kinetics on water activity, and establish—for the first time—significant thermodynamic parameters (ie, critical a H and K C3A ) that are prerequisites for numerical modeling of C 3 A hydration.