To fully understand the nature of the influence of the crystal structure
on hydration reactivity, numerous investigations [14–17] have
been performed from the perspective of theoretical calculations and
analyses of models of different structures. Early arguments that only
considered the crystal structures [18] had found that the neighboring
CaOx polyhedra were joined by common vertices, edges and faces in
β-C2S; however, γ-C2S had no shared faces. Fukuda11 ascribed the
higher hydration reactivity of β-C2S comparedto ′L-C2S to themore favorable
surface defects of crystalline β-C2S. A more promising proposal
by Taylor [19] suggested that the initial step in the reaction between calciumsilicate
andwaterwas the proton transfer fromwatermolecules to
the oxygen atoms in the calcium silicate. Recently, Durgun et al. [15,16]
and Jansang and Skibsted [17] have used first-principles calculations to
study the wide range of hydration kinetics observed in tricalcium
silicate (Ca3SiO5, C3S) and C2S. They have proposed that the high reactivity
of C3S was mainly related to the active sites around the more
ionic oxygen atoms in C3S, whereas these ionic oxygen atoms were absent
in C2S. Nevertheless, the relationship between hydration reactivity
and polymorph of C2S has never been explored from the perspective of
electronic structures.
2. Computational