Fundamental Discrepancy of Chemical Reactivity of Tricalcium Oxy Silicate (alite), Dicalcium Silicate (Belite), and Their Polymorphs: A Density Functional Theory Study

Tricalcium oxy silicate (C3S) and dicalcium silicate (C2S) are the major constituents of cement. In this study, the reactivity of polymorphs of calcium silicates is quantitatively investigated using Density Functional Theory. The result of combining the DFT calculation and the Bader charge analysis elucidates that the main difference in reactivity between C3S and C2S is the presence of oxy ions in C3S which has smaller partial charge compared to that of other oxygen in the crystals. For the C3S, the reactivity of among different C3S polymorphs is decisively affected by the Bader charge of oxy ions. In contrast, total internal energy of C2S determines the quantitative chemical reactivity of C2S polymorphs. This result suggests that oxy ion has more dominant impact on the thermodynamic stability of calcium silicates. Furthermore, total energy can be used to estimate the chemical reactivity of calcium silicates, where there is no oxy ion exists.

Automated summary

This study quantitatively investigates the reactivity of different polymorphs of calcium silicates using Density Functional Theory. The presence of oxy ions in C3S is found to be the main difference in reactivity compared to C2S. The Bader charge of oxy ions significantly affects the reactivity of different C3S polymorphs, while the total internal energy of C2S determines the quantitative chemical reactivity of its polymorphs. This suggests that oxy ions have a more dominant impact on the thermodynamic stability of calcium silicates.