The present study investigates the chlorination and migration mechanism of Tobermorite9 Å through the use of density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD). The findings reveal a negative adsorption energy value of À 2.19488 eV. The results of the charge density difference analysis reveal that the Ca atoms experience electron loss, while the Cl atom undergoes electron gain. The O atom situated at the end of the silicate chain (and silicate chain bridge) exhibits electron gain, and the Na atom experiences electron loss. The results of density of states (DOS) and partial density of states (PDOS) demonstrate that the CaÀ Cl bond was created as a result of the interaction between Ca and Cl orbitals. The evident overlaps between Na-p and O24-p orbitals lead to the formation of NaÀ O bond. In AIMD simulation, the minimum energy barrier and activation energy of sodium chloride molecule are 0.09236 eV and 0.059 eV, respectively. The findings also suggest that chloride ion diffusion is facile on hydrated calcium silicate.
Hydrated calcium silicate carbonation leads to reinforcement corrosion and strength reduction. The carbonation mechanism of Tobermorite 9 Å is researched by density functional theory calculation and ab initio molecular dynamics (AIMD). Results show that the lowest surface energy of Tobermorite 9 Å (001) slab is (001) surface. The bridge position of Ca1─Ca5 atom is the most stable adsorption position for carbon dioxide molecules. In terms of charge density difference, the results show that the Ca atom loses electrons and the O atom gains electrons. In terms of partial density of states, the results show that there are unobvious hybridization orbitals between Ca d‐ and O p‐orbitals, which leads to the formation of a very weak Ca─O bond. In terms of AIMD simulation at the temperature of 1073 K, the results show that the carbon dioxide gradually develops from adsorption to desorption on the Tobermorite 9 Å (001) surface. These findings provide profound views in understanding the carbonation of hydrated calcium silicate.
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