Investigation for Carbonation Mechanism of Tobermorite 9 Å: A Combination of DFT and Ab Initio Molecular Dynamics Study

Hydrated calcium silicate carbonation leads to reinforcement corrosion and strength reduction. The carbonation mechanism of Tobermorite 9 angstrom is researched by density functional theory calculation and ab initio molecular dynamics (AIMD). Results show that the lowest surface energy of Tobermorite 9 angstrom (001) slab is (001) surface. The bridge position of Ca1Ca5 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 CaO 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 angstrom (001) surface. These findings provide profound views in understanding the carbonation of hydrated calcium silicate.