Role of Ca/Si ratio in carbonate-induced Tobermorite Corrosion: Insights from first-principles simulations

• This study explores the role of calcium-to-silica ratio in carbonate-induced corrosion of Tobermorite surfaces. • Simulations show that higher calcium-to-silica ratios enhance the adsorption strength of carbonate ions. • Adsorption is controlled by electron transfer and orbital hybridization. Concrete durability is significantly affected by carbonate corrosion, which alters the stability of concrete structures. This study investigates the adsorption behavior of carbonate ions on three Tobermorite surfaces with different calcium-to-silica (Ca/Si) ratios using Density Functional Theory (DFT) and ab initio Molecular Dynamics (AIMD) simulations. Our results show that the adsorption strength follows the trend: Tobermorite 14 Å > 11 Å > 9 Å, with the strongest adsorption energy of −7.08 eV on the 14 Å surface. Structural and electronic analysis reveals that calcium and silicon atoms lose electrons, while carbonate oxygen atoms gain electrons during adsorption. The analysis of the density of states (DOS) demonstrates the hybridization of calcium d orbitals and oxygen p orbitals, contributing to the stability of the adsorption. Simulations of mean-square displacement (MSD) indicate that surface calcium atoms have the lowest diffusivity due to structural constraints. These findings offer insights into the corrosion mechanism of C-S-H and provide a theoretical foundation for developing more durable concrete materials.