Atomistic Insights into Silicate Dissolution of Metakaolinite\nunder Alkaline Conditions: <i>Ab Initio</i> Quantum Mechanical\nInvestigation

This study employs\ncomputational chemistry to investigate the detailed\nmechanisms behind the dissolution of thermally activated clays, which\nare emerging as promising supplementary cementitious materials (SCM)\nfor enhancing concrete properties and reducing carbon footprint. Specifically,\nthe study employs a first-principles methodology for obtaining activation\nenergies (Δ<i>E</i><sub>a</sub>) involved in the dissolution\nof metakaolinite (MK) silicate units using NaOH and KOH activators.\nThe investigation includes considerations of hydrolyzing oxo-bridging\ncovalent bonds, van der Waals (vdW) interactions, and the influence\nof water molecules surrounding alkali cations. The study employs the\nenhanced dimer method within density functional theory (DFT) to propose\nfour models for determining the activation energies required to break\noxo-bridging bonds. The results demonstrate that KOH generally requires\nlower activation energies than NaOH, particularly when considering\nvdW interactions. They also highlight the lower activation energy\nrequired for commencing the dissolution of silicate units and emphasize\nthe significance of the hydration shell around cations. The proposed\nmethodology contributes to establishing a systematic database of atomistic\nactivation energies, essential for atomistic kinetic Monte Carlo upscaling\nand mesoscopic forward dissolution rate calculations in clays. This\nholds relevance in understanding their reactivity within cementitious\nmaterials.