Multi-step nucleation of C-S-H: DFT simulation on silicate oligomerization and Si(Qn) evolution dynamics

Understanding the nucleation processes of calcium-silicate-hydrate (C-S-H) is fundamental to advancing the performance of cement. This study employs Density Functional Theory (DFT) to reveal the initial stages of C-S-H formation by focusing on silicate oligomerization. It examines the progression from monomer silicate species to the precursor formation, containing a range of silicate tetrahedra. Through DFT simulations, free energy changes and barriers of oligomerization reactions up to pentamers are obtained, unveiling an anionic condensation mechanism that establishes the kinetic and thermodynamic profile of this transformation. Observations reveal a dynamic evolution of Si species, with Si(Q3) indicating a transient presence, suggesting an intricate pathway towards the well-established silicate chain structure of C-S-H. This study provides detailed computational insight into the energy barriers, reaction pathways, and the thermodynamics of C-S-H formation, contributing substantial knowledge to the field of cement chemistry and its multi-step nucleation theory.