Mechanistic insights into calcium-silicate-hydrate nucleation from molecular dynamics simulations

The nucleation and growth of C-S-H play a prominent role in cement hydration and the microstructure development of hardened cement paste. Understanding the nucleation could enable control of the kinetics of the process, for instance designing more efficient additives. Unfortunately, experimental characterization and computational modeling of nucleation remain challenging. In this work, molecular dynamics simulations were used to investigate the formation of C-S-H aggregates from initial primary particles (PPs) in solution. Starting with a dimeric PP obtained from Evolutionary Algorithms, simulations were performed with varying Ca(OH)₂ concentrations. The results show that calcium accelerates the assemblage into stable aggregates, releasing water molecules in the process. The size and density of the PPs and aggregates are compared with recent experimental data, revealing discrepancies for complexes and PPs, but better agreement for aggregates and globules. This study provides insights, and opens new questions, on the identification of nucleation pathways of C-S-H.