Multi-step nucleation pathway of C-S-H during cement hydration from atomistic simulations

Area of Science:

• Materials Science
• Chemistry
• Civil Engineering

Background:

• Calcium Silicate Hydrate (C-S-H) nucleation is critical for cement paste rheology, microstructure, and properties.
• The atomic-scale mechanism of C-S-H nucleation, including primary particle formation and aggregation, remains poorly understood.
• Existing evidence suggests C-S-H nucleation occurs in at least two steps, necessitating further investigation.

Purpose of the Study:

• To investigate the atomic-scale structure and formation of C-S-H primary particles from ions in solution.
• To elucidate a potential formation pathway for C-S-H nucleation.
• To identify the fundamental building blocks of C-S-H.

Main Methods:

• Atomistic simulation methods, including Density Functional Theory (DFT).
• Evolutionary Algorithms (EA) for structure prediction.
• Molecular Dynamics (MD) for simulating particle formation and aggregation.

Main Results:

• Stable C-S-H clusters were identified, even at small sizes, encoding characteristic structural motifs.
• A C4S4H2 cluster candidate was identified as a fundamental C-S-H building block.
• Simulations suggest a formation pathway involving the merging of small silicate dimer clusters into larger aggregates.

Conclusions:

• The study proposes a plausible atomic-scale formation pathway for C-S-H nucleation.
• The identified C4S4H2 cluster provides insight into the basic building block of C-S-H.
• Dehydration within aggregates can lead to the formation and eventual crystallization of C-S-H building blocks.