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Kinetic origins of Löwenstein's rule compliance during early-stage aluminosilicate nucleation: A reactive molecular dynamics study
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DOI：10.1016/j.cemconres.2026.108343.png)
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Abstract
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Calcium aluminate silicate hydrate (C-A-S-H) nucleation critically influences the microstructural development of blended cementitious systems, yet the atomistic mechanisms by which Al modifies the earliest condensation stages remain poorly understood. Reactive force field molecular dynamics simulations are employed to investigate aluminosilicate cluster formation across Al/Si ratios of 0–0.30 and temperatures of 300–1000 K under high-supersaturation conditions representative of the spinodal regime. The computed activation energy for the pure silicate system (44 kJ/mol) is consistent with experimentally reported C-S-H condensation barriers (40–60 kJ/mol), validating the simulation framework. Al incorporation reduces this barrier to 15–37 kJ/mol, kinetically facilitating silicate condensation and promoting the formation of higher-connectivity aluminosilicate networks. A compositional crossover near Al/Si ≈ 0.15 marks the transition from Si-O-Al-dominated bridging to increasingly prevalent Al-O-Al linkage formation, comparison with a random-mixing baseline reveals that Al-O-Al bonds form at 5–6 times the statistically expected frequency, confirming kinetic trapping rather than random encounter as the origin of Löwenstein violations. Trajectory analysis further reveals that metastable Al-O-Al bonds reorganize into Löwenstein-compliant Si-O-Al linkages through ring-mediated rearrangement, providing an atomistic pathway for the emergence of Al avoidance in mature C-A-S-H structures. These findings provide a molecular-level kinetic complement for rationalizing Al/Si thresholds in the design of supplementary cementitious materials.
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