Alite hydration at the single grain level

Understanding cement hydration processes is crucial for achieving the desired properties in concrete. However, the nanoscale mechanism whereby calcium silicate hydrate (C-S-H) transforms, particularly regarding morphology, structure, and composition evolution, remains unclear. Here, we employed multimodal trans-mission electron microscopy (TEM) to investigate the hydration kinetics of alite at the single grain level, extracting comprehensive chemical and structural information. Our findings reveal that rapid nucleation of C-S-H occurs at the boundaries within minutes, followed by subsequent C-S-H growth. The development of C-S-H fibrils can be categorized into two distinct stages: needle elongation and texture densification. Through quantitative analysis, we estimated the growth rate of C-S-H needles to be 7 nm/min, while observing a decrease in the intrinsic porosity of C-S-H from 7.9% to 3.1% concurrent with the thickening of C-S-H lamella. Electron diffraction analysis further demonstrates the homogenization of C-S-H throughout hydration, involving structural compaction and silicate polymerization. Our work provides valuable insights into the origins of C-S-H nucleation and growth, thereby enhancing our understanding of hydration mechanisms at a fundamental level.

Automated summary

Understanding the nanoscale mechanism of calcium silicate hydrate (C-S-H) transformation during cement hydration is crucial for achieving desired properties in concrete. Through multimodal transmission electron microscopy (TEM), this study reveals that C-S-H rapidly nucleates at boundaries and then grows, with the development of C-S-H fibrils categorized into needle elongation and texture densification stages. The growth rate of C-S-H needles is estimated to be 7 nm/min, accompanied by a decrease in intrinsic porosity and thickening of C-S-H lamella. Electron diffraction analysis demonstrates the homogenization of C-S-H throughout hydration. These findings enhance our understanding of hydration mechanisms at a fundamental level.