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 transmission 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.