X-ray diffraction: a powerful tool to probe and understand the structure of nanocrystalline calcium silicate hydrates

Acta Cryst. (2013). B69, 465–473 (http://doi.org/qdb)

Sketch of the layer structure from tobermorite (top) and jennite (bottom), two model minerals commonly used to describe C-S-H crystal chemistry. Yellow polygons and purple tetrahedra respectively symbolize calcium and silicon coordination spheres.

Nanocrystalline calcium silicate hydrate (C-S-H) is the main binding phase in concrete. Despite decades of studies, many aspects of its lamellar structure remain unknown, owing to its minute size and extreme structural disorder, both producing X-ray diffraction patterns often considered diagnostic for X-ray amorphous phase. However, closer investigation of these patterns strongly suggests that C-S-H resembles nanocrystalline defective tobermorite affected by turbostratic disorder and possibly interstratification, at least for calcium to silicon ratios lower than ∼1.25.