Compositional Evolution of Calcium Silicate Hydrate ( C–S–H ) Structures by Total X ‐Ray Scattering

High‐energy X ‐ray diffraction was employed to study the structural characteristics of a set of C–S–H samples with 0.6 ≤ C/S ≤ 1.75. It has been observed that Si is tetrahedrally coordinated to O for all samples irrespective of chemical composition and the Ca–O coordination number gradually decreases from ~7 to ~6 with increasing C/S ratio. This suggests that the C–S–H structure evolves from a tobermorite‐like structure into a jennite‐like structure as a function of increasing C/S ratio as the interlayer space decreases from ~1.3 to ~1 nm. Evolution of these short‐ and medium‐range order structural characteristics in the C–S–H system is associated with the alteration of the Ca–O layers and silicate depolymerization with increasing C/S .