Mesostructure of Calcium Silicate Hydrate (C‐S‐H) Gels in Portland Cement Paste: Short‐Range Ordering, Nanocrystallinity, and Local Compositional Order

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Abstract
Transmission electron microscopy studies of calcium silicate hydrate gels in portland cement were performed. Selected area electron diffraction studies revealed diffuse rings, indicating the presence of short‐range ordering. Investigations of various regions within the gel found strong fluctuations in the diffuseness of the rings; corresponding local compositional probes showed the presence of large fluctuations in the local calcium:silicon ratio. Lattice imaging studies were then performed to determine the nature of the short‐range ordering These investigations revealed nanocrystalline regions within an amorphous matrix. The local composition within the nanocrystalline regions is believed to be homogeneous. However, strong fluctuations in the local compositional order parameter between various regions would seemingly exist. Optical diffractograms taken from individual nanocrystalline regions demonstrated the coexistence of both jennite and 1.4‐nm tobermorite structural elements, supporting the essential features of the Taylor nanophasic model.