Low-Q region Rietveld analyses were performed on C-S-H synchrotron XRD patterns, using the software MAUD. Two different crystal structures of tobermorite 11 Å were used as a starting model: monoclinic ordered Merlino tobermorite, and orthorhombic disordered Hamid tobermorite. Structural modifications were required to adapt the structures to the chemical composition and the different interlayer spacing of the C-S-H samples. Refinement of atomic positions was done by using special constraints called fragments that maintain interatomic distances and orientations within atomic polyhedra. Anisotropic crystallite size refinement showed that C-S-H has a nanocrystalline disordered structure with a preferred direction of elongation of the nanocrystallites in the plane of the Ca interlayer. The quality of the fit showed that the monoclinic structure gives a more adequate representation of C-S-H, whereas the disordered orthorhombic structure can be considered a more realistic model if the lack of long-range order of the silica chain along the c-direction is assumed. © 2012 Elsevier Ltd. All rights reserved.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-l1-004021
Acknowledgements: This publication was based on work supported in part by Award No. KUS-l1-004021, made by the King Abdullah University of Science and Technology (KAUST). The experiments at APS, beamline BESSRC 11-ID-C was supported by the U.S. DOE, Argonne National Laboratory under contract number DE-AC02-06CH11357. Also thanks to Dr. Chris Benmore for his help with the experimental measurements. We are appreciative to Dr. Luca Lutterotti for modifications of the MAUD software and advice about the analytical procedures.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.