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The C-S-H phase plays the role as the glue that holds cement paste together. We now go down from the micrometer length scale of cement paste and the millimeter scale of concrete, to examine models for the structure of the nanometer-scaled C-S-H phase. Little is known of the actual details of the atomic structure of C-S-H, as it is amorphous, so the model focuses on the nanometer scale.
At the scale of nanometers, the C-S-H gel is modelled as a two-level structure of partially overlapping spherical particles . At the macro level, the 2-D cross-section of the larger 40 nm spherical agglomerates shown in the righthand image of Fig. 20 are each composed of smaller 5 nm diameter micro level particles, as shown in the lefthand image of Fig. 20.
The particle sizes and the total porosity at each level have been chosen to be consistent with experimental data from small angle neutron scattering  and sorption measurements . The models are generated in continuum space (in a three-dimensional cube with periodic boundaries) and subsequently digitized into a 3-D digital image for the evaluation of properties. The structural models have been validated by computing sorption isotherms and the pore volume acessible to molecules of varying diameters, and comparing to experimental results . Computational techniques have also been applied to computing both the conductivity/diffusivity and the permeability of the macro-level gel structure, with reasonable agreement with experiment.