With advances in x-ray microtomography, it is now possible to obtain three-dimensional representations of a material’s microstructure with a voxel size of less than one micrometer. The Visible Cement Data Set represents a collection of 3-D data sets obtained using the European Synchrotron Radiation Facility in Grenoble, France in September 2000. Most of the images obtained are for hydrating portland cement pastes, with a few data sets representing hydrating Plaster of Paris and a common building brick. All of these data sets are being made available on the Visible Cement Data Set website at http://visiblecement.nist.gov. The website includes the raw 3-D datafiles, a description of the material imaged for each data set, example two-dimensional images and visualizations for each data set, and a collection of C language computer programs that will be of use in processing and analyzing the 3-D microstructural images. This paper provides the details of the experiments performed at the ESRF, the analysis procedures utilized in obtaining the data set files, and a few representative example images for each of the three materials investigated.

We examine the utility of the lattice Boltzmann method for modeling fluid flow in large microstructures. First, results of permeability calculations are compared to predicted values for several idealized geometries. Large scale simulations of fluid flow through digitized images of Fontainebleau sandstone, generated by X-ray microtomography, were then carried out. Reasonably good agreement was found when compared to experimentally determined values of permeability for similar rocks. We also calculate relative permeability curves as a function of fluid saturation and driving force. The Onsager relation, which equates off-diagonal components of the permeability tensor for two phase flow, is shown not to hold for intermediate to low nonwetting saturation, since the response of the fluid flow to an applied body force was nonlinear. Values of permeability from three phase flows are compared to corresponding two phase values. Performance on several computing platforms is given.

We have simulated the fast streamer stage of liquid dielectric breakdown as stochastic growth of a branching fractal tree. Breakdown and threshold properties of the fluid are represented in the random filter procedure. A range of fractal densities, from sparse to bushy, is approximated by the choice of power-law (4th-power to linear). The choice of threshold (cutoff) voltage also significantly affects the growth form. These parameters combine with the shape and concentration of the electric field, to regulate the distribution and directedness of the local discharge growth pattern. Inclusion of a voltage gradient along the streamer tree produces a secondary narrowing effect on the growth. A large grid (128 cubed) is used for the discretization. Diagonal growth paths to neighbor-vertices are included, increasing the choice of available directions for each discharge event. We use a combination of data-parallel programming and three-dimensional visnalizatiou. Complete growth histories, evolving from the voltage distribution, can he displayed in animation or in color handing against the "trials"variable, which simulates a time tick. Side views of the structures provide comparison against sub-microsecond snapshots from experiment. Results include sparse, directed trees evolving from a 4thpower-law filter; also dense trees from a linear filter, whose conical upper-envelope boundary is strongly influenced by the choice of threshold (cutoff) potential.

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