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The Visible Cement Database web site, where all the data gathered may be obtained (visiblecement.nist.gov), contains the 3-D images constructed out of the many slices generated in X-ray microtomography. The full 3-D images are 10243 voxels in size. Various programs for manipulating the images, which were used to identify and eliminate the hydration products, can be obtained from the site.
The images are in the form of circular cylinders embedded in rectangular cylinders. The data used were the pt045-h-3hv1c300 and pt045-h-3hv2c300 files, which were the top and bottom halves, respectively, of a CCRL-133 sample with w/c=0.45 paste and hydrated for 3 h. These images were combined, and then a 600 voxel x 600 voxel x 800 voxel piece was cut out and saved. This was the largest piece of the image that stayed away from the sample cylindrical boundary. A sweep of various programs [1,2] was made through this image, eliminating particles that had been cut (so did not have a realistic shape), and that were too small (less than 125 voxels in volume). Internal porosity, which was mainly an artifact of the X-ray microtomography process, was also eliminated. Figure 1 shows an original slice (a), the same slice after internal porosity has been removed (b), and the slice after artificially cut and small particles have been removed (c).
Figure 1: (a) A slice cut out from the original binarized tomographic image, (b) the same slice after internal porosity has been removed in 3-D, and (c) the same slice after artificially cut particles and small particles with volumes below 125 voxels (in 3-D) have been removed.
Spherical harmonic analysis was applied to each particle and further error checking was used to eliminate multi-particles, which are two or more particles that have been artificially "welded" together by the X-ray microtomographic reconstruction process [7]. There were over 60,000 particles with voxel volumes greater than 125 voxels in the original processed image. Only particles with voxel volumes greater than 2000 were further processed, so as to leave a margin of error above the 10 voxels per unit length cutoff and also to reduce the number of particles considered. About 1200 particles were processed and their spherical harmonic coefficients stored. A voxel volume of 2000 corresponds to a real volume of 1715 µm3 = 2000 · (0.95 µm)3. If that number is set equal to the volume of a sphere, then the diameter of the sphere that has equal volume is called the equivalent spherical diameter, and is 15 µm in this case. The maximum particle size was an equivalent spherical diameter of about 60 µm.
Next: Qualitative and quantitative Up: Main Previous: Introduction