The Visible Cement Data Set

Abstract

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.

Keywords: Plaster of Paris; cement hydration; image analysis; microstructure; visualization; x-ray microtomography.

Fig. 1

Schematic of plexiglass tubes for holding cement paste specimens.

Fig. 2

2-D image (1024 pixels by 1024 pixels) of slice 151 for unhydrated cement powder. Bright grey particles are unhydrated cement and dark grey is air-filled porosity. Greylevel bar at bottom of image indicates greylevel intensity variation from 0 (left) to 255 (right). The diameter of all slices is approximately 1 mm.

Fig. 3

2-D image (1024 pixels by 1024 pixels) of slice 151 for w/c = 0.35 cement paste hydrated for 16 h. Bright grey particles are unhydrated cement, medium grey is cement hydration products, and dark grey are water-filled or air-filled pores. Some indication of ettringite needles can be seen in the upper right portion of the image. The large void region in the top central region of the image is a processing flaw due to improper compaction in the tube mold.

Fig. 4

Greylevel histograms for 3-D (300 voxel by 300 voxel by 300 voxel) subvolumes of w/c = 0.35 cement pastes hydrated for various times.

Fig. 5

2-D image (1024 pixels by 1024 pixels) of slice 151 for w/c = 0.45 cement paste hydrated for 137 h. Bright grey particles are unhydrated cement, medium greys are cement hydration products, and dark grey are water-filled or air-filled pores. Fewer cement particles are present than in the previous image, due to the higher w/c and the longer hydration time.

Fig. 6

3-D image (64 voxels by 64 voxels by 64 voxels) for w/c = 0.45 cement paste hydrated for 137 h. Only the unhydrated cement particles are shown for clarity.

Fig. 7

2-D image (1024 pixels by 1024 pixels) of slice 151 for dry Plaster of Paris powder.

Fig. 8

2-D image (1024 pixels by 1024 pixels) of slice 251 for w/s = 1.0 Plaster of Paris hydrated for 15.5 h. Large grey particles are unhydrated calcium sulfate hemihydrate. Grey needles (typically about 50 µm in length) are calcium sulfate dihydrate product. “Pore” impressions of totally and partially reacted starting particles are easily visible.

Fig. 9

3-D image (100 voxels by 100 voxels by 100 voxels) of a portion of the w/s = 1.0 Plaster of Paris hydrated for 4 h. A variety of needle-like and flat plate crystals of calcium sulfate dihydrate can be seen.

Fig. 10

2-D image (512 pixels by 512 pixels) of the clinker brick microstructure. Slit-like pores are dark grey and solid brick material is lighter grey. The image is approximately 0.5 mm by 0.5 mm.