Version 1.0 of CEMHYD3D included three computer programs (statsimp.c, corrcalc.c, and corrxy2r.c) for analyzing a segmented image of a two-dimensional cement (powder) microstructure to obtain the necessary correlation files for the two-dimensional to three-dimensional conversion of cement particles to be described subsequently . These programs have not changed and are still available for downloading from the ftp site provided in the Introduction. For version 2.0 of CEMHYD3D , an online database of cement images was created that contains representative segmented images, along with the necessary particle size distribution (PSD) and phase correlation files for creating three-dimensional microstructures. The database contains links to the ftp locations from where the PSD and correlation files can be downloaded (available directly at ftp://ftp.nist.gov/pub/bfrl/bentz/CEMHYD3D/images). The complete database is available at http://ciks.cbt.nist.gov/bentz/phpct/database/images. Between the release of version 2.0 in 2000 and the issue of the current release, the database has nearly doubled in size, going from 14 to 27 different cements, of varying chemical composition and PSD. An example image for Cement and Concrete Reference Laboratory (CCRL) proficiency cement sample 152 is provided in Figure 1.
Figure 1: Two-dimensional processed scanning electron microscopy (SEM)/X-ray image for cement 152 issued by the CCRL in January 2004. Color assignments are: brown- C3S1, blue- C2S, grey- C3A, white- C4AF, yellow- gypsum, red- K2SO4, green- free lime and/or calcite, aqua- free silica, and pink- periclase (magnesium containing phase). Image is 256 µm x 200µm.
 Conventional cement chemistry is used in this report: C=CaO, S=SiO2, A=Al2O3, F=Fe2O3, M=MgO,S =SO3 and H=H2O.