CCRL Cements 135 and 136 have been quantitatively characterized based on SEM/X-ray imaging. The quantitative phase compositions estimated from the SEM images differ significantly from those computed using the formulas developed by Bogue. Based on the SEM/X-ray analysis, starting three-dimensional cement particle microstructures were created and hydrated using the CEMHYD3D program. Model predictions for degree of hydration, heat of hydration, and mortar strength development were compared to their experimental counterparts, with reasonably good agreement. It is planned to continue to perform the SEM and CEMHYD3D analyses on all future cements issued in the CCRL proficiency sample program and make the SEM results available in the online database available at http://ciks.cbt.nist.gov/phpct/database/images.