The particle size distributions of CCRL cements 135 and 141 were determined using laser diffraction techniques at the laboratories of Dyckerhoff Zement in Germany. For the measurements, a HELOS instrument type RODOS T4.1 from SYMPATEC GmbH, Germany1 was used. The focal distance of the HELOS instrument was set at 87.5 µm, allowing the measurement of particles with diameters between 0.25 µm and 87.5 µm. The measuring time varied between 10 s and 30 s per sample. The average PSD curves for each cement are shown in Figure 1. The PSDs measured for the two cements are seen to be quite similar, as are their Blaine finenesses (cement 135: 394 m2/kg and cement 141: 397 m2/kg) as measured via the standard ASTM C204 technique  in the CCRL testing program [4,5]. These measured PSDs are used as one direct input into the VCCTL software.