Summary

The following findings are observed:

• The measurement by LAS-W exhibited some scatter, but elimination of outliers reduced the scatter considerably.
• The measurements by LAS-D or by EZS show a very large scatter. Because of the small data set size (2 PSDs per measurement method), it is not possible to determine the source of this scatter nor to determine which, if either, of the PSDs is an outlier, unless the data are compared to all the other sets.

The possible reasons that could explain some of the scatter observed in the data from all these tests are:

• The parameters used to determine the distribution from the measurement assume certain values for material properties, such as the index of refraction of the cement and of the medium or the density of the particles. Since these parameters are not standardized, and were not reported by the participants, different laboratories may have used different or incorrect values.

• The experimental conditions, such as the dispersion medium, the preparation of the specimen (dispersion method), as well as the instrument used to measure the PSD, may have varied between laboratories.

These observations point to the difficulties in determining the correct method and value for a cement PSD. In future round-robin testing, care should be taken to ensure that the same sample preparation method is used for each technique and that the parameter values used by the operators are also the same or determined using the same method. We recommend that the ASTM committee address the issue of determining the correct experimental set-up and sample preparation protocol for each measurement method.