it would be expected that the small particles would be detected. On the other hand, the detection of larger particles above the average size aperture size could be explained by particle shape shadow effect as the particles pass through the laser beam. This could also explain the slight difference in particle size distribution (Fig. 1) between the larger fractions (600 and 710 lm). Another explanation for this finding could be attributed to the small difference in sieve size aperture of the sieves 710 and 800 lm, which was only 90 lm.