This report gives the results of a cross-testing experiment on the Sand Equivalent test involving 34 laboratories from 12 European countries. The experiment used the same three sands as were used in an experiment on the methylene blue dye adsorption test that was carried out at the same time.
When assessed by the criterion that the reproducibility standard deviation should not exceed 8 % of the average, the Sand Equivalent test is found to be just satisfactory for two sands used in the experiment, but not satisfactory for the third sand (the one that gave the lowest SE value). The results suggest that it should be possible to improve the reproducibility of the Sand Equivalent test by, for example, proficiency testing.
The repeatability of the Sand Equivalent test is such that the range of the results obtained on two test specimens from the same laboratory sample should rarely exceed 3 SE units.
It is French practice to follow a Sand Equivalent test with a determination of the fines content of the test specimen (by washing the test specimen over a 0.080 mm sieve). It would have been informative to have required the participants in the cross-testing experiment to have done this (using the 0.063 mm sieves adopted now for the determination of fines) to provide a check on the uniformity of the samples distributed in the experiment.
The results of the cross-testing experiment allow the precision of the Sand Equivalent test to be summarised by the relations:
r1 = 1.4 + 0.03(100 - X)
R1 = 1.4 + 0.25(100 - X)
for values of Sand Equivalent (X) in the range 40 <= X <= 60 SE units.