Testing of industrial products - Aggregates for construction

Flakiness Index Test - Summary

This report gives the results of two cross-testing experiments on the determination of Flakiness Index - a "European" experiment involving 20 laboratories from 12 countries, and a "French" experiment involving 9 French laboratories. (Two of the French laboratories were included in both experiments.) The same three materials were used in the experiment on the Flakiness Index test as were also used in an experiment on the Shape Index test that was carried out at the same time.

Using statistical theory, it is shown that the repeatability of the Flakiness Index test can be calculated from the test portion mass (M), the upper aggregate size (D), and the level of Flakiness Index (FI) in FI units (%), using the formula:

r1,pred = 0.0028 sqrt{ FI (100 - FI) D3 / M }

The data obtained in the European experiment give estimates of repeatability that agree with those calculated using this formula. It is recommended that laboratories should do duplicate tests regularly, and use the results to check that their repeatability agrees with that predicted by the above formula.

The formula may be rearranged to allow the test portion mass that gives a chosen level of repeatability to be calculated from the aggregate size and the level of Flakiness Index of interest. Using this result, a table can be presented giving the test portion masses required to achieve a chosen, satisfactory, level of repeatability. Further, if the masses given in such a table were to be used in practice, the repeatability of the test method could be stated simply as the chosen level of repeatability.

The results of the European experiment allow the reproducibility of the Flakiness Index test to be stated in FI units (%)as:

R1 = 0.95 + 0.226 FI

This reproducibility exceeds the level that is considered to be desirable for a test that is to be used to check the compliance of aggregates with specifications that impose an upper limit on flakiness. Using test portion masses that give a satisfactory level of repeatability will help improve the reproducibility of the Flakiness Index test. It is also recommended that laboratories should take part in regular proficiency tests. This will be of particular value for laboratories that have previously had little experience with the test.