Testing of industrial products - Aggregates for construction

Methylene Blue Test - Summary

This report gives the results of a cross-testing experiment on the Methylene Blue test involving 34 laboratories from 13 European countries. Three sands with differing levels of methylene blue dye adsorption were used.

When assessed by the criterion that the reproducibility standard deviation should not exceed 8 % of the average of the results, the Methylene Blue test is found to be far from satisfactory for the purpose of assessing the compliance of aggregates with specifications that impose an upper limit on the results of tests. It is recommended that laboratories should:

The repeatability of the Methylene Blue test is such that the range of the results of two tests on the same laboratory sample should rarely exceed 0.25 MB units.

The practice of adding the dye solution in increments of 5 mL and 2 mL imposes a lower limit on the repeatability and reproducibility of the test, so that it is not able to meet the 8 % criterion at levels of around 1.0 MB units (or less). It is recommended that the use of smaller increments should be considered if a specification limit of around 1.0 MB units (or less) is to be applied to the results of the test.

The results of the experiment allow the precision of the Methylene Blue test to be stated (in MB units) as:

r1 = 0.14 + 0.076 X

and

R1 = 0.14 + 0.622 X

where "X" represents the average of the test results.