This report gives the results of a cross-testing experiment on the determination of the total sulfur content of aggregates involving 19 laboratories from 11 countries. The materials used in the experiment were a colliery shale, an industrial slag, and a ground blast-furnace sand.
The results of the experiments show that the reproducibility of the test is not good enough for it to be used as the reference method for the determination of the sulfur content of aggregates. This is when the determinations are to be used to check that the sulfur content complies with a specification limit around 1% or 2% sulfur. It is therefore recommended that attempts should be made to improve the reproducibility of the method by proficiency tests, robustness tests or the use of reference materials, or alternatively that another method should be sought, such as that based on X-ray fluorescence spectrometry given in BS EN 196-2.
Some laboratories obtained erratic results in the experiments. The test method requires duplicate tests, so users of the test should use the available information to check their repeatability. Laboratories that obtained erratic results in the experiments should try to find the reasons, then report their findings through their National Co-ordinators to Partner 1, so that the results of their investigations can be collated and made available to all users of the test.
At present the test method requires the results of determinations of sulfur contents to be reported to the nearest 0.01%. This is necessary when checking repeatability, but for checking compliance with limits around 1% to 2% it would be more appropriate to report the results to the nearest 0.1%.
The results of the experiment allow the precision of the determination of total sulfur to be stated (in terms of the sulfur content, as a percentage by mass of the aggregate) as:
r = 0.017 + 0.081 X and R = 0.062 + 0.204 X
where "X" represents the average of the test results. These values of r and R indicate the precision of the analytical method, but do not allow for the variations that occur when reducing a laboratory sample of coarse aggregate to material that passes a 0.125mm sieve. If these equations are quoted it should be noted that they are based on results for tests on only three materials.