This report gives the results of two cross-testing experiments on the determination of the water-soluble chloride content of aggregates by Volhard titration - a "European" experiment involving 17 laboratories from 11 countries, and a "French" experiment involving 9 French laboratories. (Two of the French laboratories are included in both experiments.) The materials used in the experiments were an unwashed marine-dredged gravel, washed marine-dredged sand, and diluted sea-water.
The results of the experiments show that the reproducibility of the test is adequate for it to be used to determine the chloride content of an aggregate, when the determinations are to be used to check that the chloride content of concrete made using the aggregate complies with a specification limit. However, some laboratories obtained erratic results in the experiments. The test method requires two test portions to be tested, so users of the test will be able to check their repeatability. It is also recommended that, in future, laboratories should take part in regular proficiency tests. This will enable them to check that their results are reliable, identify problem areas, and assess the benefits of modifications to their procedures. Laboratories that obtained erratic results in the experiments should try to find the reasons, then report their findings through their National Coordinators 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 chloride contents to be reported to the nearest 0.01 per cent. However, this may conceal significant variations in the chloride contents of some products. The repeatability achieved in the cross-testing experiments justifies reporting the test results to the nearest 0.001 per cent, and this should therefore be adopted in practice.
The results of the "European" experiment allow the precision of the determination of water-soluble chlorides to be stated (in terms of the chloride ion content, as a percentage by mass of the aggregate) as:
r1 = 0.0004 + 0.029 X and R1 = 0.0006 + 0.124 X
where "X" represents the average of the test results.