Testing of industrial products - Aggregates for construction

Magnesium Sulfate Test - Summary

This report gives the results of a cross-testing experiment on the Magnesium Sulfate test involving 9 laboratories from 7 European countries. The experiment used the same three coarse aggregates as were used in an experiment on the Freeze/Thaw test that was carried out at the same time.

The reproducibility of the Magnesium Sulfate test exceeds the level of 8% 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 the freeze/thaw value. It is recommended, therefore, that laboratories should consider taking part in proficiency tests as a way of improving the reproducibility of the test.

A number of possible ways of improving the reproducibility of the Magnesium Sulfate test can be identified. For example: the tolerance permitted on the temperature of the magnesium sulfate solution could be reduced. The solution could be topped up with saturated magnesium sulfate solution at 25C whilst the specimens are being cooled after being taken out of the oven. A requirement could be imposed on the relative temperatures of the solution and the specimens at the time the specimens are added to the solution. A requirement could be added that the specimens are to be placed in the desiccator whilst they are being cooled. It would be of interest to study the rate at which the specimens loose mass during drying in the oven, to check that they reach a stable mass before the end of the 24 h drying period specified in the CEN method, and also to check that the final mass is not sensitive to the chosen drying temperature. The use should be considered of ruggedness trials to establish the sensitivity of the test results to such variations in details of the way the test is carried out.

It would be helpful if the method contained a timetable to show users how the five soaking/drying cycles can be fitted into the working week, and how the specimens are to be stored over weekends.

The results of the cross-testing experiment allow the precision of the Magnesium Sulfate test to be summarised, approximately, by the relations:

Wc = 0.14sqrt{X(100 - X)} and r1 = 0.15sqrt{X(100 - X)} and R1 = 0.52sqrt{X(100 - X)}