Testing of industrial products - Aggregates for construction

Freeze/Thaw Test - Summary

This report gives the results of a cross-testing experiment on the proposed CEN method for the Freeze/Thaw test, involving 12 laboratories from 8 countries. The same three materials were used in the experiment as in the experiment on the magnesium sulfate test that took place at the same time.

The reproducibility of the Freeze/Thaw 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. It is also recommended that the method should require checks to be made that the temperature throughout the interior of the freezing cabinet remains uniform during the freezing period of the test, and that a record of the temperature curve achieved in a test portion in the middle of the cabinet should be provided as part of the test report for every test.

The use should be considered of ruggedness trials to establish the sensitivity of the test results to variations in details of the way the test is carried out, such as the rates of cooling at various points in the cooling cycle, and the minimum temperatures achieved. Such trials would show where tolerances in the method specification need to be tightened up to improve the reproducibility of the test.

The repeatability coefficient of variation of the Freeze/Thaw test exceeds 8% too, so it is recommended that laboratories should consider carrying out regular checks of both the between-test-specimen and the between-run components of repeatability. It may also be necessary to consider steps such as increasing the number of test-specimens, or tightening up the tolerances in the method so as to reduce the run to run variability.

The experiment allows the precision of the Freeze/Thaw test to be summarised by the following functional relations:

Wc = 0.03 + 0.39 X and r1 = 0.04 + 0.36 X and R1 = 0.07 + 0.62 X