Testing of industrial products - Aggregates for construction

Details of the cross-testing experiments on the Fragmentation Dynamique test

Laboratories

20 French laboratories took part in the experiment. The laboratories have been given numerical codes. For the purposes of this report they have also been assigned letter-codes (because single-character codes are needed in the graphs).

Materials

Samples of three materials were prepared and distributed by Partner 1. The samples were prepared, for each level of the experiment, as if they were laboratory samples all taken from one bulk sample. A report describing their preparation is available (Delalande, 1994. Strength tests programme; preparation of laboratory samples. LCPC, Paris, 24 November 1994.). The same three materials were used in all the cross-testing experiments of this project involving tests of the mechanical strength of aggregates.

Data

The FD test method requires test results to be rounded to the nearest whole number. However, for the purpose of the cross-testing experiment, the test results were recorded to the nearest 0.1 FD units. This was to prevent rounding of the data affecting the assessment of the repeatability and reproducibility of the test method.

Averages and ranges

Laboratory averages are used to calculate the reproducibility of the test method, and to assess laboratory biasses. Between-test-portion ranges are used to calculate the repeatability of the test method, and to assess the repeatability of tests from individual laboratories.

The averages and ranges are shown in the histograms, and the laboratory averages are plotted in the X-Y plots.

The averages and ranges are also used to test for stragglers and outliers. Where these have been found, they are indicated throughout using a single question mark (?) to indicate a straggler, and a double question mark (??) to indicate an outlier.

Standardised values of the averages and ranges are shown in the Mandel plots. These graphs are used to identify laboratories that give rise to large laboratory biasses, or large between-test-portion ranges, in more than one level of an experiment. The horizontal broken lines in these graphs show the critical values of the "h" and "k" statistics at the 5 % and 1 % significance levels, taken from the ISO standard on precision (ISO 5725, 1994).