Testing of industrial products - Aggregates for construction

Details of the cross-testing experiment on the determination of the Particle Density of Fillers

Laboratories

20 laboratories took part in the experiment from 13 European countries. 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 fillers were prepared and distributed by Partner 4. The three materials were chosen so that they would give a wide range of particle densities.

The samples were prepared, for each level of the experiment, as if they were laboratory samples all taken from one bulk sample, and the participants were required to prepare and test duplicate test portions from each sample. Hence the measures of repeatability and reproducibility given by the experiment are consistent with the definitions of r1 and R1 used here.

The laboratory samples were prepared by fractional shovelling. A bulk sample of about 25 kg of each filler was obtained. To prepare the laboratory samples from one of these bulk samples it was tipped out onto a tray, and twenty sample-containers were arranged around the heap. A small scoop with a capacity of about 15 g was used to take sampling increments and to transfer them to the sample containers, working around the containers in order, until each container contained about 0.5 kg.

Densities of the liquids used are reported below in Table A.


Table A. Densities of liquids.
Laboratory codeLiquid density
letternumberMg/m3
A310.865
B320.99707
C69-.----
D950.862
E960.863
F1060.862
G1280.862
H1290.862
I1530.860
J1900.861
K2040.862
L2340.862
M2490.9970
N2510.997
O2520.862 to 0.864
P2600.99707
Q2730.860
R3100.869
S1700.997
T2210.861

Data

Where a participant failed to report a determination, the missing value is shown as "-.----" in the data tables. The method for determining the particle density of filler requires test results to be rounded to the nearest 0.1 Mg/m3. However, for the purpose of the cross-testing experiment, the test results were recorded to the nearest 0.001 Mg/m3. This was to prevent rounding of the data affecting the assessment of the repeatability and reproducibility of the test method.

The data were checked to make sure that the recorded measurements were consistent with the calculated values of the mass, volume and particle density of each test specimen. There were many instances where the measured and calculated values were not consistent. This could be because of calculation errors, or transcription errors, or because the calculations were carried out on values for the measurements that were rounded before being reported. Where it was obvious that a calculation error had been made, the erroneous value was corrected.

Averages and ranges

Laboratory averages are used to calculate the reproducibility of the test method, and to assess laboratory biasses. Between-test-result ranges and between-test-specimen ranges or standard deviations 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 Mandel 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 figures are used to identify laboratories that give rise to large laboratory biasses, or large between-test-result ranges, or large between-test specimen standard deviations, 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 revised ISO standard on precision (ISO 5725, 1994).