Testing of industrial products - Aggregates for construction

Particle Density and Water Absorption of Coarse Aggregate - Summary

This report gives the results of a cross-testing experiment on two test methods that are to be used to determine the particle density and water absorption of aggregate, the "pre-dried" and "SSD" methods. 20 laboratories took part from 12 countries, and three coarse aggregates were used in the experiments with differing particle densities and water absorptions.

When assessed by the criterion that the reproducibility standard deviation should not exceed 8 % of the average, the determination of the water absorption of coarse aggregate is found to have a reproducibility that fails to meet the criterion, marginally. Both the "pre-dried" and "SSD" methods of determining the particle density of coarse aggregates have adequate reproducibility for the purpose of calculating the yield of concrete mix designs, if it is assumed that errors in yield of up to 1 % are acceptable.

In principle, it should be possible to carry out the "SSD" method, and then do one further weighing to obtain the "pre-dried" result, so that laboratories that have experience with one method could obtain experience with the other from a small amount of extra work. Unfortunately the methods differ in some small details so this is not possible. Sensitivity analysis suggests that the "pre-dried" and "SSD" methods could be harmonised by using the correct density of water in the "SSD" method (allowing for temperature, as in the "pre-dried" method), and allowing a tolerance of ±3°C for the temperature of the water in the "pre-dried" method (as in the "SSD" method). Several laboratories obtained outlying between-test-result ranges in the determination of particle density and water absorption by the "SSD" method: it is therefore recommended that duplicate tests should be required in this method (as in the "pre-dried" method).

Several laboratories also obtained outlying laboratory averages in these tests, so it is recommended that the establishment of a proficiency testing scheme should be considered, to provide a means whereby laboratories can verify their data. When the volume of a pyknometer is being established, weighings should be made to an accuracy of 0.01 % of the capacity of the pyknometer (not to 0.1 % of the mass of a test portion or test specimen).

The results allow the precision of the tests to be stated as:

Pre-dried density

r1 = 0.012 Mg/m3

R1 = 0.023 Mg/m3

SSD density

r1 = 0.014 Mg/m3

R1 = 0.021 Mg/m3

SSD water absorption

r1 = 0.12 + 0.039 X %

R1 = 0.22 + 0.116 X %

where "X" represents the average of the test results.