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Methods for the determination of resistance to fragmentation

BS EN 1097 Part 2
This specification sets out two tests: the Los Angeles Coefficient (which is described as the reference test), and the Impact Test (an alternative test which can be used once a correlation to the Los Angeles test has been established). The purpose of these is to test the strength of the aggregate and how easily it breaks apart.

The test method for the Los Angeles Coefficient involves a test aggregate sample with particles between 10 mm and 14 mm in size. The sample is rotated in a steel drum (larger than that used for the micro-Deval test), which contains a projecting shelf inside, with a specified quantity of steel balls, at a speed of 31 to 33 revolutions per minute for 500 revolutions. The Los Angeles Coefficient is calculated from the proportion of the sample reduced to less than 1.6 mm in size.

The lower the coefficient the more resistance the aggregates have to fragmentation. The result is expressed as a 'category', such as LA 15 or LA 20 , where the number represents the maximum value of the coefficient for the sample.
  For use in concrete or asphalt the actual number should be declared if it is greater than 50. For unbound roadstone it should be declared if over 60.

The Impact Test requires the test sample to have particle sizes between 8 mm and 12.5 mm. It involves crushing the sample in a special impact machine by 10 blows from a height of 370 mm. The sample is then sieved using five test sieves and the impact value is calculated.

The lower the impact value the more resistance the aggregate has to fragmentation. The result is expressed as a 'category', such as SZ 18 or SZ 22 , where the number represents the maximum impact value for the sample. For use in concrete or asphalt the actual number should be declared if it is greater than 32, and for unbound roadstone if it is over 38.







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