Testing of industrial products - Aggregates for construction

The Flakiness Index test method

The principle of the method

The test consists of two sieving operations. In the first operation, the test portion is sieved into size fractions di/Di using test sieves with square holes. The sieves used for this operation are members of the ISO R20 series such that di / Di = 0.8 (approximately). In the second operation, each size fraction di/Di is sieved using a bar sieve with parallel slots of width Di/ 2.

The Flakiness Index (FI) is calculated as the mass of particles that pass the bar sieves, expressed as a percentage of the mass of the test portion.

If the three dimensions of a particle are denoted by L1, L2 and L3, with L1 < L2 < L3, then for the particle to fall within a size fraction di/Di, the middle dimension must satisfy, approximately, the inequality:

0.8 Di < L2 < Di

and for the particle to be classed as flaky, the smallest dimension must satisfy, approximately, the second inequality:

L1 < 0.5 Di

so that, according to this test method, flaky particles are those for which, approximately, their smallest two dimensions satisfy:

L1 < 0.625 L2 .

The proposed CEN method

The CEN test method has been developed from the French Standard P 18-561 (AFNOR, 1990. P 18-561 Granulats. Mesure du coefficient d'aplatissement.). The methods are identical except that the tolerances allowed on the widths of the slots in the bar sieves are stricter in the CEN method than in the French method.

Participants in the cross-testing experiment were sent copies of the method that was sent to CEN members for formal voting in May, 1995.