Flakiness index

While the shape factor, introduced in the previous section, provides a quantitative definition or description of particle shape, there are other descriptors such as flakiness ratio, flakiness index, elongation index and angularity number which are also found to be in vogue. 

Part 2 Determination of particle size — Test sieves, nominal size of apertures Part 3 Determination of particle shape of aggregates — Flakiness index Part 4 Determination of particle shape of aggregates — Shape index... 

BS 882 specifies that the flakiness index shall not exceed 40 for crushed rock. 

As flaky particles are prone to breakage when loaded, a low flakiness index is sometimes specified. 

In the UK, BS 63 specifies limits for grading and flakiness index for eight single-sized grades (50, 40, 28, 20,14,10, 6 and 3 mm). These are blended to give the required particle size distribution as specified in [8.19, 8.20]. 

Part 3 Determination of particle shape of aggregates - Flakiness index . 

The total Flakiness Index is designated as the total aggregate mass passing through each bar sieve, expressed as the percentage of the total sample mass of dry aggregates tested. 

If the Flakiness Index for each aggregate size d/D, is required, it is calculated by the mass passing through the bar sieve expressed as a percentage of mass of the respective aggregate size. 

Source Reproduced from CEN EN 933-3, Tests for geometrical properties of aggregates - Part 3 Determination of particle shape - Flakiness index,... 

More information, as well as a calculation example, is presented in CEN EN 933-3 (2012). The Flakiness Index value determined in accordance with the European specification differs from the one determined by BS 812-Part 105, which was used in the past by many countries. Thus, care must be taken to the limiting values that may have been set. 

Aggregate type Aggregate shape Flakiness Index (%) Shape adjustment Factor, Va (L/m Imm)... 

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