Flakiness Index
Understanding Flakiness and Elongation in construction aggregate
The percentages of flaky and elongated particles in aggregates determine their particle shape. For base course and construction of bituminous and cement concrete types, the presence of these particles is considered undesirable as they can cause inherent weakness and breakdown under heavy loads. Therefore, it is necessary to evaluate the shape of particles, particularly with respect to flakiness and elongation.
The Flakiness Index test determines the percentage by weight of particles whose least dimension (thickness) is less than three-fifths (0.6 times) of their mean dimension. This test is not applicable to particles smaller than 6.3mm. The Elongation Index test determines the percentage by weight of particles whose greatest dimension (length) is greater than nine-fifths (1.8 times) their mean dimension. This test is not applicable for particles smaller than 6.3mm.
Flakiness Index Test Method
The Flakiness Index test determines the percentage by weight of aggregate particles whose least dimension is less than 0.6 of their mean dimension. This test is applicable only to coarse aggregates.
To calculate the flakiness index of a sample, the weight of each fraction of aggregates passing and retaining on specified sieves is noted. The pieces of aggregate are then passed through a slot of specified thickness and weighed. The flakiness index is then calculated as the total weight of material passed through various thickness gauges, expressed as a percentage of the total weight of the sample gauged.
Relevance of Results
The Flakiness Index of aggregates used in road construction should be less than 15% and typically does not exceed 25%. It is not desirable to use flaky particles in the construction of roads, especially in the surface course, as they may break down easily when the load acts along the thin axis of the flaky flat particles. Therefore, the suitability of particles for use in road construction must be tested using the Flakiness Index test to prevent such conditions. This is the importance and relevance of the test.