Definition of Flakiness index and Elongation index

Sunday, April 7, 2013 19:45
Posted in category Transportation Engineering
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Flaky particles

The particles whose least dimension is less than 0.6 times the mean size dimensions.

Elongated particles

The particles whose greatest dimension is greater than 1.8 times the mean size dimension.

Mean size of aggregates

Mean size of aggregates is defined as the mean of two seive sizes, between which the particle is retained.

Mean size = (Passing sieve size + Retaining sieve size)/2

Flakiness index

The percentage by weight of flaky particles present in a given test sample.

Elongation index

The percentage by weight of the elongated particles present in a given test sample.

Significance and use

The particle shape of the aggregate is determined by

  1. The percentage of flaky and elongated particles that it contains.
  2. Its angularity number.

Why Flaky and elongated particles are to be avoided ?

Flaky and elongated aggreagates are to be avoided in flexible pavements. Because these causes weakness and breakdown under heavy traffic loads. In concrete pavements these reduces the workability.

BS Specification

According to BS specifications flakiness index of the aggregate used for the road construction should not be greater than 35 % and Elongation index should not be greater than 45 %.

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