Shape Tests on Aggregates – Flakiness Index and Elongation Index

Flakiness index is defined as the percentage by weight of the particles in it whose thickness is less than three- fifths (0.6 times) of their mean dimension.

  • This test is conducted to determine the thickness of the aggregates.
  • This test can help to prevent structural failures and ensure long -term safety and  stability of civil engineering projects and building structures.
  • The specifications for this test are given in IS : 2386 Part I 1963 Particle size and shape.

Flakiness index test

Procedure

  • A metal thickness gauge is the instrument used to conduct this test.
  • A sufficient quantity of aggregate is taken such that a minimum 200 pieces of any fraction is tested.
  • The sample is sieved through IS sieves as given below. 
  • The total amount passed in the gauge is measured and weighed.

Dimensions of thickness and length gauge

image 23

FLAKINESS INDEX

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flakiness

Elongation Index test

Elongation index is defined as the percentage by weight of the particles in it whose length is greater than 1.8 times of their mean dimension.

  • This test is conducted to determine the length of the aggregates.
  • When under pressure, materials having a high elongation index are more likely to distort or fracture, endangering the safety of structures. 
  • Civil engineers may make sure the materials they choose are high quality and appropriate for their intended applications by keeping an eye on the elongation index of aggregate materials.
  • The specifications for this test are given in IS : 2386 Part I 1963 Particle size and shape.
See also  Guide to Sieve Analysis Test for Fine Aggregate
elongation

Procedure

  • A metal length gauge is the instrument used to conduct this test.
  • A sufficient quantity of aggregate is taken such that a minimum 200 pieces of any fraction is tested.
  • The sample is sieved through IS sieves as given below. 
  • The total amount retained on the gauge length is weighed.

Elongation Index 

image 24

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