Exp 1 Flakiness and Elongation Index

Flakiness and Elongation Index

EXPERIMENT NO. 1:

Determination of the flakiness and the elongation index for the given aggregate. sample.

SCOPE & SIGNIFICANCE:

This test is used to determine the particle shape of the aggregate and each particle shape being preferred under specific conditions.

The significance of flakiness & elongation index is as follows;

  • The degree of packing of the particles of one size depends upon their shape.
  • Due to high surface area to volume ratio, the flaky and elongated particles lower the workability of concrete mixes.
  • Flaky and elongated particles are considered undesirable for base coarse construction as they may cause weakness with possibilities of braking down under heavy loads.
  • BS-1241 specifies a Flakiness index not exceeding 30% irrespective of the aggregate size.
  • Maximum permitted Elongated index is 35, 40 or 45% for aggregate sizes     2 ½’’ – 2’’, 1 ½’’ – ¾’’ & ½’’ – 3/8’’.
  • Both Flakiness and Elongation tests are not applicable to sizes smaller then 6.3mm i.e. ¼’’ sieve.

RELATEDTHEORY:

SHAPES OF PARTICLES

The usual shapes of the particles are;

  1. Rounded (river gravel) Flakiness and Elongation Index
  2. Flaky (laminated rock) Flakiness and Elongation Index
  3. Elongated Flakiness and Elongation Index
  4. Angular( crushed rock) Flakiness and Elongation Index

Flat_elongated IMG_1142-20mmlanarkred Round-Gravel-20-40mm1 slate-300x225 spey_chip_104

PREFERRED USE OF EACH SHAPE

Rounded aggregates are preferred in concrete roads (rigid pavements) as the workability of concrete increases due to the less friction between the surfaces.

Angular shape of the particles is desirable in granular base coarse (flexible pavement) due to better interlocking and increased stability.

Flaky and Elongated particles are considered as a source of weakness.

APPARATUS: Flakiness and Elongation IndexFlakiness and Elongation Index

  • Thickness/Flakiness Index Gauge
  • Length/Elongation Index Gauge
  • Aggregate sample to be tested

FLAKY

  • A flaky particle is the one whose least dimension (thickness) is than 0.6 times the mean size.
  • These are the materials of which the thickness is small as compared to the other two dimensions.
  • Limit of flaky particles in the mixes is 30%. If the flaky particles are greater than 30% then the aggregate is considered undesirable for the intended use.

FLAKINESS INDEX Flakiness and Elongation Index

It is the percentage by weight of flaky particles in a sample.

Procedure

  • Perform the sieve analysis on the given aggregate sample
  • The aggregates are then arranged in the into a number of closely limited particle size groups -stored orted on the test sieves into a number of closely limited particle size groups – 2 ½’’ – 2’’, 1 ½’’ – ¾’’ & ½’’ – 3/8’’
  • Each group (fraction) is weighed and tested for thickness on appropriate opening of the thickness gauge by passing each particle through slot of specified thickness along least dimension.
  • The weight of particles passing the thickness gauge is recorded for each fraction. This is the weight of flaky particles.
  • The flakiness index is calculated by expressing the weight of flaky particles as a percentage of total weight of the sample.

Calculation for Flaky Particles:

Sieve Size Weight Retained Percentage Retained Weight of Flaky Particles Individual Flakiness Index Weighted Flakiness Index
Passing Retained (gm) (%) (gm) (%) (%)
(in.) (in.)
2 1 ½ 2007.8 22.52 80.5 4.01 0.9
1 ½ 1 2926.4 32.83 853.1 29.15 9.6
1 ¾ 2177.7 24.43 585.6 26.89 6.57
¾ ½ 1076.2 12.07 291.7 27.1 3.27
½ 8-Mar 460.2 5.16 155.5 33.79 1.74
8-Mar ¼ 211.8 2.38 88.3 41.69 0.99
¼ Pan 53.4 0.6
Σ= 8913.5 Σ = 23.07

ELONGATED PARTICLES

These are the particles having length considerably larger than the other two dimensions and it is the particle whose greater dimension is 1.8 times its mean size.

Limit of elongated particles in the mixes is 45%. Thus, if the elongated particles are greater than 45%, then the aggregate is considered undesirable for the intended use.

ELONGATION INDEX

It is the percentage by weight of elongated particles in a sample. The Elongated index is calculated by expressing the weight of Elongated particles as percentage of total weight of the sample.

Calculation for Elongated Particles:

Sieve Size Weight Retained (gm) Percentage Retained Weight of Elongated Particles Individual Elongation Index Weighted Elongation Index
Passing Retained (%) (gm) (%) (%)
(in.) (in.)
2 1 ½ 2007.8 22.52 1561.5 77.77 17.52
1 ½ 1 2926.4 32.83 950 32.46 10.66
1 ¾ 2177.7 24.43 1113.8 51.15 12.5
¾ ½ 1076.2 12.07 467.5 43.44 5.24
½ 41341 460.2 5.16 185.5 40.31 2.08
41341 ¼ 211.8 2.38 80.9 38.2 0.91
¼ Pan 53.4 0.6
Σ=8913.5 Σ = 48.91

PRECAUTIONS:

  1. While sieving, care must be taken that the particles that are chocked in the sieve must no be forced down into the next sieve. Such particles should be pushed back into the same sieve.
  2. While placing different fractions on the table, place them some distance apart so that no two fractions may get mixed.
  3. Be careful while selecting the opening of the flakiness and elongation gauges for any particular fraction.Flakiness and Elongation Index Flakiness and Elongation Index





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38 Replies to “Exp 1 Flakiness and Elongation Index”

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  6. But what should we put in it’s Result?
    Should We put like the following?

    Flakiness : 30% Elongation: 45%

    or We can Put it like 30+45= 55% Flakey Elongation Index???

    Tell me about Falaky Elongation Index?

    Thanking you So Much

    How can i be in touch with you?
    means any Facebook ID?

  10. how can i get tutorials of software like primavera..???
    it requires permission
    what I can do to get permission??

  11. WHAT IF I GET THE FLANKINESS INDEX 12% AND ELONGATED 18%
    WHAT IT MEAN THEN?

  12. It is easy learning process for Civil Engineers..It really helps us…

  14. Am afraid your calculation is wrong. You have added the masses retained that is less than 5% of the total retained!!!! The Mass to be used for the final calculation should have been 6,641.30g except if you are using any other standard besides the BS. Please check!

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  18. On Thursday, December 15, 2016 10:50 PM, Tajuddin mughal wrote:

    On Thursday, December 15, 2016 10:35 PM, Tajuddin mughal wrote:

    Experiment No.1 Flakiness and Elongation of coarse Aggregates.
    The dimensions of slots of the apparatus used in your experiment and figured in your article is as follows:-
    For elongation spokes, the distance is 1.8times the average of the sieve sizes used to separate the group, and 0.6times the average of the sieve sizes is the width of the slot used in the experiment. For example; For the group passing 25mm sieve and retained on 20mm sieve the length scale spokes are 1.8*(25+20)/2=40.5mm apart and for flakiness scale the width of the slot is 0.6*(25+20)/2=13.5mm.

    This indicates that material particles longer than 40.5mm say 41mm will be elongated particles and the particles thinner than 13.5mm say 13mm will be considered flat particles. This means that the particles of the material 42mm long and 12.5mm will not qualify the test. Similar with other groups separated with other sieves.
    The National Highway Authority of Pakistan specifies the ratio as 2.5: 1. This means that the particles 25*2.5=62.5mm in length and 20/2.5=8mm thin do qualify the NHA specifications.
    The best solution to the problem is to use Vernier Calipers or the adjustable vernier used in ASTM d 4791.
    Thanks Tajuddin Mughal M E. EA consultants Karachi.
    E Mail tajuddin_ mughal@yahoo.com.

  20. sir please what is flakiness,and elongation ‘s limit sir .
    sir reply me