Experiment no 03 Determination of the flakiness and the elongation index for the given aggregate sample.
- 1. Determination of the flakiness and the elongation index for the given aggregate sample. Experiment no: 03 Engr. Sayed Shajedul Hasan.
- 2. • The particle shape of aggregates is determined by the percentages of flaky and elongated particles contained in it. For base course and construction of bituminous and cement concrete types, the presence of flaky and elongated particles are considered undesirable as these cause inherent weakness with possibilities of breaking down under heavy loads. • Thus, evaluation of shape of the particles, particularly with reference to flakiness and elongation is necessary. THE FLAKINESS INDEX OF AGGREGATES is the percentage by weight of particles whose least dimension (thickness) is less than three- fifths (0.6times) of their mean dimension. This test is not applicable to sizes smaller than 6.3mm. THE ELONGATION INDEX OF AGGREGATE is the percentage by weight of particles whose greatest dimension (length) is greater than nine-fifths (1.8times) their mean dimension. This test is not applicable for sizes smaller than 6.3mm. Engr. Sayed Shajedul Hasan. THEORY
- 3. Engr. Sayed Shajedul Hasan. SHAPES OF PARTICLES The usual shapes of the particles are; Rounded (river gravel) Flakiness and Elongation Index Flaky (laminated rock) Flakiness and Elongation Index Elongated Flakiness and Elongation Index Angular( crushed rock) 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.
- 4. Engr. Sayed Shajedul Hasan. 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.
- 5. Engr. Sayed Shajedul Hasan. APPARATUS Balance Sieves Thickness gauge- for flakiness index Length gauge- for elongation index Sieves required are 63, 50, 37.5, 28, 20, 14, 10 and 6.3 mm (Based on requirement and Gradation of Aggregate).
- 6. Engr. Sayed Shajedul Hasan. PROCEDURE • Sieve the sample through the sieves (as specified in the chart). • Take a minimum of 200 pieces of each fraction to be tested and weigh them. • To separate the flaky materials, gauge each fraction for thickness on a thickness gauge. • Weight the flaky material passing the gauge to an accuracy of at least 0.1 per cent of the test sample. • To separate the elongated materials, gauge each fraction for length on a length gauge • To separate the elongated materials, gauge each fraction for length on a length gauge • Weigh the elongated material retained on the gauge to an accuracy of at least 0.1 per cent of the test sample.
- 7. Engr. Sayed Shajedul Hasan. PRECAUTIONS • 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. • While placing different fractions on the table, place them some distance apart so that no two fractions may get mixed. • Be careful while selecting the opening of the flakiness and elongation gauges for any particular fraction. Flakiness and Elongation Index Flakiness and Elongation Index Recommended Values of Flakiness Index and Elongation Index 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. 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.
- 8. Engr. Sayed Shajedul Hasan. OBSERVATIONS Sieve size (mm) passing Sieve size (mm) retained Sample weight (g) A Weight passing thickness gauge (g) B Weight of non flaky sample (g) C Weight of aggr. retained length gauge (g) D 28mm 20mm 2621 692 1929 351 20mm 14mm 1949 261 1688 606 14mm 10mm 735 423 312 101 10mm 6.3mm 32 5 27 20 total 5337 g 1381 g 3956 g 1078 g CALCULATIONS: Flakiness Index: Τ𝐵 𝐴 × 100 = Τ1381 5337 ∗ 100 = 25.88% Elongation Index: Τ𝐷 𝐶 ∗ 100 = Τ1078 3956 ∗ 100 = 27.25% Contained: Flakiness Index+ Elongation Index = 53.13%