AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
GROUP 5 – SECTION 7
1.0 INTRODUCTION
The particles shape of aggregates is determined by the percentages of flaky and elongation particles. Flaky and elongation particles are considered undesirable as they cause weakness of the pavement. Rounded aggregates are preferred in cement concrete pavements as the workability of concrete improves. Regular shapes of particles are desirable for granular base course due to increased stability desired from better interlocking. When the shape of aggregates deviates more from the spherical shape, as in the case of angular, flaky and elongation aggregate the void content increase and hence the grain size distribution of the aggregates has to be suitable altered in order to obtain minimum voids in the dry mix on the maximum density.
2.0 OBJECTIVE
To determine the flakiness and elongation indices of the given aggregate sample 3.0 FLAKINESS INDEX
Aggregate particles are classified as flaky when they have a thickness (smallest dimension) of less than 0.6 of their mean sieve size. The flakiness index of an aggregate sample is found by separating the flaky particles and expressing their mass as a percentage of the mass of the sample tested. This test is not applicable to aggregate passing 6.30mm sieve and retained as 63.0mm sieve.
4.0 ELONGATION INDEX
Aggregate particles are classified as elongation when they have a length (greatest dimension) of more than 1.8 of their mean sieve size. The elongation index is found by separating the elongation particles and expressing their mess as a percentage of the mass of sample tested. The test is not applicable to material passing 6.30 mm sieve or retained on 50 mm sieve.
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
4.1
GROUP 5 – SECTION 7
Equipments Flakiness Index and Elongation Index
1. Metal thickness gauge
2. Test sieve
3. Trays
4. Metal length gauge
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
4.2
GROUP 5 – SECTION 7
Procedure Flakiness Index
1. The sieve sample with sieves mentioned in Table 7.1. Weight each of the individual size fractions (w1, w2, w3) retained on these sieve, other than the 63.0 mm sieve and store them in separate trays marked with their size.
2. Gauge each fraction from the respective slots in the thickness gauge weigh pieces which pass through the slots (x1, x2, x3)
4.2.1
Calculations and Results.
x x2 x3 ..... Flakiness Index 1 100 w1 w2 w3 ...... Where: x1, x2, x3 are the weight of the fractions passing from the thickness gauge w1, w2, w3 are the weight of the original sample retained as the corresponding sieve
4.3
Procedure Elongation Index
1. Sieve the sample with sieve mentioned in weight each of the individual size fractions (w1, w2, w3). Retained on these sieves other than the 50.0 mm sieve. 2. Gauge each fraction as follows, select the length gauge appropriate to the single fraction under test and gauge each particle separately by hand. Elongated particles are those whose greatest dimension prevents them from passing through the gauge. Weigh each fraction which doesn’t pass through the gauge (y1, y2, y3)
4.3.1
Calculations and Results.
y y 2 y3 ..... Elongation Index 1 100 w1 w2 w3 ...... Where: y1, y2, y3 weight of the fractions not passing through the length gauge w1, w2, w3, are the weight of the original sample on the corresponding sieve. Page 3 of 9
AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
GROUP 5 – SECTION 7
Table 2 data for Determination of Flakiness Index Aggregate Size Fraction BS test sieve nominal aperture size
Width of slot in thickness Minimum mass for Gauge or special subdivision 100% passing 100% passing sieve mm mm mm kg 63.0 50.0 33.9 ± 0.3 50 50.0 37.5 26.3 ± 0.3 35 37.5 28.0 19.7 ± 0.3 15 28.0 20.0 14.4 ± 0.15 5 20.0 14.0 10.2 ± 0.15 2 14.0 10.0 7.2 ± 0.1 1 10.0 6.3 4.9 ± 0.1 0.5 This dimension is equal to 0.6 times the mean test sieve size
Table 3 data for Determination of Elongation Index Aggregate Size Fraction
Width of slot in
BS test sieve nominal aperture size
thickness
Minimum mass for
Gauge or special
subdivision
100% passing
100% passing
mm
mm
mm
kg
50.0
37.5
78.7 ± 0.3
35
37.5
28.0
59.0 ± 0.3
15
28.0
20.0
43.2 ± 0.15
5
20.0
14.0
30.6 ± 0.15
2
14.0
10.0
21.6 ± 0.2
1
10.0
6.3
14.7 ± 0.2
0.5
sieve
This dimension is equal to 1.8 times the mean test size.
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
5.0
RESULT AND DATA ANALYSIS
i).
FLAKINESS INDEX
GROUP 5 – SECTION 7
Passing sieve (mm)
Retained sieve (mm)
Sample (gm)
Passing (gm)
Retained (gm)
28
20
5000
357
4643
20
14
2000
623
1387
14
10
1000
198
802
10
6.3
500
120
380
TOTAL
8500
1298
Flakiness Index
357 5000 100 7.14 623 2000 100 31 .15 198 1000 100 19 .8 120 500 100 24
x x 2 x3 ..... Flakiness Index 1 100 w1 w2 w3 ...... 1298 100 8500 15.27%
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
ii).
GROUP 5 – SECTION 7
ELONGATION INDEX
Passing sieve (mm)
Retained sieve (mm)
Sample (gm)
Passing (gm)
Retained (gm)
28
20
5000
5000
0
20
14
2000
1889
111
14
10
1000
949
51
10
6.3
500
429
71
TOTAL
8500
Flakiness Index
0 5000 100 0 111 2000 100 5.55 51 1000 100 11 .1 71 500 100 14 .2
233
x x 2 x3 ..... Elongation Index 1 100 w1 w2 w3 ...... 233 100 8500 2.74%
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
6.0
GROUP 5 – SECTION 7
DISCUSSION
The Flakiness Index is the mass of particles in that aggregate expressed as a percentage of the total mass of that aggregate which will pass the slot or slots of specified width for the appropriate size fraction. While elongation index test is used to determine the quantity of aggregate particles that are elongated instead of cubicle in shape. The particles are classified as flaky or elongated particles according to the rather arbitrary assumption that are particles is flaky if its flaky is loss than 0.6 times the sieve size and that a particle is elongated if its long is greater than 1.8 times the sieve size. In this experiment, flakiness index was used as independent variables and other properties such as gradation are kept constant as far as their properties met the specification required for the asphalt mixture. According to British Standard Institution (BSI-812, 1975) classifies aggregate into six classes that are rounded, irregular, angular, flaky and elongated and elongated. The rounded, irregular and angular for special purpose are group into the category an equidimensional or cuboidal. The aggregate are flaky, elongated, flaky and elongated or equal dimension are determined by the ratio of the shortest, the largest and average diameter of the particles. From the experiment, firstly we separate aggregate sample by sieving into different size fraction, each falling within a narrow size function is essentially a single-size aggregate. The sieve size rage are (20 ± 40) mm, (14 ± 10) mm and (10 ± 6.3) mm. From the data experiment, we made the calculation and discussed by the all group member. When this experiment is doing, we make some experimental error such as when sieving process is being take place. For examples, the aggregate may not trough sieve by machine and some of aggregate we shake manually by hand. Besides, the error do occur when the weighing the amount of aggregate that we need. The careless attitudes that we gauge the particles separating by hand. Maybe we pass the particles to the wrong gauge. It is because we have separate too many particles in the short time.
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
7.0
GROUP 5 – SECTION 7
CONCLUSION
Based on the objective for this experiment is to identify the flakiness and elongation index of the given aggregate samples, we indentified the flakiness and elongation is not influence each other. We get the value for the flakiness index is 15.27% and for the elongation index is 2.74%. We get so much different compare both of the two values. Aggregate particles are classified as flaky when they have a thickness (smallest dimension) of less than 0.6 of their mean sieve size. The flakiness index of an aggregate sample is found by separating the flaky particles and expressing their mass as a percentage of the mass of the sample tested. From the experiment, the mean flakiness index is 31.15 (sieve 20mm) and flakiness index is 15.27%. So we get 0.49 < 0.6. We can classify the sample as the flaky sample. Aggregate particles are classified as elongation when they have a length (greatest dimension) of more than 1.8 of their mean sieve size. The elongation index is found by separating the elongation particles and expressing their mess as a percentage of the mass of sample tested. From the experiment, the mean 14.2 (sieve 10mm) and elongation index is 2.74%. So we get 5.18 > 1.8. We can classify the sample as the elongation sample. As a conclusion, the sample that we tested are flaky and elongation, which is there are not suitable to use in parameter design. This will cause the increase of void in the mix. If we use in highway construction, we must doing more compaction to ensure that the void meet the prescribe specification.
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AGGREGATE SHAPE TEST (FLAKINESS INDEX & ELONGATION INDEX)
8.0
GROUP 5 – SECTION 7
REFERENCES
i.
British Standards Methods of determination of particle shape BS 812, Part 105, 1989.
ii.
Kenneth N. derucher and George P .Korfiatis, Material for civil and highway engineers, Prentice Hall, NJ 2nd edition,1988.
iii.
Harold N. Attkins, Highway materials, soils and concretes, 3rd edition, Prentice Hall, 1990
9.0
APPENDIX 1. Apparatus
Figure 1 : Digital Mass
Figure 2 : Shape Test Apparatus
2. During Experiment
Figure 3 : Measure Flakiness And Elongation
Figure 4 : Measure The Mass Passing And Retained Aggregate
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