Particle
shape and surface texture influence the properties of freshly mixed concrete
more than the properties of hardened concrete. Rough-textured, angular, and
elongated particles require more water to produce workable concrete than
smooth, rounded compact aggregate. Consequently, the cement content must also
be increased to maintain the water-cement ratio. Generally, flat and elongated
particles are avoided or are limited to about 15 % by weight of the total
aggregate.
AIM:
To determination of Flakiness
Index and Elongation Index of Course Aggregates.
Apparatus:
- Standard
thickness gauge.
- Standard length
gauge.
- IS Sieves of
size 63, 50, 40, 31.5, 25, 20, 16, 12.5, 10 & 6.3mm.
- Balance.
FIGURE:
Procedure:
1.
Sample - A quantity of aggregate shall be taken sufficient to
provide the minimum number of 200 pieces of any fraction to be tested.
2.
Sieving - The sample shall be sieved in proper manner
with the sieves specified in Table.
3.
Separation of Flaky material- Each fraction shall be
gauged in turn for thickness on a metal gauge of the pattern shown in Fig. 1,
or in bulk on sieves having elongated slots. The width of the slot used in the
gauge or sieve shall be of the dimensions specified in co1 3 of above Table for
the appropriate size of material.
4.
Weighing of Flaky Material - The total amount passing the
gauge shall be weighed to an accuracy of at least 0.1 percent of the weight of
the test sample.
5.
The flakiness index is the total weight of the material
passing the various thickness gauges or sieves, expressed as a percentage of
the total weight of the sample gauged.
6.
Sieving - The sample shall be sieved in proper manner with
the sieves specified in above Table.
7.
Separation of Elongated Material- Each fraction shall be
gauged individually for length on a metal length gauge of the pattern shown in
Fig. 2. The gauge length used shall be that specified in co1 4 of above Table
for the appropriate size of material.
8.
Weighing of Elongated Material - The total amount
retained by the length gauge shall be weighed to an accuracy of at least 0.1
percent of the weight of the test sample.
9.
The elongation index is the total weight of the material
retained on the various length gauges, expressed as a percentage of the total
weight of the sample gauged.
OBSERVATION:
1.
Total weight of course aggregate____________
g. (Flakiness Index)
Size of Aggregate Thickness
|
Thickness Gauge mm
|
Weight Retained on Thickness Gauge
|
Percentage of
Weight Retained (%)
|
Remark
|
|
Passing through IS Sieves
|
Retained on IS Sieves
|
||||
63 mm
|
50 mm
|
33.90
|
|||
50 mm
|
40 mm
|
27.00
|
|||
40 mm
|
25 mm
|
19.60
|
|||
31 mm
|
25 mm
|
16.95
|
|||
25 mm
|
20 mm
|
13.50
|
|||
20 mm
|
16 mm
|
10.80
|
|||
16 mm
|
12 mm
|
8.55
|
|||
12.5 mm
|
10 mm
|
6.75
|
|||
10 mm
|
6.3 mm
|
4.89
|
|||
Total
|
|||||
2.
Total weight of course aggregate________ g.
(Elongation Index)
Size of Aggregate Thickness
|
Length Gauge mm
|
Weight Retained on Length Gauge
|
Percentage of
Weight Retained (%)
|
Remark
|
|
Passing through IS Sieves
|
Retained on IS Sieves
|
||||
63 mm
|
50 mm
|
--
|
|||
50 mm
|
40 mm
|
81.0
|
|||
40 mm
|
25 mm
|
58.5
|
|||
31 mm
|
25 mm
|
--
|
|||
25 mm
|
20 mm
|
40.5
|
|||
20 mm
|
16 mm
|
32.4
|
|||
16 mm
|
12 mm
|
25.6
|
|||
12.5 mm
|
10 mm
|
20.2
|
|||
10 mm
|
6.3 mm
|
14.7
|
|||
Total
|
|||||
CALCULATION:
The
Flakiness index= Total of Percentage of Retained on Thickness Gauge (%)/100
The
elongation index= Total of Percentage of Retained on Length Gauge (%)/100
RESULT:
The flakiness index of a given sample of aggregate
is _______ %
The elongation index of a given sample of aggregate
is_______ %
