Angularity number test gives us an idea of how angular
the aggregate is. This is based on the percentage of voids in the aggregate
after compacting in a specified manner.
Angularity is the absence of roundness in aggregates. A more
rounded aggregate particle has less angularity and vice versa.
Angularity number of aggregate is the amount
(a whole number) by which the percentage of volume of voids in it after compaction
in a prescribed method exceeds 33. Where “33” is the percentage of volume of
voids in a perfectly rounded aggregate.
Angularity number test is
conducted on coarse aggregates sample to estimate the shape of aggregates.
This test helps us to determine the angularity number of the coarse
aggregate. Higher angularity number aggregates are better in interlocking. The angularity
number of coarse aggregate along with flaky index and elongation index helps us
to prepare bituminous mixes that would give satisfactory performance.
Angularity Number Test for Coarse Aggregate, Shape Test for Aggregate, IS: 2386 (Part 1)–1963
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 Metal cylinder
 Tamping rod
 Balance
 Gauging trowel
 Sieves (20, 16, 12.5, 10, 6.3 and 4.75mm)
 Metal scoop
 IS: 2386 (Part 1)–1963, Method of test of aggregates for formation of concrete
 IS: 383–1970, Specification for coarse and fine aggregate from natural source for formation of concrete
Description of
Angularity Number Test for Coarse Aggregate:
First the metal mould calibrated by filling it with water
and determining the weight of water in it. Then the mould is filled with clean
dried aggregates samples in three layers. The weight of aggregate specimens in
the mould is recorded. Determine the specific gravity of the aggregate. Finally
the angularity number of aggregate is calculated.
Preparation of
Test Sample:
The test samples consist of aggregates passes through and
retained on between the appropriate pairs of IS sieves from the following sets
given in Table 1.
Table 1:
Passing
Through IS Sieves

Retained On
IS Sieves

20 mm

16 mm

16 mm

12.5 mm

12.5 mm

10 mm

10 mm

6.3 mm

6.3 mm

4.75 mm

The aggregate sample to be tested should be dried for at least 24 hours in a well ventilated oven maintained at a temperature of 100 ÂºC to 110 ÂºC.
Procedure of Angularity Number Test for Coarse Aggregate:
 Sieve the aggregate sample with sieves specified in Table 1.
 Fill the metal cylinder with water and record its volume.
 Take sufficient quantity of aggregate to perform the test.
 Compact the aggregate in three layers, each layer being given 100 blows (strokes) using the standard tamping rod at a rate of 2 blows/second by lifting the rod 5 cm over the surface of the aggregate and then allowing it to fall freely.
 The blows (strokes) should be uniformly distributed over the surface of the aggregate.
 After compacting the third layer, fill the cylinder to overflowing and remove off the excess material with temping rod as a straight edge.
 Then weigh the aggregate (water and aggregate) with cylinder.
 Make three separate determinations and calculate the average weight of the aggregates in the cylinder.
Observation and Calculation:
Table 2: Percentage of voids in aggregate samples
Descriptions

Trail No. 1

Trail No. 2

Volume of metal measures, V₁_{ }(ml)


Volume of water required to fill the metal measures containing
aggregate, V₂
(ml)


Percentage of voids, (V₂/V₁) ⨉ 100%

Formula
for percentage of voids:
Formula
for angularity number of aggregate:
Angularity
number of aggregate = V33 = ................
Where,
W = Average weight of the aggregate filling
cylinder,
C = Weight of water required to completely
fill the cylinder and
Gs =
Specific Gravity of the aggregate.
Result:
Angularity number of aggregate =……………
Report:
The average value of three determinations,
expressed to the nearest whole number, is reported.
Safety and Precautions to the Test:
 Use safety shoes, mask and aprons at the time of test.
 Thoroughly clean and dry the container before testing.
 All parts of the equipment, used in the test, should always be kept clean.
 Specially care that no outer air should be entered when using the weighing balance.
 After the test has done, sieve should be clean by a soft brush.
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