The aggregate impact value is defined
as a relative measure of the resistance of an aggregate to sudden shock or
impact, which (in some aggregates) may differ from its resistance to a slow compressive
load.
The aggregate impact value test is an
important test of aggregates. It is done to obtain the resistance
and impact of aggregates (stones). In this test a machine is used,
which is called impact testing machine.
The aggregates have sufficient
toughness to resist their disintegration due to impact. This property is measured
by aggregate impact value test. So that aggregate impact
value test is used to determine the relative measure of the resistance
of aggregate to sudden shock or impact, which in
some aggregate differs from its resistance to a slowly applies
compressive load.
The advantages of aggregates impact value
test are that the apparatus and procedure of the test are simple. With
this test, we can obtain the resistance and impact of aggregates (stones)
even in field condition. The test can be done in a short period
whether it is at construction site.
Impact value test determines
the amount of energy absorbed by a material during fracture. This absorbed
energy gives a measure of toughness of a given material and acts as a tool to
study temperaturedependent brittleductile transition. It is used to determine
whether the material is brittle or ductile in nature.
Impact testing machine is commonly used to
determine the service life of a part or material. It evaluate an object's
capacity to withstand highrate compressive loading. Impact resistance can be among
the most challenging qualities to measure which is measured by impact testing
machine. The capacity evaluate this characteristic is particularly useful in
assessing product liability and safety.
Aggregate Impact Value Test Procedure as per IS: 2386 Part4 (1963)
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I have explained about Aggregate Impact Test. Read definition,
apparatus, IS code, procedure, observations, formula, result
and lab report about aggregate impact value test.
 Impact testing machine
 Cylinder
 A straight metal tamping rod of circular crosssection 16 mm in diameter, 45 cm to 60 cm in length and rounded at one end.
 IS Sieves
 Oven
 Weighing balance
 IS: 2386 (Part 4) 1963, Methods of test for aggregate for concrete
 IS: 383: 1970, Specification of coarse aggregate and fine aggregate from natural source for concrete
 IS: 9377: 1979, Specification of apparatus for aggregate impact value test
Procedure of Aggregate Impact Value Test:
 Take test samples of aggregates passing through 12.5 mm IS sieve and retained on 10 mm IS sieve.
 Dry theme in an oven for 4 hours at a temperature of 100 °C to 110 °C and then cool at room temperature.
 Fill the aggregates up to about 1/3 full in the cylindrical measure and tamp for 25 times with rounded end of the tamping rod.
 Fill the rest portion of the cylindrical measure by two layers (1/3 + 1/3) and tamp each layer for 25 times.
 Cut off the overflow of aggregates in cylindrically measure by tamping rod using its straight edge or by a knife.
 Then weigh the entire aggregates sample of the measuring cylinder with an accuracy to 0.01 g.
 Transfer the aggregates carefully from the cylindrical measure into the cup, which is firmly fixed in position on the base plate of machine.
 Then tamp it for 25 times with rounded end of the tamping rod.
 The hammer is raised until its lower face be 38 cm above the upper surface of aggregate in the cup and allow it to fall freely on the aggregates.
 The test sample (aggregate) is subjected to a total of 15 such blows each being delivered at an interval of not less than 1 second.
 Then remove the crushed aggregate from the cup and sieve the whole of it on 2.36 mm IS sieve until no significant amount passes through the sieve.
 Weigh the fraction (aggregates) passing through the 2.36 mm IS sieve with an accuracy to 0.1 g.
 Repeat the above steps with other fresh sample.
 Let the original weight of the oven dry sample of
aggregates be W1 g
and the weight of fraction (aggregates) passing 2.36 mm IS sieve be W₂_{ }g.
 Then aggregate impact value is expressed as the percentage of fines formed in terms of the total weight of the sample.
Observations:
Table: Impact
value of sample aggregates
Observation

Trail 1

Trail 2

Total weight of the aggregate filling the cylindrical
metal measures W₁ g


Weight of aggregate passing
through 2.36 mm sieve W₂_{ }g


Aggregate impact value
= (W₂/W₁) ⨉ 100 %

Calculations:
Formula for Aggregate Impact Value Test:
Result:
Aggregate Impact Value = ………. %
Recommended
Values of Aggregate Impact Test:
Classification
of aggregates using Aggregate Impact Value is as given below:
Aggregate Impact Value

Classification

<20%

Exceptionally
Strong

10 – 20%

Strong

2030%

Satisfactory
for road surfacing

>35%

Weak for road surfacing

Specified
limits of percent aggregate impact value for different types of road
construction by Indian Roads Congress are given below:
Sl. No.

Type
of Pavement

Aggregate
Impact Value Should Not More Than

1.

Wearing Course

30

a)

Bituminous
surface dressing


b)

Penetration macadam


c)

Bituminous
carpet concrete


d)

Cement concrete


2.

Bitumen
bound macadam base course

35

3.

WBM base course with bitumen surfacing

40

4.

Cement
concrete base course

45

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