Experiment: Determination of Aggregate Impact Value
Introduction
Road transport plays a vital role in the country’s infrastructural development. Use of
aggregates in road structure contribute massively to its strength and these should be robust
enough to withstand crushing, degradation, and disintegration. They should also be able to
transmit the loads applied from the pavement surface to the underlying layers and eventually
the subgrade. The stability of the pavement construction will suffer if the aggregates are
weak.
Sometimes the movement of the cars on the road causes impact loading, which causes the
aggregates to break up into smaller fragments. As a result, the aggregates need to be strong
enough to withstand impact-induced disintegration. The aggregate's capacity to withstand
abrupt loads indicates how tough it is. This characteristic of aggregate is measured by impact
value test.
Using a sample of bulk aggregates in a standardized way, the aggregates' strength is
evaluated. In laboratory, the Aggregate Impact Value is obtained by releasing a hammer of 15
Kg 15 times on the aggregate sample and the resulting crushed aggregates is sieved using a
2.36 mm B.S sieve. The percentage ratio of the mass of particles in the retainer to the total
mass of the aggregates used will give the Aggregate Impact Value.
For this experiment a sample having sizes 10-14mm was chosen and is being carried
according to BS 812:Part 3:1975.
Aims & Objectives
To determine the impact value of the aggregates used in pavement
construction(roads).
To assess their suitability in determine the suitability of aggregates for use in highway
pavement construction based on the impact value.
Literature review
Aggregates Impact Value (British Standard 812) provides a comparative measurement of an
aggregate's resistance to sudden shock or impact which in some aggregates differs from its
resistance to a slow compressive load.
Due to traffic loads, the aggregates are subjected to the pounding action or impact and there
is possibility of stones breaking into smaller pieces. In order to ensure that the aggregate used
in road construction has enough impact bearing capacity and stability, also known as
toughness, it is imperative to verify this.
The Aggregate Impact Value (AIV) is obtained by:
Mass of sample passing 2.36 mm B . S sieve
AIV = ×100
Total mass of sample
Classification of aggregates using Aggregate Impact Value is as given below:
Aggregate Impact Value Classification
<20% Exceptionally strong
10-20% Strong
20-30% Satisfactory
>35% Weak
Methodology
List of Apparatus
S.N Apparatus Uses
1.
It is used to crush the aggregates.
Aggregate impact testing machine
2.
It is used to separate the crushed
sample according to their sizes
BS Test Sieve
3.
It is used to hold the sample of
aggregates
Cylindrical measure
4.
It is used to compact the
aggregates.
Metal Tamping Rod
5.
It is used to measure the mass of
the aggregate used.
Weighing Balance
Procedures
1.The weight of the cylindrical measure is obtained using the electronic balance.
2.The cylindrical measure is filled with clean and dry aggregates and its weight is obtained
from the electronic balance.
3.The aggregate is transferred from the cylindrical measure to the metallic cup found at the
bottom of impact test machine.
4.The apparatus is set up as shown below in Fig prior to experiment.
5. Compact the sample by giving 25 gentle blows with the rounded end of the tamping rod in
the cylinder.
6. The hammer is raised using the lifting handle until its lower face is 380 mm above the
surface of the aggregate in the cup and allow it to fall freely on the aggregate sample.
7.The weights of an empty B.S sieve of size 2.36 mm and its retainer are measured using an
electronic balance.
8.The crushed aggregate is then transferred to the sieve and sealed with its cover.
9.The latter is then shaken 75 times and the weight of the fractions of aggregate remaining on
the 2.36mm sieve and that also retained in the retainer is measured using the electronic
balance.
10. The sum of weights of fractions retained and passing the sieve should not differ from the
original weight of the specimen by more than 1 g, else the results are discarded, and the
experiment is carried out again.
11.The experiment is repeated 3 times and the results are noted in the table below:
Experiment Number 1 2 3
A-Weight of test 2623.1 2607.1 2649.6
Sample/g
Weight of 2.36 mm 1188.1 1187.9 1188.2
sieve /g
Weight of sieve and 3183.5 3087.7 3237.3
fraction retained on
sieve /g
C-Weight of sample 1995.4 1899.8 2049.1
retained on sieve/g
Weight of retainer/g 693.0 693.3 693.2
Weight of retainer and 1320.5 1400.7 1297.5
sample passing sieve/g
B-Weight of sample 627.5 707.4 599.3
passing sieve/g
B + C/g 2622.9 2607.2 2648.4
Impact Value 31.02 27.13 22.62
Calculations:
1. The weight of sample of aggregate used is calculated by:
Wt of sample used = (Wt of measure + sample) − Wt of measure
2. The weight of sample retained on the 2.36 mm sieve is calculated by:
Wt of sample retained on sieve = (Wt of sieve + sample retained) − Wt of empty sieve
3. The weight of sample retained on the retainer is calculated by:
Wt of sample retained on retainer = (Wt of retainer + sample retained) − Wt of empty retainer
4. The total weight of aggregate retained on the 2.36 mm and retainer is obtained by:
Total Wt of sample retained = Wt of sample retained on sieve + Wt of sample retained on
retainer
5. The Aggregate Impact Value is calculated by:
B
Aggregate Impact Value = ×100
A
Observations and Results
1.The average value of the Aggregate Impact Value is:
AIV =
31.02+ 27.13+22.62
=26.92 %
3
2.A greater mass of aggregate was retained on the 2.36 mm sieve than on the retainer.
Precautions
1. To ensure that the entire load is transmitted on the aggregates, position the plunger in
the middle of the cylinder so that it falls directly on the aggregate sample and does not
contact the cylinder wall.
2. Tamping should be carried out correctly by carefully lowering the tamping rod, not by
hammering. Additionally, the aggregate surface should be uniformly tamped while
taking care to prevent frequent strikes of the tamping stick against the mold's wall.
3. Our hands and feet should be kept at a reasonable distance from machine when the
handle is raised.
Conclusion
From the calculations above, it was found that the average Aggregate Impact Value for the
aggregate sample was 26.92 %, which is the range corresponding to strong aggregate, 20 –30
%. Hence, we can conclude that the aggregate is strong enough and satisfactory.
References
1.Aggregate Impact Value Test - Procedure & Uses - [Civil Planets]
2. AIV Lab Report - AGGREGATE IMPACT VALUE INTRODUCTION Aggregates used in road
construction, should be - Studocu
3. Determination of Aggregate Impact Value - PDFCOFFEE.COM
4. Impact Test of Aggregate | Lab Test Procedure | Recommended Values For Impact Test
5. Aggregate Impact value Test Apparatus, Procedure and uses - Cement Concrete
