1.0 INTRODUCTION

Impact value of an aggregate is the percentage loss pf weight of particles passing

2.36mm sieve by the application on load by mean of 15 blows of standard hammer and drop

under specified test condition. The aggregate impact value gives a relation measure of the

resistance of an aggregate to sudden shock or impact, which in some aggregates differs from

their resistance to a slowly applied compressive load.

General: Normally the aggregate impact value of base course is 30, bituminous bound

macadam is about 35 and the cement concrete base course is 30.

Significance: The test gives an idea of toughness of the aggregate to resist facture under the

impact of moving loads.

2.0 OBJECTIVE

To determine the aggregate impact value in the laboratory.

3.0 THEORY

Aggregate Impact Value:

AIV is the percentage of fines produced from the aggregate sample after subjecting it

to a standard amount of impact.

The standard amount of impact is produced by a known weight, i.e. a steel cylinder,

falling a set height, a prescribed number of times, onto an amount of aggregate of standard

size and weight retained in a mould.

Aggregate Impact Values, (AIV’s), below 10 are regarded as strong, and AIV’s above

35 would normally be regarded as too weak for use in road surfaces.

Aggregate Impact Values and Aggregate Crushing Values are often numerically very

similar, and indicate similar aggregate strength properties.

4.0 APPARATUS

1. Impact Testing Machine:

Its consists of a cylindrical hammer of 13.5 kg. (30Ibs) sliding freely between two

vertical supports (called guides). Its fall is automatically adjusted to a height of 38cm. There

is a brass plate over which an open cylindrical steel cup of internal diameter 10.2cm and 5cm

depth is placed and fixed to the brass plate.

2. Measure: A cylinder of internal diameter 7.5cm and 5cm deep for measure aggregate.

3. Tamping rod of I cm diameter and 23cm long rounded at one end and pointed at the other

end.

4. Sieves: 12.5mm, 10mm and 2.36mm opening.

5. Balance: 5000g capacity.

6. Laboratory oven capable of maintaining a constant temperature up to 1100C.

5.0 PROCEDURE

1) Firstly, we sieved the aggregate and obtain the portion passing 12.5mm and retained

on 10mm sieve.

2) Then, we fill the aggregate in the cylindrical measure in 3 layers, we are tapping each

layers 25 times with the tamping rod. Level the surface tamping road as a using the

straight edge.

3) Measured the weight the aggregate. The weight of the aggregate was used for the

duplicate test on the same material.

4) Transfer the aggregate from the cylindrical measure to the cup in 3 layers and

compact each layer by tamping in 25 strokes with the tamping rod.

5) After that, we release the hammer for fall freely on the aggregate. The test sample is

subjected to a total of 15 blows.

6) Then, we removed the aggregate sample from the cup and sieve through 2.36 mm

sieve.

7) And lastly, We were weigh the fraction that passing the sieve.

6.0 FROMS AND CALCULATION

Sample Weight of cup

(gm)

Weight before

crush (gm)

Weight retained 2.36

mm sieve (gm)

Weight passing 2.36

mm sieve (gm)

A 784.0 306.1 240.4 65.3

B 784.0 311.3 244.4 66.3

Average 308.7 242.4 65.8

Percent Wear (Average) = (Weight LossInitial Loss ) x 100

Percent Wear (Average) = ( 65.8308.7 ) x 100

Percent Wear (Average) = 21 %

Percent Wear (Average) 21 %

7.0 DISCUSSION

Aggregate Impact Value test construct to determine the impact value of the road

aggregates and to assess their suitability in road construction on the basis of impact value.

Aggregate impact value test also gives an indication of aggregate’s toughness property which

are property of a material to resist impact.

Aggregate impact values are used to classify the stone aggregates with respect to

toughness property using Aggregate Impact Value as given below (recommended values):

AGGREGATE IMPACT VALUE CLASSIFICATION

< 20% Exceptionally Strong

10 - 20% Strong

20 - 30% Satisfactory for Road Surfacing

> 35% Weak for Road Surfacing

Based on the recommended values of Aggregate Impact Test, the result percent wear

(average) was 21% carried out from the test are suitable or recommended for road

constructions because it will not cost more than necessary in order to construct the road

surfacing.

The test equipment and the test procedure are quite simple and it determines the

resistance to impact of aggregates simulating field condition. This test can be performed even

at construction site or at stone quarry, as the apparatus is simple and portable. Aggregate

impact value test also gives an indirect indication of the strength characteristics of aggregate.

Aggregate impact value of a sample also depends on the shape factors such as

flakiness index and elongation index of the aggregates. It has been found that for majority of

aggregates, the aggregate crushing value and aggregate impact values are numerically similar

within close limits. For deciding the suitability of soft aggregates in base course construction,

aggregate impact test is commonly used.

8.0 PRECAUTIONS

1. To wear safety shoes and goggles at the time of testing.

2. Before testing, machine should be properly checked.

3. Special care should be taken when using Impact Testing Machine.

4. After test clean the sieve by a smooth brush.

5. Keep all the exposed metal parts greased.

6. Keep the guide rods firmly fixed to the base & top plate.

7. Equipment should be clean thoroughly before testing & after testing.

8. Number of compaction not more or less than 25 times each layer (3) using tamping

rod.

9. All surface must be compact uniformly.

10. Number of Impact using Impact Testing Machine must not more or less than 15 times.

11. Keep a safe distance of valuable items or hands on the cylinder hammer (13.5kg)

when using Impact Testing Machines

12. Placing the cylinder steel cup on the Impact Testing Machine when the height of the

two vertical supports less than 38cm.

9.0 CONCLUSION

From the Aggregate Impact Value test, the value obtain is 21% which are satisfactory

for road surfacing as recommended. Also, the average percent wear are 21% still not

exceeding Jabatan Kerja Raya’s Standard (Malaysia Standard), <30%. After the testing been

carried, the result of the test can be conclude that the aggregate impact value provides a

relative measure of the resistance of an aggregate to crushing under a gradually applied

compressive load. The aggregate are mild tough to have the resistance pressure under traffic

wheel loads; For example, motorcycle, car, mpv, bus and lorry. These aggregate have the

stability of the pavement structure. The strength of coarse aggregates can affect the capability

of the pavement to sustain.