Aggregates Impact Test (AIV)
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Introduction: Impact value of an aggregate is the percentage loss of weight particles passing 2.36mm sieve by the application of load by means of 15 blows of standard hammer and drop, under specified test condition. The aggregate impact value gives a relative 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. The property of a material to resist impact is known as toughness. Due to movement of vehicles on the road the aggregates are subjected to impact resulting in their breaking down into smaller pieces. The aggregates should therefore have sufficient toughness to resist their disintegration due to impact. This characteristic is measured by impact value test. The aggregate impact value is a measure of resistance to sudden impact or shock, which may differ from its resistance to gradually applied compressive load. In this laboratory activities, students are required to set up an aggregate test in order to evaluate the strength (toughness and durability) characteristics of the aggregates. Students are encouraged to develop their critical analysis skills by analyzing and presenting the experimental results appropriately. Aggregate Impact Value Test important to determine: 1. Aggregate’s toughness property (property of a material to resist impact) 2. Classify the stone aggregates with respect to toughness property as given below. Aggregate impact value (%)
Toughness Properties
<10
Exceptionally tough / Strong
10 – 20
Very tough / Strong
20 – 30
Good for pavement surface course
>35
Weal for pavement surface course
Objective:
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Aggregates Impact Test (AIV)
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To determine the aggregates impact value (AIV) of aggregate.
Apparatus: 1. 2. 3. 4. 5.
Steel cylinder Tamping rod Mould Hammer 2.36mm sieve
Procedures: 1. The aggregates sample is prepared by first sieved the aggregate and obtain the portion passing 14.0mm test sieve and retained on the 10.0mm test sieve. 2. The aggregate portion is washed and dried in the laboratory oven at constant temperature of 100⁰C and 110⁰C for not more than four hours. The aggregates sample is cooled to room temperature prior to test. 3. The aggregates is filled into the smaller steel cylinder in three layers. Each layer of aggregate is tamped for 25 times using a tamping rod. The tamping rod is adjusted to fall freely from about 50mm above the aggregate surface and it must be well uniformly spread over. The surface is levelled with the tamping rod as a straight edge to prepare the sufficient amount of aggregate on the top layer. 4. The aggregate is put into the bigger mould and applied 25 times tamping for each layer. 5. The cylinder and aggregates are weighted and the data is recorded. 6. The sample in the apparatus is assembled and the hammer is released to fall freely on the aggregates from a fixed vertical height of 380 ± 5mm. the sample is subjected to at total of manual-controlled 15 blows. 7. The aggregates sample tested is removed from the mould and sieved through 2.36mm sieve openings. 8. The aggregate fraction passing the 2.36mm test sieve is weighted. 9. The test for the same batch of aggregate sample is repeated twice. Results:
Mass of mould (g)
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Sample 1
Sample 2
Sample 3
2762
2762
2762
Aggregates Impact Test (AIV)
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Mass of mould + aggregate (g)
3140.5
3062
3077
Mass of aggregate, M1 (g)
378.5
300
315
Mass of sieve pan, 2.36mm (g)
241
241
241
Mass of sieve pan + aggregate (g)
372
322
306.4
Mass of passing aggregate, M2 (g)
131
81
65.4
AIV (%)
34.6
27
20.8
Mean value:
34.6+ 27.0+20.8 3
= 24.5%
Discussion: Toughness is the property of a material to resist impact. Due to movement of vehicles on the road, the aggregates are subjected to impact which causes them to break into smaller pieces. So, the aggregates that are going to be used in the road or highway must have UiTM Shah Alam
Aggregates Impact Test (AIV)
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sufficient toughness where the AIV test should be 10%-20%, to resist their disintegration due to impact. From the data obtained and the Aggregate Impact Value Test (AIV) that we have done, it shows that our mean value from all three samples is 24.5%. Based from the Aggregate Impact Standard, for the aggregate impact value of 24.5% which is 20% - 30% is satisfactory strong for road surfacing. It shows that this aggregate is satisfactory in term of impact value of the road aggregates and it’s suitability in road construction on the basis of impact value. A lot of advantages can be obtained from the AIV test, and one of the advantages of aggregate impact test is that the test equipment and the test procedure are simple and it can obtain the resistance and impact of stones simulating field condition. The test also can be done in short period of time whether it is at construction site or stone quarry. Higher resistance to impact can be provided in well-shaped cubical stones compared to flaky and elongated stones. The first specimen is essential to be tested from each sample of aggregate which is equal in volume; this can be ensured by taking the specimen in the measuring cylinder in the specified manner by tamping in three layers. Height of these specimens will be equal and the height of fall of the impact rammer on the specimen will be equal if all the test specimens to be tested in the aggregate impact testing mould are of equal volume. On the other hand, volume and height may vary depending on specific gravity of aggregate and shape factors. So the specified rate of application of the blows of the impact rammer may be also varying.
Conclusion:
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Aggregates Impact Test (AIV)
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After conducting this experiment, we can say that it is important to test the aggregates in order to construct a quality pavement for the highway construction. Thus, the result of the experiment, the aggregates impact value is 24.5%. This value is acceptable because it is between 20-30% which classified as satisfactory for road surfacing. The lower the value, the higher the strength of the road surface. On the other hand, the objective is achieved.
References: (n.d.).
Retrieved
7
December,
2016,
from
The
Constructor:
http://theconstructor.org/building/building-material/determination-of-aggregateimpact-value/1355/ Rasin
Instrument.
(n.d.).
Retrieved
7
December,
2016,
from
Scibd:
https://www.scribd.com/doc/22056086/Aggregate-Impact-Test Aggregate Impact Value. (n.d). Retrieved 7 December, 2016, from: https://www.engineeringcivil.com/aggregate-impact-value/ Important Aiv. (n.d). Retrieved 7December, 2016, from: https://civilblog.org/aggregate-test-important/ (n.d). Retrieved 7 Decemver 2016, from: http://civilblog.org/2014/07/16/aggregate-impact-value-test-10-important-notes-toremember/#
Appendix:
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Aggregates Impact Test (AIV)
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Aggregate Impact Value
Classification
<20%
Exceptionally Strong
10 – 20%
Strong
20-30%
Satisfactory for road surfacing
>35%
Weak for road surfacing
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