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Aggregate Impact Test How to determine Aggregate Impact Value

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 Aggregate Impact Test  How to determine Aggregate Impact Value

For determination of aggregate impact value for coarse aggregate , which passes  12.5 mm . IS sieve and retained on 10 mm. IS sieve, following two formulae are used. 

One of the major uses of aggregate impact value is that it is used for the determination of the water absorption rate of coarse aggregates. The water absorption rate of coarse aggregates is determined by means of an immersion test. The test sample is weighed and then submerged in water for a period of 24 hours. The weight of the saturated sample is then determined and the percentage water absorption rate is calculated.How to determine Aggregate Impact Value

Aggregate Impact Test  How to determine Aggregate Impact Value

Aggregate Impact Test  How to determine Aggregate Impact Value


Introduction

Determining the aggregate impact value of a material is important for several reasons. This test can provide valuable information about the quality of a construction material before it is used in a project. Additionally, the results of this test can be used to help select materials for different applications. For example, materials with a high aggregate impact value may be better suited for use in asphalt pavement.

The aggregate impact value test is relatively simple and only requires a few pieces of equipment. However, it is important to follow the procedure carefully in order to get accurate results. The significance of the test results should also be considered when interpreting them.

What is Aggregate Impact Value

Definition of Aggregate Impact Value

The aggregate impact value is a measurement of the resistance of an aggregate to sudden impact or shock, which in this case is represented by a falling steel sphere. The test is performed by subjecting the specimen of aggregate in a standard cylindrical steel cup to 15 blows of equal energy using a falling steel hammer of 500g mass.

The ratio of the mass of the fines formed to the total mass of the specimen is expressed as a percentage and is known as the aggregate impact value.

Significance of Aggregate Impact Value

The significance of aggregate impact value test is to determine the strength property of aggregates against sudden shocks or impacts. This mechanical property is important for durability purposes such as pavement design, and also for structural design purposes such as concrete mix designs.

How to determine Aggregate Impact Value

  • Apparatus Required

The apparatus required to determine the aggregate impact value are:

-An impact testing machine

-A sieve of sizes 12.5mm, 10mm and 2.36mm

-A tamping rod of circular or square cross-section 16mm in diameter and 45 to 60cm long with one end rounded off

-A cup or tray

-A balance sensitive to 0.5g

  • Procedure
The following procedure should be adopted to determine the aggregate impact value

1) The test sample consists of aggregates sized 20mm to 25mm

2) It should be thoroughly mixed and divided into two equal parts by dry shaking in a suitable container for 15 minutes   on an inclined platform with a slanting side so that one part is about one third above the other.  

  3) The aggregates from each part are filled separately into the measuring cylinder by means of a funnel until it is about two thirds full and leveled at top with the help of tamping rod inserted through it in such a way that its lower end just touches the aggregates surface without compacting them 

4) The measuring cylinder with its contents is placed in position on the base plate of the impact testing machine and rest on three spheres placed symmetrically at its corners 

5) A metal plunger is allowed to fall freely from a height of 380 + 5 mm onto the aggregates in the measuring cylinder 

6) The crushed aggregates passing through 2.36 mm IS sieve are collected in a tray

 7) The total weight (We1 gm) of aggregates retained on 2.36 mm IS sieve is determined

 8 )The percentage wear = [(W1/W2)*100] where W1 = total weight retained, W2= total weight taken

  9) The percentage wear is reported to the nearest whole number as the aggregate impact value

Importance of the test 

Significance of the test

The Aggregate Impact Value (AIV) test is conducted to determine the aggregate impact value which provides a relative measure of the resistance of an aggregate to sudden shock or impact. The significance of this test is that it measures the ability of an aggregate to resist failure under dynamic (impact) loading.

This type of loading is typically found in crushing operations, where the material is subjected to repeated impact and compression forces. By knowing the AIV of an aggregate, we can predict how well it will perform in these conditions and therefore how long it will last in service.

The AIV test is also used to assess the suitability of aggregates for use in asphaltic concrete, where high impact values are undesirable.

Conclusion

The Aggregate Impact Value (AIV) test is a useful tool to determine the aggregate impact value of coarse aggregates. The AIV is a measure of the resistance of the aggregate to sudden shock or impact, which in turn can lead to surface damage and potential deterioration of the material. It is important to perform this test in order to ensure that the materials used in construction are fit for purpose and will not cause any long-term damage.

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