Aggregate impact value test

Aggregate impact value is measure of toughness of aggregate. Toughness is the property of material which indicate its capacity which impact in sudden. Tougher the aggregate more suitable for wearing surface such as road surface. Lower the impact value stronger the aggregate, again the impact these for good quality concrete , aggregate with lower AIV (Aggregate Impact Value) is prepared. AIV should not be exceed 30 % for concrete used for wearing surface such as road work or runways or airport. AIV should not be exceed 45 % for concrete used for any non-wearing concrete work such as beam, slab, column etc.

AIM:

To determine the aggregate impact value of coarse aggregate.

Apparatus:

• Aggregate Impact Value Testing Machine.
• Sieves (12.5mm,10mm)
• Cylindrical metal measure (internal diameter 75 mm and depth 50 mm)
• Tamping Rod (10 mm in diameter and 230 mm long, rounded at one end.)
• Balance.
• Oven(300⁰c)

FIGURE:

Procedure:

(i) Sieve the material through 12.5 mm and 10.0mm IS sieves. The aggregates passing through 12.5mm sieve and retained on 10.0mm sieve comprises the test material.

(ii) Pour the aggregates to fill about just 1/3 rd depth of measuring cylinder.

(iii) Compact the material by giving 25 gentle blows with the rounded end of the tamping rod.

(iv) Add two more layers in similar manner, so that cylinder is full.

(v) Strike off the surplus aggregates.

(vi) Determine the net weight of the aggregates to the nearest gram(W).

(vii) Bring the impact machine to rest without wedging or packing up on the level plate, block or floor, so that it is rigid and the hammer guide columns are vertical.

(viii) Fix the cup firmly in position on the base of machine and place whole of the test sample in it and compact by giving 25 gentle strokes with tamping rod.

(ix) Raise the hammer until its lower face is 380 mm above the surface of aggregate sample in the cup and allow it to fall freely on the aggregate sample. Give 15 such blows at an interval of not less than one second between successive falls.

(x) Remove the crushed aggregate from the cup and sieve it through 2.36 mm IS sieves until no further significant amount passes in one minute. Weigh the fraction passing the sieve to an accuracy of 1 gm. Also, weigh the fraction retained in the sieve.

Compute the aggregate impact value. The mean of two observations, rounded to nearest whole number is reported as the Aggregate Impact Value.

OBSERVATIONS:

Observations	Sample 1	Sample 2
Total weight of dry sample (W1 gm)
Weight of portion passing 2.36 mm sieve (W2 gm)
Aggregate Impact Value (percent) = W2 / W1 X 100

Result of Impact Test

Aggregate Impact Value =

Recommended Aggregate Impact Test Values

Classification of aggregates using Aggregate Impact Value is as given below:

Aggregate Impact Value	Classification
<20%	Exceptionally Strong
10 – 20%	Strong
20-30%	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 is given below.

Sr. No.	Type of pavement	Aggregate impact value 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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