Aggregate Impact Value (AIV)
Understanding Aggregate Impact Value
Toughness is the property of a material that determines its ability to withstand impact. On roads, aggregates are constantly subjected to impacts from moving vehicles, which can cause them to break down into smaller pieces. It is crucial for aggregates to possess adequate toughness to withstand such impacts and prevent disintegration. To measure this characteristic, the impact value test is conducted. The test determines the aggregate's resistance to sudden impact or shock, which may differ from its resistance to gradually applied compressive load.
Test method
The procedure for conducting an Aggregate Impact Test (AIV) is as follows:
Prepare the test sample by selecting aggregates sized between 10.0 mm and 12.5 mm. Dry the aggregates by heating at 100-110° C for 4 hours or until constant mass is achieved, and then cool them.
Sieve the aggregates through 12.5 mm or 14mm and 10.0 mm sieves. The material passing through the 12.5 mm sieve and retained on the 10.0 mm sieve will be used as the test material.
Pour the test material into a measuring cylinder, filling it to approximately 1/3 of its depth.
Compact the material by giving it 25 gentle blows with the rounded end of a tamping rod.
Add two more layers of material to the cylinder, compacting each layer in the same manner until the cylinder is full.
Strike off any excess material from the top of the cylinder.
Determine the net weight of the test sample to the nearest gram.
Set up the impact machine on a rigid, level surface with the hammer guide columns vertical.
Fix the cup firmly to the base of the machine and place the entire test sample in it. Compact the sample by giving it 25 gentle blows with the tamping rod.
Raise the hammer to a height of 380 mm above the surface of the sample and allow it to fall freely on the sample. Repeat this process 15 times, waiting at least one second between each fall.
Remove the crushed aggregate from the cup and sieve it through a 2.36 mm sieve until no further significant amount passes in one minute.
Weigh the fraction of the sample passing through the sieve to an accuracy of 1 gram, as well as the fraction retained in the sieve.
Calculate the Aggregate Impact Value by dividing the weight of the fraction passing through the sieve by the total weight of the sample, and multiplying by 100.
Round the result to the nearest whole number, and report the mean of two observations as the Aggregate Impact Value.
What do the AIV values mean?
Here are the recommended Aggregate Impact Test values and their corresponding classifications:
Aggregate Impact Value Classification
Less than 20%: Exceptionally strong
Between 10% and 20%: Strong
Between 20% and 30%: Satisfactory for road surfacing
More than 35%: Weak for road surfacing
The Indian Roads Congress has specified the following limits for the percent aggregate impact value for different types of road construction:
Sl No Type of pavement Aggregate impact value not more than
Wearing Course
Bituminous surface dressing: 30
Penetration macadam: 30
Bituminous carpet concrete: 30
Cement concrete: 30
Bitumen bound macadam base course: 35
WBM base course with bitumen surfacing: 40
Cement concrete base course: 45
NOTE: the values stated above are informative, but do not reflect regional, product or project specification limits
Frequently asked questions (FAQ)
If the aggregate impact value is >35%, then it is classified as not suitable for use in road construction, and for any end use that requires resistance to breakage.
If the aggregate impact value is >30%, then it is classified as not suitable for most construction end uses.