AGGREGATE IMPACT VALUE TEST-10+ IMPORTANT NOTES TO REMEMBER

1. Aggregate impact value test gives an indication of aggregate’s toughness property (i.e. property of a material to resist impact)
2. Aggregate impact values are used to 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

Aggregate Impact Value Testing machine

3. The test equipment and the test procedure are quite simple and it determines the resistance to impact of stone aggregates simulating field condition.
4. This test can be performed even at construction site or at stone quary, as the apparatus is simple and portable.
5. Aggregate impact value test also gives an indirect indication of the strength characteristics of aggregate.
6. Aggregate impact value of a sample also depends on the shape factors such as flakiness index and elongation index of the aggregates.
7. It has been found that for majority of aggregates, the aggregate crushing value and aggregate impact values are numerically similar within close limits.
8. For deciding the suitability of soft aggregates in base course construction, aggregate impact test is commonly used.
9. A modified impact test is also often carried out in the case of soft aggregates to find the wet impact value after soaking the test sample in water.
10. Maximum allowable aggregate impact value of aggregate in different types of pavement material / layers as per IRC is as below

Types of pavement material / layer	Aggregate impact value, maximum, %
Sub-base course and water bound macadam (WBM) layer	50
WBM base course with bitumen surfacing	40
Built up-spray grout, base course	40
Wet mix macadam (WMM) base course and WBM surface course	30
Dense bituminous macadam binder courses	30
Bituminous Surface dressing, carpet and bituminous concrete surface	30
Cement concrete surface course	30

13. Aggregate impact valuesof soft aggregates for road constructions are as follows

Test Condition	Maximum permissible aggregate impact value of soft aggregates, %
	Sub-base and base	Surface course
Dry impact test	50	32
Wet impact test	60	39