Everything you should know about the Aggregate Impact Value (AIV)

Saad Iqbal | 🗓️Modified: June 22, 2014 | ⏳Read Time: 3 min | 👁Post Views: 759

Designation (Number): B.S. 812: Part 112: 1990.

Scope:

-Testing coarse aggregates for resistance to Impact

Aggregates:

-combination of sand, gravel, crushed stone, or other material of mineral composition
-Natural aggregates taken from quarries (natural deposits)
-Manufactured aggregates include blast furnace slag, clay and slate etc.

Aggregate Classification (ASTM C125)

Fine Aggregates are defined as aggregates passing no. 4 (4.75 mm) sieve and retained on no. 200 (75 _Micron) sieve
Coarse Aggregates are defined as aggregates retained on no. 4 (4.75 mm) sieve

Significance of Test

Aggregates used in road construction should be strong enough to resist crushing under traffic. Toughness is the property of a material to resist impact. Due to traffic loads, the road stones are subjected to the pounding action or impact and there is possibility of stones breaking into smaller pieces. The road aggregates should therefore be tough enough to resist fracture under impact.

Apparatus

Impact testing machine; the machine consists of a metal base, a detachable cylindrical cup, a metal hammer capable of sliding freely between vertical guides and fall from a height of 38 cm in the test sample cup

A cylindrical measure
Tamping rod

BS sieves; size 14 mm, 10 mm and 2.36 mm
Balance, oven, rubber mallet, metal tray and brush, etc.

Procedure

The test sample consists of aggregates passing 14 mm and retained on 10 mm sieve. Wash the sample and dry at 100 to 110 °C for four hours and cool to room temperature

Fill the cylindrical measure with the aggregate sample and tamp with 25 blows of tamping rod.
Weigh and record the mass of the sample (M1)
Transfer the sample to the machine cup and compact it by applying 25 strokes of tamping rod

Raise the hammer and allow it to fall freely on the aggregates The sample is subjected to a total of 15 aggregates. The sample is subjected to a total of 15 such blows, each being delivered at an interval of not less than one second.
Remove the crushed aggregate from the cup and sieve using 2.36 mm sieve. The fraction passing the sieve is weighed (M2). The fraction retained on the sieve is also weighed (M3). If M2 + M3 differs from M1 by more than 1 g discard the results and repeat the test.

Calculations

The aggregate impact value is expressed as the percentage of the fines formed w.r.t the total weight of the sample
Aggregate Impact Value (AIV) = (100*M2)/M1
Where:
M1 =Mass of the test specimen
M2 = Mass of the test specimen passing 2.36 mm test sieve